WO2012076876A1

WO2012076876A1 - Fire-protected composite structure

Info

Publication number: WO2012076876A1
Application number: PCT/GB2011/052413
Authority: WO
Inventors: Giovanni Marengo; Paul Clarke; Matthew Denmead; Gary Wiles; Robert Eggleton
Original assignee: Gkn Aerospace Services Limited
Priority date: 2010-12-07
Filing date: 2011-12-06
Publication date: 2012-06-14
Also published as: GB2486404A; GB201020739D0

Abstract

A fire-protected composite structure (2, 6) comprises a composite component (32, 62) having a first surface (34, 64) and a hot sprayed metallic layer (36, 66) is deposited on the first surface ((34), (64). In the event of a malfunction which generates a flame, the outer surface( 34, 64) is offered some fire protection by the hot sprayed metallic layer (36, 66). The layer (36, 66) acts as a physical barrier stopping the flame from directly acting on the composite material and also, because the metal or metal alloy of the layer (36, 66) has good thermal conductivity, the layer (36, 66) conducts the heat of the flame away from the point of impingement of the flame on the composite material, thus stopping or slowing the thermal degradation of the matrix (resin) of the composite material.

Description

Fire-protected composite structure

Field of the Invention The present invention relates to a composite structure such as a containment case for a gas turbine engine.

Background Characteristics of composite materials have meant that composite components are employed in an increasing range of applications from aerospace to automotive parts.

In the aerospace industry, for example, composite materials have been used for a number of years owing to their strength to weight ratio. The term "composite materials" (known also as "composites") is used to describe materials comprising for example glass fibre or carbon fibres and an epoxy resin (or similar). These are also known as glass reinforced plastic or carbon fibre reinforced composites. The carbon fibre reinforced composite material offers improved properties such as lower weight, improved fatigue/damage resistance, corrosion resistance and negligible thermal expansion.

The use of these materials has increased throughout the aerospace industry predominantly because of the fuel savings which can be achieved over the life of an aircraft by reducing the overall sum weight of the components making up the aircraft. Aerodynamic as well as structural components are formed of composite materials and particularly carbon fibre materials.

A composite component may be laid-up using a cloth, tape or the like pre-impregnated with resin to form a stack corresponding to the desired shape of the part to be formed. The stack is then cured either at ambient temperature and pressure or at elevated temperature and pressure in an autoclave to create a hardened component. A gas turbine engine such as a turbofan may be provided with a containment case for preventing a broken blade of the engine from exiting the engine and damaging the rest of the aircraft. For example, a containment case may be provided around the fan at the front of the turbofan engine. The containment case may be made of composite material such as carbon fibre reinforced composite material and/or Kevlar reinforced composite material. The containment case is in the shape of a generally cylindrical barrel or housing with a flange at one or both of the ends for attaching the containment case to adjacent structural components of the engine. The composite material of the containment case has a typical maximum operating temperature of 136°C. If there is a malfunction in the engine, the composite material may be exposed to a torching flame. For example, accessories such as an electronic engine controller may be mounted on the outside of the containment case together with large oil reservoirs. If the engine controller malfunctions, it may act as the source of a fire, and oil escaping from the reservoirs could then sustain the fire. The resulting torching flame will char the resin in the composite material. The reinforcement (the carbon fibre and/or the Kevlar) will remain but will no longer be supported by the resin matrix, and thus the reinforcement and the composite material will lose mechanical strength. It would be desirable to improve the fire-resistance of components that are already made of composite material. Improved fire resistance would also enable composite material to be used to make a wider range of components. For example, there are many components in the aerospace industry, and particularly components in aero-engines, that are not currently made of composite material because they must maintain structural integrity in the event of a fire. These components are therefore currently made of metal, and it would produce a weight saving if these components could be switched from being made of metal to being made of composite material.

Summary of the Invention

According to a first aspect of the present invention, there is provided a fire-protected composite structure comprising: a composite component having a first surface; and a hot sprayed metallic layer deposited on the first surface of the composite component. The hot sprayed metallic layer protects the first surface of the composite component from direct exposure to any flame produced as a result of a malfunction in the vicinity of the composite structure and helps to conduct the heat of the flame away from the point of impingement of the flame on the composite structure.

