WO1995029575A1

WO1995029575A1 - Corrosion resistant gasket for aircraft

Info

Publication number: WO1995029575A1
Application number: PCT/US1995/004862
Authority: WO
Inventors: Patrick W. Gaines; Mickey A. Williamson
Original assignee: The Boeing Company
Priority date: 1994-04-26
Filing date: 1995-04-21
Publication date: 1995-11-02
Also published as: AU2425495A

Abstract

A corrosion resistant gasket for aircraft, and more particularly to encapsulation of a conductive mesh in a pliable gel that will not become bonded to mating surfaces and will also migrate upon compression during installation to the threads of attaching hardware utilized between the instrument, antenna, and aircraft structure, thereby reducing corrosion through the attaching hardware, by providing a hermetic seal around the periphery of the envelope of the attached device.

Description

CORROSION RESISTANT GASKET FOR AIRCRAFT

RELATED APPLICATIONS

This is a continuation-in-part application, Serial No. 08/233,869 filed April 26, 1994 which is a continuation-in-part of application Serial No. 07/932,098 filed August 19, 1992.

BACKGROUND OF THE INVENTION

This invention relates to a corrosion resistant gasket for aircraft, and more particularly to encapsulation of a conductive mesh in a pliable gel that will not become bonded to mating surfaces and will also migrate upon compression during installation to the threads of attaching hardware utilized between the instrument, antenna, and aircraft structure, thereby reducing corrosion through the attaching hardware, by providing a hermetic seal around the periphery of the envelope of the attached device.

Present methods of providing coupling between mating surfaces in aircraft having aluminum structures were limited to the uses of elastomer gaskets, metallic gaskets using sealants, or a multiple use of corrosion inhibitors and plating. The elastomer gaskets would allow moisture between the mating surfaces and tended to become bonded to the two surfaces after a period of time. The metallic gaskets also had a permanent bonding problem due to the application of adhesives to reduce the moisture ingress between the two surfaces. Both elastomer and metallic gaskets tended to shift the frequency of antenna installations due to the gap they created between the two mating surfaces, causing a shift in the VSWR of the antenna. The use of the corrosion resistant compounds and sealants creates a time consuming process in application and removal and tend to crack during structure flexing, thereby allowing moisture to ingress between the mating surfaces and causing a breakdown of the inhibitors.

Also, most gaskets presently used have a base material so dissimilar to aluminum that they thereby cause galvanic corrosion, rather than prevent it, die to the fact that they cannot provide a hermetic seal by themselves and require the use of an outside sealant which when used in high vibration areas or under flexing conditions tends to crack and thereby introduces an electrolyte that creates a galvanic cell.

Other alloy meshes such as Monel, a nickel plated copper alloy manufactured by The Chomerics Co. of Woburn, Massachusetts, embedded in non- compressible silicone gels are dissimilar metals with respect to aircraft structure or aircraft antenna base, such that they are subject to corrosion themselves or cause additional corrosion through galvanic corrosion when exposed to certain unfavorable environments, and further, since not embedded in a compressible non-conductive carrier, e.g., fluorosilicone gel, cannot provide upon compression the common electrically conductive bonding between mating surfaces and electrically insulative fluorosilicone gel migration to the mounting hardware. Also, it has been proven, both by lab tests and in service applications, that the use of silicone on aircraft in areas where the silicone is either exposed to jet fuel or jet fuel vapors, the silicone deteriorates and consequently the corrosion protection is jeopardized in the use of aircraft applications.

