Computational study on the extrusion of annular shaped product considering viscoelastic characteristics

Polymer melts have viscoelastic characteristics. Many researches for the circulation flows at the comer of capillary die and die swell have been performed to investigate the complicated viscoelastic flow behaviors. This study is an extension of previous researches from the capillary die to an annular die. Flow behaviors and die swells in an annular die have been investigated in this study. Rheological properties required in computer simulation were measured through experiment. And then computer simulation of die extrusion has been performed using non-linear viscoelastic model and generalized Newtonian model. Pressure and velocity distributions inside of the annular die have been analyzed. Extruded profiles of annular shape have been predicted and analyzed. Inner and outer profiles of annular shaped extrudate were different according to the rheological models whereas pressure and velocity distributions inside of the annular die were similar. Detailed phenomena of die swell have been analyzed for various relaxation times in the PTT (Phan-Thien Tanner) model, which was used for the non-linear viscoelastic model. Swells of outer diameter, inner diameter, and thickness for diverse flow rate have been also analyzed quantitatively.