GB726490A - Improvements relating to casting metals - Google Patents

Abstract

726,490. Casting processes. GENERAL MOTORS CORPORATION. July 9, 1953 [July 23, 1952], No. 19019/53. Class 83 (1). The casting of aluminium or titanium or alloys thereof, is carried out in an atmosphere containing sufficient fluorinated hydrocarbon to prevent or reduce the formation of oxide or nitride films. Hydrocarbons which are both chlorinated and fluorinated are preferred, and preferred gases are the fluorinated derivatives of aliphatic hydrocarbons containing not more than two carbon atoms such as dichlorodifluoromethane, carbon tetrafluoride, trifluorobromomethane, trichlorofluoromethane, trifluorochloromethane, and dichlorotetrafluoroethane. The fluxing gas or vapour is introduced along with a dry inert gas such as helium or argon above the surface of the melt for a short time, and after the mould is clamped in position, a short purge with the gas mixture follows, the flow rate of the fluxing gas being maintained at approximately 20-70 per cent of the combined flow rate of the two gases. Strong reducing agent such as calcium-silicon, of the order of 0.05 per cent by weight of the melt may be added to the melt. An atmosphere of inert gas is maintained in the furnace during melting, a flow rate of 5-20 cubic feet per hour being maintained for furnaces having capacities of 5-15 lbs. The fluxing gas, at a flow rate of about 5 cubic feet per hour is introduced into the helium or argon stream and maintained for 5<SP>_</SP>10 seconds, after which the mould is placed in position and the flow continued for about 5<SP>_</SP>30 seconds, the flow rate of the fluxing gas being preferably increased during this period to about 10 cubic feet per hour for about 10-15 seconds. The metal is then poured, the gas flow being preferably stopped as tipping begins. An alloy referred to for casting turbine blades and nozzle diaphragm-vanes for gas turbines contains 1.5-3 per cent titanium and 2-4 per cent aluminium.