GB2415471A

GB2415471A - A fire resistant seal assembly

Info

Publication number: GB2415471A
Application number: GB0421527A
Authority: GB
Inventors: Richard Robson Cochrane
Original assignee: Dunlop Aerospace Ltd
Current assignee: Dunlop Aerospace Ltd
Priority date: 2004-06-23
Filing date: 2004-09-28
Publication date: 2005-12-28
Anticipated expiration: 2024-09-28
Also published as: GB0414077D0; GB0421527D0; GB2415471B

Abstract

A fire resistant seal assembly 10 extends between a surface of a container containing combustible fluid (e.g. an engine nacelle) 15 and a surface 17 of a composite duct member 18, the seal assembly including a resilient 'Z' seal element 11, a fire resistant curtain 12 and a clamping means 13 acting as a connection means. The seal member 11 has first and second end portions 14, 16 with one edge portion 22 of the curtain 12 being secured to the first end portion 14 of the element 11, which forms a seal with the container 15, and the other edge portion of the curtain and the second end portion 16 of the element 11 both being secured by connection means 13 to the surface 17 of the duct member 18.

Description

FIRE RESISTANT SEAL ASSEMBLY

Where components are attached to an aircraft engine to provide ancillary functions to the engine it is common practice to use seals between the component and the engine to prevent accidental flow of fluids into or out of the engine. Such seals used for the attachment of components to the aircraft engines operate under arduous conditions and seal integrity is critical to aircraft safety.

In service, there could be an event where seals can be exposed to a fire within the engine when the aircraft engine is on the ground and the engine has been shut down. To assess fire resistance of seals there are standard 5 and 15 minute tests in accordance with ISO 2685:1992. After test expose time the flame source is removed and the seal should show no evidence of flame penetration and there should be no or limited residual burning of the seal.

Fire resistant seals are known and simple hollow section seals with fire resistant properties are disclosed in US 3934889 and US 5251917. These seals have a multi-layer construction, the middle layer being a fire resistant felt or fibre. Fire resistant sleeving is also known for providing a sheath over cables, tubes or hose-like components.

Seals used for attachment of components to aircraft engines can be of a simple "O" ring form, a tubular form or a more complex "Z" seal type. The complexity of the seal required for an application depends on factors such as the width of gap to be sealed, movement to be taken up in the seal and pressure differential across the seal. Applications for "Z" seals would typically take up movement of up to 5 cm. Known solutions for providing fire resistance in seals are not applicable to the more demanding sealing applications requiring a "Z" seal.

In one aspect the invention provides a fireproof seal assembly to extend between a surface of a container containing a combustible fluid and a surface of a member spaced from the container, the seal assembly comprising (i) a resilient seal element having a first and a second end portion and (ii) a fire-resistant curtain, one edge portion of the curtain being secured to the first end portion of the element which, in use, is connected to the container and the other edge portion of the curtain, and the second end portion of the element being in use both secured by connection means to the surface of the member.

Preferably the resilient seal element is of generally Z shape, having an inclined bridging portion between the two end portions which are generally parallel.

Preferably the Z element is made from a silicon rubber base reinforced with woven glass fibre and Nextel fabric with an outer covering on the fire side of metallised Nextel fabric.

The curtain may be continuous sheet or it may be made of two or more portions which together form the curtain. Overlapping portions may be present.

Preferably the curtain is made of silicone rubber containing fibreglass insulation. It may also be metallic or include a gauze. In one specific case the curtain is made of portions of mineral insulation encapsulated between dimpled stainless steel foil.

In another aspect of the invention there is provided an assembly comprising a container of combustible fluid and a member spaced therefrom by a gap wherein a fireproof seal assembly as defined above extends between the container and the member across the gap.

Preferably the container is an aircraft engine.

Preferably the gap between the engine and the member is up to about 5 cm.

