Device for producing plastic molded parts having a locking ring with a wear resistant material

A device for producing plastic moldings, the device comprising:

• an extruder;
• a molding tool arranged downstream of a discharge opening of the extruder;
• a screw guided in the extruder such that the screw is rotatable and is axially displaceable, in order to transfer plasticized or liquid polymers, prepolymers and/or monomers present in the extruder into the molding tool;
• and
• a nonreturn valve arranged in an area of a free end of the screw, wherein at least one locking ring of the nonreturn valve acting against an inner circumferential wall of the extruder has a seal applied to at least part of an outer circumference of the locking ring, said seal sealing the locking ring against the circumferential wall of the extruder, sealing material of the seal of the locking ring being a wear-resistant material from the group of polyether ketones (PEK), the polyaryl ether ketones (PAEK), the polyhalogenated polyolefins, the high-molecular-weight polyolefins with a molecular weight of at least 100,000 g/mole and the polyamides (PA) including copolymers and polymer blends with said polymers, with a hardness lower than that of material of the circumferential wall of the extruder, wherein the sealing material of the seal of the locking ring has a coefficient of thermal expansion of at least 30×10−6/K.