GB1390618A - Casting of metal articles - Google Patents

Abstract

1390618 Casting processes; continuous casting DEFENCE SECRETARY OF STATE FOR 27 July 1972 [3 Aug 1971] 36402/71 Heading B3F Metal articles are cast in a mould of a metal of good conductivity, e.g. Cu, which has a R.F. induction coil therearound, the casting process including the steps of introducing metal in the mould, repelling the metal from the surface of the mould, by magnetic flux generated by the coil for at least the period of time during which the metal surface is liquid, and cooling the metal. As exemplified, a turbine blade is cast in a copper two-part mould 1, 2 (of circular external section and hollow to form coolant jackets) located in a R.F. induction coil 8. Liquid metal is poured, in a vacuum or atmosphere inert to the metal, into the pre-heated mould cavity 3. The metal takes the shape of the mould cavity but does not come into physical contact with the mould surface. Unidirectional solidification of the metal can be induced by lowering the mould from the coil during solidification or cutting off the power supply to subsequent sections of the coil 8 upwardly. A crystal growth zone (not shown), may be provided at the base of the mould for establishing a columnar crystal structure. The process can be used for Ti, Al, Cr, Zr, Nb, Mo, Ta, W and alloys of these metals and may be continuous casting. Mould coatings.-To increase electrical conductivity the mould may be of copper coated with silver. The mould may be cooled by water or gas and the induction coil may heat the mould contents. Granules of metal may be placed in the mould and melted therein by the induction coil. An iron alloy casting with a hardened surface can be prepared by melting iron-based alloy in the mould, rapidly cooling the surface parts to give hard-chilled alloy and more slowly cooling the internal parts of the casting to form a soft core. Continuous casting can be effected by supplying metal continuously or in batches to one end of an open-ended die, melting the metal in the die by induction, solidifying the casting in the die and withdrawing the casting from the other end of the die. The repulsion of the casting surface reduces friction. A casting may be heattreated or coated. A composite casting can be made by melting iron powder around a copper core in a mould. The copper core may be cooled during casting.