In another aspect there is provided a method of mounting a fireproof seal assembly between a container containing a combustible fluid and a surface of a member spaced from the container, the seal assembly comprising a resilient seal element and a fire curtain, the element having a first end portion and a second end portion, the method comprising securing an edge portion of the curtain to the first end portion of the element and securing the second end portion of the element and the second edge portion of the curtain to the surface of the member by connection means.

Preferably the connection means comprises a male part which is passed through a hole in the member and is held thereto by engaging means on the side of the member remote from the seal.

In order that the invention may be well understood it will now be described by way of illustration only with reference to the accompanying diagrammatic drawings in which: Figure 1 is a vertical sectional view through a fireproof seal assembly of the invention; Figure 2 is a vertical sectional view through another fireproof seal assembly of the invention; Figure 3 is a vertical sectional view through a third fireproof seal assembly of the invention; Figure 4 is a vertical sectional view through a fourth assembly of the invention; and Figure 5 is a vertical sectional view of another assembly of the invention.

The fire resistant seal assembly 10 of Figure 1 includes a "Z" seal member 11, a fire-resistant curtain 12 and a clamping means 13 acting as a connection means. The "Z" seal member 11 is manufactured from a silicon rubber base reinforced with woven glass fibre and Nextel fabric with an outer covering of metallised Nomex fabric to provide electrical conductivity. The "Z" seal has moulded thereto a thicker cross-section end portion 14 for sealing to the surface 15 which, in this example, is the surface of an engine nacelle.

A fire-resistant curtain 12 is manufactured from fire-resistant material such as silicone rubber embedded with heavyweight fibreglass insulation. An example of such a material is supplied by Hydrapower Dynamics Limited of Birmingham, United Kingdom as a "Firesleeve Protective Sleeving" product for hoses, pipes and cables. The Firesleeve comprises a heavyweight fibreglass insulation embedded within a smooth silicone rubber and is claimed by the supplier to be resistant to temperature extremes up to 11 00 C.

The opposite end portion 16, the upper as shown, is held against the face 17 of a composite duct member 18 by the clamping means 13 which comprises a clamping ring 19 and threaded studs 20. The clamping means 13 also retains the fire-resistant curtain 12. A hole is present in the upper portion 16 and the edge portion of the curtain. Clamping ring 19 is normally manufactured in a metallic material such as stainless steel and has attached to it a plurality of stainless steel threaded studs 20 mounted by inserting through holes (not shown) in the clamping ring 19 and spot welded in place. (Other materials could be used for the clamping ring and studs such as ceramics or polymer composites, as could other methods of joining the studs to the clamping ring, for example, bonding).

The "Z" seal is fixed to the composite duct member 18 by inserting the threaded studs 20 through aligned holes and fasteners 21 to engage with the threads (not shown) on the threaded studs 20.

The fire-resistant curtain 12 is attached to the "Z" seal by bonding at region 22 and to the clamping ring structure 13. The fire-resistant curtain 12 may contain holes (not shown) to allow for the expansion and contraction of the seal without collapsing or ballooning the fireresistant curtain 12 or "Z" seal member 11. The fire-resistant curtain is illustrated for this example fitted on the outer periphery of the seal and has been found to enhance the fire resistance of the "Z" seal considerably, even though it is the "Z" seal that is exposed to the flame source.

A further feature of this assembly is a titanium shield 23, held in place on the composite duct by fasteners 21. The titanium shield provides protection to the edges of the composite duct 18 against damage from fire and gives secondary protection of the "Z" seal member 11 where it is joined to the composite duct. The titanium shield 23 could be manufactured from a different metal such as steel or a ceramic or composite material but titanium is preferred for its low weight, retention of mechanical properties at elevated temperatures and stability in this operating environment.

The seal assembly 30 of Figure 2 comprises a "Z" seal mounted to a composite duct member 31 by fastening means 32 and sealing against an engine nacelle 33. The fire-resistant curtain 34 of Figure 2 is attached at the composite duct end of the "Z" seal assembly by clamping on the upper face 35 of the composite duct 31 and held in place by fixings 36. A bead of fire- resistant sealant 37 is applied along the joint between the fire- resistant curtain 34 and the "Z" seal member 38.

