STANDARDIZATION,PROTYPES & QUALITY:A MEANS OF BALKANCOUNTRIES’COLLABORATION

STANDARDIZATION,PROTYPES & QUALITY:A MEANS OF BALKANCOUNTRIES’COLLABORATION

October

,

7- 8

2011American Farm School“Perrotis College”Information

tel fax , e mail: protypation@auth.gr

:

./ (+30) 2310-

SECRETARIAT OF ENEPROT,19, 54633Epimenidou Thessaloniki

286.680 html: www.eneprot.gr,

8th INTERNATIONAL CONFERENCE 8th

INTERNATIONAL

UNIVERSITY

HELLENIC AMERICAN FARM SCHOOL

Thessaloniki Greece

Co-Organizers:

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DIZATION

UNIOΝ OF HELLENIC SCIENTISTSFOR PROTYPATION AND STANDARDIZATION

Alexander TechnologicalEducational Instituteof Thessaloniki

Hellenic Instituteof Metrology

1

(09:00 - 09:45) Registration

(09:45 - 10:30) Welcome Session - Opening (Chair: Ioannis Tsiafis, Byron Papathanasiou)

Opening by the General Secretary of

Macedonia-Thrace. G. Chatzikonstantinou.

(10:30 - 11:00) Coffee Break

2

(11:00 - 12:00) STANDARDIZATION, PROTYPES AND QUALITY IN

AGRICULTURE, FOOD (Chair: Ioannis Tsiafis, Konstantinos Rotsios)

DETERMINANTS OF HAZARDS THAT

AFFECT SAFETY AND QUALITY IN

AGRICULTURAL WORK.

E. Ventouri, E. Papadopoulou,

N. Hasanagas.

THE ROLE OF LABORATORY

ACCREDITATION IN INTERNATIONAL

TRADE OF AGRICULTURAL

PRODUCTS

T. Bintsis.

MEAT CONSUMPTION PATTERNS IN

GREECE (1957-2005). AN ECONOMIC

ANALYSIS.

K. Vasileiou, I. Sotiropoulos,

G. Georgakopoulos, C. Fragos,

C. Fragos.

CONSUMPTION PATTERNS OF

DAIRY PRODUCTS IN GREECE (1957-

2005). AN ECONOMIC ANALYSIS.

I. Sotiropoulos, K. Vasileiou

G. Georgakopoulos, C. Fragos,

Ch. Fragos.

(12:00 – 13:00) STANDARDIZATION, PROTYPES AND QUALITY IN EDUCATION (I)

(Chair: Stella Giossi, Erol Akata)

UNIVERSITY - BUSINESS

PARTNERSHIP DEVELOPMENT

OPPORTUNITIES RECIPROCAL.

J. Dode,A. Anxhaku,

G. Shqau.

ABOUT EDUCATION IN MASTER

DEGREE PROGRAM “TECHNICAL

LEGISLATION, STANDARDIZATION

AND QUALITY MANAGEMENT”.

M. Vicheva, B. Sandalski,

G. Djukendjiev, I. Nikolova,

R. Yordanov.

CLASSROOM RESPONSE SYSTEMS

AS INSTRUCTIONAL FEEDBACK

TOOLS: CAN THEY SUPPORT THE

STANDARDIZATION OF SCIENCE

TEACHING FORMATIVE ASSESS-

MENT IN SECONDARY EDUCATION?

T. Pierratos,

H. Polatoglou.

QUALITY MANAGEMENT IN

EDUCATION ACCORDING TO ISO

9001:2008 AND IWA 2:2007

STANDARDS.

C. Poustourli,

A. Papastamatis,

E. Valkanos.

(13:00 – 14:00)

(14:00 - 15:00) STANDARDIZATION, PROTYPES AND QUALITY IΝ EDUCATION (II)

(Chair: Philippos Papadopoulos, Hariton Polatoglou)

THE DETERMINANTS OF QUALITY IN

EDUCATIONAL LEADERSHIP WITH A

LIFELONG LEARNING HORIZON.

S. Giossi

MODELS FOR THE LIFE LONG

TRAINING IN GREECE AND THE

CONTRIBUTION OF “ENEPROT” TO

THEIR CREATION.

A. Zachariadis,

K. Athanassiadis,

T. Bastianos,

K. Christodoulopoulou.

PARADOXICAL DIFFICULTIES IN

TEACHING THE MATERIAL SCIENCE

TO MECHANICAL ENGINEERING

STUDENTS OR "CAN AN ENGINEER-

ING STUDENT DO AS AN ENGINEER?”

