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Title:
FASTENER CAP ASSEMBLY
Document Type and Number:
WIPO Patent Application WO/2014/118510
Kind Code:
A1
Abstract:
A method of providing a sealed cavity around one end of a fastener (32) passing through a structure (34). A cap assembly is provided. The cap assembly has a base (2) terminating at a base rim (22); a plunger (1) fitted over the base, the plunger comprising a plunger body, and a skirt (8) extending outwardly from the plunger body, the skirt terminating at a skirt rim (11). A bead of sealant material (30) is provided in a pocket (9) defined by the skirt. The plunger or the base comprises a cap (7) with an end wall opposite the skirt rim or the base rim. The structure or fastener is engaged with the base rim, with the bead of sealant material engaging the skirt in the pocket and set back from the structure as the base rim engages the structure or the fastener. The plunger is pushed towards the structure so that the plunger slides axially relative to the base from a first position to a second position, the skirt of the sliding plunger pushing the bead of sealant material in the pocket into engagement with the structure so that the sealant material flows to form a seal against the structure and the cap provides the sealed cavity around the one end of the fastener. Finally the sealant is cured so that the sealant adheres the plunger to the structure.

Inventors:
DOBBIN RICHARD (GB)
CREW DARREN (GB)
Application Number:
PCT/GB2014/050170
Publication Date:
August 07, 2014
Filing Date:
January 22, 2014
Export Citation:
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Assignee:
AIRBUS OPERATIONS LTD (GB)
International Classes:
B64D45/02; F16B33/00; F16B37/14
Domestic Patent References:
WO2012107741A12012-08-16
Foreign References:
DE10148414C12003-03-06
US4659273A1987-04-21
EP2551187A12013-01-30
Attorney, Agent or Firm:
BEATSON, Matthew (Aerospace AvenueFilton, Bristol BS99 7AR, GB)
Download PDF:
Claims:
A method of providing a sealed cavity around one end of a fastener passing through a structure, the method comprising: a. providing a cap assembly comprising: i. a base terminating at a base rim; ii. a plunger fitted over the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt terminating at a skirt rim; and iii. a bead of sealant material in a pocket defined by the skirt, wherein the plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim; b. engaging the structure or the fastener with the base rim, wherein the bead of sealant material is engaging the skirt in the pocket and set back from the structure as the base rim engages the structure or the fastener; c. after step b, pushing the plunger towards the structure so that the plunger slides axially relative to the base from a first position to a second position, the skirt of the sliding plunger pushing the bead of sealant material in the pocket into engagement with the structure so that the sealant material flows to form a seal against the structure and the cap provides the sealed cavity around the one end of the fastener; and d. curing the sealant so that the sealant adheres the plunger to the structure.

The method of claim 1 wherein the skirt rim is set back axially from the base rim and set back axially from the structure when the plunger is in the second position.

3. The method of claim 1 or 2 wherein the cap comprises a cap body surrounding a cap cavity, the end wall closing the cap cavity, the cap body is formed with a stop, and the stop engages the tube when the plunger is in the second position to prevent the plunger from sliding further beyond the second position towards the structure. 4. The method of any preceding claim wherein the plunger has an annular recess or protrusion which is substantially parallel with a plane of the skirt rim, the base has an annular protrusion or recess which is substantially parallel with a plane of the base rim, and the method further comprising interlocking the recess or protrusion in the plunger with the protrusion or recess in the base. 5. The method of claim 3 wherein the recess or protrusion in the plunger interlocks with the protrusion or recess in the base when the plunger is in the first position.

6. The method of claim 3 wherein the recess or protrusion in the plunger interlocks with the protrusion or recess in the base when the plunger is in the second position. 7. The method of any preceding claim wherein after curing in step d the sealant material is adhered to the cap assembly via a first interface and to the structure via a second interface, and an adhesive strength of the first interface is greater than 100N.

8. The method of any preceding claim wherein the plunger body engages the base around a majority of its circumference as it slides axially relative to the base.

9. A cap assembly for forming a sealed cavity around one end of a fastener, the cap assembly comprising: a. a base terminating at a base rim; and b. a plunger which is fitted over the base and slidably movable in an axial direction relative to the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket for receiving a bead of sealant material and terminating at a skirt rim, wherein the base is partially received within the plunger and partially protrudes from the plunger so that the skirt rim is set back axially from the base rim, and the plunger body engages the base around a majority of its circumference; wherein the plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim.

10. The cap assembly of claim 9 wherein the cap comprises a cap body surrounding a cap cavity and an end wall closing the cap cavity, the plunger is slidably movable in an axial direction relative to the base from a first position to a second position in which the skirt rim is set back axially from the base rim, an axial spacing between the rims reducing as the plunger slides axially from the first position to the second position, and the cap body is formed with a stop which engages the base or the plunger when the plunger is in the second position and prevents the plunger from sliding further beyond the second position to further reduce the axial spacing between the rims. 11. A cap assembly for forming a sealed cavity around one end of a fastener, the cap assembly comprising: a. a base terminating at a base rim; and b. a plunger which is fitted over the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket for receiving a bead of sealant material and terminating at a skirt rim, wherein the base is partially received within the plunger and partially protrudes from the plunger so that the skirt rim is set back axially from the base rim; wherein the plunger or the base comprises a cap with a cap body surrounding a cap cavity and an end wall closing the cap cavity, the plunger is slidably movable in an axial direction relative to the base from a first position to a second position in which the skirt rim is set back axially from the base rim, an axial spacing between the rims reducing as the plunger slides axially from the first position to the second position, and the cap body is formed with a stop which is positioned to engage the base or the plunger when the plunger is in the second position and prevent the plunger from sliding further beyond the second position to further reduce the axial spacing between the rims.

