ANALYSIS OF COLD STRIP ROLLING UNDER HYDRODYNAMIC LUBRICATION

A model is proposed for cold strip rolling under hydrodynamic lubricat ion which combines the finite-element analysis of the strip with the r efined analysis of the lubricant film. The viscosity of the lubricant is assumed to depend on both the pressure and the strain rate, whilst the strip is modelled as rigid-perfectly plastic material. The thickne ss of the lubricant film is assumed to vary parabolically from inlet t o exit. The effects of various process variables (the reduction, the r oll-radius-to-strip-thickness ratio, the lubricant viscosity and the r oll velocity) on the interfacial stresses, the roil force and torque a nd the film thickness are studied. It is shown that the interfacial no rmal stress remains generally uniform over the are of contact and in n o case develops a 'friction-hill'. Ln the proposed model, the roll for ce remains virtually unaffected by both the lubricant viscosity and th e roll velocity and thus remains insensitive to lubrication. At high r eduction or for a low value of the roll-radius-to-strip-thickness rati o, the film thickness becomes very small, requiring the use of high-vi scosity lubricant or a large roll speed to maintain hydrodynamic lubri cation.