To widen the variety of process-relevant test methods for rubber applications, laboratory-scaled rubber extruders (with roll feeders) are available for torque rheometers. These measuring extruders are specially designed to simulate extrusion processes and simultaneously control and evaluate the process parameters.

The measuring rubber extruder machine can easily be equipped with a large number of dies which, according to their geometry are suitable for a variety of applications. Three different methods are presented below, which may be helpful in solving problems in the processing of unvulcanized rubber.

Automatic Extrusion-Capillary Measurement Capillary measurements show their advantage where information about the flow behaviour of an unvulcanized compound is required as an absolute value.

Injection moulding processes (e.g. for seals and O-rings) can be mentioned as an application, where rheological factors influence the success of the process to a great extent. Due to the narrow clearances and high rubber compound melt flow rate, extremely high shear rates can occur in the injection channels. On the other hand, the final filling of the mould is slow and the applied shear is low.

As a rule, rubber compounds exhibit pseudo-plastic flow behaviour. Various shear stresses can be exerted on a rubber compound during processing. Because the viscosity is highly dependent on the shear rates, it is imperative that the viscosity be characterized as a function of the relevant shear rates. The processing engineer’s main goal is the determination of these relationships for the injection moulding process.