Hydrostatic extrusion behaviour of high density polyethylene

The solid state processing of a high density polyethylene by hydrostatic extrusion at room temperature has been investigated. The extrusion pressure for a given extrusion ratio is found to depend on the pressure fluid used, the die angle and the velocity of extrusion. The strain hardening behaviour of the resulting extrudates is found to be independent of the extrusion ratio. An effective flow stress equation which accounts for the dependence of the flow stress of high density polyethylene on strain, strain rate and hydrostatic pressure is developed and used in an analysis of the extrusion process based on the upper bound approach. The calculated values of the extrusion pressure as a function of the various extrusion variables are in reasonable agreement with the experimental results.