| 摘要 |
PURPOSE:To prevent the intrusion of sand into a product part in the stage of casting in a vacuum casting mold which consists of silica sand for molding coated with a plastic film by forming the cavity for the sprue prior to charging of the silica sand in the stage of forming separately the cup and bar of the sprue. CONSTITUTION:The sprue bar 21 is formed integrally with the pattern 22 and after the film is formed, the sprue cup 21' enveloped by the film is lowered to be brought into tight contact with the bar 21. A heater 30 is contained in the cup 21' to melt-cut the tightly adhered film and at the same time to weld the films at the outside circumferential part to each other. A molding flask is set and the silica sand for molding is put into the flask and is molded, then the cup 21' is raised and a top surface film is put on. The inside of the flask is then sucked to a negative pressure. The sprue cavity is thus formed prior to putting of the silica sand for molding into the flask in the above-mentioned manner, by which the danger for the intrusion of the sand to the mating faces 20 of the film is eliminated and therefore the intrusion of the sand into the product part is obviated. |
