Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Internally threaded fastener element – e.g. – nut – etc. – Multipart
Patent
1990-10-26
1992-02-04
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Internally threaded fastener element, e.g., nut, etc.
Multipart
411156, 411278, 411533, F16B 3708, F16B 3922
Patent
active
050855506
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF INVENTION
This invention relates to locking-nut assemblies of the type consisting of a nut and a locking washer.
Very many different designs of locking-nut assemblies have been proposed and many are satisfactorily in use. However known assemblies may allow the nut to become loose in particularly arduous conditions. For example a rotary machine which rotates at a speed of up to 15000 rpm may be driven by a belt which engages a pulley mounted on the machine shaft. The end of the shaft is threaded and the pulley is held on the shaft against a shoulder by a locking-nut assembly. There is no driving formation such as a key, flat or taper on the shaft and the driving torque between the pulley and the shaft is dependent solely on the frictional forces generated by tightening the locking-nut assembly. Normally the shaft rotates clockwise and therefore the nut tends to tighten. However in certain circumstances rotation occurs in an anti-clockwise direction and this has a tendency to loosen conventional locking nut assemblies using either a split helical locking washer or a spring washer. If the nut loosens too far then it will not retighten when the pulley again rotates in a clockwise sense and drive between the pulley and shaft will be lost.
The conventional assemblies presently used rely for their effectiveness on the locking washer maintaining an axial force on the nut, when the latter tends to unscrew, which keeps the flanks of the complementary threads on the nut and the shaft in frictional engagement. This force is less, when the nut has slightly backed off from its fully tightened position, than when it is fully tight but is usually sufficient to prevent further unscrewing. However in arduous conditions such as mentioned above or in vibratory static conditions conventional locking-nut assemblies can come loose.
In addition to conventional designs using split helical or spring locking washers as mentioned above, there have been other more complex proposals which have formed the subjects of old patents but which, so far as the applicant is aware, have never been put into practice.
Thus GB A 341 333, which dates from 1931, describes a locking-nut assembly in which a nut has a spigot on which is mounted a conical washer. In one embodiment the spigot is of greater length than the thickness of the washer and acts as a stop to prevent flattening of the washer as the nut is tightened. In another embodiment the underside of the nut is conical and acts as a stop when the washer comes into contact with it. In both embodiments the stop acts to prevent flattening of the washer and so that the latter is not stressed beyond its elastic limit. The patent describes that the washer exerts a continuous high pressure on the nut to lock it. There are also frictional forces between the abutting faces of the nut and the washer and of the washer and the workpiece. There is a clearance between the bore of the washer and the spigot when the nut has been tightened.
In GB A 129 476, which dates from 1919, a separate nut and washer are disclosed. When the washer is flattened it frictionally engages the threads of the bolt under the nut. Thus the frictional locking effect of the conventional spring washer is enhanced by the additional frictional engagement of the washer with the threads of the bolt. In this arrangement there would in practice be great difficulty in removing the washer from the bolt in spite of what is said in the patent.
A somewhat similar but more complex arrangement is shown in GB A 1 027 674 in which a separate washer of a synthetic resin material is moulded about a spigot on the nut and when the nut is tightened down the washer is compressed axially and thus expands radially into engagement with the threads of the bolt on which the nut is mounted. Again the locking effect is caused by the flanks of the threads on the nut engaging the flanks of the threads on the bolt and the frictional forces between the washer and the bolt threads and between the washer on the one hand and the nut and the face of the
REFERENCES:
patent: 985826 (1911-03-01), McLaughlin
patent: 1384019 (1921-07-01), Johnston et al.
patent: 2380994 (1945-08-01), Pummill
patent: 2887891 (1959-05-01), Perez
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