E. Akata.

THE CONTRIBUTION OF SCHOOL

TEXTBOOKS IN PROMOTING EQUAL-

ITY: SIGNIFICANCE AND SPECIFICA-

TIONS.

A. Maidou,

H. Polatoglou.

3

(15:00 – 16:30) STANDARDIZATION, PROTYPES AND QUALITY IN CONSTRUCTIONS,

ENVIRONMENT (Chair: George Banias, Branimir Sandalski)

MECHANICAL RESISTANCE AND STABILITY OF CONCRETE STRUCTURES IN MARINE ENVIRONMENT, ANALYSED ACCODING TO REGULATION (EU) No 305/2011 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL OF 9 MARCH 2011.

N. Barovsky.

CREATING POTENTIALS FOR

STANDARDISATION IN HISTORIC

MASONRIES RESTORATION.

G. Zacharopoulou.

STANDARDS IN HOUSING

DEVELOPMENT BUILDINGS IN

AKÇAKOCA/ĐZMĐT.

N. Erdoğan.

WASTE MANAGEMENT AS

REQUIREMENT OF ISO 14001 –

SITUATION AND PROBLEMS IN

SERBIA.

M. Krsmanovic,

J. Ruso, A. Horvat.

INTEGRATED MANAGEMENT

SYSTEMS FOR CONSTRUCTION

(ICMS).

C. Poustourli.

TOTAL QUALITY MANAGEMENT IN

THE CONSTRUCTION INDUSTRY.

C. Poustourli,

D. Ioannidis.

(16:30 – 17:00) Coffee Break

(16:30 – 17:00)

ENSURING THE ACCURACY OF THE

COORDINATE SYSTEM FOR TESTING

OF MEASURING AND POSITIONING

INSTRUMENTS.

G. Dukendjiev, R. Jordanov.

QUALITY MANAGEMENT FOR

AUTOMATED PRODUCTION OF ARMATURES FOR ELECTRICAL HAND TOOLS.

D. Tchakarsky, T. Vakarelska, P. Tomov, R. Dimitrova.

CLASSIFICATION OF PUNCHING

OPERATIONS TO OPTIMIZE THE

MACHINING OF PIPES.

S. Kartunov,

L. Tsanov.

BASIC ASPECTS OF A SUSTAINABLE

DEVELOPMENT TRAINING IN THE

HIGHER EDUCATION IN BULGARIA.

G. Pandev.

STOCHASTIC MODELING OF

STOCKS MANAGEMENT IN FLEXIBLE

MANUFACTURING SYSTEM.

A. Dumitrascu, B. Lepadatescu,

A. Fota.

(17:00 - 19:00) MEETING OF THE BALKAN COORDINATING COMMITTEE

4

(09:30 - 11:15) PROTOTYPING AND CERTIFICATION

(Chair: Konstantinos Athanasiadis, Vladimir Misha)

DIGITAL PROTOTYPING AND

POSSIBILITIES FOR CAD/CAE KINEMATIC

AND DYNAMIC ANALYSIS OF DRUM BALL

MILLS WITH DIFFERENT TYPES OF

GRINDING BODIES.

T. Damjanov, B. Grigorov,

E. Kostadinov.

SIMULATION OF THE ROUGHING AND

LAMINATE PROCESSES.

B. Lepadatescu, A. Dumitrascu, A. Fota .

A PROPOSED APPROACH IN POINTS CLOUD DISCRETIZATION TECHNIQUES.

A. Mihalache, G. NagîŃ, O. NiŃă,

I. Manole (Poşchin), M. Rîpanu.

THE RESPONSIBILITY OF THE CERTIFYING

AUTHORITY IN DEFINING THE SCOPE OF

QMS ACCORDING TO EN ISO 9001:2008.

L. Smedarchina, O. Nikolov.

INFLUENCE OF FEATURES OF COMPANIES

AND OBSTACLES IN BUSINESS ACTIVITIES

ON CERTIFICATION TO ISO MANAGEMENT

SYSTEM STANDARDS - THE CASE OF

COMPANIES OPERATING IN BALKAN

COUNTRIES.

