Development of On-line Model of Forward Slip on Tandem Cold Strip Mill

Abstract

Compared with the rolling conditions of mild steels, those of high tensile strength steels (HTSS) are very different, because of their high flow stress. Dimensional accuracy of the thickness at the top end of industrially rolled HTSS is lower, compared with mild steel. This is because predicted rolling force for HTSS is not accurate sufficiently. This problem is due to not only the used flow stress model, but also the rolling theory model. If the standard Hill’s rolling force equation and the standard Bland and Ford’s forward slip equation are used, a large discrepancy between the two estimated friction coefficients is observed in high slip region for HTSS. In this study, the authors propose new practical equations for the forward slip. The equation takes into account the effects of non-constant flow stress and of friction coefficient over the roll bite so that the equations are applicable to HTSS rolling conditions. The Bland and Ford’s equation has been modified to introduce 2 new parameters (C and B). Parameter C corresponds to the change of the friction coefficient in the roll bite, and parameter B corresponds to that of the flow stress. The new equations have been installed into an actual set-up model of steel works. Improvements in prediction accuracy of rolling force and forward slip are confirmed.