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Pesin A.M.
SCIENTIFIC SCHOOL OF ASYMMETRIC ROLLING IN MAGNITOGORSK
Abstract. The article presents some results of studies of Scientific School of Asymmetric Rolling in Magnitogorsk. This paper presents a classification and practical application of the asymmetric rolling processes. Further development of the asymmetric rolling process is their use as a severe plastic deformation method for ultra-fine structures of the metal.
Keywords: scientific School, classification, asymmetric rolling, shear deformation, severe plastic deformation, parts of large bodies of revolution, finite element method modeling.
Over 30 years Metal Forming Department at the Higher Professional Institution «Magnitogorsk State Technical University» has been developing the scientific direction of both current and new technologies of asymmetric plate rolling. This direction is headed by V. Sal-ganik and dissertations for Ph. D degree on this theme were written by A. Pesin (scientific supervisor M. Polya-kov), V. Rudakov, V. Lunev, I. Vier, G. Kunitsyn (scientific supervisor V. Salganik), K. Kuranov, D. Chikishev (scientific supervisor A. Pesin), M. Chernyakovsky (scientific supervisors V. Salganik, A. Pesin). A. Pesin, G. Kunitsyn (scientific advisor V. Salganik) and V. Sal-ganik have written doctorate dissertations.
Since the foundation of Magnitogorsk scholar collaborations with V. Vydrin, L. Ageev (Chelyabinsk school), V. Potapkin, V. Fedorinov, A. Satonin (Kramatorsk school), S. Kotsar, V. Tretiakov, J. Mukhin (Lipetsk school), V. Polukhin, A. Pimenov, V. Skorokhodov, A. Traino, B. Kucheriaev have been established.
Nowadays several scientific projects have been carried out together with K. Dyja, A. Kawalek from Technical University in Czestochowa (Poland), K. Mori from Technical University in Toyohashi (Japan), V. Fedorinov, A. Satonin from State Engineering University in Donbass (Ukrain).
Metal Forming Department at the Higher Professional Institution «Nosov Magnitogorsk State Technical University» has solved the following challenging issues: 1) the processes of asymmetric rolling have been classified; 2)
statics, geometry and kinetics of vertically asymmetric deformation site have been described; 3) special cases of vertically asymmetric rolling have been investigated; 4) a new integrated process of vertically asymmetric rolling and plastic bend of plate mill has been developed; 5) metal cross-section in horizontal asymmetric rolling has been investigated; 6) new technical schemes in horizontally and vertically asymmetric rolling have been found.
These days the research is focused on the following directions: 1) shape control of the front end of the strip in plate rolling; 2) ultrafine grain structure in asymmetric intensive plastic deformation.
1. The classification process of asymmetric rolling
Due to different criteria, there are various approaches to the cases, which take place in asymmetric rolling. The scientists from Magnitogorsk scholar have suggested the classification containing 3 hierarchal levels [1, 2]. The upper level regards the causes of asymmetry occurred deliberately or evoked by any disturbances. The next level considers asymmetry in space in relation to either horizontal or vertical plane or to both of them. Finally, the lower level includes factors that can define asymmetry (geometric, frictional, elastic, kinematic, etc.) Asymmetry of different kinds often occurs simultaneously.
These days the technical approaches to purposeful asymmetry in the vertical plane are widely spread and
promoted. The purposeful asymmetry is determined by the following main factors:
1) geometric asymmetry specified by roll geometry and inlet and outlet angles of the rolled stock; 2) kinematic asymmetry related to different velocity of roll periphery; 3) surface asymmetry concerned the quality and properties of the surface on working rolls and strip and its firm and rough surface; 4) physical and mechanical asymmetry caused by different physical and mechanical properties between Young's E-modulus and Poisson's ratio in the working rolls as well as mechanical and physical properties of rolled stock through thickness; 5) contact asymmetry developed due to substances that get into the deformation site between the surfaces of the working rolls and metal from outside; 6) temperature asymmetry
provoked by nonuniform heating of metal and working rolls in rolling.
Asymmetry in the vertical plane alters kinematics in the deformation site i.e. changes in length of backward and forward creeps in the upper and lower rolls. Considering this fact, the following cases of asymmetric rolling are depicted:
1) a common case, when the deformation site has got 2 kinematic areas - backward and forward creep but their length in the upper and lower areas aren't equal (Fig. 2a);
2) a semi-extreme case when a roll has two areas -backward and forward creeps and the other - only one area: either backward or forward creep (Fig. 2b);
3) an extreme case when one roll has only a backward area and the other - a forward creep (Fig.2c).
