buletin stiintific

98
EDITURA POLITEHNICA BULETINUL TIIN IFIC SCIENTIFIC BULLETIN Ş Ţ al Seria MECANIC of Transactions on MECHANICS Tomul 54(68), Fascicola 2, 2009 ISSN 1224-6077 Universit ii „POLITEHNICA” din Timi oara, România the „POLITEHNICA” University of Timi oara, Romania ăţ ş ş Ă

Transcript of buletin stiintific

Page 1: buletin stiintific

EDITURA POLITEHNICA

BULETINUL TIIN IFIC

SCIENTIFIC BULLETIN

Ş Ţal

Seria MECANIC

of

Transactions on MECHANICS

Tomul 54(68), Fascicola 2, 2009ISSN 1224-6077

Universit ii „POLITEHNICA” din Timi oara, România

the „POLITEHNICA” University of Timi oara, Romania

ăţ ş

ş

Ă

Page 2: buletin stiintific

II

Editor-in-Chief Assoc. Prof. PhD. Eng. Mihaela POPESCU,

Politehnica University of Timisoara, Romania

Associate Editor-in-Chief Assoc. Prof. PhD. Eng. Aurel RĂDUŢĂ

Politehnica University of Timisoara, Romania Editorial Board

Prof.PhD. François AVELLAN, Ecole Polytechnique Federale de Lausanne, Suisse

Sen. lecturer Herbert JELINEK, Charles Sturt University, USA

Prof.PhD.Eng. Mircea BĂRGLĂZAN, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Inocenţiu MANIU, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Liviu BERETEU, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Livius MILOŞ , Politehnica University of Timisoara, Romania

Prof.PhD. Didier BOUVARD, Institut National Polytechnique de Grenoble, France

Prof.PhD.Eng.Vasile NĂSTĂSESCU, Academia Tehnica Militara, Bucuresti, Romania

Prof.PhD.Eng. Waltraut BRANDL, University of Gelsenkirchen, Germany

Prof.PhD.Eng. Zbiniew OLESIAK, Technical University of Opole, Poland

Prof.PhD.Eng. Ioan DUMITRU, Politehnica University of Timisoara, Romania

Conf.dr.ing. Aurel RĂDUŢĂ, Politehnica University of Timisoara, Romania

Prof.docent dr.ing. Arpad A. FAY, University of Miskolc, Hungary

Prof.PhD.Eng. Laszlo POKORADI, University of Debreceni, Hungary

Prof.dr. Pier Giorgio FEDOLFI, IFOA Regio Emilio, Italiy

Prof.PhD.Eng. habil Winfried Maria RUSS, Technical University of Munchen, Germany

Prof.PhD.Eng.Traian FLEŞER, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. habil Peter STURM, Technical University of Graz, Austria

Prof.PhD.Eng.Tudor ICLĂNZAN, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Viorel SERBAN, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. habil Ioana IONEL, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Dumitru ŢUCU, Politehnica University of Bucharest, Romania

Prof.PhD.Eng. Eugen ISBĂŞOIU, University of Bucharest, Romania

Prof.PhD.Eng. Nicolae VASILIU, Politehnica University of Bucharest, Romania

Editorial Secretary

Assoc.Prof.PhD.Eng. Emilia Georgeta MOCUŢA Politehnica University of Timisoara, Romania

Reviewers

Prof.PhD.Eng. Liviu Eugen ANTON, Politehnica University of Timisoara, Romania

Prof.PhD.Eng.habil Ioana IONEL, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Alexandru BAYA, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Mihai JĂDĂNEANŢ, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Liviu BERETEU, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Ion MITELEA, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Waltraut BRANDL, University of Gelsenkirchen, Germany

Assoc.Prof.PhD.Eng. Georgeta Emilia MOCUŢA, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Florin BREABĂN, Université Artois IUT Bethune, France

Prof.PhD.Eng. Virgiliu Dan NEGREA, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Victor BUDĂU, Politehnica University of Timisoara, Romania

Assoc.Prof.PhD.Eng. Mihaela POPESCU, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Gheorghe CIOARĂ, Politehnica University of Timisoara, Romania

Assoc.Prof.PhD.Eng. Aurel RĂDUŢĂ, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Gheorghe DRĂGĂNESCU, Politehnica University of Timisoara, Romania

Assoc.Prof.PhD.Eng. Daniel STAN, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Ion DUMITRU, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Viorel Aurel ŞERBAN, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Traian FLEŞER, Politehnica University of Timisoara, Romania

Assoc.Prof.PhD.Eng. Dănuţ ŞOŞDEAN, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Octavian GLIGOR, Politehnica University of Timisoara, Romania

Prof.PhD.Eng. Marin TRUŞCULESCU, Politehnica University of Timisoara, Romania

Page 3: buletin stiintific

III

CONTENTS

201 THE INFLUENCE OF DEPOSITION PROCESS ON CORROSION AND SLIDING WEAR BEHAVIOR OF WC-Co COATINGS INFLUENŢA PROCEDEULUI DE ACOPERIRE ASUPRA COMPORTAMENTULUI LA COROZIUNE ŞI UZARE PRIN ALUNECARE A STRATURILOR CERMET WC-Co

Ion-Dragoş UŢU, Gabriela MARGINEAN, Dragoş BUZDUGAN, Ioan SECOŞAN, Viorel-Aurel ŞERBAN

1

202 M.A.G WELDING BEHAVIOUR OF NAVELS CONSTRUCTIONS STEELS COMPORTAREA LA SUDARE M.A.G. A OŢELURILOR PENTRU CONSTRUCŢII NAVALE

Ion MITELEA, Liviu UDRESCU

5

203 THE EVALUATION OF THE CRACKING PIPE’S MATERIALS AND THEIR BEHAVIOR TO CREEP EVALUAREA COMPORTARII LA FLUAJ A UNOR CONDUCTE DE CRACARE

Mihai HLUŞCU, Pavel TRIPA, Marius DUMBRAVĂ

13

204 RECORDED CRACKS IN THE SHAFT OF A HYDRAULIC BULB TURBINE FISURI INREGISTRATE IN ARBORELE TURBINEI HIDRAULICE

Ilare BORDEAŞU, Mircea Octavian POPOVICIU, Marian Dragoş NOVAC, Marian BĂRAN

19

205 PROBLEMS WHEN USING ULTRASONIC WELDING FOR AUTOMOBILE CABLES PROBLEMELE UTILIZĂRII SUDĂRII CU ULTRASUNETE A CABLURILOR DE AUTOMOBILE

Mihaela POPESCU, Emilia Georgeta MOCUŢA, Constantin MARTA, Angela CÂNEPARU, Remus BELU-NICA

25

206 EVALUATION OF THE PROPERTIES OF THE PRODUCT GAS GENERATED FROM THE GASIFICATION OF SOLID RECOVERED FUELS EVALUAREA PROPRIETĂŢILOR GAZULUI GENERAT PRIN GAZIFICAREA COMBUSTIBILILOR SOLIZI RECUPERAŢI

Loránd KUN, Gregory DUNNU, Jörg MAIER

31

207 AIR-FUEL i-x DIAGRAM FOR GASOLINE-BIOETHANOL BLENDS DIAGRAMA i-x AER-COMBUSTIBIL PENTRU AMESTECURI DE BENZINĂ- BIOETANOL

Adrian IRIMESCU

37

208 METODA SKETCH BASED 3D MODELING SKETCH BASED 3D MODELING METHOD

Cristian CIOANĂ, Tudor ICLĂNZAN, Cristian COSMA

43

Page 4: buletin stiintific

IV

209 THE CALCULATION OF THE VARIATION OF SQUEEZING FOR THE VALVE SEAT SINTERED IN THE CYLINDER-HEAD OF ENGINE M511 CALCULUL PIERDERILOR DATORATE VARIAŢIEI STRÂNGERII SCAUN DE SUPAPĂ-CHIULASĂ LA MOTORUL M511

Adela FILIP, Ion NICOARĂ

49

210 ENERGETICALLY-BASED CONTROL FOR SOLAR HEATING SYSTEMS CONTROLUL PE BAZE ENERGETICE AL SISTEMELOR SOLARE DE ÎNCĂLZIRE

Richárd KICSINY

55

211 THE FUELL CELL, AN OPTION FOR DESCENTRALIZED POWER AND HEAT GENERATION AND AUTOMOTIVE INDUSTRY PILE DE COMBUSTIE, CA ALTERNATIVĂ ÎN INDUSTRIA AUTOMOBILELOR ŞI A PRODUCERII DE ENERGIE ELECTRICĂ ŞI TERMICĂ ÎN SECTORUL DESCENTRALIZAT

Adriana TOKAR, Arina NEGOIŢESCU

63

212 COMPARISON BETWEEN CH4 AND CO2 CONCENTRATIONS IN BIOGAS FOR DIFFERENT TYPES OF BIOMASS COMPARATIE INTRE CONCENTRATIILE DE CH4 SI CO2 DIN BIOGAZ PENTRU DIFERITE TIPURI DE BIOMASĂ

Adrian Eugen CIOABLĂ

67

213 THE OPTIMIZATION OF A CASTING DIE USED FOR THE PROCESSING OF FERROMAGNETIC NANOCRYSTALLINE ALLOYS IN THE SHAPE OF RODS OPTIMIZAREA UNEI MATRIŢE DE TURNARE PENTRU OBŢINEREA ALIAJELOR NANOCRISTALINE FEROMAGNETICE SUB FORMĂ DE BARE

Mircea VODĂ, Cosmin CODREAN, Carmen OPRIŞ, Eugen POPESCU

71

214 INDUSTRIAL DESIGN – A WAY FOR DESIGNING PLESURABLE PRODUCTS AND HUMAN INTERFACES DESIGNUL INDUSTRIAL – O CALE SPRE REALIZAREA DE PRODUSE ŞI INTERFEŢE ATRACTIVE

George BELGIU, Dan Andrei ŞERBAN, Gabriela NEGRU-STRĂUŢI

77

215 STRESSES CORROSION EVALUATION TESTING IN PROCESS EQUIPMENTS ÎNCERCĂRI COFITEN PENTRU EVALUAREA COROZIUNII SUB TENSIUNE PENTRU ECHIPAMENTE DE PROCES

Traian FLEŞER, Dumitru ŢUCU

83

Page 5: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

THE INFLUENCE OF DEPOSITION PROCESS ON CORROSION AND SLIDING WEAR BEHAVIOR OF

WC-Co COATINGS

Ion-Dragoş UŢU*, Gabriela MĂRGINEAN**, Dragoş BUZDUGAN*, Ioan SECOŞAN*, Viorel-Aurel ŞERBAN*

*Faculty of Mechanical Engineering, Bv.Mihai Viteazu No.1, 300222 Timişoara, România Email: [email protected], [email protected], [email protected]

**University of Applied Sciences Gelsenkirchen, Neidenburger Str. 10, 45877 Gelsenkirchen, Germany Email: [email protected]

Abstract. Tungsten carbide coatings are one of the most widely used wear-resistant coatings in industry, in particular in aerospace, automotive, transportation and power generation systems. These protective coatings are usually applied on the surface of components using thermal spray processes including plasma spraying, high velocity combustion or detonation gun. In this paper different tests were performed on WC-Co coatings deposited by the high velocity oxygen-fuel spraying (HVOF) and plasma spraying (APS) methods in order to see their sliding wear and corrosion behavior. The substrate selected for depositions was a C45 steel. Several analytical techniques, including X-ray diffraction and scanning electron microscopy (SEM) were used to characterize the microstructures formed during the spraying process. The sliding wear behavior was determined using the pin-on disk method and the corrosion resistance of the materials was measured by electrochemical method. Keywords: tungsten carbide; plasma spraying; high velocity oxygen-fuel spraying; corrosion; sliding wear 1. Introduction

Sliding wear is significant in many industries and as such there is a need to improve the wear resistance of critical components. The high sliding wear resistance of hardmetals is conferred by the ductile metallic matrix. The sliding and/or abrasive wear resistance of sintered hardmetals is generally improved by a reduction in the binder volume fraction and a decrease in the carbide particle size [1].

In order to protect the surfaces of components, novel coating techniques are increasingly used. Thermal spray processes have relatively high deposition rates and are capable of depositing most materials that have a liquid phase.

The application sectors range from heavy industries such as aerospace, automotive, power generation and steel making, to electronics and biochemistry. Specific coating materials are chosen for each protective function [2].

Tungsten carbide coatings are one of the most widely used wear-resistant coatings in history, in particular aerospace, automotive, transportation and power generation systems.

These protective coatings are usually applied on the surface of components using thermal spray processes including plasma spraying, high velocity combustion or a detonation gun. The high temperature of the spray torch, the chaotic character of the processes and the rapid cooling of deposits associated with these techniques result in

Page 6: buletin stiintific

2complex chemical transformations and lead to the formation of metastable phases within the coatings.

The plasma spraying method has been fairly well studied and the main phenomena which occur are substantial thermal decomposition of tungsten monocarbide (WC) giving rise to the formation of ditungsten carbide (W2C) and mixed WxCoyCz type carbides, as well as to the appearance of metallic tungsten. The presence of oxygen in air plasma spraying was found to favour these transformations and to promote the nucleation of a noticeable quantity of oxycarbides which are undesirable for wear resistance.

High velocity oxygen-fuel (HVOF) spraying uses considerably lower temperatures compared with those used in thermal plasmas and because of this it has been found to be a very suitable for spraying low melting alloys and cermets [3].

The goal of this paper was to investigate the influence of deposition process on WC-Co coatings properties.

2. Experimental procedure. The material used in this experiment was a

WC-Co 83 17 sintered powder Thermico SJA 765/7 which was deposited on a C45 steel substrate using both Atmospheric Plasma Spraying (APS) and High Velocity Oxy-Fuel (HVOF) spraying techniques.

The morphology of the powder and of the sprayed samples has been characterized by scanning electron microscopy and X-ray diffraction technique using a Cu-Kα radiation.

The sliding wear resistance was determined using the pin-on-disk method by calculating the variation of the wear track depth with applied load. The normal load applied of the ball (WC-Co with a 6 mm diameter) was 5 N, the relative velocity between the ball and surface was v = 20 cm/s, and the testing distance 1000m ( the trajectory was a circle with a radius of 5.4 mm). The relative humidity was 65%.

The corrosion behaviour of the materials was measured by cyclic voltammetry. The tests were carried out in 0,001 M sulphuric acid solution, using an electrochemical corrosion cell and a potentiostate from Fa. Radiometer. The applied potential was varied between - 1000 and 1000 mV (versus saturated calomel electrode – SCE) using a rate of 50 mV/min.

3. Results and discussions. 3.1. Powder and coating morphology

The morphology of the used powder is shown in the SEM micrographs at different magnitudes (figure1). The particle size is about – 15 +5 μm.

SEM micrographs at different magnifications (200x and 2000x) of the coatings deposited by APS and by HVOF techniques are presented in figures 2 respectively 3. Comparing the images it can be observed that the APS sprayed samples present a high degree of porosity (see arrows).

gFigure 1. SEM micrographs of the WC-Co 83 17 powder

Figure 2. SEM micrographs of the WC-Co coatings deposited by APS

Page 7: buletin stiintific

3

Figure 3. SEM micrographs of the WC-Co coatings deposited by HVOF

In case of HVOF sprayed sample (figure 3 2000x) it can be noticed that the coating is more dense with a lower porosity than the APS sprayed coating. This can be explained by the high velocity of the particles during the HVOF deposition.

The XRD patterns of the WC-Co sprayed coatings (figure 4) show no differences regarding the phases formation. It can be observed that there is no change in phases regardless of the method of spraying applied, both coating contain WC and W2C phases.

(a) (b)

Figure 4. X-ray diffraction pattern of sprayed coatings by APS(a) and by HVOF(b)

3.2. Wear resistance tests The pin on disk tests indicated that sliding

wear resistance of the coatings deposited by APS and HVOF methods is quite similar but much smaller than that of the base material. The results are summarized in table 1 and the sliding wear rates histograms are shown in figure 5.

0

200

400

600

800

1000

1200

1400

1600

Wea

r Rat

e 10

-7(m

m3/

N/m

)

Materials

C45 WC-Co-HVOF WC-Co-APS Figure 5. Sliding wear rates of the samples tested

Table 1. Wear rates

3.3 Corrosion tests

From the polarisation curves (figure 6) of the tested materials it can be seen that significant modification in the corrosion resistance of the materials occurred. This can be observed by comparing the values of the corrosion potential (Ucorr) and current density (icorr) for the three samples summarized in table 2. The icorr values were shifted from 0.0843 mA/cm2 to 0.0058 mA/cm2 (0.0245 mA/cm2). A low value for icorr indicates an improvement in the corrosion behavior. This theoretical affirmation leads to the conclusion that the sample-WC-Co deposited by HVOF technique has the best corrosion resistance.

It can be noted that sample B (WC-Co-APS) compared to sample A (C 45) shows only a slight increase in corrosion resistance. This was influenced by the presence of cracks and pores in the coating microstructure deposited by APS

Material Wear rate [mm3/N/m]

Wear rate * 10-7[mm3/N/m]

C 45 0.0001579 1579 WC-Co-HVOF 0.000004871 48.71 WC-Co-APS 0.000004521 45.21

Page 8: buletin stiintific

4which allowed the sulphuric acid to penetrate the coating down to the substrate, testing predominantly the corrosion resistance of the latter one.

Figure 6. Polarisation curves of tested samples:

A –C45, B – WC-Co-APS, C – WC-Co-HVOF in 0.001M H2SO4

Figure7. Macroscopic image of the samples

investigated

Table 2. Measured values of the corrosion parameters

From the macrographic images (figure 7) of the corroded samples it can be observed that the tested area of sample A shows the most pronounced deterioration in comparison with samples B and C (having the less affected tested area)[3]. 4. Conclusions.

Analyzing the sliding wear behavior of the tested materials (C 45, WC-Co-APS, WC-Co-HVOF), it was found that cermet coatings had a similar wear rate, much smaller than substrate material.

The corrosion tests in 0.001M sulfuric acid solution showed the best corrosion resistance of the WC-Co-HVOF sprayed coating in comparison

with the base material C45 and WC-Co-APS sprayed material.

In conclusion, it can be said that the cermet coatings are able to protect surfaces exposed both, to wear and corrosion attack, the best results being obtained using the HVOF spraying method. References 1. H. Chen, C. Xu, Q. Zhou, I.M. Hutchings, P.H.

Shipway, J. Liu, Micro-scale abrasive wear behaviour of HVOF sprayed and laser-remelted conventional and nanostructured WC-Co coatings Wear 2005, vol. 258, pp. 333-338, ISSN 0043-1648

2. H. Hamatani, Y. Miyazaki, Optimization of an electron beam remelting of HVOF sprayed alloys and carbides, Surface and Coatings Technology 2002, vol. 154, pp. 176-181, ISSN 0257-8972

3. A. Karimi, Ch. Verdon, G Barbezat, Microstructure and hydroabrasive wear behaviour of high velocity oxy-fuel thermally sprayed WC-Co, Surface and Coatings Technology 1993, vol. 57, pp. 81-89, ISSN 0257-8972

INFLUENŢA PROCEDEULUI DE ACOPERIRE ASUPRA COMPORTAMENTULUI LA COROZIUNE ŞI UZARE PRIN ALUNECARE A STRATURILOR CERMET WC-Co Rezumat Straturile cermet WC-Co sunt unele dintre cele mai utilizate straturi de protecţie antiuzură în industrii ca cea aerospaţială, a automobilelor, transportului şi sistemelor de producere a energiei. Acestea sunt de obicei aplicate pe suprafaţa componentelor utilizând procedee de pulverizare termică, de exemplu pulverizarea cu plasmă, pulverizarea termică de mare viteză sau pulverizarea prin detonaţie. S-a studiat comportamentul la uzare prin alunecare şi comportamentul la coroziune al straturilor cermet WC-Co, depuse prin pulverizare termică în plasmă (APS) şi prin pulverizare termică cu flacără de mare viteză (HVOF), pe un substrat de oţel de îmbunătăţire C 45. Mai multe metode de analiză ca difracţia de raze X, microscopia electronică cu baleiaj au fost utilizate în vederea caracterizării structurii straturilor rezultate după depunere. Comportamentul la uzare prin alunecare a fost determinat utilizându-se metoda “pin on disk”, iar rezistenţa la coroziune a materialelor a fost masurată prin metoda electrochimică.

Electrochemical data Sample icorr (mA/cm2) Ecorr (mV)

A 0.0843 - 322.3 B 0.0245 - 154.6 C 0.0058 - 140.5

Scientific reviewers: Waltraut Brandl, University of Gelsenkirchen, Germany Roland Cucuruz, “Politehnica” University of Timisoara, România

Page 9: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

M.A.G WELDING BEHAVIOUR OF NAVELS CONSTRUCTIONS STEELS

I. MITELEA*, L. UDRESCU*

Faculty of Mechanical Engineering, Bv. Mihai Viteazu, No 1, 300222, Timisoara, Romania [email protected], [email protected]

Abstract. The paper contents the experimental researches obtained by MAG welded steels for naval constructions delivered as hot-rolled plates shape having the thickness of 20 mm, selecting as addition material a full wire S12Mn2Si. The quality appreciation of the welded joints was performed by sclerometric examinations, mechanical tests, and optical micrographics investigations. Keywords: low alloyed steel, MAG welding, structure, properties 1. Introduction

The steels from this category are manufactured according with the technical prescription of the Romanian Naval Register. Their main particularity results from the specific calculus rules and consists by modification of the chemical composition with the product thickness in order to assure a unique value of the flow limit by every executed product from a steel mark.

The difficulties appeared in case of welding by melting of these steels depend on the cold cracking tendency, as a result of a relative high equivalent carbon content and assurance of a suitable tenacity in welding and in the heat affected zone (H.A.Z).

The present paper approaches the MAG weldability aspects of steels delivered as plates shape hot rolled, using as addition material a full wire S12Mn2Si. 2. The experimental procedure

In order to study the physico-mechanical characteristics of the deposited metal by MAG welding using a full wire S12Mn2Si, having the diameter of 1.2 mm, a butt welding was realized.

The base material was a hypoeutectoid steel for welded structures delivered as hot rolled plates shape with thickness of 20 mm.

The parameters of the thermal welding regime are presented in table 1.

)/(12.01000

6021000

60 mmKJvUI

vUI

vUIkE

s

as

s

as

s

asl

⋅=

⋅⋅⋅=

⋅⋅⋅

⋅=

[1]

The welding succession is shown in figure 1 and the temperature between two successive passings was 220-280.

1 2 3

6

9

12

4

8

11

14 16 15

13

1

75

Figure 1. The deposition succession of the

welding lines

Page 10: buletin stiintific

6After the welding process, mechanical

metal cutting were performed in order to obtain samples for resilience and static tensile tests (figure 2).

Table 1. Thermal welding regime

No. Ua [V]

Is [A]

ts [s]

ls . [cm]

El [KJ/mm] Q [l/min] vs

[cm/min] ts

[min] 1. 23 170-190 69 30 11.42 13-14 26.08 1.15 2. 23 170-190 88 30 24.18 13-14 20.54 1.46 3. 23 170-190 117 30 32.30 13-14 15.38 1.95 4. 23 170-180 106 30 28.34 13-14 17.04 1.76 5. 23 160-180 138 30 35.98 13-14 13.04 2.3 6. 23 180 108 30 29.81 10 16.66 1.8 7. 23 180 88 30 24.18 10 20.54 1.46 8. 23 180 100 30 27.49 10 18.07 1.66 9. 23 180 100 30 27.49 10 18.07 1.66 10. 23 180 55 30 15.07 10 32.96 0.91 11. 23 180 98 30 27 10 18.40 1.63 12. 23 180 142 30 39.08 10 12.71 2.36 13. 22 160-170 87 30 21.06 10 20.68 1.45 14. 22 160-170 71 ;30 17.13 10 25.42 1.18 15. 22 160-170 80 30 19.31 10 22.55 1.33 16. 23 160 102 30 25.03 10 17.64 1.7

15 15

A

70

h 22

min

h

10

10

10

22m

in 10

10

10

27.5min 27.5min

Mechanical cutting

Flame cutting

Res

erve

L=2

50+2

h

ø1010

10

10

5

5

B

A

B

A-A

B-B

Figure 2. The obtaining of resilience and tensile samples

By the resilience samples the positioning of

the notch was made in the deposited metal and the tension samples were executed from the deposited metal. Also, samples with transversal faces were cut, which were necessary for the macro- and micrographic analysis and sclerometric examinations too.

3. Evaluation and interpretation of the results 3.1 Sclerometric examinations

The hardness tests were performed on samples with transversal faces respecting the actual normatives.

The arrangement of the hardness traces, on two normal directions (I-I, II-II) , is presented in figure 3, and the obtained results are summarized in table 2.

Page 11: buletin stiintific

7Based on the obtained results one can

conclude that the welding technology is suitable establish and the used addition material assures mechanical characteristics for the deposited metal (D.M.) similar with the base material (B.M.). 3.2 Static tensile tests

The mechanical tests are used both for the quality control of materials obtaining processes and for the transformations occurred during the processing techniques.

The determination of the mechanical characteristics makes possible the appreciation of the limit solicitations and of the conditions when a material can be exploited without any cracking risks.

According with the figure 1 the static tensile testing was performed on samples from the deposited metal (figure 4).

From the breaking elongation curves according with the applied load the following mechanical characteristics were determined: - breaking resistance Rm = Fp/So = 408.15

N/mm2;

- yield stress Rp0.2 = Fp0.2/So = 316.6 N/mm2; - breaking elongation A5 = L-Lo/Lo x 100 = 14

%; - reduction of area Z = So-S / So x 100 = 62 %.

3.3 Dynamic impact bend tests

These tests characterize the weld joining tendency to a fragile breaking. For investigations prismatic samples with a V nozzle were used (figure 5).

The materials were tested at the environment temperatures and at – 20 °C.

The obtained experimental results are presented in table 3.

Because the values of the breaking energy are higher than 27 J at temperature of - 20 °C, one can conclude that the deposited metal has a sufficient plasticity reserve. The results dispersion is normal taking in account the fact that after welding no annealing treatment for normalization was performed. The prescription of such a heat treatment offers the advantage of tenacity characteristics improvement and the reduction of the experimental values dispersion.

1.5

I

I

II II

0.5

Figure 3. The arrangement directions of the hardness traces

R 5

35 3550

60

150 min

M 1

2

ø 1

0

Figure 4. The shape and the dimensions of the static tensile sample

3.4 Micrographics examinations The research of breaking surfaces needed

microfractographies images by electronic microscope.

Figures 6 and 7 present some microfractographies images performed on impact

bend strength samples broken at temperatures of 20 and – 20 °C.

The breaking surfaces of the tested samples at the environment temperature have a ductile character (the breaking is preceded by an important plastic deformation) and a fibred aspect (figure 7).The samples broken at temperature of

Page 12: buletin stiintific

8– 20 °C present mainly a fibred aspect, although some zones with crystalline aspect appear (figure 6a). In the speciality literature one considers that the ductile-fragile transition

temperature is the testing temperature whereon 50 % from the breaking surface has a fragile character.

