GB2402643A - A welding process using a cooling chamber - Google Patents

Abstract

A welding region is cooled by a coolant in a chamber 44 achieved by sealing (30) housing 28 to a workpiece 4. The process and apparatus may be used when welding a passage element 10 to a workpiece 4 having a metallic substrate 24 provided with a thermal barrier coating 26, to prevent spalling of the coating. The workpiece 4 may be a wall of a combustion engine of a gas turbine engine, and the passage element 10 may comprise a dilution chute which is to be welded to the wall 4. A passage 16 in the passage element 10 is preferably plugged by a closure element 48 to prevent the coolant the passage 16. The housing 28 is preferably clamped on the workpiece 4.

Description

A WELDING PROCESS

This invention relates to a welding process, and is particularly, although not exclusively, concerned with a welding process conducted on a component which may be adversely affected by the heat generated during welding.

Some components, for example components used in the aerospace industry, are provided with thermal barrier coatings (TBCs) which may comprise plasma-sprayed ceramic materials. A bond coat may be provided between the substrate material (usually metal) and the TBC to accommodate differential thermal expansion between the substrate and the coating. Nevertheless, when subjected to the intense heat of welding, there is a danger that the coating will crack and flake off, an effect known as "spelling". This problem arises in particular in the overhaul of combustion chambers for gas turbine engines. Such combustion chambers are conventionally made from alloys which are resistant to very high temperatures, and are coated, on the internal surfaces, with a TBC. In order to reduce the temperature of combustion gases emerging from the combustion chamber before they reach the turbine stage of the engine, combustion chambers often have dilution chutes, which allow cool air to be admitted to the combustion chamber to dilute the hot combustion gases.

The dilution chutes are welded to the wall of the combustion chamber and, during overhaul, are usually replaced. The heat generated during the welding of the new dilution chutes tend to cause spelling of the TBC.

Attempts have been made to alleviate this problem by applying a copper chill to the internal surface of the combustion chamber during welding. However, the copper chill draws the welding heat through the TBC and so does not effectively prevent spelling.

According to the present invention there is provided a welding process conducted on a component, in which process a chamber is formed between the component and a - 2 housing which sealingly contacts the component, and in which coolant is supplied to the chamber to cool the component.

If the component comprises a metallic substrate with a TBC, a process in accordance with the present invention enables the TBC to be effectively cooled so as to prevent spelling, while welding takes place on the metallic substrate. In such a process, the housing contacts the TBC.

The housing may be in the form of a cup having an open face, the cup being sealed to the component at the open face.

If the component has an aperture in the region exposed to the chamber, the aperture may be closed by a suitable plug, throughout the welding process, so as to avoid the escape of coolant through the aperture. The aperture may receive a passage element to be welded to the component in the welding process, in which case the plug closes the passage in the passage element.

According to another aspect of the present invention, there is provided apparatus for use in a welding process as defined above, the apparatus comprising a housing having an open face, sealing means extending around the periphery of the open face to form a seal against a component to be welded, the apparatus further comprising securing means for securing the housing to the component and supply means for supplying coolant to the housing.

The securing means may comprise a clamping mechanism for securing the housing to the component. The clamping mechanism is preferably disposed outside the housing, and may comprise at least one draw bar for engagement with the component to secure the housing to the component. The draw bar is preferably connected to a clamping member which is attached to the housing at an end region of the housing opposite the open face so that the housing is clamped between the component and the clamping member. In a preferred embodiment, two draw bars are provided on opposite sides of the housing. 3

The apparatus may comprise a plug for closing a passage extending through the component. In a preferred embodiment, the plug comprises a closure element for sealingly engaging one end of the passage, and a reaction element, connected to the closure element, for engaging the opposite end of the passage. The closure element and the reaction element may be connected to each other by a screwthreaded mechanism so that the elements may be moved towards and away from each other to engage and disengage the ends of the passage.

The reaction element may be provided with at least one peripheral recess to provide access to the underlying component for welding.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a partial sectional view of a combustion chamber of a gas turbine engine; Figure 2 is a sectional view of apparatus in use in a welding operation performed on a combustion chamber wall; Figure 3 is a plan view of a component of the assembly of Figure 2; and Figure 4 shows part of the assembly of Figure 2.

Figure 1 shows an annular combustion chamber having inner and outer walls 2, 4 disposed within a casing 6. A fuel supply arrangement 8 is mounted on the wall 6 for delivering fuel to the combustion chamber.

The walls 2, 4 are made from a substrate 26 of metallic material, such as a temperature-resistant alloy which is provided on the surface facing inwardly of the - 4 combustion chamber with a TBC 28, for example of plasma-sprayed ceramic material.

The outer wall 4 is provided with a circumferential array of dilution chutes 10 through which dilution air can pass from the space between the casing 6 and the outer wall 4 to the interior of the combustion chamber, in order to cool the combustion gases before reaching the turbine stage of the engine, represented by an array of fixed nozzle guide vanes 12.

The dilution chutes 10 (see Figure 2) each comprise a cylindrical portion 14 providing a passage 16, and a flange 18 at one end. Each dilution chute 10 is fitted into an aperture 20 in the outer wall 4, and secured in place by welds 22 around the periphery of the flange 18.

In service, combustion chambers, including the dilution chutes 1O, become degraded and consequently the dilution chutes are replaced during periodic overhaul of the combustion chambers. This entails removing each dilution chute 10 and replacing it by a new one.