Fig.1. Classification of asymmetric rolling processes
c
Fig. 2. Scheme of asymmetric deformation site: a - common case, b - semi-extreme case, c - extreme case
2. Statics, geometry and kinematics of vertically asymmetric deformation site
Mathematical description of asymmetric deformation site shows geometric ambiguity - while the radius of rolls and strip thickness in the inlet and outlet are well-known, the boundary points of the arc in the inlet and outlet cross-section are not depicted. Their rotation in the center of the rolls causes this situation. The asymmetric deformation site has got an area where friction goes to the opposite sides on the opposed areas of the arcs. It gives a rotation moment in the deformation site. As a result we get the above mentioned sectional rotation that is experimentally confirmed.
For a mathematical model of asymmetric rolling the balance of the whole deformation site that was influenced by contact loads and tensions of the outer parts of the strip were very favourable [1-3]. As a result, we received the following contact stresses through the length of the deformation site in common case (Fig. 3), where we observe all three kinematic areas, including forward, backward and mixed creeps. Both curves of contact stresses have two breaks in the cross-section corresponding to neutral one on each of the rolls. If one break on each curve is a point of neutral cross-section, the other break is a certain reaction on the opposite roll.
3. New integrated process of vertically asymmetric rolling and plastic bend of thick sheet
The mathematical models enable to calculate an extreme case when the whole deformation site is a mixed area, as well as a semi-extreme case when the deformation site has got two areas: either forward and mixed or backward and mixed. The mathematical models were confirmed experimentally by specialists in Czestochowa Technical University in Poland [4]. We got the mathematical model of integrated process of vertically asymmetric rolling and plastic bend for large rotary bodies (Fig. 4) [5-12].
Fig.3. Search of normal contact stresses
a
b
b
a b
Fig.4. Integrated process of asymmetric rolling and plastic bend: a - scheme, industrial experiment at Mill 4500at the OSJC «Magnitogorsk Iron and Steel Works»
The integrated process has three stages: vertically asymmetric rolling, when the front end of the sheet does not touch the detector roll; non-adjusted integrated process of vertically asymmetric rolling and plastic bend, when the front end of the sheet touches the detector roll; adjusted integrated process of vertically asymmetric rolling and plastic bend, when the front end of the sheet separates from the detector roll.
This technology gives us rotation items as a cylinder segment with 45°-60° angle made of stainless steel and following parameters: thickness - 40-220 mm, width - 4300 mm, length - 5000 mm, radius of curve -1850-5000 mm.
The technology of large rotary bodies has been implemented at the OSJC «Magnitogorsk Iron and Steel Works». The cover units have been manufactured and installed for two converters in the oxygen-converter plant at the OSJC «Magnitogorsk Iron and Steel Works». The economical revenue of this technology is over $1 million.
This technology has a serious drawback such as a strong dynamic blow, when the front end of the sheet touches and shifts over the fixed detector roll. The upper roll has abrupt rolling process that can damage the equipment. It is caused by rigid fixing of the detector roll. To solve this problem new ways of this technology have been introduced: 1) roller aprons have been fixed to follow the detector roll; 2) the detector roll moves in the target track; 3) different speed of rolls have been used to increase accuracy of the curve .
The mathematical modeling shows the fact that new technical and technological changes makes a dangerous difference of moments decrease to 1.5-2.5 compared to the fixed detector roll. This work has been supported by the Grant of Analytical Target Program of the Russian Federation (grant №2.1.2/4390 Scientific development and enhancement of technical systems including new processes of metal items of large bodies of the fixed curve and by the grant «Participation in youth scientific contest» (UMNIK 2009) organized by the Fond of Small Business in scientific and technical sphere together with Federal Agency of Science and Innovations and Educational Agency.
4. The shape of the front end in plate rolling
These days Metal Forming Department at the Higher Educational Institution «Nosov Magnitogorsk State Technical University» studies asymmetric modes to decrease ski-effect in plate rolling at Mill 5000 at the OSJC «Magnitogorsk Iron and Steel Works» (Fig. 5).
Fig.5. Ski-effect in plate rolling at Mill 5000 at the OSJC «Magnitogorsk Iron and Steel Works»
In plate rolling the rolls, which move at similar speed, bend vertically the front end of rolled stock. It is caused by geometrical, frictional and temperature asymmetry through the height of the deformation site. The rising vertical bend leads to the rolled stock stuck in the rolls of outlet table in the machine of preliminary melting. To decrease the vertical bend of the front end of the rolled stock in plate rolling it is necessary to apply kinematic asymmetry - difference in speed of the working rolls.
