GB2308154A

GB2308154A - Fastener

Info

Publication number: GB2308154A
Application number: GB9625288A
Authority: GB
Inventors: Mark Bagnall
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1995-12-11
Filing date: 1996-12-05
Publication date: 1997-06-18
Anticipated expiration: 2016-12-05
Also published as: GB9525310D0; GB9625288D0; GB2308154B

Description

FASTENINGS AND ASSEMBLIES This invention relates to fastenings and assemblies including fastenings, and to methods of securing a fastening to a threaded component.

Many fixings include an internally-threaded nut or fastening secured in place on an externally-threaded bolt or similar device. These fixings have the advantage that they can provide an adjustable clamping force, they can provide a secure retention and they can be used to clamp about members of differing thickness.

Threaded nut assemblies do, however, suffer from several disadvantages. First, it is often necessary to rotate the nut through several complete rotations in order to secure it to the bolt or the like. This can be time-consuming and, if the assembly is used in an inaccessible location, it may not be easy to effect. Second, there is an inherent risk with threaded fastenings that the threads on the two components be incorrectly aligned, or crossed, causing damage to the components when they are tightened. This can also prevent secure retention and may make release of the components difficult.

Push-on, twist-off fastenings are also known, which have some form of resilient engagement with a threaded component and in which the fastening can be pushed onto the threaded component. These fastenings can be screwed to tighten fully and can only be removed by unscrewing. Examples of such fastenings are described in EP5 17281, GB2155534, GB2275732, GB2179113, EP165026 and EP517279. It is preferable that these forms of fastenings can be tightened with a minimal rotation, that they will provide a secure retention and that the fastening can be assembled on the component easily.

It is an object of the present invention to provide an improved fastening and an assembly including a fastening, and a method of securing a fastening to a threaded component.

According to one aspect of the present invention there is provided a fastening for mounting an externally-threaded component, the fastening having a plurality of resilient tabs projecting internally of the fastening and inclined at an angle to the axis of the fastening such that the tabs deflect inwardly as the fastening is pushed axially onto the externally-threaded component in one direction and engage the thread to prevent axial displacement of the fastening in the opposite direction, the spacing between the tabs being such that in their natural state when one tab is engaged with the thread of the externally-threaded component, the others of the tabs are not fully engaged, the tabs being flexible to enable axial displacement of the ends of the fully engaged tabs such that tightening of the fastening brings at least one of the others of the tabs into full engagement with the thread.

The fastening preferably has n tabs spaced from one another by 1/n of a pitch of the threaded component, and the tabs may be arranged in two rows. The tabs preferably have a shallow curvature lying on the surface of a common cylindrical plane. The inner edge of the tabs preferably has an acute angle. The angle at which the tabs are inclined to the axis may be such that a normal from the flank of the thread of the threaded component is inclined below a centre line along the tabs in the direction of tightening of the fastening.The angle is preferably substantially 37.4 . The tabs are preferably arranged such that tightening the fastening brings successive tabs into full engagement with the thread spaced from one another by substantially 1500. The fastening may be moulded from a plastics material and may have a plurality of external flats.

According to another aspect of the invention there is provided an assembly comprising an externally-threaded component and a fastening according to the above one aspect of the invention.

The externally-threaded component may include a cable gland.

According to a further aspect of the invention there is provided a method of securing a fastening to an externally-threaded component, the fastening having a plurality of resilient, flexible tabs projecting internally of the fastening and inclined at an angle to the axis of the fastening the spacing between the tabs being such that in their natural state when one tab is engaged with the thread of the externally-threaded component, the others of the tabs are not fully engaged, comprising the steps of pushing the fastening axially onto the component so that the tabs deflect inwardly and snap over each pitch of the external thread and subsequently rotating the fastening so that the engaged tab flexes to enable axial displacement of the end of the engaged tab allowing at least one of the others of the tabs to be brought into full engagement with the thread.

A cable gland assembly and its method of use, according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partly-sectional side elevation view of the assembly; Figure 2 is a side elevation view of the fastening separated from the assembly, along the line II of Figure 1; Figure 3 is a side elevation view of the fastening from the opposite direction from Figure 2; Figure 4 is a development of Figure 2 showing the entire inside surface of the fastening; Figure 5 is a section through a part of the fastening mounted on the assembly showing a fully engaged tab; Figure 6 is a section through a part of the fastening mounted on the assembly showing a tab that is not fully engaged; and Figure 7 is a section through a part of the fastening showing a fully engaged tab that is flexed by tightening of the fastening.

With reference first to Figure 1, the cable gland assembly comprises a moulded tubular body 1 made of a rigid plastics material, such as nylon. The body 1 is about 33mm long and has an axial bore 10 extending along its length. At its left hand end, the bore 10 is about 1 lmm in diameter but, at its right hand end, this is increased to about 16mm, so as to form an internal annular shoulder 11. A rigid plastics washer 12 is located as a loose fit within the right hand end of the bore 10 in engagement with the shoulder 11. A resilient sealing gland 13 abuts the right-hand end of the washer 12, within the bore 10. The gland 13 projects from the right hand end of the body 1 and can be compressed about a cable (not shown) extending along the bore 10, by tightening an end cap 14, which engages an external screw thread 15 on the body.

