Mechanical Principles of the Screw Extrusion Machine

Abstract

The screw extrusion machine is briefly described and submitted to a dimensional analysis resulting in generalized relations between, on the one hand, pressure developed, rate of discharge, and drive-power and, on the other, viscosity of plastic extruded, speed of machine, and a characteristic dimension. The velocity distribution of an assumed ideally viscous so-called plastic material within a rectangular screw thread is determined, and expressions for discharge and pressure developed are derived in terms of its dimensions. These expressions are used to discuss the effect of increasing the number of “starts” on a screw and a method of rating extrusion machines is proposed so as to allow an adequate description of the capacities of such machines.