GB2077876A

GB2077876A - Nuts

Info

Publication number: GB2077876A
Application number: GB8112084A
Authority: GB
Original assignee: EFG Ltd
Current assignee: EFG Ltd
Priority date: 1980-04-30
Filing date: 1981-04-16
Publication date: 1981-12-23
Also published as: CA1161285A; DE3116981A1; GB2077876B; ES267236Y; ES267236U; NL8102139A; FR2481765A1; AU6993181A; SE8102700L; IT8167582A0

Abstract

A self-locking nut has a nut body (2) in which the bore (3) which receives the threaded shank of a cooperating bolt has a reduced bore diameter portion (5) which may be unthreaded, is reinforced by at least one external band (7) located around the reduced bore diameter portion, and formed of a material having a tensile strength greater than that of the material of the nut body (7), which is preferably nylon or glass fibre filled epoxy resin for use with aircraft structural components made of similar materials. In Figure 4 the reinforcement comprises a single band the external configuration of which conforms to the external configuration of the nut body (1') as a whole. <IMAGE>

Description

SPECIFICATION Nuts This invention relates to nuts. More particularly it is concerned with the provision of relatively inexpensive self-locking nuts which are relatively simple in form and easy to manufacture and which are reliable in use. The present invention has been developed with the particular needs of the aero-space industry in mind, but locking nuts constructed in accordance with the present invention are not restricted to use in that industry alone.

Locking nuts have had a long and chequered history. The first reliable self-locking nuts comprised a conventional hexagonal metal nut body at one axial end of which was superimposed and rigidly held in position a collar of fibrous or similar material having a central hole whose diameter was equal to or a little greater than the core diameter of the thread. When a bolt was inserted into such a nut, it would perform in the conventional manner until the advancing bolt came up against the fibrous collar. At this point the axial resistance of the collar forces the threads of the nut and bolt together and thus induces a torque resistance to the rotation of the nut upon the bolt. As the bolt is further screwed into the nut, it plastically deforms the collar into a counter-thread, thus introducing a secondary torque resistance.

This type of self-locking nut was rapidly and universally adopted and has been given the technical term "stiff-nuts". Numerous improvements upon this basic arrangement were devised, particularly to ensure that the fibrous collar did not tend to rotate relative to the nut body, for any such rotation would weaken or destroy the locking properties of the nut.

With the development of plastics the adoption of these materials in industry since the second world war, plastics have been substituted for the fibours collar in the conventional stiff-nuts, with some success.

There have, of course, been very many other proposals for the construction and manufacture of self-locking nuts. Indeed, it is fair to say that the literature, and particularly the patent literature, in this art is replete with paper proposals. The great majority of these proposals have proved unmitigated failures. Designs which appeared in the laboratory to work adequately have been found insufficiently reliable in practical field tests and in large scale manufacture. Very many of the prior proposals involved altogether too complicated engineering to make the nuts at an economical price.

There is a continuing need in the industry for simple reliable and cheap self-locking nuts.

Additionally, there are special requirements in the aero-space industries and in other industries where weight reduction is of paramount importance for simple cheap and reliable light weight nuts. There is also an unsatisfied need for simple cheap and reliable self-locking nuts for use where magnetic or other reasons require that the mass of metal in a nut must be kept to a minimum.

Attempts to produce self-locking nuts from plastics material have generally failed. Our own experiments have demonstrated first that the allplastics stiff-nut, being elastic of nature, does not provide the desired amount of torque resistance; secondly that there is a tendency for the nut to spread or burst outwardly through its side walls and/or in the axial direction of the nut as a result of the tightening which provides a locking function. This feature is both undesirable in itself and may lead to destruction of the nut.

We have now found that by a simple expedient cheap and reliable self-locking nuts can be made from plastics materials without the locking action tending to result in bursting of the nut.

In accordance with the present invention, there is provided a self-locking nut, comprising: a nut body, having a threaded bore opening at one axial end thereof and adapted to receive the threaded shank of a co-operating bolt, the bore terminating within the nut body in a reduced bore diameter portion, the maximum diameter of which is less than the maximum diameter of the remainder of the bore; the nut body being formed of a plastics or other light-weight material and being reinforced by at least one external band, ring or sleeve, formed of a material having a tensile strength greater than the material of the nut bdy and located about the outside of the nut body in said reduced bore diameter portion.

The nut body is most preferably formed of a plastics material such as nylon to which other materials may be added to influence base material properties: such as glass fibres. The use of a glass fibre filled epoxy resin as the plastics material is of particaular value since nuts in accordance with this invention manufactured of such a material will avoid the corrosion problem which has arisen with conventional self-locking nuts when manufactured from certain steels and light alloys and used with the glass-reinforced epoxy resin components now increasingly used in aircraft structures. The material of the external band, ring or sleeve will then need to be chosen appropriately to avoid corrosion in the nut.

Preferably the reduced diameter portion of the bore is unthreaded and has a diameter equal to or greater than the core diameter of the thread.

The reinforcement may be provided in situ by insertion in the mould when the nut body is being formed by injection or other appropriate process.

The reinforcement may consist of one or more complete rings coaxial with the axis of the bore, or of one or more complete bands similarly located.

It may be shrunk on to the otherwise finished nut body, which may have a generally cylindrical configuration in said reduced bore diameter portion.

