GB2517473A

GB2517473A - Cap with injected sealant

Info

Publication number: GB2517473A
Application number: GB1314994.3A
Authority: GB
Inventors: Richard Dobbin
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2013-08-21
Filing date: 2013-08-21
Publication date: 2015-02-25
Also published as: GB201314994D0

Abstract

A cap for a fastener with an annular skirt 220 that includes an annular pocket 240 between the skirt and base, an inlet hole 251 that can connect to a sealing material injection device 260 and an outlet hole 270 that can allow air to escape the pocket 240. The inlet and outlet holes 251 270 may be positioned on opposite sides of the cap. The skirt 220 may also include a tubular projection (250 fig 1) leading to the inlet hole 251 that connects to the sealing material injection device 260. The skirt 220 may be integrally formed with the annular base 210. The skirt may have a first part 223 integrally formed with the annular base 210 and a second part 610 made of a different, more flexible, material to the first part 223. The second part 610 may be fitted over the first part 223. The body of the cap may include one or more projections (400 fig 4) that extend into the central cavity. The skirt may have a single outlet hole 270.

Description

CAP WITH INJECTED SEALANT

FIELD OF THE INVENTION

The present invention relates to a cap for forming a sealed cavity around an end of a fastener protruding from a structure. It also relates to a joint with such a cap, and a method of forming such ajoint.

BACKGROUND OF THE iNVENTION

A known cap for forming a scaled cavity around an cnd of a fastcncr protruding from a structure is described in WO-A-2012/107741. The cap has a two part construction with an inner cap and an outer cap. Sealing material is provided between the caps, and the outer cap is pushed down to force the sealing material into an annular pocket and form a seal with the structure.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a cap for forming a sealed cavity around an end of a fastener protruding from a structure. The cap comprises: a cap body with an annular base terminating at a rim which surrounds an opening into a central cavity; an annular skirt providing an annular pocket between the skirt and the base; an inlet hole in the skirt, wherein the inlet hole is in fluid communication with the pocket and arranged to interconnect with a sealing material injection device to provide a flow of sealing material through the skirt via the inlet hole into the pocket; and an outlet hole in the skirt, wherein the outlet hole is in fluid communication with the pocket and arranged to enable air to escape the pocket through the skirt via the outlet hole as the sealing material flows from the inlet hole into the pocket.

A second aspect of the invention provides a joint comprising: a structure; an end of a fastener protruding from the structure; and a cap according to the first aspect forming a sealcd cavity around the end of a fastener, the cap comprising a cured sealing material in the pocket which secures the cap to the structure.

A third aspect of the invention provides a method of assembling such a joint, the method comprising: fitting the cap over the end of the fastener; interconnecting the inlet hole with a sealing material injection device and providing a flow of sealing material from the scaling material injection device through thc skirt via thc inlet hole into the pocket, air escaping the pocket through the skirt via the outlet hole as it does so.

The cap body and the skirt may be formed by separate parts as in WO-A- 2012/107741, but more preferably at least part of the skirt is integrally formed with the annular base (for instance by injection moulding).

The annular skirt typically surrounds a cap axis. The inlet and outlet holes may be positioned side-by-side on the same side of the cap axis, but more preferably they are positioned on opposite sides of the cap axis.

The inlet hole may be just a hole in the skirt which is suitable sized to receive a nozzle of the injection device. However more preferably the skirt comprises a tubular projection which projects outwardly from the skirt and provides an injection channel leading to the inlet hole, and the tubular projection is arranged to interconnect with the sealing material injection device.

The inlet hole, injection channel and tubular projection may be of any shape, but typically they are circular in cross-section.

The rim of the annular base typically lies in a plane. This enables the rim of the annular base to contact a planar surface of the structure around its frill circumference.

The skirt terminates at a skirt rim which may be set back from the rim of the annular base, but more typically it lies in the same plane as the rim of the annular base.

