Anchor nut

Abstract

An anchor nut 20 for insertion into a hole in a workpiece comprises a tail 22 for inserting into the hole, a collar 28 for preventing over-insertion of the anchor nut 20 into the hole, and a fastener

Description

FIELD OF THE INVENTION [1] The present invention relates to an anchor nut, a kit of parts for installing an anchor nut, and to a method of installing an anchor nut. The invention is particularly suitable for use in aircraft. BACKGROUND OF THE INVENTION [2] With reference to Figure la, an aircraft 2 is shown having wings 4. The wings 4 (and other parts of the aircraft) may comprise multiple parts which are joined together by fasteners. In particular, the wings 4 comprise multiple access holes 6, for inspection of the inside of the wing 2. These access holes 6 are closed by a cover which is secured in place with fasteners. [3] With reference to Figure lb, part of an access hole 6 is shown in more detail in a schematic cross section. The access hole 6 is an interruption in the wing skin 8. The hole 6 is closed by the cover 10, which is held in place by fasteners 12 engaged in the nuts 14 which are attached to the cover 10. The fasteners 12 extend through the cover 10 and wing skin 8. [4] When the fasteners 12 are inserted into the nuts 14, there is no access from the inside of the wing 4 to hold the nuts 14 in place. Accordingly the nuts 14 are captive nuts, secured to the cover 10, so that fasteners 12 can be secured with access only from outside the wing 4. Since the inside of wing 4 may be used to carry fuel, the captive nuts 14 may also be sealed for fuel sealing purposes. [5] The wings 4 represent an area of the aircraft 2 that encounters a significant amount of stress and flex during normal usage. Accordingly, the holes in the cover 10 that receive the fasteners 12 represent a possible concentration of stress in the cover 10 as well as a potential initiation point for cracks. Accordingly, the hole is cold worked before installation of the fastener 12 in a usual way - a bush is installed in the hole and a mandrel is pulled through the bush to increase the resistance of the hole to fatigue. The captive anchor nut 14 is then installed on the cover 10. [6] The present invention seeks to provide an alternative way to cold work a hole in an aircraft part, such as the cover 10, while installing a captive nut 14, simplifying the cold working process or at least providing an alternative to existing techniques. SUMMARY OF THE INVENTION [7] A first aspect of the disclosure provides an anchor nut for insertion into a hole in a workpiece, the anchor nut comprising: a tail for inserting into the hole, the tail comprising an external thread for driving the anchor nut into the hole; a collar for preventing over-insertion of the anchor nut into the hole; and a fastener hole comprising a nut internal thread for receiving a fastener, wherein the fastener hole extends through the collar and into the insertable portion. [8] Preferably, the external thread extends over a portion of the tail. [9] Optionally, the fastener hole extends all the way through the insertable portion.

[10] Preferably, the anchor nut further comprises a head that extends from the collar away from the tail, wherein the fastener hole extends through the head.

[11] Preferably, the anchor nut further comprises a drive feature for engaging with a tool for driving the anchor nut into the workpiece.

[12] A further aspect of the disclosure provides a kit of parts for installing an anchor nut into a hole in a workpiece, comprising the above mentioned anchor nut, and a bush for fitting into the hole in the workpiece, the bush comprising: a bush hole for receiving the insertable portion of the anchor nut; and a bush internal thread for engaging with the external thread of the anchor nut within the bush hole.

[13] Preferably, the bush comprises a split that extends from an outer face of the bush to the bush hole, for assisting expansion of the bush away from the bush hole when the anchor nut is inserted in the bush hole.

[14] Optionally, the split extends the length of the bush hole.

[15] Optionally, the bush comprises at least one breakable portion adjacent to the split, adapted to break when the bush is expanded by the insertion of the anchor nut.

[16] Optionally, the bush further comprises a bush collar for preventing over insertion of the bush into the hole in the workpiece.

[17] Optionally, the kit may further comprise a lubricant for assisting the insertion of the anchor nut into the bush.

[18] A further aspect of the disclosure provides an aircraft comprising a member defining a hole, the aircraft further comprising: an anchor nut as described above inside the hole; and a bush inside the hole, the bush comprising: a bush hole which receives the tail of the anchor nut; and a bush internal thread engaged with the external thread of the anchor nut.