I. Mijatovic.

TOWARDS A STANDARDISATION OF THE

INTERACTION PROCESSES BETWEEN

VOLUNTEER ORGANIZATIONS AND PUBLIC

LEGAL ENTITIES.

H. Polatoglou, D. Nalmpantis.

QUALITY ASSURANCE ISSUES IN GREEK

COMPANIES PROVIDING SERVICES: A

LITERATURE REVIEW.

A. Adamidou, Y. Nikolaidis.

(11:15 - 11:30) Coffee Break

(11:30 - 13:30) STANDARDIZATION, PROTYPES AND QUALITY

IN PRODUCTION, LOGISTICS (Chair: Dimitris Folinas, Nikolay Barovsky)

SIMULATION AND PRIMARY PRINCIPAL

ALGORITHMIZATION OF CONFORMITY

ASSESSMENT OF PRODUCTS.

B. Sandalski, B. Georgiev,

B. Ilieva.

QUALITY MODEL FOR SEMANTIC “IS”

STANDARDS. E. Folmer.

COGNITIVE RADIO: AN “ENABLER” FOR FUTURE EVOLUTION OF COMMUNICATIONS SYSTEMS.

I. Chochliouros,

A. Spiliopoulou.

PERSPECTIVES FOR DEVELOPING

MODERN ENERGY-AWARE SELF-

GROWING NETWORKS.

I. Chochliouros.

INVESTIGATING THE LINKS AMONG

INVENTORY TURNOVER AND FINANCIAL PERFORMANCE.

D. Folinas,

C. -Yi Shen.

CASE STUDY REGARDING THE

IMPLEMENTATION OF RISKS

MANAGEMENT PROCEDURE FOR

FLEXIBLE MANUFACTURING SYSTEMS.

A. Dumitrascu,

B. Lepadatescu,

A. Fota.

CERTIFIED GREEK COMPANIES OF

WOOD AND FURNITURE AND CERTIFIED

WOOD PRODUCTS.

E. Kollias,

A. Christodoulou.

OUT OF THE MAIN STREAM: THE

HELLENIC PATH TO DEVELOPMENT

A. Zachariadis, D. Folinas,

D. Mylonas

5

(13:30 - 14:15) CONCLUSIONS

(Chair: Stella Giossi, Ivana Mijatovic)

Special

keynote Common Agricultural Policy of Eu with

Consumers for Consumers.

E. Kekeleki,

(General Secretary of KEPKA,

Member EESC and Member

ECCG)

(14:15 - 15:15) FAREWELL LUNCH

COMMITTEES

BALKAN COORDINATING COMMITTEE

ALBANIA

Agim Anxhaku Director of Regulatory Reform & Quality Infrastructure,

Ministry of Economy, Trade and Energy of Albania.

Vladimir Misha Quality Systems Expert, Directorate of Accreditation.

BULGARIA

Radoslav Kotev Bulgarian Union of Standardizers (BUS).

Branimir Sandalski President of Bulgarian Council for Voluntary Certification.

FYROM

Laszlo Kocsis South East European University.

GREECE

Konstantinos Athanassiadis President of the Hellenic Institute of Metrology,

Gen.Secretary of ENEPROT.

Angelos Zachariadis Chairman of ENEPROT.

ROMANIA,

Adriana Fota Transylvania University of Brasov.

Badea Lepadatescu Transylvania University of Brasov.

SERBIA

Jovan Filipovic Belgrade University.

Ivana Mijatović Belgrade University.

SLOVENIA

Aleksander Janeš University of Primorska.

TURKEY

Erol Akata Istanbul Aydin University.

Nevnihal Erdogan Kocaeli University.

6

GREEK ORGANIZING COMMITTEE

Chairman: Ioannis Tsiafis, Assoc. Prof., Aristotle University of Thessaloniki.

Vice Chairman: Antonia Moropoulou, Prof., Vice Rector of National Technical University of Athens.

Konstantinos Adamopoulos Assist. Prof., Aristotle University of Thessaloniki.

Konstantinos Athanassiadis President of the Hellenic Institute of Metrology.

Dimitris Folinas Assoc. Prof., Alex. Technological Educ. Institute of Thessaloniki.

Stella Giossi Dipl.Econ., MBA, Quality Consultant & Auditor.

Philippos Karipidis Vice President of the Alex. Technol.Educ. Institute of Thess.

Nikolaos Karnavos Technical Chamber of Greece/ Dept of Cent Macedonia.

