Numerical simulation of a single‐screw plasticating extruder

Abstract A fully‐predictive steady‐state computer model has been developed for a single‐screw plasticating extruder. Included in the model are a model for solids flow in the feed hopper; a variation of the Darnell and Mol model for the solids conveying zone; a variation of Tadmor's melting model for the melting zone; an implicit finite difference solution of the mass, momentum, and energy conservation equations for the melt‐conveying zone of the extruder and die; and a predictive correlation for the extrudate swell at the die exit. A temperature‐ and shear‐rate‐dependent viscosity equation is used to describe the melt‐flow behavior in the model. The parameters in the viscosity equation are obtained by applying regression analysis to Instron capillary rheometer data. Given the material and rheological properties of the polymer, the screw geometry and dimensions, and the extruder operating conditions, the following are predicted: flow rate of the polymer, pressure and temperature profiles along the extruder screw channel and in the die, and extrudate swell at the die exit. The predictions have been confirmed with experimental results from a 11/2 in. (38 mm) diameter, 24:1 L/D single‐screw extruder with a 3/16 in. (4.76 mm) diameter cylindrical red die. High‐ and low‐density polyethylene resins were used.