GB2287765A

GB2287765A - Screwthreaded locking device

Info

Publication number: GB2287765A
Application number: GB9405776A
Authority: GB
Inventors: Keith Lyons
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-03-23
Filing date: 1994-03-23
Publication date: 1995-09-27
Also published as: GB9405776D0

Abstract

A dished spring washer 2 is secured to a threaded washer 3 and has a biting surface at its outer periphery for engagement either with a workpiece 14 (Fig 14) or (by inversion) with a nut or bolthead 19 (not shown). As the spring washer 2 is flattened, the threads 10 of the softer threaded washer 3 are compressed against the bolt threads. The neck 12 of the threaded washer 3 and the hole in the spring washer 2 are of rounded square section. Gripping recesses 7 in the spring washer 2 have projecting and chamfered edges, and ridges are provided on the concave surface of the washer 2. <IMAGE>

Description

DESCRIPTION LOCKING DEVICE The present invention relates to a locking device.

Nore particularly the present invention relates to a locking device for locking bolts or nuts in an in use position.

Spring steel locking washers have previously been employed to lock bolts, self tapping screws, nuts and like members in an, in use, position. United Kingdom Patent Specification GB 1600015 discloses a locking washer having a screw thread formed in a central bore thereof, which locking washer is substantially dish shaped for deformation and resultant compression against a surface when screwed up against the surface, deformation of the locking washer increasing friction between the washer and the screw threaded member onto which it is screwed. In this prior construction at least one recess is provided in the washer periphery to increase the frictional engagement of the washer with the surface. The washer may be made of plastics or other suitable materials.Spring steel is preferred since, due to its high resilience and strength, a strong locking force can be applied to the thread of the bolt or like member.

However, where a washer of a suitably resilient material is required to be several thread revolutions thick, problems arise in that the washer thickness restricts its compliance. Additionally, the large force applied over several threads by the washer in tension can damage the thread of the threaded member thereby reducing the life span of the washer and preventing re-use.

The aim of the present invention is to provide a locking device for bolts or the like, which locking device seeks to overcome at least some of the problems of the above mentioned prior art construction.

According to the present invention there is provided a locking device comprising a compression washer and a threaded washer, the compression washer being dish-shaped with a central bore therein, and made of a resilient material, at least one recess being formed the periphery of the compression washer, the threaded washer having a bore which is provided with a thread comprising several complete revolutions, the threaded washer being connected to the compression washer so that a threaded member can be threadedly engaged in said threaded bore and extend through said central bore.

In use with a threaded member eg a bolt engaged in said threaded bore and passing through the said central bore, the bolt may be also passed through a workpiece and engaged in a threaded bore in a fixed member. As the bolt is tightened the compression washer will be deformed between the workpiece and said threaded washer, the threads of the threaded washer thus being pressed against the threads of the bolt to frictionally resist rotation of the bolt.

This grip is achieved by the friction between the head of the bolt and the threaded washer and the friction between the compression washer and the workpiece. Advantageously the threaded washer and compression washer are integrally interconnected so that relative movement therebetween is prevented.

The locking device in accordance with the present invention thus provides a means for improved locking on a threaded member the present invention allowing the compression washer to be sufficiently thin as to retain its compliance while distributing its compressive force over several threads and so provide for secure locking.

Preferably the threaded washer is made of a softer material than the compression washer thereby enabling them to be more easily locked together. The threaded washer should also be of a softer material than the threaded member onto which it will be locked so that the threaded washer thread will strip in preference to the threaded member, it being the cheaper of the two components.

When used on a bolt the locking device of the present invention is locked between the bolt head and adjacent surface and when used under a nut on a threaded shaft with the compression washer against the nut, the nut will always be frictionally held on the threaded shaft even when slackened.

