| 摘要 |
PROBLEM TO BE SOLVED: To provide good cooling effect even by shortening an injection molding cycle time and to eliminate stringiness by inserting a plurality of strips into a section of a sprue bush near a nozzle touching portion. SOLUTION: About 2 to 5 strips 6 are inserted into a section of a sprue bush near a nozzle touching portion 5. The strips 6 are formed in a V-shaped curved shape from a viewpoint of uniform electrodepositing properties in the case of electroforming the strips 6. In main machining, electroforming is easy from a viewpoint of difficulty of machining and polishing of its inner surface. After a brass bar is perpendicularly cut from its side, sectional V-shaped grooves are cut at a plurality of positions in a given length from its end, cut at its periphery by an NC lathe to form a matrix, satisfactorily polished, then electroformed in a solution containing a nickel sulfamate as a main component by using the matrix, nickel is adhered to a predetermined thickness, then the matrix is drawn, cut by the lathe to produce a completed product. Thus, a distance between an inner wall near the portion 5 and a center gets short, a contact area of molten resin is increased to improve its cooling effect. Then, even when a molding cycle time is shortened, stringiness can be eliminated.
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