12. The cap assembly of claim 10 or 11 wherein the stop comprises a shoulder formed in an inner or outer surface of the cap body.

13. The cap assembly of claim 12 wherein the shoulder is an annular shoulder which extends around a circumference of the inner or outer surface of the cap body.

14. The cap assembly of any of claims 9 to 13 wherein the base is the cap, the plunger comprises an inboard plunger opening, the base comprises an inboard end including the base rim which protrudes from the inboard plunger opening, and the plunger further comprises an outboard plunger opening opposite the inboard plunger opening.

15. The cap assembly of any of claims 9 to 13 wherein the plunger is the cap, and the base comprises an inboard base opening surrounded by the base rim and an outboard base opening surrounded by an outboard base rim, the outboard base opening being opposite the inboard base opening.

16. The cap assembly of any of claims 9 to 15 wherein the plunger has an annular recess or protrusion which is substantially parallel with a plane of the skirt rim, and the base has an annular protrusion or recess which is substantially parallel with a plane of the base rim.

17. The cap assembly of claim 16 wherein the recess or protrusion in the plunger interlocks with the protrusion or recess in the base when the plunger is in the first position.

18. The cap assembly of claim 16 wherein the recess or protrusion in the plunger interlocks with the protrusion or recess in the base when the plunger is in the second position.

19. The cap assembly of any of claims 9 to 18 further comprising a bead of sealant material in the pocket and engaging the skirt.

20. The cap assembly of any of claims 9 to 19 wherein the end wall completely closes an outboard end of the cap.

21. The cap assembly of any of claims 9 to 20 wherein the base has three or more protrusions which extend inwardly into an interior of the base and are spaced apart around a circumference of the interior of the base.

22. The cap assembly of any of claims 9 to 21 wherein the cap assembly is in a non- installed state.

23. A kit of parts for forming a cap assembly according to any of claims 9 to 22, the kit comprising: a. a base terminating at a base rim; and b. a plunger which can be fitted over the base so that it is slidably movable in an axial direction relative to the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket for receiving a bead of sealant material and terminating at a skirt rim; wherein the plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim, and the plunger body and the base are shaped so that the plunger body can engage the base around a majority of its circumference when the plunger is fitted over the base. 24. A kit of parts for forming a cap assembly according to any of claims 9 to 22, the kit comprising: a. a base terminating at a base rim; and b. a plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket for receiving a bead of sealant material and terminating at a skirt rim; wherein the plunger or the base comprises a cap with a cap body surrounding a cap cavity and an end wall closing the cap cavity, the plunger can be fitted over the base so that it is slidably movable in an axial direction relative to the base from a first position to a second position in which the skirt rim is set back axially from the base rim, and the cap body is formed with a stop which is positioned to engage the base or the plunger when the plunger is in the second position and prevent the plunger from sliding further beyond the second position to further reduce the axial spacing between the rims.

25. A joint comprising: a structure; a fastener passing through the structure; and a cap assembly providing a sealed cavity around one end of the fastener, the cap assembly comprising: a. a base terminating at a base rim; and b. a plunger which is fitted over the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket receiving a bead of sealant material and terminating at a skirt rim, wherein the plunger body engages the base around a majority of its circumference; wherein the sealant material in the pocket adheres the plunger to the structure, and the plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim, the cap providing the sealed cavity around the one end of the fastener. 26. The joint of claim 25 wherein the skirt rim is set back axially from the base rim and set back axially from the structure, the cap comprises a cap body surrounding the sealed cavity, the end wall closes the sealed cavity, and the cap body is formed with a stop which engages the base or the plunger to prevent the plunger from sliding axially relative to the base towards the structure to reduce the axial spacing between the rims.

27. A joint comprising: a structure; a fastener passing through the structure; and a cap assembly providing a sealed cavity around one end of the fastener, the cap assembly comprising: a. a base terminating at a base rim; and b. a plunger which is fitted over the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket receiving a bead of sealant material and terminating at a skirt rim; wherein the sealant material in the pocket adheres the plunger to the structure, the skirt rim is set back axially from the base rim and set back axially from the structure, the plunger or the base comprises a cap with a cap body surrounding a cap cavity and an end wall closing the cap cavity, the cap cavity provides the sealed cavity around the one end of the fastener, and the cap body is formed with a stop which engages the base or the plunger to prevent the plunger from sliding axially relative to the base towards the structure to reduce the axial spacing between the rims.

28. The joint of claim 27 wherein the sealant material is adhered to the cap assembly via a first interface and to the structure via a second interface, and wherein a surface area of the first interface is greater than a surface area of the second interface.

29. The joint of any of claims 25 to 28 wherein the sealant material is adhered to the cap assembly via a first interface and to the structure via a second interface, and wherein the first interface comprises a plunger interface between the sealant and the plunger and a base interface between the sealant and the base.

30. The joint of any of claims 25 to 29 wherein the sealant material is adhered to the cap assembly via a first interface and to the structure via a second interface, and wherein an adhesive strength of the first interface is greater than 100N.

