GB2466298A - Sealing method and apparatus - Google Patents

Abstract

A method of assembling two components 20, 30 together having a hollow seal 32, 40 therebetween, the method comprising the steps of i) at least partially deflating the seal 32, 40 prior to, ii) assembling the two components 20, 30 together and iii) inflating the seal 32, 40 to seal between the components 20, 30. A method for disassembling the two components 20, 30 is also claims in addition to a gas turbine engine comprising two components 20, 30 for assembly together and having a hollow seal 32, 40 therebetween, characterised in that the engine comprises a means 44, 46, 48, 50 for at least partially deflating the seal 32, 40.

Description

SEALING METHOD AND APPARATUS

The present invention relates to a seal arrangement suitable for sealing between two bodies and subject to compression and often shear therebetween.

Components that close together often need to have seals therebetween to prevent fluid or air movement across the boundary. In a gas turbine engine nacelle, this particularly applies to splitter fairings, commonly called C-ducts, that form an aerodynamic cover for services that cross from a core engine to a fan case. An inside surface of the fairing forms part of a fire zone boundary, which means that there must be no significant leakage of flammable fluid. Thus the seals must be sufficiently compressed to ensure that they operate adequately, including taking up movement during normal operation of the engine. There are difficulties in providing this seal compression whilst allowing the parts to be easily installed. This is because the component (including seals) must be forced into a smaller space to provide the required compression.

Conventional elastomeric fire seals are constructed from silicon rubber and fibres and are used widely on aero engines. The fibres are usually glass, ceramic or steel.

Geometric constraints sometimes result in seals closing between surfaces that slide over one another shearing the seal. This shearing often results in severe crimping damage causing leakage and ultimately seal failure. The option to withstand the damage by using heavier duty seals greatly increases the closing load required which further exacerbates the shearing problem and increases the load-carrying requirement and hence cost and weight of the seal and its installation.

This problem is usually solved in a number of ways including forcing the whole assembly into place, designing the parts so that they are assembled into position before locking them together, making seals very flexible, forcing the whole assembly into place. However, there is significant risk of damaging the seals and having non-optimal seal compression. Creasing of seals after assembly of the two components leads to low seal life and inherent ineffectiveness. It is possible to make seals very flexible, but these seals are less able to seal properly and makes them more prone to damage and shortens their service life.

Therefore it is an object of the present invention to provide a method of assembling a seal between two of more components that are brought together, that prevents creasing and does not significantly increase sealing forces to overcome the above mentioned problems.

In accordance with the present invention there is provided a method of assembling two components together having a hollow seal therebetween, the method comprising the steps of i) at least partially deflating the seal prior to ii) assembling the two components together and iii) inflating the seal to seal between the components.

In another aspect of the present invention there is provided a method of disassembling two components from one another and having a hollow seal therebetween, the method comprising the steps of i) at least partially deflating the seal prior to ii) disassembling the two components.

Preferably, the seal comprises a valve and a compression means is moved between one end of the seal and the other end where the valve is positioned.

In accordance with yet a further aspect of the present invention there is provided a gas turbine engine comprising two components for assembly together and having a hollow seal therebetween, characterised in that the engine comprises a means for at least partially deflating the seal.

Alternatively, the seal comprises a first and second chambers and only one of the chambers is deflated by the means for deflating.

Preferably, the means for at least partially deflating the seal comprises a pump.

Alternatively, the means for at least partially deflating the seal comprises mechanical compression means.

The present invention will be more fully described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic section of part of a ducted fan gas turbine engine attached to an aircraft structure; Figure 2 is a section CC in Figure 1 and shows a general configuration of a nacelle having openable C-shaped ducts; Figure 3 is an enlarged view on D in Figure 2 showing a seal between the C-shaped doors and a bifurcation part; Figure 4 is a side view of the seal in Figure 3 that is subject to a closure force and a shearing force; Figure 5 is a view on Arrow C in Figure 3 showing apparatus for removing gas from a seal prior to assembly of the C-shaped doors and a bifurcation part and is in accordance with the present invention; Figure 6 is a cross-section through a first embodiment of a seal in accordance with the present invention; Figure 7 is a cross-section through a second embodiment of a seal in accordance with the present invention.

Referring to Figure 1, a ducted fan gas turbine engine generally indicated at 10 has a principal and rotational axis XX. The engine 10 is attached to the aircraft 9, usually to a wing or fuselage, via a pylon 8.

The engine 10 comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, and intermediate pressure turbine 17, a low-pressure turbine 18 and a core exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and comprises the intake 11, two generally C-shaped ducts 20, which define bypass ducts 22, and an exhaust nozzle 23.

