To provide a hollow core which is small in variance and easy in forming by pouring a molten metal in a molten metal tank, setting a gas introducing rod in a hole for introducing the gas, applying the casting pressure to cast the molten metal into a cavity, solidifying the molten metal in contact with the cavity surface to some degree, pulling out the gas introducing rod to introduce the gas, and returning the remaining molten metal into the molten metal tank to take out the hollow core.
A gas introducing rod is inserted in a gas introducing hole, and a molten aluminum 50 is poured in a molten metal tank 30. The air introduced from a casting pressure inlet 31 presses up the molten metal 50 and fills a metallic cavity 10 therewith. After the cooling for a specified time, a solidifying part 50a of the molten metal in contact with the metallic cavity 10 is solidified, while the molten metal 50b inside is in a molten condition. The set gas introducing rod 40 is drawn out and the air is introduced from an upper part into the metallic cavity 10. When the air is introduced in the metallic cavity 10, the non-solidified metal 50a is returned to the molten metal tank 30 by the self weight, and a hollow core is taken out by opening the metallic cavity 10.
KAWAKAMI YOSHIHIRO
NISHIMURA YOSHIMICHI
NISHIKAWA SHINICHI
MUTO NOBUKI
NISSAN MOTOR