The present invention is further described hereinafter, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a side elevation of one embodiment of a locking device constructed according to the present invention; Fig. 2 is a side elevation of the compression washer of the locking device of Fig. 1; Fig. 3 is an axial cross section of the compression washer of Fig. 2 along the line A-A in Fig 4; Fig. 4 is a plan view from below of the compression washer of Fig. 2; Fig. 5 is a side elevation of the threaded washer of the locking device of Fig. 1; Fig. 6 is an axial cross section of the threaded washer of Fig. 5 along the line B-B in Fig 8; Fig. 7 is an axial cross section of a further embodiment of threaded washer suitable for use in the present invention; Fig. 8 is a plan view from below of the threaded washer of Fig. 5;; Fig. 9 is an axial cross section of the locking device of Fig. 1 along the line C-C in Fig 10; Fig. 10 is a plan view from below of the locking device of Fig. 1; Fig. 11 is a side elevation of the locking device of Fig. 1, positioned on a bolt so that the compression washer of the device will face a surface against which it is to be locked; Fig. 12 is an axial cross section of the locking device and bolt of Fig. 11 where the bolt is partially screwed through a surface and through an aperture in a workpiece which is tobe attached to said surface; Fig. 13 is an axial cross section of the bolt and locking device of Fig. 11 where the bolt has been screwed through the surface such that the outer periphery of the compression washer of the locking device touches the workpiece;; Fig. 14 is an axial cross section of thebolt and locking device of Fig. 11 where the bolt has been tightened against the surface such that the bolt head now abuts against the threaded washer of the locking device; Fig. 15 is an axial cross section of the bolt and locking device of Fig. 11 the bolt having fully compressed the locking device against the workpiece and bolt thread; Fig. 16 is a side elevation of Fig. 15; Fig. 17 is an axial cross section of the bolt and locking device of Fig. 11 where the bolt is partially withdrawn from the surface, workpiece and locking device; and Fig. 18 is a side elevation of Fig 17.

Referring to Fig. 1 of the accompanying drawings a locking device 1 constructed according to the present invention is illustrated and comprises two parts, a compression washer 2 and a threaded washer 3 which parts are connected to one another by connection means 12,21 best seen in Fig 9.

The compression washer 2 is described in more detail with reference to Figs. 2, 3 and 4 of the accompanying drawings, the threaded washer 3 is described in more detail with reference to Figs. 5, 6, 7 and 8 of the accompanying drawings; and the connection means 12 are described in more detail with reference to Figs. 9 and 10 of the accompanying drawings.

Referring to Figs. 2, 3 and 4 the compression washer 2 is a resilient and substantially dish-shaped, metal washer which is adapted to tension itself against a surface when compressed against it. It is substantially annular in shape (Fig. 4) and has a convex upper surface 4, and a concave lower surface 5.

A central bore 6 serves as a female mating member for a threaded stud or bolt and is generally rectangular with arcuate corner regions in plan view. The washer 2 has a periphery 20 in which a plurality of recesses 7 are formed, which peripheral recesses are defined by two edges 8 and 8,' one of which edges 8 passes substantially radially inwardly from the washer periphery 20. These edges serve two bite a surface against which they are locked when compressed.

Referring to Figs. 5, 6 and 8 the threaded washer 3 is generally a flattened T shape in side elevation.

A threaded bore 9 runs through the washer 3 and has a plurality of thread turns 10 formed therein. The Tshape has a generally rectangular cross sectioned stem 12 (Fig 8) which forms said connection means, the stem 12 or male mating member locking into the female mating member or central bore 6 of the compression washer 2 to form the locking device 1 of the present invention.

In an alternative embodiment of the threaded washer 3 shown in Fig 7, the bore 9 is countersunk as at 11, in its upper surface 22.

The stem or male mating member 12 which extends axially through the central bore 6 has side walls 13 which are concave (Fig. 6). and which are complimentary in shape to the convex wall of the bore 6 in the compression washer so that the compression washer so that the compression washer and threaded washer can be snap locked together - see Fig 9.

