IE45489B1 - Improvements in/or relating to split nuts - Google Patents

Description

The present invention relates to split nuts which comprise a plurality of segments which cooperate together and replace a conventional one-piece nut for use on a stud or bolt.

Although in smaller Bizes split nuts may be more 5 expensive to manufacture, they may be more economic if account is taken of the cost of fitting the nut onto a stud or bolt.

More particularly split nuts offer a great potential advantage in connection with the removal of the nut from the bolt,·.

This is particularly the case Where the bolt is exposed to the risk of damage, corrosion or coating with foreign material which could cause a conventional one-piece nut to jam on the thread. However, hitherto split nuts have been of a complex design and therefore expensive to produce and often expensive to fit. Frequently, such split nuts have relied on captive devices to hold the nut segments together and generally the nut segments differ from one another, for example by having left and right engagement features.

In United States Patent Specification 3797336 segmented nut arrangements are described. One embodiment comprises a nut formed in ttvo halves with a circumferential spring clip located in a groove to hold the.nut halves together and to urge them into clamping engagement around a bolt or stud. However, the arrangements described rely on the use of special tools which would prevent the split nut arrangement being used where restricted access occurred. The object of the special tools is to spread the segments of the nut so as to disengage the segments from the screw thread so as to permit the nut to be rapidly positioned at the location at which it A3 489 can be tightened. A different tool is required when the split nut is to be removed after ‘loosening. This patent specification does, however, describe the use of a chamfered end face at one end of the split nut to engage a corresponding shaped washer so that as the nut is tightened a wedging effect clamps the nut segments firmly around the bolt.

There is, nevertheless, still an unfulfilled demand ' for a split nut arrangement which can be applied easily in most situations, and yet is still a strong nut. Furthermore, consistently correct application is vital, even if the fitter is giving the operation less than his full attention.

According to one aspect of the present invention, there is provided an element which forms half of a split nut assembly, the other half of the split nut assembly being a substantially identical element which is inverted relative to the first element. The element is thus arcuate in shape and extends around an axis which coincides with the axis of the bolt on which the split nut is to be fitted. The element has an inner screw threaded surface, an outer peripheral surface to be engaged in order to rotate the element and respective end faces which are chamfered so that in use the chamfered surfaces of two elements forming the split nut engage a corresponding surface of a washer or a workpiece so that as the split nut is tightened, the elements are urged into clamping engagement around the bolt. The element also has first and second side faces extending between the inner and outer surfaces with at least one of the side faces having location means associated therewith and formed so that in use the location means interengage with the location means of the other element of the split nut only when the other element is inverted relative to the first element. This causes the elements to be positioned relative to one another in the axial direction, and incorrect assembly is prevented.

To assemble the nut, one of the elements is inverted relative to the other element, and the screw threading on the inner surface of the elements is such that when two elements are assembled to form the split nut, a screw thread is provided leading from one end of the nut to the other.

The present invention is defined in the claims appended to the specification and the above description is given for the purpose of indicating one form, of the invention. There will now be described further advantageous features which may be used in embodiments of the present invention.

Preferably both of the side faces of the element have first and second corresponding location members, for example the first location member in each case comprising a projection and the second location member comprising a recess.

It is convenient that the pair of location members of each of the side faces is the same as the other pair and preferably the first and second location members are symmetrically disposed relative to a central plane which extends through the middle of the split nut element and at right angles 2S to the axis of the element.

Preferably the side faces of each nut element are slightly set back from an axial plane passing through the axis of the element and at right angles to the central plane. Thus the nut element is not a true half nut and this feature permits a small clearance so that the nut’-plements way be tightly clamped towards one another when they are tightened on a bolt in co-operation with a counterbore workpiece or washer.

So that identical split nut elements can be used, the screw threading is such that when the nut is viewed as a true half nut a line on the plane of the split at the mid-height of the nut element passes substantially through the centre of a crest of the thread at one side of the element and on the other side of the element passes substantially through the centre of the root of a thread. The chamfer on each end face can be conical, although alternatively a domed or spherical face could be provided and although theoretically this may be preferable from a strength point of view because of the true rocking motion permitted, it may be more convenient in practice simply to adopt a chamfer of conical shape.

