Anti-backflow valve for injection molding machines

Abstract

An anti-backflow valve for mounting on the forward end of a plasticating screw rotatably and translatably carried in a tubular barrel of an injection molding machine. The valve includes a rod-like body member that extends forwardly of the plasticating screw for rotation relative to the screw and for axial translation relative to the screw for a limited distance. A retaining sleeve is threadedly secured to the forward end of the screw to define a forward stop to limit axial outward movement of the body member relative to the screw. The outer surface of the retaining sleeve includes a valve seat that is engagable with a sealing surface on a screw tip that is carried at the forward end of the body member. The screw tip includes flow passageways extending substantially axially therethrough to provide communication between the space ahead of the screw and an area behind the screw tip and between the screw body and the screw-receiving tubular barrel. At least one sealing ring is carried by the body member and the retaining sleeve to prevent flow of plasticated material therebetween. The ability of the body member to rotate relative to the screw avoids breakage of the screw tip during a cold start-up condition when solidified plastic material from a previous operation of the machine surrounds the screw tip.