Description:
FASTENER CAP ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to a cap assembly for forming a sealed cavity around one end of a fastener, a kit of parts for forming a cap assembly, a method of installing a cap assembly, and a joint formed using a cap assembly.

BACKGROUND OF THE INVENTION

A known cap assembly for forming a sealed cavity around one end of a fastener is described in WO-A-2012/ 107741. The assembly comprises an inner cap member with an annular base terminating at an edge which surrounds an opening into a central cavity, and an outer cap member which fits over the inner cap member. The outer cap member has an annular base which forms an annular flange extending outwardly from the inner cap member at a point which is set back from the edge of the annular base of the inner cap member so as to define a pocket between the flange and the base. A sealant material is provided between the inner plunger member and the outer plunger member. During installation the outer plunger member is pushed down so the sealant material flows into the pocket and adheres the cap to a structure. In one embodiment the outer cap has vanes which engage the inner cap.

Another known cap assembly for forming a sealed cavity around one end of a fastener is described in WO-A-2012/118855. The assembly has an outer cap filled partially with sealant, and an inner collet. The outer cap engages the inner collet via a plurality of lock ribs, and the sealant extrudes between the cap and the collet via the gaps between the lock ribs.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a method of providing a sealed cavity around one end of a fastener passing through a structure, the method comprising: providing a cap assembly comprising: a base terminating at a base rim; a plunger fitted over the base, the plunger comprising a plunger body, and a skirt extending outwardly from the plunger body, the skirt terminating at a skirt rim; and a bead of sealant material in a pocket defined by the skirt, wherein the plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim; engaging the structure or the fastener with the base rim, wherein the bead of sealant material is engaging the skirt in the pocket and set back from the structure as the base rim engages the structure or the fastener; pushing the plunger towards the structure so that the plunger slides axially relative to the base from a first position to a second position, the skirt of the sliding plunger pushing the bead of sealant material in the pocket into engagement with the structure so that the sealant material flows to form a seal against the structure and the cap provides the sealed cavity around the one end of the fastener; and curing the sealant so that the sealant adheres the plunger to the structure.

In WO2012/ 107741 the sealant material is extruded into the pocket through a gap between the inner and outer caps by the action of the outer cap. In contrast with WO2012/ 107741, the sealant material in the method of the present invention is loaded into the pocket before the cap assembly is installed: in other words before the base rim engages the structure or fastener and before the plunger is slid towards the structure. This makes it easier to push the plunger towards the structure since the sealant material does not need to be extruded into the pocket by the action of the plunger.

Preferably the plunger body engages the base around a majority of its circumference as it slides axially relative to the base. This prevent or at least impedes the flow of sealant material into this sliding interface between the plunger and the base.

The invention also provides a cap assembly for forming a sealed cavity around one end of a fastener. The cap assembly comprises: a base terminating at a base rim; and a plunger which is fitted over the base and slidably movable in an axial direction relative to the base, the plunger comprising a plunger body, and a skirt extending outwardly from the plunger body, the skirt defining a pocket for receiving a bead of sealant material and terminating at a skirt rim, wherein the base is partially received within the plunger and partially protrudes from the plunger so that the skirt rim is set back axially from the base rim. The plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim. According to one aspect of the invention the plunger body engages the base around a majority of its circumference. According to another aspect of the invention the cap comprises a cap body surrounding a cap cavity and an end wall closing the cap cavity, the plunger is slidably movable in an axial direction relative to the base from a first position to a second position in which the skirt rim is set back axially from the base rim, an axial spacing between the rims reducing as the plunger slides axially from the first position to the second position, and the cap body is formed with a stop which engages the base or the plunger when the plunger is in the second position and prevents the plunger from sliding further beyond the second position to further reduce the axial spacing between the rims. The cap assembly may comprise a bead of sealant material in the pocket and engaging the skirt. Where the cap assembly is in a non-installed state (that is, when it is not engaged with the structure or the fastener) then the bead of sealant material may be in the pocket when the cap assembly is in such a non-installed state. Alternatively the cap assembly may be provided without sealant in the pocket, the sealant being loaded into the pocket by a user immediately prior to installation.

The invention also provides a kit of parts for forming a cap assembly. The kit comprises: a base terminating at a base rim; and a plunger which can be fitted over the base so that it is slidably movable in an axial direction relative to the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket for receiving a bead of sealant material and terminating at a skirt rim. The plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim.

According to one aspect of the invention the plunger body and the base are shaped so that the plunger body can engage the base around a majority of its circumference when the plunger is fitted over the base.

According to another aspect of the invention the plunger or the base comprises a cap with a cap body surrounding a cap cavity and an end wall closing the cap cavity, the plunger can be fitted over the base so that it is slidably movable in an axial direction relative to the base from a first position to a second position in which the skirt rim is set back axially from the base rim, and the cap body is formed with a stop which is positioned to engage the base or the plunger when the plunger is in the second position and prevent the plunger from sliding further beyond the second position to further reduce the axial spacing between the rims.