Konstantinos Kokkolakis Director, Civil Protection-Decentralized Admin. of Maced.-Thrace.

Nikolaos Mousiopoulos Deputy Chairman of the Gov. Board of the Intern. Hellenic Univ.

Eleftherios Pitsokos Supervisor in Forestry of Polygyros Chalkidikis.

Konstantinos Rotsios American Farm School.

Theocharis Zagas Assoc. Prof., Aristotle University of Thessaloniki.

GREEK SCIENTIFIC COMMITTEE

Stamatis Angelopoulos Assist. Prof., Alex. Technological Educ. Institute of Thessaloniki

Dimitrios Aidonis Lecturer, Alex. Technological Educ. Institute of Thessaloniki

Konstantinos Athanassiadis President of the Hell. Inst. of Metrology, Gen. Secr. of ENEPROT.

Katia Baltzaki PhD, Electrical Engineer.

George Banias Dr. Mechanical Eng. MSc, International Hellenic University.

Evangelos Chrysafides Assis. Prof., Aristotle University of Thessaloniki.

Ioannis Chochliouros Telecommunications Engineer, M.Sc., Ph.D.

Nikolaos Depountis Dipl. Mech. Eng. NTUA, Quality and Project Mngnt Advisor.

Dimitrios Folinas Assoc. Prof., Alex. Technological Educ. Institute of Thessaloniki.

Stella Giossi Dipl. Econ. M.B.A., Quality Auditor & Consultant.

George Kapetanos Dr. Mechanical Engineer, ELOT SA/Certification Division.

Nikolaos Litinas Dipl. Eng., President of the Certification Council of ELOT.

Dimitrios Mylonas MSc, Economist - Legal advisor - Accountant A’ Class.

Yiannis Nikolaidis Assis. Prof., University of Macedonia, Greece.

Philippos Papadopoulos Dr. Acting Academic Dean of Perrotis College, Amer. Farm Schl.

Nikolas Papakonstantinou Dipl. Agriculture, Quality Consultant.

Konstantinos Papas Dipl. Engineer, Quality Consultant.

Hariton Polatoglou Assoc. Prof., Aristotle University, Vice- Chairman of ENEPROT.

Aikaterini Poustourli PhD in TQM, Dipl. Production & Mngnt Engineer, TEI of Serres.

Sotirios Psimenos Mech. Engineer.

Vlachos Dimitris Assist. Professor of International Hellenic University.

Stefanos Zaoutsos MSc, PhD, Associate Prof. in Technological Educ. Institute of

Larissa.

201

SIMULATION OF THE ROUGHING AND LAMINATE PROCESSES

Enescu Ioan Faculty of Mechanical Engineering

“Transilvania” University of Brasov

enescu@unitbv.ro

Lepadatescu Badea

Faculty of Technological Engineering and Industrial Management

“Transilvania” University of Brasov

lepadatescu@unitbv.ro

Dumitrascu Adela-Eliza Faculty of Technological Engineering and Industrial Management

“Transilvania” University of Brasov

dumitrascu_a@unitbv.ro

Fota Adriana Faculty of Technological Engineering and Industrial Management

“Transilvania” University of Brasov

fota.a@unitbv.ro

Abstract

When a metal strip is passed through a rolling mill to produce an appreciable reduction in thickness, the plastic deformation is generally large compared with the elastic deformation so that the material can be regarded as being rigid plastic. In the first instance the elastic deformation of the rolls may also be neglected. We tried to answer to the main question: how are the elastic contact stress and deformation between curved face in contact influenced by surface roughness?

Many processes involve the passage of a strip or sheet of material through the nip between rollers. In this paper we consider the strip to be perfectly elastic and investigate the stress in the strip, the length of the arc of contact with the roller, the maximum indentation of the strip

202

and the precise speed at which it feeds through the nip in relation to the surface speed of the rollers. If the strip is wide and the rollers are long in the axial direction it is reasonable to assume plane deformation.

Keywords: contact, elastic, laminate, strip, rollers, rough, friction.

Introduction

In the first instance the elastic deformation of the rolls may also be neglected. For continuity of flow, the rolled strip emerges from the nip at a velocity greater than it enters, which is in inverse proportion to its thickness if no lateral spread occurs. Clearly the question of sticking and slipping between the rolls and the strip, arises in the metal rolling process .In the hot rolling the absence of lubricant and the lower flow stress of the metal generally mean that the limiting frictional traction at the interface exceeds the yield stress of the strip in shear so that there is no slip in the conventional sense at the surface.

