Extruder injection apparatus and method

Abstract

A plasticating apparatus including a rotating screw having a helical flight disposed within and cooperating with the inner wall of a heated barrel. Resinous material is introduced to a helical valley extending along said flight to be plasticated by said screw and advanced towards an outlet opening. The screw has a metering section for working said resinous material at high temperature. The bottom surface of the helical valley in said metering section is divided into side by side relatively shallow and relatively deep levels having a depth differential therebetween. The relatively shallow and relatively deep levels extend along the bottom surface of the helical valley in side by side helical paths. The side by side helical paths have a different pitch than the pitch of the helical flight so that the helical flight periodically interrupts the helical paths. The depth of the shallow level remains substantially uniform in the metering section and the depth of the deep level also remains substantially uniform in the metering section. The depth differential between the shallow and deep levels is bridged by a descending-ascending shoulder without any intervening barrier flight. During operation, the level differential induces a continuous tumbling and mixing action upon the molten resin in the mixing section.