Table 2 Results of the sclerometric examinations

No. Direction of investigation

Researched zone

Hardness HV5 No. Direction of

investigationResearched

zone Hardness

HV5 1. I-I D.M. 357 46. I-I D.M. 221 2. I-I D.M. 357 47. I-I D.M. 225 3. I-I D.M. 356 48. I-I D.M. 229 4. I-I D.M. 353 49. II-II B.M. 271 5. I-I D.M. 353 50. II-II B.M. 280 6. I-I D.M. 345 51. II-II B.M. 280 7. I-I D.M. 341 52. II-II B.M. 286 8. I-I D.M. 341 53. II-II H.A.Z. 296 9. I-I D.M. 293 54. II-II H.A.Z. 336

10. I-I D.M. 306 55. II-II H.A.Z. 303 11. I-I D.M. 268 56. II-II D.M. 283 12. I-I D.M. 265 57. II-II D.M. 257 13. I-I D.M. 262 58. II-II D.M. 303 14. I-I D.M. 268 59. II-II D.M. 296 15. I-I D.M. 254 60. II-II H.A.Z. 321 16. I-I D.M. 277 61. II-II H.A.Z. 325 17. I-I D.M. 293 62. II-II H.A.Z. 313 18. I-I D.M. 274 63. II-II H.A.Z. 321 19. I-I D.M. 277 64. II-II H.A.Z. 306 20. I-I D.M. 274 65. II-II H.A.Z. 329 21. I-I D.M. 277 66. II-II D.M. 299 22. I-I D.M. 251 67. II-II D.M. 293 23. I-I D.M. 251 68. II-II D.M. 274 24. I-I D.M. 244 69. II-II D.M. 268 25. I-I D.M. 257 70. II-II D.M. 262 26. I-I D.M. 262 71. II-II D.M. 260 27. I-I D.M. 246 72. II-II D.M. 265 28. I-I D.M. 246 73. II-II H.A.Z. 293 29. I-I D.M. 244 74. II-II H.A.Z. 293 30. I-I D.M. 257 75. II-II H.A.Z. 303 31. I-I D.M. 246 76. II-II H.A.Z. 296 32. I-I D.M. 260 77. II-II D.M. 293 33. I-I D.M. 254 78. II-II D.M. 280 34. I-I D.M. 254 79. II-II D.M. 286 35. I-I D.M. 265 80. II-II D.M. 271 36. I-I D.M. 254 81. II-II D.M. 286 37. I-I D.M. 244 82. II-II D.M. 260 38. I-I D.M. 265 83. II-II H.A.Z. 289 39. I-I D.M. 265 84. II-II H.A.Z. 289 40. I-I D.M. 241 85. II-II H.A.Z. 296 41. I-I D.M. 246 86. II-II B.M. 280 42. I-I D.M. 234 87. II-II B.M. 286 43. I-I D.M. 239 88. II-II B.M. 286 44. I-I D.M. 244 89. II-II B.M. 280 45. I-I D.M. 219 90. II-II B.M. 280

Page 13: buletin stiintific

9

55

A

11 0.12 A 45º 10

8 10

0.12

= =

Rc=0.25 90º±2º

Figure 5 The shape and the dimensions of the impact bend strength samples

Table 3. The results of the tenacity tests

Breaking energy, KV,J Sample Testing temperature, °C Experimental

values Average value

1. 88 2. 57 3.

+ 20 62

69

4. 34 5. 39 6.

- 20 34

36

3.4 Micrographics examinations

The research of breaking surfaces needed microfractographies images by electronic microscope.

Figures 6 and 7 present some microfractographies images performed on impact bend strength samples broken at temperatures of 20 and – 20 °C.

The breaking surfaces of the tested samples at the environment temperature have a ductile character (the breaking is preceded by an important plastic deformation) and a fibred aspect (figure 7).

The samples broken at temperature of – 20 °C present mainly a fibred aspect, although some zones with crystalline aspect appear (figure 6a). In the speciality literature one considers that the ductile-fragile transition temperature is the testing temperature whereon 50 % from the breaking surface has a fragile character.

Because, in the present case the breaking surface is mainly ductile, results the transition temperature is below – 20 °C.

In order to show the welded joint structure, macroscopic, general, microscopic and detailed examinations were performed.

The macroscopic examination shows the structural and chemical composition heterogeneities appeared by welding and every time precede any microscopic analysis.

For experiments, the used samples were cut normally on the welding longitudinal axis (samples with transversal faces). The chemical attack using the NITAL reactive (10 %) permitted the defining of the macroscopic profile of the welded joint (figure 8), the lack of the defects from the root zone, of the joining defects, pores and slag inclusions.

Also, it can be observed the execution order of the welding lines and the annealing treatment effect obtained by multi passes welding.

The micrographic analysis offers observations about the welded joint quality and eventually about the welding technology optimisation. Figures 9…12 present some microstructural images obtained in different joining zones. Analyzing these images one can observe:

- appearance in the exterior zone of the deposited metal of a structure composed from Widmannstaetten ferrite and bainite, which lead to the hardness increasing;

- in the central zone of the deposited metal a ferrito-troostitic structure, provoked

Page 14: buletin stiintific

10either the normalization or the incomplete annealing treatment; such of structure decrease the hardness and improves the tenacity characteristics;

- in the H.A.Z. a ferito-pearlito-troostice structure with a soft tendency towards

Widmannstaetten type and a increased granulation (N = 5-6); the hardness increasing in this case is not significant;

- in the B.M. a ferrito-pearlitic structure specific to a hypoeutectoid steel for the welded constructions.

3 µm

3 µm a - mixed breaking, ductile + fragile b – ductile breaking

Figure 6. The micrographic aspects of the impact bend strength samples broken at T = – 20 °C

3 µm

3 µm a - ductile breaking b – ductile breaking

Figure 7. The micrographic aspects of the impact bend strength samples broken at T = + 20 °C

Figure 8. The macroscopic aspect of the welded joint

Page 15: buletin stiintific

11

20 µm

40 µm 250:1 500:1

Figure 9. Deposited metal – exterior zone

20 µm

40 µm 250:1 500:1

Figure 10. Deposited metal – central zone

20 µm

40 µm 250:1 500:1

Figure 11. Heat affected zone

Page 16: buletin stiintific

12

20 µm

40 µm 250:1 500:1

Figure 12. Base Material 3.5 The chemical composition of the

structure From the MAG welded joint a sample was

cut containing only the deposited metal used further for the chemical analysis.

The chemical composition determination of

the deposited metal was made by spectral methods.

The obtained results are presented in table 4, they demonstrating that the welding technology was correct elaborated and the used addition material assures good physico-chemical characteristics for the deposited metal.

Table 4. The chemical composition of the deposited metal Chemical composition, % Sample C Mn Si P S Ni Cr

Deposited metal 0.11 1.98 0.72 0.021 0.019 0.11 0.10

STAS norms

1126-87

max.

0.12

1.80 …

2.20

0.60 …

0.90

max.

0.03

max.

0.03

max.

0.30

max.

0.20 4. Conclusions

The optimal parameters of the thermal welding regime using a full wire of S12Mn2Si have the following values: Is=160-180 A; Ua=22-23 V; vs=18-30 cm/min; Q=10-13 l/min.

The mechanical characteristics values of the welded joints offer a high operating safety of the realized products both under the mechanical resistance aspects and of the plasticity reserve.

The microstructure of the welded joint zones is composed from Widmannstaetten ferrite and a small proportion of baininte in the exterior zone of the deposited metal, which provokes its soft hardening. References 1. I. Mitelea, B. Radu – Matalografia îmbinărilor

sudate, Editura de Vest, Timişoara, 2006,ISBN (10)973-36-0433-X

2. R. Probst, H. Herold Kompendium der Schweißtechnik, Schweißmetallurgie, DVS-

Verlag GmbH, Düsseldorf, 1997, ISBN 3-87155-159-7

3. M. Subana and J. Tusek, Dependence of melting rate in MIG/MAG welding on the type of shielding gas used, Journal of Materials Processing Technology, Volume 119, Issues 1-3, 20 December 2001, pp. 185-192, ISSN 0924-0136

COMPORTAREA LA SUDAREA M.A.G. A OŢELURILOR PENTRU CONSTRUCŢII

NAVALE Rezumat Lucrarea conţine rezultate experimentale obţinute la sudarea M.A.G. a oţelurilor pentru construcţii navale, livrate sub formă de table laminate la cald cu grosime de 20 mm, selectând ca material de adaos sârmă plină S12Mn2Si. Aprecierea calităţii îmbinărilor sudate s-a făcut prin examinări sclerometrice, încercări mecanice şi investigaţii micrografice optice şi electronice.

Scientific reviewers: Waltraut BRANDL , Fachhochschule Gelsenkirchen, Germany Victor BUDĂU, University “Politehnica” of Timişoara, Romania

Page 17: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

THE EVALUATION OF THE CRACKING PIPE’S MATERIALS AND THEIR BEHAVIOR TO CREEP

Mihai HLUŞCU*, Pavel TRIPA*, Marius DUMBRAVĂ*

* Mechanical Engineering Faculty, Bv. Mihai Viteazu No. 1, 300222 Timişoara, România, [email protected], [email protected], [email protected]

Abstract. The estimation of the lifetime for equipments and installations working at high temperatures represent an actual problem. In the last years, there have been proposed a lot of methods in order to evaluate the lifetime for the equipments working under creep conditions. In the frameworks of the paper, some results regarding the behavior of pipes belonging to a methane gas cracking reactor are presented. Pipes worked on about 160.000 hours under a pressure of 14 atm and a temperature of 800°C. The behavior of the pipes under above mentioned pressure has been calculated and plotted. Creep tests were performed at 650 and 800°C, and on these bassis was evaluated the creep strength of the material. With “Larson-Miller” method the results were prolonged for spans shorter than 10.000 hours. The creep strength variation curves, drawn for 1000 and 100000 hours can be used for predictions about the lifetime at different temperatures. Keywords: mechanical characteristics, creep curve, creep strength, Larson-Miller parameter, high temperature. 1. Stresses quantification within the pipe’s walls

The quantification of stress is required so that we can compare the stress from the real load with the one from the classic load of creep of a cylindric test piece loaded to a monoaxial stretch.

The dimensions of the pipe’s wall are: - inner radius: a=16[mm]; - outer radius: b1=22[mm] and b2=30[mm]. Outer load: - inner pressure: pi=14[at.]= 1,418[MPa]; - working temperature: determined by reliable

measures on the pipe’s walls. The stresses that appear in the pipe’s wall can

be determined with the relations suited for the tube with thick walls. The stress is a capital and three-axial one. Because the values of the stress are relatively small, it can be considered that the strain is elastic and as a loading state, can be described by an equivalent stress, calculated with:

2)-( + )-( + )-( = (r)

2rz

2zt

2tr

echσσσσσσσ (1)

On the strength of the above relations, we

obtained the variation curves of the stress represented in figure 1 (for b1=22[mm]). The stresses’ distribution for b2=30[mm] is very much alike, having the extreme values smaller then the ones in figure1.

It can be noticed that the maximal values of the stresses are obtained on the pipe’s inner wall, pipes with outer radius b1=22[mm], and they have the following values:

[MPa] |1,418-| = || [MPa]; 4,602 = r,t, σσ maxmax [MPa]. 5,214 = [MPa]; 1,592 = ech,z, σσ maxmax (2)

For b2=30[mm], according to the expectations, we have found smaller values for all the stresses’ components, the maximum equivalent stress beeing:

Page 18: buletin stiintific

14[MPa] 3,432 = echσ

If on the thickness of the pipe’s wall is a

temperature variation of 5oC, the radial, σr, longitudinal, σz, and circumferential, σt, stresses, will have a variation, which is calculated with the following relations:

(3)

(4) The thermal stresses’ variations are

represented in figure 2. The maximum values are obtained for circumferential and longitudinal stresses and are: -8,904 [MPa], at inner surface,

σri

E α⋅ T⋅2 1 μ−( )⋅

1ln k( )⋅ ln ρ i( )−

k2

1 k2−

11

ρ i( )2−⎡⎢

⎢⎣

⎤⎥⎥⎦

⋅ ln k( )⋅−⎡⎢⎢⎣

⎤⎥⎥⎦

⋅:=

Wall’s thickness, [mm]

Stre

sses

, [M

Pa]

Figure1. Stresses’ distribution for b1=22[mm]

Wall’s thickness, [mm]

Stre

sses

, [M

Pa]

Figure 2. Thermal Stresses’ distribution for b1=22[mm]

σzi

E α⋅ T⋅2 1 μ−( )⋅

1ln k( )⋅ 1− 2 ln ρ i( )⋅− 2

k2

1 k2−

⋅ ln k( )⋅−⎛⎜⎜⎝

⎞⎟⎟⎠

⋅:=

σt i

E α⋅ T⋅2 1 μ−( )⋅

1ln k( )⋅ 1− ln ρ i( )−

k2

1 k2−

11

ρ i( )2+⎡⎢

⎢⎣

⎤⎥⎥⎦

⋅ ln k( )⋅−⎡⎢⎢⎣

⎤⎥⎥⎦

⋅:=

Page 19: buletin stiintific

15and 7,205 at outer surface. The maximum radial stress is obtained in the middle of the wall and it is: -0,637 MPa. 2. Creep tests, For the quantification of the creep resistance limit, at the following temperatures : θ1=650 and θ2=800°C.

For the quantification of the creep resistance limit, σR/1000/θ, at temperatures of 650°C and 800°C,

have been made creep attempts until breakage, on 4 test pieces. The attempts have been made in special conditions, provided by Technical Prescriptions "C29-93",[6], with a creep machine with 3 posts, model ZST 3/2. Each test piece had been loaded to a different load, constant from the beginning until the end of the attempt, registering : the value of the stress, time until breakage and the values of the strains, so that we can draw the creep curves.

The shape of the creep curves, ε=f(t), is a

regular one, the curves having all the three creep stages. In figure 3 is presented the creep curve for σ=180 [MPa] and for θ=650°C.

The results of the attempts are presented in Table 1, where: θ and σ are the temperature and the stress whereat the attempts have been made; tr=the time until the breakage of the test piece, [hours]; εr= The specific strain at breakage, [%]; έmin= The creep’s minimal speed [1/hours]; PLM= The "temperature-time" parameter proposed by Larson-Miller.

As the direct extrapolation of the results is possible for spans maximum 10 times bigger then the span of the longest attempt made and the number of the available test pieces was small, it was prefered the extrapolation of the results with the parametric method "Larson-Miller". Accordingly to this method, we can calculate the following parameter:

] C + )tlg( [ T = P rLM ⋅ (2) where: - T= the temperature of the attempt, [°K], - tr= the time until the breakage of the test piece [hours],

- C= the extrapolation constant specific to each material; it’s value can be considered to be C=20.

The values pairs, [PLM-log(σr)], conformable to each attempt, represented in a chart, form the "Main Curve" of the material. In figure 4 was drawn the regression line, which estimates the points determined experimentally, regression line obtained with the program MCAD 6-PLUS and which has the following expression: P101,407 - 5,048 = )( LM

-4r ⋅⋅σlog (3)

The experimental points are best described by a

second grade curve, figure 5, determined with the program "TABLECURVE", and which has the following expression: )P( c + P b + a = )( 2

LMLMr ⋅⋅σlog (4) where: a=-2,0203522; b=5,0168181·10-4; c= -1,4497386·10-8.

With relation (4), using program MATCAD, it was calculated the sustained endurances’ values for seven different time values: 1000; 2000; 3000; 5000; 10000; 20000 si 100000 hours. For the above spans, we have determined the following temperature endurances: 650, 700, 750, 800, 850, 900 and 950°C. With these values it was drawn the sustained endurances’ variation curves within the following time limits : 1000 si 100000 hours,

Time, [hours]

0.3

0

ε1 i

400 t1 i

0 4 8 12 16 20 24 28 32 36 400

0.043

0.086

0.13

0.17

0.21

0.26

0.3

Cre

ep st

rain

, ε, [

%]

Figure 3. Creep Curve at 650°C and the stress of 180 [MPa]

Page 20: buletin stiintific

16figure 6. The curves have the temperature as their parameter.

With the above relation, using the program MATCAD, it was calculated the sustained

endurances’ values for eight different time values: 1000; 2000; 3000; 5000; 10000; 20000; 30000 and 100000 hours, (Table 2).

Table 1. Experimental creep tests No. test

specimen

θ [°C]

σ [MPa]

tr [h]

εr [%]

έmin·103 [1/h]

PLM [ ]

1 650 180 40 24,87 2,270 19940 2 650 160 559 21,32 1,528 20090 3 650 140 194 31,75 0,231 20570 4 650 130 321 33,62 0,159 20770 5 800 80 11 30,86 9,470 22580 6 800 60 69 42,14 3,110 23380 7 800 50 186 7,23 1,030 23490 8 800 40 299 53,2 0,432 24120

Figure 4. The estimation of the Main Curve with a regression line

Table 2. Creep resistance limit for different temperatures

Creep resistance limit, σR/θ/t, [MPa] θ,

[°C] 1000

[hours]

2000

[hours]

3000

[hours]

5000

[hours]

10000

[hours]

20000

[hours]

30000

[hours]

100000

[hours]

650 124,67 116,11 111,00 104,00 95,00 87,33 82,22 68,89

700 88,55 79,80 75,00 69,00 61,67 54,67 51,11 40,00

750 57,33 50,60 46,67 41,78 36,11 31,11 28,70 21,44

800 33,89 28,89 26,11 22,89 19,18 16,37 14,83 10,00

850 18,14 15,33 13,55 11,44 9,33 7,69 6,70 4,33

900 9,00 7,55 6,67 5,55 4,33 3,33 3,00 1,66

950 4,22 3,22 2,55 2,22 1,89 1,11 1,10 0,50

Larson-Miller parameter, PLM

Cre

ep re

sist

ance

lim

it, lo

g σ r

Page 21: buletin stiintific

Figure 5. The Main Curve for Pipe’s Material

Figure 6. The Variation of the Creep Resistance Limit, having temperature as parameter

3 Conclusions:

3. 1. The creep attempts have pointed out a big strain capacity until breakage, (30...50%), which excludes the possibility of fragile tearing.

3. 2. Because the number of the used test pieces was small, the maximum span of the attempts was of only 321 hours and the maximum temperature of the attempts, of only 800°C; the estimation through the extrapolation of creep’s characteristics for spans bigger then 10000

hours and for temperatures bigger then 850°C is purely orientative.

3. 3. On the strength of the maximum equivalent stress’ value, σech,max= 5,214 [MPa], (calculated with relation (1), for the preasure pI=14 [atm.]), have been determined, with:

max,

/000.10/

ech

Rcσσ θ= (5)

Cre

ep re

sist

ance

lim

it, lo

g σ r

Larson-Miller parameter, PLM

Breaking time, tr, in [hours]

Cre

ep re

sist

ance

lim

it, σ

r/θ, [

MPa

]

Page 22: buletin stiintific

18the following safety coefficients: → la 650°C ⇒ c = 18,27; → la 700°C ⇒ c = 11,8; → la 750°C ⇒ c = 6,93; → la 800°C ⇒ c = 3,69; → la 850°C ⇒ c = 1,79. These coefficients still confirm the exploatation

results of the material and it certifies the remarkable good endurance of the alloy INCOLLOY 800 in temperature variation conditions. 6. References 1. M. Hluşcu, “Consideraţii asupra fluajului oţelurilor

termorezistente în condiţii de temperatură variabilă”, Teză de doctorat, Timişoara, 2001 (Considerations on the creep of heat resistant steels under variable

temperature conditions, doctor's degree theses ) 2. D.R. Mocanu şi alţii, Încercarea materialelor , Vol.I,

Editura Tehnică, Bucureşti, 1982. 3. ***”MATCAD-Probleme de calcul numeric şi

statistic”, Editura Albastră, ClujNapoca,1995. 4. *** : ASRO Magazin 5. *** ”Prescripţii Tehnice pentru verificarea

deformaţiilor şi modificărilor structurale ale conductelor şi elementelor cazanelor de abur care funcţionează la temperaturi ridicate”, Prescriptii Tehnice ISCIR, Editura Tehnică, Bucureşti, 2003, (Technical prescriptions to check deformations and structural changes of pipelines and boiler elements working under high temperature conditions )

6. Prescripţii Tehnice C 10/1-2003 Cerinte Tehnice

privind montarea, instalarea, exploatarea, verificarea conductelor de abur şi de apă fierbinte sub presiune (PT ISCIR C 10/1-2003 Technic requirements regarding the assambling, installing, exploitation, repair, and verification of pressure steem and hot water pipelines) EVALUAREA COMPORTARII LA FLUAJ A UNOR CONDUCTE DE CRACARE Rezumat

Estimarea duratei de viaţă pentru echipamentele şi instalaţiile ce lucrează la temperaturi înalte, reprezistă o problemă actuală. În ultimii ani, s-au propus mai multe metode de evaluare a perioadei de viaţă pentru echipamentele ce lucrează în condiţii de fluaj. În contextul lucrării de faţă, sunt prezentate unele rezultate cu privire la comportamentul conductelor dintr-un reactor de cracare cu gaz metan. Conductele au fost exploatate continuu pentru aproximativ 160.000 ore, la o presiune de 14 atmosfere şi la o temperatură de 800oC. Comportamentul conductelor sub presiunea mai sus menţionată a fost calculat şi reprezentat grafic. Încercările de fluaj s-au efectuat la 650oC şi la 800oC, iar pe baza acestora s-a evaluat rezistenţa la fluaj a materialului conductelor. Cu metoda ”Larson-Miller” rezultatele au fost prelungite pentru intervale de timp mai scurte de 10.000 ore. Curbele de variaţie ale rezistenţei la fluaj, reprezentate grafic pentru 1.000 şi 100.000 ore, pot fi utilizate pentru prelungirea perioadei de exploatare a echipamentelor şi instalaţiilor ce lucrează la temperaturi înalte, la diferite temperaturi.

Scientific reviewers:

Ion DUMITRU, “Politehnica” University of Timişoara, Romania Nicolae FAUR, “Politehnica” University of Timişoara, Romania

Page 23: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

RECORDED CRACKS IN THE SHAFT OF A HYDRAULIC BULB TURBINE

Ilare BORDEAŞU *, Mircea Octavian POPOVICIU *,

Marian Dragoş NOVAC **, Marian BĂRAN **

* “Politehnica” University of Timişoara, Mechanical Engineering Faculty, Bv. Mihai Viteazu, No.1, Timisoara 300222, Romania, [email protected], [email protected]

** Hidroelectrica Iron Gates,Str Calugareni, No 1, Dr.Tr. Severin , 220037, Romania, [email protected], [email protected]

Abstract. Paper analyzes the failure appeared in the joint between the flange and the cylindrical body of the shaft. The aspect of the cracks is presented in some photographs. Taking into account this aspect, the material used, the processing and the running conditions it resulted the stringent necessity to study the fatigue process with the aim to establish the time interval after which the zone must be carefully examined to avoid important running damages. Keywords: cracks, chemical composition, corrosion, fatigue 1. Introduction

Repeated observations, of the bulb turbine shafts at Iron Gates II hydraulic power plant, resulted in discovering a critical zone in which appear numerous cracks disposed in parallel on the surface of the shaft. The failures have the length of about 10…15 mm and the depth of about 1…2 mm. The critical zone is placed in the vicinity of the flange coupling the shaft with the turbine runner. In order to analyze the causes that determine both the failure initiation and their subsequent development, there were realized photographs, the most significant being presented in the present paper. Examining those photographs was reached the conclusion that the failure was produced by fatigue phenomena, unavoidable during the running of turbines with horizontal axis.

The paper has to offer the answers for the following questions: description of the problem, what is done by other people, what the authors did, what is new, what is my contribution.

2. Shaft material and processing procedures

For different turbines, two distinct manufacturing processes were used to obtain the shaft. In the first one, the shaft is constituted from three distinct parts welded together (Figure 1).

Figure 1. The shaft of the hydraulic turbine (geometry

and applied forces)

Page 24: buletin stiintific

20For the second one, the shaft is forged from a

single piece. In the first case the two pieces closer to the electric generator are processed through forging but the flange for coupling with the hydraulic turbine runner is processed by casting. A heat treatment was applied after welding. In both cases, the half-finished shaft was machined to obtain the final dimensions and the prescribed surface roughness. The joint zone between the flange and the shaft was obtained by lathe cogging (Ra = 20 μm) [4-9].

As processing material, in both cases, was used the 2ΓC steel, having the following mechanical characteristics: Rm = 470.88 N/mm2, Rp02= 255.05 N/mm2, and the following chemical composition: C = 0,16…0,22%, Mn = 1…1,3 %, Si = 0,60…0.80%, Cr, Ni, Cu < 0,3% şi P , S <0.03%. From the chemical composition it can be seen that the quantity of chromium and nickel is insufficient to give a good corrosion resistance, inclusively inter crystalline corrosion. Taking into account the influence of the manganese upon the crystalline grains, we can appreciate that the principal alloy element determines a rough structure of the half- finished flange. Especially in the case of cast pieces, it result both great crystalline grains and a certain unevenness of their dimensions [3], [14-16]. In figures 2 and 3 the corrosion at the shaft surface can be clearly seen. It is determined by the reduced content of chromium and nickel in the chemical composition of the selected steel. Because the shaft of horizontal turbines is always subjected to fatigue, the existing corrosions spots represent starting points for cracks [1], [10-13], [15-16].

In figure 4 (taken for the turbine no. 1, H.E.P.P. Iron Gates II) the corrosion spots are preferentially arranged under circumferential lines. This situation is particularly critical because it predetermine the crack path.

Figure 2. Pitting corrosion (Turbine no. 9 – H.P.P. Gogoşu)

Figure 3. Pitting corrosion (Turbine no.1, H.E.P.P. Iron Gates II)

Figure 4. Preferential disposed corrosion pits (Turbine

no.8, H.E.P.P. Iron Gates II)

Taking into account the fact that the existing failures were generated through fatigue, we present some considerations regarding the importance of the surface finish for such situations. For large structural parts the finishing operation through mechanical processing is a very expensive one. On the other hand coarse roughness behaves as initiation points both for corrosion and for cracks. The recommendations are to increased smoothness of the surfaces [2]. From this point of view, we consider that the existing roughness is too great. In consequence it is recommendable: to improve the surface finish, locally, in the dangerous zone (for example with a manual held grinding machine, with felt disk, using simultaneously an abrasive paste); to eliminate the water in the same zone (for example by using a better tightening to forbid the access of water in the flange joint zone).

Page 25: buletin stiintific

213. The quantitative analyze of cracks, the manner in which they are formed and their propagation All the failures were examined in the field; a few of them are presented in the photographs of the present paper. The observations and the discussions can be followed by examining those pictures.

Figure 5. Recorded cracks

Analyzing the crack aspects in figure 5, the following conclusions can be obtained:

• the fillet zone between the flange and the cylindrical part of the shaft is placed in a humid zone; because that circumstance implies corrosion, the probability of fatigue cracks occurrence is increased;

• the crack develops under an arc of circle; • the failure has a notched shape, as a result

of the by the propagation among the structural grains [3], [6-9] and is specific for fatigue failures;

• the painted protection coating disappeared completely and the surface is covered with oxides coating.

Figure 6. Recorded failures

Analyzing the crack in figure, resulted the following conclusions:

• the failure has a notched shape, specific for fatigue failures;

• the crack was initiated in two separate planes, but after that they meet into a single failure (see the striking elbow); this aspect suggest the influence of the structured unevenness resulted from casting;

• on the failure edge there can be seen some spots which suggest that after the crack initiation it occur an accentuated chemical reaction.

Figure 7. Recorded failures

Analyzing the image in figure 7 it has been found that:

• the notched aspect of the circumferential crack presents pitting; we consider that those pitting constitutes the initiation points for the cracks; from here the failure develops both in the circumferential direction and the middle of the shaft;

• the aspect of the surface without cracks present a great roughness specific for cogging machining;

• the swelling zones of the painted coat suggest the existence of chemical reactions and the fact that the painting is on the point to be removed;

• red spots can be seen on the edge of the crack which suggest that simultaneous with the failure initiation both the surface and inter crystalline corrosion is accentuated.

Examining the image in the figure 8 it can be seen that:

• at the beginning the cracks were initiated and developed in multiple planes; such an aspect is typical for details manufactured from semi-products with

Page 26: buletin stiintific

22structural deficiencies or if they were subjected to an incorrect machining procedures (chromium carbides, great and non homogeneous structure grains, inadequate machining etc.) and subjected to cyclic and not symmetrical stresses (determined by an incorrect assembling or the incorrect distribution of the moving masses of the details subjected to complex stresses rotation-bending- compression + tension); the propagation path is different probably because the crack encountered some very resistant grains determined by the manganese as the principal alloy component;

Figure 8.a Cracks developed in multiple Planes

Figure 8.b Cracks developed in multiple parallel planes

• the aspects of the cracks is clearly those

specific for fatigue failure; the darkness of the paint, used for identifying and appreciation of the failure importance, show that the crack depth is profound and shaft repair works are needed;

• it were been observed zones in which, the cracks present a tendency to develop in

the joining zone after the direction of the cone generating line;

• the crack depth is important in both planes (circumferential and after the cone generating line); it was evident that the failure is old and the running with it resulted in the increase of the depth.

