TESTING AND MEASURING Measurement of Wall Shear Stress for Identification of Wall Slip Effects in Rubber Compounds 

The wall slip of various rubber compounds has far-reaching effects on the design of extrusion dies and extruder screws as well as on viscosity measurements. However, in most cases it is not possible to determine under which circumstances a compound adheres to the wall or slides.

Rheological material data and empirically determined material laws are used in order to design extrusion and injection moulding dies and screws. However, wall-slipping fluids pose a challenge when determining this material data. For example during viscosity measurements in a high pressure capillary rheometer, wall slip does not typically occur over the entire capillary length but only sets in at lower pressures. The exact point depends on the material itself.