Measurements of friction in cold flat rolling

Abstract

The effect of reduction, rolling speed and material properties on the variation of interfacial frictional and normal stresses in the roll gap during cold flat rolling is studied. The results confirm the conclusions of earlier research, emphasizing the dependence of the coefficient of friction, and hence the interfacial shear stress, on the process parameters. Preliminary experiments, using mineral oil with 1% oleic acid as lubricant, show the possible existence of hydrodynamic lubrication, at least over part of the contact area. The validity of the data is substantiated by comparing the roll separating forces, measured by transducers located under the bottom workroll, to those obtained by integrating the measured roll pressure distribution over the arc of contact. The comparison is found to be favorable, indicating that in spite of its shortcomings, the embedded pin technique gives reliable measurements. An empirical relationship, giving the average coefficient of friction in terms of density, real contact area, rolling speed, and normal load, is developed.