PURPOSE: To prevent sinking from developing without being effected by the height of a boss and at the same time under the state that the height of the boss is stabilized by a structure wherein a slit, which is provided along the outer periphery at the root of the boss and through which the pressure of gas or liquid is applied, and a fluid circuit, by which said slit is connected to the outside of a mold, are provided.
CONSTITUTION: Molten resin is filled through a sprue 5 in a product part 7 and a boss part 8. If cooling proceeds as is, sinking develops on the surface 23 of the boss 8 due to the shrinkage of the resin. However, when high gas or liquid pressure is applied to a core fluid circuit 22 from the outside of a mold after the filling of the resin, said pressure is transmitted through a fluid circuit 21 and a slit 20 to the root of a boss 8 so as to press the resin at the root. Thus, said resin is pressed to a cavity side, resulting in preventing sinking from developing. In addition, since the slit 20 is fine, no resin enters the slit and consequently no clogging of the slit occurs.
HARA YOSHIHIRO
KANDA TSUMORU
TAMAI SHOJI
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