Patent GB-1425868-A (GB)
Title: Method of regulating the pressure in a low-pressure casting plant
IPC: B22D18/08
Filed: 1973-06-12
Abstract: 1425868 Pressure casting machines REGIE NATIONALE DES USINES RENAULT and AUTOMOBILES PEUGEOT 12 June 1973 [22 June 1972] 27984/73 Heading B3F [Also in Division F1] A low pressure casting apparatus comprises a furnace 1 containing molten metal 2, a mould 37, a pipe 38 through which molten metal passes from the furnace to the mould under the action of gas pressure in a space 3, a first control means 52 located between the furnace and the mould bottom, a second control means 53 disposed in the mould bottom, and a third control means 54 disposed in the upper portion of the mould, the said control means being used to regulate the pressure in the space 3. Gas from a source 4 passes to the space 3 via lines 60 and 20, a regulator 21, a line 22 a pair of throttle valves 24 and 24a, and a pair of valves 18 and 18a, the arrangement being such that when valves 18 and 18a are open the output from valve 18a is greater than the output from valve 18. The space 3 may be vented to the atmosphere via a valve 16. A line 42 connects the space 3 with pressure exchange devices 25 and 27 each consisting of a vessel containing a liquid overlying which is a gas, the said liquid being in communication with a liquid column, 28 and 30 respectively, which thus displays the pressure existing in the space 3. The connection between the device 27 and the column 30 may be blocked by a valve 33. The column 30 communicates with a first chamber 44 of a pressure comparator 31 which operates to equalize the pressure in its two chambers 44 and 46. Thus when the valve 33 is closed a constant pressure equal to the pressure displayed by the column 30 is maintained in a line 43. At the beginning of a casting cycle the solenoid valves 11, 12, 13 and 14 are actuated simultaneously. This results in the closing of the vent valve 16, the opening of valve 33 and the actuation of distributors 17 and 17a which in turn results in the opening of valves 18 and 18a and allows gas to flow to the space 3 to force molten metal up the pipe 38. When the metal contacts the switch 52, the solenoid valve 13 is de-energized thus causing valve 18a to close and resulting in a reduced gas flow to the space 3 via valve 18 only. When the metal contacts the switch 53, the solenoid valve 14 is de-energized causing the valve 33 to close and thus isolate the column 30. The column 30 remains isolated during the subsequent operations of the cycle thus causing a fixed reference pressure to be maintained in the line 43. The pressure in the space 3 continues to rise and the resulting difference between the pressures in lines 42 and 43 respectively is sensed by a distributor 19 which sends a control signal to the pressure regulator 21. When the metal contacts the switch 54, the solenoid valve 13 is actuated and the valve 18a opened so that the pressure in the space 3 now rises at a high rate. When the difference between the pressures in the lines 42 and 43 reaches a predetermined value, the distributor 19a moves to cut off the supply of gas to the distributor 17a and thus brings about the closing of the valve 18a. The pressure continues to rise slowly until it exceeds the reference pressure by a quantity equal to the preset value of the distributor 19, the latter then moving to close the valve 18 and thus shut off completely the supply of gas to the space 3. After allowing time for the casting to cool the valves 11 and 12 are de-energized to vent the space 3 and prepare the apparatus for the next casting cycle.