Plastifying unit in injection-moulding machines with a nonreturn valve

A plasticizing unit for an injection molding machine, said plasticizing unit comprising

• a plasticizing cylinder,
• a rotatable and axially displaceable screw arranged in said plasticizing cylinder, said screw having a screw head, and
• a non-return valve comprising a basic body fixed to said screw head, said basic body comprising at least three blades having rear surfaces facing said screw head, and a tapered region between said blades and said screw head, said non-return valve further comprising support elements provided on said rear surfaces of said blades, said support elements having support surfaces which are made of a wear-resistant material, a stop ring fixed between said tapered region and said screw head, and a barrier sleeve which encloses said tapered region with radial play, said barrier sleeve being axially displaceable between said supporting surfaces and said stop ring, said barrier sleeve having a support surface which comes into contact with said support surfaces of said support elements, said support elements consisting of pins having axes which are oriented at right angles to the supporting surface of the barrier sleeve.