Figure 9a Numerous cracks (depths till 1,3 mm, length till 30 mm)

Figure 9b Repair work procedure

The image presented in figure 9 lead towards the following conclusions:

• initially there appear numerous crack lattice, distributed in many planes and oriented both under the circumference or generating lines, specific for bending ad torsion fatigue failure;

• the great number of this cracks is determined by the great number of the initiation points generated firstly by the manufacturing procedure (the surface roughness) but also by the variation in of the material properties in different points;

• depending on the crack depth, the repair work consisted in a new machining

Page 27: buletin stiintific

23operation (see Fig. 9b) in order to eliminate the cracks and to reduce the surface roughness; when possible a heat treatment is added.

The image in Figure 10 leads to the following conclusions:

• the cracks are generated and oriented in multiple planes; the length varies from 0.5 mm. to 30 mm. and the depth is small till 2 mm;

• the traces on the flange suggest the protected painting coating was removed through scraping; in these areas there appear also rusted spots which testify that the zone was subjected to a humid environment.

Figure 10 . Turbine no.1, cracks disposed in parallel whit small depths

4. Conclusions 1. The presented images and their analyzes suggest that the failure produced in the joining zone shaft flange – shaft cylindrical body is determined by the specific stresses, the material chosen, the manufacturing procedure and the running conditions (humidity). 2. The turbine running was in conformity with the allowed regimes and was continuously supervised and controlled. 3. The evaluation of the fatigue behavior of the bulb turbines shafts, using adequate computing procedures and professional software, are recommended

ACKNOWLEDGMENTS The present work has been supported by

the National University Research Council Grant (CNCSIS) PNII, ID 34/77/2007 (Models Development for the Evaluation of Materials Behavior to Cavitation), and Nr. RU

177/10.10.2008, BC 146/13.10.2008 (“Analiză privind soluţia de fiabilizare a arborelui turbinelor aplicată cu ocazia retehnologizării hidroagregatelor din CHE Porţile de Fier II. Propuneri de metodologie de urmărire în timp a stării arborilor turbinelor din CHE Porţile de Fier II şi CHE Gogosu”/ Analyze of the reliability solutions for the horizontal hydraulic turbine of the Power Plant Iron Gates II, applied in the upgrading period). Proposals for the shaft states examination methodology applied to the turbines of the Power Plants Iron Gates II and Gogoşu). References 1. I. Anton, - Turbine hidraulice, Editura Facla,

Timisoara, 1979. 2. M. Bărglăzan, I. Bordeaşu, M. Popoviciu,

V. Bălăşoiu, M. Madaras, C.D. Stroiţă, Asupra fiabilităţii mecanismului de reglare al paletelor aparatului director la turbinele axiale de tip bulb, Hervex 2007, ed. a XV-a, Secţiunea 1, Studii şi cercetări teoretice şi experimentale, noiembrie 2007, pp. 26-30, ISSN 1454-8003

3. M. Bărglăzan, I. Bordeaşu, M. Popoviciu, Analysis of the Guide Vane Regulating Apparatus for Bulb-Type Units, Machine Design, Monograpf University of Novi Sad, Faculty of Technical Sciences, 2007, pp. 191-196, ISSN 1821-1259

4. I. Dumitru, L. Marşavina, Introducere în Mecanica ruperii, Ed. Mirton, Timişoara, 2001.

5. R.G. Forman, V.E. Kearney, R.M. Engle, Numerical analysis of crack propagation in cyclic-loaded structures, Journal of Basic Engineering, Trans. ASME, Vol. 94, 1967, pp. 181-186, ISSN 0021-9223

6. J. A. Hartner, AFGROW users guide and technical manual, Wright-Patterson Air Force BASE, Ohio, 2008,

7. I. Mitelea, V. Budău, - Studiul metalelor, Indreptar tehnic, Editura Facla, Timisoara, 1987

8. Th. Pavelescu, I. Bordeaşu, M. Popoviciu, V. Bălăşoiu, A. Hadar, Considerations regarding the cracks of the stay vanes of a great dimensions kaplan turbine, Scientific Bulletin of the “Politehnica” University of Timisoara, Transactions on Mechanic, Special Issue, Tom 53 (67), Timisoara, 2008, pp.143-152, ISSN 1224-6077

9. Th. Pavelescu, I. Bordeaşu, M. Popoviciu, V. Bălăşoiu, Upon the problems of the cracks of the stay vanes of a great dimensions kaplan turbine, Hervex 2008, ed. a XV-a, Sectiunea 1, Studii si cercetari teoretice si experimentale, noiembrie 2008, pp. 67-78, ISSN 1454-8003

10. M. Popoviciu, I. Bordeasu, Necesitatea valorificarii micropotentialului hidraulic din România, Buletinul AGIR, Energii Alternative, 2007, pp.62-68, ISSN 1224-7928

Page 28: buletin stiintific

2411. M. Popoviciu, I. Bordeaşu, Tehnologia fabricaţiei

sistemelor hidraulice, Editura Politehnica, 1998, ISBN 973-9389-00-7

12. O. Rusu, M. Teodorescu, N. Laşcu-Simion, Oboseala metalelor, vol.1, Editura Tehnică, Bucureşti, 1992

13. J. E. Shigley, C. R. Mischke, Mechanical Engineering Design, Fifth Edition, McGraw-Hill, New Zourk, 1989

14. K. Walker, The effect of stress ratio during crack propagation and fatigue for 2024-T3 and 7075-T6, ASTM STP 462, ASTM, 1970

15. *** Analiză privind soluţia de fiabilizare a arborelui turbinelor aplicată cu ocazia retehnologizării hidroagregatelor din CHE Porţile de Fier II. Propuneri de metodologie de urmărire în timp a stării arborilor turbinelor din CHE Porţile de Fier II şi CHE Gogosu, (Analyze of the reliability solutions for the horizontal hydraulic turbine of the Power Plant Iron Gates II, applied in the upgrading period). Proposals for the shaft

states examination methodology applied to the turbines of the Power Plants Iron Gates II and Gogoşu) Contract nr. BC 146/13.10.2008

16. *** Fatigue Design Handbook, Second Edition, SAE, Warrendale, 1988

FISURI INREGISTRATE IN ARBORELE TURBINEI HIDRAULICE Rezumat Lucrarea analizează ruptura aparută la îmbinarea dintre flanşa şi corpul cilindric al arborelui. Aspectul fisurilor este prezentat în unele fotografii. Luând în considerare, materialul utilizat, procesarea şi condiţiile de funcţionare, rezultă necesitatea stringentă de a se studia procesul de oboseală, cu scopul de a se stabili intervalul de timp după care zona trebuie examinată cu grijă pentru a evita deteriorări importante la funcţionare.

Scientific reviewers: Mircea BARGLAZAN, “Politehnica” University of Timişoara, Romania

Lucian MADARAS, “Politehnica” University of Timişoara, Romania

Page 29: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

PROBLEMS WHEN USING ULTRASONIC WELDING FOR AUTOMOBILE CABLES

Mihaela POPESCU*, Emilia Georgeta MOCUŢA*,

Constantin MARTA**, Angela CÂNEPARU**, Remus BELU-NICA*** * Mechanical Engineering Faculty, Bv. Mihai Viteazu No. 1, 300222 Timişoara, România,

[email protected], [email protected] ** ISIM Timişoara, Bv Mihai Viteazu No. 30, Timişoara, [email protected], [email protected]

*** Eftimie Murgu University, Piaţa Eftimie Murgu No. 1, Reşiţa,320085, [email protected] Summary. The ultrasonic welding of cooper automobile cable system technological elements and characteristics of welding equipment have been detailed (illustrating the preparation, cleaning, welding). It is presented the control stages of quality assurance pocesus [1÷8]. Keywords: Automobile cables, cooper cables, ultrasonic welding, conductivity copper 1. Generalities

Automobile cables, made out of copper are ultrasonic joined with remarkable results. The properties of copper and its alloys that influence the welding process, advantages and disadvantages are indicated in Table 1 [2].

The use of copper to manufacture automobile cables is conditioned by the properties included in Table 2 and the influence of impurities on pure copper conductivity in figure 1.

2. Cables - general problems

In each auto vehicle there are, besides the electric energy producer, a generator and a battery, a lot of electric consumers (headlight, windshield wiper motor, starter etc.) and designation, guiding and adjustment systems (injection electronic system, catalyser etc.).

In order to keep into the auto vehicle a running general electric system, there should exist certain mutual electric connections between these components. These connections are realized by means of the automobile cable system [8].

As a cable system consists in more wires, each wire must be insulated separately, to avoid short-circuits with other cables. That is the reason why an electric cable is made of an electric conductor (stranded wire- the most frequently copper) and an insulated cover on above (plastic materials – the most often PVC or rubber).

Figure 1. Influence of impurities

As wires/cables should conduct different

current intensities, different sections of wires are necessary. These sections are calculated by

Page 30: buletin stiintific

26multiplying the area of the circular section of the conductor (stranded wire) to the number of

stranded wires in the cable. Table 2. presents usual sections of cables [2, 5, 7].

Table 1. Details on influences of copper properties on its welding behaviour

Properties influencing the welding operation

Disadvantages Applied measures

Parts are quickly heated Parts are quickly cooled Preheating Very strong heat sources welding

Extend under heat Cracks produce Preheating Creating the possibility of constriction and expansion of components

Absorbs the oxygen during the welding operation

Cracks appear Pores are forming

Protection of the melted pool by: - fluxes - electrode covering

Hydrogen penetrates the heated metal

Pores are forming Cracks appear (hydrogen disease)

Fluxes and electrode covering are dried

Table 2. Main characteristics of copper

Characteristic name Unit Values Annealed copper copper Density Kg/m3 8950 Melting temperature oC 1083 Fracture strength Rm N/mm2 200…250 400…490 Percentage elongation after fracture A % 50…30 4…2 Brinell hardness HB 40…50 80…120 Elasticity module E N/mm2 122000 126000 Electric resistivity ρ at 20oC Ωm 17.241.10-9 17.7.10-9

Resistivity temperature coefficient K- 3.39.10-3

Thermal conductivity at 20oC W/mK 3.9398 Linear expansion coefficient α K- 1.77.10-6

Recrystallization annealing temperature v 400…700

Table 3 Cable sections No. Conductor section [mm2] 1 0.35 0.5 0.75 1.0 2 1.5 2.5 4.0 6.0 3 10.0 16.0 25.0 35.0

• Classification of cables

PVC wall cable for auto vehicles with reduced thickness - are the most frequently used in the cable system and are assembled, for example, as supplying cables and signalling cables for lights, for indicating tools, for lifting windows. The structure of such a cable is presented in figure 2.

Figure 2. PVC wall cable for auto vehicles

Covered cable - that has another soft plastic

material cover over the insulating one, to protect against mechanical damages. They should be assembled especially where it is considered to be the highest dirty area, by sand and water spattering and stone hitting and where there is no protection from the car body. The structure is presented in Figure 3

Figure 3. Covered cable

The material of wires the cable consists in

has the following characteristics: diameter – 0.1…6mm, length 5mm…7m, electric resistance at

Page 31: buletin stiintific

2720o - 40Ω/Km, insulating material is a copolymer from ethylene vinyl acetate or polyurethane with the hardness 85± 5 HRC.

The base material for the given application is the copper conductor E-Cu 58 F21 DIN 40500 T 5, which resists at the temperature of 150oC for 240 hours (10 days) after being immersed in a 5% concentration solution.

The minimum initial elongation is 200% and after 168 hours (7 days) of loading at the temperature of 150 oC it reaches 125%, and after 150 oC loading 432 hours (18 days) it reaches 25%, respectively.

3. Fabrication flux – welding 3.1. Fabrication flux – presentation

The fabrication flux of automobile cable system is presented in figure 4:

Figure 4 Stages in the fabrication flux of

automobile cable system

• Deposit: In the deposit place all the material

necessary to fabricate the cable system is received and checked out as regards quantity and quality [4, 5]. Here from materials can have the following line:

- to the cutting shop In the cutting shop both hoses and wires are

cut at the necessary sizes. Wires are to be provided with fittings and contacts. The processed material will be transported to the band, to the working place or will be transported to preassembling place for ulterior works.

- to the preassembling shop At the preassembling shop processing

operation are performed, which could not be made by the cutting machines or which needed too much time to be band worked as the speed of the band could be not respected.

- to the work band The cable is put on the working line

according to the order. Separate modulus forming the whole cable system, will be assembled considering the instructions of each working place. So, there is, generally, wire area (where all parts and wires belonging to the cable system are put on a board) and the binding area (assembled wires are to be fixed by binding). On the band there are

performed special operations, too as for example: the ultrasonic welding, screwing in [1, 4]. 3.2. Application of ultrasonic welding in automobile cables

The ultrasonic welding process is applied in more fields, in electro techniques and electronics in the fabrication on micro components in welding aluminium and copper wires and sheets on different shape and size semiconductor components. It is also used for the capsulation of electronic components that should be protected by the atmospheric contamination. Electric current conductive components from different materials (aluminium, copper, silver) are ultrasonic welded as well as calibrated thin wires with high electric resistance used as filaments in different ignition devices of chemical reactions or explosions, [1÷8].

The ultrasonic welding is applied in the fabrication of thermocouples which imposes the achieving of metallic connections between different materials.

The ultrasonic welding process uses high frequency vibrations. It is realized by overlapping the parts to be welded on a welding “anvil”, as in figure 5 [1, 4].

Figure 5. Placing components

After placing, a certain pressing force is

applied to the parts to be welded. Then the upper side (or inferior one, according to the device) vibrates longitudinally due to the sonotroda which transmits the wave coming from the ultrasonic power generator, as in figure 6.

Figure 6. Pressure application

This process leads to the mutual friction of

the parts to be welded. The ultrasonic energy disperses the thin oxide layer from the surface of

Page 32: buletin stiintific

28the metals to be welded (cleaning the surface) and then the mixture is produced of the metal atoms without its melting. Atoms activated by this process mutually associate producing a true metallurgical link between parts. So, there results the fixing of the two metallic components, without filler material and melting (figure 7) [4, 5].

Figure 7. Fixing components - Presentation

In case there are more conductors, they are

vertically overlapped up to the superior available limit, then the following wires on a next run to the first package, on vertical plan, too.

In placing the conductors, always that having the thickest stranded wire section is located as near as possible to the sonotroda (the lowest).

Not always conductors having the smallest section and the thinnest stranded wires, for example the conductor of 0.35mm2 has thicker stranded wires than the 0.5mm2 section conductor.

The placing of the package is made so that the insulating distance up to the beginning of the weld should be 3- 5 mm and the distance from the end of the wires and the welding node is 0-1 mm.

Figure 8 illustrates the form of sonotroda, of the anvil, and of the mobile compacting parts as well as the placing mode of two conductors in the device [4, 6].

Figure 8. Stages: anvil – sonotroda

Placing example

When welding three conductors: 0.5mm2, 0.35 mm2, and 2.5 mm2 in section, the stages are as follows:

• The first to be placed on the anvil is that of 2.5 mm2 in section • The second, upward is that of 0.35 mm2 in section • The third, the last one upward is that of 0.5 mm2 in section • The placing modality is illustrated in figure 9 [8]

Figure 9 Placing conductors – placing order

• Wires compacting and measurement of the pressed package height • Switching out the ultrasonic vibrations, performance of the welding and measurement of the welded package height • Untie the mobile parts to free the welded package

The stages of the ultrasonic welding process are illustrated in figure 10.

An inspection system is applied; it is capable to check the automobile cable system with a much more speed than that of the human operator and to eliminate the subjective factor.

The ability to recognize defects and to stop production as soon as possible, immediately after the appearance of the defect is very important. This system can be applied to control materials in different fabrication stages of the technological process. All is developing in real time and so the cost of the immediate detection of defects is much reduced. Systems can realize the inspection of a representative set of welds, where from their characteristics are to be learned, adapting them to the requirements of the fabrication stage. So, the automated control system equipment can use different additional helpful technologies such as a profile to reduce defects that have appeared after the ultrasonic welding operation.

The inspection to be applied to the cables consists in: • Visual testing of welds: [SR EN 970] it looks for stranded wires not to be crashed, not to be out of the weld, an overheating of the weld is not allowed, no cracks are allowed in the weld, no inclusions, welding of tined wires is not allowed.

Page 33: buletin stiintific

29• Bending testing: consists in bending wires two times upward at 90o and then return to the initial position. Following this test the breaking of the stranded wires is not allowed. Measurement test –

exfoliation test: the wire having the smallest section is exfoliated in the node. The testing is made without insulating elements at nodes.

a – preparation of wires b – placing wires

c – welde wires d – control of wires

e – sleeve insulated wires f – textile band insulated wires

Figure 10. Stages a-f of the ultrasonic welding process

Table 4 presents the minimum values of the exfoliation force depending on the minimum section. None of the individual values should be smaller than the minimum value.

Table 4. Exfoliation force

A (mm) 0.35 0.50 0.75 1.0 1.50 2.50 4.0 6.0 10.0

F (N) 12 15 23 35 45 70 100 1301 165

• Measurement test – tensile force: to avoid the appearance of shear forces opposed forces are selected so that the longitudinal axis of the node is parallel with the stresses wire. The section of the

opposed wire should be greater than of the tested wire. The parameters of the control device are presented in table 5.

Table 5. The parameters of the control device

A (mm) 0.35 0.50 0.75 1.0 1.50 2.50 4.0 6.0

F (N) 60 80 120 160 200 250 350 400

Where: A – section of the wire; F – tensile force • Auditor control: In the serial production the visual testing of the cable system is performed twice on the shift and defects are registered in an error file.

Page 34: buletin stiintific

30• Visual testing of the operator: the self testing of the operator consists in the 100% control of the following characteristics: the wire insulation is not allowed to be damaged or deformed; the surface should have a uniform aspect. 4. Conclusions 4.1. The problems of the automobile cable system have been dealt with. It insisted on the problems related to copper and its alloys, on the copper welding behaviour, respectively [1÷8]. 4.2. The fabrication flux was presented with details on the application stages. 4.3. The ultrasonic welding of automobile cable system, technological elements and characteristics of the equipment have been detailed with particularization on the given case, illustrating the preparation, cleaning, welding and control stages. 4.4. It deals with aspects related to the quality assurance of the automobile cable system, insisting on the compulsory control of the cables. References 1. G. AMZA: Ultrasunetele: aplicaţii active,

Editura AGIR, BUCUREŞTI, 2006, ISBN 973-27-0942-1

2. J.R. DAVIS: Copper and copper alloys, ASM International Handbook, 2001, ISBN 0-87170-689-X

3. K. HANAZAKI: Cross section of wire welded by ultrasonic, YAZAKI TECHNICAL

REPORT, 2002, no. 23, pp. 10-12, ISSN 0386-3794

4. A. JAQUEMOD; J.PH. TOCK; J.M. BALAGUER; F. LAURENT; L. VAUDAUX: Qualification and start of production on the ultrasonic welding machines for LHD Interconnections, IEEE Transactions, 2006, vol. 16, issue 2, pp. 1729-1732, ISSN 1063-6706

5. L.F. JEFFUS; Welding – Principles and applications, 2002, ISBN 1-4018-1046-2

6. T. KUPRYS; J. JANUTENIENE; R. DIDZIOKAS; Strength of copper wire connections welded by ultrasonic, MECHANIKA, 2007, no. 3(65), pp. 30-33, ISSN: 1392-1207

7. H. LIPOWSKY and E. ARPACI: Copper in the automotive industry, Ed. Wiley-VCH, 2007, ISBN 978-3-527-31769-1

8. xxx: Flat cable connector for ultrasonic welding. European Patent Application EP 1014516

PROBLEMELE UTILIZĂRII SUDĂRII CU ULTRASUNETE A CABLURILOR DE AUTOMOBILE Rezumat Sudarea cu ultrasunete a cablurilor de cupru pentru sistemul electric al automobilelor este detaliat sub aspectul caracteristicilor tehnologice ale echipamentelor de sudare (ilustrarea fazelor de pregătire, de curăţare, de sudură). Se perzinta etapele de control ale procesului de asigurare a calităţii [1 ÷ 8].

Scientific reviewers: Ion MITELEA, “Politehnica” University of Timişoara, Romania

Victor BUDĂU, “Politehnica” University of Timişoara, Romania

Page 35: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224-6077 Fasc. 2, 2009

EVALUATION OF THE PROPERTIES OF THE PRODUCT GAS GENERATED FROM THE GASIFICATION OF

SOLID RECOVERED FUELS

Loránd KUN*, Gregory DUNNU**, Jörg MAIER** * Mechanical Engineering Faculty, Romania, Bv. Mihai Viteazu No. 1, 300222 Timişoara, România

e-mail: [email protected] ** University of Stuttgart, Institute of Process Engineering and Power Plant Technology, Germany

Abstract. Within the context of European Union (EU) energy policy and sustainability in waste management, recent EU regulations demand energy efficient and environmentally sound disposal methods of Municipal Solid Waste (MSW). Currently, landfill is the preferred option in the EU and many other countries. Within the waste management hierarchy thermal disposal especially incineration is a viable and proven alternative. In recent years, pyrolysis and gasification technologies have emerged to address these issues and show a potential to improve the energy output. This paper presents the gasification with air of Solid Recovered Fuels (SRF) in a bubbling fluidized bed (BFB) reactor under six different operating conditions. The composition of the syngas has continuously been measured by online gas analysis and by the discontinuous method, gas chromatography. The tar content has also been determined, by absorption in isopropanol and gravimetric analysis. The energy content of the generated syngas and the efficiency of the SRF-to-syngas conversion were examined. Keywords: gasification, solid recovered fuels, syngas, bubbling fluidized bed, cold gas efficiency 1. Introduction

In recent years, the quantity of MSW has increased significantly in the EU and other industrialized and developing countries raising the question of its sustainable disposal management. Within the waste management hierarchy, thermal disposal, especially incineration with energy recovery, is desired, viable and an option often used in industrialized nations. In the EU, incineration of MSW lags currently behind the established waste management option, landfill. However, the situation differs considerably between the Member States. While considerable advances have been made in the older Member States regarding the reduction of the MSW quantity disposed of to landfills, the new Member States, such as Romania, Poland and Bulgaria,

still rely nearly 100% on this technology. Given the EU landfill directive 1999/31/EC and the recent approval of the new waste incineration directive 2000/76/EC [1], more stringent requirements are imposed on the landfill option, which turns waste management in favor of incineration among preferential waste minimization, reuse and recycling.

Moreover, in the recent past and in the future, thermal waste disposal is and can not only be seen as a thermal treatment process for inertization and the reduction of the amount of MSW by weight and volume. Thermal disposal methods provide also for recovery of the chemical energy of MSW demanded by the Integrated Pollution, Prevention and Control (IPPC) directive 96/61/EC. Thus, MSW is to be seen as a valuable indigenous source of fuel abundant

Page 36: buletin stiintific

32especially in consumer-oriented societies able to substitute or supplement fossil fuels in power generation and other industrial processes thus ensures the security of energy supply.

Thermal treatment technology (including gasification) applied to MSW is considered one of the best approaches to reduce land-filling in terms of environmental impact, energy recovery and preservation of natural resources.

Gasification and pyrolysis are well proven energy efficient and environmentally sound technologies providing also for the processing of MSW.

Gasification of SRF is not a new technology, it comes with the following recognized advantages: the usage of renewable resources helps to save the fossil reserves and makes the technology sustainable, the resulting syngas has a large number of potential applications (Figure 1), low environmental impact by extensive gas cleaning. This technology enables a wide range of energy resources to be converted into environmentally friendly chemicals and fuels.

Figure 1. Syngas utilization routes

In case of utilization in a decentralized

process, such as a gas turbine or internal combustion engine, the syngas has to meet strict regulations regarding the pollutant concentrations and the NCV. The centralized process, on the other hand, which means the co-incineration of the gas in a burner along with a primary fuel such as coal or oil, does not require extensive cleaning, provided that the existing facility has the necessary flue gas cleaning equipment installed.

In this work SRF was gasified with air under different operating conditions. The energy content of the syngas and the efficiency of the SRF-to-syngas conversion are examined. 2. Solid Recovered Fuels

The term Solid Recovered Fuels summarizes all non-hazardous waste streams usable for energy recovery in waste incineration [2], co-incineration or gasification plants. SRF are basically composed of the non-hazardous high calorific fractions from MSW, i.e. paper, cardboard, textile and plastic materials.

Generally, in order to obtain SRF, MSW undergoes a mechanical treatment, during which the different fractions are separated, or a

mechanical biological treatment (MBT), which implies an additional biological drying stage.

A picture of the SRF used during the experiments is shown in Figure 2.

Figure 2. SRF derived from MSW

The Net Calorific Value (NCV) of SRF

syngas can be compared to the NCV of syngas produced by the gasification of biomass. According to the literature [3], the NCV of biomass syngas is usually between 4-6 MJ/Nm3 when gasified with air, and 10-15 MJ/Nm3 when gasified with oxygen.

Page 37: buletin stiintific

33The possible utilization routes (co-

combustion also including gasification) for SRF are presented in Figure 3.

Figure 3. SRF utilization routes [2]

3. Experimental setup

The gasification experiments were conducted in an electrically heated fluidized bed reactor. The reactor can be operated either as a

bubbling or a circulating fluidized bed facility. A schematic overview of the facility is given in Figure 4.

Figure 4. Bubbling/circulating fluidized bed reactor [4]

Page 38: buletin stiintific

34 The main element of the reactor is a

stainless steel tube with a diameter of 108 mm in the bed section, and 135 mm in the freeboard section. The reactor has an overall height of 3000 mm. Along its axis, the reactor is equipped with different locations for secondary air injection. It has five, separately controlled electrical heating zones, of approximately 3.6 kWe each, which can produce an operating temperature of maximum 1000 °C. Primary air can be preheated to 600 °C [5]. The facility can be operated with coal, biomass or SRF. The dosing units are composed of double-screw feeding devices and electronic scales. As fluidizing agent, oxygen, air and/or steam can be chosen. Ash removal is realized using a cyclone and a ceramic candle filter. The bed material consists of quartz sand, whereas different particle sizes have to be used for the two operating modes. During measurement, flue gases are extracted at the top of the recirculation loop.

During the experiments, the facility was operated in BFB mode. As fluidizing agent, air was chosen. As bed material, quartz sand with particle sizes between 200-400 µm was chosen.

The SRF with particle sizes < 5 mm was fed to the reactor bed at a mass flow rate of 3 kg/h.

Experiments were conducted under different operating conditions, at reactor temperatures between 700 and 850 °C, respectively fuel-air ratios (λ) between 0.25 and 0.35. These value ranges were chosen in order to evaluate the influence of operating temperature and λ on the product gas composition.

The product gas’s composition was continuously analyzed using an on-line gas analyzer to measure the concentrations of H2, CH4, CO, CO2 in the syngas. Minor gas compositions, e.g. C2H4, C2H6, C3H6, C3H8 and C4H10, were determined using the discontinuous method, by gas chromatography. The gas chromatographer used for the discontinuous determinations was equipped with a Thermal Conductivity Detector (TCD).

The tar content of the gas has also been determined. There is no unique definition of the term tar, but there is a broadening consensus in defining it as organic contaminants with a molecular weight larger than benzene (78 kg/kmol) [6]. The methodology in this case was absorbtion in isopropanol followed by gravimetric laboratory analysis using a rotary evaporator. The flow chart for the tar absorbtion setup is presented in the following figure:

Figure 5. Tar capture setup

After the hot syngas (over 250 °C) exited

the reactor, it entered the liquid quench zone, where it was mixed with the cold isopropanol (-20 °C) supplied by the recirculation pump.

