Surface finish and friction in cold metal rolling

The cold metal rolling industry needs reliable and accurate models to improve predictions of surface finish and friction and thus increase productivity and improve quality. These models are used in setup programs for schedule optimisation, for on-line control algorithms and to help determine process improvements. In most cold rolling operations, lubricant is used to reduce frictional forces, to protect the roll and strip surfaces, and to act as a coolant. The amount of oil drawn into the roll bite and the initial surface roughness are the critical factors determining friction in the contact and surface finish of the product (Schey, 1983a and 1983b). Figure 4.1(a) illustrates schematically the inlet to the bite during a strip rolling operation. Neglecting for the moment the surface roughness on the roll and strip, a 'smooth' film thickness hs at the end of the inlet can be determined by integrating Reynold's equation. Wilson and Walowit (1972) derive an expression for hs as