Rotor blade manufacture

Abstract

A method is provided of processing one or more blades of a row of blades which forms part of a rotor for a gas turbine engine. The method includes: providing a rotor disc having a slot for mounting one or more blades; applying tape at one or both sides of the slot such that when the blades are loaded in the slot the tape reduces a range of tilt angles which can be adopted by the blades; loading the blades in the slot; and performing a processing operation on the loaded blades.

Claims

1. A method of grinding tips of one or more blades of a row of blades which forms part of a rotor for a gas turbine engine, the method including: providing a rotor disc having a slot for mounting one or more blades; applying tape at one or both sides of the slot such that, when each of the one or more blades is loaded in the slot, the tape reduces a range of tilt angles which can be adopted by the blade; loading the one or more blades in the slot; performing a grinding operation on a blade tip of each of the loaded one or more blades; and removing the tape from the disc after the grinding operation.

2. The method according to claim 1, wherein the slot is a circumferential slot for mounting a plurality of the blades.

3. The method according to claim 1, wherein: the rotor disc has a plurality of axial slots for mounting respective ones of the blades, the tape is applied at one or both sides of each slot, and the blades are loaded in the slots.

4. The method according to claim 1, wherein the tape reduces the range of tilt angles by at least 50%.

5. The method according to claim 1, wherein: each of the one or more blades has a laterally-projecting platform that extends over a rim of the disc, and the tape reduces the clearance between each of the platforms and the rim and thereby reduces the range of tilt angles that can be adopted by the one or more blades.

6. The method according to claim 1, wherein the tape reduces the distance across a mouth of the slot and thereby reduces the range of tilt angles that can be adopted by the one or more blades.

7. The method according to claim 1, wherein the tape is a polymer tape.

8. The method according to claim 1, wherein the tape has an adhesive layer for adhering to the rotor disc.

9. The method according to claim 1, further comprising balancing each of the one or more blades before the blade is processed.

10. The method according to claim 1, further comprising applying a protective coating to each of the loaded one or more blades to protect the blade from debris generated during the grinding operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows a longitudinal cross-section through a ducted fan gas turbine engine;

(3) FIG. 2 shows a typical abradable liner tip rub profile;

(4) FIG. 3 shows an axial root blade on the left and circumferential root blade on the right;

(5) FIG. 4 shows schematically three tilt positions in which a blade can rest relative to a disc;

(6) FIG. 5A shows schematically a ground profile of two blades resting in two positions during the grinding process, and FIG. 5B shows schematically the ground blades with resting positions swapped during a period of use;

(7) FIG. 6 shows schematically a rearwards directed view of blade tip of a blade with an axial root for different levels of tilt;

(8) FIG. 7A shows schematically a blade loaded in a circumferential slot of a disc and set at its nominal location, FIG. 7B shows the blade in the same slot but tilted to its maximum rearward location, FIG. 7C shows the same disc, but now with tape applied along the edges of the slot, FIG. 7D shows the blade loaded in the slot of the taped disc and set at its nominal location, and FIG. 7E shows the blade in the slot of the taped disc and tilted to its now reduced maximum rearward location;

(9) FIG. 8 shows respective distributions for the manufacturing tolerances of a blade and a disc, the horizontal distance between the two dashed vertical lines at the centres of the two distributions indicating a nominal radial clearance between the underside of the blade platform and the rim of the disc when the blade is centrifuged outwardly in its zero tilt location; and

(10) FIG. 9 shows schematically a blade loaded in an axial slot of a disc, with tape applied at the mouth of the slot.

DETAILED DESCRIPTION OF EMBODIMENTS

(11) The method of the present disclosure can reduce the range of available blade tilt angles during the tip grinding process, allowing all the blades to be accurately and consistently located so that a more concentric rotor can be ground. It also has utility in other processing operations such as measurement verification of blade concentricity.

(12) In the case of a grinding process performed on a circumferentially slotted disc, the method can involve applying layers of adhesive tape to the front and/or rear disc rim edges, to act effectively as a controlled, and removable, coating on the disc surface which supports both sides of the blade. The blades are then loaded over the tape layer, balanced, coated with a protective paint, and ground. During the subsequent standard wash process to remove the paint, the tape is loosened, and can then be pulled out by hand, cut, and unthreaded from the circumference of the disc.

(13) FIG. 7A shows schematically a blade 500 loaded in a circumferential slot 502 of a disc 504 and set at its nominal location (i.e. zero tilt angle). FIG. 7B shows the blade in the same slot but tilted to its maximum rearward location.

(14) FIG. 7C shows the same disc, but now with tape 506 applied along the edges of the slot 502. As illustrated by FIG. 7D, which shows the blade loaded in the slot of the taped disc and set at its nominal location, the tape reduces the clearance between the blade platform 508 and the rim of the disc. In this way, the range of tilt angles which can be adopted by the blade is reduced, as illustrated by FIG. 7E which shows the blade tilted to its now reduced maximum rearward location. A small residual amount of tilt is advantageous for facilitating assembly of the blades into the rotor and for avoiding excessive vibration during processing.

(15) The tape can be a heavy duty polymer film tape. Preferably it has good adhesion properties to the metal of the rim and leaves no residue on removal. Further it should be sufficiently strong to be pulled off by hand without significant stretching or breaking. For example, the tape can be polyester silicone adhesive masking tape. Different thicknesses of tape can be used depending on the amount of original blade tip to be eliminated and on the manufacturing tolerances of the slot and the blades. Multiple layers of tape can be used to obtain desired overall tape thicknesses. For example, FIG. 8 shows respective distributions for the manufacturing tolerances of the blade and the disc, and the horizontal distance between the two dashed vertical lines at the centres of the two distributions indicating a nominal radial clearance R between the underside of the blade platform and the rim of the disc when the blade is centrifuged outwardly in its zero tilt location. In this scenario a total tape thickness of about 70% of R can remove most of the range of tilt angles, while ensuring that even in a worst case scenario (with blade and rim at the limits of their manufacturing tolerances) the blade can still be loaded into the slot. The total tape thickness can be provided e.g. with a double layer of tape. A thinner tape can be used in a multilayer with thicker tape to fine tune the overall tape thickness.

(16) Preferably the tape also has a smooth top surface which allows easy sliding of blades over the tape during build.

(17) The tape can be wide enough to have some amount hanging over the outer disc edge so that it can be easily gripped by hand and pulled off. The after-grind wash process typically assists in loosening the adhesion of the tape to make it easier to remove after wash.

(18) The method can also be used to reduce the range of tilt angles of blades of an axially slotted disc during blade tip grinding. FIG. 9 shows schematically, for example, a blade 510 loaded in an axial slot 512 of a disc 514, with tape 516 applied at the mouth of the slot to reduce the distance across the mouth and thereby reduce the range of tilt angles which can be adopted by the blade.

(19) By providing a narrower distribution of ground blade lengths, the method can reduce casing rub and tip leakage, resulting in specific fuel consumption improvements which may be of the order of 0.1-0.2%. In addition, the method reduces instances of rubbing-induced blade cracking.

(20) While the disclosure 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. For example, although the above embodiments show the tape applied along both sides of the slots, it is also possible to apply the tape only along one side of a given slot. Accordingly, the exemplary embodiments of the disclosure 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.

(21) All references referred to above are hereby incorporated by reference.