Factors affecting the shape of strip emerging from a rolling mill

Abstract

Today, more than ever before, economic pressures require that strip should be produced to a uniform and accurate gauge both along the length and across the width and, in the absence of applied forces, that it should lie flat on a flat surface. Unfortunately, none of the theories on the mechanics of rolling which predict roll force and torque in flat rolling, directly assist the mill designer or strip manufacturer to understand why, or how, such factors as roll bending, camber, friction, tension, and initial shape contribute to non-uniformity of gauge or bad shape. Consequently, following a briefreview of some recent publications on strip shape, a qualitative analysis of the causes of shape and gauge variation is presented based on fundamental principles ofplasticity and the mechanics of rolling, to assist mill designers and operating companies to arrive at a better understanding of the factors affecting gauge and shape so that each may be more able to take appropriate corrective action. It is clear from experiences in rolling that shape and its control are parts of a complex subject since, for example metallurgical, thermal, and frictional variations in the unrolled stock and the mechanical condition of the mill are difficult to control continuously. Consequently, it is inevitable that this qualitative analysis provides only a partial solution. Nevertheless, a pair of work rolls responds to the material in them through the forces produced by the yield stress, friction, and the reduction of area effected, however, these variations in factors arise, so, by employing Mohr's strain and stress circles andfrom a knowledge of the ideal pressure distribution within the roll gap as provided by theories on the mechanics of rolling, explanations of spread or lateral flow, axial flow, and residual stress patterns are given which are in accord with observations.