Low pressure die-casting machine and low pressure die-casting method

A low pressure die-casting apparatus including a metal mold having a casting port, and a ladle unit for retaining and transporting a predetermined amount of a molten metal in a metal pot to the casting port, the ladle unit having an upper portion, a bottom portion having a molten metal intake/discharge port formed therein, and an inner surface defining a molten metal accumulation space, the apparatus comprising:

• the intake/discharge port of the ladle unit having a cross-sectional area in a range of from 20 to 80 mm.sup.2, and the bottom portion of the ladle unit being operative to pressure contact with the casting port;
• a molten metal pressurizing means switchable to one position for selectively applying pneumatic pressure to the accumulation space in order to positively discharge the molten metal through the intake/discharge port to the metal mold, the molten metal pressurizing means being switchable to another position;
• a switching means connected between the molten metal pressurizing means and the upper portion of the ladle unit and switchable between a first position for isolating the accumulation space from an atmosphere and a second position for providing fluid communication between the accumulation space and the atmosphere;
• and
• a controller connected to the switching means and producing a first signal for driving the switching means between the first position and the second position, the controller also being connected to the molten metal pressurizing means and producing a second signal for selectively driving the molten metal pressurizing means between the one position and said another position;
• further comprising a transfer means for transferring the ladle unit between the pot and the casting port;
• and
• suction means in communication with the molten metal accumulation space for reducing a fluid pressure therein during transfer of the ladle unit by the transfer means;
• wherein the suction means comprises:
• a pressurized fluid source;
• an ejector connected to the pressurized fluid source for continuously providing a negative pressure therein because of a flow of the pressurized fluid in the ejector;
• and
• a change-over means connected to the controller and being fluidly connected to the accumulation space, the change-over means having a first change-over position disconnecting from the ejector and a second change-over position connecting to the ejector for applying negative pressure in the accumulation space;
• and
• wherein the switching means comprises:
• a valve body having a first communication hole formed therein for providing direct fluid communication between the valve body and atmosphere, a second communication hole formed therein for providing fluid communication between the upper portion of the ladle unit and the molten metal pressurizing means, a third communication hole formed therein, and a bore formed therein in communication with the upper portion;
• an opening/closing valve movable in the valve body for selectively closing the bore and thereby blocking communication between the first communication hole and the accumulation space;
• a pneumatic cylinder mounted on the valve body and defining therein an internal space;
• a piston connected to the opening/closing valve and movable in the pneumatic cylinder, the piston dividing the internal space into a first chamber and a second chamber;
• and
• a cylinder driving mechanism for moving the piston to thereby move the opening/closing valve toward and away from the bore, the change-over means being fluidly connected to the third communication hole.

A low pressure die-casting apparatus including a metal mold having a casting port, and a ladle unit for retaining and transporting a predetermined amount of a molten metal in a metal pot to the casting port, the ladle unit having an upper portion, a bottom portion having a molten metal intake/discharge port formed therein, the intake/discharge port remaining open in the presence of the molten metal, and an inner surface defining a molten metal accumulation space, the apparatus comprising:

• the intake/discharge port of the ladle unit having a cross-sectional area in a range of from 20 to 80 mm.sup.2, and the bottom portion of the ladle unit being operative to pressure contact with the casting port;
• a molten metal pressurizing means switchable to one position for selectively applying pneumatic pressure to the accumulation space in order to positively discharge the molten metal through the intake/discharge port to the metal mold, the molten metal pressurizing means being switchable to another position;
• a switching means connected between the molten metal pressurizing means and the upper portion of the ladle unit and switchable between a first position for isolating the accumulation space from an atmosphere and a second position for providing fluid communication between the accumulation space and the atmosphere;
• and
• a controller connected to the switching means and producing a first signal for driving the switching means between the first position and the second position, the controller also being connected to the molten metal pressurizing means and producing a second signal for selectively driving the molten metal pressurizing means between the one position and said another position.