Thermal behavior of steel rolling with nonconventional rolls
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INTRODUCTION
IN steel rolling, the roll is used as a tool to deform the strip. The process occurs at extremely high pressure and high velocity; in hot rolling, the temperature is also especially high. This causes the work and backup rolls to be changed frequently because of wear or spalling even if undamaged by catastrophic fracture or other major failures. The surface finish and profile of the rolls must be closely controlled during roiling. Roll wear gradually changes the finish and profile of the roll. This leads to an unacceptable surface finish and dimensional changes on the rolled products and finally causes the rolls to be withdrawn for dressing and eventually discarded. The work roll is removed from the mill much more frequently than the backup roll. m Recently, as the hot-rolling condition has become more severe, technology to extend roll life has become increasingly critical. Several techniques have been developed to increase roll life simply by placing high contact strength or high wear resistance materials on the roll surfaces. Three of them, the coated, sleeved, and carbide rolls, are commonly used. The first one involves coating the roll surface with a very thin layer of chromium or tungsten. [2.3,41 Some refractory carbides and ceramics have also been used as coating material.I4.sl The second method creates a relatively thicker sleeve, leading to a bilayer or s l e e v e d roU. 16'7'81 The third one uses highly wear-resistant carbides as the roll material, t9'l~ These nonconventional rolls possess a substantially lower rate of wear and give a more consistent surface finish to the rolled product. In spite of the fact that these nonconventional roils have been successfully applied to several rolling processes, very little information is available on the subjects of roll-cooling control and its effect on the rolling process with nonconventional rolls. Therefore, the purpose of the present study is to provide basic information on the influence of nonconventional rolls on the thermal behavior of the steel-rolling process. Knowledge of the A.A. TSENG, Associate Professor, and P.F. SUN, Graduate Student, are with the Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA 19104-2875. Manuscript submitted November 2, 1990. METALLURGICAL TRANSACTIONS A
thermal behavior of the process can contribute not only to better control of the shape or thermal crown of the rolled product but also to insights into the lubricant behavior and the metallurgical structure of the product. Moreover, because of a lack of design information on thermal behavior, nonconventional rolls have only been applied to a few types of mills. For example, sleeved rolls are not popular in strip mills and carbide rolls are limited to relatively small sizes. Therefore, the present study can lead to new roll designs for enlarging the usage of these nonconventional rolls. In this article, the current status of nonconventional rolls is first reviewed. The formulation of the numerical model used in the present s
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