Rubber Extrusion - Some Aspects and Open Questions*

Abstract

The rheology of rubber compounds is considerably more complex than that of thermoplastic melts, since both the viscoelastic material behaviour of the rubber and the way in which the rheological properties of the rubber are influenced by the fillers are of importance. Models for describing flow and vulcanisation behaviour and also models for describing parts (sections) of the extrusion process have frequently been derived from the field of thermoplastics and are based on simplifying assumptions which fail to consider some of the phenomena specific to rubber. When the extrusion process is analysed, certain special processing properties of rubber are encountered, such as increased shear rates due to fillers, yield stress phenomena and wall-slippage effects. These have to be taken into consideration in order to achieve a more precise description of the processes involved. The essential advances in rheology and in process modelling are leading to a better understanding of the process and hence to improvements in product quality, raw material utilisation and energy input. This paper shows the possibilities and constraints of present-day process description for a number of sub-areas of rubber extrusion and puts forward open questions.