After exiting the bottle in the liquid quench zone, the syngas passed through three further bottles containing isopropanol, in order to ensure that all the tar compounds were retained in the solvent.

Further on its way, the syngas was dried with silica-gel, it passed through the flow regulator, the rotameter, and the gas clock. Its temperature and relative pressure were also measured in parallel. Finally it got burned in the burner.

The above obtained solution was submitted to a gravimetric tar analysis, which consisted of the controlled evaporation of the isopropanol in a

Page 39: buletin stiintific

35rotary evaporator. A picture of this laboratory equipment is presented in the following figure:

Figure 6. Rotary evaporator

The working principle of this equipment is

basically simple. The flask with the sample is positioned on the rotating head and lowered into the heated water bath (55 °C). A vacuum pump is attached to the system and it lowers the pressure in the system, close to 0 mbar, if necessary (in our case 100 mbar). Thus, heated, agitated by the rotation of the flask and in a low pressure chamber, the isopropanol evaporates and it rises to the upper part of the chamber where it condenses on a spiral condenser, cooled by tap water. From the condenser, the condensed isopropanol flows into the collector flask, at room temperature. 4. Results and discussion

Maintaining a constant SRF mass flow into the reactor is still problematic and it represents a challenge to be solved in the future applications of this technology.

It was found that by rising the operating temperature, the tar quantity contained in the product gas has increased.

The Cold Gas Efficiency (CGE) – the thermal efficiency of the gasification process reported to the standard conditions of the product gas (1013 mbar, 273 K) – has also been calculated.

The experimental results show that for an operating temperature range between 700 and 850 °C, at constant λ = 0.3, the tar contained in the syngas varied between 4.0 and 5.6 g/Nm3, while the NCV of the gas was 3.7 - 4.6 MJ/Nm3 at a CGE of 50 – 62 %.

The resulted syngas can be categorized as a low quality gaseous fuel, comparable to the syngas obtained from the gasification of biomass.

5. Conclusions The experiments have demonstrated that the

gasification of SRF in a fluidized bed facility is feasible and it allows the integration of waste derived fuels into the energy supply chain. The best configuration produced syngas of NCV of 4.6 MJ/Nm3, (850°C). and the highest conversion of SRF-to-syngas also occurred at the same configuration.

The presented technology has a huge potential in the new EU Member States, such as Romania and Bulgaria, where landfilling is basically the sole waste management option. The implementation of SRF gasification technology for the production of syngas to be co-incinerated in existing fossil power plants may seem the economically and technologically sound solution, but it poses environmental issues due to the relatively high concentrations of heavy metals, chlorine, sulfur and organic compounds in the syngas. Since the currently installed gas cleaning equipment is not suitable for retaining the mentioned pollutants, the best final utilization of the produced syngas would be the utilization in a decentralized process for the production of different chemicals or fertilizers. References 1. R. Berger, M. Michel, M. Specht, Marquard- T.

Möllenstedt, , T. Weimer, High temperature CO2 absorbtion – A new technology for CO2 capture and hydrogen production, Proceedings of the International Nordic Bioenergy Conference, Finland, 2003

2. D. Brown, , M. Gassner, T. Fuchino, F. Maréchal, Thermo-economic analysis for the optimal conceptual design of biomass gasification energy conversion systems, Applied Thermal Engineering, Volume 29, Issues 11-12, Elsevier, August 2009, ISSN: 1359-4311

3. T. Hilber, UPSWING – An advanced waste treatment concept compared to the state-of-the-art, PhD Thesis, Cullivier Verlag, Göttingen, 2008, ISBN : 978-3-86727-563-7

4. J. Maier, A. Gerhardt, G. Dunnu, T. Hilber, Solid Recovered Fuels (SRF) – Determination of combustion behavior, CEN/TC 343 – WG4 N 0201– Technical Report – DRAFT (WI 00343035)

5. T. Malkow, Novel and innovative pyrolysis and gasification technologies for energy efficient and environmentally sound MSW disposal, Waste Management, Volume 24, Issue 1, Elsevier, 2004, DOI: 10.1016/S0956-053X(03)00038-2

6. ***: http://www.btgworld.nl/, Accessed: 2009-07-20

Page 40: buletin stiintific

36EVALUAREA PROPRIETĂŢILOR GAZULUI GENERAT PRIN GAZIFICAREA COMBUSTIBILILOR SOLIZI RECUPERAŢI Rezumat În cadrul politicii energetice şi de sustenabilitate în managementul deşeurilor din Uniunea Europeană (UE), recentele normative adoptate impun metode cu eficienţă energetică ridicată şi nepoluante, în ceea ce priveşte depozitarea deşeurilor solide municipale. La ora actuală, depozitarea în gropi de gunoi este opţiunea preferată în UE şi în multe alte ţări. În ierarhia managementului deşeurilor, dispunearea pe cale termală, în special incinerarea, este o alternativă viabilă

demonstrată. Recent tehnologiile de piroliză şi gazificare câştigă tot mai mult teren, acest lucru explicându-se prin potenţialul lor de a ridica eficienţa procesului. În această lucrare se prezintă gazificarea cu aer a combustibililor solizi recuperaţi într-o instalaţie în strat fluidizat, în condiţiile a şase configuraţii de operare. S-a analizat în mod continuu compoziţia gazului de sinteză generat prin analiză online şi în mod discontinuu, prin cromatografie. S-a determinat de asemenea conţinutul de gudroane, prin absorbţie în izopropanol şi analiză gravimetrică. S-au analizat conţinutul energetic al gazului de sinteză şi eficienţa transformării combustibilului solid în fază gazoasă.

Scientific reviewers: Ioana IONEL, “Politehnica” University of Timişoara, Romania

Dorin LELEA, “Politehnica” University of Timişoara, Romania

Page 41: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

AIR-FUEL i-x DIAGRAM FOR GASOLINE-BIOETHANOL BLENDS

Adrian IRIMESCU*

* Faculty of Mechanical Engineering, Bv. Mihai Viteazu No 1, 300222 Timişoara, Romania, [email protected] Abstract. As they are obtained from biomass, biofuels can significantly contribute to green house gas emissions reduction. The use of bioethanol for fuelling spark ignition engines raises an array of problems in the fields of fuel production, transport and other applications. In order to limit engine components damage due to the use of ethanol, different blending proportions of gasoline and alcohol are used, with the maximum limit of ethanol content being 10% for use in engines build to run on gasoline only. In vehicles equipped with engines built to run on gasoline as well as high ethanol concentration fuel blends, so called flex fuel vehicles, up to 85% bioethanol mixed with gasoline can be used, fuel blend commercially known as E85. An important aspect of ethanol as a fuel is its high latent heat of vaporization, making cold starts during winter very difficult. Using the air-fuel enthalpy-mass participation (i-x) diagram, a final mixture state can be calculated, as well as the quantity of fuel that actually evaporates. Keywords: bioethanol, spark ignition engines, air-fuel mixture, i-x diagram 1. Introduction

As biodiesel has become the main biofuel for compression ignition (CI) engines, bioethanol seems to be the fuel most likely to be used as an alternative for spark ignition (SI) engines. Bioethanol is a renewable energy source as it is obtained from biomass, and using it as a fuel produces less pollutant emissions.

The use of ethanol in SI engines is widely known on local levels in countries like Brazil for several decades. Only recently the interest for this biofuel has become a general issue [1]. Ethanol can be used in pure form E100 or as a blend with different proportions (E10 – 10% ethanol blend with 90% gasoline, E85 – 85% ethanol blend with 15% gasoline). One aspect of gasoline-ethanol blends is that they require a very high purity of ethanol (maximum water content is 1% in the US and 0.2% in Europe) compared to E100 which may contain up to 4.4% water, a product that can be obtained by classic distillation, with far lower cost [2]. Bioethanol is used in CI engines blended

with diesel fuel (Scania uses E95 – a blend of 95% bioethanol and 5% diesel – for fueling buses equipped with diesel engines [3]), but only at an experimental level.

Ethanol is an alcohol with a molar mass of 46.0684 kg/kmol [4], it contains two carbon atoms, six hydrogen and one oxygen atom, with the chemical formula of C2H5OH (figure 1). Energy density is lower compared to gasoline, while the energy contained in stoechiometric air-fuel mixtures is very close for both fuels (table 1). One important property of ethanol is its high enthalpy of vaporization, much higher then that of gasoline. This makes cold start during winter very difficult. A positive aspect is that using ethanol increases engine volumetric efficiency due to lower mixture temperatures. Another advantage of ethanol use in SI engines is that spark advance can be optimized, given the higher octane rating compared to gasoline, with an increase of combustion efficiency. In the US ethanol is

Page 42: buletin stiintific

38frequently used as an additive to improve gasoline octane rating (table 2).

An important property of ethanol is that it is fully miscible with water. By classic distillation 95,6% grade alcohol can be obtained, concentration level at which water and ethanol evaporate and condense together. Even if standard purity is assured, ethanol can be contaminated

with water even from air contained humidity. Thus an azeotropic solution forms inside the storage tanks that can separate from gasoline in a distinct layer at the bottom of the tank. Research on this issue showed that in ethanol-gasoline blends with more then 15% ethanol content phase separation does not occur and corrosive activity is greatly reduced [2].

Figure 1. Ethanol molecular structure [5]

Table 1. Fuel properties [4], [6]

Fuel Density [kg/l]

Energy density [MJ/l]

Stoichiometric mixture energy

density [MJ/kg]

Stoichiometric air-fuel ratio [kgair/kgfuel]

Vaporization enthalpy at 20°C [kJ/kg]

Gasoline 0,72 – 0,78 30,2 – 33,95 2,67 – 2,77 14,7 360 E10 0,73 – 0,78 29,30 – 32,67 2,67 – 2,77 14,1 420 E85 0,78 – 0,79 22,45 – 22,99 2,67 – 2,69 9,8 850

Ethanol 0,79 21,15 2,68 9 930

Table 2. Fuel octane rating [6]

Fuel MON [-]

RON [-]

Sensibility [-]

Gasoline 82 92 10 Ethanol 96 129 33

E10 83.4 95.7 12.3 2. Air-fuel i-x diagram

Mixture formation in port fuel injection SI engines is a complex heat and mass exchange process between intake air and injected fuel, with droplet size being the most important factor. The fuel droplets gradually evaporate in contact with air, a process very similar with water evaporation. Thus, the idea of using an enthalpy-fuel mass participation i-x diagram for air-fuel mixtures came about, like the humid air Mollier diagram [7].

When plotting the air-fuel i-x diagram several hypothesizes were used. Humid air was considered a mixture of ideal gases, given the low vapour partial pressure. Thus, ideal gas mixture laws like the Dalton and Amagat laws can be applied. Gasoline is a mixture of hydrocarbons with different boiling points at a given pressure level. For the i-x diagram plotting, gasoline was replaced with a mixture of four paraffin components, hexane (C6H14), heptane (C7H16), octane (C8H18) and decane (C10H22), a mixture with a distillation curve very close to that of

Page 43: buletin stiintific

39gasoline. Previous work on the i-x gasoline diagram replaced the fuel with three components [7], however, four components give calculations a better precision. Based on the distillation curve,

molar participations (yi) for every one of the four components can be calculated (figure 2).

Figure 2. Distillation curve for gasoline

Equations (1), (2), (3), (4) and (5) written

for a fuel with n components, allow for molar participations to be calculated at every point of the i-x diagram.

vvlli yyyyyii⋅+⋅= (1)

ii

i lv

sv y

p

py ⋅= (2)

1yn

1ili=∑

=

(3)

1yn

1ivi=∑

=

(4)

1yy vl =+ (5)

where yi is the molar participation of component i, with l standing for liquid and v for vapour, psi the saturation pressure for component i, measured in Pa and pv vapour pressure of the fuel vapour in the air-fuel mixture, measured in Pa.

After calculating yvi, yli and pv, vapour (xvi) and liquid (xli) fuel mass participations can be found using equation (6) and (7).

ii vL

i

v

vv y

MM

pppx ⋅⋅−

= (6)

ii lv

l

L

i

v

vl y

yy

MM

ppp

x ⋅⋅⋅−

= (7)

where xvi and xli are the vapour and liquid fuel mass participations in the air-fuel mixture, p is the absolute pressure of the mixture measured in Pa, Mi the molar mass of component i, and ML molar mass of air, both measured in kg/kmol.

Finally, fuel enthalpy (ic) can be calculated with equation (8), air enthalpy (iL) with (9) and mixture enthalpy (i) is the result of adding the two, with equation (10).

∑∑

=

==

⋅+

+⎟⎟

⎜⎜

⎛⋅+⋅⋅=

n

1iiv

n

1ipl

n

1ipvc

rx

cxcxti

i

iliivi

(8)

Page 44: buletin stiintific

40tci

LpL ⋅= (9)

cL iii += (10) where ic is the fuel enthalpy measured in J/kg, t is the mixture temperature in °C, cp constant

pressure heat capacity in J/(kg K), r latent heat of vaporization in J/kg, iL air enthalpy measured in J/kg and i air-fuel mixture enthalpy in J/kg.

The diagram is plotted (figure 3) by uniting enthalpy points calculated at dew point (constant pressure) and at constant temperature.

Figure 3. Gasoline air-fuel i-x diagram

Figure 4. E10 air-fuel i-x diagram

Page 45: buletin stiintific

41 The diagram can be divided into two areas,

the area above the so called saturation line and the one below. Saturation line is not a very precise definition, as with multi-component fuels like gasoline, liquid continues to evaporate even if more fuel is added after the first drops of fuel appear when one of the components reaches its saturation point. In the case of a single component fuel, the saturation line is the actual line where

any fuel added above an actual quantity does not evaporate. The saturated domain, where the mixture is formed by air, vapour and liquid fuel droplets, is situated below the saturation curve. The non-saturated domain, where the fuel is entirely evaporated, is found above the saturation line, and is much wider for higher temperature levels.

Figure 5. E85 air-fuel i-x diagram

Figure 6. E100 air-fuel i-x diagram

Page 46: buletin stiintific

42

Ethanol was added to the four components used to calculate gasoline properties, with the corresponding volumetric participations of a gasoline-ethanol blend E10 (figure 4) and E85 (figure 5). The influence of 10% ethanol mixed with gasoline is not significant, as the diagram closely resembles that of air-gasoline mixtures. Mixture enthalpy for E10 is slightly higher than that for gasoline at the same temperature level (figures 3 and 4). Higher mixture enthalpy means lower air-fuel mixture temperature after the fuel is partially or fully evaporated. An interesting phenomena is that saturation lines (or dew point lines) draw closer as the concentrations of ethanol increases, while the saturated domain widens. A narrow non-saturated domain means that less fuel can be evaporated when high concentrations of ethanol are mixed with gasoline. This is the reason why pure alcohol is used for fuelling engines only in regions where ambient temperature levels are always higher than 15°C. In countries like Canada, E85 fuel blends are actually a mixture of 75% ethanol and 25% gasoline during winter, as higher concentrations of alcohol would make engine cold starts very difficult. The i-x diagram for pure ethanol (E100) has a very different shape (figure 6), with straight lines at constant temperature in the saturated domain. 3. Conclusions

As biofuels have a great potential of carbon dioxide emissions reduction, they are very likely to be used on a wide scale. Given its low toxicity level, and because the production process is well known and understood, bioethanol is probably the best candidate as a biofuel for use in spark ignition engines.

Using air-fuel i-x (enthalpy i – fuel mass participation x) diagrams plotted for different gasoline-ethanol blends, the effect of alcohol mixed with fossil fuels used in spark ignition engines can be evaluated. The i-x diagram can prove a very useful tool when studying the effect of fuelling spark ignition engines with gasoline-bioethanol fuel blends. References 1. D. Iorga, A. Irimescu, L. Mihon, I. Vrabie,

L’Utilisation d’une méthode numérique de calcul basée sur les équations du diagramme i-x air-

combustible, pour la détermination des paramètres du mélange carburant d’un moteur à injection de l’essence à l’extérieur de cylindre, COFRET ’08, 11-13 juin 2008, Nantes, France, ISBN 2-6905267-61-5

2. S. Soimekallio, R. Antikainen, Assessing the sustainabilitz of liquid biofuels from evolving technoşogie, Ed. VTT, 2009, ISBN 978-951-38-7291-5

3. *** Automotive Engineer, The Magazine for the Industry, May 2008, Volume 33, No 5, pp. 41

4. *** Biofuels International, September 2008, Issue 4, Volume 2, pp. 67-71, ISSN 1754-2170

5. *** Feedstocks of the future, Biofurls feedstoks, Feedstocks of the future, Biofuels International, September 2007, Issue 4. volume 1. pp. 22-23 6. *** Fuel specifications and fuel property issues and

their potential impact on the use of ethanol as a transportation fuel – Oak Ridge National Laboratory Ethanol Project, Subcontract No. 4500010570, December 16, 2002

7. *** www.ethanolstatistics.com

DIAGRAMA I-X AER-COMBUSTIBIL PENTRU AMESTECURI DE BENZINĂ-

BIOETANOL Rezumat Fiind obţinuţi din biomasă, biocombustibilii pot contribui în mod semnificativ la reducerea emisiilor de gaze ca efect de seră. Utilizarea bioetanolului pentru alimentarea motoarelor cu aprindere prin scânteie ridică o serie de probleme specifice atât în domeniul producţiei cât şi în cel al transportului. Pentru a limita efectele negative ale etanolului asupra pieselor componente, concentraţia maximă de alcool utilizată în amestec cu benzina pentru alimentarea motoarelor construite, pentru a funcţiona cu benzină este de 10%. În cazul autovehiculelor echipate cu motoare construite pentru a putea fi alimentate atât cu benzină cât şi amestecuri cu o concentraţie mare de etanol, vehicule care în limba engleză sunt denumite „flex fuel vehicles”, se poate utiliza un amestec cu până la 85% alcool în amestec cu benzina, amestec cunoscut sub denumirea comercială de E85. Un aspect important al etanolului utilizat ca şi combustibil este căldura latentă de vaporizarea foarte ridicată, ceea ce poate îngreuna semnificativ pornirea la rece pe timp de iarnă. Utilizând diagrama entalpie-participare masică (i-x), se poate determina temperatura finală a amestecului, ca şi cantitatea de combustibil care se evaporă.

Scientific reviewers: Dănilă IORGA, “Politehnica” University of Timişoara, Romania

Ioana IONEL, “Politehnica” University of Timişoara, Romania

Page 47: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

SKETCH BASED 3D MODELING METHOD

Cristian CIOANĂ*, Tudor ICLĂNZAN*, Cristian COSMA*

* Faculty of Mechanical Engineering, Bv. Mihai Viteazu No 1, 300222 Timişoara, Romania, Email: [email protected], [email protected], [email protected]

Abstract: Objects that we use in everyday life are the product of centuries of scientific and technological development. Engineering work in general has the final realization of technical objects, which materializes as a result of complex production processes. Main stages of a product are: defining a general concept of the product, the technical project, the establishment of manufacturing technology, the experimental design and product approval, production itself. Before you start designing a product it has to be chosen the work methodology. The most famous methodologies are the Bottom-Up and Top-Down methods. In this paper will be explained the methodology of both approaches, also explaining the method called Sketch based 3D modeling, and in which category belongs. Keywords: Top-Down, sketch, spline curves. 1. Introduction

To better understand the definition of Product Design we must first define the area in which is used. Thus, Industrial Design is (as the Industrial Society of America defiance it) professional service for creating and developing concepts and specifications that optimize the function, value and esthetics of products for mutual benefit of both producer and consumer.

Industrial design is a form of art applied anywhere functionality and esthetics of products can be improved, to be manufactured later. Its role is to create solutions for engineering, marketing, brand development or sales. Design success is measured by the profits it’s making to the producer and the pleasure it’s offering for consumers.

Top-Down and Bottom-Up are two approaches for the manufacture of products. These terms have been applied for the first time in

nanotechnology by Foresight Nanotech Institute in 1989 in order to distinguish between molecular manufacturing (to mass-produce large atomically precise objects) and conventional manufacturing (which can mass-produce large objects that are not atomically precise).

Bottom-Up approach is seeking to have small parts, building more complex assemblies, while top-down approach seeks to create complex systems, controlling directly the subassemblies.

The methods Bottom-Up and Top-Down are strategies of processing information and ordering of knowledge, involving most of the time using a soft, but also scientific theories. In practice, they can be regarded as a style of thinking and teaching. In many cases, top-down is used as a synonym of analysis or decomposition, and Bottom-Up of synthesis.

Page 48: buletin stiintific

44

Top-Down approach is essentially a decomposing system, starting with the finished product, to gain knowledge on its subsystems. In this approach, first is formulated an overview of the system, indicating the first level of subsystems. Each subsystem is then stylish to the last detail, sometimes disintegrating him in more additional subsystem levels..... until the specification is reduced to the basics.

Bottom-Up approach is like Puzzle games, putting together small components to create systems, making the original systems to become a sub-system in a more complex and new system. In such of approach basic individual elements of the system are first specified in detail. These elements are then linked together to form more complex subsystems, which then in turn are linked, sometimes in several levels, until it reaches a higher level system. This strategy often resembles the "seed" being first small, but eventually develops in complexity.

In Mechanics using software such as Pro Engineer, Solidworks, etc., users can design pieces like products just later on, first the pieces may be combined together to form the final product ..... more complex and superior. This approach has a weakness, we need to use much intuition to decide the functionality that the assembly will provided. Software for 3D modeling allows the creation and manipulation of geometric objects extremely sophisticated and have been widely adopted by engineer’s experts in industry. Engineering skills, artistic, architectural have their role in their methodology, but a new skillset should be developed to work with digital tools. Given the reliability of current digital tools, often 3D models are not approaching that of the physical form, so still traditional methods are used.

In particular, in the early stages of designing a 3D model, the paper and pencil are usually used to quickly create and modify the concept drawings. However, there is currently no mechanism to integrate easily these drawings in the digital 3D concept. Currently, plans are not used for nothing more than visual reference points in the design phase, but can be converted into 3D models by the artists [1, 2, 3].

2D drawings where the raw material of the design/manufacturing, principles of descriptive geometry and design have been developed and applied to engineering problems. 2D drawings still

play an important role in engineering practice and in many cases serve as final documentation that guide the production, manufacture and assembly of products. However, 2D drawings are limited, tend to unnecessarily extend the design cycle, thus compromising product quality and increase manufacturing costs. These weaknesses arise primarily from issues that present difficulties to inspect 2D drawings, to verify the accuracy without creating physical prototypes and to use them directly in the next stage. So, sometimes is necessary to convert 2D drawings into 3D drawings and thus removing the above disadvantages [4].

2. Method sketch based 3D modeling

The paper presents a new style for 3D modeling, which includes the integration of scanned images, drawings, in the modeling process. These images serve as a guide for the user when they are modeling the virtual object. The method is called Sketch based 3D modeling and we can say that is part of Top-Down methodology. One can say this, because the designer is using the drawings to make a better image of the new product [5].

This method is based on creating 3D models sketching the important curves of the product, thus making the frame.

The curves witch is composing the skeleton are drawn up according to the 2D drawings that represent the views of the product: Top view, Front view and Side view. In figure 1 is shown the methodology of this approach.

Figure 1. Steps of Sketch based 3D

modeling approach

Page 49: buletin stiintific

45

Is mentioned the use of spline curves (B-spline) without mentioning the definition and their usage; thereof, curve splines such are interpolation curves controlled by points witch are respect the condition and continuity of the curve. Shape control is made through the change of the points and angle of contact; this makes them more difficult to handle for the creation of so called Free forms.

Otherwise, are noted generating surfaces that will shape the product. Modeling using surfaces (Surface modeling) defines not only the edges of 3D objects but also its surfaces. We can generate two types of surfaces; surfaces obtained by using lines or curves and also NURBS (Non Uniform Rational Basis Spline) witch are called Freeform surfaces consist of B-Splines, obtained using 3D outlines, which allow the formation of links with spline points in different areas. Areas with freeform have no fixed points, they can change like the designer wants, resulting in new models. Designer can modify the surface by changing the position of points in space. Forms can be in a wide range of surfaces whose shape can not be measured, only approximated. The models formed by surfaces don’t have the property to calculate the volume or weight [6, 7, 8]. 3. Work Methodology

In this paper, using the method Sketch based 3D modeling, it’s developed a mouse (Dell model), from pictures of it. The proposed model is shown in figure 2.

Figure 2. Dell Mouse

Modeling was carried out in SolidWorks

2008, software that has become a standard in 3D design, proof being that 80% of users who have worked initially in 2D programs. To ensure greater productivity, SolidWorks provides design tools for everyday activity. Thus there are specific applications for designers of machinery and

equipment, dies, folded plates, consumer goods, providing methodologies and familiar design cycles for these areas. SolidWorks allows import files in 23 different formats (native as ProE, UG, DWG, etc., and neutral as: IGES, STEP, ACIS, STL, VDA etc.). 3.1 Steps taken in the modeling

After it the mouse pictures where obtained, that represent the 4 views (Front, Bottom, Top, and Side) and it was measured gauge dimensions of mouse, followed: 1). Placing the *.* jpg files in the appropriate planes (figure 3).

Figure 3. Isometric views

Using the function , Solid works allows the user to insert pictures in a sketch, modifying the dimensions and rotating angles. The pictures dimensions where modified so that it will be a 1:1 scale. 2). Drawing the spline skeleton of the model. In the following steps have worked with the screen split in two, using in the same time the Top view and the Front view (figure 4).

Figure 4. The working screen

Page 50: buletin stiintific

46

The skeleton of the model is composed of both plane sketches but also 3D sketches. Using the points of the spline curves, was followed the contour of the pictures, switching between the two views, trying to adjust the spline in such way that it will take the form of the model. In figure 5 is showed how to trace the splines, obtaining the desired contour by altering the position of points that compose spline curve.

Figure 5. Arranging the points that compose the spline

curve to the contours photo

After creating several sketches which accurately copy the lines that define the contours we will have the spline skeleton (figure 6), all the sketches will be made only in half, after creating the surfaces we can use the Mirror function to obtain a perfect symmetry of the model.

Figure 6. Mouse skeleton

3). Surface generation that will create the form of the model. The main functions used where those of Loft Surface and Planar Surface. In figure7 can be observed how the basic shape of the model is created using the sketches created earlier.

a, b c

Figure 7. a, b, c. Modeling the shape of the part

Page 51: buletin stiintific

47

From this moment is observed the contribution of Top-Down method, because we know have the assembly (not fully detailed), but we can start extracting the components, using areas of separation and then the Split function (figure 8).

After extracting the components we can start modifying them (detailing) making them suitable for the electric parts, and for the manufacturing process.

After extracting and creating all the components, so that the assembly is finished, we can save all as separated parts and modify them for technological point of view (figure 9).

a

b

c

Figure 8. a, b, c. Button extraction and combining the middle part

Figure 9. The final assembly

This method is used to build models with

complicated forms, witch are hard to design directly with splines. In general, a sketch is a quick way to record an idea for later use.

Artist's sketches primarily serve as a way to try out different ideas and establish a composition before undertaking a more finished work, especially when the finished work is expensive and time consuming.

Hand sketches, photographs and other 2D images can be imported and displayed in 3D. This makes it significantly easier to trace over the sketches to create a 3D model.

Page 52: buletin stiintific

48

These images can be oriented in any direction and viewed from any perspective regardless of the work plane.

4. Conclusion

The paper presents a method (Top-Down) used in several industries: automotive, aeronautics, programming, and management organization, architecture, etc. In the mechanical field after the designer is informed of the client's needs a team of professionals make a study of similar products. A design plan is done, and preliminary drawings of the product are then outlined respecting the plan drawn up.

Conclusive drawings are then chosen to be improved and studied, and then the study is presented to the customer. The customer is choosing the favorite design, and then the designer is dealing with the choice of material and finish specifications and preparation of the assembly.

Using Sketch based 3D modeling the designer can start creating the product using the drawings previously created, shaping the product and from it, all subassemblies and components that compose it.

