GB1216776A - Metal casting and solidification - Google Patents

Abstract

1,216,776. Casting machines and processes. NORTH AMERICAN ROCKWELL CORP. 2 April, 1968 [23 June, 1967], No. 15848/68. Heading B3F. [Also in Division F4] An apparatus for producing thin-walled castings from a reactive metal, particularly aluminium and its alloys, in a vacuum or an inert atmosphere is disclosed. Metal pouring.-In Fig. 1, molten or solid metal is introduced into a crucible 19 and heated by an indirect electric arc. A thermocouple 50 is provided to determine the melt temperature. The crucible 19 is mounted to be rotatable about a horizontal axis on a bearing 24. To pour the charge, the crucible is inverted and the melt falls through an open valve 13 into a moulding chamber 12. Rotation is effected by a sprocket 27 and chain 56 powered by two hydraulic motors (61, 62). The rate of rotation for thin-walled aluminium castings should be 180 degrees per second or above. The crucible is 4 feet above the mould. Melting in the mould.-In Fig. 12, a solid metal charge is held in the top of a mould assembly 303 upon a finely woven graphite cloth 313 within crucible sides 309. Melting is effected by electrical resistance heaters 315, the temperature of the melt being determined by a thermocouple 336. When the desired temperature is reached, an operator pushes a rod 319 which breaks the graphite fabric and allows the melt to fall into the mould cavity. Moulds.-The mould 77 in Fig. 1, is made of high-density non-porous graphite mounted on a chill plate 74 with sheets of asbestos in between the mould and chill plate. Below the chillplate is mounted a water-cooling coil 75 and through the centre of the chill plate a watercooled chill-block 90 projects into the mould cavity to form a base moulding surface. The chill-block 90 also serves as an ejector for the finished casting. In Figs. 9 and 12 the moulds are formed of two halves 207, 208; 307, 308 which are bound together by glass fibre fabric 209; 310 and held in zircon sand 210; 311 in a flask 206; 306. A water-cooling chamber 205; 305 is provided below the flask. All the above moulds are provided with resistance heating elements 86; 213, 214, 215; 313, 314 and water-cooled radiation shields 89; 216, 317. Heating and cooling moulds.-Before pouring, the moulds are heated to at least 0À8 of the temperature of the melt to be cast therein. After pouring, water is passed through the mould bases 74; 205; 305 to commence cooling. In Fig. 1, the chill block 90 is also supplied with water and the mould heater 86 switched off. Upward solidification of the melt takes place. The solid cast product is preferably removed from the mould before cooling so that the cycle time of the casting operation is reduced. In Fig. 9, after pouring the mould heaters 213, 214 and 215 are switched off in that order in dependence of the three thermocouples 231, 232, 233 reaching a preset temperature below the solidification point of the casting alloy, thus ensuring upward solidification within the mould.