Patent GB-910579-A (GB)
Title: Cast turbine blades and the manufacture thereof
IPC: B22C9/10
Filed: 1961-05-31
Abstract: 910,579. Injection-moulding machines. GENERAL MOTORS CORPORATION. May 31, 1961 [June 8, 1960], No. 19637/61. Class 87(2). [Also in Groups XXII and XXVI] A cast turbine blade comprises a hollow aerofoil portion, ribs extending longitudinally on the internal surfaces thereof, the ribs on the one surface being spaced from those on the opposite surface, supports spaced at intervals along the length being provided to interconnect the internal surfaces. The blade comprises an aerofoil portion 10, a root 16, blade platform 12 and a stem 14 formed with a cooling fluid inlet 13 between the root and the platform. The concave surface 18 is formed on its internal surface with ribs 19 and the convex surface 20 is formed on its internal surface with ribs 21, a number of connecting pieces 22 extending between the opposite internal surfaces. The blade is manufactured by first forming a core having the form of the hollow passage within the finished blade as indicated in Fig. 5, having longitudinally extending grooves 32, 34 which correspond to the ribs 19, 21 of the final blade, also with spaced openings 36 which correspond to the connectors 22 of the final blade. A wax pattern is then formed over the core having the same form as the external configuration of the finished blade. The core with wax covering is then investment cast in a refractory material, the wax material then melted out so as to leave a mould into which molten blade material is then cast. The core material is finally removed by a leaching process. An injection-moulding apparatus for moulding the core is shown in Figs. 6, 7 and 10, the apparatus comprising upper and lower die block members 48, 44 with which are associated plate members 50, 46 which are moved into abutment with the members 48, 44 during the moulding operation, as shown in Fig. 7. Dies 49, 56 are mounted within the die blocks 44, 48 respectively and together form a cavity 51, see Fig. 10. Two series of parallel plates 52, 58 may be projected through the dies into the cavity 51 so as to form the grooves 32, 34 of the moulded core, see Fig. 5. The plates 52 are attached to the plate 46 and the plates 58 to the plate 50. The die block 44 is normally spaced from the plate 46 by means of cam members 114, 116 which have flat portions 126, 128 and are secured to L-shaped cranks 110, 112. In operation, the cranks are engaged by the projections 150, 152 on a member 148 which moves downwardly, the cranks are turned through 90 degrees and the flat portions of the cams engage pads 130, 132 on the plate 46 whereby the die block member 44 and the plate move into abutment as in Fig. 7. The parallel plates 52 are thereby projected into the mould cavity 51, Fig. 10. The die block 48 is similarly normally spaced from the plate 50 by means of cam members 138, 140 having flat portions 139, 141 which are secured to L-shaped cranks 134, 136. In operation, the cranks are engaged by the projections 150, 152 and are turned through 90 degrees whereby the die block 48 and the plate 50 move into abutment. A plate member 68, shown in a raised position in Fig. 6, normally rests on the plate 50 and carries a cylinder 76 from which core material may be injected into the die cavity 51 through openings 78, 80. A plate member 74 carrying a piston 82 is mounted on guide rods 75 and is moved downwardly by means of hydraulic pressure; the plate 74 also carries the member 148 on which the projections 150, 152 are formed. The upper and lower die blocks 48, 44 are held together by means of a pair of hooks 84, 86. In operation the die blocks are held together, the plate 68 is resting on the plate 50 and a biscuit of ceramic mix is in the cylinder 76. The plate 74 is then moveddownwardly and as it does so, the projections 150, 152 first engage the cranks 134, 136 so that the plate 50 moves into contact with upper die block 48 and the parallel plates 58 are projected into the die cavity 51, the projections 150, 152 then engage the cranks 110, 112 so that the plate 46 moves into contact with the lower die block 44 and the parallel plates 52 are projected into the die cavity 51, as shown in Fig. 10. The piston 82 then enters the cylinder 76 and the ceramic mix is injected into the mould cavity 51. The moulded core, Fig. 5, is subsequently removed, dried and fired. The core is then placed in an injection fixture having a cavity in the shape of the blade to be cast and a wax pattern is then formed about the core. The wax covered core is then coated with ceramic wash, placed in a flask or sleeve into which a refractory mixture is poured and then allowed to set. Heat is then applied to melt out the pattern, and molten casting material is then poured into the mould cavity formed by melting out the wax pattern material. After solidifying, the refractory mould body is broken away, the casting is then immersed in a solvent solution whereby the core material within the cast body is dissolved or leached out. Specification 872,705 is referred to.