A precision on-line model for the prediction of roll force and roll power in hot-strip rolling
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I. INTRODUCTION
IN hot-strip rolling, a capability for accurately predicting the roll force and roll power is crucial for sound process control. In the past, on-line prediction models have been developed mostly on the basis of Orowan’s theory[1] and its variations.[2,3,4] However, the range of process conditions in which desired prediction accuracy could be achieved was rather limited, mainly because of many simplifying assumptions inherent to Orowan’s theory. As far as the prediction accuracy is concerned, a rigorously formulated finite-element (FE) process model is perhaps the best choice. Metal flow is influenced by the temperature distributions in the strip because the flow stress is strongly dependent on temperatures. On the other hand, temperature distributions in the strip are affected by heat generation caused by plastic deformation and interface friction and also by the velocity field in the strip, resulting in strong correlations between the mechanical and the thermal behavior of the strip. Such a coupled aspect of the problem was first considered by Zienkiewicz et al.[5] when attempting to predict the steadystate thermomechanical behavior of the strip using an FE process model. Similar works were conducted by Beynon et al.,[6] and Kumar et al.[7] The rigid-plastic material behavior was assumed in these works. However, they were rather incomplete in the sense that the interdependence between the thermal behavior of the strip and that of the work roll was not taken into account. Consequently, either the heat flux to the roll or the strip-surface temperature at the roll/ strip interface had to be assumed. Such a shortcoming was partly resolved by Pietrzyk and Lenard,[8] who simultaneously calculated the temperatures in a segment of the work roll in the bite region as well as those in the strip. Later, Yamada et al.[9] and Hwang et al.[10] rigorously treated the interdependence by conducting a coupled analysis of the steady-state thermomechanical behavior of the strip and the thermal behavior of the entire work roll using FE process models. Recently, Sun and Hwang developed a two-dimensional (2-D) FE process model[11] and a three-dimensional (3-D) FE process model[12] for the coupled analysis of the W.J. KWAK, Postdoctoral Research Engineer, J.H. LEE, Research Assistant, and S.M. HWANG, Professor, are with the Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang, 790784, Korea. Contact e-mail: [email protected] Y.H. KIM, Research Scientist, is with the Stainless Steel Research Group, POSCO Technical Research Laboratories, Pohang, 790-785, Korea. Manuscript submitted October 29, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
thermomechanical behavior of the strip and that of the work roll. However, an FE process model in general requires a large central processing unit (CPU) time, rendering itself inadequate for on-line purpose. In this article, we present an FE-based on-line prediction model applicable to precision-process control in a finishing mill. Described wa
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