The screw thread 15 extends along the entire length of the body, except for a hexagonal flange 16 formed integrally of the body, which projects radially outwards midway along its length. The thread 15 is a single-start thread with a pitch of 1 .5mm and an external diameter of 20mm.

As so far described, the assembly is entirely conventional.

The assembly is mounted in a circular hole 2 of a bulkhead 3, with the right-hand face of the bulkhead being engaged by the left-hand surface of the flange 16. A washer may be used on either side of the bulkhead if desired. The left-hand face of the bulkhead 3 is engaged by a push-on nut or fastening 5 of novel construction.

With reference now to Figures 2 to 7, the nut 5 is moulded from a rigid plastics such as nylon or Delrin (an acetyl plastics) and is 8mm long with an external diameter of 28.5mm.

Externally, the nut 5 has a collar 50 at the right-hand end, which is of circular section and is 1.5mm long. To the left of the collar 50, the nut is formed with six flats 51 separated from one another by rounded regions 52. Internally, the nut 5 has a bore 53 of circular section and a diameter of 24mm, the bore opening at both ends of the nut. Twelve tabs 54 to 65 project inwardly of the bore towards the right-hand end of the nut. The tabs 54 to 65 are equally disposed around the nut in two rows. The spacing between the two rows is 1/12 pitch and the spacing between the tabs in each row is 60 , the tabs in one row being spaced midway between the tabs in the other row. A different number n of tabs could be used spaced from one another by 1/n of a pitch.The tabs are all inclined to the left at an angle O to the axis of 37.4 and are of rectangular shape being 4mm wide, 0.8mm thick and approximately 6mm long. The tabs have a shallow curve across their width, presenting a smooth convex surface when viewed from the left, so that the inner, free ends 66 of the tabs lie on a cylindrical plane of circular section and diameter 18.574mm. The free ends 66 are also angled parallel with the helical thread 15 on the body 1 and are cut at an angle a of 82.6 so that the inner edge of the tabs form an acute angle.

As shown in Figure 5, the shape, size and angle of the tabs 54 to 65 is such that the free end of one of the tabs 54 to 65 lies flat against the forward inclined surface of the external thread 15 on the body 1 and contacts the apex of the adjacent, forward turn of the thread. It can be seen that, in this position, the fully engaged tab prevents rearward axial displacement of the nut 5 unless there is unscrewing rotation. The angle of the tabs is selected such that a normal 'N' drawn from the flank of the thread through the centre of the free end of the tab does not extend parallel with the tab, but is inclined forwardly (that is, in the direction of tightening of the nut 5) below the centre line 'L' extending along the length of the tab. Any force exerted to pull the nut 5 rearwardly off the body 1 will cause a force to be exerted on the thread along the line 'L'.The resultant of this force will tend to push the free end of the tab radially in, further into engagement with the thread. By contrast, if the line 'L' were to be inclined below the normal run', the resultant force would tend to push the free end of the tab radially outwards. The other tabs are not similarly engaged against the inclined faces of the external thread, but lie across the apex of one of the turns of the thread and are deflected outwardly against their resilience, as shown in Figure 6. These non-engaged tabs exert an axially-directed force that tends to push the nut 5 rearwardly and, thereby, urges the end of the engaged tab into engaging contact with the inclined flank of the thread.

The nut 5 is readily assembled on the body 1 by pushing the nut axially forwardly onto the left-hand end of the body without the need to rotate the nut relative to the body.

In Figure 4, the inclined line T indicates the line of one pitch of the thread 15 of the body 1 and the line T' indicates the start of the next pitch of the thread. The tabs 54 to 65 are only shown schematically, with square ends, to indicate their position relative to the thread line - Figure 4 does not show the actual shape of the ends of the tabs. The thread 15 is shown as being aligned only with the left-hand tab 54 in the upper row; it is not exactly aligned with any other of the tabs 55 to 65. Figure 4 indicates the natural state of the tabs, that is, before they are subject to any axial flexing. This condition exists when the nut 5 is loosely positioned on the body 1 and, because only one tab is fully engaged with the thread 15, the retention of the nut on the body is relatively weak.If the nut were pushed further onto the body, a downward movement in Figure 4, different ones of the tabs would engage the thread.

More particularly, a movement of 1/12 of a pitch would bring tab 59, which is the tab nearest to the thread 15, into full engagement with the thread'and would cause tab 54 to deflect outwardly over the apex of the thread and come out of full engagement. A further movement of 1/12 of a pitch will bring the next tab 64 into full engagement. Further movements of 1/12 of a pitch would bring successive tabs into full engagement in the sequence:57, 62, 55, 60, 65, 58, 63, 56, 61, 54, 59, 64 and so on. The sequence of engagement of the tabs one after the other is chosen such that successive tabs are spaced from one another by 1500, that is, one tab to the side of the tab that is directly opposite.Because the tabs engage one at a time in steps of 1/12 of a pitch, and because the inclined surface of the tabs is smooth, pushing the nut onto the body is relatively smooth, requiring only a low force. This also enables any misalignment of the tabs with the thread to be easily corrected when the nut is brought into abutment with the flange.