For example, when the composite structure is installed in a gas turbine engine, the hot sprayed metallic layer may face into a void such as an internal cavity of a fancase or a fan duct and any flame that appears in the void and impinges on the composite structure will damage the composite structure less and/or damage it more slowly.

In a preferred embodiment, the first surface is annular and the hot sprayed metallic layer is an annular layer. In a preferred embodiment, the composite component comprises a tubular main body and the first surface is a tubular surface of the main body.

For example, it is usually possible to use a machine to lay-up composite material in an annular configuration, because a rotatable mould may be used, and a machine such as an automated tape laying (ATL) machine can rotate the mould and the head of the machine lays-up the composite material on the mould. After the composite material has been cured, the machine could be fitted with a hot metal spraying head and the metallic layer could then be sprayed on in an annular configuration as the mould is rotated. To avoid the need to switch heads, the machine could be provided with two heads or one head that combines both functions of tape- laying and metal spraying.

It may only be necessary to protect the part or parts of the first surface that are likely to be exposed to a flame in the event of a malfunction. Alternatively, substantially the entire first surface could be covered with the hot sprayed metallic layer.

In a preferred embodiment, the first surface is a radially-outwardly facing surface. Such a surface may be easier to hot metal spray than an inwardly-facing surface in relation to providing access for a spray head. The composite component that is protected may be a containment case or an outer guide vane of an aero-engine. The composite material of the composite component may be carbon fibre in a suitable resin matrix such as epoxy resin.

The hot metal sprayed layer may be copper or copper alloy such as copper-manganese alloy. According to a second aspect of the present invention, there is provided a gas turbine engine comprising a composite structure in accordance with the first aspect of the present invention.

According to a third aspect of the present invention, there is provided a containment case for a gas turbine engine, comprising an annular housing made of composite material and having an annular external surface; and a hot sprayed metallic layer deposited on the annular external surface of the housing.

In a preferred embodiment, the annular housing has first and second opposite ends and the hot sprayed metallic layer is deposited on the annular external surface as an annular layer extending from the first end to the second end of the housing. The hot sprayed metallic layer may cover substantially the entire external surface of the annular housing. Alternatively, some area(s) of the external surface could be masked off so that they are not sprayed if they do not need to be protected. In a preferred embodiment, a first annular flange is integral with an end of the housing and is made of composite material; and a hot sprayed metallic layer is deposited on the first flange. In many embodiments a continuous layer is used to form the hot sprayed metallic layers on the first flange and on the housing. In a preferred embodiment, a second annular flange is integral with the end of the housing opposite to the first annular flange and is made of composite material; and a hot sprayed metallic layer is deposited on the second flange. In many embodiments a continuous layer is used to form the hot sprayed metallic layers on the second flange and on the housing. In a preferred embodiment, an annular internal surface of the housing does not have a hot sprayed metallic layer deposited thereon. If in use the internal surface will be shielded by other components or the internal volume will be sealed from exposure to any flame in the event of a malfunction, there is no need to protect the internal surface. In any event, spraying an internal surface can be difficult in terms of access for the spraying equipment.

In a preferred embodiment, the or each composite material is carbon-fibre reinforced composite. It is convenient to be able to use the same machine to machine lay-up in a continuous operation all of the composite material of the housing and the flange(s).

In a preferred embodiment, the matrix of the composite material is epoxy resin.

In a preferred embodiment, the or each hot sprayed metallic layer comprises copper or copper alloy. Thus, for example, the same spray head may be used to spray the housing and the flange(s).

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a diagrammatic side view of a turbofan engine, partly cut away to show a containment case, a fan blade and an outer guide vane.

Fig. 2 is a diagrammatic perspective view of the containment case of Fig. 1 which is an embodiment of a fire-protected composite structure in accordance with the present invention.

Fig. 3 is a cross-sectional enlargement of the part of the wall of the containment case circled with dashed line in Fig. 2 showing the hot sprayed metallic layer which provides the fire protection feature. Fig. 4 is a diagrammatic perspective view of the outer guide vane of Fig. 1 which is an embodiment of a fire-protected composite structure in accordance with the present invention.