In plate rolling with different speed of the working rolls the bend can occur in the direction of the roll with higher speed or in the direction of the roll with lower speed. When the sheet decreases in thickness to 8-32 mm, the impact of different speed of the working rolls can be ambiguous. In the light draft the bend occurs in the direction of the roll with lower speed; in high draft the bend occurs in the direction of the roll with higher speed. Moreover, under certain circumstances, there is a neutral point when the vertical bend of the front end of the sheet does not occur in rolling with different speeds. Neutral point is a special point, which is not influenced by different speeds.
The scientists of the scholar developed a finite element mathematical model of stress and deformation metal state in the asymmetric deformation site with different temperature. The model was adjusted at Mill 5000 at the OSJC «Magnitogorsk Iron and Steel Works». New asymmetric modes of deformation have been elaborated due to the impact of the shape of the deformation site on the direction of bend of the front end of the sheet in rolling with different speeds.
5. Ultrafine grain structure in asymmetric intensive plastic deformation
Industrial technologies of flat long rolled stock produced of ultrafine grain materials can be based on the well - known process of metal forming such as rolling. However, classic symmetric rolling has a number of drawbacks: monotoneness and the lowest level of deformation so this process cannot be used for ultrafine grain structure.
One of the most efficient methods of intensive plastic deformation for flat long ultrafine grain metal materials as a strand and sheet is asymmetric rolling. It includes methods of intensive plastic deformation and has the following essential criteria to get an ultrafine grain structure: 1) high shearing deformation in each stage of treatment; 2) high level of accumulated shearing deformation e=2,0^4,0; 3) non-monotoneness of deformation; 4) high tension in the deformation site to get flawless metal; 5) simultaneous impact on materials with high deformation of pressure and shift.
In the asymmetric site at the opposite arcs of the contact friction moves to the opposite sides that lead to the change of cross-sections and shearing deformations which are necessary for to get ultrafine grain structure. For in-
stance, mathematical modeling shows the increase in shearing deformations throughout the cross-section of the strand as much 9 times compared to symmetric rolling (Fig. 6) [13]. The extreme cases of asymmetric rolling have better effect of fine crushing of metal.
On the one hand, asymmetry leads to decreasing in friction negative impact that leads to deformation pressure increasing. On the other hand, the site has considerable shearing deformation and strain rate rises (Fig. 7).
Special schemes of mechanical deformation to get an ultrafine grain structure can be applied: 1) asymmetric rolling, i.e. common case of asymmetry; 2) rolling-drawing, an extreme and non-extreme case of rolling; 3) deformation between the fixed element and driven roll that is also an extreme and non-extreme case of rolling. However, processes of asymmetric rolling belong to those methods of intensive plastic deformation where initial and final parameters do not coincide and it restricts it application.
The criterion of an ultrafine grain structure in asym-
metric rolling: 1) scalar value r = + 6exy for
flat deformation state which characterizes accumulated intensity of the shift deformation and that is defined by 2
tensor components: pressure deformation £ and shift deformation £ ; 2) slope angle ^ of vertical cross section. Target levels: r > 2 ; (p> 45°.
Asymmetric rolling can increase the intensity of shift deformation through the cross-section of the sheet (up to 3.5) and can be used to get an ultrafine grain structure for strands and sheets.
a
b
Strain 10%
30%
50%
70%
80%
Fig.6. Distortion of vertical lines of asymmetric and symmetric rolling www.vestnik.magtu.ru.-------------------------------
Fig.7. Field of strain rate in asymmetric and symmetric rolling
References
Pesin A.M. Modelirovanie i razvtie processov asimmetrichnogo deformirovanja dlja povyshenija jeffektivnosti listovoj prokatki. Dokt. Diss. [Modeling and development of the processes of asymmetric deformation to improve sheet rolling: thesis]. Magnitogorsk, 2003. 395 p. Salganik V.M., Pesin A.M. Asimmetrichnaja tonkolistovaja prokatka razvtie teorii, tehnologii i novye reshenija [Asymmetric rolling of thin sheet the development of theory, technology and new solutions]. Moscow MISIS, 1997. 192 p.
