The Flow of a Power-Law Fluid in a Melt-Fed Single-Screw Extruder

Abstract

A simple numerical procedure is proposed for the solution of the two-dimensional power-law flow equations for a wide channel with a moving boundary. The results are used to construct a complete model of the isothermal operation of a single-screw extruder in terms of the compression ratio, the relative lengths of the compression and the metering sections, and the power-law index of the material. It is shown that a number of the main features of screw extrusion are predicted by the model. By way of examples it is shown that, in application, the isothermal condition can be relaxed, and satisfactory correlation between the theory and experiment can be obtained, by the use of an average extrusion temperature. The model provides a broad theoretical framework, by which the relative significance of the geometric parameters and the power-law index on the throughput-pressure characteristics of the screw extrusion can be examined, and the experimental results collated and extrapolated. Examples of the solution are presented in the form of contour plots to assist designers and users of single-screw pumping machines.