The seal assembly 40 of Figure 3 comprises the features of Figure 1 with a modified titanium shield. The titanium shield 41 of Figure 3 is extended at section 42 over the outer surface 43 of the fire-resistant curtain 44.

The assembly can be formed in a variety of ways. For example, the member 18 may be movable, in which case one end portion of the seal is placed on the surface 15 and the other end portion and the curtain are connected to the member 18 which is then secured in position.

This is done by passing the male member through aligned holes in the components and through a hole in the member 18 and then affixing the nut, so subjecting the seal to compressive forces. (The drawings show the seal assembly stylistically and the seal bridge portion 11 and the curtain may not be aligned as shown.) The different embodiments and curtain free seal were subjected to a 5 minute fire exposure test conducted in accordance with ISO 2685:1992. Results are given in the following Table.

TEST SEAL TEST RESULT

Baseline "Z" Seal After-burn of seal for 20 minutes _... . _. . . . . __. .. . Example 1 (Figure 1) After-burn of seal for 80 seconds Example 2 (Figure 2) After-burn of seal for 60 seconds Example 3 (Figure 3) After-burn of seal for 30 seconds The "Z" seal contact feature identified as 14 in Figure 1 and present in Figure 2 and Figure 3 seals against the surface of the engine nacelle to provide a conductive path from the conductive material of the "Z" seal member in such events as lightening strikes.

The invention is not limited to the embodiments shown. For example, in embodiments shown the fire-resistant curtain member is illustrated as being sealed to the "Z" seal member on the opposite surface to the seal face but this is not necessarily so.

In the assembly of Figure 4, the seal is as shown earlier, but the curtain consists of an upper fire shield portion 50A and a lower such portion SOB. The uppermost portion 50C of portion 50A is anchored to the outer edge of the duct flange and extends downwardly; the lowermost portion 50D of the lower portion 50C is anchored to the end portion of the seal. The portions can slide relative to each other and are made of mineral insulation encapsulated between dimpled foils made of stainless steel.

In the assembly of Figure 5 the fire curtain is one piece of a thin type of gauze shield.

LS/BW3.8.04 P5086GB.Des

Claims

1. A fireproof seal assembly to extend between a surface of a container containing a combustible fluid and a surface of a member spaced from the container, the seal assembly comprising (i) a resilient seal element having a first and a second end portion and (ii) a fire-resistant curtain, one edge portion of the curtain being secured to the first end portion of the element which, in use, is connected to the container and the other edge portion of the curtain and the second end portion of the element being in use both secured by connection means to the surface of the member.

2. An assembly according to Claim 1, wherein the resilient seal element is of generally Z shape, having an inclined bridging portion between the two end portions which are generally parallel.

3. An assembly according to Claim 2, wherein the Z element is made from a silicon rubber base reinforced with woven glass fibre and Nextel fabric with an outer covering on the fire side of metallised Nextel fabric.

4. An assembly according to any preceding Claim, wherein the curtain is made of silicone rubber containing fibreglass insulation, is metallic or includes a gauze.

5. An assembly according to any preceding Claim, wherein the curtain is made of mineral insulation encapsulated between dimpled stainless steel foil. v q

6. An assembly according to any preceding Claim, wherein the container is an aircraft engine.

7. An assembly according to Claim 6, wherein the gap between the engine and the member is up to about 5 cm.

8. A method of mounting a fireproof seal assembly between a container containing a combustible fluid and a surface of a member spaced from the container, the seal assembly comprising a resilient seal element and a fire curtain, the element having a first end portion and a second end portion, the method comprising securing an edge portion of the curtain to the first end portion of the element and securing the second end portion of the element and the second edge portion of the curtain to the surface of the member by connection means.

9. A method according to Claim 8, wherein the connection means comprises a male part which is passed through a hole in the member and is held thereto by engaging means on the side of the member remote from the seal.