The non-return assembly is at the end of the screw. Its purpose is to allow the screw to build a shot and inject plastic into the mold. This moving back and forth of the screw is referred to as reciprocating. There are two types of non-return assemblies typically used, the check-ring assembly and the ball-check assembly. The components of the check-ring non-return assembly are; screw tip, check-ring, and seat. As the screw turns the check-ring is moved toward the nozzle allowing material to move through In front of the screw. This allows a shot to be built. When the screw moves straight forward without turning, the check-ring moves back toward the hopper and forms a seal with the seat.
This allows material to be injected into the mold and prevents material from flowing back over the screw flights.
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