Typically the outboard end of the skirt lies in a first plane and the skirt rim lies in a second plane. Preferably a centre of the outlet hole is positioned closer to the first plane than to the second plane.

In one embodiment the skirt has a first part which is integrally formed with the annular base from a first material and terminates at a first rim which is not in the same plane as the rim of the annular base, and a second part which is formed from a second material which is more flexible than the first material, wherein the second part terminates at the skirt rim which is in the same plane as the rim of the annular base.

The second part may be bonded or otherwise secured to the first part (for instance by two-part moulding) or it may bc fitted over thc first part to form a ncstcd arrangement.

The cap body typically contacts the end of the fastener. Optionally the cap body has one or more projections, the (or each) projection extending inwardly into the central cavity and gripping the end of the fastener. In a preferred embodiment the projections comprise three or more axially extending ribs.

The skirt extends from an outboard end where it meets the cap body, to a skirt rim.

Similarly thc pocket extends from an outboard end proximate the outboard end of the skirt, to an inboard end proximate the skirt rim. The pocket may have a uniform width, or it may have a width which increases as it extends from its outboard end to its inboard cnd.

The skirt may have two or more outlet holes, but this is less preferred than only a single outlet hole. Providing only a single outlet hole ensures that the pocket fills with sealing material (without air gaps) before sealing material is forced out of the outlet hole.

The cured sealing material typically fills the outlet hole and optionally also protrudes out of the outlet hole. The detection of a flow of sealing material out of the pocket through the outlet hole may be used as a trigger to stop the flow of sealing material.

Typically the joint is installed on an aircraft, most preferably where the structure forms part of an aircraft fuel tank.

BRIEF DESCRTPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-section of ajoint taken along a line A-A in Figure 4; Figure 2 is a cross-section taken along the line A-A in Figure 4 before the sealing material has been injected, showing an injection nozzle fined to the cap; Figure 3 is a plan view of the cap; Figure 4 is an underside view of the cap; Figure 5 is a cross-section of an alternative cap; and Figure 6 shows the cap installed on a panel.

DETAILED DESCRIPTION OF EMBODIMENT(S)

A joint 100 shown in Figure 1 comprises a structure 110 such as an aircraft skin panel.

An end 120 of a fastener protrudes from the structure. The fastener comprises an axially extending shaft 121 which passes through the structure 110, a nut 122 screwed onto the shaft 121, and a pair of washers 123, 124 between the nut 122 and the structure 110. The washer 123 has a spherical concave surface 125 which bears against a similarly shaped convex surface 126 of the nut 122, thus enabling the shaft 121 to extend at an acute angle to the surface 110 (rather than at a right-angle as in Figure 1).

A cap encloses the end 120 of the fastener and will be described in detail with reference to Figure 2. The cap has a cap body with a domed outboard (upper) part 200 and a cylindrical base 210 terminating at a rim 211 which surrounds an opening into a central cavity 130. The rim 211 lics in a plane so it can intimately cngagc with the planar surface of the structure 110 around its full circumference when the cap is fitted over the end 120 of the fastener as shown.

The cap body is formed with six axially extending ribs 400 which project inwardly into thc ccntral cavity as shown most clcarly in Figure 4. Thc ribs 400 grip thc cylindrical outer faces of the washers 123,124 as an interference fit, securing the cap in place.

An annular skirt 220 extends from an outboard (upper) end 221 where it meets the cap body to an inboard (lower) skirt rim 222 which lies in the same plane as the rim 211 of the annular base. Like the rim 211, the skirt rim 222 also contacts the planar surface of the structure 110 around the full closed circumference of the skirt rim 222. The skirt has a flared outboard (upper) pad 223 which extends away from the body at an acute angle to a cap axis 230, and a cylindrical inboard (lower) part 224 which extends parallel with the cap axis 230.

