The Mechanics of Thick Slab Rolling

Abstract

The classical rolling theories are based on the equilibrium of forces on assumed homogeneously deforming elements within the roll gap. Such theories, e.g. Sims' theory, grossly underestimate roll load and torque when rolling slabs that are thick in relation to the roll diameter, a condition which is most commonly encountered in primary rolling mills. Consequently a new theory, based on the shearline field solution for indentation, was developed for rolling conditions where the mean stock thickness in the roll gap, hm exceeds the length of the arc of contact, φ. Simulated hot rolling, using pure lead as a model material, and cold rolling of aluminium alloy were performed on a laboratory mill to verify the theoretical predictions of roll load and torque. Experiments were performed with both smooth and knurled rolls to investigate the effect of friction. Also, the effect of slab width on roll load and torque was investigated. Additionally, measurements were made on a production mill in the works to ensure that the theoretical model was applicable to full scale rolling and to identify the problems in implementing the theoretical work in a production environment. Yield stress data in the form of stress-strain curves were obtained by means of a cam plastometer for the alloy steels rolled in the works. It was shown that, provided the yield stress of the slab is known with certainty, the theory enables very accurate prediction of roll load over the range 1 < h/φ  < 8.74. Predictions of roll torque, although less accurate than those for roll load, were within 15% of the measured values. The new theory may, therefore, be used reliably for mill scheduling purposes within the thick-stock range. Furthermore, the new theory enables calculation of the stress state within the roll gap and hence conditions leading to centre unsoundness may be identified.