Core positioning

Abstract

A method locates and maintains a core in fixed space relationship within the interior of a shell mould. The method provides at least one pin extending into the core with at least one axial end of the pin protruding from the core. A wax pattern having an outer surface is formed by encasing the core and at least one protruding axial end of the pin in wax such that at least one protruding axial end of the pin terminates at the outer surface of the wax pattern. A shell mould is formed around the wax pattern such that, upon removal of the wax pattern, and in a subsequent casting process for production of hollow metal components, at least one protruding axial end of the pin abuts the shell mould, thus fixing the pin and maintaining a position of the core relative to the mould. The protruding axial end of the pin has an enlarged head.

Claims

1. An apparatus for locating and maintaining a core in a fixed space relationship within an interior of a shell mould, the apparatus comprising: at least one pair of two aligned pins, each having a shaft portion extending into the core, an axial end of each pin protruding from the core in opposite directions, the axial end of each pin having an enlarged head portion; the shaft portion of each pin being completely contained within the core with an end of the shaft portion of one pin opposing an end of the shaft portion of the other pin of the two aligned pins, with a space in the core between the end of the shaft portion of the one pin and the end of the shaft portion of the other pin; the core and the axial end of each pin being encased within a wax pattern having an outer surface, the axial end of each pin being flush with the outer surface of the wax pattern; and the wax pattern being encased within the shell mould, such that, upon removal of the wax pattern, and in a subsequent casting process for production of a hollow metal component, the axial end of each pin abuts the shell mould thus fixing the at least one pair of the two aligned pins and maintaining a position of the core relative to the shell mould.

2. The apparatus according to claim 1, wherein further comprising: a second pin that extends all the way through the core and has two protruding axial ends each with a respective enlarged head portion.

3. The apparatus according to claim 1, wherein further comprising: a second pin that extends into the core and has another axial end terminating within the core.

4. The apparatus according to claim 3, wherein the other axial end of the second pin terminating in the core has an enlarged head portion.

5. The apparatus according to claim 1, wherein there is a plurality of pins each extending into/through the core.

6. The apparatus according to claim 1, wherein further comprising: a second pin that comprises an axially elongated shaft portion between opposing axial ends, wherein the axially elongated shaft portion of the second pin extends through/into the core.

7. The apparatus according to claim 1, wherein the enlarged head portion in the axial end of each pin has a greater transverse cross sectional profile than a respective shaft portion of each pin.

8. The apparatus according to claim 1, wherein the enlarged head portion in the axial end of each pin is integral with a respective shaft portion of each pin.

9. The apparatus according to claim 1, wherein the hollow metal component is a cast component having a cavity or channel in a gas turbine engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 shows a prior art method/apparatus;

(3) FIG. 2 shows a ducted fan gas turbine engine incorporating a series of turbines each having aerofoil blades formed using a method according to an embodiment; and

(4) FIG. 3 shows a method/apparatus according to an embodiment.

DETAILED DESCRIPTION

(5) With reference to FIG. 2, a ducted fan gas turbine engine incorporating a series of turbines each having a plurality of aerofoil blades formed using a method disclosed herein is generally indicated at 10 and has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, the propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, an intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

(6) During operation, air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

(7) The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

(8) For forming the turbine blades, an investment casting process is used in which a ceramic core 3 is located and maintained in a fixed space relationship within the interior of a ceramic shell mould 4. This is shown in FIG. 3.

(9) A ceramic core 3 is provided with a plurality of pins 1A, 1B, 10, 1D and 1E.

(10) Two of the pins 1A, 1B each have a respective axially elongated shaft portion 5A, 5B extending through the ceramic core 3. The shaft portions 5A, 5B are completely contained within the ceramic core with each pin having two protruding opposing axial ends comprising enlarged head portions 6A, 6A, 6B, 6B. The enlarged head portions 6A, 6A, 6B, 6B of the pin 1A, 1B are integrally formed with the respective shaft portion 5A, 5B.

(11) Two of pins 1C, 1D form a pair of aligned pins, each having a shaft portion 5C, 5D extending into the ceramic core 3. The shaft portions 5C, 5D are completely contained within the ceramic core as is one axial end 6C, 6D of each pin 1C, 1D. The respective opposing axial ends each comprise an enlarged head portion 6C, 6D. The enlarged head portions 6C, 6D are adhesively fixed to the respective shaft portions, 5C, 5D.

(12) Each enlarged head portion 6A, 6A, 6B, 6B, 6C, 6D abuts the ceramic core.

(13) One of the pins 1E has a shaft portion 5E with opposing axial ends each comprising an enlarged head portion 6E, 6E. One enlarged head portion 6E protrudes from the ceramic core 3 whilst the other enlarged head portion 6E is embedded within the ceramic core 3.

(14) In one pin 1A, the enlarged head portions 6A, 6A are frusto-conical. In one pin, 1B, the enlarged head portions 6B, 6B are semi-spherical. In the pair of aligned pins, 1C, 1D, the enlarged head portions 6C, 6D are ellipsoid. In one pin 1E, the protruding enlarged head portion 6E is ellipsoid and the enlarged head portion 6E embedded within the core is frusto-conical.

(15) A wax pattern 2 having an outer surface 7 is formed by encasing the ceramic core 3 and the enlarged head portions 6A, 6A, 6B, 6B, 6C, 6D, 6E of the pins 1A-1E in wax such that the protruding axial ends of the pins 1A-1E terminate at the outer surface 7 of the wax pattern 2.

(16) The depth of the wax in the wax pattern 2 matches the axial extension of the enlarged head portions 6A, 6A, 6B, 6B, 6C, 6D, 6E of the pins 1A-1E.

(17) The enlarged head portion 6E of the pin 1E embedded within the ceramic core 3 abuts the inner surface of the wax pattern 2.

(18) A ceramic shell mould 4 is formed around the outer surface 7 of the wax pattern 2 by applying a ceramic slurry to the wax pattern 2 and letting it set and harden. The enlarged head portions 6A, 6A, 6B, 6B, 6C, 6D, 6E of the pins 1A-1E abut the inside of the ceramic shell mould 4.

(19) Upon removal of the wax pattern 2 (by melting), the enlarged head portions 6A, 6A, 6B, 6B, 6C, 6D, 6E of the pins 1A-1E forming the protruding axial ends of the pins 1A-1E are fixed between the ceramic shell mould 4 and the ceramic core 3 thus maintaining the spacing of the ceramic core 3 from the ceramic shell mould 4.

(20) After firing of the ceramic shell mould 4, molten metal is poured into the cavity between the ceramic shell mould 4 and the ceramic core 3 with the enlarged head portions 6A, 6A, 6B, 6B, 6C, 6D, 6E of the pins 1A-1E becoming captive in the cast metal once cooled such that the pins 1A-1E are retained within the turbine blade even under the effect of centrifugal force.

(21) On completion of the casting process, the ceramic core 3 and ceramic shell mould 4 are removed physically and/or chemically.

(22) While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.