PURPOSE: To enable to hold the inside of a casting under high pressure by providing an outer side plunger which forces molten metal into a die, and an inner side plunger which prevents the pressure drop in the casting caused by cooling.
CONSTITUTION: The molten metal for one shot is supplied to a sprue 5, and the pressure oil passed through a change-over valve 10 is supplied to the pressure oil port (a) of an outer side cylinder 3 via a pressure control valve 12 and a pilot check valve 14, whereby an outer side plunger 4 is pushed and the molten metal is sent into a die 6. Since an inner side plunger 8 is mounted to an outer side plunger 4, the molten metal is pushed simultaneously. In this state, the pressure in the die 6 rises. When this pressure reaches a specified value, it is detected with a pressure switch 15 which in turn operates a change-over valve 11. The pressure oil passed through the change-over valve 11 is supplied from the pressure oil port (c) of the inner side cylinder 7 via a pressure control vavle 13, so that the inner side plunger 8 is operated. Here, even if the pressure of the inner side plunger 8 is higher than the pressure of the outer side plunger 4, the outer side plunger 4 is prevented from retreating by a pilot check valve 13.
MORIMOTO SHIYOUGO
NOZAWA KATSUTOSHI
