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; loading the blades in the slot and loading the wax blocks in or adjacent the slot, the wax blocks being configured and positioned such that, on loading, the blades shear material from the wax blocks, the sheared wax blocks reducing a range of tilt angles which can be adopted by the blades; and performing a processing operation on the loaded blades.

Claims

1. A method of processing 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; loading the blades in the slot and loading pre-formed wax blocks in or adjacent to the slot, the wax blocks being configured and positioned such that, on loading, the blades shear material from the wax blocks, the sheared wax blocks reducing a range of tilt angles which can be adopted by the blades; and performing a processing operation on the loaded blades.

2. A method according to claim 1, wherein the processing operation is grinding the blade tips.

3. A method according to claim 1, wherein the wax blocks reduce the range of tilt angles by at least 50%.

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

5. A method according to claim 1, wherein the disc has a plurality of axial slots for mounting respective blades, the blades being loaded in the slots and the wax blocks being loaded in or adjacent the slots.

6. A method according to claim 1, wherein the blades have laterally-projecting platforms which extend over a rim of the disc or laterally-projecting seal wings, and respective wax blocks are positioned beneath the platforms or seal wings.

7. A method according to claim 1, wherein respective wax blocks are positioned in the slot beneath the roots of the blades.

8. A method according to claim 1 which further includes balancing the blades before the blades are processed.

9. A method according to claim 1, which further includes applying a protective coating to the loaded blades to protect the blades from debris generated during the processing operation.

10. A method according to claim 1, which further includes removing the wax blocks from the rotor.

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. 5 shows schematically (a) a ground profile of two blades resting in two positions during the grinding process, and (b) 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. 7 shows schematically (a) a side view of a root of a blade loaded in an axial slot of a disc, (b) a bottom view of the root of the blade loaded in the axial slot, and (c) a side view of a blade loaded in a circumferential slot of a disc; and

(9) FIG. 8 shows schematically (a) a bottom view of the roots of two neighbouring blades loaded in respective axial slots formed in a rim of a disc, and (b) a side view of a blade loaded in a circumferential slot of a disc.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) 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 validation of rotor concentricity.

(11) This can be achieved by loading the blades and wax blocks in the circumferential slot or axial slots of a rotor disc, balancing the blades, coating with a protective paint, and grinding the tips of the blades. During the subsequent standard wash process to remove the paint, the wax blocks are also washed out. The wax blocks operate by providing a force on the underside of the blades, for example, pressing on seal wing, root, or platform under surfaces.

(12) The wax blocks can provide a suitably hard surface on which to locate the blades. Advantageously, the surface of the wax blocks is sheared when assembled between the blades and the disc. To account for manufacturing variation in the blades and the disc, the wax blocks can be configured so as to be large enough to fit the largest possible clearance between a given blade and the disc. When the clearance is smaller, the blocks are then sheared so that they accurately self-size to fit the exact geometry. A chamfered edge can be provided on the wax blocks and sized to the tolerance band of possible blade and disc fits, allowing easy placement and self-sizing of the wax piece during assembly.

(13) FIG. 7 shows schematically (a) a side view of a root 510 of a blade loaded in an axial slot 502 of a disc 504 (b) a bottom view of the root 510 of the blade 500 loaded in the axial slot, and (c) a side view of a blade 500 loaded in a circumferential slot 502 of a disc 504. In both cases, a wax block 506 is positioned between the underside of the root and the bottom of the slot, the top face of the block being sheared off on insertion by the hard edge of the blade root, sizing the block to the exact clearance geometry. The block may also have a tab 512 which protrudes sideways from under the root, allowing a tool to be inserted to aid fitting of the block under the root. One such wax block is inserted under each blade root.

(14) FIG. 8 shows schematically (a) a bottom view of the roots 510 of two neighbouring blades 500 loaded in respective axial slots formed in a rim of a disc (not shown), and (b) a side view of a blade 500 loaded in a circumferential slot 502 of a disc 504. In FIG. 8(a), the wax block 506 is positioned between the rim of the disc and the undersides of neighbouring platforms 508 which project laterally from either side of each blade to extend over the rim. The block sits on the rim of the disc, and has a flat upper face which locates against its platforms. The block is shearable by the hard edges of the platforms on insertion to form a tight fit. In FIG. 8(b), the wax block 506 is positioned between the bottom of the slot 502 and the undersides of neighbouring seal wings 514 which project laterally from either side of the root of each blade. The block locates horizontally and vertically using locating faces on the side and bottom of the slot, and has a quarter-circular face which locates against its seal wings. The block is shearable by the hard edge of the seal wings on insertion to form a tight fit.

(15) 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.

(16) 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. 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.

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