GB710334A - Improvements in precision casting - Google Patents

Abstract

710,334. Moulding processes ; patterns ; cores ; extracting castings. POWER JETS (RESEARCH & DEVELOPMENT), Ltd. March 9, 1951 [March 17, 1950], No. 6759/50. Class 83 (1). [Also in Group V] In a method of making a cored precision casting by means of a refractory core embedded in an expendable pattern of readily fusible material, the core extends through the length of a split die used for moulding the pattern and is accurately located by separable parts which are removed from the ends of the core when the pattern is removed from the die. The core is preferably of fused silica, commercially available in the form of tubes and after casting is dissolved from the metal by caustic soda. Other suitable materials include porcelain, sillimanite, alumina, zircon, magnesia, carbon or a refractory metal. The invention is described as applied to the casting of a turbine blade having internal passages for cooling fluid. A wax pattern is formed in a die comprising an upper part 2 and a lower part 1 having detachable end plates 4, 7 drilled to receive silica tubes 9 and inserts 10 slotted to receive the ends of silica strips 12 to form passages through the root portion 13a of the blade 13. End plates 4, 7 are secured by pegs 6, 8 and the die parts 1, 2 are aligned by dowels 3. Wax is injected into the die through openings in the plate 7. The removal of the silica cores from the cast metal is preferably carried out in molten caustic-soda under a pressure of about 110 lbs. per square inch. Instead of wax other expendable material such as frozen mercury or a very low melting point alloy may be used for the pattern.