When the nut 5 abuts the bulkhead 3, the user tightens the nut by rotation. This causes any axial slack between the nut and the bulkhead to be taken up and, when no further axial displacement of the nut is possible it causes flexing of the tabs. Initially, only one tab (for example, tab 60) will be in full engagement with the thread so rotation of the nut in a tightening sense will cause the tab 60 to bow outwardly, as shown in Figure 7. The tip of the tab is displaced resiliently axially by a small distance whilst maintaining full engagement. As the thread 15 moves forwardly relative to the nut 5, by 1/12 of a pitch (equivalent to a rotation of 30 ), it will come into full engagement with the tip of previous tab 55 to have been in full engagement, so that two tabs 60 and 55 are now fully engaged. A further tightening of the nut by 30 will further flex the first engaged tab 60, will flex the second engaged tab 55 and will bring a third tab 62 into full engagement. The location of two successive tabs, as mentioned above, is selected so that they are as close as possible to being directly opposite one another. In this way, if any two tabs are fully engaged, they will provide a well spaced and balanced restraining support for the nut.

Spacing the tabs by less than one pitch assures that the rotation needed to tighten the nut is kept to a minimum and that the tightening is achieved progressively. The nut is also suitable for use on bodies with short threads, since the tabs can be spaced over a short axial distance within the nut.

The invention can be used to avoid completely any need for rotation on assembly, thereby simplifying automated assembly. The nut need not be open at both ends, as described above, but could be closed at one end in the form of a cap or other closure. For example, the nut could be a dust cap for a tyre valve or the lid of ajar or container. The resilience provided by the tabs helps make the assembly resistant to vibration, so that the nut remains tight under the influence of vibration.

Filling and sealing of a container can be simplified by avoiding the need for any rotation, whilst the lid can be removed and replaced readily in the conventional way.

It will be appreciated that the nut could be made of different materials, such as metal, providing the tabs are sufficiently flexible to enable at least two tabs to be brought into full engagement with the thread on tightening.

Claims

1. A fastening for mounting an externally-threaded component, the fastening having a plurality of resilient tabs projecting internally of the fastening and inclined at an angle to the axis of the fastening such that the tabs deflect inwardly as the fastening is pushed axially onto the externally-threaded component in one direction and engage the thread to prevent axial displacement of the fastening in the opposite direction, wherein the spacing between the tabs is such that in their natural state when one tab is engaged with the thread of the externally-threaded component, the others of the tabs are not fully engaged, and wherein the tabs are flexible to enable axial displacement of the ends of the fully engaged tabs such that tightening of the fastening brings at least one of the others of the tabs into full engagement with the thread.

2. A fastening according to Claim 1 having n tabs spaced from one another by 1/n of a pitch of the threaded component.

3. A fastening according to Claim 1 or 2, wherein the tabs are arranged in two rows.

4. A fastening according to any one of the preceding claims, wherein the tabs have a shallow curvature lying on the surface of a common cylindrical plane.

5. A fastening according to any one of the preceding claims, wherein the inner edge of the tabs has an acute angle.

6. A fastening according to any one of the preceding claims, wherein the angle at which the tabs are inclined to the axis is such that a normal from the flank of the thread of the threaded component is inclined below a centre line along the tabs in the direction of tightening of the fastening.

7. A fastening according to any one of the preceding claims, wherein the angle at which the tabs are inclined to the axis is substantially 37.4 .

8. A fastening according to any one of the preceding claims, wherein the tabs are arranged such that tightening the fastening brings successive tabs into full engagement with the thread spaced from one another by substantially 1500.

9. A fastening according to any one of the preceding claims, wherein the fastening is moulded from a plastics material.

10. A fastening according to any one of the preceding claims, wherein the fastening has a plurality of external flats.

11. A fastening substantially as hereinbefore described with reference to the accompanying drawings.

12. An assembly comprising an externally-threaded component and a fastening according to any one of the preceding claims.

13. An assembly according to Claim 12, wherein the externally-threaded component includes a cable gland.

14. A cable gland assembly substantially as hereinbefore described with reference to the accompanying drawings.

15. A method of securing a fastening to an externally-threaded component, the fastening having a plurality of resilient, flexible tabs projecting internally of the fastening and inclined at an angle to the axis of the fastening the spacing between the tabs being such that in their natural state when one tab is engaged with the thread of the externally-threaded component, the others of the tabs are not fully engaged, comprising the steps of pushing the fastening axially onto the component so that the tabs deflect inwardly and snap over each pitch of the external thread and subsequently rotating the fastening so that the engaged tab flexes to enable axial displacement of the end of the engaged tab allowing at least one of the others of the tabs to be brought into full engagement with the thread.

16. A method of securing a fastening to an externally-threaded component substantially as hereinbefore described with reference to the accompanying drawings.

17. Any novel feature or combination of features as hereinbefore described.