Backflow valve in extruder head - internally grooved ring turns to admit or close flow to diametrical slots

摘要

In a backflow valve inside the head of extruders the material flows into a chamber before the head and is extruded when the screw moves forwards axially; a pressure ring slides inside the head, it fits closely inside the barrel wall and has an inner passage for the material flow, this passage is open/closed according to the position of the ring. The passage covers only part of the ring which has two rotary positions, in the one position the passage connects to another passage in the head whilst in the other the latter passage is closed. Arrangement prevents backflow even at the start of the screw stroke; there are no narrow flow passages.