SUMMARY OF THE INVENTION

The present invention provides a gasket which prevents the ingress of moisture and or other contaminates between the surfaces of aluminum causing corrosion or galvanic corrosion in this area. The gasket is constructed so that it eliminates present electrical bonding methods through the attaching screws and provides a positive bond through the structure to the base of the instrument, antenna, and/or aircraft skin lap joints, electrical receptacle outlets, waste outlets, lavatory installations and galley installations. Besides providing electrical bonding through surface to surface contact, eliminating all aspects of corrosion, the gasket is capable of reducing corrosion through the attaching hardware by migrating the insulating properties of the gasket onto the threads of the attaching hardware upon compression. Although the gasket is shown in certain illustrative embodiments herein in aircraft applications, it is also useful in marine applications where salt water corrodes aluminum or steel installations and where maintaining electrically conductive properties between mating surfaces is a serious problem.

By using the present flexible gasket comprising silver-plated stranded aluminum when low electrical bonding resistance is required in certain aircraft installations requiring to be less than 0.02 milliohm encapsulated in a fluorosilicone gel, application time is reduced, as we as removal and elimination of structural and component damage during removal. Since the fluorosilicone gel provides a hermetic seal under high vibration, flexing conditions, aerodynamic conditions of up to 0.8 Mach, and internal aircraft pressure of over 30 P.S.I. , there is no fear of an introduction of either an outside, or inside introduction of an electrolyte that would create a galvanic cell. For the purposes of cost reductions in applications that do not require extremely low bonding resistance requirements, and only need to be less than 1 milliohm, then the metallic mesh or expanded screen can be of the same surface structure type currently used in the manufacture of aircraft structures. This is accomplished by the encapsulation of the resent conductive mesh or screen in a pliable fluorosilicone gel or fluorosilicone thixotropic compound described in Mil-R- 25988, Class I, Grade 40 except that the material is uncatalyzed and unvulcanized so as to provide a hermetic seal rather than an outside environmental seal that will not become bonded to mating surfaces.

The present gasket provides a hermetic seal between two mating surfaces and provides corrosion protection between those surfaces that the pliable material is in contact with, including attaching hardware that is migrated to the threads during mating of the surfaces. The internal mesh or screen provides a positive electrical bond to reduce lightning strike and improve antenna performance.

In contrast to the material described e.g. in U.S. Patent 4,900,877, the insulating material must be made from a fluorosilicone material that may be made from a commercial colloidal substance or from a thixotropic fluorosilicone material that is uncatalyzed, unvulcanized and free from bubbles and voids so as to provide a hermetic seal from the outside environment as well as to contain internal aircraft contaminates from migrating from the connector orifice to the outer edge of the instrument or antenna that the gasket is mated between. The conductive mesh or screen must also have a minimum hole opening of 0.065 inch with a minimum of 8 holes per inch with the X monofilament dimension to be twice that of the Y dimension so as to provide pliable conformity to the aircraft contour and provide surface contact to the mating surfaces at fifteen inch pounds of compression. The conductive material must also be of a low resistance so as to provide the integrity needed for system performance and against the hazards encountered with lightning strike. This precludes the use of any type of material that is identified as E.M.I, shielding material, since these types of materials consist of higher resistive materials such as Monel that provide against high frequency penetration or High Intensity Radiated fields (H.I.R.F.) protection.

With the present gasket, application time is minimal and removal time is equal to the application time, and further, structural and component damage is eliminated during removal.

The present gasket further protects the installation in harsh environments of aircraft fluids, altitude immersions to 75,000 feet, vibration, structural flexing, and temperatures of -65° to 350°F.

DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to embodiments thereof shown for purposes of illustration in the accompanying drawings wherein:

FIG. 1 is an exploded view of the layup of layers of a sandwich structure used to form different geometry gaskets;

FIG. 2 is a gasket having a geometry suitable for a marker beacon antenna subsequent to assembly and die cutting of the sandwich structure layup of FIG. 1:

FIG. 3 is an alternative die cutting of the sandwich structure layup of FIG. 1 having a geometry suitable for an instrument gasket for mounting a total air temperature instrument to an aircraft structure mating surface;

FIG. 4 is an exploded view of a gasket layup according to FIG. 1, utilizing a mesh in the sandwich structure;