[19] According to a second aspect of the present disclosure, there is provided a method of installing an anchor nut into a hole in a workpiece, the method comprising: providing an anchor nut as described above; providing a bush, the bush being sized to just fit within the hole in the workpiece, the bush comprising: a bush hole for receiving the insertable portion of the anchor nut; and a bush internal thread for engaging with the external thread of the anchor nut; inserting the bush into the hole in the workpiece; and screwing the anchor nut into the bush, so as to secure the anchor nut within the hole in the workpiece.

[20] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[21] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[22] Figure la shows a schematic view of an aircraft;

[23] Figure lb shows a cross section of part of an access hole and associated cover affixed to an aircraft;

[24] Figure 2 shows a perspective schematic view of an anchor nut according to an embodiment of the disclosure;

[25] Figure 3 shows a perspective schematic view of a bush according to an embodiment of the disclosure;

[26] Figure 4 shows a schematic view of a bush inserted into a workpiece;

[27] Figure 5 shows a schematic view of an anchor nut being inserted into the bush; and

[28] Figure 6 shows a schematic cross section of an anchor nut and bush in situ in a workpiece. DETAILED DESCRIPTION OF EMBODIMENT(S)

[29] Figure 2 shows a perspective view of an anchor nut 20 according to an embodiment of the present disclosure. The anchor nut 20 comprises a tail 22 for inserting into a workpiece, securing the anchor nut 20 within a workpiece and cold working the workpiece as will be explained below.

[30] The anchor nut 20 further comprises a head 24, which may protrude from the workpiece after insertion of the tail 22 into the workpiece. The head 24 and tail 22 together have an anchor nut hole 26 through them for accepting a fastener. The anchor nut hole 26 runs longitudinally along the anchor nut 20 from the tail 22 to the head 24. In other words the head 24 and tail 22 together take the form of a hollow cylinder, with the anchor nut hole 26 being substantially coaxial with the anchor nut 20.

[31] The anchor nut 20 may further comprise a collar 28, which extends substantially radially away from the axis of the anchor nut 20 and forms a substantially flat surface that in use may abut the surface of a workpiece the nut is inserted in. The collar 28 may serve as an indicator that the anchor nut has been sufficiently inserted into a workpiece, and / or as a limit to prevent over insertion into a workpiece.

[32] On at least a portion of the outside of tail 22 the anchor nut 20 comprises an external thread 30 for inserting and securing the anchor nut 20 within a threaded hole. The external thread 30 may extend the length of the tail up to the collar 28 (if present), or extend along only a portion of the tail 22. In some embodiments and in the absence of collar 28 the external thread may extend along substantially the entire length of anchor nut 20, including head 24. The external thread 30 may be continuous or comprise interruptions.

[33] The anchor nut 20 is intended for insertion into a workpiece to act as a captive nut, to receive a fastener within the anchor nut hole 26. It is also intended to be used to cold work the workpiece during insertion by use with a bush. Figure 3 shows a perspective view of a bush 34 according to an embodiment of the present disclosure. The bush 34 is in the form of a hollow cylinder, with a bush hole 36 running the length of the cylinder for receiving the anchor nut 20. The bush hole 36 comprises a bush internal thread 38 on at least a portion of the inside of the bush hole 36 for engaging with the external thread 30 of anchor nut 20.

[34] The anchor nut 20 and bush 34 are so dimensioned so as to be used to cold work a hole in a workpiece. With reference now to Figure 4, the first step of using the anchor nut 20 and bush 34 in this way is shown. Firstly, the bush 34 is inserted into a workpiece hole 52 in a workpiece 50. The bush 34 has an outer diameter sized to just fit inside the workpiece hole 52 in the workpiece 50. Either this is by way of a very small clearance fit, or a transition fit allowing the bush 34 to be persuaded into the workpiece hole 52 without substantially damaging or deforming bush 34.

[35] Ideally, the bush 34 should line the inside of the workpiece hole 52 along its entire length. The bush 34 may be prepared to be already the right length for doing this, or might be cut to size after insertion into the workpiece hole 52. In embodiments, the bush 34 may have a protrusion to prevent over-insertion into the workpiece 50, akin to the collar 28 of the anchor nut 20. Depending on where stress concentrations are expected in workpiece 50, in some embodiments the bush 34 may only extend through part of the workpiece hole 52, for example towards the top or the bottom of the workpiece hole 52.

