Test MethodBack calculation of the entrance pressure of capillary dies by means of measurements with slit dies

A new procedure for determination of the pressure loss correction of melt pressures within the framework of material characterization of rubber compounds is proposed. For that purpose, experiments with a capillary viscometer were performed. Using only capillaries with diameters up to 2 mm, the melt pressure is measured before the capillary entry instead of inside the capillary. Therefore, entrance and outlet pressure losses are not considered by such measurements.Common correction methods are well suited for plastics but not necessarily for rubber compounds. Back calculation of the pressure in the capillary is based on the measured pressure before the entry of the capillary. To improve this back calculation, additional experiments with slit dies were performed. With such experiments, the melt pressure in the capillary can be determined. Comparison of both experimental data allows identification of one scalar parameter that describes the ratio of pressure loss correction and measured pressure for capillary dies. The investigation was performed with various rubber compounds used in industry, mainly EPDM and carbon black in different compositions, and results for two materials are reported here. Moreover, different temperatures were considered.