Patent ID: 6857867
Filing Date: 2005-02-22
Classification: B29C

Abstract:
1. A backflow prevention device in combination with a plasticizing and injection screw axially movable in a plasticizing cylinder of an injection molding machine, comprising: a base body defined by an axis, said base body having a leading head portion and a trailing neck portion of a diameter which is smaller than a diameter of the head portion, said base body formed with at least one channel for passage of plastic melt by the screw to an anterior screw space, said channel having an inlet opening; a check valve disposed in the channel; a pressure ring disposed on the base body; and a locking ring, bearing against an inner wall of the plasticizing cylinder and moving in an axial direction between open and closed positions, said locking ring being so positioned behind the head portion of the base body in the area of the neck portion as to define a gap with the base body, said locking ring having a leading stop surface, which is in sealing contact with a confronting base of the head portion, when the locking ring is in the open position, and a trailing stop surface, which is in sealing contact with the pressure ring, when the locking ring is in closed position, wherein the inlet opening of the channel is so disposed in the base body that the leading stop surface of the locking ring is prevented from completely overlapping the inlet opening, when the locking ring is in open position.