Predictions of flow behaviors and entrance pressure drop characteristics of a rubber compound in a capillary die using various rheological models

Rubber compounds have highly viscoelastic properties. The viscoelastic behaviors that have been exhibited during die extrusion include die swell and vortices in regions of sudden contraction. In this study, the application of rheological models to the capillary die extrusion process is investigated. Experiments and simulations were conducted using a fluidity tester and finite element analysis, respectively. The velocity distributions, velocity profiles, pressure drops, and vortices at the capillary die entrance were analyzed through computer simulations for various viscoelastic models [i.e., Phan-Thien and Tanner (PTT), Giesekus, POMPOM, simplified viscoelastic, and generalized Newtonian models]. Different models exhibited different pressure drops and different velocity profiles in the capillary die. Only the full viscoelastic models (PTT, Giesekus, and POMPOM) predicted the vortex at the corner of the reservoir that is the capillary die entrance. However, the simplified viscoelastic and generalized Newtonian models did not predict the vortex. All the viscoelastic models studied in this article predicted the die swells in various ways, and these were compared with the experimental results. The PTT and simplified viscoelastic models exhibited good agreement with the experimental results of the die swells.