GB2293636A

GB2293636A - A self-locking nut

Info

Publication number: GB2293636A
Application number: GB9419658A
Authority: GB
Inventors: John Williamson
Original assignee: Errut Products Ltd
Current assignee: Errut Products Ltd
Priority date: 1994-09-28
Filing date: 1994-09-28
Publication date: 1996-04-03
Anticipated expiration: 2014-09-28
Also published as: GB9419658D0; GB2293636B

Abstract

A self-locking nut (10) has a left-handed thread (24), and is for securing rotating tools to bolts, shafts or spindles so as to utilise the self-tightening principle. Nylon plugs (28) are screwed or bonded in bores (26) to extend as far as the inner diameter of the screwthread (24). Alternatively, the plugs (28) may be replaced by a deformable sleeve in the nut bore (22) or a penetrable diaphragm across the bore (22). The washer (14) may be secured by welding, adhesive or friction, or may be omitted. The nylon plugs (28) (etc) prevent finger-tightening of the nut (10). <IMAGE>

Description

A SELF-LOCKING NUT The invention relates to a self-locking nut or locknut.

It is long established practice that potentially dangerous items such as rotating cutters, grinders, blades, discs, circular saw blades and other tools are held in position by clamp plates. These clamp plates are secured on a threaded shaft or spindle by a nut whose thread is cut so that is is continuously tightened by the friction generated by the rotating motion of the tool. This means that the threads on the shaft and nut are left-handed to utilise the conventional direction of rotation of a tool about its shaft or spindle. In some systems, the blade is effectively keyed to an unthreaded shaft by means of flats. However, in such a system, the assembly is clamped together before use by a left-hand threaded bolt which screws into the end of the shaft and is thus continuously tightened by the shaft rotation.

Such "self-tightening designs are generally considered to be intrinsically safe. h'owever, the true safety of these designs depends entirely on the self-tightening principle which, in turn, depends upon good frictional contact (direct or indirect) between the nut or bolt and the shaft or spindle. All tools utilising the self-tightening principle carry instructions that nuts or bolts used to secure the tools must be tightened with a spanner or other torque-applying tool. If these instructions are carried out, the self-tightening action will be effective in virtually all cases. No minimum torque is specified or, indeed, needed: even a modest spanner force will be sufficient to ensure sufficient frictional contact to implement the self-tightening principle.

However, it occasionally happens that such tools or cutters come loose or detached and this can have extremely dangerous consequences, particularly with tools rotating at up to 20,000 rpm. Accidents are almost always due to the nut not being tightened sufficiently to allow the self-tightening principle to come into effect. Lack of sufficient tightening, combined with a situation wherein switching off the power driving the tool leads to rapid decelaration or wherein the tool is powered intermittently as a check before starting the intended work, can cause the nut or bolt to work loose. This then permits the tool to become detached from the shaft or spindle.

The most likely reason for the tool operator to fail to tighten the nut or bolt is an interruption in his concentration between initially applying the nut or bolt with the fingers and tightening it with a spanner or wrench. If the operator is distracted after initially applying the nut or bolt, he may later forget to tighten the nut or bolt fully using the appropriate torque-applying tool. Tightening the nut or bolt with the fingers is very rarely sufficient to bring the self-tightening principle into operation.

There is clearly a need for a means of securing a rotating tool onto a shaft or spindle which is reliable, reduces still further the risk of the tool becoming detached from the shaft or spindle and is also cost effective to produce. It is an object of the present invention to provide such a securing means.

The invention provides a self-locking nut having a threaded bore, wherein the thread of the bore is left-handed. Advantageous features are set out in the subsidiary claims.

Until now, all known self-locking nuts have had right-hand threaded bores. Therefore, they have been completely unsuitable for use in the present application, i. e. to secure rotating tools to shafts or spindles so as to utilise the self-tightening principle. However, using a self-locking nut to secure the tool on the shaft or spindle means that the risk of the self-locking nut working loose in a direction which is opposite to that used to advantage in the self-tightening principle is greatly reduced. Also, the cost of manufacturing a self-locking nut having a left-handed thread is not significantly greater than the cost of manufacturing a self-locking nut having a right-handed thread.A further advantage is that, with many designs of self-locking nut, a considerable torque is required to apply it to the threaded shaft or spindle, the required torque being greater than that applicable with the operator' 5 fingers. Thus a tool must be used to fit the self-locking nut and hence the risk of failing to tighten the nut with a spanner or wrench is substantially eliminated. Once in place, the self-locking nut will not be able to work loose, even if it is not in contact with the rest of the assembly or if it is tilted to create the maximum possible tendency to do so.

