Experimental and Numerical Investigation of the Die Swell Phenomenon of Rubber Blends

Rubber profiles fabricated by means of extrusion are widely used in civil engineering, e.g., in pipeline constructions and for window sealings. 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, basically of the so-called die swell. The swelling of the extrudate when emerging from a capillary is typical for non-Newtonian viscoelastic fluids. The viscosity of rubber blends is obtained by means of experiments with a capillary-viscometer. In this contribution it is shown how the die swell of a capillary experiment is computed by means of pressure measurements. For this objective information concerning the normal stress state in the capillary is required. Experiments with a torsion-viscometer allow a back calculation of the normal stress state and, thus, the computation of the die swell. An adaptation of the capillary-viscometer allows the experimental investigation of the die swell. Thus, a validation of the computed die swell can be realised.