Chapter 4 - Surface Finish and Friction in Cold Metal Rolling

Abstract

This chapter focuses on the mechanics of lubrication in cold rolling in the industrially relevant mixed lubrication regime. It highlights the importance of bulk deformation of the strip in facilitating asperity crushing. Hydrodynamic pressure is induced in the lubricant due to the entraining action of the roll and strip. The Reynolds' equation is modified to include the effect of roughness. The interaction between the deformation of asperities and the hydrodynamic pressure has been effectively modeled and predictions of film thickness and surface roughness are in good agreements with measurements. Frictional models have also been successfully developed for the mixed lubrication regime, both for strip and foil rolling. However the mechanisms of friction on the contact areas are still not clear. Although traditionally this has been supposed to be due to boundary lubrication, empirical models suggest some hydrodynamic action probably due to a micro-plasto-hydrodynamic lubrication (MPHL) oil film. However, useful models of MPHL have been developed for the alternative scenario, where oil trapped in isolated pits in the inlet is drawn out in the bite due to sliding between the roll and strip.