Embodiments of self-locking nut constructed in accordance with the present invention are described hereinbelow by way of Example only with reference to the accompanying drawings, in which: Figure 1 shows an end view of an embodiment of nut in accordance with this invention; Figure 2 shows a sectional view taken along the line Il-Il in Figure 1; and Figures 3 and 4 show views similar to those of Figures 1 and 2 of an alternative embodiment also constructed in accordance with this invention.

The self-locking nut generally indicated 1 in Figures 1 and 2 comprises a nut body 2 suitably moulded or cast from a relatively hard plastics material such as a hard nylon. The nut body has a threaded bore 3 which progresses inwardly from one axial face 4 of the nut body. The thread may be any of the conventional threads whereby the bore 3 is adapted to receive the threaded shank of a co-operating bolt of the same conventional thread. The bore terminates within the nut body in a reduced bore diameter portion 5 which, in the particular arrangement illustrated, penetrates through to the other axial end face of the nut body. Reduced bore diameter portion 5 must in general have a diameter which is less than the maximum diameter of the main threaded portion 3 of the bore and may itself be threaded, though not to the full depth of the thread.However, in the preferred arrangement portion 5 is unthreaded and has a diameter which is greater than or equal to (and preferably a little more than equal to) the core diameter of the threaded portion 3. A metal band 7, suitably made of aluminium, steel or other material having good tensile properties is provided as reinforcement about the outside of the plastics nut body 2 in the unthreaded portion 5 of the bore. In the particular arrangement illustrated in Figures 1 and 2, band 7 extends along substantially the whole length of the unthreaded portion of the bore from end face 6.

Other arrangements are possible. The reinforcement need not always extend over the full axial length of the unthreaded portion. It might even extend over some of the threaded portion. It need not be closed but may be formed as a helix formed of wire stock. The reinforcement, whatever form it takes, may be conveniently formed about the outside of the nut body when the latter is being formed by injection moulding or other appropriate process. In the preferred arrangement, as for the illustrated arrangement, the reinforcement is shrunk on or pressed on to.a generally cylindrical end portion 8 of the otherwise finished nut body.

In operation, when the nut 1 is offered up to a co-operating bolt, the nut will turn freely on the bolt until the bolt reaches the end of the threaded portion 3 within the nut body; thereafter, the thread of the bolt will press against and then cut into and/or deform and compress the material of the nut body in the unthreaded portion 5. The resistance to forward movement of the bolt will, as in the conventional stiff-nut, tend to press the threads of nut and bolt together axially in a locking fashion. Additional resistance to further threading of the nut on to the bolt or unthreading of the nut from the bolt is created by direct resistance between the material of the unthreaded portion 5 of the bore and the bolt thread.The metal band 7 tends to resist radially outward deformation of the nut body over the unthreaded length of the bore so tending to add to the locking effect and at the same time resisting radially outward bursting damage to the nut body. It also improves the axial strength of tne nut against stripping of the thread.

Although the illustrated embodiment of the nut has the configuration externally of an hexagonal nut with a cylindrical collar or crown, the invention is not so limited. The external configuration of the nut body may take various of the conventional forms, including conventional hexagaonal forms having less than six or more than six faces on the nut body, or the so-called "anchor" nut form. The band, ring or sleeve, is then suitably shaped, at least on its radially outer side, to conform to the basic external configuration of the nut.

Figures 3 and 4 illustrate, in views generally similar to those of Figures 1 and 2, a nut 1 formed in a conventional hexagonal external configuration. The nut is otherwise essentially as described with reference to Figures 1 and 2 above. It will be seen that metal band 7' is hexagonal both internally and externally its external dimension corresponding with that of the nut as a hole. We have found that this embodiment has advantages over the arrangement of Figures 1 and 2 in that the bearing surface for a spanner or the like is significantly increased. At the same time the risk of damage to the nut at its external edges during tightening is manifestly reduced.

Claims

1. A self-locking nut comprising a nut body, having a threaded bore opening at one axial end thereof and adapted to receive the threaded shank of a co-operating bolt, the bore terminating within the nut body in a reduced bore diameter portion, the maximum diameter of which is less than the maximum diameter of the remainder of the bore; the nut body being formed of a plastics or other light-weight material and being reinforced by at least one external band, ring oro sleeve, formed of a material having a tensile strength greater than the material of the nut body, and located about the outside of the nut body in said reduced bore diameter portion.

2. A self-locking nut according to Claim 1, wherein the nut body is formed of nylon with the optional addition of a finely divided inclusion to influence base material properties.

3. A self-locking nut according to Claim 1, wherein the nut body is formed of a glass-fibre filled epoxy resin.

4. A self-locking nut according to any of Claims 1, 2 or 3, wherein the reduced diameter portion of the bore is unthreaded and has a diameter equal to or greater than the core diameter of the thread.

5. A self-locking nut according to any preceding claim, wherein the reinforcement consists of one or more complete rings coaxial with the axis of the bore, or of one or more complete bands or sleeves the axis or axes of which is (are) coincident with the axis of the bore.

6. A seif-locking nut according to Claim 5, wherein the reinforcement comprises a single band the external configuration of which conforms to the external configuration of the nut body as a whole.

7. A self-locking nut according to any of Claims 1 to 4, wherein the reinforcement comprises a helix formed of wire stock.

8. A self-locking nut according to any preceding claim, wherein the reinforcement is provided in situ by insertion in the mould when the nut body is formed by injection or other appropriate process.

9. A self-locking nut accordong to Claims 5 or 6, wherein the reinforcement is shrunk on to or pressed into place over the otherwise finished nut body in said reduced bore diameter portion.

1 0. A self-locking nut substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.