| 摘要 |
PURPOSE:To prevent an increase in the humidity of a sand mold core by water and to obtain a pattern for casting having a desired shape with high accuracy by covering the outside surface of the sand mold core with a hydrophobic film. CONSTITUTION:The premolded sand mold core 2 is installed in the prescribed position in a lower metallic mold 6. A coating material is preliminarily coated on the outside surface of the sand mold core 2 and is dried so that the outside surface of the core 2 is held coated with the hydrophobic film 9. The upper and lower metallic molds 5, 6 are then joined to close the metallic mold 4. Beads of plastic for expansion subjected preliminarily to primary foaming up to a prescribed expansion rate are inserted into a cavity 7 formed between the inside surface of the mold 4 and the outside surface of the core 2. The beads are heated to make secondary foaming by injecting steam into the cavity through many small holes formed to the mold 4, then the foamed plastic fills in the cavity 7 in enveloping the core 2. The pattern 1 for casting having the desired shape is obt. when the molds 5, 6 are opened and the molding is taken out. |