The invention also provides a joint comprising: a structure; a fastener passing through the structure; and a cap assembly providing a sealed cavity around one end of the fastener, the cap assembly comprising: a base terminating at a base rim; and a plunger which is fitted over the base, the plunger comprising a plunger body and a skirt extending outwardly from the plunger body, the skirt defining a pocket receiving a bead of sealant material and terminating at a skirt rim, wherein the sealant material in the pocket adheres the plunger to the structure, and the plunger or the base comprises a cap with an end wall opposite the skirt rim or the base rim, the cap providing the sealed cavity around the one end of the fastener.

According to one aspect of the invention the plunger body engages the base around a majority of its circumference.

According to another aspect of the invention the skirt rim is set back axially from the base rim and set back axially from the structure, the cap comprises a cap body surrounding the sealed cavity, the end wall closes the sealed cavity, and the cap body is formed with a stop which engages the base or the plunger to prevent the plunger from sliding axially relative to the base towards the structure to reduce the axial spacing between the rims. The following comments apply to all of the above aspects of the invention.

Preferably the plunger body engages the base around a majority of its circumference when viewed in cross-section transverse to the axial direction. Small gaps may be present (or in the case of the joint, regions of sealant which has flowed from the pocket during installation) but preferably the plunger body engages the base around its entire circumference when viewed in cross-section.

Preferably the plunger body and the base have inner and outer surfaces respectively which are in engagement and have substantially the same shape (for instance circular) around their full circumference when viewed in cross-section transverse to the axial direction. In some embodiments of the invention the plunger body comprises a collar terminating at a plunger rim which surrounds a plunger opening, and the skirt extends outwardly from the body at a point which is set back from the plunger rim so that the pocket is between the collar and the skirt. The point which is set back from the plunger rim is set back in an axial outboard direction, that is a direction which is parallel with an axis of the cap assembly and directed from the opening into the cavity. In other embodiments the plunger body does not have such a collar so the pocket is between the base and the skirt.

The skirt may extend radially at right angles from the plunger body, and then down axially to form the pocket, but more preferably it is flared so that it extends at an acute angle to the body which is less than 90° but greater than 0°. Typically the acute angle is between 20° and 40°.

The stop preferably comprises a shoulder formed in an inner or outer surface of the cap body. Optionally the shoulder is an annular shoulder (which may be circular or non-circular) which extends around a circumference of the inner or outer surface of the cap body. The shoulder may engage an end surface of the base or the plunger, or it may engage a complementary shoulder in the base or the plunger.

The rims may lie in the same plane when the plunger is in the second position, or more preferably the skirt rim is set back axially from the base rim and (in the case of the joint) set back axially from the structure when the plunger is in the second position.

Preferably the plunger has an annular recess or protrusion which is substantially parallel with a plane of the skirt rim, the base has an annular protrusion or recess which is substantially parallel with a plane of the base rim, and the method further comprises interlocking the recess or protrusion in the plunger with the protrusion or recess in the base when the plunger is in the first or second position. The annular recess and protrusion may be circular or non-circular, depending on the shape of the cap assembly. The recess and protrusion ensure that the plane of the skirt rim remains aligned parallel with the plane of the base rim, and can be used to hold the plunger and base securely in place. Where they interlock in the second position, then they can interlock via a "snap-fit" connection which provides a tactile indication to a user that the plunger is in the second position.

Optionally the plunger has three or more annular recesses or protrusions which are substantially parallel with a plane of the skirt rim, the base has three or more annular protrusions or recesses which are substantially parallel with a plane of the base rim, and the method further comprises interlocking the recesses or protrusions in the plunger with the protrusions or recesses in the base as the plunger slides from the first position to the second position. The annular recesses and protrusions may be circular or non-circular, depending on the shape of the cap assembly. Preferably the base is partially received within the plunger and partially protrudes from the plunger opening so that the skirt rim is set back axially from the base rim. Typically the plunger rim lies in a plane which is set back axially from a plane of the base rim.

The plunger may comprise the cap. In this case the base may also comprise a cap but more preferably it is open at both ends - that is the base has a second opening opposite the base rim.

The base may comprise the cap. In this case the plunger is preferably open at both ends - that is the plunger has a second opening opposite the skirt rim.

The sealant material preferably comprises a flowable material such as polysulphide. The bead of sealant material may be contained entirely within the pocket before the plunger is pushed to the second position, or more preferably it protrudes from the pocket.

The end wall may completely close an outboard end of the cap, or it may have one or more small holes which allow air to escape as the plunger is moved to its second position.

Preferably the base has three or more protrusions which extend inwardly into an interior of the base and are spaced apart around a circumference of the interior of the base (which circumference may be circular or any other shape). Typically the fastener is received within the base and engages the base, optionally via the three or more protrusions of the base which extend inwardly into the interior of the base and are spaced apart around its circumference.

Typically the body has an inner face and an outer face, and at least part of the inner face and/or the outer face of the body is substantially cylindrical. Preferably the end wall has a domed shape.

After curing, the sealant material is adhered to the cap assembly via a first interface and to the structure via a second interface. Typically a surface area of the first interface is greater than a surface area of the second interface. The first interface may consist of a plunger interface between the sealant and the plunger, with no interface between the sealant and the base. Alternatively the first interface may comprise a plunger interface between the sealant and the plunger and a base interface between the sealant and the base. Typically an adhesive strength of the first interface, after curing, is greater than 100N and most preferably it is greater than 300N.

Preferably the base rim engages the structure or the fastener. In a preferred embodiment the base rim engages the structure.

