GB2568069A - A nut cap - Google Patents

A nut cap Download PDF

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Publication number
GB2568069A
GB2568069A GB1718214.8A GB201718214A GB2568069A GB 2568069 A GB2568069 A GB 2568069A GB 201718214 A GB201718214 A GB 201718214A GB 2568069 A GB2568069 A GB 2568069A
Authority
GB
United Kingdom
Prior art keywords
shell
nut cap
shells
projections
nut
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1718214.8A
Other versions
GB201718214D0 (en
Inventor
Dobbin Richard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Operations Ltd
Original Assignee
Airbus Operations Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Airbus Operations Ltd filed Critical Airbus Operations Ltd
Priority to GB1718214.8A priority Critical patent/GB2568069A/en
Publication of GB201718214D0 publication Critical patent/GB201718214D0/en
Publication of GB2568069A publication Critical patent/GB2568069A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16BDEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B37/00Nuts or like thread-engaging members
    • F16B37/14Cap nuts; Nut caps or bolt caps
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16BDEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B33/00Features common to bolt and nut
    • F16B33/004Sealing; Insulation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B64AIRCRAFT; AVIATION; COSMONAUTICS
    • B64DEQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
    • B64D45/00Aircraft indicators or protectors not otherwise provided for
    • B64D45/02Lightning protectors; Static dischargers

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Cooling, Air Intake And Gas Exhaust, And Fuel Tank Arrangements In Propulsion Units (AREA)

Abstract

A nut cap for shielding a fastener attached to a structure such as an aircraft wing comprises an inner shell (1) and an outer shell (2) arranged to cover and be secured to the inner shell (1). The inner and outer shells (1, 2) together define an opening (3) to receive the fastener along a receiving axis L and mutually interlocking securing features (10, 11, 12, 13, 14, 15) angularly spaced about the receiving axis L whereby to secure the shells (1, 2) together. The interlocking securing features (10, 11, 12, 13, 14, 15) define a sliding fit rotationally about the receiving axis L to allow the features to be rotated into locking engagement with each other by relative rotational movement of the inner and outer shells (1, 2).