An annular pocket 240 is provided between the skirt 220 and the base 210. The pocket 240 extends from a closed outboard end 241 at the outboard end 221 of the skirt, to an open inboard end 242 at the skirt rim 222. Due to the flared shape of the outboard part 223 of the skirt, the pocket 240 has a width which increases as it extends from its outboard end 241 to its inboard end 242.

The skirt has a tubular projection 250 which projects outwardly from the skirt and provides an injection channel leading to a circular inlet hole 251. The tubular projection 250 is arranged to interconnect with a nozzle 260 of a scaling material injection device to provide a flow of scaling material through the skirt via the inlet hole 251 into the pocket 240. In this case they are interconnected by receiving the projection 250 within the nozzle 260, although the opposite arrangement is also possible.

A suitable sealant material is a polysulphide sealant such as Naftoscal (R) MC238B, MC238A, or MC7SO available from Chemetall Group.

The skirt also has a circular outlet hole 270 on an opposite side of the cap axis 230 to the inlet hole 251. The outlet hole 270 is in fluid communication with the pocket 240 and is arranged to enable air to escape the pocket 240 through the skirt via the outlet hole 270 as the sealing material flows from the inlet hole 251 into the pocket. When the pocket is full, thcn the prcssurc in the pocket incrcascs until it forces scaling material to escape the pocket through the skirt via the outlet hole 270. When this flow of sealing material out of the outlet hole 270 is visually observed, the flow of sealing material from the scaling material injection device 260 is stopped and the device 260 is removed.

In an alternative arrangement (not falling within the scope of the present invention) the skirt could be formed with a cut-out in the skirt rim 222 rather than an outlet hole 270 in the body of the skirt in which the outlet hole 270 is a closed hole with a portion of skirt between the outlet hole and the skirt rim. Such a cut-out would permit air to escape the pocket between the skirt rim 222 and the structure, rather than escaping through the outlet holc 270 in thc body of thc skirt. However it would suffer from two problems comparcd with the arrangcmcnt of Figurc 1-4. Firstly thc skirt rim 222 could no longer contact the structure 110 around its full closed circumference.

Secondly, thc position of thc cut-out wodd makc it morc likcy that thc scaling material would escape before the pocket is completely ifill.

The sealing material is then allowed to cure, leaving a cured sealing material 140 (shown in Figure 1) in the pocket which secures the cap to the structure and forms a seal around the cavity 130. This seal prevents the ingress of water or other contaminants into the cavity 230, and also prevents plasma or other out-gassing products from exiting the cavity 230 in the event of a lightning strike. The cured sealing material has a small stub 141 protruding from the outlet hole 270. Cured sealing material also fills the injection channel and the inlet hole 251.

The outlet hole 270 has an axial position which is closer to an axial position of the closed outboard end 241 of the pocket than it is to an axial position of the inboard end 242 of the pocket. In other words, a centrc of the outlet hoic 270 is positioncd closcr to the plane of the outboard end 241 of the pocket than to the plane of the rims 211, 222. Positioning the outlet hole 270 towards the outboard (top) end of the pocket 240 in this way is prcfcrred sincc it ensurcs that thc pockct is completcly frill (without air gaps) bcforc thc scaling matcrial starts to flow out. Also, providing only a singlc outlet hole 270 in the skirt (rather than multiple outlet holes) ensures that the sealing material only starts flowing out when the pocket is completely full.

All parts of the cap are integrally formed by injection moulding or similar. A suitable material is a g'ass filled p&yctherimide (PE!) resin such as Ultem 2400 or Ultcm 2310, available from SABIC Innovative Plastics Holding BY.

An alternative cap is shown in Figures 5 and 6. The flared part 223 of the skirt is integrally formed with the annular base 210 from a first material (such as Vltem 2400 or Ultem 2310) and terminates at a first rim 600 which is set back axially so it is not in the same plane as the rim 211 of the annular base 210. A second part 610 of the skirt is fitted over the flared part 223 to form a nested arrangement. The second part 610 has a hole through which the projection 250 protrudes, and an outlet hole 620 which is aligned with the other outlet hole 270.

