Flow analysis of natural rubber in a capillary rheometer. 2: Flow patterns and entrance velocity profiles in the die

Abstract

Abstract An investigation was carried out to determine the effect of variations in test conditions, such as die geometry, for example die entry angles, on the flow patterns observed in the die of a Davenport Extrusion Rheometer. In addition, the velocity profile near the die entrance was determined for different piston displacements. The results indicate that the velocity profile generated in the capillary near the die entrance was parabolic in form. However, there appeared to be a non‐zero velocity at the capillary wall. Melt fracture was observed, this being linked with the appearance of a disturbance in the flow along the capillary, the disturbance being of a converging helical form.