References 1. C. Cioană, Modern Technologies and Practices in

Product Design, Timisoara, 2008 2. S. I. Golovin, N. A. Veselov, Automatic

reconstruction of curved solids from three orthographic projection, Moscow State University

3. T. Grossman, R. Balakrishnam, G. Kurtenbach, G. Fitzmaurice, A. Khan, B. Buxton, Creating principal 3D curves with digital tape drawing,Preceedings of measuring behavier, 2008, 6 international Conference on Methods and Techniques in Behavioral Research, Maastricht, The Netherlands, 26-29 august ,2008, ISBN 978-90-74821-81-0

4. T. Grossman, R. Balakrishnan, etc. Creating Principal 3D Curves with Digital Tape Drawing, 1999, pp. 161-169

5. P. Jiantao, R. Karthik, A 3D Model Retrieval Method Using 2D Freehand Sketches, V.S. Sunderam et al. (Eds.): ICCS 2005, LNCS 3515, pp. 343 – 346, 2005, Springer-Verlag Berlin Heidelberg 2005

6. H. Lee, H Soonhung, Reconstruction of 3D interacting solids of revolution from 2D orthographic views, Korea Advanced Institute of Science and Technology, 2005

7. P. Santos, A. Stork,: An integrated Approach to Virtual Tape Drawing for Automotive Design, Technical University of Lisbon, Portugal

8. A. Schmidt, G. Khan, Kurtenbach, On expert performance in 3 D curve-drawing tasks, Proceedings of the 6-th Eurographics Symposium on Sketch-based Interfaces and Modeling, New Orleans, Louisiana ,2009,pp.133-140,ISBN 978-1-60558-602-1

9. B. Shin, Y. Shin, Fast 3D solid model reconstruction, Computer Aided Design, 1998,vol.30 ,pp.171-179, ISBN 0408008245/0-408-00824-5

10. V. S. Sunderam, G. D. Van Albada, PMA Sloot, Computational Science, ICCS 2005, %-th International Conference ,Atlanta, may 22-25,2005,ISBN 978-3-540-26043-1

11. S. Tsang, R Balakrishnan, etc. A suggestive Interface for Image Guided 3D Sketching, Austria, 2004

12. J. Yu, H. Yhang, A Prototype Sketch-Based Architectural Design System with Behavior Mode, Simon Fraser Universitz, Canada, 2007

METODA SKETCH BASED 3D MODELING Rezumat Obiectele pe care le folosim în viaţa de zi cu zi sunt produsul a secole de dezvoltare tehnologică şi ştiinţifică. Activitatea inginerească, în general, are ca finalitate realizarea de obiecte tehnice, care se materializează în urma unor procese de producţie complexe. Etapele principale ale realizării unui produs sunt: definirea unui concept general al produsului, realizarea proiectului tehnic, stabilirea tehnologiei de fabricaţie, realizarea modelului experimental şi omologarea produsului, fabricaţia propriu-zisă. Înainte de a începe proiectarea unui produs trebuie aleasă metodologia de lucru. Cele mai renumite sunt metodele Bottom-Up şi Top-Down. În prezenta lucrare se va explica metodologia de lucru a ambelor abordări, prezentând de asemenea metoda Sketch based 3D modeling şi din ce categorie face parte. Totodata se va prezenta şi un studiu de caz, aplicaţia fiind un digitizator de mouse.

Scientific reviewers: Danuţ ŞOŞDEAN, “Politehnica” University of Timişoara, Romania

Daniel STAN, “Politehnica” University of Timişoara, Romania

Page 53: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54(68) ISSN 1224 - 6077 Fasc. 2, 2009

THE CALCULATION OF THE VARIATION OF SQUEEZING FOR THE VALVE SEAT SINTERED IN THE

CYLINDER-HEAD OF ENGINE M511

Adela FILIP*,Ion NICOARĂ** *drd. National College V.Lucaciu, Baia Mare, Bulevardul Republicii no. 54/46, [email protected]

** prof. univ. dr. ing. Polytechnic University Timisoara, [email protected]

Abstract. The present paper aims at pointing out the influence of the thermal coefficient of expansion established for sintered tests/samples on the variation of squeezing the valve seats-cylinder head in order to increase the reliability of the distribution system. Starting from the proposed recipe, there have been obtained by sintering in certain conditions of temperature and pressure valve seats whose mechanical properties undergo different methods of investigation. Thus, we can improve the performances of the thermal engines; increasing the reliability of the valve seat interface from the valve by the progress of the wear in close connectivity with the ratio of copper obtained, respectively the thermal treatment applied; it is foreseen the possibility to design the expansion gap between valve seat and valve, respectively the valve lever. Keywords:valve seats, thermal engines, sintering, squeezing the valve seats-cylinder head 1. Introduction

The squeezing joints, more frequent in the machine industry make the taking over and the transmitting the tasks by forced contact of the interlinked surfaces, as a result of their elastic deformation.

The advantages of using the squeezing joints deal with the simplicity of the constructive solution, the high bearing capacity, relatively reduced gauge, low costs, good centering of the parts, saving scanty materials, and so on.

It must be mentioned that squeezing joints also have a series of disadvantages: there are a strong concentrator of tensions; the squeezing can weaken in time decreasing the hardness and bearing capacity; it needs the usage of special devices to mount and dismount, in which situations there can appear deteriorations of the

contact surfaces; they require high precision in machining the contact areas.

The binding joints, at the same rate of squeezing, ensure a bearing capacity of (1.5-2) times higher than the cold compressed joints.

2. The calculation of the pressure necessary

to make the transmission of the tasks These joints can transmit an axial force or a

moment of twisting (separately or simultaneously). In order to decrease the axial force of pressing, the shafts and the bores bevel/dull. The friction force when pressing are different from the back pressure forces. When back pressing, first it must be surmounted the force FI

ax because of static friction, superior to FII

ax characteristic to sliding friction. The relations corresponding to transmitting

an axial force Fax or of a moment Mtc are:

Page 54: buletin stiintific

50

axf FpdlNF ≥⋅⋅π⋅μ=⋅μ= * (1)

tcff MpddFM ≥⋅π⋅μ

=⋅=22

*2 (2)

From the relations above it results the contact pressures in the 2 distinct cases:

**a

axF pdl

Fp ≤

μπ= (3)

atcM pld

Mp *

2* 2

≤μπ

= (4)

In the case of simultaneous transmission of a force and a moment of torsion, the condition to take over the tasks is expressed in the relation:

22* 2

⎟⎠⎞

⎜⎝⎛+=μπ

dMFdlp tcax (5)

From where it results the contact pressure:

*2

2* 21a

tcaxrez pdMF

dlp ≤⎟

⎠⎞

⎜⎝⎛+

μπ= (6)

Where d and l are the diameter and the length of the joint and µ- the frictional coefficient, with values specific to the mounting and dismounting phases.

3. The calculation of the necessary

squeezing Knowing the pressure and the dimensions

of the fit offer the possibility to establish the necessary squeezing for transmitting the tasks as well as the fields for gauge and shafts tolerance [1].

The 2 effective diameters, of the shaft (da) and of the bores (db), are different (da > db), but after the mounting they reach a common diameter d, resulted from the broadening of the bore with Δb and the reduction of the diameter of the shaft with Δa:

dda a −=Δ (7)

hddb −=Δ (8)

The squeezing obtained in this case is:

baddddddS haha Δ+Δ=−+−=−= )()( (9)

And the relative squeezing:

=relS %1000dS

1000d

dd ba ⋅=⋅− (10)

In conformity with the theory of elasticity, the dependence between the theoretical squeezing St , pressure and the geometrical and material characteristics of the elements from the joint is like this (Lamé ‘s relation):

dpSt*= [ ]mμ10

EC

EC 3

b

b

a

a ⋅⎟⎟⎠

⎞⎜⎜⎝

⎛+ (11)

For the calculations of the necessary squeezing Snec ,there must be made corrections which should reflect the effect of the elasto-plastic deformation of the micro-irregularities of the contact surfaces, Sr (and to make the levelling height ), the state of supplementary stress because of dynamic tasks Sd as well as the uneven dilatation of the shaft and the bore, Sto :

+= tnec SS 0tdrt

n

1jj SSSSS +++=∑

=

(12)

Where:

( )( )mRRS zbzar μ+= 2.1 (13)

In which Rza and Rzb represent the height of the irregularities of the contact surfaces of the shaft, respectively of the bore.

⋅= 5.4zR 97,0aR⋅ (14)

( ) ( )[ ] [ ]mttttdoS oaaobbt μ⋅−α−−α= 310 (15)

In which αb,a are the ceofficients of linear thermal dilatation for the shaft, respectively for the bore, and tb,a represent the operating temperature of the 2 parts (t0 – the mounting temperature) [2].

For ta=tb=t, relation becomes:

( )( ) )(1030 mttdoS abt μ−α−α= (16)

Sd is considered by estimating the supplementary forces that work over the joint.

Knowing the necessaryy squeezing gives the possibility to establish the tolerance fields of the 2 interlinked surfaces.

Ensuring the transmission of the tasks in the most disadvantageous mounting conditions

Page 55: buletin stiintific

51(corresponding to the making of minimal squeezing) is ade by choosing the right low limit of the tolerance field of the shaft (ai), for a certain tolerance field of the bore:

∑=

++≥n

jjtSi SSAa

1 (17)

In the relation above As is the upper deviation of the tolerance field of the bore.the upper deviation of the tolerance field of the shaft as (if admitting a certain degree of accuracy)gives the measure of the maximum squeezing: aS=Smax.

4. The calculation of the maximum pressure and of the pressing and depressing forces

The maximum squeezing has as an effect a maximum contact pressure

max*p

*1max

pS

SS

t

n

jjSTAS

=∑=

(18)

value that compares to the critical pressure:

( ) caacrd

ddp σ−

= 2

21

2*

2 (19)

( ) cbbcrd

ddp σ

−= 2

2

222*

2 (20)

Where σca,b represent the flow limits of the material of te shaft and respectively of the bore.

5. The calculation of the heating or

undercooling temperatures The safety of the joint imposes in the most

unfavourable cases of operating to admit some values μ=μsliding restμ≅ 47,0

To make the joint or to depress there are used mechanical or hydraulic presses according to the value of forces Fp or Fd and the shafts and bores get beveled/dulled.

In the case of the shriveled parts, the difference of temperature between the shaft and the bore necessary to mount freely is established with the relation:

djSt

b

STASα

+=Δ 3

max10

(21)

Where j is the mounting clearance, equal to the minimum positive allowance.

The heating temperature of the bore is:

( )Cttt o500+Δ= (22)

where t0 is the temperature of the environment it is added 500 (or a increment of 15..30%) to compensate the coolness during mounting.[3]

In case undercooling is applied as a joining process, the undercooling temperature is established with the relation:

djS

tta

STAS

α

+−= 3

max0

10 (23)

Figure 1 Mounting by squeezing

Establishing the accuracy in the execution of the parts and the choice of the fit is made in accordance with the operational requirements imposed as well as the technological possibilities of manufacturing at the same time taking into account how economical the mounting or the processing.

Running fits are used when the mounted parts make rotating motions and/or of translation one towards the other during operating or when the parts are mounted or dismounted often or are replaced frequently. The rate of size tolerance(size accuracy)and the rate in mounting allowance are established according to the quantity and the type of the requirements, the relative speed between the elements of mounting, the time of the movements, the length of the mounting, the frequency of replacements, the temperature and lubrication conditions.

Medium fits are used to ensure a precise centering of the shaft in the bore, to obtain an

Page 56: buletin stiintific

52impervious joint and for the cases in which the mounting and dismounting of the parts must be done relatively easy and without deteriorating the contact surfaces. In order to ensure the fixed binding of the parts of the joint it is necessary to provide them with safety elements (pins, keys).

An important problem for this fits is that of knowing the probability of tolerance and squeezing that appear in mounting. The probable fit is considered that tolerance or that squeezing that result when mounting the parts if their size is 1/3 of the fundamental tolerance, respectively of the limit size corresponding to the maximum of material. The values given in standard are for the hypothesis that the production process is regulated as a consequence, otherwise the probability of the fit is calculated in accordance with the size for which the technological process is considered regulated.

Close fits are used in the situations in which for certain requirements and temperature conditions, the relatively fixed binding of the interlinked parts is made without using some supplementary elements of fixing. By squeezing, on the contact surfaces there appear a state of induced stress in proportion with the force of squeezing. because of the deformation of the material of the parts and the difficulties of mounting and dismounting, these fits are assigned when it is not necessary the dismounting of the mounted parts until the end of the operating process [4].

Generally the higher the mechanical and thermal requirements of the mounting are, the bigger the bindings should be. When designing these fits it must be taken into account the fact that as a result of flattening the asperities, the effective squeezing will be smaller than the one calculated on the basis of the dimensions. A method applied especially when designing and manufacturing new products consists of the following: depending on the destination, the operating parameters and the conditions of exploitation of the product, for each mounting shaft-bore it is calculated (after establishing the nominal size) the tolerance or the squeezing necessary when mounting and operating in the system. It is imposed that the designer calculates not a single value (for example the theoretically necessary one) of the tolerance or the squeezing but the limits between which the tolerances or the squeezing can be allowed so that they permit the normal operation of the parts in the conditions established. having these limits it is calculated the tolerance of the fit with the following relations:

dDaj TTJJT +=−= minmax (24)

dDas TTSST +=−= minmax (25)

dDai TTSJT +=+= maxmax (26)

From these relations one can calculate the tolerances of the bore TD and the shaft Td , considering them either of equal value or by adopting for the bore a higher level of tolerance with 1 up to at most 2 accuracy classes, being known the fact that the bores are processed harder than the shafts. After the tolerances TD and Td have been calculated it is adopted a standardised fit in one of the systems of fits(bore or basic shaft).

The valve seat can be bored directly in the cylinder head for cast iron cylinder heads, or it can be a separate part in the shape of a ring, which is shriveled in the case of cylinder heads made of aluminum alloys. The squeezing varies between 0.045-0.155mm.

Between the tappet or lever and the valve spindle it is necessary to be a thermal tolerance of 0.15-0.45 mm for the induction valve and of 0.2-0.8mm for the exhaust valve.

Adjusting the thermal tolerance between the lever and the valve is made cold or hot to allow the free dilatation of the valve and to avoid it remaining open when the engine is hot. The tolerance increases during exploitation making abnormal noises, reducing the time and the lift of the valves, worsening the filling of the cylinders with fuel-air mixture or air and scavenging

The valve seat is mounted with squeezing:

(0.045..0.115)mm

Smax=0.115 mm (27)

Δt=300

The nominal diameter of the fit d=35 mm

For the original valve seat αA=13*10-6 degree-1

J=αA Δtd-Smax

J=0.0215 mm=21.5 μm (28)

Page 57: buletin stiintific

53

Table 1 Calculations of thermal tolerance and the variation of squeezing for different types of engine units.

Variation of squeezing(μm)

Variation of squeezing(μm)

Variation of squeezing

(μm)

Nr

Sym

bol

Cuc

ompo

sitio

n of

(%)

Com

pact

ion

pres

sure

(*

100M

Pa)

Sint

erin

g Te

mpe

ratu

re

(o C)

Dila

tatio

n co

effic

ient

α

(*10

-6 d

egre

e-1)

Ther

mal

tole

ranc

e(μm

)

Engine unit made of heat-resisting steel

Engine unit made of

aluminium alloy

Engine unit made of cast iron

1 9 II 9 7 1270 12.46 15.83 +5,67 +110,67 -25,83

2 12 II 12 7 1270 13.07 22.23 -0,735 104,265 -32,235

3 12 - 12 10 1150 12.55 16.77 4,725 109,725 -26,775

4 6 I 6 7 1150 12.7 18.35 +3,15 +108,15 -28,35

5 6 - 6 10 1150 12.53 16.56 4,935 109,935 -26,565

6 6 II 6 7 1270 11.58 6.59 +14,91 +119,91 -16,59

7 12 I 12 7 1150 12.57 16.98 4,515 109,515 -26,985

8 9 - 9 10 1150 12.26 13.73 +7,77 +112,77 -23,73

6.Conclusions The variation of squeezing for the seat of the

induction valve depends on the dilatation coefficient and the type of material the cylinder head is made of.

On the long run, by knowing the established physical parameters as well as the variation of squeezing when mounting the valve seat one can design the thermal tolerance lever – valve in order to increase the reliability of the distribution system.

References 1. V. N Antsiferov, A. V. Babushkin, Yu. V, Sokolkin,

A. A., Shatsov, A. A Chekalkin, Features of powder material deformation with cyclic loading, Powder Metallurgy and Metal Ceramics, Vol. 40, no. 11-12, pp.569-572 , 2001, ISBN 1068-1302

2. O. V. Campian, I. B Turturica, I. Lascu, Models for fatigue cracks propagation through residual stress areas. In: Motor vehicle and transportation, mvt , Editura Orizonturi Universitare ,Timişoara, ISBN-10 973-638-284-2

3. A. Irimescu, D.Iorga, ,Studies and research on formation of the mixture by injection in Diagram IX

Omul şi mediul ,Editura Eurostampa, Timişoara, 24 mai 2007, ISBN 978-973-687-555-7

4 L. Madaras, D. Ostoia, V. Argesanu, Influence of sealing the combustion chamber of a diesel engine pollution,National Seminar Machine, Braşov, pp.145-150, 2005

5. L.Mădăras, D.Ostoia, S. Holotescu, Infuenta losses on the work indicated unsealed idling,g Scientific Bulletin of the „Politehnica” University of Timisoara Transactions on Mechanics, Tomul 51(65), 2006, Fascicola 2 ,ISSN 1224–6077

CALCULUL PIERDERILOR DATORATE VARIAŢIEI STRÂNGERII SCAUN DE SUPAPĂ-CHIULASĂ LA MOTORUL M511 DATORATE DILATĂRII TERMICE LUCRĂRII Rezumat Lucrarea de faţă îşi propune să evidenţieze influenţa coeficientului de dilatare termică determinat pentru probe sinterizate, asupra variaţiei strângerii scaun de supapă-chiulasă, în scopul creşterii fiabilităţii sistemului de distribuţie.

Pornind de la reţeta propusă, s-au obţinut prin sinterizare în anumite condiţii de temperatură şi

Page 58: buletin stiintific

54presiune scaune de supapă ale căror proprietăţi mecanice sunt supuse analizei prin diferite metode de investigare.

Prin interpretarea în juxtapunere a rezultatelor determinărilor se va evidenţia una din variantele de material care corespunde cerinţelor tehnice.

Astfel se pot extrage câteva concluzii: se poate proiecta reţeta pulberilor şi tehnologia de fabricaţie în vederea sinterizării unor variante de scaune de supapă destinate îmbunătăţirii performanţelor motoarelor termice; creşterea fiabilităţii la interfaţa supapă – scaun de

supapa prin creşterea la uzură în strânsă conectivitate cu procentul de cupru conţinut, respectiv tratamentul termic aplicat; se preconizează posibilitatea proiectării jocului termic supapă-scaun de supapă, respectiv culbutori - supape.

Scientific reviewers: Viorel Aurel ŞERBAN, “Politehnica” University Timisoara, Romania

Corina GRUESCU, “Politehnica” University Timisoara, Romania

Page 59: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

ENERGETICALLY-BASED CONTROL FOR SOLAR HEATING SYSTEMS

Richárd KICSINY*

* Department of Physics and Process Control, Faculty of Mechanical Engineering, Szent István University, Gödöllő H-2103, Gödöllő, Páter K. u. 1, Hungary, e-mail: [email protected]

Abstract This paper is an introduction to the realization and application of a physically-based mathematical model of solar heating systems. The model was realized in TRNSYS 16 simulation environment which is well recognized and frequently-used in scientific researches of transient thermal processes. The model is flexible and can be easily adapted to a wide range of particular solar heating systems being a good tool for analysis and development. The model was adopted as an application to the particular solar heating system at the campus of Szent István University, Gödöllő. A new energetically-based control was developed and compared with the generally used on/off control method which operates with fixed temperature differences. Based on the relevant simulations it is shown that compared to the ordinary control the energetically-based control provides remarkable advantages and savings concerning the auxiliary heating energy. This result should be valid for any systems similar to the particular one in Gödöllő. Keywords: physically-based model, TRNSYS, energetically-based control. 1. Introduction In view of the possibility of capturing solar energy in solar thermal applications and the increasing amount of such installations, it is important to develop efficient solar heated systems. In order to improve any simple or combined solar heating system, physically-based modeling is an exact, theoretically appropriate tool. The aim of this work is to realize a mathematical model corresponding to solar heating systems that takes into account all the substantial energy components, as well as the physically-based specifications of them. The physical bases are well described in details by [2]. The model should be

flexible for being easily adaptable for a wide range of solar heating systems. Generally speaking, a new energetically-based control method is presented and compared with the commonly used control which operates with fixed on/off temperature differences. 2. Introduction of the investigated heating system and the physically-based model 2.1. Main characteristics of the solar heating system at the Gödöllő campus A monitored combined solar heating system which has been installed at the campus of Szent István University (SIU), Gödöllő, Hungary is sketched in figure 1. (For

Page 60: buletin stiintific

56

then it is called SIU-system.) The term combined means actually that the installation has more than one consumer. It preheats water for an outdoor swimming pool, and in the idle period of this operation, domestic hot water for a nearby kindergarten. If necessary, auxiliary gas heated boilers are also included, operating in the same time with the solar heating. The main system components are the flat plate solar collector field, with a total area of 33.3 m2, oriented to the south with an inclination angle of 45°, the plate heat exchangers, a 700 m3 outdoor swimming pool with a surface of 350 m2

, and a 2000 liter solar storage tank. According to the mentioned figure, the following parameters were monitored: temperatures (T, °C), specific solar irradiance (I, W/m2) and volumetric flows ( v , m3/s). The measurements database refers to the year 2001, apart from minor interruptions. 2.2. Modeling of the system On the basis of the time-separated operation, a distinct model has been elaborated for kindergarten (Figure 2-3), which is further detailed. The problem was solved by the TRNSYS 16 [4] and, for some particular

calculations, by the MAPLE 8 software packages. The main system units have been located in distinct sub-models, that are already available in TRNSYS and can be used independently too. Such parts are the collector sub-model (Type 832 in TRNSYS [3]), the heat exchanger sub model (Type 5b), the stratified solar storage sub-model (Type 60c), the sub-model of the pumps (Type 114), the sub-model of the pipes (Type 31) and the sub-models for different control method possibilities (Type 2b with the related Equation blocks). The model can be run with inputs from special components. One of them is the “Meteorological database” component (Type 109) which uses a selected weather data file available in the program and the other is for the domestic hot water load (“Load profile” (Type 9c)) that also calls an external data file (Figure 2). Notations in Fig. 2.: Ig: global solar irradiance on collectors’ plane, W/m2, Ta: outside, ambience temperature, °C,

lV : domestic hot water load, l/h, Ts: calculated solar storage temperature, °C.

Figure 1. Simplified scheme of the combined solar heating system at the campus of SIU.

Filter

Poolloop

Aux. gas

heater Controlvalve

Heat exchanger

Swimming pool Volume: 700 m3, surface: 350 m2

Tap water inlet

Hot wateroutlet

Auxiliarygas

boiler 22 kW

284 litres

Solar storage

tank 2000 lit. Kindergarten

loop

Collector field

33,3 m 2

Collectorloop

Kindergarten

Page 61: buletin stiintific

57

The model determines and takes into account all energy components influencing the performance and the efficiency of the solar heating system, like the irradiated energy on the collectors’ plane, the utilized energy by the collectors, the transferred energy in the heat exchanger as well as the solar energy that finally used up by the consumers. The possibility of auxiliary heating according to the all- time consumption is also involved in the model. Because of the limits in volume the specification of the other describing equations, which can be found along with their origins in the relevant TRNSYS documentation [2], is omitted. 3. Development of the energetically-based control During the investigations the following one dimensional partial differential equation [4], relating to the energy conservation law, is needed. This

equation models the cooling and delaying effects in pipelines of hydraulic systems.

)( , paTTkxTVc

tTcA −−

∂∂

−=∂∂ ρρ (1)

where A : area of pipe cross section, m2, c : specific heat of pipe fluid, J/(kg°C), k : overall heat loss coefficient of the pipe, W/m/K, T : temperature of pipe fluid, °C, paT , : temperature of pipe ambience, °C, x : coordinate along the pipe, m, V : volumetric flow in the pipe, m3/s, ρ : mass density pipe fluid, kg/m3, t : time, s. The used energy balance equation and the equation of the Bosnjakovic-coefficient for a counter flow heat exchanger is expressed by the following mathematical relation, in correspondence with figure 4.

Meteorologicaldatabase

Load profile

I g

aT Model of thesystem for

kindergartenoperation

lV

sT

Additional(arbitrary)

outputs

Figure 2. Flowchart of the model for kindergarten operation.

Type31-7

Type31-6

Type5b

Type114-2 Type114Type109-TMY2

Equations 2 Equations 1

Type31-2 Type31-5

Type31-3 Type31-8 Collector(832)

Equations 4

Equations 3Type2b ordinary control

Type60cNoHeat

Type31-4

Type31

Type2b energetically-based control for both pumps

Type2b energetically-based control for the kindergarten pump

Type9c Load profile

Figure 3. Flowchart scheme of the model in TRNSYS worksheet,

Page 62: buletin stiintific

58

inhkouthkinhkinhc TTTT ,,,,,,,, )( −=−Φ (2)

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−−−

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−−−

2

1

12

1

2

1

1

1exp1

1exp1

WW

WAk

WW

WW

WAk

hh

hh

ε

ε (3)

where Φ : Bosnjakovic-coefficient for a counter flow heat exchanger, inhcT ,, : inlet temperature to the heat exchanger from the direction of the collector field, °C,

inhkT ,, : inlet temperature to the heat exchanger from the direction of the solar storage, °C,

outhkT ,, : outlet temperature from the heat exchanger to

the solar storage, °C, εhk : overall heat transfer coefficient of the heat exchanger between the working fluids, W/(m2K), hA : area of heat exchanger surface

between the working fluids, m2, 1W : the smaller heat capacity flow rate of the two working fluids (in our particular SIU-system it belongs to the water in the kindergarten loop), W/K, 2W : the greater heat capacity flow rate of the two working fluids (of the collector fluid in the SIU-system), W/K. The pumping is economical in view of energy and costs. The following criteria must be always satisfied:

• When the pumps are on, the medium which is to be heated must feed more heat energy per time unit than

the amount of electric consumption by the pumping:

wkw

p

VcP

>Δ (4)

where TΔ : warming temperature difference of the medium which is to be heated if the pumping is on °C,

pP : actual electric consumption of the pumping in the

collector- and in the kindergarten loops, W, wc : specific heat of water, J/(kg°C), wρ : mass density of water, kg/m3. • The cost of the saved auxiliary (gas) energy per

time unit by heating with solar energy the medium that is to be heated, also must be more than the cost of the consumed electric energy of the pumping:

gwkw

ep

CVcCP

>Δ (5)

Notations: gC : specific cost of gas energy, e.g. in

HUF/MJ, eC : specific cost of electric pumping energy, e.g. in HUF/MJ.

cVsT

c,h,inT

c,h,outT

Tk,h,in

k,h,outT

kV

kindergartenloop

collector loopTk,s,in

c,outT

Figure 4. Simplified scheme of the solar heating system in kindergarten operation.

3.1. Description of the energetically-based control Based on the ordinary control method, which is commonly used in solar heating systems, a new energetically-based control has been elaborated for kindergarten operation, applying principles that are similar to the swimming pool operation.

