The development of mathematical models for single screw plasticating extruders has been covered extensively in the literature [1 – 7]. By far, the majority of these studies have concentrated on melt extruders or the melt conveying section of plasticating extruders. The main reason for this is that the analysis and modelling of melt flow is far simpler than that of solids conveying and melting of the polymer. Applications for melt fed extruders can be found in the polymer processing industry, for example, in the homogenization and pelletization of the polymer immediately after polymerization. Most extruders used in the plastics industry, however, are plasticating extruders, that is, they are fed by polymer in solid granular form. The solid polymer granules flow by gravity in the hopper and into the screw channel where they are compressed, conveyed down the screw channel, and then melted.