Screw Extrusion of Plastics

Abstract

The main object of the work reported here was to find a rational design method for granule-fed single-screw extruders used for plastics processing. The first half of the paper contains a brief review of the literature on extrusion theory. Also the existing theory of Newtonian melt flow is extended to the granule-fed extruder and predictions of the behaviour of granule-fed machines are made. In addition the extruder flow equation for non-Newtonian ‘power law’ fluids is solved. In the second part of the paper are described experiments on polythene extrusion which demonstrate that qualitatively this non-Newtonian polymer behaves as predicted in the first part. An adequate correlation of flow results for the melt zones of the screws used is obtained, using an ‘apparent’ viscosity with a shear rate correction to allow for non-Newtonian behaviour. Outputs can be predicted within about 25 per cent using the design method recommended as a result of the work, but power consumption predictions tend to be low, and further attention must be given to that aspect.