Pressure profiles in plasticating extruders

Abstract

AbstractThe pressure distribution through the melting and melt zones of a plasticating extruder is discussed, and an analysis is described for predicting the pressure profile. In the stable melting zone, the pressure profile is calculated based on flow in the melt pool, and the pressure is strongly influenced by the flow of the solid bed of plastic. The solid bed flow is primarily determined by the polymer rigidity in the screw compression section. If the size (through a melting analysis) and the velocity (through a solid bed acceleration parameter) of the solid bed along the screw channel are reasonably approximated, the pressure profile is reasonably approximated by this analysis. Inaccurate representations of the size or velocity of the solid bed can yield inaccurate pressure profile prediction.In the unstable melting region, the assumption of a complete melt yields reasonable pressure predictions. The introduction of these concepts into an extrusion model permits a more accurate prediction of the operating RPM of a given screw design in a given machine.