GB2274698A

GB2274698A - Fastening device for tubular parts

Info

Publication number: GB2274698A
Application number: GB9301361A
Authority: GB
Inventors: Peter James Clark
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-01-25
Filing date: 1993-01-25
Publication date: 1994-08-03
Anticipated expiration: 2013-01-25
Also published as: GB2274698B; GB9301361D0

Abstract

A fastening device comprises a polymeric bung 1 including an annular portion 1a having an external shoulder 1b abutting an end of a tube 4, four arms 1c distributed around and extending axially inwards from the portion 1a, and an internally threaded steel bush 3 held captive among the arms 1c. The bush 3 is chamfered at 3a to enable the bush to be inserted through among radially inward protrusions 1e of the arms 1c. The bush 3 is of square or hexagonal cross-section to co-operate with the non-circular internal surface of the arms 1c, to deter rotation thereof relative to the bung 1 and, upon rotation of the bolt 2, the chamfered end of the bush 3 bears against correspondingly inclined surfaces 1f of the arms 1c to cam those arms 1c outwardly against the internal surface of the tube 4. The outer end of the bung 1 is formed as a saddle to receive a tube 5 formed with bores 5a for receiving the bolt 2. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO FASTENING DEVILS According to one aspect of the present invention, there is provided an expandible bung for insertion into an end of a tubular part, comprising a portion of annular form for encircling a rotatable, threaded, elongate member, and a plurality of portions distributed around and extending in a common axial direction from the annular portion for insertion into said end and for camming away from the axis of the bung by rotation of said elongate member to engage frictionally the internal surface of the zone of said end.

According to another aspect of the present invention, there is provided a fastening device, comprising a rotatable, threaded, elongate member, and an expandable bung, said bung comprising a portion of annular form for encircling said member and a plurality of portions distributed around and extending in a common axial direction from the annular portion and cammable away from the axis of the bung by rotation of said elongate member to engage frictionally an internal surface of an end zone of a tubular part.

Owing to the invention it is possible to provide a simple and reliable fastening device for fastening the tubular part to another part.

The rotatable, threaded, elongate member is preferably in the form of an externally threaded bolt and advantageously carries at its inner end an internally threaded bush which, on rotation of the bolt in a sense to move the bush towards the outer end of the bolt, cams the aforesaid plurality of portions away from the axis of the bung to press those portions firmly against the internal surface of the end zone of the tubular part. The external periphery of the bush is of a non-circular cross-section and the aforesaid plurality of portions present internally a non-circular shape overall in order to deter the bush from simply rotating with the bolt rather than moving along the bolt.The outer periphery of the axially outer end zone of the bush is preferably chamfered and/or part of the internal peripheral shape presented by the aforesaid plurality of portions is formed to converge progressing axially outwards, to provide one or more inclined surfaces whereby the bush can cam the aforesaid plurality of portions away from the axis of the bung. The bush is advantageously held captive among the aforesaid plurality of portions so as to be held ready to receive the inner end of the bolt.The bush and the bung may be such that, prior to insertion of the bung into the tubular part and prior to the screwing of the bolt into the bush, the bush can be pressed axially through between the inner ends of the aforesaid plurality of portions which yield resiliently radially outwards to allow the bush to be received therebetween and then return to hook behind the inserted bush to retain it captive. The bung and the bush may additionally be such that the bush is only temporarily captive and may be removed therefrom during any subsequent dismantling of the fastening device. The aforesaid plurality of portions are preferably of a material, for example a polymeric material, more compressible than spring steel.Although such more compressible material is less able that spring steel to "bite" into the internal surface of the end zone of the tubular part, it is better able to adjust itself to small increases in diametral dimension of the end zone, which may occur under the continuous radially outward pressure of the aforesaid plurality of portions thereon. Thus, the aforesaid plurality of portions engage frictionally within the end zone without "biting into the internal surface thereof. For the same reason, i.e. that the device is better able to adjust itself to small increases in diametral dimension of the end zone, additionally or alternatively the bush could be made at least partly of polymeric material.

The bung preferably includes an external peripheral shoulder whereby the bung bears upon the free extremity of the end zone, so that the bung may be readily correctly positioned within the tubular part before the threaded elongate member is rotated to cam the aforesaid plurality of portions outwardly, and also so that the bung cannot be inadvertently pushed or allowed to slide too far into the tubular part. The outer end of the bung may take the form of a saddle for receiving the other part to be fixed to the tubular part, with that other part having the bolt extending therethrough and urging the other part firmly into the saddle. That other part may also be tubular. On the other hand, that other part could take the form of a foot, for example, or even the outer end of the bung itself could take the form of a foot, for example, such as a foot on tubular furniture.

The tubular part (and the other part) may be of polymeric material, or of metallic material, for example.

The aforesaid two parts may be at any reasonable orientation to each other and may be of any reasonable cross-section internally or externally.

The invention is applicable not only to tubular furniture, but such a wide variety of applications as tubular exhibition stands, brooms, and action toys.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows an axial sectional view of a fastening device, and Figure 2 shows an end view of an expandible bung of the device seen in the direction of the arrow II in Figure 1.

Referring to the drawings, the fastening device includes a bung 1 formed of a polymeric material, for example Nylon 6. The bung 1 includes a portion la of annular form for closely encircling an externally threaded bolt 2 of the fastening device, the bolt 2 including a head 2a having a screwdriver slot 2b. The annular portion la includes an external shoulder ib for abutting against an end of a tube 4 which is to be fastened to a transverse tube 5.

