Experimental Identification of Viscoelastic Properties of Rubber Blends by Means of a Torsional Rheometer

The dimensioning of injection heads for the extrusion of rubber profiles is exclusively based on empiric knowledge of the non-linear flow behaviour of elastomers. The swelling of the extrudate when emerging from a capillary is typical for viscoelastic fluids, such as polymers and rubber blends, respectively. Therefore, the experimental investigation and numerical treatment of this swelling behaviour is of high interest. This was one of the motivations for starting a research project in the field of rubber blend technologies. The knowledge of die swell phenomenon is important for manufacturing rubber profiles. Thus, the final goal of this project is the numerical prognosis concerning injection heads and tools for the extrusion of rubber. The research work is performed in a co-operation with Semperit Technische Produkte Ges.m.b.H & Co KG which provides the rubber blends as well as the experimental devices. So far, several non-vulcanised rubber blends, containing mainly Ethylene propylene diene monomer (EPDM) and carbon black in different compositions, have been investigated. These are used for window sealings, pipeline constructions and various parts of cars. The materials are described as nonNEWTONian fluids with pseudo-plastic melt behaviour, i.e. the viscosity decreases with increasing shear strain rate.