The second part 610 is formed from a second material which is more flexible than the material forming the flared part 223, and terminates at a skirt rim 630 which is in the same plane as the rim 211 of the annular base. The structure has a planar part 640 and a raised part 650. The flexible second part 630 of the skirt can flex to form a raised lip 660 where it engages this raised part 650 of the structure. A suitable material for the second part 610 is a chemically resistant elastomer qualified for ifiel tank and adherable to sealant, for example Viton (R) fluoroelastomer available from Du Pont.

Alternatively it could be made from cured sealant using a two stage moulding process.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

Claims 1. A cap for forming a sealed cavity around an end of a fastener, the cap comprising: a. a cap body with an annular base terminating at a rim which surrounds an opening into a central cavity; b. an annular skirt providing an annular pocket between the skirt and the base; c. an inlet hole in the skirt, wherein the inlet hole is in fluid communication with the pocket and arranged to interconnect with a sealing material injection device to provide a flow of sealing material through the skirt via the inlet hole into the pocket; and d. an outlet hole in the skirt, wherein the outlet hole is in fluid communication with the pocket and arranged to enable air to escape the pocket through the skirt via the outlet hole as the sealing material flows from the inlet hole into the pocket.
2. The cap of claim 1 wherein the annular skirt surrounds a cap axis, and the inlet and outlet holes are positioned on opposite sides of the cap axis.
3. The cap of any preceding claim wherein the skirt comprises a tubular projection which projects outwardly from the skirt and leads to thc inlet hole, and the tubular projection is arranged to interconnect with the sealing material injection device to provide the flow of sealing material through the skirt via the inlet hole into the pocket.
4. The cap of any preceding claim wherein at least part of the skirt is integrafly formed with the annular base.
5. The cap of any preceding claim wherein the rim of the annular base lies in a plane, and the skirt terminates at a skirt rim which is in the same plane as the rim of the annular base.
6. The cap of claim 5 wherein the skirt has a first part which is integrally formed with the annular base from a first material and terminates at a first rim which is not in the same plane as the rim of the annular base, and a second part which is formed from a second material which is more flexible than the first material, wherein the second part terminates at the skirt rim which is in the same plane as the rim of the annular base.
7. The cap of claim 6 wherein the second part is fitted over the first part to form a nested arrangement.
8. The cap of any preceding claim wherein the skirt extends from an outboard end where it meets the cap body to a skirt rim, and wherein the pocket extends from an outboard end proximate the outboard end of the skirt rim to an inboard end proximate the skirt rim.
9. The cap of claim 8 wherein the pocket has a width which increases as it extends from its outboard end to its inboard end.
10. The cap of claim 8 or 9, wherein the outboard end of the skirt lies in a first plane and the skirt rim lies in a second plane, and a centre of the outlet hole is positioned closer to the first plane than the second plane.
11. The cap of any preceding claim wherein the cap body further comprises one or more projections, the (or each) projection extending inwardly into the central cavity.
12. The cap of any preceding claim wherein the skirt has only a single outlet hole.
13. A joint comprising: a structure; an end of a fastener protruding from the structure; and a cap according to any preceding claim forming a sealed cavity around the end of a fastener, the cap comprising a cured sealing material in the pocket which secures the cap to the structure.
14. The joint of claim 13 wherein the cured sealing material fills the outlet hole and optionally also protrudes out of the outlet hole.
15. A method of assembling the joint of claim 13 or 14, the method comprising: fitting the cap over the end of the fastener; interconnecting the inlet hole with a sealing material injection device; and providing a flow of sealing material from the sealing material injection device through the skirt via the inlet hole into the pocket, air escaping the pocket through the skirt via the outlet hole as it does so.
16. The method of claim 15 ifirther comprising: detccting scaling material cscaping the pocket through the skirt via thc outlct hole, and stopping the flow of sealing material from the sealing material injectioti device in rcsponse to said dctection.