WO2001054857A1

WO2001054857A1 - Thermal processing apparatus and method

Info

Publication number: WO2001054857A1
Application number: PCT/GB2001/000244
Authority: WO
Inventors: Adrian Eric Bosworth; Peter Leslie Daykin; Alan Leighton
Original assignee: Sermatech Repair Services Limited
Priority date: 2000-01-27
Filing date: 2001-01-23
Publication date: 2001-08-02
Also published as: GB0101688D0; GB2361444A; GB0001753D0; AU2001226962A1

Abstract

There is disclosed apparatus (10) for use in the thermal processing of a component (1) such as an aero-engine turbine or compressor blade. The apparatus (10) comprises holding means (13) for retaining a first part of the component (1) in a fixed position and forming means (21) spaced from the holding means (13) and adapted to hold a second part of the component (1) in a desired position and/or orientation relative to the first part. In use, a component (1) is mounted within the apparatus (10) such that a first part of the component (1) is retained by the holding means (13) in a fixed position. The forming means (21) is then applied to a second part of the component (1) such that it is held in a desired position and/or orientation relative to the first part. The component (1), whilst held in the apparatus (10) is then subjected to thermal treatment, eg by being placed in a preheated oven, typically at 500-700 °C for a period of several hours.

Description

Title: Thermal Processing Apparatus and Method

This invention relates to the thermal processing of components which have become deformed in use. It is particularly applicable to the reforming of aero- engine turbine or compressor blades and the like.

Aero-engine turbine and compressor blades are manufactured with very precise shapes and dimensions. However, wear and physical damage occur during use of the blades and this necessitates replacement or repair. Because of the cost of replacement, it is desirable to repair such damaged blades wherever possible and so it is standard practice for damaged compressor blades to be reformed, rather than simply replaced. The shape of the blade may be characterised by angular parameters (eg that known as "stagger angle") which may be measured at one or more positions along the length of the blade. In order for a reformed blade to be acceptable these parameters must be measured and must fall within precisely defined tolerances.

The stages in the repair of a damaged compressor blade generally vary, depending on whether the blade has suffered damage resulting in the loss of metal, or has simply been deformed. Where the blade has simply been deformed, it may be subjected just to reforming. However, where the blade has been damaged, the damaged portion of the blade will typically be cut away and a piece of replacement metal welded onto the blade, the replacement piece of metal then being machined to match the contour of the original blade. The repaired blade is then reformed to the precise original shape. Even where the machined blade has the desired shape, it will generally still be required to undergo stress relief thermal treatment and this may lead to the introduction of deformity.

It is known to reform components such as aero-engine turbine or compressor blades by placing the component in a chamber containing a ceramic die having a surface contour which corresponds to the desired shape of the component. The component rests on the die and is covered by an inert material. The chamber is then sealed, pressure is applied and the die is heated to a sufficient temperature for the component to re-adopt the desired shape.

The prior art process of the type described suffers from the disadvantages that it requires the preparation of precisely formed dies. In order to achieve a sufficiently high throughput of components, a correspondingly high number of such dies is required and this is expensive. Furthermore, the reformed components are generally only acceptable if they conform to precisely defined tolerances and the failure rate using the known reforming method may be too high.

There have now been devised improved apparatus and methods for thermal processing of components such as aero-engine turbine and compressor blades which overcome or substantially mitigate the above or other disadvantages.

According to the invention, there is provided apparatus for use in the thermal processing of a component such as an aero-engine turbine or compressor blade, which apparatus comprises holding means for retaining a first part of the component in a fixed position and forming means spaced from the holding means and adapted to hold a second part of the component in a desired position and/or orientation relative to the first part.

The apparatus according to the invention is advantageous primarily in that it can be used to hold the component in the desired form whilst subjected to thermal treatment which causes the component, if initially deformed, to revert to that form and to retain that form during processing and after removal from the apparatus. The apparatus is relatively inexpensive and can be configured in such a way as to accommodate several components at once, leading to the possibility of relatively high throughput of components. The proportion of components which are successfully reformed to within acceptable tolerances may also be higher than is the case for the prior art.

The apparatus conveniently takes the form of a component holder of box section form. In such a case, one internal wall of the holder may be provided with sockets adapted closely to receive one end of components to be reformed, and the opposite wall is provided with openings through which the components project. Most preferably, forming members which engage the projecting part of the components are mounted externally on that wall in fixed locations and act upon the projecting components in such a manner as to retain or bring the components into the desired shape.

In the particular case of aero-engine turbine or compressor blades, the sockets mounted within the component holder are preferably dimensioned and configured closely to receive the blade root. The forming members are preferably plates with openings which correspond to the desired contour of the blade, such plates being fitted over the projecting ends of the blades. Means are provided to position the plates in the desired positions on the component holder and to lock them in that position. In the case of a deformed blade, this will generally necessitate the application of some force to the plate so as to twist the blade into the desired form, the blade then being held in that form by locking of the plate to the component holder.

