The prediction of pressure losses as well as the corresponding temperature rises in a converging flow has always been an important issue in polymer science. Especially for thermosetting rubber compounds the bulk temperature is a crucial parameter for the curing reaction and the cure time reduction. This contribution proposes a simplified, non-isothermal analytical solution for the converging flow problem taking shear and elongational dissipation into account. For the analysis of the flow patterns a visualization technique of the converging flow of rubber compounds into the capillary of a High Pressure Capillary Rheometer (HPCR) was developed. Shear viscosity was ascertained also using a HPCR and elongational viscosity was calculated in a new analytical approach from the same data. Therefore it was possible to get an idea of the elongational behavior of the rubber compounds at very high strain rates. To verify the calculation experiments on a rubber injection molding machine were made in an industrial scale. A test mold equipped with a range of different conical dies was used to purge the rubber compounds into open air. The average bulk temperature of the compounds was ascertained by means of a thermocouple and the pressure in front of the die was measured using a pressure transducer. The bulk temperature increase showed a dependence on the flow rate and the cone angle with the flow rate being dominant. The new model enables the prediction of the average bulk temperature with an average error of less than 5 per cent and is therefore ready to use in industrial applications for a calculation of potential cure time reductions.