A Study on the Effect of Drawing on Extrudate Swell in Film Casting

Abstract

We present a numerical study of the film casting process, with a focus on the effect of the draw ratio on the swelling of the extruded sheet. So far, studies regarding film casting have dealt mainly with the phenomenon of neck-in and have neglected swelling of the material as it emerges from the die lips. Knowledge of the amount of swelling is important for accurate determination of the effect of stretching and orientation phenomena. The problem is tackled by studying the gap-wise swelling of the sheet or film as it emerges from a wide rectangular die and is subsequently drawn down under different draw ratios. The material is treated as viscoelastic by utilizing the Linear Phan Thien-Tanner (LPTT) model. Newtonian simulations are also carried out. A decoupled iterative algorithm is used for the determination of the shape of the extruded sheet, based on the fact that the sheet’s surfaces belong to streamlines. Our results are in qualitative agreement with results in the literature, with the latter being limited in number and available mainly for the (similar) process of fiber melt spinning.

Keywords

• extrudate swell
• viscoelastic
• film casting