Fig. 5 is a cross-sectional enlargement of the part of the wall of the outer guide vane circled with dashed line in Fig. 4 showing the hot sprayed metallic layer which provides the fire protection feature.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description of the specific embodiments are not intended to limit the invention to the particular forms disclosed. On the contrary, the invention covers all modifications, equivalents and alternatives falling within the spirit and the scope of the present invention as defined by the appended claims. Description of Embodiments

Fig. 1 is a diagrammatic side view of a turbofan engine 1 having a fan case 11 defining a fan duct 12 which contains a rotating disc of fan blades 13. The fan blades 13 rotate around a central longitudinal axis 14 of the engine 1.

The fan case 11 is annular and is centred on the longitudinal axis 14. The fan case 11 is shown partly cut away in Fig. 1 in order to diagrammatically illustrate the fact that the fan case 11 includes an annular containment case 2 positioned around the periphery of the disc of fan blades 13 in order to contain any broken fan blade 13. The containment case 2 comprises a generally-cylindrical barrel or housing 3 at the front end of which is an outwardly-extending annular flange 41 and at the rear end of which is an outwardly-extending annular flange 42.

The containment case 2 is centred on the longitudinal axis 14 of the engine 1 and is held in position by being fastened to other components of the fan case 1 1 such as an annular front inlet 51 and an annular rear case 52. The flanges 41 and 42 may be provided with holes for fasteners which are used to attach the containment case 2 to the structure of the front inlet 51 and the rear case 52. The engine 1 has an core engine 15 which is connected to the fan case 11 by a plurality of circumferentially spaced-apart outer guide vanes 6 which extend radially outwards from the core engine 15 to the rear case 52. There is a generally-enclosed void or space 16 between the containment case 2 and an annular outer fairing 17 of the fan case 11. Ancillary components of the engine are located in the void 16 such as an electronic engine controller 18 and an oil reservoir 19.

Fig. 2 is a diagrammatic perspective view of the containment case 2 of Fig. 1. The housing 3 is shown as being exactly cylindrical with a circular cross-section, but it could be varied to be slightly tapered in the direction of the longitudinal axis 14 and/or to have a non-circular cross- section such as an oval cross-section. The actual internal contour or profile of the housing 3 may be optimised to suit the requirements of a particular engine 1. The housing 3 comprises an annular wall 31 made of composite material and incorporating a fire protection system. Fig. 3 is a cross-sectional enlargement of the part of the wall 31 circled with dashed line in Fig. 2 and shows the hot sprayed metallic layer which provides the fire protection characteristic. The wall 31 comprises an annular wall portion 32 which is made of composite material and has a generally-cylindrical inner surface 33 and a generally-cylindrical outer surface 34. The composite material may be carbon fibre reinforced composite material and/or Kevlar reinforced composite material. The composite material is in the form of pre-impregnated unidirectional tape containing any suitable thermosetting resin such as epoxy resin and may be laid-up on a mould or mandrel by an ATL machine. The machine may lay-up the plies 35 of composite material to form a stack having the required depth with the tape of the plies being laid-up circumferentially of the central axis 14 and obliquely to the central axis 14.

After the wall portion 32 has been cured, it is hot sprayed (flame sprayed) with a metal or metal alloy such as copper or copper alloy such as copper-manganese alloy. Copper and copper alloy are relatively cheap and provide a relatively uniform coating when sprayed. Also, if any areas are not to be sprayed and therefore masking is to be used, copper and copper alloy work well when being sprayed against mask(s) defining the area(s) that are to be spray coated. The copper or copper alloy also conforms well to the curved shape of the outer surface 34 onto which it is being sprayed.

A suitable spraying gun is the Mark 66E-Man produced by Metallisation Limited of Dudley, West Midlands, United Kingdom in combination with its associated control equipment. The spraying gun may make repeated passes over the outer surface 34 to build up the required thickness of the hot sprayed metallic layer 36 that is deposited on the outer surface 34. The layer 36 may be 0.05 mm thick, but may range from 0.01 to 0.5 mm in thickness, or from 0.03 to 0.2 mm in thickness. The exact thickness can be chosen depending on the thermal conductivity that is required and the spraying gun can be programmed to make the necessary number of passes to build up that thickness. The hot spraying produces a coating having particles with a mean diameter typically between 30-150 μιη.

