GB1327478A - Process for the preparation of shell moulds - Google Patents

Abstract

1327478 Mould for turbine wheels HOWMET CORP 1 Sept 1970 [8 Sept 1969] 41743/70 Heading B5A A shell mould for the metal casting of a turbine wheel which includes radially extending blades 22, Fig. 1, cast integrally with a hub, is moulded by forming a disposable air foil pattern either of blades connected to a rim 20, or preferably of blades and rim integrally injection moulded, of wax or of various stated thermoplastics, which is continuously rotated repeatedly alternately to immerse the pattern in a tank of slip composition, and then to coat the slip in a stucco spray to form a mould shell, the pattern being removed by melting or flashing at elevated temperature e.g. 1500 at 2100‹F., prior to or after joining the shell to interfitting mould portions 60, 74, Fig. 9, defining the hub and a pouring spout for the metal. The slip composition and spray coating may comprise respectively ceramic material and alundum or zircon, or alternatively graphite flour with colloidal graphite and graphite particles. A plurality of patterns, each on a sleeve 30, Fig. 3, interengaging at 34, 36, are mounted on a rotary shaft 38, Fig. 2, for the immersion and coating. The shaft 38 may be mounted on a conveyer which is engaged during movement to effect rotation of the shaft 38 as it travels through immersion, drainage, and coating stations. Alternatively, the rotating shaft 38 and a spray hood 44 are relatively horizontally displaceable to effect the spraying, and the shaft 38 and an immersion tank 42 are relatively horizontally and vertically displaceable, to effect the alternate spray coating and immersion. After removal of the drum and sleeves 26, 30 the pattern is removed by heating when the shell may simultaneously be cured. Each shell on the sleeves 30 may be separated during moulding of the shell by thin discs of rigid paper or plastics abutting the sleeve portions 33, or alternatively adjacent shells may be separated prior to or subsequent to removal of the pattern by cutting through to the portions 33 by a wire brush or grinding wheel during rotation of the shells. The mould part 60, dimensioned to span an open end of the mould to define the hub, is separately formed either, for repeated use, from metal or graphite preferably cored for the passage of water coolant, or as a disposable ceramic shell by compression of injection moulding, slip casting, or by alternate dip coating and stucco coating of a disposable pattern. The mould part 60 and a pouring spout 74, which may similarly be moulded of ceramic material, are joined to the air foil shell by ceramic clips, or by ceramic adhesive e.g. sodium silicate metal phosphate, at surfaces 70, 66, and 80, 76, which adhesive may be. cured by heating simultaneously with any uncured ceramic mould parts and the removal of disposable patterns from any or all of the mould parts. After preheating the assembled mould, the turbine wheel is cast by pouring molten metal into the stationary or rotating mould.