The gas turbine engine 10 works in the conventional manner so that air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first airflow A into the intermediate pressure compressor 13 and a second airflow B which passes through the bypass ducts 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the airflow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines 16, 17, 18 respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

The fan 12 is circumferentially surrounded by a structural member in the form of a fan casing 24, which is supported by an annular array of outlet guide vanes 25.

Engine accessories such as the EEC 26 and oil tank are mounted on the fan casing 24.

In Figure 2 the two generally C-shaped ducts 20 are hinged at the pylon 8 or sometimes at the top of the engine and are rotatably openable to allow access to the engine 10. Such a configuration is well known in the art. The C-shaped ducts 20 close abutting a bifurcation 30 at their free ends 29. There is also a bifurcation at the top dead centre of the engine 10. It is important for the C-shaped ducts 20 and bifurcation 30 to be sealed to prevent air leakage and to act as a fire barrier.

In Figures 3 and 4 the bifurcation 30 is partly formed by a disconnect panel 30, through which electronics and fluid pipes are routed thereby enabling easy disconnect for engine servicing. The disconnect panel 30 has a conventional flexible seal 32 that is made from a generally circular walled and reinforced rubber element. In service it has been found that the closing action of the C-shaped ducts 20, direction indicated by arrow F (also see arrows G and H in Fig 4), against the seal 32 causes the seal 32 to crease, pulling it away from the disconnect panel 30 as shown in region E. In Figure 4, Arrow H shows the direction of the closure force. Thus the compressive load or closure load H is also accompanied by a shear load G. Thus the seal can be broken, allowing leakage to occur with the potential of fire moving across the seal 32 also. This is clearly undesirable.

In addition to the attempts to prevent creasing of the seal mentioned earlier, another prior art solution has been to apply a lubricant to the seal 32 or the free end 29 of the C-shaped ducts 20, however, this is not always carried out during service and has been found to have variable success.

Referring now to a first embodiment of the present invention described in Figures 5 and 6, a seal 40 comprises a generally circular wall 41, forming a chamber 43, and flat extensions 42 to provide a flat bonding surface to the panel 30. The seal 40 is situated between the C-shaped duct 20 and the panel 30. The present invention relates to removal of the air from the chamber 43 to deflate the seal so that it lies flatter against the panel 30 and allows the panel 20 to assume its closed' position, before inflation to form a seal.

Figure 6 schematically shows a number of apparatus to remove some or substantially all the gas/air from the chamber of the seal 40. In a first example, a reversible pump 44 is attached via a pipe 46 to the seal 40. The pump 44 is capable of both evacuating the seal and inflating it.

In another embodiment, the seal 40 comprises a valve 48, preferably at one end of the seal. Here the seal is mechanically compressed, such as with a roller 50, by rolling it along the seal 40 from one end to toward the valve 48. Once evacuated the valve 48 is then closed, the panel 20 is closed or assembled to the component 30 and then the valve 48 released; the seal's elasticity being sufficient for it to self inflate or it may be forcibly inflated.

The present invention also lends itself to a new method of sealing and which comprises the step of removing gas, usually air, at least partly, from the interior of the seal 40. The seal 40 then collapses onto the panel 30 enabling assembly of the C-shaped doors onto the panel or bifurcation part. Gas is then allowed to return into the interior of the seal to inflate it, via inflation means or self-elastic recovery, and provide sealing between the components.

This allows the components to be designed and made as independent items and fitted together without having to be concerned about seal compression. The components may therefore be designed to have a much smaller gap therebetween and hence enable improved fitting or mechanical integrity of for example the nacelle. Therefore there is also a lower risk of seal damage during assembly and the present invention allows quicker and easier assembly giving a cost reduction. Advantageously, the seal is designed optimally for its in-service operation rather than being compromised by assembly considerations.

Referring to Figure 7, the seal 40 is generally an omega' shape in cross-section, similar to the seal in Figure 5, however this seal 40 comprises a first and a second chamber 52, 54. The flat extensions 42 are bonded to the panel 30 to secure the seal in place. The first chamber 52 is adjacent the panel 30 and is inflatable / deflatable via an openable valve 56. The second chamber 54 comprises an array of orifices 58, along the length of the seal, to allow the seal 40 to partially compress when the panels 20 and 30 are brought together. The seal is again made from a resilient material such as an elastomer which biases the seal against the two panels. However, the first chamber 52 is connected to a pump 44 as described above and can partially collapse the seal, allowing partial or even adequate clearance between panels 20, 30 during assembly.

Thus the second chamber 54 is able to accommodate additional compression. The first chamber 52 is about half the volume of the seal and therefore it requires less deflation and inflation reducing operation time and energy consumption.

It should be apparent to the skilled person that other forms of seals and shapes of seals can be substituted provided they are capable of being inflated and deflated in accordance with the scope of the present invention. The seal 40 may be segmented, such that each or one particular segment may be inflated/deflated where necessary.