According to another aspect of the invention there is provided a method for the thermal processing of a component such as an aero-engine turbine or compressor blade, which method comprises the steps of a) mounting the component in apparatus as defined above such that a first part of the component is retained by the holding means in a fixed position, b) applying the forming means to a second part of the component such that it is held in a desired position and/or orientation relative to the first part, and c) subjecting the component, whilst held in the apparatus, to thermal treatment at elevated temperature.

The thermal treatment is preferably carried out under non-oxidising conditions, eg under vacuum or in an inert atmosphere, eg an atmosphere of a gas such as argon. The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which

Figure 1 is a side view of an aero engine compressor blade such as may be reformed by the method of the invention;

Figure 2 is a view of the compressor blade of Figure 1 from above;

Figure 3 is an end view of a blade holder forming part of processing apparatus according to the invention;

Figure 4 is a plan view of an end portion of the blade holder of Figure 3;

Figure 5 is a plan view of a forming plate used in association with the blade holder of Figures 3 and 4; and

Figure 6 is a sectional view on the line VI-VI in Figure 4, showing also a forming plate engaged with the blade holder.

Referring first to Figures 1 and 2, an aero engine compressor blade such as may be reformed using the apparatus and method according to the invention is generally designated 1 and comprises a blade portion 2 and a blade root 3 by which the blade 1 is located in the engine. The blade portion 2 is relatively thin and has a complex twisted shape. In use, the blade portion 2 is liable to become deformed and/or damaged, eg by impact with foreign objects (commonly birds) or as a result of high temperatures and loads to which the blade 1 is exposed. For economic reasons, it is standard practice for damaged compressor blades to be reformed, rather than simply replaced. The shape of the blade may be characterised by angular parameters (eg that known as "stagger angle") which may be measured at one or more positions along the length of the blade. In order for a reformed blade to be acceptable these parameters must be measured and must fall within precisely defined tolerances.

In the case of a blade which has suffered damage resulting in the loss of metal, the damaged portion of the blade is cut away and a piece of replacement metal welded onto the blade, the replacement piece of metal then being machined to match the contour of the original blade. The repaired blade is then reformed to the precise original shape. Where the blade has simply been deformed, however, it may be subjected just to reforming.

Figures 3 and 4 show a blade holder 10 which forms part of apparatus by which compressor blades 1 such as that shown in Figures 1 and 2 may be reformed. The blade holder 10 is formed in stainless steel and, as can be seen from Figure 3, is generally of box section. The upper wall 11 of the blade holder 10 is formed with a series of circular openings 12. Figure 4 shows only the end portion of the blade holder 10, with three such openings 12. The actual number of openings 12 in the illustrated embodiment is eight, but any convenient number may be provided, depending on the overall dimensions of the blade holder 10, the size and nature of the blades 1 to be reformed etc.

Each opening 12 defines a station at which a blade 1 may be positioned for thermal processing. At each station a locating socket 13 is fitted to the internal surface of the lower wall 14 of the blade holder 10, in alignment with the respective opening 12 in the upper wall 11. In Figure 4 only one such socket 13 is shown. Each socket 13 is fixed by a pair of lugs 15 which are mounted in bores 16 in the lower wall 14 of the blade holder 10 and engage in corresponding bores in the socket 13, and a pair of threaded screws 17 which pass through countersunk bores 18 in the lower wall and engage in threaded bores in the socket 13. The socket 13 is dimensioned and configured so as closely to receive the blade root 3 of a blade 1 in such a way as to hold the blade root 3 in a fixed orientation relative to the blade holder 10.

Adjacent each opening 12, the upper wall 11 of the blade holder 10 is provided with a pair of upstanding bosses 19 mounted in bores 20 in the upper wall 11 of the blade holder 10. In use, the bosses 19 engage the forming plate 21 shown in Figure 5. The forming plate 21 is generally rectangular and, like the blade holder 10 and other components, is formed in stainless steel. The outlines of the forming plates 21 are shown in faint lines in Figure 4.

As can be seen in Figure 5, the forming plate 21 has a generally central area 22 which is recessed and within which an opening 23 is cut. The opening 23 has elongate limbs which correspond precisely to the desired shape of compressor blades 1 which are to be processed, at the level of the forming plate 21 when the blade 1 is loaded into the blade holder 10.

The forming plate 21 is also provided with a pair of openings 24 which enable the forming plate 21 to be fitted over the bosses 19. The openings 24 are formed in part with a pair of orthogonal flat surfaces such that engagement of the bosses 19 with those flat surfaces produces precise positioning of the forming plate 21 in both X- and Y- dimensions.

