GB802134A - Improvements in moulds and methods of producing same - Google Patents

Abstract

802,134. Making moulds. BRIGHT, T. J. R. Nov. 30, 1954 [Dec. 7, 1953], No. 34027/53. Class 87(2). [Also in Group XXII] A reusable multiple part ceramic or other non-metallic high temperature resisting mould, the parts incorporating means for ensuring accurate relative location but being capable of separation for the removal of a finished casting, is made by the lost-wax process, the pattern, of e.g. wax, low melting point alloy such as 58 per cent bismuth, 48 per cent tin, including two or more parts permanently secured to or forming an integral part of an intervening parting plate which serves to separate the mould parts during their formation, the parting plate having on its opposite faces locating means for producing identical registering recesses and projections in and on the mould parts which interengage when the mould parts are separated from the parting plate and assembled together to ensure accurate relative location of the mould parts during use. The fusible pattern for a hollow rectangular section tube is cast in a die, Figs. 1, 2 comprising side walls 14, 15, inner surface defining portions 21, 22 and a parting plate 12. The side walls 14, 15 are connected by a two piece cap plate 18 having semi-circular pouring holes 19 and base blocks 13. Dowels 24, 28 and plugs 26 also serve to locate and fasten the assembly. The parting plate 12 has a series of cavities 27 which connect the die cavities on both sides of the plate so that when the pattern material is poured the holes 27 are filled therewith and connect the pattern portion on one side of the plate to that on the other. After pouring and solidification, the die is disassembled leaving the pattern 31 and parting plate 12 on the base blocks 13, Fig. 4. Cavities 25 in the parting plate are provided with plugs 33, Fig. 10, which have been accurately fitted to the corresponding cavity by grinding-in to form corresponding projections and recesses in the mould parts. The assembly is then repeatedly dipped in a slurry, initially a fine slurry and then a coarse slurry, until a thickness of preferably 1/16-1/8 inch is built up, the ends of the parting plate and the base blocks being wiped clean after each dipping. After setting the pattern is melted out, the parting plate removed and the mould parts re-assembled. The mould parts may be fired before or after removal of the parting plate. A two part ceramic top 60, Fig. 7, with pouring orifices 19 is provided, and located by ribs 61 which engage in the top of the mould cavity, the mould after firing having been machined to an accurately defined length. Instead of using the ceramic base blocks 13 to act as the mould base, a mould bottom similar to the top 60 may be used, metal base blocks 13 then being used. In a modification, Fig. 14, the mould is shaped externally so that it may be supported in presses or other automatic machinery, and the pattern therefore is made in a die, Fig. 11, comprising three parts on each side of the parting plate. The cavities 54 and apertures 55 improve the mould cooling. The Provisional Specification refers also to the use of additional cooling means such as compressed air or other gas or suitable liquid and to the use of synthetic resin as a pattern material.