Extruder screw comprising entry and homogenising sections - has longitudinally divided flight land resulting in identical parallel dual threads, one open, the other blind-ended

摘要

The extruder screw of the parent patent is divided into an entry zone and a plasticising or homogenising zone. At the upstream end of the plasticising zone, a flight land extending from the entry zone, divides longitudinally so that a new flight land is formed, in the plasticising zone, between the resulting 2 flight lands. This new flight land is open at the tip of the screw. However, a flight land, starting in the entry zone, ends "blind" at the screw tip. Plasticised material can pass from this flight land into the twin thread (formed by the division of the screw as described) over 1 of the dual flight lands, which has some radial tolerance between flight land edge and the inner wall of the extruder barrel. The material accumulates in the twin thread and conveyed toward the screw tip. The improvement comprises increasing take-up volume and throughout constructing indentically pitched all screw threads of flight lands in the plasticizing zone parallel to one another.