The determination of material parameters required for numerical simulations of rubber extrusion processes is based on laboratory analytical methods, which neglect the influence of shear history on the material in the extrusion process. Rubber compounds are also prone to flow anomalies such as wall slip depending on the compound composition. The neglect of these effects leads to pronounced deviations between simulation and practice. The aim of the research project is to improve the analytical and simulative methods for the design of rubber extrusion tools by empirically determined correction factors and characteristic diagrams.
To provide these, extensive experimental investigations are carried out on EPDM rubber compounds with varying carbon black content using extrusion rheometers on two rubber extruders of different sizes (Ø 32 mm, Ø 60 mm). By using two screw geometries (conveying thread, screw with bar breakthrough), the influence of the load history on the flow properties is taken into account under comparable process conditions. In order to determine the sliding velocities, various approaches from the literature are examined with regard to their suitability and a characteristic diagram is set up to take into account sliding effects depending on the carbon black content, the temperature and the load history. In addition to wall slip effects, rubber compounds also tend to exhibit pronounced non-isothermal effects. For this purpose, the exit temperatures of the extrudate strands are recorded using IR thermal imaging cameras. The extrudate outlet temperature is estimated by developing an analytical calculation model.
The numerical flow simulations are carried out with the open source software openFOAM. The simulations are then validated in experimental investigations and the results are documented in a guide.