GB1438644A - Low-pressure casting - Google Patents

Abstract

1438644 Apparatus for low pressure die casting STERLING METALS Ltd 25 June 1973 [23 June 1972] 29426/72 Heading B3F [Also in Divisions F1 and G1] In a low pressure casting apparatus in which molten metal 3 is forced up a feed tube 5 into a mould by gas pressure in a space 7, the pressure in the space 7 is controlled so as to maintain the level of metal in the tube 5 above the level of the metal 3 in the pot 2 but below the top of the tube 5 between successive casting operations. The apparatus is provided with pressure-sensitive switches P 1 , P 2 , P 3 and P 4 , pressure governors R 1 , R 2 , R 3 and R 4 , non- return valves N 1 and N 2 , solenoid valves S 1 , S 2 , S 3 , S 4 and S 5 , flow controllers F 1 , F 2 and F 3 and valves or toggle switches T 1 and T 2 . Compressed air or inert gas is introduced into the apparatus through an inlet line 10. Between casting operations, the solenoid valve 5, is closed and the level of metal in the tube 5 is maintained at the required height by gas supplied to the space 7 through a line 11. The pressure-sensitive switch P 2 causes the valve S 2 to close when the required pressure has been reached in the space 7, and causes the valve S 2 to re-open if the pressure falls again, e.g. owing to leakage. To force molten metal up the tube 5 and into the mould, the valve S 1 is opened to allow gas to pass to the space 7 via a line 13. An increased pressure may then be applied to the metal in the mould by opening the valve T 1 to allow gas to flow through a line 14. Alternatively, the valve T 1 may be open during the filling of the mould and closed when the mould is full. After a predetermined time, the valve S 1 is closed and the valve S 4 opened to allow the gas in the space 7 to escape through a line 16. When the pressure has fallen sufriciently for the switch P 3 to be actuated, the valve S 3 is closed and the pressure necessary to maintain the metal in the tube S at the required height is maintained as described above. When the valve S 4 opens, the switch P 4 senses the temporary increase in pressure in the line 16 and starts a timer which is set to allow adequate time for depressurization of the mould before opening or unlocking the mould. The adjustment of the switches P 2 and P 3 and the flow controllers F 1 , F 2 and F 3 to compensate for the changes in pressure and rates of flow necessary as the level of the metal in the pot 2 falls may be effected by a single control.