Description

A NUT CAP
TECHNICAL FIELD
The present invention relates to a nut cap injected with sealant used to protect fasteners in a structure, and more particularly to a nut cap comprising a separate inner and outer shell with sealant injected between the shells used to protect fasteners in a structure and more particularly in a composite structure.
BACKGROUND TO THE INVENTION
Nut caps are used extensively in aircraft and other structures where it is required to create a seal over a fastener to prevent leakage of fluids contained within the structure through an aperture for the fastener.
Such nut caps are also extensively used on fibre reinforced plastics (FRP) composite structures such as aircraft wings and fuselages and other structures which may be exposed to the weather to prevent damage to the structure from lightning strike. With FRP structures, a metallic fastener passing through the structure will provide a conducting path for electricity. Thus, with aircraft fuel tanks formed in a wing structure, for example, if an external fastener is struck by lightning, it will provide a current path to an interior of the tank. This will potentially create a source of sparks or plasma within the tank which may ignite fuel or fuel vapour and potentially cause an explosion. Non-conducting nut caps placed over the fasteners within the tank will act to contain any such fire risks.
The nut cap is generally a bell shape, having a closed end and an open end, and is arranged to receive a fastener through the open end along a receiving axis of the nut cap and to cover the end of the fastener and be sealed to the structure around the fastener at the open end. The inner shell usually engages the fastener and is often secured to the fastener with some kind of interlocking engagement. The outer shell defines an injection orifice at the closed end of the bell and, together with the inner shell, defines a sealant passage to an annular sealant escape orifice at the open end of the bell.
In order to seal the nut cap to the surrounding structure, once the nut cap is in place over the fastener, sealant is injected through the injection orifice and passes through the sealant passage between the inner and outer shells and emerges at the annular escape orifice whereby to form an annular seal between the nut cap and structure, after setting or curing of the sealant.
In order to ensure that sealant passes uniformly through the passage to fill the annular orifice as it emerges therefrom, sealant is injected into the nut cap between the inner and outer shells at considerable pressure. If the inner and outer shells are not securely fixed together, the outer shell will tend to become detached from the inner shell by the pressure of sealant therebetween.
It is known to secure together the inner and outer shells with a series of securing features angularly spaced about the receiving axis and in the form of snap fit catches each with an inwardly directed projection defined on the outer shell engaging behind a cooperating outwardly directed projection on the inner shell when the shells are pressed together. Current nut caps are manufactured from polyetherimide (PEI) which is a somewhat brittle material and, on smaller nut caps in particular, there is insufficient shell material in the angular space between the catches to allow the requisite flexure to occur for damage-free engagement of the catches. Distal portions of the projections tend to be snapped off, during engagement. This leads to insecure engagement of the catches and the inner and outer shells being forced apart upon injection of sealant.
In an effort to solve this problem, adhesive has been applied between the inner and outer shells to adhere them together. However, this solution adds significant expense to each nut cap and for that reason is not satisfactory.
It is an object of the invention at least partly to overcome the disadvantages of the prior art.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a nut cap for shielding a fastener attached to a structure, the nut cap comprising an inner shell and an outer shell arranged to cover and be secured to the inner shell, the inner and outer shells defining an opening to receive the fastener therein along a receiving axis and mutually interlocking securing features angularly spaced about the receiving axis whereby to secure the shells together, the interlocking securing features defining a sliding fit rotationally about the receiving axis to allow the features to be rotated into locking engagement with each other by relative rotational movement of the inner and outer shells. The provision of a rotational sliding fit for the interlocking securing features removes the need for a snap fit which has been the cause of breakage of one or more securing features on current designs.
The mutually interlocking securing features may comprise projections defined on the outer shell engaging behind cooperating projections on the inner shell.
A first said shell may include guides rotationally to guide the projections on a second said shell into engagement with the cooperating projections on the first shell.
The guides may be adapted to exert a camming action on the said projections on the second shell whereby to draw the shells more fully into engagement with one another during relative rotation of the shells.
A detent may be provided to prevent rotational disengagement of cooperating projections from one another. Such a detent or detents will act to maintain cooperating projections in locked relationship with each other and prevent separation of the inner and outer shells.
The detent may be formed by a transition between a said guide and projection on the first shell. Such a transition may comprise a step.
According to a second aspect of the invention there is provided a fastener assembly comprising a series of nut caps according to the invention attached to a series of fasteners.
According to a third aspect of the invention there is provided a structural assembly, said structural assembly comprising a fastener assembly according to the second aspect sealably attached to a structure.
The structural assembly may comprise fibre reinforced plastics composite material and may be comprised in an aircraft structure such as a fuel tank.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:Figure 1 is a vertical section through a nut cap, according to the prior art;
Figure 2 shows an enlarged view of detail II of Figure 1 with some further structure;
Figure 3 is an enlarged view of detail III of Figure 2;
Figures 4a - c are vertical sectional views of a nut cap according to the invention taken at differing angular positions around the nut cap;
Figure 5a is a horizontal sectional view of the nut cap of Figure 4a, taken on the line A-A;
Figure 5b is a horizontal sectional view of the nut cap of Figure 4b, taken on the line B-B;
Figure 5c is a horizontal sectional view of the nut cap of Figure 4c, taken on the line C-C;
Figure 6a is a bottom plan view of the nut cap of Figure 4a;
Figure 6b is a bottom plan view of the nut cap of Figure 4b;
Figure 6c is a bottom plan view of the nut cap of Figure 4c;
Figure 7 is a vertical part sectional view of the nut cap of Figure 4a, and
Figure 8 is a partial sectional view of an assembly according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, Figure 1 shows a nut cap according to the prior art comprising an inner shell 1 and an outer shell 2. Both shells 1, 2 are made of brittle PEI. The inner shell 1 has a lower opening 3 to receive a fastener and nut (not shown) therein along a receiving axis L. A lower edge 4 of the inner shell 1 is designed to contact a structure 26 to which the fastener is to be attached.
The outer shell 2 has a central inlet funnel 5 to receive sealant under pressure from an outside source such as a sealant gun (not shown). The funnel 5 opens into a series of channels 6 to conduct the sealant towards the lower edge 4 of the inner shell. The arrows shown indicate the direction of flow of sealant whilst being injected.
In Figures 2 and 3 are shown a mutually interlocking securing feature in the form of a snap fit catch arrangement 7. The arrangement 7 has a first hook 8 on the inner shell 1 cooperating in snap engagement with a second hook 9 on the outer shell 2. The hooks 8, 9 enter into snap engagement when outer shell 2 is passed downwardly (direction as shown in the drawings) over inner shell 1. Owing to the brittle nature of PEI and the fact that, on smaller nut caps, there is very little material circumferentially of the nut cap to flex when the hooks are pressed into snap engagement, breakages of parts or all of the hooks 8, 9 have been occurring. This has led to insecure attachment of the outer shell to the inner shell, particularly when sealant is being forced between the inner and outer shells 1, 2.
Turning now to Figures 4 to 7, a nut cap according to the invention is shown. The construction of the nut cap of the invention is very similar to that of the prior art device of Figures 1, 2 and 3 and like features are given like reference numerals.
The securing features of the invention are in the form of three projections 10, 11, 12 on the outer shell 2 angularly spaced around the shell which, by relative rotation of the inner and outer shells 1, 2 together, slidably engage behind cooperating projections 13, 14, 15, respectively on the inner shell 1. In contrast to the prior art, when the outer shell 2 is slid over the inner shell 1, along the receiving axis L, the projections 10, 11, 12 pass through slots 16, 17, 18 formed in a circumferential ridge 19 on the inner shell
I. Once through the slots 16, 17, 18, the projections 10, 11, 12 mounted on the outer shell 2 may be rotated about the receiving axis L so as to be guided by guide surfaces 20, 21 (and not shown) formed on the underside of the circumferential ridge 19. The guide surfaces 20, 21, slope towards the lower opening 3, as the projections 10, 11, 12 are rotated towards the projections 13, 14, 15 on the inner shell 1. This slope exerts a camming action on the projections 10, 11, 12 as they are rotated to draw the outer shell 2 more fully into engagement with the inner shell 1.
Detents in the form of steps (not visible in these drawings) between the projections 10,
II, 12 and their corresponding guide surfaces 20, 21 (and not shown) prevent rotational disengagement of the projections 10, 11, 12 from their cooperating projections 13, 14, 15.
Figure 8 is a partial sectional view of an assembly according to the invention and shows the outer shells 2 of two exemplary nut caps sealed in position with sealant 27 to joined walls 24, 25 of an aircraft wing fuel tank. The sectional detail shows a countersunk fastener 23 passing through the walls 24, 25 and being secured in position by a nut 22. A stepped washer 28 is interposed between the nut 22 and wall 25. The step on the washer may be used to secure the nut cap in position by means of a hook 28, as shown in figure 2 of the prior art.
Thus the nut cap of the invention differs from the prior art nut cap of Figures 1, 2 and 3 in its securing features. Rather than the snap fit arrangement of Figures 1, 2 and 3, the nut cap of the invention has interlocking securing features defining a sliding fit rotationally about the receiving axis L. This arrangement removes the need for a snap fit of the securing features and therefore removes any danger of their breakage.
Although the invention has been described above with reference to one or more preferred examples or 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. For example, although the nut cap has been shown with three sets of interlocking securing features, this number could be reduced to two or increased as required. Similarly, although bell shaped inner and outer shells are illustrated, any other suitable shape may be used.
Where the term “or” has been used in the preceding description, this term should be understood to mean “and/or”, except where explicitly stated otherwise.

