1 Introduction

During commercial flat rolling of steel and aluminium strips control of the coefficient of friction at the roll/work piece contact is achieved by careful choice of the lubricant. The choice also affects the productivity and the surface quality of the rolled strips. Improving these is the prime objective of the producers. At the present time oil-in-water emulsions are used when cold rolling steel or hot rolling aluminium. Neat oils are used mostly when cold rolling aluminium. In most applications the twin objectives are cooling of the surfaces and the provision of sufficient amount of oils in the roll/strip contact zone.

Control of the coefficient of friction presupposes knowledge of its magnitude. While there is a reasonable understanding of the frictional mechanisms at the roll/strip interface during flat rolling, the actual magnitude of the coefficient of friction there is still largely a matter of conjecture. In this context it is appropriate to quote Roberts [ROB 97]:

"Of all the variables associated with rolling, none is more important than friction in the roll bite. Friction in rolling, as in many other mechanical processes, can be a best friend or a mortal enemy, and its control within an optimum range for each process is essential".

The transfer of thermal and mechanical energy at the roll/metal interface is responsible for the quality of the resulting surfaces. In cold rolling, inappropriate magnitudes of friction forces cause unacceptable surfaces. In hot rolling surface defects, accelerated...