The end of the fastener may protrude from the structure, in which case the base rim surrounds the protruding end of the fastener. Alternatively the end of the fastener may lie flush with the structure or be countersunk within the structure, in which case the base rim surrounds the hole in the structure in which the fastener is countersunk. Preferably the plunger does not engage the structure. Preferably the plunger does not engage the fastener. Most preferably the plunger does not engage either the structure or the fastener.

The cap assembly may be provided for the purpose of spark containment, for instance on an aircraft or a fuel tanker. In this case at least part of the structure through which the fastener passes typically comprises a composite material, and the fastener is electrically conductive. The structure may comprise a pure composite material, or a hybrid composite/metal material. Typically the composite material is a laminar fibre- reinforced composite material, where the fibres are a conductive material such as carbon, and the matrix between the fibres has low conductivity. Where the cap assembly is provided for the purpose of spark containment then the sealed cavity provides a volume of air into which plasma, gasses or other bi-products of sparking can be contained. Alternatively the cap assembly may be used to seal the end of a fastener to prevent the ingress of a liquid (such as fuel). In this case the structure may not contain any composite material.

The structure typically comprises a pair of structural parts (for instance panels) which are joined together by the fastener.

The fastener may comprise a shaft with a head at one end; and a collar fitted to a second end of the shaft (the collar may for instance be a nut which is screwed onto the shaft, or a collar which is swaged onto the shaft). The plunger may be used to form a sealed cavity at either the first or second end of such a fastener. The end of the fastener may be housed within the cap assembly, or it may be countersunk within the structure (in which case the end of the fastener will lie outside the cap assembly).

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a kit of parts for forming a cap assembly;

Figure 2 is a cross-sectional view of the cap assembly in a first installation state taken along a line B-B in Figure 3; Figure 3 is a cross-sectional view of the cap assembly taken along a line A-A in Figure 2;

Figure 4 is a cross-sectional view of the cap assembly in a second installation state; Figure 5 is an enlarged cross-sectional view of part of the assembly of Figure 4;

Figure 6 is a cross-sectional view of a cap assembly according to a second embodiment of the invention in a first installation state taken along a line D-D in Figure 7; Figure 7 is a cross-sectional view of the cap assembly taken along a line C-C in Figure 6;

Figure 8 is a cross-sectional view of the cap assembly in a second installation state;

Figure 9 is an enlarged cross-sectional view of part of the assembly of Figure 7; Figure 10 is a cross-sectional view of a cap assembly according to a third embodiment of the invention in a first installation state taken along a line F-F in Figure 11 ;

Figure 11 is a cross-sectional view of the cap assembly taken along a line E-E in Figure 10;

Figure 12 is a cross-sectional view of the cap assembly in a second installation state; Figure 13 is an enlarged cross-sectional view of part of the assembly of Figure 12;

Figure 14 is a cross-sectional view of a cap assembly according to a fourth embodiment of the invention in a first installation state taken along a line H-H in Figure 15;

Figure 15 is a cross-sectional view of the cap assembly taken along a line G-G in Figure 14;

Figure 16 is a cross-sectional view of the cap assembly in a second installation state; and

Figure 17 is an enlarged cross-sectional view of part of the assembly of Figure 16.

DETAILED DESCRIPTION OF EMBODIMENT(S) A kit of parts for forming a cap assembly is shown in Figure 1. The kit comprises a plunger 1 and a base 2, each formed from a moulded polymer such as polyetherimide ULTEM 2400, or an epoxy. The plunger 1 and the base 2 each have an inboard end and an outboard end (at the bottom and top respectively in the orientation of Figure 1).

The plunger 1 has a generally cylindrical body with an outboard part 4a and a collar 4b at its inboard end. Both parts 4a, 4b have substantially cylindrical inner and outer faces. The collar 4b terminates at an annular plunger rim 5 at its inboard end which surrounds a circular plunger opening 6a into a plunger cavity 6. A domed end wall 7 closes the plunger cavity 6 at its outboard end opposite the plunger opening 6a and plunger rim 5. A frustoconical skirt or flange 8 extends outwardly from the outer face of the body at the junction between the parts 4a, 4b, at a point which is set back axially from the plunger rim 5 in the outboard direction. An annular pocket or trough 9 is defined between the outer face of the collar 4b and the inner face of the skirt 8.

The pocket 9 has an annular opening 10 between the plunger rim 5 and a rim 11 of the skirt. A surface area of the pocket 9 (given by the sum of the areas of the cylindrical outer face of the collar 4b and the frustoconical inner face of the skirt 8) is greater than the area of the pocket opening 10. The inner face of the cap body is formed with an annular shoulder 12 running round its circumference. The inner face of the cap body is also formed with series of annular ridges 13 running round its circumference as shown in Figure 2. The shoulder 12 and ridges 13 all lie in planes which are substantially parallel with the plane of the plunger rim 5 and the skirt rim 11. The plunger rim 5 lies in approximately the same plane as the skirt rim 11.

The base 2 has cylindrical inner and outer faces 20, 21, the inner face 20 being shown in Figure 3. The base terminates at a circular inboard base rim 22 which surrounds an inboard base opening, and a circular outboard base rim 24 which surrounds an outboard base opening. Thus the base is open at both its inboard (lower) and outboard (upper) ends. Six semi-cylindrical ridges or protrusions 25 extend inwardly from the inner face 20 of the base into its interior and are spaced apart equally around its circumference. The ridges 25 run along the full axial length of the base. The outer face 21 of the base has a series of annular grooves 26 shown in Figure 2 which lie substantially parallel to the planes of the base rims 22, 24 and match the pitch and shape of the ridges 13 in the plunger.

