Anti-backflow valve for injection molding machines

Abstract

An anti-backflow valve for mounting on the forward end of a plasticating screw of an injection molding machine. The valve includes a rod-like member that extends forwardly of the plasticating screw, and is relatively rotatable therewith. The rod-like member is axially retined in position relative to the screw by a retaining ring that engages with the forward end of the screw and that includes a valve seat. The outwardly extending end of the rod terminates in a stop that is spaced forwardly of the valve seat. An annular sealing ring includes an outer surface that engages the inner surface of the barrel and an inner surface that is radially spaced from the rod-like member to provide a flow passage therebetween. The ring is positioned between the forward stop and the valve seat and is freely axially movable therebetween. The relative rotation permitted between the rod and the rotating screw, coupled with the minimal rotation of the annular sealing ring relative to the barrel and with the stop, results in fewer wear surfaces and thereby permits the valve structure to be made from less wear-resistant, and therefore less expensive materials. Additionally, the ability of the screw to rotate relative to the rod-like member avoids breakage of the rod-like member tip during a cold start-up when solidified plastic material is present around the rod-like member.