It is for the condition of no slip encountered in hot rolling that the most complete analyses of the process have so far been made. We saw in the previous section that interfacial friction inhibits plastic reduction, so that in cold rolling the strip is deliberately lubricated during its passage through the rolls in order to facilitate slip.

At entry the strip is moving slower than the roll surfaces so that it slip backwards , at exit the strip is moving faster so that slips forwards. At same points in the nip, referred to as the “neutral point” the strip is moving with the same velocity as the rolls. At this point the slip and the frictional traction change direction. In reality, however, we should not expect this change to occur at a point. In the last section, when a thin elastic strip between elastic rollers was being examined, we saw that plastic deformation and slip would initiate at entry and exit ; in between there is a region of no slip and no plastic deformation. It seems likely there for that a small zone

Of no slip will continue to exit even when appreciable plastic reduction is taking place in the nip as a whole. Current theories of cold rolling, which are restricted to the idea of a neural point must be regarded as complete slip solutions. The static indentation of a strip by rigid frictionless cylinders was considered briefly. The stresses in an elastic strip due to symmetrical bands of pressure acting on opposite faces have been expressed by Sneddon in terms of Fourier integral transforms. The form of these integrals is particularly awkward and most problems require elaborate numerical computations for their solution.

1. AN ELASTIC MODEL OF THE LAMINATE PROCESS

The complete solution of a problem involving the plane deformation of a rigid perfectly plastic material calls for the construction of a slip field. So far this has been achieved only for the condition of no slip line field. So far this has been achieved only for the condition of a slip line field. So far this has been achieved

203

only for the condition of on slip, which applies to lot rolling. Before looking at these solutions we shall examine the elementary theories, with and without slip, which derive from von Karman. (1925). The geometry of the roll bite, neglecting elastic deformation, is shown in Figure 1. The mean longitudinal (compressive) stress in the strip is denoted by and the transverse stress at the surface by [1]. Equilibrium of the element gives:

φφφσ Rdqpdxx )sincos( += (1) and

φφφσ Rdqphd x 2)cossin()( −= (2) In this simple treatment it is assumed that in the plastic zone xσ and zσ are related by yield criterion

kzx 2=−σσ (3) Nevertheless by combining equations (1), (2), and (3) we obtain

{ } )cossin(2)2tan( φφφ qpRkqphdtd

−=−+ (4)

which is von Karman equation. It is perfectly straightforward to integrate this equation numerically to find the variation in contact pressure )(φp once the frictional conditions at the interface are specified.

Figure 1: The geometry of the roll bite, neglecting elastic deformation. Before electronic computer were available, however, various simplifications of von Karman equation were proposed to facilitate integration. For relatively large rolls equation were proposed to facilitate integration. For relatively large rolls it is reasonable to put φφ ≈sin , 1cos ≈φ etc. and to retain only first order terms inφ . The roll profile is then approximated by [2]

RxhRhh /20

20 +≈+≈ φ (5)

Making these approximations in (3), neglecting the term q tan compared with p, and changing the position variable from φ to x give

204

qRxk

dxdph 24 += (6)

An addition, it is consistent with neglecting second order terms in φ to replace h by the mean thickness.

2. ELASTIC CONTACT MODEL OF ROUGHING SURFACE

The stresses in an elastic strip due to symmetrical bands of pressure acting on opposite faces have been expressed by Sneddon (1951) in terms of Fourier integral transforms. The form of these integrals is particularly awkward and most problems require elaborate numerical computations for their solution. However, when the thickness of the strip 2b is much less than the arc of contact 2a an elementary treatment is sometimes possible. The situation is complicated further by friction between the strip and the rollers. We can analyses the problem assuming (a) no friction ( 0=μ ) and (b) complete adhesion ( ∞→μ ), but our experience of rolling contact conditions leads us to expect that the arc of contact will, in fact, comprise zones of both “stick” and “slip”. We will look first at a strip whose elastic modulus is of similar magnitude to that of rollers, and write [3]

αα

νν

−+

=−−

=11

/)1(/)1(

222

121

EEC (8)

Where: α is defined by the equation (11), and 1.2, refers to the strip and the rollers respectively.