Referring to Figs. 4 and 8 it will be appreciated that the generally rectangular shape of the bore 6 and the complimentarily shape of the stem 12 locks the threaded washer 3 to the compression washer 2 thereby preventing relative rotation. Whilst the aperture 6 and stem 12 are generally rectangular as illustrated they can of course be any complimentary, non-circular shape, as desired.

The general principles of the use of the locking device 1 will now be described with reference to Figs.

11 to 18 of the accompanying drawings, in which a workpiece 14 is secured to a surface 15 using a bolt 16 and the locking device 1.

Fig. 11 shows the locking device 1 screwed onto an externally screw threaded member, in this case bolt 16. The bolt 16 has a thread 18 on to which the locking device 1 is threaded, is screwed into a threaded bore 17 in surface 15, through workpiece 14 (Fig. 12) such that the concave lower surface 5 of the compression washer 2 faces the workpiece 14. The degree of curvature of the compression washer 2 is chosen to suit the required locking strength. The bolt 16 is then tightened until the compression washer 2 touches the workpiece 14 (Fig. 13). At this point the threads 10 on the threaded washer 3 provide little resistance to the bolt 16 as it is screwed into the threaded bore 17 in surface 15. Indeed, little resistance is felt until the head 19 of the bolt 16 touches the threaded washer 3 (Fig. 14).

Once the slackness between the bolt 16, workpiece 14 and locking device 1 has been taken up further screwing of the bolt is resisted by the locking device 1, and additional torque must be applied to the bolt 16 to compress and flatten the compression washer 2.

On compressing the compression washer 2 against surface 15 the tensioning washer 2 compresses the threaded washer 3, thus compressing the threads 10 of the threaded washer 3 against the threads of the bolt 18 along much of the length of the threaded washer 3.

The compression washer 2 of the locking device is eventually completely flattened (Fig. 15). While the increased friction is maintained it is extremely difficult to unscrew the bolt 16.

Alternatively the compression washer can be modified so that in the washer's compressed, flattened state the peripheral edges 8 (Fig. 16) of the compression washer 2 bite into the workpiece 14 to increase the friction between the washer 2 and the workpiece 14. For this purpose the edges 8 may be depressed or deformed to project slightly below the lower surface of the washer. The edges 8 may also be chamfered. Additionally, ridges may be formed on the washer surface to increase the frictional effect.

When an attempt is made to unscrew the bolt 16 (Figs.

17 and 18) the locking device 1 is prevented from turning with the bolt 16 due to the biting action of the edges 8 which oppose rotation of the washer relative to the workpiece 14. Thus, the locking device remains compressed, the threads of the bolt and threaded washer maintain a firm frictional contact, and the workpiece 14 remains firmly clamped to the surface 15. A high resistance to the bolt 16 is thus maintained until the bolt thread 18 is clear of the workpiece 14.

Therefore, if the bolt 16 is acted upon by a force, such as vibration which could normally cause the bolt 16 to unscrew from the workpiece the considerable friction between the washer thread 10 and the bolt thread 18 will resist the unscrewing of the bolt 16 not only for the first few turns, but for the full unscrewing length of the bolt 16.

In the embodiment of the present invention described hereabove the periphery of the washer bore 6 is shaped to locate around the periphery of the stem 12 so as to lock the tensioning washer 2 to the threaded washer 3 and prevent relative rotation therebetween. However, the connection means between the tensioning and threaded washers 2,3 can alternatively be any means, for example, screw threads or brazing can be used. The connecting method should -however prevent relative rotation such that when the compression washer tensions itself against a surface it merely compresses the threaded washer against the member onto which it is screwed.

Preferably the threaded washer 3 is made of a softer material than the bolt 16 or like member, so that the threaded washer 3 will give more on compression against the threaded member's threads so providing a strong grip but without causing damage eg the stripping of the thread 18 on the bolt.

Where the locking device of the present invention is used in conjunction with a nut on a threaded member as opposed to a bolt, the locking device, if mounted with the concave surface of the compression washer 2 facing the workpiece, will maintain the workpiece clamped in position but will not resist the unscrewing of the nut. However, when inverted the washer 2 will move with the nut on unscrewing but will resist unscrewing from the nut as the compression washer will grip the underside of the nut with the threads of the nut and threaded washer being held against the thread of the threaded member.