Pesin A.M. New technological solutions based on the modeling of asymmetric rolling. Steel, 2003, no. 2, pp. 66-68. Dyja H., Pesin A.M., Salganik W.M., Kawalek A. Asymetriczne walcowanie blacli cienkicli: teoria, teclinologia i nowe rozwiazania: Seria Monografie nr 137. Wydawnictwo Politechniki Czestochowskiej. Czestochowa, 2008, 345 p.
Pesin A., Salganik V., Trahtengertz E., Drigun E. Development of the asymmetric rolling theory and technology / Proceedings of the 8-th International Conference on Metal Forming. Krakow / Poland / 3-7 September, 2000. Metal Forming 2000. Balkema / Potterdam / Brookfield / 2000. pp. 311-314.
Pesin A.M., Salganik V.M., E.M. Drigun, Chikishev D.N. Ustrojstvo dlja asimmetrichnoj prokatki tolstolistovogo metalla. [Device for asymmetrical rolling metal plate]. Patent RF, no. 38646, 2004. Pesin A.M., Salganik V.M., E.M. Drigun, Chikishev D.N. Ustrojstvo dlja asimmetrichnoj prokatki tolstolistovogo metalla. [Device for asymmetrical rolling metal plate]. Patent RF, no. 2254943, 2005.
8. Pesin A., Salganik V., Sverdlik M., Pustovoytov D., Chikishev D. Theoretical Basis and Technology Development of the Combined Process of Asymmetric Rolling and Plastic Bending. Proceedings of the 2011 International Conference on Mechanical Engineering and Technology UK ICMET 2011, ASME Press, 2011, USA, pp. 95-98.
9. Pesin A.M., Salganik V.M., Chikishev D.N. Improvement of production technology of large parts of bodies of revolution on the basis of mathematical modeling. Proizvodstvoprokata. [Production of rolled]. 2007, no. 3, pp. 34-40.
10. Pesin A.M., Salganik V.M., Dyja H., Chikishev D.N., Pustovoitov D.O., Kawalek A. Asymmetric rolling: Theory and Technology. HUTNIK-WIADOMOSCI HUTNICZE. 2012, no 5, pp. 358-363.
11. Pesin A.M., Salganik V.M., Chikishev D.N., Drigun E.M. Razvitie teorii i tehnologii poluchenija detalej krupnogabaritnyh tel vrashhenija: monografija. [The development of the theory and technology of parts of large bodies of revolution: monograph]. Magnitogorsk: «NMSTU», 2010, 102 p.
12. Salganik V.M., Pesin A.M., Chikishev D.N., Lokotunina N.M., Pustovoitov D.O. Prilozhenija teorii plastichnosti k razrabotke i analizu tehnologicheskih processov [Applications of the theory of plasticity in the design and analysis process]. Magnitogorsk: «NMSTU», 2012, 251 p.
13. Pesin A.M., Pustovoytov D.O., Perehogih A.A., Sverdlik M.K. Simulation of shear strain in the extreme case of asymmetric sheet rolling. Vestnik Magnitogorskogo gosudarstvennogo tehnicheskogo universiteta im. G.I. Nosova. [Vestnik of Nosov Magnitogorsk State Technical University]. 2013. no 1, pp. 65-68.
Kawalek A., Dyja H.
ANALYSIS OF VARIATIONS IN ROLL SEPARATING FORCES AND ROLLING MOMENTS IN THE ASYMMETRICAL ROLLING PROCESS OF FLAT PRODUCTS
Abstract. The paper presents the results of investigation into the effect of roll peripheral speed asymmetry on the force and energy parameters of the process for the conditions of normalizing rolling of plates in the finishing rolling stand. Keywords: numerical modelling; asymmetrical rolling; roll rotational speed asymmetry factor.
1. Introduction
An important problem that drives the upgrading of plate rolling mills are increasing demands on the geometrical dimensions of finished products. These demands force the manufacturers to implement roll gap control systems that helps to maintain stability and improve the geometrical parameters of rolled strip.
Works [1-4] have demonstrated that by using asymmetrical plate rolling process, improvement in the quality of plate geometry can be achieved. The idea behind the asymmetrical rolling technology consists in taking ad-
vantage of the positive effects of the asymmetrical deformation zone, which include primarily the reduction of the total roll separating force and the enhancement of the product service properties.
The asymmetrical rolling system relies chiefly on a direct action being exerted on the strip in the deformation zone, in which, owing to an asymmetry introduced to the working roll peripheral speed, longitudinal tensile stresses occur, whose effect is analogous to that of tension and back tension in continuous rolling mills. These stresses have the effect of reducing the magnitude of unit pressure in the roll gap and enhancing the equalization of the non-