An embodiment of the present invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a enlarged plan view of a self-locking nut according to the present invention; Figure 2 is a cross section taken along the line II-II of Figure 1; and Figure 3 is a perspective view of the self-locking nut of Figures 1 and 2.

The figures show a self-locking nut 10 according to the present invention. The self-locking nut 10 essentially comprises a nut 12 and a washer 14. The nut 12 has a generally hexagonal outer portion 18 adapted in conventional manner to engage with standard spanners and other torque-applying tools in the usual way. The nut 12 also has a shank 20 which is dimensioned to receive the washer 14.

The nut 12 has a central bore 22 which extends through the entire width of the nut 12. The central bore 22 is internally threaded along its entire length.

The thread 24 is left handed and is dimensioned so as to cooperate with an appropriate bolt, shaft or spindle in conventional manner.

The nut 12 also has two diametrically opposed bores 26 which extend from the central bore 22 through the outer portion 18 in a direction parallel to the plane of the washer 14. Plugs 28 are located in the bores 26 and these are conveniently made of nylon although other plastics materials are suitable. The plugs 28 are held in place in the bores 26 by means of a suitable bonding material or adhesive. The plugs 28 could alternatively be located by means of screw threads. The plugs 28 each extend into the respective bore 26 as far as the minor diameter of the central bore 22, ie. as far as the internal diameter of the central bore 22 before the thread is cut. It is essential that the plugs extend beyond the major diameter of the screw thread 24.

The washer 14 engages with the shank 20 of the nut 12 and is of standard configuration and materials. The outer diameter of the washer 14 is larger than the outer diameter of the outer portion 18 of the nut 12 and its effect is to reduce the stresses transferred between the nut 12 and an object located, when the nut is in use, adjacent the washer 14. The washer 14 can be secured to the nut 12 by welding or by any other appropriate means, e. g. by an adhesive or merely by friction.

When the self-locking nut 10 shown in Figures 1 and 2 is to be put to use, an appropriate bolt, shaft or spindle is introduced into the central bore 22 of the nut 12. Continued relative rotation between the self-locking nut 10 and the bolt, shaft or spindle forces the external thread of the bolt, shaft or spindle into engagement with the inner ends of the plugs 26.

The plugs 26 are thus highly compressed and deformed during this procedure such that an extremely tight fit is achieved between the bolt, shaft or spindle and the self-locking nut 10. The extremely tight fit prevents any unwanted movement or working loose of the self-locking nut 10 with respect to the bolt, shaft or spindle. Mso, the torque required to bring the self-locking nut 10 into appropriate contact with the bolt, shaft or spindle is far higher than could be achieved by human fingers. Therefore, since it is essential that the self-locking nut 10 be applied using a torque-applying tool, the risk of insufficient tightening taking place when the self-locking nut 10 is used to secure rotating tools is substantially eliminated.Furthermore, any torque applied to the self-locking nut 10 by virtue of the rotation of an adjacent tool will serve only to tighten the self-locking nut 10 on the bolt, shaft or spindle as opposed to causing the self-locking nut 10 to loosen.

It will be appreciated that the invention is not limited to the embodiment illustrated in the drawings.

Other forms of locknut or self-locking nut are known; in particular, it is possible to achieve a tight fit between the bolt, shaft or spindle and the nut 12 in other ways. For example, instead of the plugs 28 the nut 12 could incorporate a deformable sleeve within the central bore 22, the sleeve being deformable by introduction of the bolt, shaft or spindle.

Alternatively, the nut could incorporate a diaphragm or other penetrable barrier at a point along the central bore 22 through which the bolt, shaft or spindle passes during location of the self-locking nut 10. Such an arrangement would have a similar effect to that of the plugs 28. Also, the washer 14 is not an essential part of the invention; it could be omitted altogether or formed integrally with the nut 12. Further, if the plugs 28 are present, it will be appreciated that any number of plugs can be employed and that, if more than one is present, they need not be equi-spaced about the central axis of the nut 12.

Claims

1. A self-locking nut having a threaded bore, wherein the thread of the bore is left-handed.

2. A self-locking nut as claimed in claim 1, wherein at least one plug extending into the threaded bore beyond the major diameter thereof is provided.

3. A self-locking nut as claimed in claim 2, wherein two diametrically opposed plugs are provided.

4. A self-locking nut as claimed in claim 2 or 3, wherein the or each plug is made of nylon.

5. A self-locking nut as claimed in any one of the preceding claims, wherein a washer is provided on the self-locking nut.

6. A self-locking nut as claimed in any one of the preceding claims, wherein the self-locking nut comprises means for preventing the location of the self-locking nut onto a correspondingly threaded bolt, shaft or spindle other than by means of a torque-applying tool.

7. A self-locking nut substantially as hereinbefore described with reference to the accompanying drawings.