POLYMER FRICTION UNDER CONDITIONS OF DEFORMATION PROCESSING.

Abstract

The sliding friction behavior of low density PE and HDPE with normal pressure and velocity is investigated for unlubricated conditions using the conventional friction measuring arrangement. Apart from its dependence on velocity, the coefficient of friction is found to vary significantly with normal pressure. The investigation of friction at very high contact pressures, as encountered in deformation processing, has been carried out for the case of direct extrusion using an instrumented extrusion die with movable head. The variation of extrusion and die-head force with ram travel is recorded for particular ram speeds. The extrusion data has been analyzed assuming von Mises' yield criterion and spherical velocity fields. The frictional shear stress of low density PE is found to be of the order of its bulk shear strength which is in agreement with the adhesion theory of friction.