In figure 4 where used the following notations: outcT , :

outlet temperature of the collector field, °C, inhcT ,, : inlet temperature to the heat exchanger from the collector field, °C, inskT ,, : inlet temperature to the

Page 63: buletin stiintific

59

solar storage from the direction of the heat exchanger, °C, outskT ,, : outlet temperature from the solar storage

to the heat exchanger, °C, cV : volumetric flow in the

collector loop, m3/s, kV : volumetric flow in the kindergarten loop, m3/s Inside the storage there is no heat exchanger and it is not separated hydraulically from the kindergarten loop. The elaborated control is presented in Figure 4. Case a: outcT , , inhkT ,, , inskT ,, and sT are monitored

continually. Assuming switched on pumps inhcT ,, is

calculated from outcT , based on equation (1). As result

outhkT ,, is determined by equation (2). outhkT ,, minus

inhkT ,, is the controlling temperature difference of the energetically-based control for both pumps. This is the one that is compared continuously with the switching off temperature difference - offTΔ - that is the stricter economical criteria according to (4) and (5) with

inhkouthk TTT ,,,, −=Δ and with the switching on

temperature difference - onTΔ - that is equal to offTΔ

plus the chosen hysteresis value - hystTΔ = 2 °C.

Case b: inskT ,, and sT are monitored continually. Now the controlling temperature difference is

sinsk TTT −=Δ ,, . It is compared continuously with the

switching off temperature difference - offTΔ - that is the stricter economical criteria according to (4) and (5) and with the switching on temperature difference -

onTΔ - that is equal to 2,0+Δ offT °C. The collector pump works by Case a. The kindergarten pump works by the OR relation between Case a, and b. Thus, in conclusion, pP is not equal for these cases. 3.2. Description of the ordinary control used for comparison Generally the ordinary control is supposed to switch off the pumps if cT is less with a chosen value than

sT (e.g.: 2 °C) and switches on for another prescribed difference (e.g.: 5 °C). The ordinary control does not deal with heat losses, one simply uses it as a reference

prescribed switching off temperature difference, greater than 0 °C to ensure that the pumps work only if they take positive thermo energy into the kindergarten loop. Furthermore, this value should be as small as possible in order to gain the most of the solar potential. The efficiency of the ordinary control is maximized to assure a control, while comparing it to the new, energetically-based one. So, to consider the biggest but still real losses in the system, let us calculate with 55 °C temperature in the kindergarten loop, 10 °C in its environment and -5 °C in the environment of the collector loop. Considering the parameters of the SIU-system and assuming switched on pumps, the minimal value of outhkT ,, can be determined by equation (1) and the stricter condition of (4) and (5). (Here sinsk TTT −=Δ ,, .)

inhkT ,, can be also determined from sT by (1). The

minimal value of inhcT ,, from (2) and outcT , from

inhcT ,, and (1) can be also calculated. The resulted

soutc TT −, is the switching off temperature difference of the ordinary control. The hysteresis value is the same as in the energetically-based control (2 °C). 4. Comparative results of the ordinary- and the energetically-based control According to the aforementioned example, the model has been run with the ordinary as well as with the energetically-based control then the results have been compared. Simulation setups are according to the parameters of the SIU-system: investigated modeled day numbers are 1-5 April. The Meteonorm data for Prague was used, since in TRNSYS database this place is the closest to Hungary and it is absolutely appropriate to test the new control. The relevant TRNSYS weather file is: CZ-Praha-115180.tm2. The consumption load is based on the realistic profile of for five days, without bathtub or shower with 1990 liters/day [5].

0η = 0,74, as catalog data of the optical efficiency of the collectors, and LU = 7 W/m2/K, recommendation from [6] to the overall heat loss coefficient of the collectors. The collector field is about 15 meters distance from the heat exchanger. The value of hh Ak ε = 5000 W/K is determined from

Page 64: buletin stiintific

60

data given by manufacturer. cV = 0 or 1,08 m3/h and

kV = 0 or 0,65 m3/h, as well pP = 0 or 120 W was used for both pump sand 0 or 60 W only for the kindergarten pump. This is real nowadays when economic and modern pumps are generally available. The heating effect of the pumps into the working fluids is neglected. Initial temperatures are: collector field: 5 °C (initial ambience temperature of the day 1st April), both sides of the heat exchanger: 20 °C (assumed temperature of the maintenance house), solar storage: 20 °C (discharged solar storage), pipelines between the heat exchanger and the solar storage: 16 °C, which is the initial solar storage temperature minus 4 °C, because the pipe water has come from the solar storage before and its insulation is good: k =0,025 W/m/K by catalogue data. cc = 3623 J/(kg°C), specific heat of collector fluid, cρ =1034

kg/m3 collector fluid mass density. Volume of the collector field: 27 liter, volume of collector side of the heat exchanger: 2,5 liter. For kindergarten side: 2,6 liter. gC =3,3 HUF/MJ,

eC =11,1 HUF/MJ. The heat loss coefficient of the storage is 1 W/m2/K. Figure 5 shows the solar irradiance and the outside air temperature generated by the TRNSYS weather file for the simulated days, 1-5 April. Figure 6 and 7 show the results of the simulations comparing the two control methods. The dashed (blue) lines in figure 6 and 7 note the ordinary control, the smooth (red) ones note the energetically-based control. For both controls figure 6 shows the average solar storage temperature, figure 7 shows the sum of the consumed solar energy from the storage and the internal energy change of the storage (compared to the initial internal energy).

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60 70 80 90 100

110

120

time, h

Sola

r ir

radi

ance

, W/m

^2

-3-1135791113151719

Out

side

tem

pera

ture

, °C

Solar irradiance on collectrors' planeOutside temperature

Figure 5. Solar irradiance and outside air temperature for 1-5 April.

13

18

23

28

33

38

43

48

0 10 20 30 40 50 60 70 80 90 100

110

120

time, h

Tem

pera

ture

, °C

Energetically-based controlOrdinary control

Figure 6. Average solar storage temperature by both controls.

Page 65: buletin stiintific

61

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100

110

120

time, h

Gai

ned

sola

r en

ergy

, (kW

h)

Energetically-based controlOrdinary control

Figure 7. Gained solar energy for the kindergarten by both controls.

Table 1. Results of the simulations for both controls at the end of the simulations (end of 5th April).

Average storage

temperature, °C

Gained solar energy for the kindergarten,

kWh

Saved auxiliary (gas) energy, kWh

Electric consumption of pumping, kWh

Ordinary control 30,3 234,2 - 3,7 Energetically-

based control

31,5 239,4 5,2 5,0

5. Conclusions Based on the simulation results it can be stated that under the same weather conditions the new, energetically-based control is able to reduce 5,2 kWh solar energy for the consumer, compared to case when the ordinary control is used as generally in practice. It means a significant, 2,2 % extra gained solar energy. It is important in itself how to extract as much solar thermal energy as we can, but it should be also noted that 1,3 kWh electric consumption surplus applies by the new control. Considering the costs, it depends on the actual energy prices if it worth or not. In the present example ge CC / = 11,1 /3,3 so the price of 5,2 kWh – 11,1/3,3x1,3 kWh = 0,83 kWh gas energy is clearly saved. It should be said that the electric energy of the pumping also increases to some extent, so it is important to ponder the electric consumption surplus together with the extra gained solar energy. 6. Acknowledgements The author expresses special thanks to those who contributed with a great extent to this work: Professor

István Farkas from the Department of Physics and Process Control, Szent István University, Gödöllő, Hungary for the help in making appropriate research conditions, Professor Klaus Vajen from the Department of Solar and Systems Engineering, University of Kassel, Germany for the help in making appropriate research conditions and specially for the supply with the TRNSYS simulation environment, János Buzás from the Department of Physics and Process Control, Szent István University for his help in many technical details and to the staff of the Department of Solar and Systems Engineering, University of Kassel for their help in many details. This work has been supported by the Hungarian State Eötvös Scholarship. References 1. B. Bourges, European Simplified Methods for Active Solar System Design. Kluwer Academic Publishers for CEC, 1991, ISBN 07923 18757 2. J. A. Duffie, W. A. Beckman, Solar Engineering of Thermal Processes. John Wiley and Sons, New York, 1991, ISBN 0-471-51056-4 3. I. Farkas, I. Vajk, Modelling and Control of a Distributed Collector Field. Energy and the Environment, I. /ed. by

Page 66: buletin stiintific

62

B.Frankovic/, Croatian Solar Energy Association, October 23-25, 2002, Opatija, pp. 91-99, ISBN 953-96054-6-6 4. R. Heimrath, M. Haller, Project Report A2 of Subtask A: The Reference Building, the Reference Heating System, A report of IEA SHC – Task 32. Graz University of Technology, Institute of Thermal Engineering, 2003, ISSN 1396-4011 5. U. Jordan, K. Vajen, DHWcalc, version 1.10 - Tool for the Generation of Domestic Hot Water (DHW) Profiles on a Statistical Basis, University of Kassel, Institute of Thermal Engineering, Solar and Systems Engineering, 2003. 6. S. A. Klein, et al. A Trunsys Transient System Simulation Program. Solar Energy Laboratory, University of Madison, USA, 2005, ISBN 0-415-27056-1 CONTROLUL PE BAZE ENERGETICE AL SISTEMELOR SOLARE DE ÎNCĂLZIRE Rezumat Lucrarea este o introducere în realizarea si aplicarea unui model matematic fizic al sistemelor solare de încalzire. Modelul a fost realizat în mediu de simulare TRNSYS 16

care este bine cunoscut şi frecvent utilizat în cercetarile ştinţifice ale proceselor termice tranzitorii. Modelul este flexibil şi poate fi usor adaptat unui domeniu larg de sisteme solare de încalzire, fiind un instrument bun pentru analiză şi dezvoltare. Modelul a fost adoptat ca aplicaţie a unui sistem solar de încălzire, particular în campusul Universităţii Szent István, Gödöllo. S-a realizat o comandă/control nouă pe baze energetice şi a fost comparată cu comandă/control utilizată în general on/off (deschis/închis), metodă care operează cu diferenţe fixe de temperatură. Pe baza simularilor relevante se arată că în comparaţie cu comanda/controlul obişnuit, comandă/control pe baze energetice furnizează avantaje şi economii remarcabile, privind energia auxiliară de încălzire. Acest rezultat ar trebui sa fie valabil pentru orice sistem similar, pâna la cel particular din Gödöllo.

Scientific reviewers: Ioana IONEL, “Politehnica” University of Timişoara, Romania

Mihai JĂDĂNEANŢ, “Politehnica” University of Timişoara, Romania

Page 67: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

THE FUELL CELL, AN OPTION FOR DESCENTRALIZED POWER AND HEAT GENERATION AND AUTOMOTIVE

INDUSTRY

Adriana TOKAR*, Arina NEGOIŢESCU* * Mechanical Engineering Faculty, Bv. Mihai Viteazu No. 1, 300222 Timişoara, România,

[email protected], [email protected]

Abstract. In this paper are presented some considerations concerning the fuel cells as an option for automotive industry and descentralized power and heat generation. There are described two types of fuel cells operating at high temperatures: molten-carbonate fuel cells (MCFCs) and solid oxide fuel cell (SOFC). The high-temperature fuel cells MCFC and SOFC provide heat at a high temperature level, which makes many applications for industry possible. Keywords: fuel cell, energy conversion, electrolysis process, fuel reforming high temperature 1. Introduction

The fuel cell is one option for decentralized power and heat generation with very high efficiency and very low emissions. The functionality of the fuel cell corresponds to the inversion of the water electrolysis. During water electrolysis water is split into hydrogen and oxygen by applying voltage to two electrodes.

If the reaction is run backwards and the electrodes are surrounded by hydrogen (or hydrogen rich gas) and oxygen (or air) the highly exothermic detonating gas reaction (combining hydrogen and oxygen into water) causes measurable direct voltage and release of heat. In order to continuously keep the process running, a consistent process gas supply has to be ensured. Classic pollutants like CO und NOx are not produced. Although fuel cells convert hydrogen and oxygen to power, they must also be capable to use standard fuels, mainly fossil fuels. But in the last years also technologies for the production of hydrogen are investigated more and more.

2. Fuel cells types A fuel cell is an electrochemical energy

conversion device that converts hydrogen and oxygen directly into usable electrical energy - with water and heat byproducts – without combustion (figure 1) [1]. Fuel cell technologies are of different types, depending on their electrolyte. Some of the different electrolyte types include phosphoric acid (PAFC), molten carbonate (MCFC), solid oxide (SOFC), and proton exchange membrane (PEMFC). PAFC and PEMFC are low temperature fuel cells and their operating temperature is 200°C and 90°C respectively. By contrast, SOFC and MCFC are high temperature fuel cells with operating T of 1000°C and 650°C respectively. Fuel cells are mainly divided according to their operational temperature as is presented in Table 1 [2]. The high-temperature fuel cells MCFC and SOFC provide heat at a high temperature level, which makes many applications for industry possible. The heat of the low-temperature fuel cells is mostly used for heating purposes.

Page 68: buletin stiintific

64

Table 1. Fuel cells types according to operational temperature

Fuel cell type Symbol

Operational temperature

Alkaline Fuel Cell AFC Polymer Electrolyte Fuel Cell PEFC Phosphoric Acid Fuel Cell PAFC Direct Methanol Fuel Cell DMFC

Low‐temperature: 80 – 220 °C

Molten Carbonate Fuel Cell MCFC Solide Oxid Fuel Cell SOFC

High temperature: 600 – 1000 °C

3. High temperature fuel cells presentation

In the high-temperature fuel cells (MCFC and SOFC), CO in the fuel stream acts as a fuel. However, it is likely that the water-gas shift reaction is occurring and the fuel for the actual fuel cell is actually hydrogen.

CO+ H2O => CO2 + H2 (1)

Fuel reforming can be done in facilities of

different scales. The reforming can be done at a large scale in a central facility like a chemical plant. This can result in pure hydrogen, either as a high-pressure gas or as a liquid. This would then be delivered to fuel cell users. The fuel reforming can also be performed on an intermediate scale in a location such as a gasoline station. Gasoline or diesel fuels would be refined and delivered to the station with the current infrastructure. Onsite equipment would reform the fossil fuel into a mixture composed primarily of hydrogen, but could include other molecular components such as CO2 and N2. The purity of this hydrogen will depend on ongoing developments in techniques to cost-effectively separate H2 from other gases. This hydrogen

would likely then be delivered to customers as a high-pressure gas.

Finally, the fuel reforming process can be performed on a small scale on an as-needed basis immediately before its introduction into the fuel cell. One example would be for a fuel cell-powered vehicle to have a gasoline tank on board that would use the existing infrastructure of gasoline delivery. An on-board fuel processor would reform the gasoline into a hydrogen-rich stream that would be fed directly to the fuel cell. At the present time, it is not practical to perform separation of other products of the reforming process from the hydrogen at this small scale. Automotive fuel cell technology remains a promising alternative energy solution, but it also brings many challenges, including those concerning materials, manufacturing and associated costs [2].

In the longer term, most, if not all, of the hydrogen used to power fuel cells could be generated from renewable resources such as wind or solar energy. The electricity generated at a wind farm could be used to split water into hydrogen and oxygen. This electrolysis process would produce pure hydrogen and pure oxygen. The hydrogen could then be delivered by pipeline

Figure 1. Schematic representation of a fuel cell System

Page 69: buletin stiintific

65to all end-users. Such a shift in source of energy has been described as a hydrogen economy. Much has been written about the future potential of this energy use.

Fuel cells generate electricity from a simple electrochemical reaction in which an oxidizer, typically oxygen from air, and a fuel, typically hydrogen, combine to form a product, which is water for the typical fuel cell. Oxygen (air) continuously passes over the cathode and hydrogen passes over the anode to generate electricity, by-product heat and water. The fuel cell itself has no moving parts – making it a quiet and reliable source of power.

The electrolyte that separates the anode and cathode is an ion-conducting material. At the anode, hydrogen and its electrons are separated so that the hydrogen ions (protons) pass through the electrolyte while the electrons pass through an external electrical circuit as a Direct Current (DC) that can power useful devices. The hydrogen ions combine with the oxygen at the cathode and are recombined with the electrons to form water. The reactions are shown below:

Anode Reaction: 2H2 => 4H+ + 4e- (2)

Cathode Reaction: O2 + 4H+ + 4e- => 2H2O (3) Overall Cell Reaction: 2H2 + O2 => 2H2O (4)

Individual fuel cells can then be combined

into a fuel cell "stack." The number of fuel cells in the stack determines the total voltage, and the surface area of each cell determines the total current. Multiplying the voltage by the current will yield the total electrical power generated. Power (Watts) = Voltage (Volts) X Current (Amps) [5]. 3.1. Molten-carbonate fuel cells (MCFCs)

Molten-carbonate fuel cells (MCFCs) are high-temperature fuel cells that operate at temperatures of 600°C and above.

Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic matrix of beta-alumina solid electrolyte (BASE). Since they operate at extremely high temperatures of 650°C (roughly 1,200°F) and above, non-

precious metals can be used as catalysts at the anode and cathode, reducing costs.

Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60 percent, considerably higher than the 37-42 percent efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be as high as 85 percent. The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. 3.2. Solid oxide fuel cell (SOFC)

A solid oxide fuel cell (SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material and, as the name implies, the SOFC has a solid oxide, or ceramic, electrolyte. Advantages of this class of fuel cells include high efficiencies, long term stability, fuel flexibility, low emissions, and cost. The largest disadvantage is the high operating temperature which results in longer start up times and mechanical/chemical compatibility issues.

Figure 2. Diagram of Molten-carbonate fuel cells (MCFCs)

Page 70: buletin stiintific

66

Solid oxide fuel cells have a wide variety

of applications from use as auxiliary power units in vehicles to stationary power generation with outputs from 100 W to 2 MW. They operate at very high temperatures, typically between 500 and 1,000°C. Typical values for efficiency of a single SOFC device are around 60 plus percent. However, the byproduct gases can be used to fire a secondary gas turbine to improve electrical efficiency. This enables efficiency to reach as much as 85% in these hybrid systems, called combined heat and power (CHP) device. In these cells, it is most common to have oxygen ions diffusing through a solid oxide electrolyte material at high temperature to react with hydrogen on the anode side. 4. Conclusions

The application of the fuel cell in decentralized CHP supply corresponds to the application of combustion engines in block heat and power plants. Fuel cells are covering the basic load while oil or gas boilers are responsible for the temporally limited peak load. Besides, micro fuel cells (starting at 1 kW electric power) are promoted to supply residential homes with electric power and heat [3]. The advantages of fuel cells are:

- Extremely low emissions without any secondary measures; - The limits of the theoretically ideal Carnot process do not apply to this process. Thus fuel cells have a very big potential for generating power and heat with high efficiency. - Efficiency of this process is almost independent of the unit size, high part load performance; - Simple modular set-up and low maintenance effort; - Little noise;

The fuel cells have a few disadvantages, as very high acquisition costs. Higher output (> 1 MW electric power) is difficult to realize and another problem - which is not that serious though- is start-up time of the plants which still amounts to a couple of hours from a cold state. References 1. S. Birch Bac2 the future for fuell-cell materials.

Automotive Engineering International, SAE International, Nov. 2008, ISBN 9111 1464-2859

2. A. Holdway, O. Inderwildi, Fuel cells, a concise overview, 2004, pp. 58-62, ISSN 2041-5028

3. M. A. Laughton, Fuel cells, Power Engineering Journal, vol 16, issue 1, 2002, pp. 37-47, ISSN 1479-8344

4. A. D. Little, Inc, Opportunities for Micropower and Fuel Cell/Gas Turbine Hybrid Systems in Industrial Applications Publication. Office of Energy Efficiency and Renewable Energy, 2000, ISBN 952-214-157-7

5. *** Cogeneration (CHP) Technology Portrait Institute for Thermal Turbomachinery and Machine Dynamics. Energytech, Austria

PILE DE COMBUSTIE, CA ALTERNATIVĂ ÎN INDUSTRIA AUTOMOBILELOR ŞI A

PRODUCERII DE ENERGIE ELECTRICĂ ŞI TERMICĂ ÎN SECTORUL DESCENTRALIZAT

Rezumat

Sunt prezentate aspecte privind pilele de combustie, ca o opţiune în industria automobilelor şi a producerii de energie electrică şi termică, în sectorul descentralizat. Sunt descrise două tipuri de pile de combustie care funcţionează la temperaturi înalte:MCFCs şi SOFC. Aceste pile de combustie furnizează căldură la un nivel ridicat de temperatură ceea ce face posibilă aplicarea acestora în industrie.

Scientific reviewers:

Virgiliu Dan NEGREA, “Politehnica” University of Timişoara, Romania Mihai JĂDĂNEANŢ, “Politehnica” University of Timişoara, Romania

Figure 3. Diagram of Solid oxide fuel cell (SOFC)

Page 71: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

COMPARISON BETWEEN CH4 AND CO2 CONCENTRATIONS IN BIOGAS FOR DIFFERENT

TYPES OF BIOMASS

Adrian Eugen CIOABLĂ* * Faculty of Mechanical Engineering, Bv. Mihai Viteazu No. 1, 300222 Timişoara, Romania,

[email protected] Abstract. Obtaining biogas from biomass is one of the methods used over time in different countries, using different materials and recipies for obtaining large quantities with good qiality of the produced biogas. For this it’s verry important to know the material chemical composition, the C / N ratio, and also the quantity of organic matter inserted inside the reactors. At the Unconventional Energies Laboratory at the Mechanical Engineering Faculty there exists a pilot installations for testing different types of biomass in order to obtain the best solution in matter of quantity and quality for the biogas using anaerobic fermentation. Related with the main components that exists in biogas, the concentration of CH4 and CO2 is verry important related with obtaining good quality biogas. The forward applications for the obtained biogas can be related to combustion, regardless if there is a boiler or an engine. Keywords: biogas, biomass, anaerobic fermentation

1. Introduction

Biogas is slowly becoming verry popular in different countries, related with producing energy from renewable resources. China is one of the global leaders regarding the total biogas quantity produced each year, while in Europe, Germany is one of the most involved countries in obtaining biogas from animal dejections and vegetabel residues.

The field of application for biogas is whidely spread, involving the use in generators, and even engines.

From the main components that can be found in biogas, one of the most important is CO2, besides methane, which, in large percentages can affect the quality of the produced biogas.

Because of this, during the experiments conducted at the Unconventional Energies Laboratory at the Mechanical Engineering Faculty at Politehnica University from Timisoara, one of the main studies regarding the biogas composition was determining the methane and CO2 concentrations.

Considering two different types of vegetable biomass, one of the made from wood, and another being of agricultural origin, after monitoring the process of anaerbic fermentation, we can observe the differences in CH4 and CO2 concentrations for each one of them.

Figures 1 and 2 show the general aspect for beech dust and grains of corn waste, while in Table 1 are described some of the general properties of two different types of biomass.

Figure 1. Beech dust material

Page 72: buletin stiintific

68

Figure 2. Grains of corn waste

Table 1. Properties for the beech dust and grains

of corn waste

2. Experiment and diagrams The measurements were made before and after

washing the biogas inside a system composed of two filters, one used to diminuate the H2S concentration and one used for washing CO2.

There were made three determinations, one at the initial moment, before the moment of large methane production the second one was after 40 – 45 days, a period considered to be present peak points for methane concentrations and the last measurement was made close to the end of the process.

The measurements were made for both of the reservoirs of the installation.

In Figures 3 and 4 are presented the CH4 and CO2 concentrations for the beech dust at the initial moment.

CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 3. CH4 and CO2 concentration: first

reservoir, measurement no.1

CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash

Figure 4. CH4 and CO2 concentration: second reservoir, measurement no.1

From the two diagrams it can be observed that

the values for the methane concentration is between 54% before the washing system and 57% after the washing system, while CO2 concentration is around 43 – 46%.

In this period, as it can be seen, the methane concentration is low.

In Figures 5 and 6 is presented the variation of the concentration for the methane and CO2 in the peak period.

CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash

Figure 5. CH4 and CO2 concentration: first reservoir, measurement no.2

CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash

Figure 6. CH4 and CO2 concentration: second reservoir, measurement no.2

No Sam- ple

Humi-dity

[%]

Hygros-copic

Humi- dity [%]

Ash con-tent

[%]

High calo- rific

value [kJ/kg]

Low calo- rific

value [kJ/kg]

1

Grains of corn waste

13.91 1.50 1,88 15933 14488

2 Beech dust 6.43 0.51 0,92 17751 16322

Page 73: buletin stiintific

69From Figures 5 and 6 it can be observed that the

methane concentration reaches a peak point at 58 – 59% while CO2 concentration decreases to about 40%.

Last measurement was made close to the end of the period of the process of biogas formation and the methane and CO2 concentrations are presented in figures 7 and 8.

CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1before wash % CO2 R1 after wash

Figure 7. CH4 and CO2 concentration: first reservoir, measurement no.3

CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 8. CH4 and CO2 concentration: second reservoir,

measurement no.3

As it can be seen from Figures 7 and 8, the methane concentration decreases again, while CO2 concentration rises to a value of about 47%.

In Figures 9 and 10 are presented the concentrations for methane and CO2 for the second type of biomass, grains of corn waste.

CH4 and CO2 concentration variation

35

37

39

41

43

45

47

49

51

53

55

57

59

61

63

65

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 9. CH4 and CO2 concentration: first reservoir,

measurement no.1

CH4 and CO2 concentration variation

35

37

39

41

43

45

47

49

51

53

55

57

59

61

63

65

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 10. CH4 and CO2 concentration: second

reservoir, measurement no.1

From the figures it can be observed that even if it’s in the starting period, the concentration of methane is higher than in case of beech dust and the values are close to 63%, while CO2 concentration resides to about 36 – 37% after the washing system.

In figures 11 and 12 there are presented the values for the peak period, when the methane concentration is the biggest.

CH4 and CO2 concentration variation

30

3234

3638

4042

44

4648

505254

5658

6062

6466

6870

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 11. CH4 and CO2 concentration: first reservoir,

measurement no.2

CH4 and CO2 concentration variation

3032

34363840

424446

485052

5456

58606264

666870

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 12. CH4 and CO2 concentration: second

reservoir, measurement no.2

In the peak period, the methane concentration is about 67% in the first reservoir and 68% in the second one. The CO2 concentration is the lowest in this point, about 32 – 33%.

In Figures 13 and 14 are presented the CH4 and CO2 concentrations for the last period, when the process it’s almost to an end.

Page 74: buletin stiintific

70CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 13. CH4 and CO2 concentration: first reservoir,

measurement no.3 CH4 and CO2 concentration variation

40

42

44

46

48

50

52

54

56

58

60

0 100 200 300 400 500 600

Time [s]

Con

cent

ratio

n [%

]

% CH4 R1 before wash % CH4 R1 after wash % CO2 R1 before wash % CO2 R1 after wash Figure 14. CH4 and CO2 concentration: second

reservoir, measurement no.3

For this period it can be observed that the methane conentrations decreases to about 58 – 59% while the CO2 concentrations increases to a value of about 40 – 42%.

3. Conclusions

Related with the type of biomass, the quality and quantity for the obtained biogas can vary in large ranges.

Some of the most important elements that exist in biogas are methane and CO2.

The connection between those two elements involves a direct increse / decrease of one while the other decreases / increases.

In our case, there were consedered two types of biomas, grains of corn residue and beech dust and it was determined the variation of the methane and CO2 concentrations for the two materials in relation with three different periods : in the beginning of the formation of methane, in the peak point and in the end period of the process.

From the diagrams it can be seen that the agricultural biomass produces biogas with a higher concentration of methane while wood residues can produce biogas with a lower methane concentration, thus making the use of agricultural residues more suited for this kind of aplication.

References

1. A. E. Cioablă, I. Ionel, M. Jădăneanţ, A. Savu, Study regarding the production of biogas using biomass resulting from agricultural residues at the Unconventional Energies laboratory at Politehnica University of Timisoara, A 21-a Conference „Procesing 2008”, Beograd, 4-6 iun 2008.