If the cone in each case is considered to have an axis coinciding with the axis of the element, then the angle of the conical face to the axis is preferably in the range 30° to 75°, and an angle of about 60° is particularly preferred since this permits the split nut to be tightened with a relatively small amount of rotation and a very strong structure can be provided with a split nut of standard height and without making the counterbore in the washer or workpiece excessively deep.

The invention extends to the combination of two elements to form a split nut. This combination may also include a relatively thick washer having a countersink corresponding - 5 in shape to the chamfer, tha washer being thick enough to resist the bursting pressures applied when the nut is tightened The opposite side of the washer may be substantially planar but may also have a serrated surface to facilitate frictional engagement, with the washer with the workpiece.

Use of at least preferred embodiments of the invention permit substantial advantages to be obtained over the prior art known to the applicant. The nut element is of simple, design and each of the two elements forming the split nut can be identical. Strong and readily installed split nuts can be - 6 provided readily by known manufacturing techniques ab a relatively low price and manufacture to within very close tolerances is possible· Not only can the split nut be lighter than a conventional 5 nut, bub blie split nut embodying theinvention may be applied rapidly and, for example, the split nut can be tightened with about a quarter of a turn in the case of a fairly coarse threaded nut. Furthermore, the design can ensure that correct assembly occurs and the axial alignment of the two elements in the split nut obviates the risk of one of the elements being a portion of a thread displaced in the axial direction. If such an occurrence were permitted to happen, although the nut may appear to be tightened it would be much less strong than it should be since one Of the elements would not be correctly seating on the washer or workpiece.

Furthermore, complex captive devices are obviated and the enormous practical operational difficulties of having loft and right elements are avoided.

Although it is preferred to provide the side faces in 20 planes extending parallel to the axis of the element, this is not essential. For example the planes could be at a small angle such as 10° to the axis. ..

Should a stiffnut be required, i.e. a nut which tends bo be more firmly retained or locked in position than a conventional nut, then a spring clip may readily be mounted around the periphery of the assembled, split nut.

A preferred embodiment of the invention will now be described for the purpose of illustration with reference'to ' - 7 Figure 2 is a plan view of.tho element; Figure 3 is a side view of the element;’ Figure 4 is an axial cross-sectional view of an assembly comprising a split nut, a washer and a'bolt.

Referring first to figures 1-3» the element 1 comprises a threaded inner surface 2 which in this embodiment is threaded according to British Standard Whitworth» an outer peripheral surface 2a having the shape of half a hexagon, first and second end surfaces 3 and 4 and side faces 5 end 6. Each of the end faces 3 end 4 is chamfered to provide a substantially half-annular shoulder 7 which in this embodiment IS is conical, the angle between the axis and the cone being 60°, Each of the side faces 5 and 6 has first and second locating members, which in this embodiment are provided respectively by a raised rectangular block 8 and a similarly shaped recess 9 in which the hlbck 8 would be a loose fit. The block 8 2Q and recess 9 in each case are substantially symmetrically disposed about a central plane Λ-A which is normal to the axis of the element, the recess being enlarged to provide a clearance when a block of another element is inserted. The plane A-Λ will intersect the plane of the split at a line which if tho nut element were projected to bo a truo half nut would, on ope side of the element, pass through the centre of the crest of the screwthread and on the other side pass through the centre of the root of the thread, the element having a U 4 8 3 / single 'start* Indicated nt XU. Λ split nut is assembled by talcing two identical elements and inverting one of the elements relative to the other so that at one end of tho split nut the end face 3 of one element is adjacent the end face 4 of the -other element and the side faces 5 and side faces 6 confront one another.

The raised block 8 of each element engages into the opposed recess 9 in the other element and thus the elements are axially aligned and motion in a direction normal to the axis is also limited.

