Experimental validation of contact models for cold-rolling processes

Abstract

Many functional properties of a cold rolled strip such as wear resistance, friction in a forming process, and optical properties depend on its surface finish. Accurate modelling of the real contact area is critical in predicting the surface finish of strips after cold rolling processes. The aim of this work is to experimentally verify existing contact models to predict the surface finish of industrially cold rolled strips. For this purpose, rolling trials were done on a two high mill under boundary lubricated conditions at several combinations of thickness reduction, rolling speed, and roll and strip roughness. The surface finish of the rolled strip for a given rolling condition is predicted using selected contact models. Further, a new deterministic approach to calculate the average asperity slope is proposed. Statistical properties of the three dimensional surface topography of rolled strips are compared with surfaces predicted employing selected contact models. The surface finish of measured and model-predicted surfaces showed very good agreement for strips rolled with a smooth roll. However, for strips rolled with rough rolls, a significant difference was observed in the surface height distribution between the measured and model-predicted surfaces. It was shown in these experiments that a non-uniform rise of valleys plays an important role on the surface finish of strips rolled with a rough roll.