Studies on wire coating extrusion. I. The rheology of wire coating extrusion

Abstract

AbstractWire coating extrusion was studied, both experimentally and theoretically, using a pressure‐type die. For the experimental study, a wire coating apparatus of laboratory scale was constructed, consisting of a pay‐off device, extruder, cross‐head and pressure‐type die, cooling trough, and take‐up device. The materials used were low‐ and high‐density polyethylenes and thermoplastic rubber. The following measurements were taken during the experiments: (1) the axial pressure profiles in the die, (2) melt flow rate, and (3) take‐up speed. The measurements were then used to determine the effect of the rheological properties of the polymers on the performance of the wire coating operation. It was found that a reduction in axial pressure gradient and a reduction in the recoverable elastic strain of a molten polymer at the die exit can be realized as the speed of the wire is increased. For the theoretical study, using a power‐law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymer being extruded. Solution of the system equations permitted us to predict the velocity profile and shear stress distributions of a molten polymer inside a pressure‐type wire coating die.