Return flow shut-off device for an injection unit in an injection moulding machine

A backflow blocking arrangement for an injection unit of an injection molding machine, the machine having a plasticising screw (1) with a front end for carrying the backflow blocking arrangement, the backflow blocking arrangement comprising a screw tip (8), a blocking bush (3) and a blocking sleeve (2), each having a base body material, the screw tip having friction surfaces (14), the blocking bush and the blocking sleeve each having sealing and friction surfaces (4, 5, 6), at least one of the friction and sealing surfaces (4, 5, 6, 14) being formed by a protective layer comprising a fusion metallurgical compound of said base body material and an additive material, characterized in that the screw tip (8) comprises a metal base material and at the friction surfaces (14) of the screw tip the additive material comprises at least one of:

• metals, carbides, carbonitrides, borides, carboborides, silicides, sulfides and oxides;
• the screw tip including a mixed layer between the base body material of the screw tip and an outer layer of the screw tip that includes the additive material, the mixed layer being thinner than the outer layer and both the outer layer and the mixed layer including base body material of the screw tip and specific proportions of the additive material, said outer layer and mixed layer being made from metallic mixed crystals and chemical compounds which contain material of the base body and the additive material.