Prior to installation on a fastener as shown in Figure 2, the plunger 1 is fitted over the base 2 to form a cap assembly shown in Figure 2. The plunger and base are urged together until a number of the annular ridges 13 are received in corresponding annular grooves 26 as shown in Figure 2. The ridges 13 and grooves 26 hold the plunger and base securely in place prior to installation and ensure that the plane of the plunger rim 5 remains aligned parallel with the plane of the base rim 22. In the configuration of Figure 2 the base is partially received within the plunger cavity 6 and partially protrudes from the opening 6a at the inboard end of the plunger cavity so that the plunger rim 5 and skirt rim 11 are set back axially from the base rim 22 in the outboard direction by a distance Dl.

After the plunger has been fitted over the base to form a cap assembly shown in Figure 2, a band of poly sulphide sealant material 30 is installed in the pocket 9. The sealant is extruded from a nozzle to apply a metered quantity into the pocket. As the sealant is extruded, the nozzle and/or the cap assembly is moved so the sealant forms a bead around the full circumference of the pocket 9. The bead over-fills the pocket so that part of the sealant material 30 fills the pocket and part protrudes from the opening 10 of the pocket as shown in Figure 2. The sealant may be applied in a single pass around the pocket or as a series of layers laid down in a series of passes. Optionally the nozzle may be angled at an acute angle to the plunger axis to ensure that sealant is fed all the way into the corner 31 of the pocket. The sealant can be applied immediately prior to installation or could be supplied pre-installed in a frozen state.

The cap assembly is used to form a sealed cavity around a protruding end of a fastener assembly as shown in Figure 2. The fastener assembly comprises a metal bolt 32 passing through a composite panel 34. A washer 35 is fitted onto the protruding part of the bolt 32. An internally threaded metal nut 33 is screwed onto the bolt 32 and compresses the washer 35 against the panel 34. Optionally the washer 35 and nut 33 may have spherical surfaces as described in WO2012/107741 to enable the fastener to be fixed to the panel even though the bolt is not perpendicular to the panel.

In a first installation step shown in Figure 2 the cap assembly is pushed onto the fastener until the inboard rim 22 of the base engages the panel 34. The base 2 is sized so that the protrusions 25 engage the cylindrical outer surfaces of the nut 33 and washer 35 as a frictional or interference fit. The protrusions 25 provide a standoff between the fastener and the inner face 20 of the base. They also grip the fastener so that the cap assembly is prevented from falling off under the action of gravity if the panel 34 is downward facing (that is, if the panel 34 is in the opposite orientation to Figure 2). Next the plunger 1 is pushed inboard towards the panel 34 and slides axially relative to the base from the first position shown in Figure 2 until the shoulder 12 engages the outboard rim 24 of the base in a second position shown in Figure 4. The rims 5, 11 are set back from the base rim by a distance Dl when the plunger is in the first position of Figure 2 and by a smaller distance D2 when the plunger is in the second position of Figure 4.

The skirt 8 of the sliding plunger 1 pushes the sealant 30 against the panel which then flows to form a seal against the panel as shown in Figure 4. The inboard protruding part of the base 2 prevents the flowing sealant from flowing directly into the cavity 6 during this process. In comparison with the outer plunger in WO-A-2012/ 107741, only a relatively small amount of force is required to push the plunger 1 down from the first position of Figure 2 to the second position of Figure 4. The sealant then cures and adheres the cap assembly to the panel 34.

As can be seen in Figure 3, the inner surface of the body of the plunger 1 and the outer surface 21 of the base are both circular when viewed in cross-section transverse to the axis of the cap assembly in the axial direction of motion of the plunger as it is pushed down. These two circular surfaces engage each other as a frictional fit (by way of the ridges 13 and protrusions 26) around substantially their full circumference without any large gaps. When the cap assembly is in a pre-installation state, before the base is pushed onto the fastener, then both the inner surface of the body of the plunger 1 and the outer surface 21 of the base will be substantially the same shape in cross-section (circular in this case). When the base is pushed onto the fastener, then the outer surface 21 of the base will distort slightly from a circular cross-section to form a three-lobed shape (each lobe corresponding with a respective one of the protrusions 25). The body of the plunger 1 is sufficiently flexible that it will also distort slightly so that its inner surface forms a similar three-lobed shape and continues to engage the outer surface 21 of the base around substantially its full circumference.

As the plunger 1 moves from the first position of Figure 2 to the second position of Figure 4, it continues to engage the outer surface 21 of the base (by way of the ridges 13 and protrusions 26) around substantially its full circumference without any large gaps. The absence of such large gaps prevents, or at least impedes, the flow of sealant into the sliding interface between the plunger and the base. If a small amount of sealant does flow into this sliding interface, then this may be beneficial since it creates an additional bond between the plunger and the base. The undulating shape of the interface (created by the interlocking ridges 13 and grooves 26) will tend to prevent sealant from flowing all the way into the cavity 6.