FIG. 5 is an exploded view of a gasket layup according to FIG. 1, utilizing a knit in the sandwich structure; and

FIG. 6 is illustrative of the method of assembly of an aircraft antenna to an aluminum outer surface aircraft skin subsequent to removal of release liners from the layup of FIG. 5 and prior to compression of the aircraft antenna to the aircraft surface.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Turning now to FIG. 1, wherein a silver-plated aluminum monofilament is woven into a mesh or knot electrically conductive structure 1 which is seen to be positioned intermediate adjacent layers of compressible gel 2; electrically conductive structure 1 and adjacent layers of compressible gel 2 are then seen to be further sandwiched between liners 3 applied to each side of the outer surfaces of layers of compressible gel 2 to protect layers and the gel 2 mesh 1 structure against contaminants prior to use. The layers 1, 2, and 3 of the sandwich assembly of FIG. 1 are assembled together and die cut out into the geometry of an antenna gasket 14, as shown in FIG. 2. A plurality of holes 12 are suitable positioned in antenna gasket 14 for attaching hardware 22 utilized to attach the antenna 20 (seen in FIG. 6) to the aluminum aircraft skin surface 30.

Gasket 33, of FIG. 3 is die cut from the sandwich assembly layup of FIG. 1 to a geometry suitable for mounting an aircraft instrument to aircraft structure. Gasket 33 includes suitable holes 35 for mounting hardware (not shown) for fastening the instrument down on gasket 33 to the aircraft structure (not shown).

Release liners 3 of FIGS. 1, 4, and 5 is of the type used to protect adhesive transfer on labels. Mesh 5 of the sandwich layup of FIG. 4 is a tight weave, 3 mil. of larger, plated with a 1 mil. silver metal on a 3 mil. aluminum monofilament. In the sandwich layup of FIG. 5, instead of a mesh 4, as in FIG. 4, a knit in the form of a sock 4 is utilized, so that a spacer or non-conductive material can be inserted as shown at 40 between the outer surfaces of sock 4, so that as to make the inserted spacer or non-conductive material conductive and at the same time prevent corrosion between two adjoining parts.

Where a weave sock 4 includes therewithin a non-conductive spacer inserted at 40 between the sides of weave sock 4 and utilized in the gasket assembly of FIG. 6 for fastening antenna 20 down to aluminum aircraft skin surface 30, a conductive corrosion-proof gasket results which eliminates the previous dielectric spacer effect that reduced antenna performance, thereby providing an electrically conductive bonding between the two mating surfaces.

Prior to compression of the gasket assembly of 6 by tightening down of mounting hardware 22 upon aircraft antenna 20 to aluminum aircraft skin surface 30, protective release liners 3 (shown in FIG. 5) are removed, and in the compression step, gel layers 2 are compressed to result in a gasket having a thickness of the center conductive woven silver-plated aluminum monofilament structure of between about 0.31 and 0.010 inches. The present gaskets eliminate any electrolyte between two mating components after compression and achieve one electrical bond between the two mating surfaces. Since the gasket provides a hermetic seal by itself, the need for additional sealants commonly used by other types is not required with the fluorosilicone gel or thixotropic gasket with a conductive inner mesh.

Claims

What is claimed is:

1. A gasket comprising in combination: a woven silver-plated monofilament layer; and, a fluorosilicone gel embedded in said woven silver-plated monofilament layer.

2. The gasket of claim 1 wherein said woven silver-plated monofilament layer comprises a weave 3 mil. or greater of 1 mil. silver-plated 3 mil. aluminum monofilament.

3. A method of electrically conductively bonding opposing mating surfaces comprising the step of: providing a pair of layers of fluorosilicone gel; disposing an electrically conductive woven member between said pairs of layers of fluorosilicone gel; inserting said conductive woven member pair of layers of fluorosilicone gel between the opposing mating surfaces; and then compressing the opposing mating surfaces together, thereby electrically conductively bonding said opposing mating surfaces together.

