Analysis of Thermal Camber Control in Rolling Mills

Abstract

The demand for wider, thinner rolled steel has led to an increasing interest in the control of the strip “shape”. Mechanisms for controlling shape include roll bending, roll tilt (or mill steer) and spray pattern control. This paper will principally focus on an analysis of the spray control system and the associated interaction between adjacent zones.This paper decribes a new approach to shape control, a mathematical model is derived for the dynamic thermal expansion of the rolls of the a tandem cold rolling mill. The model structure has been specifically designed to facilitate control studies. The system is highly non-linear but the model suggests how the system can be linearized by an appropriate input signal transformation. The linearized system then represents a coupled multi-input multi-output dynamical system linking the cooling water sprays to the measured exit strip shape. This linearized model leads to a dynamical decoupling procedure which reduces the system to a set of single-input single—output control systems.Apart from the application to shape control, the method proposed here has more general applicability since the same kind of problem arises in a variety of cross-machine probelms.