PURPOSE: To omit a process for plugging an opening part in the case of trying the leakage test of a product after casting and to use an auxiliary core as a supporting material for carrying a product and to reduce the cost by pulling out a main core while remaining the auxiliary core.
CONSTITUTION: The strength at a part except a first core print part 22h at the main core 22 is lowered by the heat of molten metal so as to be capable of the plastic deformation and at the same time, a reciprocal binding force, in which the other end can be pulled out by pulling out the one end, is produced. As the same way, the auxiliary core 24 has high strength at a second core print part 24h and the neighborhood thereof but lowers the strength at the other part by the heat of the molten metal so as to be capable of the plastic deformation, and at the same time, the reciprocal binding force, in which the other end can be pulled out by pulling out the one end, is provided. By this method, the fitting part between the recessed part 22m of the main core 22 and the projecting part 24m of the auxiliary core 24 can be removed by applying the force in the separating direction to both parts.
OKADA YUJI
SHIRAKAWA HIROICHI
TOMITAKA SHUICHI
