PURPOSE: To form a uniform metal protective film on the surface of a nozzle assembly by coating a tacky fluid and powdered metal thereon and heating the coated nozzle in a vacuum furnace.

CONSTITUTION: A nozzle assembly is dipped in an acrylic resin lacquer and then, powdered nickel alloy. The process can coat a body section 80 surface of an assembly, a collar section 94 surface and a sleeve section 96 surface by an acrylic resin lacquer and adhere a powdered nickel alloy the lacquer. The coated assembly is placed in a vacuum furnace 130 and the pressure therein is reduced. Further, a vacuum furnace 130 is gradually heated up to 1,204.4°C and then, the powdered nickel on the surface of an assembly is heated to form a protective film whose thickness is almost uniform. Said protective film is also formed in a well for molten molding material.