Reverse flow valve in extruder head - having ring sliding backwards against a face when screw moves forwards

摘要

A reverse flow valve in an extruder screw head has a freely sliding ring between a wall and a stop surface, with its outer surface sliding inside the barrel while its inner surface leaves a gap for fused polymer flow. A shoulder on the screw head located between the stop face and the wall, has a section to mate with this flow gap inside the ring, leaving space inside the ring; the shoulder opens the flow gap at least when the ring lies up against the front stop face but closes the gap before that position is reached. The system produces virtually uniform weight of mould charge irrespective of the state of the polymer in the extruder barrel.