In order to weld a replacement dilution chute 10 to the outer wall 4 without spelling of the thermal barrier coating 26, the apparatus shown in Figure 2 is used. This apparatus comprises a cup-shaped housing 28 having an open face surrounded by a peripheral edge carrying a seal 30. The housing 28 has a coolant inlet 32 and a coolant outlet 34 of larger diameter than the inlet 32. A clamping member in the form of a bar 36 is secured to the housing 28, for example by welding, at an end opposite the open face surrounded by the seal 30. A pair of draw bars 38 are fixed to the clamping bar 36. As shown in Figure 2, the draw bars extend through pre-existing holes 40 in the outer wall 4, and receive nuts 42 which are tightened to press the open face of the housing 28 into firm contact with the TBC 26. The housing 28 and the region of the outer wall within the seal 30 thus form a chamber 44.

The apparatus also comprises a plug assembly 46. Before the housing 28 is fitted, the replacement dilution chute 10 is placed in the aperture 20 and the plug assembly 46 is installed. The plug assembly 46 comprises a nut 48 having a continuous sealing - 5 surface 50. A draw bar 52 is secured to the nut 48 and, in the assembled condition shown in Figure 2, extends through the passage 14 to project beyond the plane of the outer wall 4. A washer 54 having a central aperture 56 is placed over the draw bar 52 in contact with the flange 18 of the dilution chute 10. A nut 58 is placed on the draw bar 52 and tightened so as to bring the seat 50 into sealing contact with the lower end of the cylindrical portion 14, so isolating the passage 16 from the chamber 44.

As shown in Figure 3, the washer 54 has a generally circular periphery with three equally spaced recesses 60. As can be appreciated from Figure 2, these recesses leave exposed portions of the flange 18 for welding, as indicated by a welding gun electrode 62.

In operation, the apparatus comprising the housing 28 and the plug assembly 46 is assembled as shown in Figure 2, and coolant, for example liquid CO2 or another suitable gas or liquid is supplied to the chamber 44 through the inlet 32. The coolant fills the chamber 44, so directly contacting the TBC 26, and can be discharged through the outlet 34. The flange 18 is then welded to the metallic substrate 24 of the outer wall 4 at the locations exposed by the recesses 60 in the washer 54. Thus, with a washer as shown in Figure 3, three welds 22 are formed around the periphery of the flange 18.

Since any heat generated by the welding operation is rapidly removed by the coolant in the chamber 44, an excessive increase in temperature of the thermal barrier coating 26 is avoided, so that spelling is prevented.

The coolant outlet 34 has a larger capacity than the inlet 32 to enable coolant to drain away safely without creating high pressure within the chamber 44 in the event of, for example, vaporization of a liquid coolant.

By isolating the passage 16 from the chamber 44, leakage of coolant into the region of the welding operation is avoided, so that welding can take place safely. / - 6

Claims (19)

1 A welding process conducted on a component, in which process a chamber is formed between the component and a housing which sealingly contacts the component, and in which coolant is supplied to the chamber to cool the component.

2 A process as claimed in claim 1, in which the housing is in the form of a cup having an open face, the housing being sealed with respect to the component at the open face.

3 A process as claimed in claim 1 or 2, in which the region of the component which is exposed to the chamber is provided with an aperture, which aperture is plugged during the welding process.

4 A welding process as claimed claim 3, in which a passage element is disposed within the aperture, the passage element being welded to the component in the welding process, a passage in the passage element being plugged during the welding process.

A welding process as claimed in any one of the preceding claims, in which a thermal barrier coating is present on the face of the component exposed to the chamber.

6 A welding process as claimed in any one of the preceding claims, in which the component is a wall of a combustion chamber of a gas turbine engine.

7 A welding process as claimed in claim 6 when appendant to claim 4, in which the passage element comprises a dilution chute.

8 A welding process as claimed in claim 1 and substantially as described herein. l

9 Apparatus for use in a welding process in accordance with any one of claims 1 to 8, the apparatus comprising a housing having an open face, sealing means extending around the periphery of the open face to form a seal against a component to be welded, the apparatus further comprising securing means for securing the housing to the component and supply means for supplying coolant to the housing.

Apparatus as claimed in claim 9, in which a clamping mechanism is provided for securing the housing to the component.

11 Apparatus as claimed in claim 10, in which the clamping mechanism is disposed for engagement with the component at a position outside the housing.

12 Apparatus as claimed in claim 10 or 11, in which the clamping mechanism comprises at least one draw bar connected to the housing for engagement with the component.

13 Apparatus as claimed in claim 12, in which the draw bar is mounted on a clamping member which is secured to the housing at an end region of the housing opposite the open face.

14 Apparatus as claimed in any one of claims 9 to 13, in which a plug is provided for closing a passage extending through the component.

Apparatus as claimed in claim 14, in which the plug comprises a closure element for sealing engagement with an end of the passage.

16 Apparatus as claimed in claim 15, in which a reaction element is connected to the closure element for engagement with the other end of the passage. - 8

17 Apparatus as claimed in claim 16, in which the reaction is connected to the closure element by a screwthreaded mechanism.

18 Apparatus as claimed in claim 17, in which the reaction element is connected to the closure element by a screwthreaded draw bar.

19 Apparatus as claimed in any one of claims 16 to 18, in which the reaction element is recessed to expose a welding region.

Apparatus for use in a welding process, the apparatus being substantially as described herein with reference to, and as shown in, Figures 2 to 4 of the accompanying drawings.