2. A. E. Cioablă, I. Ionel, M. Jădăneanţ, F. Popescu, A. Savu, State of the art on biogas from biomass residues at the unconventional energies laboratory at Politehnica University of Timisoara, Scientific Bulletin of the “Politehnica” University of Timişoara,România, Transactions on Mechanics, Tom 52 (66), 2007, Fascicola 7, 2007, ISSN 1224-6077. 3. A. E. Cioablă, I. Ionel, I. Pădurean, A. Ţenchea, F. Popescu, A Savu, Biogas production from agricultural residues. Test rig and results, Revista Metalurgia Internaţional, vol. XIV (2009), numărul 3, pp. 40 – 44, ISSN 1582 – 2214 4. G. Grassi, O. Paste, T. Fiällström, Recovery of semi-arid desertic lands through biomass schemes, 2-nd World Conference on Biomass for Energy, Industry and Climate Protection, 10-14 may 2004, Rome, Italy, pp. 451-454, ISSN 1018-5593 COMPARAŢIE ÎNTRE CONCENTRAŢIILE

DE CH4 ŞI CO2 DIN BIOGAZ PENTRU DIFERITE TIPURI DE BIOMASĂ

Rezumat Obţinerea biogazului din biomasă este una din metodele utilizate de-a lungul timpului în diferite părţi ale lumii, utilizând material organic variat precum şi diferite reţete pentru cantităţi cât mai mari de metan, adică biogaz de calitate cât mai bună. Din acest motiv este extrem de importantă cunoaşterea compoziţiei chimice a materialului organic, raportul C / N, precum şi cantitatea de masă organică introdusă în bioreactoare. Laboratorul de Energii Neconvenţionale din cadrul Facultăţii de Mecanică, este dotat cu o instalaţie experimentală pilot care permite testarea diferitelor tipuri de biomasă pentru a identifica soluţia optimă în privinţa cantităţii şi calităţii biogazului obţinut prin fermentaţie anaerobă. În privinţa principalelor componente ale biogazului, concentraţia de CH4 şi de CO2 sunt determinante pentru biogaz de bună calitate. Ca şi aplicaţii ale biogazului, prin combustia acestuia se obţine energie termică în cazane, sau energie termică şi electrică în cazul alimentării cu biogaz a motoarelor cu ardere internă.

Scientific reviewers: Ioana IONEL, “Politehnica” University of Timişoara, Romania

Mihai JĂDĂNEANŢ, “Politehnica” University of Timişoara, Romania

Page 75: buletin stiintific

SCIENTIFIC BULLETIN OF

THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA TRANSACTIONS ON MECHANICS

BULETINUL ŞTIINŢIFIC AL UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA

SERIA MECANICĂ Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

THE OPTIMIZATION OF A CASTING DIE USED FOR THE PROCESSING OF FERROMAGNETIC

NANOCRYSTALLINE ALLOYS IN THE SHAPE OF RODS

Mircea VODĂ *, CosminCODREAN,* Carmen OPRIŞ*, Eugen POPESCU*

*Mechanical Engineering University Timisoara, Bv Mihai Viteazu, No 1, 300222, e-mail: [email protected], [email protected]

[email protected], [email protected] Abstract. The paper presents a study in which computer simulation is used in order to optimize a

casting die used for the processing of ferromagnetic nanocrystalline alloys. After the simulation, the results were verified experimentally. Structural investigations using X-Ray diffraction were used to certify the possibility of processing nanocrystalline structures using casting dies with 65-70 mm diameter. Keywords: ferromagnetic nanocrystalline alloys, optimization, computer simulation, casting die 1. Introduction

Nanocrystalline alloys represent a new category of materials at the border between classic crystalline and amorphous materials, having a series of distinct properties. From the structural point of view, nanocrystalline materials are considered those materials that have a crystalline structure with grain sizes between 1 … 100 nm. The interest that these materials present is justified by [1,2]:

- their structure (different from both the crystalline as well as the amorphous structure)

- the possibility of processing them even from components that normally do not alloy;

- specific properties that make them useful in numerous fields.

Starting from 1988, an increased interest showed the possibility of processing

nanostructured ferromagnetic alloys, together with the discovery of nanocrystalline alloys known commercially as „FINEMET” [2]. The microstructure of these alloys is constituted from an amorphous matrix in which crystals with nanometric dimensions are distributed. These alloys with nanocrystalline structure were processed by controlled crystallization of the amorphous phase.

In the next years, other families of nanostructured Fe-Co-Si-B-Cu-Zr based alloys were developed, for different practical applications, known commercially as NANOPERM and HITPERM. These alloys proved to have excellent soft magnetic properties, compared with ferromagnetic crystalline alloys or even amorphous (figure. 1), these properties being strongly influenced by the crystalline grain size (figure 2). One can see that for the crystalline

Page 76: buletin stiintific

72 grain size below 100 nm, the coercitive field varies after the D6 law.

Since the nanocrystalline ferromagnetic alloys present an excellent combination of high magnetic permeability and low coercitive field, it is expected that they compete the ferromagnetic amorphous alloys in different practical applications, such as magnetic liquids, magnetic bands reading heads, different sensors etc.

105

104

103

102

106

0 0,5 1 1,5 2 2,5

Δ

Δ

• •

Rel

ativ

e pe

rmea

bilit

y at

1 k

Hz

Magnetic saturation induction [T]

Nanocrystalline alloys

Fe-Si-B-Nb-Cu Fe-Zr-B

Fe-Si steell

Ferrite

Empirical limit

Fe based amorphous

alloys

Co based amorphous

alloys

Figure 1. Magnetic saturation induction and relative permeability for different

soft magnetic materials [2]

1 μm1 nm 1 mm 0,001

0,01

0,1

1

10

100

ο

ο

ο

Δ Δ

Δ Δ

• •

• •

• •

Graine size

Nan

ocry

stal

line

allo

ys

Coe

rciti

vity

, [A

/cm

]

Amorphous alloys

Permalloy

50NiFe

Fe-Si d6

1/d

Figure 2. Variation of the coercitive field

with the grain size [2] Usually, in the case of metal alloys,

nanocrystalline structures can be obtained by rapid cooling of the melt, or by the controlled crystallization of amorphous phase [2, 3].

At the cooling of a melt, metastable phases (by rapid cooling) may be formed, or stable phases (at normal cooling). As seen in figure 3, the increase of the cooling rate moves the TTT curves to left, modifying the crystallization temperature from TX to T’X. At cooling with cooling rates higher than the critical cooling rate, tangent to the knee of the curve of crystallization

start, the nucleation is suppressed and the underquenched liquid will transform in an amorphous solid. If the cooling rate is lower than the critical speed (vcr), so that it intersects the crystallization starting curve, a nanocrystalline structure will be formed.

The amorphous phase is a metastable phase, characterized by a free energy higher than of the crystalline phase. Therefore, the crystallization represents the irreversible final stage of the transformation of metallic glasses at heating.

solid + liquid crystalline

solid Crystalline solid +

Amorphous solid

amorphous solid

v2

v1 vcr

log t [s]

T [oC]

Tf

TX T’X

Figure 3. TTT diagrams for the formation of metastable phases (dotted line) and of stable phases (continuous line) at cooling of a melt

In order to pass from the metastable state to

the stable state, the system must receive a supplemental energy necessary for the pass through an intermediary metastable state. This minimum supplementary energy necessary to pass into a stable state is called activation energy, and it is proportional with the kinetic stability (TX-Tg) of the amorphous metal, and it is a measurement of the structural rearrangements necessary for the crystallization.

2. Experimental research

Pressure die metal casting method [3, 4]

was used in order to obtain bulk nanocrystalline alloys. The equipment used for the processing of magnetic ribbons that exists in the labs of the Materials Science and Welding Department of the Mechanical Engineering Faculty in Timisoara was modified to meet the requirements for the processing of amorphous alloys. Pressure casting in a copper die was used, by replacing the existing cooling roll and its entraining system with a copper die and an appropriate fixing system.

The experiments consist in the processing of rods from a nanocrystalline ferromagnetic alloy, using the pressure casting in a copper die method. The bulk nanocrystalline alloy is from

Page 77: buletin stiintific

73 the Fe71Cr4Ni1Ga4P12Si5C3 family. The experiment aimed to obtain a solid nanocrystalline alloy in two different stages:

- obtaining a primary alloy with a chemical composition favourable to nanostructure;

- the primary alloy is re-melted and then pressure cast in a copper die.

The raw materials were inserted in the furnace, combining them will lead to the formation of a crystalline alloy in the first stage (the temperature in the furnace is up to 1280oC). The primary alloy that was processed was cast in a die in the shape of a bar, 13 mm diameter, inserted than in a quartz crucible, re-melted and then injected in the copper die (figure 4). This process lead to obtaining rods with 2 mm diameter and 20 mm length. 3. Computer simulation of thermal transfer

at casting in a copper die The purpose of this simulation is to find the

ideal thickness of the copper die’s wall, in order

to ensure the processing of a nanocrystalline structure, by an efficient dissipation of the heat generated by the melt that is to be injected in the die’s centre.

Figure 4. The rod casted in the copper die

We start with designing the die (figure 5),

using the Inventor program. The part simulated in this first stage is a reproduction of the die existing in the Materials Science and Welding Department.

Figure 5. The 47 mm piece, designed using Inventor

After importing the geometry in the

simulation environment, Ansys in this case [5], we impose the experimental conditions and wait for the results to be generated.

The conditions imposed for this simulation are:

- the piece has material properties; - the temperature in the centre of the

shell is 1280oC;

- the temperature of the environment is 22oC for the first simulation, and this value is to be modified after to 15oC, simulating thus cold water;

- time period is 5 seconds. Following the simulation, we follow the

efficiency of the die in dissipating the heat in the imposed time period. The result that is wanted is the lowest possible temperature of the exterior wall.

Page 78: buletin stiintific

74

As visible in figure 6, the temperature on the exterior wall is 146,4oC after 5 seconds. This first simulation is a confirmation of the data from the experiments conducted in the Materials Science and Welding Department; that is

encouraging, since one can affirm that a result obtained by a simulation may be considered as a viable information source for practical experiments based on these results.

Figure 6. The 47 mm piece at normal temperature

The same piece is simulated next, but for an

environment temperature of 15oC and 10oC. The result is not amazing, but an evident change takes place (figure 7), the temperature on the exterior wall is now 141,3oC and 135,58oC. These values for the temperature are obtained for the same time

period of 5 seconds, not according to the real conditions, but this value was kept in order to modify just one value during the simulation.

Figure 7. The 47 mm piece at 10oC

Page 79: buletin stiintific

75

The same simulation procedure is applied

next. A piece with a 67 mm exterior diameter is used this time, (20 mm higher than the reference die). For this piece, the efficiency of the supplementary thickness is obvious (figure 8). For

a time period of 5 seconds and an interior temperature of 1280oC, the temperature on the exterior wall reaches 53,67oC.

Figure 8. The 67 mm piece at normal temperature

For the simulation using the same piece, but

different environment temperatures, 15oC and 10oC, the results do not change much; the temperature on the exterior surface of the die is

46,85oC for 15oC, and 41,96oC for 10oC (figure 9).

Figure 9. The 67 mm piece at 10oC

For the confirmation of the results obtained

so far, a die with the diameter lower (10 mm) than the reference piece was simulated, but the results

do not satisfy the objective of this experiment, that is to obtain the lowest temperature on the exterior surface in the shortest time possible.

Page 80: buletin stiintific

76

Structural investigations using X-Ray diffraction, made on the DRON 3 diffractometer from the Materials Science and Welding Department, with the radiation of a Mo anode with the wave length λ = 0,71 Å (figure10),

certify the possibility of processing nanocrystalline structures using casting dies with 65-70 mm diameter.

Figure 10. Diffractograme of the nanostructured alloy using rapid cooling of the melt

4. Conclusions

In order to obtain the lowest temperature of the exterior surface in the lowest possible time period, one must ensure that the thickness of the die wall is not higher than 17 mm – that is 47 mm exterior diameter of the piece – and that corresponds to the reference piece, which used in real conditions ensured the processing of a nanocrystalline alloy. Also, it is recommended that the thickness of the mould’s wall is a minimum of 32 mm – that means an exterior diameter of 67 mm, in order to obtain ferromagnetic characteristics for the alloy.

One can diminish the size of the die’s wall thickness if the exterior wall of the mould works in a cooling environment that can ensure a temperature below 20oC. The nanostructure is obtained if the temperature of the melt is the lowest possible, and the thickness of the die’s wall is the highest possible.

References 1 C., Codrean, V.A. Serban, D. Buzdugan,

D. Utu, Experiments regarding the elaboration of bulk amorphous soft magnetic iron based alloys as rod shape, Scientific Bulletin of Politehnica University of Timişoara, Fasc. 4, 2008, pp. 16-19, ISSN 1224-6077

2 J. M., Grenèche, Soft Magnetic Nanocrystalline Alloys, Journal of Optoelectronics and Advanced Materials Vol. 5, No. 1, March 2003, pp. 133 – 138, ISSN 1454-4164

3. V.A. Şerban, C. Codrean, The syntthesis methods analysis of ferromagnetic nanostructured alloys, Scientific Bulletin of the “Politehnica” University of Timisoara, Transaction on Mechanics Tom 50(64), 2005, pp. 17-20, ISSN 1224-6077

4. V.A. Şerban, C. Codrean, D. Uţu, Bulk amorphous soft magnetic iron based alloy with mechanical strength and corrosion resistance, Key Engineering Materials Vol. 399 (2009), pp. 37-42, ISSN 1662-9795

5. M. Vodă, Analiza fiabilităţii sistemelor mecanice procesată în Ansys (Analysis of the relibility of mechanical systems processed in Ansys), Ed. Orizonturi Universitare, Timişoara, 2006, ISBN(10)973-638-303-2, (13) 978-973-638-303-8 OPTIMIZAREA UNEI MATRIŢE DE TURNARE PENTRU OBŢINEREA ALIAJELOR NANOCRISTALINE FEROMAGNETICE SUB FORMĂ DE BARE Rezumat

Lucrarea prezintă un studiu, în care este utilizată simularea computerizată pentru optimizarea unei matriţe de turnare, utilizată pentru obţinerea aliajelor feromagentice nanocristaline. După simulare, rezultatele au fost verificate experimental. Au fost realizate investigaţii structurale prin difracţie de raze X, certificând obţinerea structurilor nanocristaline la diametre ale matriţelor de turnare de 65-70 mm.

Scientific reviewers:

Viorel-Aurel ŞERBAN, Politehnica University of Timisoara, Romania Bogdan RADU, Politehnica University of Timisoara, Romania

Page 81: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

TRANSACTIONS ON MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITĂŢII „POLITEHNICA” DIN TIMIŞOARA, ROMÂNIA SERIA MECANICĂ

Tom 54 (68) ISSN 1224 - 6077 Fasc. 2, 2009

INDUSTRIAL DESIGN – A WAY FOR DESIGNING PLESURABLE PRODUCTS AND HUMAN INTERFACES

George BELGIU*, Dan Andrei ŞERBAN*, Gabriela NEGRU-STRĂUŢI*

* Mechanical Engineering of Timişoara, Mihai Viteazu No.1, Timisoara 300222, Romania e-mail: [email protected]; [email protected]; [email protected]

Abstract. At first, this paper was motivated by the need to move away from a simply functional methodology for usability, and focused on a more practical approach to human-product interface. Currently, the validation of the means for design and production show the way to a virtual standardization of the products on the market. In the sharp competition between the companies, Industrial Design is apprehensive with all the human aspects of products and their rapport to civilization and the nature. The engineer is in charge for the product and their impact on culture and natural world. The designer’s role is product's development is: safety, form, color, maintenance and, most importantly, the cost. Product design shares out: (i) consumer products and (ii) industrial products. An industrial design engineer is required to be involved in several research and development activities: human performance, human-machine interface, environment, and the product-design itself. In this paper we show the optimization of these activities in a case in point of a self balancing scooter. Keywords: Industrial Design, Industrial Engineering, Management, CAD. 1. Introduction

The aim of this paper was to create a new design for a self balancing scooter, from an industrial design purpose. We used self-balancing scooter kit as an optimization basis example for a mechatronics project. The new model will have to be built after the principles of the self-balancing scooter and integrate the modifications proposed by the students who worked on the project.

Three small series models will be proposed (with relatively simple construction, having the possibility of being manufactured in workshops), each having a different design and a different construction. The optimum model will be selected after different criteria.

For the develpement of the models and the thesis, the following software was used: (i) Dassault Systems SolidWorksTM 2009 – used for

the 3D desing of all models presented in the paper; (ii) COSMOSWorksTM (integrated in SolidWorksTM 2009 under the name of SolidWorks SimulationTM) – used for the finit element analysis of the models; (iii)SolidCAMTM 2008 (integrated in SolidWorksTM 2009) – used for creating a NC program for the rapid prototyping; (iv)Adobe PhotoshopTM – used for processing the pictures shown in the paper. 2. SEGWAY™: hystory of the self-

balancing scooter Segway™ is a 2 wheel electric self-

balancing vehicle. The scooter is driven by 2 independent DC motors and uses the operator´s body motion to drive/steer itself. So, in order to go forward, the operator leans forward, in order to break/go backwards, the operator leans back, and in order to steer it left or right, the operator

Page 82: buletin stiintific

78 turns the “Lean Steer” handle bar. It uses a set of gyroscopes and acceleratometers to detect the lean of the vehicle and transform this movement into signals that are processed by a microcontroller and transformed into command signals for the electric motors.

Currently, Segway™ has 2 commercial models, the i2 and the x2. The i2 model is suitable for inner city use, on public roads or bicycle tracks. It is used by some US Police departments. The x2 is more of an off-road vehicle and it is used by some as a replacement for the golf car. 3. Functioning principle and technical

details The self-balancing scooter is a mecha-

tronics system that uses electronic components and computer programming to achieve stability and to drive the vehicle.

Mechatronics (name coming from combining mechanics and electronics) is an engineering branch which integrates different “classical” engineering disciplines such as mechanical engineering, electronical engineering, control engineering, computer engineering, etc. It has a large application range, from automation, control system, servomechanics to medical and bio-medical systems, expert systems, and com-puter engineering.

The scooter is made up of 2 wheels on each side of a platform-like chassis, which also supports the control shaft. Each wheel is powered by an independent DC motor. There is no axel between the wheels, so they can have different turning speeds. Thus, the steering is accomplished by rotating one wheel faster than the other. The motors are powered by a pair of rechargeable batteries, and are commanded by a microcontroller. When turned on, the scooter will rest in a vertical position, if the rider isn’t commanding it otherwise. For this, the micro-controller must know which way is up, so that it could send according signals to the motors. For this, it uses a gyroscope (or a system of gyroscopes, depending on the model), combined with a micro pendulum called an accelerometer. These components are also responsible for driving the scooter. Thus, in order to move the scooter in either way, the rider must lean forward (for moving forward) or lean back (for moving backwards). When the scooter has an angular movement, the gyroscope detects it and transforms it into an impulse, which is “translated” by the microcontroller and converted

into a signal for the motors. For the steering, the scooter uses a potentiometer to detect angular variations of the control shaft, and again, the signals are processed by the microcontroller, who sends signals to the motors and thus, this 2 components act as an “electronic differential”.

Commercial models have a user interface that lets the driver know the instant speed of the scooter and the battery life. 4. The new model

The paper’s goal was to integrate the suitable modifications into a new model. Several workgroups of designers took care of different aspects, from computer programming of the microcontroller to chassis optimizations. The most important changes will be pointed bellow. The most important modification to the current prototype is acquisition of the new wheels with integrated brushless 36V/250W DC motors. The motors have a torque of 10.6 Nm and can reach a frequency of 300 rpm (figure 1).

Figure 1. Rendered wheel.

The electronics support will hold the

batteries and circuit boards, as well as the bearing support. There are 2 circuit boards that have the dimensions: 100x150x30mm and 70x100x30mm respectively. The scooter will use 3 100x150 x30mm batteries. The support will have 2 2,5mm thick construction steel plates. 5. Proposed models

Three concept models were discussed. These models have a relatively simple con-struction, and they can be materialized (more or less) in workshops (some components require CNC machining, CNC cutting/brake pressing or

Page 83: buletin stiintific

79 rapid manufacturing). 3 models will be proposed for this section: 5.1. Model I This model is based on the architectural principle of compact structure designs, so the useless volumes were reduced as much as possible. It has a supporting platform built out of a welded pipe frame and an aluminum plate. The housing will be build from polymers most like through Rapid Manufacturing technologies.

The frame is made out of 4 welded steel bars, among which one is bent. They can be obtained by cutting a bar to the necessary dimensions. The front bar can be bent with a mechanic or hydraulic bar bender. The dimensions for the bars will be:

• 1262mm for the front bar • 640mm for the back bar • Two 714mm bars for the middle “X”

The drawings for the front bar, and also, the design for the whole frame is shown below.

Figure 2. Rendered Base-Assembly, model 1.

The housing along with the dashboard has

the most complex shape from all the small series models. Effectively, it can only be built through Rapid Manufacturing processes. It consists of 3 parts, 2 of them being fixed onto the aluminum platform with 4 Hexagon bolt grade C ISO 4016 M8x30 – N screws and 4 Hexagon Grade C ISO 4034 M8 – N nuts, and the third one being detachable (fixed wit 6 buttons), so the user can access the electronics, especially the batteries. Rapid Manufacturing is a relatively new method of producing functioning prototypes. Its main advantage over classical prototype manufacturing techniques is the short time needed to complete the product (a few hours, while conventional methods would require days or even weeks). There are several known methods of Rapid Manufacturing, each with different applications. For example, Silicone Rubber Molding or Vacuum casting produce silicone molds used for

polymer injection, Spray metal tooling produce aluminum or zinc molds for polymer injections, Spin casting can create metal products, etc. Most of the Rapid manufacturing methods are protected with invention patents by the companies that developed them. The most suitable Rapid manufacturing method for these parts is Vacuum casting.

Figure 3. Rendered General Assembly, model 1.

Vacuum casting is a Rapid Manufacturing

process used in order to produce functional products made out of polymers. This technology requires a master model that can be done conventionally or through Rapid Prototyping methods. First, the separation line must be determined, and covered with tape. Then, the prototype must be suspended in the casting frame (which can be made out of different parts, from plywood pieces to toy blocks). After that, the silicone mix will be prepared and poured into the casting frame. In order to avoid air inclusions, the mold will be degassed in a special oven, and then dried. After a given time, the mold will be taken out of the oven and cut in half around the separation line. The prototype will be removed from the mold, which is now ready for casting the given polymer in order to create the functioning products.

Rapid prototyping is a method of obtaining prototypes directly from CAD drawings or models. There are 2 categories of RP: additive RP and subtractive. The most important additive

Page 84: buletin stiintific

80 Rapid prototyping techniques are Stereolito-graphy, Fused deposition modeling, Laminated object manufacturing, Selective LASER sintering, 3D printing. The most common subtractive Rapid prototyping method is milling. For our parts, almost every Rapid prototyping method is suitable, the biggest difference being the detail of the product. 5.2. Model II Model overview. Model II has a much more voluminous build, being meant to be used in off-road environments, having an aggressive look as result of using a bulbar (who’s role is rather aesthetic then functional). Its primary components are made out of sheet metal, which can be either bent and cut or welded.

Figure 4. Rendered Base-Assembly, model 2.

The platform has the role of supporting

every component of the scooter. It consists of a bent 2,5mm metal sheet. The cutting, tapping and bending can be done with a CNC press, who can do all the operations in one fixing.

Figure 5. The flange assembly, model 2. The flange is the intermediary part between

the wheels and the platform. It is a cut piece of

construction steel of 50 , with 8 M8 holes and a

9 hole. Also, the flange will be assembled on the

wheel first, with 4 Slotted Cheese Head ISO 1207 M8x10 screws. Then, it will be assembled with another 4 Slotted Cheese Head ISO 1207 M8x10 screws to the platform (figures 5, 5 and 6).

The reinforcements are 5mm thick construction steel plates, bended over 90°, with 2 welded ribs for better resistance, and have the role of adding stability to the platform region that supports the wheel - flange assembly. 2 mirrored reinforcements will be used, one for each wheel.

Figure 6. Rendered General Assembly, model 2.

5.2. Model III Model overview. This model has a retro design, being based on interbellum and World War II period motorcycle models like the BMW R75 or the Zündapp series. It has a combination of square shapes with abrupt edges (obtained by assembly) and smooth round edges (obtained either by rolling sheet metal or by casting). The chosen

Page 85: buletin stiintific

81 paint colour was pale brown because it was largely used on the vehicles of that era.

For this model, a piece of bended steel was used to fix the wheels onto the platform. An intermediary piece was mounted in between, in order to get a clearance so that the wheels don’t touch the edge of the platform.

Again, the cutting, drilling (of the normal holes and the countersink holes) and taping can be done manually, with the aid of a normal machine or CNC machine. The wheel-intermediary part-flange module will be assembled with ISO 7045-1 M8x10 pan head cross recessed screws, and the module will be fixed to the platform with ISO 7046-1 M8x10 countersink flat screws tightened with grade 4034 C hex nuts. A general assembly of this model is shown in figure 7.

Figure 7. Rendered General Assembly, model 3.

6. Conclusions

The optimum model was determined with the weight proprieties method. This method is used for selecting the best candidate when more proprieties are taken into account. A weight is given to every propriety, depending on its importance. The value of the weight propriety is obtained by multiplying the numerical value of the given candidate with the weight factor . In order to obtain correct results, each value of certain propriety must be scaled.

As future works regarding the new model:

the whole assembly will be checked with Finit Element Analysis, not just the flange. This will require a lot of work, and may be done by another student; detailed execution drawings for each part will be made; the rapid prototyping for the carapace and the dashboard, along with the construction of the electronics support will be done, in order to analize potential assembly problems; if the 2 aspects from above determine some problems, the remake of the model will be necesarry; research in order to try to evade the self-balancing scooter patent will be done. References 1. J.R. Baldwin, D.Sabourin, Impact of the Adoption of

Advanced Information and Communication Technologies on Firm Performance in the Canadian Manufacturing Sector, Micro-Economic Analysis Division, Ottawa, K1A 0T6, Statistics Canada, Facsimile Number: (613) 951-5403, Ottawa, 2001, ISBN 0-662-31016-0

2. R. Batenburg, R. Helms, J. Versendaal, The maturity of Product Lifecycle Management in Dutch Organizations. A strategic alignment perspective. Available from: http://www.cs.uu.nl/research/ techreps/repo/CS2005/2005-009.pdf. Accessed on: 2009-04-22.

3. A. Bruzzone, P. Lonardo, E. Rossi, Production Process and Inventory Management for Machine Tool Companies: Analysis and Development of Optimisation Models, International conference on smart machining systems , NIST, Gaithersburg, March, 13-15, 2007, Available from: http://smartmachiningsystems.com/slides/nistBruzzone1D.pdf, Accessed on: 2009-02-10.

4. T.Childs, K. Maekawa, T. Obikawa, Y. Yamane, Metal Machining. Theory and Applications, John Wiley & Sons Inc, New York, 2000,ISBN 0 470 39245 2

5 J.Clark, Human resource management and technical change, SAGE Publications Ltd, London, 1994, ISBN 0-8039-8786-2

6. D. Dornfeld, Sustainable Design and Manu-facturing: Can we “Engineer our way” to a Sustainable Future?, 2007, Available from: http://www.citris-uc.org/files/energy_ rese arch, Accessed on: 2009-05-22.

7. D. Grote, The Performance Appraisal Question and Answer Book: A Survival Guide for Managers, AMACOM – American Management Association, New York, www.amacombooks.org, 2002, ISBN 0-8144-0747-1

8 F. Jovane, E. Carpanzano, Research and Innovation in Manufacturing Systems in Lombardia: from regional to inter-regional and European successful activities, Bi-regional Workshop Lombardia-Baden-Wüerttemberg, Stuttgart, January the 29th, 2007, Available from: http://www.regstrat.net/

Page 86: buletin stiintific

82

download/stuttgart/2007-01-29_jovane.pdf, Ac-cessed on: 2009-04-16.

