BEHAVIOR OF POLYMERIC PARTICULATE SOLIDS UNDER PRESSURE.

A substantial amount of work has been done in the theory of melting and shaping operations where the physical situations render themselves amenable to mathematical modeling. However, the area of particulate solids conveying in the processing equipment, such as injection molding and extrusion, is not well understood. In the mathematical model for the plasticating extruder, the solid in the feed section and in the melting zone is considered as a solid plug with constant density; furthermore, the solid is assumed to be in complete contact with the metal wall. The voids between pellets and the true area of contact between the solid bed and the metal walls are not considered. As a result, computer simulations of the plasticating screw extrusion process often fail to generate satisfactory results. This study examines the bulk density change due to compaction so that the density of the solid material in the screw can be incorporated in the screw extrusion simulation. The actual area of contact of the pellets with the metal wall is also being investigated. It allows for more accurate calculation of the forces exerted on the solid bed for the estimation of the pressure fields in the feed section and possibly melting section. Experimental data are included.