The hot spraying leaves the layer 36 having a generally-cylindrical outer surface 361 which provides the outer surface of the wall 31. The hot sprayed metallic layer 36 is left as the outermost or external layer of the wall 31 and is not shielded by other coatings or layers. This enables the layer 36 to perform its fire protection function in an effective manner when exposed to a flame because the layer 36 is in direct contact with the flame. The layer 36 may cover the entire surface of the outer surface 34 and is thus an annular layer extending from the front end 321 to the rear end 322 of the wall portion 32. If complete coverage is not required for some reason, then one or more areas 323 could be masked off during the hot spraying so that they are not covered with the hot sprayed metallic layer 36. The flanges 41 and 42 are made of the same composite material as the housing 3 and are integral with the front and rear ends 321, 322 of the wall portion 32. The hot sprayed metallic layer 36 may be extended forwards and rearwards to cover the outwardly-facing surfaces of the flanges 41 and 42. The inner surface 33 of the wall portion 32 is not sprayed because it is, in use, covered with components such as a forward acoustic panel, an impact liner which carries an abradable liner on its inner peripheral surface, and a rear acoustic panel. Thus a flame is not able to impinge directly on the inner surface 33. With reference to Fig. 1, the situation may be considered of the engine controller 18 malfunctioning and becoming hot and starting a fire in the void 16. The fire may damage the oil reservoir 19 and the leaking oil could then sustain the fire. The engine controller 18 and oil reservoir 19 are located on or adjacent to the wall 31 of the housing 3 and the composite material of the wall is vulnerable to being damaged by the fire. The outer surface 34 of the wall portion 32 is offered some fire protection by the hot sprayed metallic layer 36. The layer 36 acts as a physical barrier stopping the flame from directly acting on the composite material and also, because the metal or metal alloy of the layer has good thermal conductivity, the layer 36 conducts the heat of the flame away from the point of impingement of the flame on the composite material, thus stopping or slowing the thermal degradation of the matrix (resin) of the composite material.

Figs. 2 and 3 show an example of applying a fire or flame protection system to an aerospace component such as a fan case that is usually made of composite material.

Figs. 4 and 5 show an example of applying the present invention to an aerospace component that is not usually made of composite material. Fig. 4 is a diagrammatic perspective view of the outer guide vane 6 shown Fig. 1. Such a component is usually made of metal because it needs to maintain its structural integrity in the event of being exposed to a flame in the fan duct 12 such as might occur in the event of a malfunction in the core engine 15. The outer guide vane 6 is made of composite material and incorporates a fire-protection layer.

The outer guide vane 6 is in the form of a strut or pylon and comprises a tubular wall 61. Fig. 5 is a cross-sectional enlargement of the part of the wall 61 circled with dashed line in Fig. 4 and shows the hot sprayed metallic layer which provides the fire protection characteristic.

The wall 61 comprises an annular wall portion 62 which is made of composite material and has an inner tubular surface 63 and an outer tubular surface 64. The plies 65 of the composite material may be laid-up and cured in the same general manner as discussed above in relation to the wall portion 32.

After the wall portion 62 has been cured, it is hot sprayed (flame sprayed) with a metal or metal alloy such as copper or copper alloy such as copper-manganese alloy to deposit a hot sprayed metallic layer 66 on the outer surface 64, in the same general manner as discussed above in relation to the layer 36.

The hot spraying leaves the layer 66 having an annular outer surface 661 which provides the outer surface of the wall 61. The hot sprayed metallic layer 66 is left as the outermost or external layer of the wall 61 and is not shielded by other coatings or layers. This enables the layer 66 to perform its fire protection function in an effective manner when exposed to a flame in the fan duct 12 because the layer 66 is in direct contact with the flame. The layer 66 may cover substantially the entire area of the outer surface 64 and is thus an annular layer extending from one end 621 to the other end 622 of the wall portion 62. If complete coverage is not required for some reason, then one or more areas could be masked off during the hot spraying so that they are not covered with the hot sprayed metallic layer 66. The inner surface 63 of the wall portion 62 is not sprayed because it is, in use, part of a sealed void into which a flame from a malfunctioning core engine 15 cannot easily enter. Thus a flame is not easily able to impinge directly on the inner surface 63.