9. K. Lawson, New Employee Orientation, ASTD - Society for Human Resource Management, New York, 2002 , ISBN 9781562863180

10. R. Kamalini, M. Fisher, K. T. Ulrich, Managing Variety for Assembled Products: Modeling Component Systems Sharing. Manufacturing and Service Operation Management, vol. 5, no. 2, 2003,

pp. 142-156, ISSN 1523-4614. 11. S. F. Krar, A. R. Gill, P. Smid, S. Krar, Technology

of Machine Tools, McGraw-Hill Higher Education; 6th edition, 2004, ISBN 0078307228

12. K. Lee, Principles of CAD/CAM/CAE Systems, Addison-Wesley, 1999, pp. 291-319, Massachusetts, ISBN 0-201-38036-6,

13. M. Mader-Clark, Job Description Handbook, 2nd Edition, NOLO, New York, 2008, ISBN 9781413307573

14. T. D. Marusich, D. A., Stephenson, S. Usui, S. Lankalapalli, Modeling Capabilities for Part Distortion Management for Machined Components. Available from: http://www.thirdwavesys.com/ news/published_papers.htm. Accessed on: 2009-05-23.

15. J. H. McConnell, Auditing your human resources department: a step-by-step guide, AMACOM – American Management Association, New York, 2001, www.amacombooks.org, ISBN 0-8144-7076-9,

16. A. S. More, W. Jiang, W. D. Brown, A. P. Malshe, Tool wear and machining performance of cBN-TiN coated carbide inserts and PCBN compact inserts in turning AISI 4340 hardened steel, Journal of Materials Processing Technology, vol. 180, pp. 253–262, ISSN 0924-0136

17. Q. Ni, W. F. Lu, W. P. Fang, K Yarlagadda, An extensible product structure model for product lifecycle management in the make-to-order environment. Concurrent Engineering: Research

and Applications (CERA), 16(4). pp. 243-251, ISSN:1531-2003, http://eprints.qut.edu.au/ 14638, Accessed on: 2009-04-16.

18. D. A. Serban , Self balancing scooter, Final Report, Fachhochschule Gelsenkirchen, Fachbereich Maschinenbau, Universitatea Politehnica Timisoara, 2009

19. T. Tani , Product Development and Recycle System for Closed Substance Cycle Society, First International Symposium on Environmentally Conscious Design and Inverse Manufacturing, pp.294-299 ,Tokyo Japan, 1999. ISBN 0-7695-0007-2,

20. M. Yallese, J. F. Rigal, K. Chaoui, L. Boulanouar, , The effects of cutting conditions on mixed ceramic and cubic boron nitride tool wear and on surface roughness during machining of X200Cr12 Steel (60HRC), Proceedings of the Institution of Mechanical Engineers, Part B. Journal of Engineering Manufacture, 2005.vol. 219, pp. 35–55, ISSN 0954-4054

21. J. M. Zurada, Introduction to Neural Systems, West Publishing Company, New York, 1992, ISSN 0018-9391

DESIGNUL INDUSTRIAL – O CALE SPRE REALIZAREA DE PRODUSE ŞI INTERFEŢE ATRACTIVE Rezumat Lucrarea prezintă un punct de plecare nou în metodologia proiectării funcţionale, focalizându-se în mod realist asupra interfeţei om – produs. Folosind tehnici moderne de Design Industrial, s-a prezentat un model practic de optimizare a unui produs – în acest caz un scuter autobalansat, pentru care s-au prezentat trei variante constructive concrete.

Scientific reviewers: Aurel RADUŢĂ, “Politehnica” University of Timisoara, Romania

Daniel STAN, “Politehnica” University of Timisoara, Romania

Page 87: buletin stiintific

SCIENTIFIC BULLETIN OF THE „POLITEHNICA” UNIVERSITY OF TIMISOARA, ROMANIA

Transactions on MECHANICS BULETINUL ŞTIINŢIFIC AL

UNIVERSITAŢII “POLITEHNICA” DIN TIMIŞOARA, ROMANIA SERIA MECANICA

Tom 54(68) ISSN 1224 - 6077 Fasc. 2, 2009

STRESSES CORROSION EVALUATION TESTING

IN PROCESS EQUIPMENTS

Traian FLEŞER*, Dumitru ŢUCU* * Mechanical Engeneering Faculty, Bv. Mihai Viteazu, No 1, 300222, Timisoara, Romania

E-mail: [email protected], [email protected]

Abstract: The welded joints behaviour of construction steel pipes (S265 and S355) is evaluated in a technological process steam environment. A program is run, which envelopes further deformation in aggressive environment exposure, mechanical trials, and metallographic examinations. The results showed different effects of degradation, correlated to welded joints nature respective initial welded qualification. The results are used for preliminary long time capacity use. Keywords: unalloyed steels, welded joints, stresses coro-ssion, metallographic examination, mechanical tests.

1. Introduction The effects of increasing pressure, temperature, fluide agressivite in technical systems are the acceleration of component materials deterioration. Metals and their alloys are, more or less, stabile in time, in concrete conditions used. In technological installations for steam production, water represents the raw material. Therefore, it’s important to know metallic materials behaviour under stress corrosion effect. Corrosion rate is influenced by metal’s composition and structure, surface condition´s, reference and type of stresses, fluid’s concentration and nature etc. For preventing those disadvantages, it is necessary the complete knowledge of this phenomenon, its nature, the factors that influence the corrosion rate, as well as proper protection means. The projet unit and user unit aims for conservation the usage characteristics correlated with pipe material´s, followed purpose and environment concrete conditions where the technical system is used. The user must prove technical and economical efficiency, which impose intensive exploitation regimes of installations, in reliability and risk

checked. The corrosion phenomenon is more active in condition circulation is carefully evaluated because of the proved turbulence over the metallic components. The resulted condense during installation is took up through pipes which are prefigured with condensate and recast separators devices in the system’s thermic circuit. The corrosion phenomenon develops through surface condition and geometry modification, through structural or chemical transformation of the used metallic material, with consequences over the reliability diminishes in exploitation to plate sheet reduced thickness and increased hydraulic losses. Important is the fact that this effects increase with pressure and temperature raise, the exigencies regarding the water quality which is feeding the steam generator are increasing, too. Mechanical and chemical water treatment can’t affect the development of material damage phenomenons associated with corrosion effects. The presence of contaminants in water produces

Page 88: buletin stiintific

84 84 deposits on the heat interchange surfaces, which influences the thermo transfer, facilitates the appearance and development of corrosion, the steam is not pure anymore and the final cumulative effect drives to a decreased reliability and efficiency of the thermo-energetic installation. The research program aims the effects tresses corrosion tension (COFITEN) of basic set base metal (MB) and welded joints areas: heat afected zone (HAZ), welded metal (WM) of two unalloyed steels. Corrosion evolution testing is assured through application of our own programs for testing and evaluation, by mounting the tests in devices set on the technological and condenses pipes (especially “continuous purging”). Are included mechanical tests, metallographic evaluation to characterize unalloyed steels the pipes behaviors, to corrosion under stress and steam effect transported condense. 2. Materials and methodology

The investigation objects are welded and unwelded pipes made with unalloyed steel S265 (butt-jointed welded ring Ø410 x 8 x 360 mm). It is equivalent with P265GH steel (SR EN 10216-2-2003). Unalloyed pipe steel S355 (butt-jointed welded rings Ø133 x 9 x 305 mm), is comparable with steels from: Germany– St 45.8, USA – A 106 group A, Sweden – 1243 – 44, UK HFS 23, France – TU 47. The welding has been done according to Welding Procedure Specification(WPS) and technical speciphical prescription. The experimental program is directed to obtaining specific characteristics for qualifying the materials used through: - corrosion behaviour evaluation on COFITEN tests (specimen with 127x20x6 mm); - chemical composition analysis; - metallographic examination; - mechanical tests: traction, shock bending, hardness determination. From the analyzed steels, as basic materials and afferent welded joints, 12 tests were performed with holding times of 396 and 625 hours respectively, at 573 K – steam temperature, in the detailed procedure conditions for corrosion under tension COFITEN test procedure : specimen mark 1 ÷ 6 for unalloyed steel S265 and mark 7 ÷ 12 for pipes unalloyed steel S355.

3. Results 3.1. Evaluation of unused welded joints a. The unalloyed steel S265 has a general destination for general construction. The S355 unalloyed pipe steel. When analyzing the chemical

composition, respective mechanical characteristics, the analyzed steels complied with delivery norms previously specified. It has a remarquable chipping workability and plastic deformation capacity. The steels welding behaviour do not raise any problems, if the qualified technologies are used. b. Metallographic analysis put in evidence a weld (WM) realized with: - two layers at afferent joint pipe, Ø410 x 8 x 360 mm, unalloyed steel S265, - three layers at afferent joint pipe Ø133 x 9 x 305 mm, from unalloyed pipe steel S355. There were not found any welding defects with ultrasonic NDT. The basic material microstructure (MB) is formed from ferrite and pearlite. In welding metal(WM) we have acicular ferrite together with ferrite and pearlite. c. Tensile tests give fracture localisation, in base material localized with an appreciate deformation before failure. d. Bending test at normal temperature to 180º on check bars that had stretched root, respective compressed used. Every RBB check bar tested from each material cracked when it reached 105°, respective 114°. The other check bars were bent at 180° without any material cracking. The 180° angle reached shows an adequate cold bending capacity for these welds. When repeating the test on two specimens sampled from each joint, a test on a RBB from pipes unalloyed steel, with tensile strength Rm = 450 MPa, cracked at 107°. At a more careful look were found presence of some little discontinuity in for the welding material, under the recorded limit seemed in the welding qualification normative. e. The impact testing was done on Charpy V specimens at 273 K, in order to compare MB, HAZ, WM areas. At afferent welded joint of unalloyed steel S265 basic material, it was obtained KVmin= 33 J in MB. The highest value was obtained in VWT (84 J). At afferent welded joint the pipes unalloyed steel, with tensile strength Rm = 450 MPa, basic material it was obtained KVmin= 36 J in VWT. The highest value (63 J) was obtained in MB. These values overflows the equivalent minimum KCU2 = 40 J.cm-2 for P265GH steel, respective 60 J.cm-2 for unalloyed steel S265, according to specific delivery normative. Regarding the analyzed area (MB, HAZ, and respective WM) the values of fracture energy are close and between the mentioned areas there are no significant differences. f. The results for HV 10 hardness determination, do not show significant differences between welded areas and even between situated valued

Page 89: buletin stiintific

85 85 close to the interior plate (“wall”), respective exterior plate of the pipes. On the exterior layer, between unalloyed steel S265, with tensile strength Rm = 370 MPa, welded areas the hardness is 139-185 HV10. For S355 pipes unalloyed steel, with tensile strength Rm = 450 MPa, the hardness is between 150 - 196 HV10. The interior layer hardness is approximately 10-15 % lower than the exterior layer hardness. The difference between individual values was max. 46 HV10. At this level of differences between areas, respective hardness individual values, the problem of material brittleness susceptibility is out of the question.

3.2. Examination and test program on COFITEN samples a. Visual examination of the specimens aspects (the initial remanant deformation through bending device, pre-tensioned before testing, at 290 ± 1 K (17 ± 1° C) constrained to COFITEN test assay is represented in figure 1. During test under corrosive environment activity, were effectuated supplementary deformations. The aspect and condition of the examined check bars confirms the keeping of the specified condition from the basic material test assay procedure and similar welded joints, respective the surveillance instructions. It is concluded that the check bars don´t have persistence cooling deposits from the corrosive steam. The fluid did action on a large area in a continuous mode (way) through a correct initial adjustment and on going, too. The check bars’ surface aspect constrained to corrosion and the corrosion spot area detail is presented in figure 2. The macroscopic evaluation did not show any evidence regarding crack imperfection types or other nonconform aspects. The macroscopic aspect of COFITEN basic metal tests, with examined weld after free bending, shows a high plastic deformation capacity. The colour cast of the tested check bars is grey to black and characterizes the corrosive fluid effect. b. After testing, under the steam action and after disassembly, the specimens had the permanant deformation (table 1). For the identification of eventual micro cracks, the predeformed specimens were constrained to free bending (unguided). In table 1 are mentioned the final bending angles, the recorded forces and the purposed shifting with 30 mm diameter (d=4g), after supplementary deformations.

Figure 1. Check bar constrained to corrosion

specimen, before COFITEN test assay

Figure 2. Initial aspect of the deformed spot area

detail After analyzing the table results, was found that there aren’t significant systematic decelerations between the required forces of the basic material check bars and afferent welds. Also, as the deformation increases from 5 to 15 mm, it can not be distinguished a similarity of the applied forces between analyzed tests belonging to the same specimens group. The force increasing was situated between 16 and 47 %. The final angles are more approached at welded joints tests (70 - 79, respective 71 - 78 degrees), than the basic materials (67- 82, respective 68 – 81degrees. The results are used for preliminary long time capacity use. c. Metallographic examination. c1.The median longitudinal section macroscopic examination sampled from COFITEN check bars at analyzed tests, constrained to steam corrosion action did not show any corrosion cracks or any other none conform aspects regarding the examined surface. c2. The microscopic examination according to EN 1321 and SR ISO 643 was made on the characteristic welded joint areas constrained to steam corrosive action from the thermo circuits.

Page 90: buletin stiintific

86 86 The corrosive action constrained area was longitudinally sectioned through the “corrosion spot “, assuring that the examination surface is, in the test longitudinal plan. In BM is found the presence of structural constituents in granular form (ferrite-pearlite nature). The granulation has 6 - 8 points according to SR ISO 643. In the basic metal examination area were not detected fabrication defects and corrosion cracks. The corrosion depth ≤ 0.15 mm. In WM, the structures are typical casting with dendrite pearlite-ferrite with elongated dendrites on the thermal flux direction. On little areas were partially developed acicular ferrite structures who do not overcome 2 points (W2). “The corrosion spot” formed on the steam-check bar material

direct contact area where the most corroded area appears; the other areas present reduced corrosion phenomenons. The corroded depth area is 0,04 - 0,16 mm. On the heat affected zone (HAZ1, HAZ2), the structure is granular pearlier-ferrite with acicular ferrite and with agrain size of 4 to 6 according to the scale of SR ISO 643. The examined areas did not present any micro cracks in the steam-metal contact areas. The corroded depth is 0.07 - 0.16 mm. It’s found out that the identified microstructures are typical representative of the materials and exposure conditions. The corrosion phenomenon affected up to 2% the pipe’s wall thickness.

Table 1. Technical parameters to free bending of specimens.

Deflection[mm] /Force [N]No.Mark

Condi- tion#

Initial deformation [°] Angle after corrosion [°]5 10 15

Free bending final angle[°]

1 2 3 4 5 6 7 8 9

10 11 12

1 2 3 4 5 6 7 8 9

10 11 12

WM WM WM MB MB MB WM WM WM MB MB MB

17 18 17 17 18 17 17 17 18 18 17 17

21,5 24,0 19,0 19,5 17,5 22,0 21,0 18,0 20,0 17,5 19,5 21,5

530 545 680 665 480 500 735 770 643 605 770 595

583 605 770 740 540 544 700 890 715 680 885 650

620 635 912 843 565 735 735

1045 775 715

1030 695

70 72 79 82 67 72 71 78 73 68 81 71

# - MB- basic material, WM – welded joint. d. The hardness spots arrangement diagram is according to norme. The relative error E is ±3%. The fidelity relative error is ±4%. For the ΔHB estimator determination the HV10 hardness values were equaled in HB hardness units. The ΔHB estimator represents the local structural hardening between two area, especially the strained (TS) and compressed (CS) hardening areas reported to the neutral area (NS):

( ) ( )

( )[ ]%100

min

min,max ⋅−

=ΔNS

NSCSTS

HBHBHB

HB (1)

When ΔHB > 50 %, it appears a local structural hardening, and when ΔHB ≤ 50 %, it appears a local structural softening. In table 2 is the ΔHB values calculated, only on 2 of the 12 testing specimens. Based on the determined ΔHB estimator, we can support the fact that: • It is found out a significant scattering for the

calculated estimators’ values, even for the basic materials from areas, respective

approached test from the pipe’s circumference.

• At the BM on the strained fiber, respective compressed fiber, compared with median fiber, it can’t be detected a general tendency regarding the cold hardening degree.

• On the basic material assembly, were obtained reduced values for the ΔHB estimator (3.49 % for a product specifications. After weld bending test assays it is found out a weaker plastic deformation capacity steel-test on S355 pipes unalloyed steel and high values (50.33 %) towards the strained surface for the unalloyed steel S265.

• It is remarked the pronounced local sensitivity for the welded areas in comparison with the adjacent BM.

• The evaluations put in evidence significant differences between analyzed welded joints HAZ’s having unalloyed steel S265, as basic material (8.91 %, respective 52.32 %), explained by the material metallurgic lack of homogeneity, generating a different behavior

Page 91: buletin stiintific

87 87

under the work environment. • It is found out a reduced dispersion for the

WM estimator values, for the both tested materials, in comparison with other basic materials.

Table 2. The ΔHB estimator calculated.

ΔHB Estimator [%] Test mar-king

Evaluated area# Strained fiber

(FS) Compre-ssed fiber

(FC) MB1 37,09 24,50

HAZ1 19,87 17,88 WM 43,04 23,84

HAZ2 42,38 25,17

1

MB2 50,33 28,48 MB1 37,09 24,50

HAZ1 19,87 17,88 WM 43,04 23,84

HAZ2 42,38 25,17

2

MB2 50,33 28,48 # - MB- basic material, HAZ - heat affected zone, WM – welded joint 4. Conclusions

4.1.The structural examinations and hardness tests effec- tuated on the COFITEN check bars test samples, tested on the “continuous purging” circuit attests that unalloyed steel S265, respective S355 pipes unalloyed steel and welded joints have differential crack corrosion resistance under tension on this thermic circuit, approximately 2% pipe plate thickness, for maximum 625 hours, at 573 K – steam temperature. 4.2. The microstructures are typical and representative for materials and exposed condition:

• in the basic metal (MB): the presence of structural constituents in granular form (ferrite-pearlite nature) and the granulation 6-8 points according to SR ISO 643.

• in the welded metal (WM), the structures are casting typical with dendritic aspect, pearlite-ferrite with elongated dendrites on the thermo direction flow.

• in the heat afected zone (HAZ1, HAZ2), the structure is pearlite-ferrite granularly with acicular ferrite and in granular net with 4-6 points according to SR ISO 643.

4.3. The weld joints short term mechanical test assays not used in exploitation showed evidence of adequate resistance characteristic, conform to material and associated to presence of weld defects at weld’s root. The welding processes must be evaluated regarding specifications conformity. 4.4. The dynamic bending test (Charpy V specimens) assays results shows an adequate tenacity for all welded areas.

4.5. The HV10 hardness was situated between 151-227 units for unalloyed steel S265, and 172-233 units for S355 pipes unalloyed steel, in MB, WM, and respective HAZ. 4.6. The obtained results confirm that the used steam during experiments contributes differentially, locally and affects the fragility sensitivity together with non-homogenity of the analyzed metallurgic areas. This is sustained by the ΔHB estimator, too. For the thermo influenced area evaluation and for the adjacent basic material the COFITEN fragility sensitivity depends on the welding process, because the hardening estimator reached occasionally 50%. References 1. I. A. Dolgov, R. A. Sadrtdinov,V.A. Gorchakov,

Yu. P., V.G. Rybalko, D. V. Noovgorodov, Analysis of the development of stress corrosion cracking in pipelines of compressor stations, Russian Journal of Nondestructive Testing,vol.44, no.1, ian. 2008, pp. 68-75ISSN 1061-8309( 1608-3385 ).

2. T. Fleşer, The industrial technical systems inspection and maintenance. Edit. POLITEHNICA Timişoara, 2006, pp. 490, ISBN(10)973-8359-45-7, ISBN(13)978-973-8359-45-7.

3. S.Kadry,Corrosion Analysis of stainless steel, European Journal of Scientific Research, vol.22, no.4, 2008, pp. 508-516, ISSN 1450-216X

4. K.Koji, H.Musumya, O.Takeshi,Evaluation of the stress corrosion cracking characteristics of brass,Journal of Material Testing Research Association of Japan,vol. 50, no. 3, 2005, pp. 140-146, ISSN 0285-2470

5. E.O. Olorunniwo, I. I. Benjamin,A.A. Adeniyi,Evaluation of pipeline corrosion in sour-gas environment,Anticorrossion Methods and Materials,vol.54,issue 6,2007,pp.346-353,ISSN 0003-5599

6. J. T. H. Pearce: Corrosion – a lyman’s guide INSIGHT, 2003, vol. 39, nr.1, London, pp. 10–16, ISSN 0931-0509

7. P. Thirumalai, R. Ravi, G. T. Parthiban, potential monitoring system for corrosion of steel in concrete,Advances in Engineering Software, vol.37, issue 6,,june,2006,pp.375-381, ISSN 0965-9978

8. R. Traicu, Predictiv mentenance system to energetical system with 420 t/h boiler application. PhD Thesis, UPT, 2001.

9. M. Trusculeşcu, s.a. Thermoenergetical systems. Reliability. Editure Politehnica, Timişoara, 2003, ISBN 973-625-026-1.

10. C.W Wegot: Sthalschlüssel 1995, Verlag Sthalschlüssel. Wegot GmbH, Berlin, pp. 276-277, ISBN 3-922599-117

Page 92: buletin stiintific

88 88

ÎNCERCĂRI COFITEN PENTRU EVALUAREA COROZIUNII SUB TENSIUNE PENTRU

ECHIPAMENTE DE PROCES Rezumat Este evaluată comportarea îmbinărilor sudate a oţelului pentru conducte S265, S35, utilizate la transportul aburului tehnologic. În programul experimental derulat,

iniţial probele în stare tensionată îndoite, sub acţiunea de lungă durată a aburului, sunt supuse ulterior încercărilor mecanice şi examinărilor metalografice. Rezultatele evidenţiază efectele diferenţiate ale degradării, corelat cu natura îmbinărilor sudate, respectiv calificarea tehnnologiei de sudare. Rezultatele se utilizează pentru preliminarea duratei de viaţă a respectivelor conducte.

Referenti stiintifici: Dumitru MNERIE, “Politehnica” University of Timişoara, Romania Zbinieck OLESIAK, Technical University of Opole, Poland

Page 93: buletin stiintific

NEWS

The paper having the theme FATIGUE BEHAVIOUR OF METALLIC MATERIALS, authors prof.dr.eng.VODA MIRCEA and lecturer dr.eng. , CODREAN COSMIN, was issued by Politehnica Publishing House Timisoara, under the collection “Material science”. It was structured on 4 chapters, in a logical succession, as it follows:

1. Generalities (Fatigue testing, classifications, fatigue testing and loading nodes, calibration of the testing machines) 2. Endurance testing at constant amplitude (loading classification, endurance diagrams, nature and dispersion of fatigue testing results, establishing the endurance limit of materials etc.) 3. Crack fatigue testing (Use of fracture mechanics, testing methods, crack length measurement, testing mode, representation of results) 4. Methods to improve the fatigue strength of metallic materials (Constructive solutions to improve the fatigue strength, technological procedures to improve the fatigue strength).

This paper represents a syntheses material in the field of material fatigue and addresses to students when working on licence, master and doctor’s degree, as well as to engineers that have in charge the maintenance, integrity and durability of structures.

Page 94: buletin stiintific

NEWS The paper CASTING, author prof. dr. eng. CUCURUZ LAURENTIU ROLAND, was issued by Politehnica Publishing House Timisoara, under the collection “Industrial engineering”. It was structured on 4 chapters, in a logical succession, as it follows:

1. Forming materials (casting sands, binding materials for shapes and cores, filler materials for forming mixtures, forming mixtures, powders, glues, lutes and casting paints, execution of shapes and cores) 2. Casting properties (Physical properties of casting alloys, solidification types, flowing capacity, filling capacity, supplying capacity, trends in forming cavities and hot cracking) 3. Design of as cast parts (Constructive requirements for cast parts, influence of stress distribution by design measures, technological additions) 4. Design of casting network (Establishing the minimum section of the casting network, and the casting time, calculus of the casting network on the basis of the minimum section, slag collector,

design of the foot for the feed box, dimensioning of the feed box, special supplying network, feeders and coolers).

Page 95: buletin stiintific

The Scientific Bulletin of the Faculty of Mechanics within POLITEHNICA University of Timişoara, as it was in 1929. This is a copy of the cower who are existing in the archives of the Faculty of Mechanics.

Buletinul Ştiinţific al Facultăţii de Mecanica din Universitatea POLITEHNICA din Timişoara, aşa cum se prezenta în anul 1929. Copia este a coperţii Buletinului din arhiva Facultăţii de Mecanică

Page 96: buletin stiintific

A SHORT HISTORY OF THE JOURNAL

The history of this journal of "Politehnica" University of Timisoara is strongly related to its creation under the name Polytechnic School of Timisoara (Ecole Polytechnique de Timisoara). Due to the changes of names and development of new areas of specialization, the university journal has been adapted several times during its long history. These adaptations are presented below in a synthetic history.

Polytechnic School of Timisoara

1925 The first number in a single series for all areas of specialization in technical, mathematical, physical and chemical sciences

1925 and Bulletin Scientifique de l'Ecole Polytechnique de Timisoara

1928-1947 (Comptes Rendus des Seances de la Societe Scientifique de Timisoara)

1948 Bulletin de Science et Technique de la Polytechnique de Timisoara, ISSN 0563-5594

1949 - Change of name to Polytechnic Institute of Timisoara

1949 Buletinul de Stiinta si Tehnica al Institutului Politehnic din Timisoara (Bulletin for Science and Technique of Polytehnic Institute of Timisoara, Naucino-tehniceskij biuleten' Politehniceskogo Instituta Timisoara, Bulletin des Science et Technique de L'Institut Polytechnique de Timisoara)

1956-1969 Buletinul stiintific si tehnic al Institutului Politehnic Timisoara (Scientific and Technical Bulletin of Polytehnic Institute of Timisoara), New series ISSN 0373-4374

1970 Editing on areas of specialization (series) specific to the main engineering fields of the Institute

- Chemical Series, ISSN 0366-3701

- Civil Engineering Series, ISSN 1220-0573

- Mechanical Engineering Series, ISSN 0373-4390

- Mathematics-Physics-Theoretical and applied mechanics Series, ISSN 0366-3779

Page 97: buletin stiintific

1970-1971 Buletinul stiintific si tehnic al Institutului Politehnic Timisoara, Seria Mecanica (Scientific and Technical Bulletin of Polytechnic Institute of Timisoara, Mechanical Engineering Series), ISSN 0373-4390

1972 - Change of name to "Traian Vuia" Polytechnic Institute of Timisoara

1972 - 1974 Buletinul stiintific si tehnic al Institutului Politehnic "Traian Vuia" Timisoara, Seria Mecanica (Scientific and Technical Bulletin of "Traian Vuia" Polytechnic Institute of Timisoara, Mechanical Engineering Series), ISSN 0253-2026

1975 - 1977 Buletinul stiintific si tehnic al Institutului Politehnic "Traian Vuia" Timisoara (Scientific and Technical Bulletin of "Traian Vuia" Polytechnic Institute of Timisoara) [Single series] Mathematics, Physics, Theoretical and applied mechanics, Electrical engineering, Civil engineering, Chemistry, ISSN 1220-0581

1978-1990 Buletinul stiintific si tehnic al Institutului Politehnic "Traian Vuia" Timisoara (Scientific and Technical Bulletin of "Traian Vuia" Polytechnic Institute of Timisoara, Mechanical Engineering Series), ISSN ISSN 0253-2026

1990 - Change of name to Technical University of Timisoara

1991-1994 Buletinul stiintific si tehnic al Universitatii Tehnice din Timisoara Scientific and Technical Bulletin of Technical University of Timisoara, Mechanical Engineering Series), ISSN

1995 Buletinul stiintific si tehnic al Universitatii Tehnice din Timisoara, Seria Mecanica (Scientific and Technical Bulletin of Technical University of Timisoara, Transactions on Mechanics), ISSN

1996 - Change of name to "Politehnica" University of Timisoara

1996 - Today; Buletinul stiintific al Universitatii "Politehnica" din Timisoara. România, Seria Mecanica (Scientific Bulletin of "Politehnica" University of Timisoara, Romania, Transactions on Mechanics), ISSN 1224-6077

(Also see http://www.upt.ro/cercetare/publicatii_upt.php)

Page 98: buletin stiintific