Claims (11)

1. A nut cap for shielding a fastener attached to a structure, the nut cap comprising an inner shell and an outer shell arranged to cover and be secured to the inner shell, the inner and outer shells defining an opening to receive the fastener therein along a receiving axis, and mutually interlocking securing features angularly spaced about the receiving axis whereby to secure the shells together, the interlocking securing features defining a sliding fit rotationally about the receiving axis to allow the features to be rotated into locking engagement with each other by relative rotational movement of the inner and outer shells.
2. A nut cap according to claim 1, in which the mutually interlocking securing features comprise projections defined on the outer shell engaging behind cooperating projections on the inner shell.
3. A nut cap according to claim 1 or 2, in which a first said shell includes guides rotationally to guide the projections on a second said shell into engagement with the cooperating projections on the first shell.
4. A nut cap according to claim 1, 2 or 3, in which the guides are adapted to exert a camming action on the said projections on the second shell whereby to draw the shells more fully into engagement with one another during relative rotation of the shells.
5. A nut cap according to any preceding claim, including a detent to prevent rotational disengagement of cooperating projections from one another.
6. A nut cap according to claim 5, in which the detent is formed by a transition between a said guide and projection on the first shell.
7. A nut cap according to claim 6, in which the transition comprises a step.
8. A fastener assembly comprising a series of nut caps according to any preceding claim attached to a series of fasteners.
9. A structural assembly, comprising a fastener assembly according to claim 8 wherein the nut caps are sealably attached to a said structure.
10. A structural assembly according to claim 9 in which the structure comprises an aircraft fuel tank.
11. A structural assembly according to claim 10, in which the aircraft fuel tank comprises fibre reinforced plastics composite material.
GB1718214.8A 2017-11-03 2017-11-03 A nut cap Withdrawn GB2568069A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB1718214.8A GB2568069A (en) 2017-11-03 2017-11-03 A nut cap

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB1718214.8A GB2568069A (en) 2017-11-03 2017-11-03 A nut cap

Publications (2)

Publication Number Publication Date
GB201718214D0 GB201718214D0 (en) 2017-12-20
GB2568069A true GB2568069A (en) 2019-05-08

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB1718214.8A Withdrawn GB2568069A (en) 2017-11-03 2017-11-03 A nut cap

Country Status (1)

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GB (1) GB2568069A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3136452A1 (en) 2022-06-13 2023-12-15 Hutchinson DOUBLE SHELL LIGHTNING CAP WITH IMPROVED ASSEMBLY

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014170672A1 (en) * 2013-04-19 2014-10-23 Airbus Operations Limited Injectable cap

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014170672A1 (en) * 2013-04-19 2014-10-23 Airbus Operations Limited Injectable cap

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3136452A1 (en) 2022-06-13 2023-12-15 Hutchinson DOUBLE SHELL LIGHTNING CAP WITH IMPROVED ASSEMBLY
EP4292944A1 (en) 2022-06-13 2023-12-20 Hutchinson Double shell lightning protection cap with improved assembly

Also Published As

Publication number Publication date
GB201718214D0 (en) 2017-12-20

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)