| 摘要 |
PROBLEM TO BE SOLVED: To secure a good cooling effect even when the injection molding cycle time is shortened, so that the gate part is cut securely and sharply, simultaneously with mold opening, by providing plural ridges on a cross-section near the tip of a gate. SOLUTION: About 2 to 5 rides are provided on a cross-section near the tip of a gate. When it is manufactured with electroforming, the ridges should have a V shape or a curved shape from the viewpoint of uniformity in electroforming. The side of a brass bar is cut vertically. Grooves with a V-shaped cross-section are made there at a plurality of locations up to the length about 10 mm from the tip end. The outer peripheral part is machined with an NC lathe to prepare a matrix. After polishing, electroforming is performed with the matrix in an nickel sulfamate soln. to coat it with nickel having an average thickness of about 4 mm. Then the matrix is taken out, an the nickel part is machine with a lathe to obtain a finished bush part product in which there are plural ridges 6 near the tip of the gate bush, the distance between the inner wall and the center of the bush is shortened, and the contact area between a molten plastic and the inner wall of the bush is made larger. Accordingly, the cooling effect is raised so that the gate part can be cut sharply without generating defects such as stringing even when the injection molding cycle time is shortened. |