In the event of the core engine 15 malfunctioning and a flame bursting into the fan duct 12, the outer surface 64 of the of the wall portion 62 is offered some fire protection by the hot sprayed metallic layer 66. The layer 66 acts as a physical barrier stopping the flame from directly acting on the composite material and also, because the metal or metal alloy of the layer 66 has good thermal conductivity, the layer 66 conducts the heat of the flame away from the point of impingement of the flame on the composite material, thus stopping or slowing the thermal degradation of the matrix (resin) of the composite material.

Because the outer guide vane 6 now has an enhanced fire protection characteristic by virtue of the hot sprayed metal layer 66, the outer guide vane 6 may be manufactured from composite material (in relation to the structural component, i.e. the wall portion 62) instead of being manufactured from metal. Thus the outer guide vane 6 has a reduced weight.

There have been described embodiments of a fire-protected composite structure 2, 6 comprising: a composite component 32, 62 having a first surface 34, 64; and a hot sprayed metallic layer 36, 66 deposited on the first surface 34, 64 of the composite component 32, 62.

There have been described embodiments of a containment case 2 for a gas turbine engine 1, comprising: an annular housing 3 made of composite material and having an annular external surface 34; and a hot sprayed metallic layer 36 deposited on the annular external surface 34 of the housing 3.

Claims

1. A fire-protected composite structure comprising:

a composite component having a first surface; and

a hot sprayed metallic layer deposited on the first surface of the composite component.

2. A fire-protected composite structure according to claim 1, wherein the first surface is annular and the hot sprayed metallic layer is an annular layer.

3. A fire-protected composite structure according to claim 1 or 2, wherein the composite component comprises a tubular main body and the first surface is a tubular surface of the main body.

4. A fire-protected composite structure according to claim 2 or 3, wherein the first surface is a radially-outwardly facing surface.

5. A fire-protected composite structure according to any preceding claim, wherein the composite component is an outer guide vane of an aero-engine.

6. A fire-protected composite structure according to any one of claims 1 to 4, wherein the composite component is a containment case of an aero-engine.

7. A fire-protected composite structure according to any preceding claim, wherein the composite component comprises carbon-fibre reinforced composite.

8. A fire-protected composite structure according to any preceding claim, wherein the composite component comprises matrix material which is epoxy resin.

9. A fire-protected composite structure according to any preceding claim, wherein the hot sprayed metallic layer comprises copper or copper alloy.

10. A gas turbine engine comprising the fire-protected composite structure of any one of the preceding claims.

11. A containment case for a gas turbine engine, comprising:

an annular housing made of composite material and having an annular external surface; and

a hot sprayed metallic layer deposited on the annular external surface of the housing.

12. A containment case according to claim 11, wherein the annular housing has first and second opposite ends and the hot sprayed metallic layer is deposited on the annular external surface as an annular layer extending from the first end to the second end of the housing.

13. A containment case according to claim 11 or 12, wherein:

a first annular flange is integral with an end of the housing and is made of composite material; and

a hot sprayed metallic layer is deposited on the first flange.

14. A containment case according to claim 13, wherein:

a second annular flange is integral with the end of the housing opposite to the first annular flange and is made of composite material; and

a hot sprayed metallic layer is deposited on the second flange.

15. A containment case according to any one of claims 11 to 14, wherein an annular internal surface of the housing does not have a hot sprayed metallic layer deposited thereon.

16. A containment case according to any one of claims 11 to 15, wherein the or each composite material is carbon-fibre reinforced composite.

17. A containment case according to any one of claims 11 to 16, wherein the or each composite material comprises matrix material which is epoxy resin.

18. A containment case according to any one of claims 11 to 17, wherein the or each hot sprayed metallic layer comprises copper or copper alloy.

19. A containment case substantially as herein described with reference to, or with reference to and as illustrated in, the accompanying drawings.

20. An outer guide vane substantially as herein described with reference to, or with reference to and as illustrated in, the accompanying drawings