[36] With reference now to Figure 5, the second stage of using the anchor nut 20 and bush 34 to cold work a hole are depicted. The anchor nut 20 is brought up to the bush 34, and the tail 22 is introduced to the bush hole 36. With the external thread 30 engaged with bush internal thread 38, the anchor nut 20 is rotated so as to drive the tail 22 into the bush 34 and workpiece 50.

[37] The tail 22 and external thread 30 are sized so as to be slightly larger than the bush hole 36 and bush internal thread 38, meaning that as the anchor nut 20 is driven into the bush 34 and workpiece 50, the bush 34 is forced to expand radially outwards into the workpiece 50. This cold works the workpiece hole 52, improving the fatigue properties of the workpiece 50. An interference fit is also created between the bush 34 and the workpiece 50 which means that the bush 34 and therefore the anchor nut 20 will remain firmly in place within the workpiece hole 52.

[38] Inserting the anchor nut 20 into the bush 34 may involve significant force being exerted on the anchor nut 20 so as to provide an appropriate level of cold working. In such circumstances a lubricant may be beneficial for reducing the amount of force required. For example, a liquid lubricant may be added to the bush internal thread 38 or the anchor nut external thread 30. Alternatively, a thin film dry lubricant or powdered dry lubricant may be provided.

[39] Optionally and as shown in Figure 3, the bush 34 may comprise a split 40, for aiding radial expansion of the bush 34. Preferably, the split 40 extends the length of the bush 34, representing an interruption in the circumference of the hollow cylinder. The split 40 is preferably substantially aligned with the axis of the bush 34. However, the split 40 may extend along only part of the length of the bush 34, or be at an angle to the bush 34. Furthermore the bush 34 may have two or more splits 40, either linearly aligned and / or radially separate depending on the desired expansion of bush 34.

[40] Optionally, the split (or splits) 40 may be interrupted by one or more bridges 42. These bridges are preferably thinner or weakened points in the circumference of the bush 34 which keep the shape of the bush intact before use but may be stretched or even separated under radial expansion of the bush 34. For example, the radial width of the bridge 42 may be substantially less than the radial width of the rest of the bush 34, or the bridge 42 may be scored where it connects to the rest of bush 34 so as to concentrate stress in a weaker area to aid expansion of the bush 34.

[41] With reference now to Figure 6, the anchor nut 20 and bush 34 are shown in place within a workpiece 50, in schematic cross section according to an embodiment of the present disclosure. The bush 34 sits in the workpiece hole 52 in an interference fit. The bush internal thread 38 is engaged with the anchor nut 20 external thread 30, and the collar 28 abuts the workpiece 50.

[42] The anchor nut 20 is adapted to receive a fastener so as to secure the workpiece 52 in some appropriate fashion. For example, the workpiece may be a cover 10 as shown in Figure lb, with the anchor nut 20 acting as captive nut 14. In such an embodiment, the fastener may be inserted into the anchor nut 20 entering the anchor nut hole 26 by the tail 22. However, in other embodiments the fastener may be inserted into the head 24 of the anchor nut.

[43] In any case, the anchor nut 20 may feature a nut internal thread 32 for engaging with an appropriate fastener. This may be a conventional thread that extends through some or all of the anchor nut hole 26. Alternatively, the nut internal thread 32 may comprise a series of ridges for retaining a fastener, possibly with the addition of an adhesive to bind the fastener and anchor nut 20 together.

[44] In the case that the anchor nut 20 is to be used in a cover 10 (or in various other applications), it may be desirable to seal the anchor nut hole 26. In such cases the anchor nut hole 26 might not extend the hole length of anchor nut 20, so that the anchor nut 20 is sealed. For example, the anchor nut hole 26 might end in the head 24, which could have a solid end. Alternatively, once anchor nut 20 has been inserted into a workpiece 50, the anchor nut hole 26 might be capped by introducing a separate part to cap the hole off - for example, a cap that sits over the head 24 of the anchor nut 20. The cap might be secured in any conventional way, for example cooperating with features on the outside of anchor nut 20 and / or the workpiece 50 and / or being adhered to it and / or the workpiece 50 by an adhesive or sealant.

