Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1996-05-03
1997-12-30
Gorgos, Kathryn L.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
118500, 204297R, 205110, 205128, 205136, C25D 502, C25D 1706
Patent
active
057025746
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/GB/02777, filed on Dec. 21, 1994.
This invention relates to blades for turbines and compressors and in particular relates to the production of blade tip seals.
It is known to provide at the tip of a gas turbine blade a tip portion comprising abrasive particles which are embedded in a matrix, the tip being intended to run against the surface of a shroud of a material which is softer than the abrasive particles. By this means, it is possible to produce, by the abrasive action of the particles on the shroud, a gap between the tip and the shroud which is very small, thus minimising gas losses. In one particular example where this technique is used, the matrix comprises a major part of cobalt and minor parts of chromium, tantalum and alumina while the lining material of the shroud comprises a major part of cobalt with minor parts of nickel, chromium and aluminium and a small quantity of yttrium. Various methods for producing such tips have been proposed. In one example, detonation spray coating of the matrix is used. In another example there is first produced an inner tip portion of mainly nickel and cobalt with additional ingredients by casting as a single crystal and the inner tip portion is, after shaping, diffusion bonded to the tip of the blade body. The abrasive portion of the tip is then formed on the inner tip portion by electrodeposition of alternating layers of chromium and nickel about the abrasive particles. The outer tip portion can then be aluminised to produce a matrix alloy of NiCrAl.
There has been described in GB-A-2241506 a method of producing a gas turbine blade having an abrasive tip which comprises producing a binding coat on the tip of the blade body by electrodeposition, the binding coat comprising MCrAlY where M is one or more of iron, nickel and cobalt, anchoring to the binding coat coarse particles of an abrasive material by composite electrodeposition from a bath of plating solution having the abrasive particles suspended therein, and then plating an infill around the abrasive particles. It has been found that this method, all stages of which are of a metal plating nature and are therefore relatively inexpensive and readily controllable, produces a very effective abrasive blade tip.
There is also described in WO 94/19583, published 1 Sep. 1994, a process in which turbine rotor blades are assembled on a compressor or rotor disc and abrasive tips are produced on the tips of the assembled blades by electrodeposition or by electroless deposition.
Production of the tips on the assembled blades has several advantages, the chief of which is that it is possible to carry out various production steps on the assembled disc without subsequent disassembly. The previous practise was for the blades to be assembled on the disc and for the tips of the blades to be machined to produce a properly balanced disc. The blades were then marked, disassembled from the disc, individually mounted on a jig, tipped, removed from the jig and then reassembled on the disc in the same order and positions that they previously occupied. By proceeding in accordance with the invention of WO 94/19583, one of the two assembly operations, jigging and dejigging, the marking and the disassembly are avoided and unbalancing due to the blades being re-assembled in slightly different attitudes or positions from those previously adopted is obviated.
With the processes referred to above which involve electrodeposition, it is necessary, in order to limit the deposition to the tip areas of the blades, to wax mask all other areas of the blades and of the jig by which the blades are supported during the deposition process. Masking is achieved by grit blasting to provide a key for the masking wax where the surface of the blades will not be damaged by such blasting, then inserting an assembly comprising a support and the blades mounted thereon into a wax bath to mask all surfaces of the support and blades and then removing the wax from the tips of the blades. After the tips have been produced,
REFERENCES:
patent: 4088560 (1978-05-01), Swinehart et al.
patent: 4151063 (1979-04-01), Nelson
patent: 4808275 (1989-02-01), Ohzora et al.
patent: 5076897 (1991-12-01), Wride et al.
patent: 5486281 (1996-01-01), Gruver et al.
Chatterley Martin Patrick
Foster John
Taylor Alan
Denninger Douglas E.
Gorgos Kathryn L.
Leader William T.
Praxair S.T. Technology, Inc.
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