| 摘要 |
PURPOSE:To manufacture efficiently castings of high quality under low pressure by dropping the compressed air pressure to bring the molten metal in a stalk slightly lower than the charging port of the stalk upon ending of one shot and charging the molten metal by exerting pressure in the next shot. CONSTITUTION:Air is fed from a compressor to the inside of a low pressure casting furnace 12 through a pressurization control valve 14 and solenoid valve 16a, whereby molten metal is cast under low pressure. Thereafter, the valve 16a is closed, a solenoid valve 16b is opened, and the air is fed through a residual pressure control valve 18 to the inside of the furnace 12. At the same time, the pressure in the furnace 12 is decreased gradually by opening a reducing valve 34. The decrease in the pressure is transmitted to the pressurizing chamber 24 of a differential pressure controller 20, where a diaphragm 22 detects the differential pressure from a residual pressure chamber 26. When the pressures in the chambers 24, 26 balance, a proximity switch is operated to close the valve 34. In this state, the molten metal level in the stalk is held in the position slightly lower than the charging port of the stalk. The valve 16b is closed and the valve 16a is opened to carry out the next pressure casting. |