[45] In order to drive the anchor nut 20 into the bush 34 and workpiece 50, there should be some means of imparting a rotational force into the anchor nut 20 (so as to rotate it within the bush 34), as well as a linear driving force (so as to avoid pulling the bush 34 out of the workpiece 50). The skilled person will realise that such a drive feature may be implemented in a number of different ways. For example, the collar 28 could constitute a drive feature, or alternatively, the head 24 could comprise a drive feature. The drive feature could simply comprise an outer perimeter that can be finger tightened (if a low force is needed) or that could engage with a tool, such as a spanner or socket. For example, the head 24 or collar 28 could have a hexagonal or other regular outer perimeter for engaging with a tool. Alternatively, the drive feature could be a recessed feature within the collar 28 or head 24. For example, the head 24 could comprise a hexagonal hole for receiving a hex key, or slot for receiving a screwdriver. Furthermore the collar 28 could comprise one or more recesses around head 24 for engaging with a tool to drive the anchor nut 20.

[46] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[47] The above embodiments are to be understood as illustrative examples of the invention. Equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

[48] It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments.

[49] It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

[50] It should be noted that throughout this specification, “or” should be interpreted as “and / or”.

[51] Although the invention has been described above mainly in the context of a fixed-wing aircraft application, it may also be advantageously applied to various other applications, including but not limited to applications on vehicles such as helicopters, drones, trains, automobiles and spacecraft.

Claims

1. An anchor nut for insertion into a hole in a workpiece, the anchor nut comprising:A tail for inserting into the hole, the tail comprising an external thread for driving the anchor nut into the hole;a collar for preventing over-insertion of the anchor nut into the hole; andA fastener hole comprising a nut internal thread for receiving a fastener, wherein the fastener hole extends through the collar and into the insertable portion.

2. An anchor nut according to claim 1, wherein the external thread extends over a portion of the tail.

3. An anchor nut according to claim 1 or 2, wherein the fastener hole extends all the way through the insertable portion.

4. An anchor nut according to any preceding claim, further comprising a head that extends from the collar away from the tail, wherein the fastener hole extends through the head.

5. An anchor nut according to any preceding claim, further comprising a drive feature for engaging with a tool for driving the anchor nut into the workpiece.

6. A kit of parts for installing an anchor nut into a hole in a workpiece, comprising the anchor nut of any one of claims 1 to 5, and a bush for fitting into the hole in the workpiece, the bush comprising:a bush hole for receiving the insertable portion of the anchor nut; anda bush internal thread for engaging with the external thread of the anchor nut within the bush hole.

7. A kit of parts according to claim 6, wherein the bush comprises a split that extends from an outer face of the bush to the bush hole, for assisting expansion of the bush away from the bush hole when the anchor nut is inserted in the bush hole.

8. A kit of parts according to claim 7, wherein the split extends the length of the bush hole.

9. A kit of parts according to claim 7, wherein the bush comprises at least one breakable portion adjacent to the split, adapted to break when the bush is expanded by the insertion of the anchor nut.

10. A kit of parts according to any one of claims 6 to 9, wherein the bush further comprises a bush collar for preventing over insertion of the bush into the hole in the workpiece.

11. A kit of parts according to any one of claims 6 to 10, further comprising a lubricant for assisting the insertion of the anchor nut into the bush.

12. An aircraft comprising a member defining a hole, the aircraft further comprising: an anchor nut according to any one of claims 1 to 5 inside the hole; and a bush inside the hole, the bush comprising:a bush hole which receives the tail of the anchor nut; anda bush internal thread engaged with the external thread of the anchor nut.

13. A method of installing an anchor nut into a hole in a workpiece, the method comprising: providing an anchor nut according to any one of claims 1 to 5;providing a bush, the bush being sized to just fit within the hole in the workpiece, the bush comprising:a bush hole for receiving the insertable portion of the anchor nut; anda bush internal thread for engaging with the external thread of the anchor nut; inserting the bush into the hole in the workpiece; andScrewing the anchor nut into the bush, so as to secure the anchor nut within the hole in the workpiece.

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