The sealed cavity 6 provided by the cap assembly contains any sparking, plasma or out-gassing caused by a lightning strike. The cap assembly may be immersed in fuel, in which case the sealant also prevents the ingress of fuel into the cavity. Air from the plunger cavity 6 can escape as the plunger is pushed towards the panel by passing through the sliding interface between the base and the plunger and then through the interface between the sealant and the base. Alternatively a small hole may be provided in the apex 7a (Figure 4) of the domed end wall 7 to allow this air to escape more easily. This hole can be filled with polysulphide sealant or epoxy resin after installation to fully seal the cavity 6 around the fastener.

The panel may be flat as shown in Figure 1 or it may have raised features (not shown) on both sides, which may be for example fillets, ribs or spar flanges. The rim of the skirt 8 is set back axially from the panel 34 and the base rim 22 by a distance D2 when the plunger is in the second position of Figure 4 and 5. This enables the plunger to be positioned close to such raised features.

The sealant material 30 is adhered to the cap assembly 1 ,2 via a first interface and to the panel 34 via a second interface as shown in Figure 5. The first interface comprises a plunger interface between the sealant 30 and the plunger 1 and a base interface between the sealant 30 and the base 2. A surface area of the first interface (given by the sum of the areas of the cylindrical outer face of the collar 4b, the frustoconical inner face 8a of the skirt 8, the annular rim 5, and the cylindrical outer face 21 of the base 2 between the plunger rim 5 and the base rim 22) is greater than a surface area of the second interface. This large surface area reduces the risk of adhesive failure at this first interface 4b, 8a, 5, 21. If the sealed cap assembly is pulled away from the panel 34, then failure will typically occur by adhesive failure at the first interface or by cohesive failure within the bead of sealant 30. Preferably the strength of the adhesive bond is of the order of 400-500N at both the first and second interfaces. Optionally the shoulder 12 in the plunger can be omitted so the plunger can be pushed all the way down to engage the panel 34. However this arrangement is less preferred because it reduces the area of the first interface and prevents the plunger from being positioned close to any raised features in the panel 34. It also prevents a seal being formed between the sealant and the base. A cap assembly according to a second embodiment of the invention is shown in Figures 6-9. In contrast to the embodiment of Figure 1, the base is formed as a cap rather than the plunger. Although the cap assembly is not shown as a kit of two parts, it can be provided as an unassembled kit as shown in Figure 1.

The cap assembly comprises a plunger 101 and a base 102, each formed from a moulded polymer such as polyetherimide ULTEM 2400, or an epoxy. Many parts of the plunger 101 and base 102 are similar to the first embodiment, so such similar parts will not be described again.

The plunger 101 has a body with an outboard part 104a and a collar 104b. Both parts 104a,104b have substantially cylindrical inner and outer faces. The plunger 101 is open at both its inboard (lower) and outboard (upper) ends. The rim 111 of the skirt 108 curves upwards at its end to form an outwardly extending flange.

The inner face of the plunger body is formed with an annular shoulder 112 running round its circumference towards its outboard end, and a single annular recess or groove 113 also running round its circumference, towards the inboard end of the collar 104b. The shoulder 112 and recess 113 lie in planes which are substantially parallel to the planes of the rims 105, 111, 124. The collar 104b is shorter than the axial extent of the skirt 108 so that the plunger rim 105 is set back axially in the outboard direction from the skirt rim 111.

The base 102 is a cap having a tubular body with cylindrical inner and outer faces 120, 121. A domed end wall 117 closes the base cavity 106 at its outboard end opposite a base opening at the inboard end of the base. Six cut-outs are formed in the inner face of the base, leaving six semi-cylindrical ridges or protrusions 125 extending inwardly from the inner face 120 of the base into the base cavity 106 and spaced apart equally around its circumference. The outer face of the base is formed with an outboard facing annular shoulder 127 running round its circumference, and a single annular ridge or protrusion 128 also running round its circumference, towards its inboard end. The shoulder 127 and ridge 128 lie in planes which are substantially parallel to the plane of the base rim 122.

In the configuration of Figure 6 the base is partially received within the plunger and partially protrudes from the inboard end of the plunger by a distance D3.

After the plunger has been fitted over the base to form a cap assembly shown in Figure 6, a band of polysulphide sealant material 130 is installed in the pocket using a similar process to the one described above.

The plunger 101 is pushed inboard towards the panel and slides axially relative to the base from the first position shown in Figure 6 until the shoulder 112 of the plunger engages the shoulder 127 of the base in a second position shown in Figure 8, and the ridge 128 is received in the recess 113 as a snap fit as shown in Figure 9. The ridge 128 and recess 113 ensure that the planes of the rims 122, 111, 105 remain parallel, and hold the plunger and base securely in place while the sealant cures. They also interlock via a "snap-fit" connection which provides a tactile indication to a user that the plunger is in the second position.

The plunger rim 105 is set back from the base rim in the outboard direction by a distance D3 when the plunger is in the first position of Figure 6 and by a smaller distance D5 when the plunger is in the second position of Figures 8 and 9. The skirt 108 of the sliding plunger 101 pushes the sealant 130 which flows to form a seal against the panel as shown in Figures 8 and 9. The protruding part of the base 102 prevents the flowing sealant from flowing into the base cavity 106 during this process. The sealant then cures and adheres the cap assembly to the panel.

As the plunger 101 moves from the first position of Figure 6 to the second position of Figure 8, it engages the outer surface 121 of the base around substantially its full circumference without any large gaps as shown in Figure 7. The absence of such large gaps prevents, or at least impedes, the flow of sealant into this sliding interface between the plunger and the base.

