| 摘要 |
PURPOSE:To prevent damage of a sand mold by providing 1st vent holes facing inward to the projecting parts on the opposite surface sides of molding sand of a main pattern body and disposing 2nd vent holes communicating with the 1st vent holes to the inside of the main pattern body. CONSTITUTION:The pattern A is constituted of the half arc-shaped main pattern body 12 and the plural projecting parts 13. Three recesses 14 are formed between the projecting parts 13. The recesses 14 are formed with pockets of the sand mold at the time of packing the molding sand 11 therein. Three pieces each of the 1st vent holes 15 are formed at a prescribed pitch to the respective projecting parts 13 so as to center at the axial center of the body 12 and ventable plugs are fitted into both end parts. The 2nd vent holes 17 are further formed to the body 12 from below and are communicated with the 1st vent holes 15 and external air vent holes 9a. The external air flows through the vent holes 15, 17 into the recesses 14 to prevent a vacuum state at the time when the molding sand 11 packed in the recesses of the pattern A parts from the mold.
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