The locking device of the present invention can be used in conjunction with a bolt which at some point along its length has an unthreaded portion. This unthreaded portion serves to retain the locking device on the bolt between the unthreaded portion and the bolt head unless unscrewed therefrom by the user.

The locking device of the present invention can be used with self tapping screws in a similar manner to the above described use with bolts.

The present invention thus provides a simple but efficient locking device for use in securing a threaded member in a threaded bore.

Claims

1. A locking device comprising a compression washer and a threaded washer, the compression washer being dish-shaped with a central bore therein and made of a resilient material, at least one biting surface being formed at the periphery of the compression washer, the threaded washer having a bore which is provided with a thread comprising several complete revolutions, the threaded washer being connected to the compression washer so that a threaded member can be threadedly engaged in said threaded bore of the threaded washer and through said central bore of the compression washer

2. A locking device as claimed in claim 1, in which the threaded washer is made of a softer material than the compression washer.

3. A locking device as claimed in 1 or 2, in which the threaded washer is made of softer material than the threaded member.

4. A locking device as claimed in any one of claims 1 to 3, in which the compression washer comprises a mating member and the threaded washer comprises a complementary mating member.

5. A locking device as claimed in claim 4, in which the mating members are male and female mating members

6. A locking device as claimed in claim 5, in which the male mating member is a stem on the threaded washer and the female mating member is the bore in the compression washer.

7. A locking device as claimed in any one of claims 1 to 6, in which the compression and threaded washers are connected so that relative movement therebetween is prevented.

8. A locking device as claimed in claim 7, in which the threaded washer and the compression washer are brazed to each other.

9. A locking device as claimed in any one of claims 4 to 8, in which the mating members can be snap locked together.

10. A locking device as claimed in any one of the preceding claims, in which the compression washer is made of spring steel.

11. A locking device as claimed in any one of the preceding claims, in which the at least one biting surface is formed by providing at least one recess in the peripheral wall, which recess is defined by two edges one of which passes substantially radially inwardly from the periphery of the compression washer and the other of which passes along a line such that said one edge is not faced by said other edge.

12. A locking device as claimed in claim 11, in which the one edge of each recess is depressed slightly to project out of the concave surface of the compression washer.

13. A locking device as claimed in claims 11 or 12, in which said one edge is chamfered.

14. A lcoking device as claimed in any one of claims 1 to 13, in which a concave surface of the compression washer is provided with ridges therein.

15. A method of securing a workpiece to a surface using a locking device as claimed in any one of claims 1 to 14, said method comprising the steps of positioning the locking device against the workpiece so that the workpiece is sandwiched between the concave lower surface of the compression washer and the surface, and passing a threaded member through the workpiece and surface so as to tighten the locking device against the workpiece such that the concave lower surface of the compression washer is flattened and the at least one biting surface of the compression washer locks against the workpiece.

16. A method of securing a workpiece to a surface using a locking device as claimed in any one of claims 1 to 14, comprising the steps of positioning the locking device against the workpiece so that the workpiece is sandwiched between the threaded washer and the surface, and passing a threaded member through the workpiece and surface so as to tighten the locking device against the workpiece such that the concave lower surface of the compression washer is flattened and the at least one biting surface of the compression washer locks against a nut or bolt head attached to the threaded member.

17. A method as claimed in claim 15 or 16, in which the flattening of the compression washer causes the thread of the threaded washer to lock against the thread of the threaded member passing there through.

18. A locking device constructed and arranged substantially as herein before described with reference to and as illustrated in any of Figs. 1 to 8 of the accompanying drawings.

19. A method of securing a workpiece to a surface using a locking device substantially as hereinbefore described with reference to and as illustrated in any of Figs. 1 to 18 of the accompanying drawings.