In use the workpiece must have a counterbore of suitable shape or alternatively a strong thick washer with a suitable counterbore must be used. Figure 4 illustrates the latter alternative in which a strong washer 12 is provided on a bolt 13, the washer having a conical counterbore corresponding to the chamfer 7 provided on the nut elements 1Λ and IB.

An optional spring clip 16 is shown in Figure 4, this being substantially annular with concave confronting end faces for engagement with a tool adapted to press the clip open for fitting and removal. The clip 16 can greatly X increase the resistance to rotation of the nut when tightened. The use of powder metallurgy is particularly suitable for manufacturing tho nut elements since a high degree of accuracy can be obtained by the use of known techniques.

Furthermore, the present invention offers the advantage of tho element being formed readily and economically in a die.

Sintered steel split nuts, it is believed, can be I manufactured to comply with required standards tor conventional low carbon steel nuts and sintered copper infiltrated steel split nuts, it. is believed, can'be made to comply with standards for high strength nuts, Where a conically counterborod washer is ' used, this can readily be made by cold forming or powder metallurgy.

Regarding the economics of use, it has been reported that the cost of fitting a conventional nut is about four . times the cost of the nut. It is expected that split nuts . embodying the present invention in smaller sizes would be slightly more expensive than equivalent conventional nuts but actual experience has shown that fitting is about four times as fast, and thus it may fcs cheaper in many applications to usenubs according to the present invention. The invention can be especially useful in many instances particularly where demanding service conditions exist.

Where it is expected that nuts will have to be removed in due course for maintenance purposes, the present invention offers considerable time saving potential, particularly where there is a high risk of corrosion or damage to the screw thread. Such damage could make it difficult or impossible to remove a conventional nut without burning or cutting.

A s 16 3 In many engineering situations, accessibility is extremely difficult but nuts embodying the present invention can be applied and removed quickly because turning the nut through a small angle is all that is necessary.

Apart from the above advantages, a split nut embodying the present invention can be mechanically superior to a conventional nut ih that a better load distribution is applied to the threads. It has been established that with conventional nuts, most of the load is taken on the first thread because the pitch of the bolt increases due to tension and the pitch of the nut decreases due to compression, and also the nut expands away from the bplt under the wedging action of the threads thus further effectively decreasing the pitch of the nut on the first few threads. Use of the present invention with a conical washer forces the two split nut elements firmly onto the bolt and a slight rotation of the two elements occurs so that the free end of the nut contracts more than the loaded end. According to this theory, this nut rotation causes an effective increase in the pitch of the nut so that the load is taken up more evenly. The applicant offers the above theoretical explanation as an aid to understanding the present invention only and does not wish to be bound by the accuracy or completeness of this theory.

Tests have been conducted with embodiments of the invention and it has been demonstrated that a strength advantage over equivalent conventional nuts is provided.

Tests were conducted on three-quarter inch nuts and experiments extended to the chamfer angle being 60°, 55° and 50°. The £ ΰ 4 8 9 nuts embodying the present invention were consistently stronger, the extra strength varying from a few per cent up to more than twenty per cent.

It is suggested that the optimum chamfer angle is 5 about 60° (taken between the surface of the cone and its axis). Smaller cone angles would result in the nut having a greater height in order to accommodate a spanner and more rotation would be necessary to tighten and remove the nut. Furthermore a stronger washer would be required to accommodate the.bursting load.

Claims (18)

1. CLAIMS:10

1. An element for use with a substantially identical element to form a split nut, the clement (a) being arcuate in shape and extending approximately 180° about an axis which when the element is in use, will coincide with the axis of a threaded bolt on which the split nut is engaged, (b) extending in the axial direction between first and second end faces thereof, (c) having an outer peripheral surface (d) an inner screw-threaded eurface for threadably engaging said bolt, (e) first and second side faces each extending between the inner and. outer surfaces, (f) said first side face havixig location means formed such that when said split nut is assembled from two elements, the first and face of one element is at the same end of the split nut as the second end face of the other element and the respective first side faces are adjacent with the respective location means of the side faces interengaging and locating the elements relative to one another in the axial direction, (g) the screw threading on said inner surface being such that when said split nut is assembled a screw thread leading from one end of the nut to the other is provided, and (h) said first and second end faces being chamfered such that when in use tho chamfered surfaco of ono enA face will engage on a corresponding surface of a washer or a work piece thereby urging the elements of the split nut to clamp around the bolt.