4. In combination in an aircraft: an aluminum aircraft skin surface; an aircraft antenna; a gasket disposed intermediate said aircraft antenna and said aluminum aircraft skin surface; and, said gasket comprising a woven silver-plated aluminum monofilament structure.

5. The combination according to claim 4 wherein said gasket has a thickness of between about 0.030 and 0.010 inches.

6. A gasket disposed on an aircraft skin surface comprising in combination: a woven monofilament layer comprised of the same material as said aircraft skin surface; and, a fluorosilicone gel embedded in said woven monofilament layer.

7. A method of electrically conductively bonding opposing mating surfaces comprising the steps of: providing a pair of layers of fluorosilicone compound; dispersing an electrically conductive woven member between said pair of layers of fluorosilicone compound; inserting said conductive woven member pair of layers of fluorosilicone compound between the opposing mating surfaces; and, then compressing the opposing mating surfaces together, thereby electrically conductively bonding said opposing mating surfaces together and providing a hermetic seal.

8. In combination in an aircraft are aircraft skin surface; an aircraft antenna; a gasket disposed intermediate said aircraft skin surface; and, said gasket comprising a woven monofilament structure having an electrical bonding resistance of less than one milliohm thereby dispensing lightning change forces exceeding about 200,000 amperes.

9. A method of electrically conductively bonding opposing mating surfaces comprising the step of: providing a pair of layers of thixotropic compound; disposing an electrically conductive woven member between said pairs of layers of thixotropic compound; inserting said conductive woven member pair of layers of thixotropic between the opposing mating surfaces; and then compressing the opposing mating surfaces together, thereby electrically conductively bonding said opposing mating surfaces together.

10. A gasket disposed on an aircraft skin surface comprising in combination: a woven monofilament layer; and, a fluorosilicone thixotropic compound embedded in said woven monofilament layer.

11. A gasket for providing a hermetic seal between two surfaces comprising in combination: a conductive structure disposed between said surfaces for providing electrical contact between said surfaces; a gel for sealing the space between said surfaces; and, said conductive structure having a minimum hole opening of 0.065 inch with a minimum of 8 holes per inch.

12. A gasket for providing a hermetic seal between two surfaces comprising in combination: a conductive structure disposed between said surfaces for providing electrical contact between said surfaces; a gel for sealing the space between said surfaces; and, said gel comprising a thixotropic flurosilicone material.

13. A gasket for providing electrical bonding between two surfaces under compression comprising an expanded aluminum mesh having a monofilament height of 0.016 inch and a thickness of 0.008 inch impregnated with an unvulcanized, uncatalized material in an uncured state.

14. A gasket for electrical bonding between two mating surfaces comprising a knitted aluminum mesh impregnated with a fluorosilicone elastomer.

15. A gasket according to Claim 14 having the further characteristic that when compressed and exposed o temperatures of -65 to 400 degrees F. will not retain memory and further will not adhere to either of said two mating surfaces.

16. A gasket according to Claim 13 that when compressed between said two surfaces forms an outer bead at the edge of said two mating surfaces thereby providing a hermetic seal for eliminating corrosion from outside contaminates.

17. A gasket according to Claim 13 having the further characteristic that when compressed between said two mating surfaces an one surface has an opening for an interconnect forms a seal around the orifice to eliminate corrosion from internal contaminates from migrating from the inside to the anter periphery of said two mating surfaces.

18. A gasket for providing a hermetic seal between two surfaces comprising in combination: a conductive structure disposed between said surfaces for providing electrical contact between said surfaces; a gel for sealing the space between said surfaces; and, said conductive structure having a minimum hole opening of 0.065 inch with a minimum of 8 holes per inch; and, said conductive structure having an X monofilament dimension twice that of the Y dimension thereby providing surface contact to the mating surfaces at fifteen pounds compression.