[ ] [ ][ ] [ ]2211

2211

/)1(/)1(/)1(/)1(GGGG

νννν

α−+−−−−

= (9)

If the strip is thick ( )( ab ≥ it will deform like an elastic half-space. At the other extreme, when ab ≤ , the deformation is shown in Figure2. The compression of the roller is now much greater than that of the strip so that the pressure distribution again approximates to the Hertz

2/122 )/1(2)( axaPxp −=π

(10)

The strip is assumed to deforms with plane sections remaining plane so that the compression at the centre of the strip is given by

1

21

1

21 )1(2)0()1(

aEPb

Epbd

πνν −

=−

= (11)

205

Figure 2: The deformation at the other extreme (b≤a).

If the deformed surfaces of the strip are more approximated by circular of radius R’, then

12

21

2

)1(42'

1Ea

Pbad

R πν−

== (12)

The rollers are flattered from a radius R to R’ so that

)'

11/()1(4

2

222

RREPa −

−=

πν (13)

Eliminating R’ from (12) and (13) gives

abC

aa

o

+= 1)( 2 (14)

Where: 21

222 )/)1(4( EPRao ν−= is the semi-contact width for vanishingly thin-

slip. With friction leas rollers the longitudinal stress in the strip xσ is either zero or equal to any external tension in the strip. Due to the reduction in thickness, the strip extends longitudinally, whilst the roller surface compresses to the Hertz theory, so that in fact frictional tractions q(x) arise (acting inwards on the strip) whether or not materials of the strip and rollers are the same. For equilibrium of an element of the strip we have:

)(1 xqbdx

d x =σ

(15)

Slip between the rollers and the strip is governed by the equation (16)

)(// 21.

xu

xu

cyVs xxxx

∂∂

−∂∂

+−= ψξ (16)

In addition, it is consistent with neglecting second order terms in φ to replace h by the mean thickness.

Where: VVV xxx /)( 21

.δδξ −≡ and VVV yy /)( 21

.δδξ −≡ are the creep rations γ is the

non-dimensional spin parameter, cVxx )( 21 ωω − , and 21

)(abc = .

In a stick region: 0..

== yx xx In additional, the resultant tangential traction must not exceed its limiting value:

206

),(),( yxpyxq μ⟨ (17) And, the direction of q must oppose the velocity:

.

.

),(

),(),(),(

yxs

yxsyxqyxq

= (18)

If there is no slip equation (11) reduces to:

ξ−=∂∂

−∂∂

xu

xu xx 21 (19)

Where: ξ is the creep ratio 221 /)( VVV − of the strip relative, to the periphery of the rollers. The longitudinal strain in a roller within the contact arc is given by equation.

⎟⎟⎠

⎞⎜⎜⎝

⎛−

+−

=∂∂

)(1

1

1

1

1

211 xp

Exu

xx

νν

σν (20)

The integral equation (10) is satisfied by the traction:

21

22 )(2

)141()(

xa

xpabxq o

−+

−=αβ (21)

Where: β is defined by the equation:

⎥⎦

⎤⎢⎣

⎡−+−−−−

=2211

2211

/)1(/)1(/)21(/)21(

21

GGGG

νννν

β (22)

The distribution of traction and also the stress difference (sx-sy ) to the centre plane of the strip are show in Figure 3.

Figure 3: The distribution of traction and also the stress difference (sx-sy ) to the centre

plane of the strip.

Conclusions

Ensure In the paper was proposed a model of investigation the stress in the strip for laminated process taking into consideration the process parameters as length of the arc of contact with the roller, the maximum indentation of the strip,

207

the speed at which the sheet of material feeds through the nip in relation to the surface speed of the rollers considering the strip perfectly elastic.

It was used the theory of contact mechanics how are the elastic contact stress and deformation between rigid plastic in contact, influence by surface deformation and stress in laminate and the roughing process.

The result of the research can be used for the designing of the installation of processes for laminate metal strip to improve their efficiency and reliability.

Acknowledgement

This work was supported by CNCSIS –UEFISCDI, project number PN II – IDEI code PCE_756 / 2008, no. 641 / 2009.

References [1] JOHNSON, K.L., 1985, Contact mechanics, Cambridge, University Press.

[2] PAVELESCU, D., MUSAT, M. & TUDOR, A., 1977, Tribologie, Editura Didactica si Pedagogica, Bucuresti.

[3] DRAGHICI, G., 1977, Tehnologia Constructiilor de Masini, Editura Didactica si Pedagogica, Bucuresti.