Modeling and optimum shape design of polymer extrusion die

Abstract

Coat-hanger dies are widely used in polymer processing for the production of film and sheet. To get high quality products, the effect of process conditions has to be fully understood, and the flow field within a coat-hanger die has to be controlled by an optimum design of die geometry. The polymer melt flow in a coat-hanger die should be analyzed precisely using three-dimensional flow model because the cross-sectional shape of flow changes significantly along the main flow direction, especially in the transition region between manifold and slot section. Thermal effect is one of the most important process parameters to be considered in extrusion process due to the dependence of flow field and material property of polymer melt on temperature field. The non-isothermal polymer melt flow in a coat-hanger die is studied through three-dimensional simulation based on finite element method to investigate the effect of viscous dissipation and thermal control. The ultimate goal of die analysis is to develop an optimum design tool that can determine the optimum geometry of extrusion dies for a given process condition. The objective is fulfilled by application of inverse formulation to die design problem with three-dimensional flow modeling. The three-dimensional model of non-isothermal polymer melt flow in a coat-hanger die is developed and solved using finite element method. Streamline upwind/Petrov-Galerkin method is applied to energy equation to eliminate oscillatory temperature profile. The effect of viscous dissipation is investigated from the temperature contours and flow rate distributions at die exit. Temperature field shows non-uniformity at die exit plane with hot region near the side wall. The effect of thermal control is investigated by varying the die wall temperature. The change of flow rate distribution with the die wall temperature is examined. Total pressure drop is also found to be dependent on die wall temperature. Three-dimensional optimum design of a ...