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United States Patent 4349044
Douris , ê et al. September 14, 1982

Non-return device at the screwhead of screw injection molding machines

Schirmer September 14, 1982

Abstract

In a screw injection molding machine comprising a non-return device at the screwhead, said device comprising a pressure ring which is displaceable on the screwhead between front and rear abutments, is guided in the cylinder by its outer periphery and defines a flow gap with its inner periphery, a check valve for closing the flow gap against reverse flow is disposed near the front of the pressure ring whereby to facilitate rapid response of the non-return device without loss of material and obtain a substantially constant weight of injected material, particularly in the case of materials of low viscosity. The check valve may comprise a lightweight washer or valve ring.