The forming plate 21 is also provided with a pair of slots 25 which, in use, are aligned with corresponding slots 26 formed in the upper wall 11 of the blade holder 10. As shown in Figure 6, wedges 27 are inserted through the slots 25 in the forming plate 21 and the slots 26 in the upper wall 11 of the blade holder 10. Insertion of the wedges 27 in this manner forces the forming plate into the desired orientation, with the bosses 19 abutting the flat surfaces of the openings 24.

In use, blades 1 to be processed are inserted into some or all of the stations corresponding to the openings 12 in the blade holder 10. The blades 1 are held by the blade roots 3 in the locating sockets 13. Forming plates 21 are then fitted over the tips of the blades 1 , which project through the openings 12. In the case of deformed blades, the orientation of the forming plates 21 will differ somewhat from the desired orientation. To bring the forming plates 21 into that desired orientation (and hence to bring the blades 1 into the desired configuration) wedges 27 are inserted through the slots 25 and 26.

The blade holder 10 loaded with blades 1 in this fashion is then introduced into an oven which is preheated to a temperature in the range 500-700°C. Heating at such a temperature for a sufficient period, typically from 2-24 hours, (generally under vacuum or in an inert atmosphere) leads to reforming of deformed compressor blades 1 by a creep forming process, the blades 1 adopting a shape determined by the fixed orientations of the locating sockets 13 and forming plates 21. Blades 1 which had the correct shape when introduced into the apparatus are held in that shape so that the generation of deformities during the thermal treatment process is prevented.

The blade holder 10 is removed from the oven, the wedges 27 are released and the forming plates 21 removed. The compressor blades 1 are then removed from the blade holder 10 and checked in conventional manner for conformity with permitted tolerances.

Claims

1. Apparatus for use in the thermal processing of a component such as an aero-engine turbine or compressor blade, which apparatus comprises holding means for retaining a first part of the component in a fixed position and forming means spaced from the holding means and adapted to hold a second part of the component in a desired position and/or orientation relative to the first part.

2. Apparatus as claimed in Claim 1 , which is in the form of a component holder of box section.

3. Apparatus as claimed in Claim 2, wherein one internal wall of the holder is provided with sockets adapted closely to receive one end of components to be reformed, and the opposite wall is provided with openings through which the components project.

4. Apparatus as claimed in Claim 3, which is for the thermal processing of a aero-engine turbine or compressor blade, and wherein the sockets mounted within the component holder are dimensioned and configured closely to receive the root of such a blade.

5. Apparatus as claimed in Claim 3 or Claim 4, wherein forming members which engage the projecting part of the components are mounted externally on said opposite wall in fixed locations and act upon the projecting components in such a manner as to retain or bring the components into the desired shape.

6. Apparatus as claimed in Claim 5, wherein the forming members are plates with openings which correspond to the desired contour of the component, such plates being fitted over the projecting ends of the components.

7. Apparatus as claimed in Claim 6, wherein means are provided to position the plates in the desired positions on the component holder and to lock them in that position.

8. Apparatus as claimed in Claim 7, wherein said means comprise projections mounted on the component holder and corresponding openings formed in the plates, within which openings the projections are received.

9. Apparatus as claimed in Claim 8, wherein said projections are of at least part-circular cross-section and said openings are formed with a pair of orthogonal flat surfaces such that engagement of the projections with those surfaces brings about precise positioning of the plates in two orthogonal dimensions.

10. Apparatus as claimed in any one of Claims 7 to 9, wherein said means further comprise corresponding apertures in the component holder and the plate which are adapted to be brought into registration and thereby to position the plate upon the component holder.

11. Apparatus as claimed in Claim 10, wherein the plate is positioned upon the component holder by means of locating members driven through the apertures.

12. Apparatus as claimed in any preceding claim, which is of stainless steel.

13. A method for the thermal processing of a component such as an aeroengine turbine or compressor blade, which method comprises the steps of a) mounting the component in apparatus as claimed in any preceding claim such that a first part of the component is retained by the holding means in a fixed position, b) applying the forming means to a second part of the component such that it is held in a desired position and/or orientation relative to the first part, and c) subjecting the component, whilst held in the apparatus, to thermal treatment at elevated temperature.

14. A method as claimed in Claim 13, wherein the thermal treatment is carried out under non-oxidising conditions.

15. A method as claimed in Claim 14, wherein the thermal treatment is carried out under vacuum or in an inert atmosphere.

16. A method as claimed in any one of Claims 13 to 15, wherein the elevated temperature is in the range 500-700°C.

17. A method as claimed in any one of Claims 13 to 16, wherein the component is subjected to thermal treatment for a time period in the range 2- 24 hours.