2. , An element as claimed in claim 1, wherein both of said side faces have respective first and second corresponding location means.

3. An element as claimed in claim 2, wherein the pair of location means on each side 'face are the same as the other pair and each of the first and second location means are symmetrically disposed relative to the central 5 plane of the element, the central plane being at right angles to the axis of the element and passing through the middle thereof.

4. An element as claimed in any one of the preceding claims, wherein said location means comprises a projection and a 10 recess in the side face, the arrangement being such that the elements of the split nut are located also with respect to movement in the planes of the side faces.

5. An element as claimed in claim 4, wherein the projection is a rectangularly shaped block located adjacent to the 15 outer edge of the side face and the recess has a corresponding shape and location.

6. An element as claimed in any one of the preceding claims, wherein the chamfer of each end face provides a surface lying on a cone having an axis which coincides with the 20 axis of the element.

7. An element as claimed in claim 6, wherein said cone subtends an angle to said axis in the range 30° to 75°.

8. An element as claimed in claim 7 wherein said angle is approximately 60°. 25

9. An element as claimed in any one of the preceding claims, wherein said arcuate shape extends slightly less than 180° to provide a clearance between the adjacent side faces when a split nut is assembled.

10. Λη element as claimed in any one of the preceding claims, wherein the outer surface is· part hexagonal, the side faces meeting the outer surface at the middle of flats of the hexagon.

11. An element for use as half of a split nut substantially as herein described with reference to the accompanying drawings.

12. A combination comprising two elements each of which, is as claimed in any one of the preceding claims for forming a split nut.

13. A combination as claimed in claim 12, and further comprising a relatively thick washer compared to conventional washers for conventional nuts, the washer being shaped and dimensioned to co-operate with the elements and press them radially inwardly when the nut elements are tightened, the chamfer on the washer corresponding to the chamfer of said elements.

14. A combination as claimed in claim 13, wherein the other side of said washer is substantially planar but has an irregular surface for biting into a workpiece to resist rotation.

15. A combination as claimed in any one of the preceding claims 12-14, and further comprising a bolt.

16. A combination as claimed in any one of the preceding claims 12-15, and further comprising a spring ring adapted to fit around the outer surface to urge the split nut elements toward one another.

17. A method of securing together two workpieces having

18. aligned apertures comprising (a) taking a combination a's claimed in claim 15, and passing the shank of the bolt through the apertures, locating the two elements on the threaded shank . adjacent a conically counterbored face of a washer or the workpiece, and tightening the nut by rotation with a spanner through part of a turn. An element shaped for use as half a split nut and comprising (a) an outer peripheral surface for engagement by a tool to rotate the element about an axis which in use coincides with the axis of the split nut, (b) an inner screw-threaded surface extending around the axis, (c) first and second end faces at each axial end of the element which are chamfered for engaging a countersink-type bore in a washer or a workpiece to be engaged, (d) side surfaces extending in planes extending substantially radially and longitudinally of the axis, (e) first and second complementary location means on at least one of said side surfaces and disposed symmetrically on either side of a central plane of the element extending at right angles to said axis and through the middle of the element, the first and second locating means extending a part only of the distance between the central plane and 434 8 3 the axial end of the element, (f) and the screw threading on said inner surface corresponding to a thread in respect of which a line extending across a true half nut at the 5 intersection of said central plane and the plane of the split, passes through substantially the centre of a root of the thread on one side and substantially through the crest of the thread on the other side of the nut element whereby the . 10 split nut is formed by locating the element with a second identical element which is inverted to position its second end face at the same end of the split nut as the first end face of the first element and the complementary locating means IS interengage.