The rim 111 of the skirt 108 is set back axially from the panel and from the base rim 122 by a distance D5 when the plunger is in the second position of Figure 9. This enables the plunger to be positioned close to any raised features.

Optionally the shoulders 112, 127 can be omitted so the plunger 101 can be pushed all the way down to engage the panel.

A cap assembly according to a third embodiment of the invention is shown in Figures 10-13. As with the previous embodiment, the base is formed as a cap rather than the plunger. Although the cap assembly is not shown as a kit of two parts, it can be provided as an unassembled kit as shown in Figure 1.

The cap assembly comprises a plunger 201 and a base 202, each formed from a moulded polymer such as polyetherimide ULTEM 2400, or an epoxy. Many parts of the plunger 201 and base 202 are similar to the previous embodiments, so such similar parts will not be described again.

The plunger 201 has a body 204 with substantially cylindrical inner and outer faces. The plunger 201 is open at both its inboard (lower) and outboard (upper) ends. A frustoconical skirt or flange 208 extends outwardly at the inboard end of the body 204. In contrast to the previous embodiments the plunger 201 has no collar at its inboard end, so an annular pocket or trough 209 is defined between the outer face of the base 202 and the inner face of the skirt 208.

The inner face of the plunger body is formed with series of annular ridges 213 running round its circumference which all lie in planes substantially parallel with the plane of the outboard plunger rim 224 and the skirt rim 211.

The base 202 is a cap having a tubular body with cylindrical inner and outer faces. A domed end wall 217 closes the base cavity at its outboard end. Axially extending protrusions 225 extend inwardly from the inner face of the base. The outer face of the base is formed with an outboard facing annular shoulder 228 (Figure 13) and a series of annular grooves 226 running round its circumference and lying in a plane substantially parallel to the plane of the base rim 222. A band of polysulphide sealant material 230 is installed in the pocket 209 prior to installation using a similar process to the one described above. The plunger 201 is pushed inboard towards the panel and slides axially relative to the base from the first position shown in Figure 10 until the inboard end of the plunger body 204 engages the shoulder 228 of the base in a second position shown in Figures 12 and 13. The skirt rim 211 is set back from the base rim 222 in the outboard direction by a distance D6 when the plunger is in the first position of Figure 10 and by a smaller distance D7 when the plunger is in the second position of Figures 12 and 13.

As the plunger 201 moves from the first position of Figure 10 to the second position of Figure 12, it engages the outer surface of the base around substantially its full circumference without any large gaps. The absence of such large gaps prevents, or at least impedes, the flow of sealant into the sliding interface between the plunger and the base. If a small amount of sealant does flow into this sliding interface, then this may be beneficial since it creates an additional bond between the plunger and the base. Also, if small gaps are present then this will provide a pathway for any small bubbles of air in the upper corner of the pocket 209 to escape as the plunger is pushed down. The ridges 213 and recesses 226 ensure that the planes of the rims 211, 222 remain parallel, and hold the plunger and base securely in place while the sealant cures.

Optionally the shoulder 228 can be omitted so the plunger 201 can be pushed all the way down to engage the panel 34.

A cap assembly according to a fourth embodiment of the invention is shown in Figures 14-17. As with the previous embodiment, the base is formed as a cap rather than the plunger. Although the cap assembly is not shown as a kit of two parts, it can be provided as an unassembled kit as shown in Figure 1.

The cap assembly comprises a plunger 301 and a base 302, each formed from a moulded polymer such as polyetherimide ULTEM 2400, or an epoxy. Many parts of the plunger 301 and base 302 are similar to the previous embodiment, so such similar parts will not be described again.

The inner face of the plunger body 304 is formed with a single annular ridge 328 at its outboard end, running round its circumference and lying in a plane substantially parallel with the plane of the outboard plunger rim and the skirt rim 311. The base 302 is similar to the base 202 except that it only has a single annular groove 313 towards the outboard end of its cylindrical body.

The plunger 301 is pushed inboard towards the panel and slides axially relative to the base from the first position shown in Figure 14 until the inboard end of the plunger body 304 engages the shoulder 329 of the base in a second position shown in Figures 16 and 17. The interlocking ridge 328 and groove 313 ensure that the planes of the rims 311, 322 remain parallel, and hold the plunger and base securely in place while the sealant cures. They also interlock via a "snap-fit" connection which provides a tactile indication to a user that the plunger is in the second position. The skirt rim 311 is set back axially from the base rim 322 in the outboard direction by a distance D8 when the plunger is in the first position of Figure 14 and by a smaller distance D9 when the plunger is in the second position of Figures 16 and 17.

As the plunger 301 moves from the first position of Figure 14 to the second position of Figure 16, it engages the outer surface of the base around substantially its full circumference without any large gaps.

Optionally the annular shoulder 329 can be omitted so the plunger 301 can be pushed all the way down to engage the panel.

In all embodiments of the invention where various features are described as being annular, these parts are also circular. Note however that in the case of a non-circular (for instance square or hexagonal) cap assembly then these annular features will have a non-circular shape. Therefore the term "annular" is used herein to refer to a feature (for instance a shoulder, protrusion or recess) which runs round a circumference of the cap assembly regardless of the shape of that circumference. 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.