Roll cooling and its relationship to roll life
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I.
INTRODUCTION
IN the rolling process,
metal is subjected to compressive plastic deformation by the rotating rolls. The processes involve extremely high pressures and high temperatures which may produce large enough stresses in the rolls to cause roll wear or spalling. However, the surface finish and profile of the rolls under operation must always be closely controlled. Roll wear or spalling gradually changes the finish and/or profile, which leads to dimensional changes in the roll, eventually requiring refurbishment or replacement. The expenses of downtime and labor for changing rolls, regrinding, and heat treatment, as well as the cost of the rolls themselves, are the major expenditure in mill operation, t~t Roll wear or spalling can be greatly affected by roll cooling. Improper or insufficient cooling causes large thermal gradients near the roll surface, inducing thermal stresses which accelerate roll spalling. In addition, relatively high temperatures reduce the strength and wear resistance of the rolls and create difficulties in obtaining proper roll profile, thus deteriorating surface finish as well as the metallurgical structures of the rolled product. ~n'21 As a consequence, the thermal behavior of the work rolls in a rolling mill has always been of great concern to the mill designer or operator, especially in designing effective cooling systems to keep the temperature or thermal stresses within allowable ranges. In order to study the influence of cooling practices on the roll life and shape, a good understanding of the thermal behavior of the rolling process is essential. Considerable work has been done on studying the thermal behavior of the roll in rolling processes. In analytical approaches, Cerni e t al. I31 provided a transient analytical solution based on a Lagrangian formulation for the temperature distribution in a roll subjected to entire
A.A. TSENG, Associate Professor, F.H. LIN, A.S. G U N D E R I A , and D.S. NI, Graduate Students, are with the Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA 19104. Manuscript submitted December 29, 1988. METALLURGICAL TRANSACTIONS A
circumferential convective cooling and to a line h, source. Hogshead Ial simplified Cerni e t a l . ' s approach provide a convenient analytical expression. Pavlossoglo used a Laplace transformation technique to study 1 thermal behavior of a rolling process without any wa spray cooling. Patula, t6j with a Eulerian formulation, tained a steady-state solution for a rotating roll subjecl to prescribed surface heat input over one portion a convective cooling over another portion of the circu ference. Yuen tTJ extended Patula's solution to include 1 effect of a strip scale layer. Tseng et al.tS~ enhanced Gec and Winer's t9~ rotating cylinder solution to study the a minum rolling process. In numerical approaches, Sekimoto e t al. t~~ studi the roll surface temperature using an unsteady oi dimensional model. Parke and Baker ~111 developed two-dimensional (plane) finite-difference model t o : v
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