The bung 1 also includes a plurality of, in this case four, arm-like portions ic distributed around and extending axially inwards from the annular portion la for insertion as a sliding fit into the end of the tube 4. The arm-like portions ic have their radially outer surfaces chamfered at their distal ends at id to facilitate insertion into the tube 4.The fastening device finally includes an internally threaded steel bush 3 which is held captive among the arm-like portions ic. At its axially outer end, the bush 3 is externally chamfered at 3a to enable the bush 3 to be inserted manually among the distal ends of the arm-like portions ic through among respective radially inward protrusions le of the distal ends of the arm-like portions ic. The chamfered axially outer end of the bush 3 comes to bear against correspondingly inclined surfaces if of the portions ic and the protrusions le hook behind the inserted bush 3 to retain it captive within the bung 1. The armlike portions ic have gaps ig thereamong.The bush 3 is of a square or hexagonal external peripheral cross-section to deter rotation of the bush 3 about the axis of the bung 1 relative to the bung. The outer end of the bung 1 is in the form of a saddle with a surface lh complementary to the external peripheral surface of the tube 5, which is formed with diametrally aligned bores 5a for receiving the bolt 2.

The method of using the fastening device is as follows.

Before inserting the bung 1 into the tube 4, the user inserts the bush 3 to among the arm-like portions ic until the protrusions le hook behind the bush 3. Then the items 1 to 5 are assembled into the condition shown in Figure 1, the precise order of assembly being variable, one being now explained. The bung 1 is slid into the end of the tube 4 until the shoulder Ib abuts that end. The tube 5 is laid in the saddle surface lh and the bolt 2 is inserted through the bores 5a and through the annular portion la until its inner end meets the outer end of the bush 3. The bolt ? is now rotated to cause the bolt to screw through the bush 3 until its head 2a abuts the tube 5 and the outer end of the bush 3 contacts the surfaces if. The condition shown in Figure 1 is thus attained. Continued rotation of the bolt 2 causes the bush 3 to move axially outwardly to bear increasingly forcefully against the inclined surfaces if.

Not only does this cause the head 2a of the bolt 2 to press the tube 5 firmly into the saddle, but also the arm-like portions ic are cammed increasingly radially outwardly to produce increasing frictional engagement of those portions against the internal surface of the end zone of the tube 4.

While this increasing frictional engagement is occurring, the arm-like portions ic are simultaneously compressed slightly axially by the bush 3, thus tending to press the tube 4 firmly against the shoulder ib.

Claims

1. An expandible bung for insertion into an end of a tubular part, comprising a portion of annular form for encircling a rotatable, threaded, elongate member, and a plurality of portions distributed around and extending in a common axial direction from the annular portion for insertion into said end and for camming away from the axis of the bung by rotation of said elongate member to engage frictionally the internal surface of the zone of said end.

2. A bung according to claim 1, wherein said plurality of portions presents internally a non-circular shape overall.

3. A bung according to claim 1 or 2, wherein part of the internal peripheral shape presented by said plurality of portions is formed to converge progressing axially outwards, to provide one or more inclined surfaces whereby said camming is produced.

4. A bung according to any preceding claim, wherein said plurality of portions are arranged to yield resiliently radially outwards to allow a bush to be inserted therebetween and then to return to hook behind the inserted bush to retain the bush captive.

5. A bung according to any preceding claim, wherein said plurality of portions is of a material more compressible than spring steel.

6. A bung according to any preceding claim and including an external peripheral shoulder whereby the bung bears upon the free extremity of said zone.

7. A bung according to any preceding claim and whereof the outer end of the bung takes the form of a saddle for receiving another part to be fixed to said tubular part.

8. A bung according to any one of claims 1 to 6, wherein the outer end of the bung takes the form of a foot.

9. A fastening device, comprising a rotatable, threaded, elongate member, and an expandible bung, said bung comprising a portion of annular form for encircling said member and a plurality of portions distributed around and extending in a common axial direction from the annular portion and cammable away from the axis of the bung by rotation of said elongate member to engage frictionally an internal surface of an end zone of a tubular part.

10. A device according to claim 9, wherein said elongate member is in the form of an externally threaded bolt.

11. A device according to claim 9 or 10, wherein said elongate member is threadedly engaged at its inner end by an internally threaded bush which, on rotation of said elongate member in a sense to move the bush towards the outer end of said elongate member, cams said plurality of portions away from the axis of the bung to press those portions firmly against the internal surface of said end zone.

12. A device according to claim 11, wherein the external periphery of the bush is of a non-circular cross-section and said plurality of portions presents internally a noncircular shape overall to deter the bush from simply rotating with the elongate member rather than moving along the elongate member.

13. A device according to claim 11 or 12, wherein the outer periphery of the axially outer end zone of the bush is chamfered and/or part of the internal peripheral shape presented by said plurality of portions is formed to converge progressing axially outwards, to provide one or more inclined surfaces whereby the bush can cam the said plurality of portions away from the axis of the bung.

14. A device according to any one of claims 11 to 13, wherein the bush is held captive among said plurality of portions so as to be held ready to receive the inner end of said elongate member.

15. A device according to any one of claims 11 to 14, wherein the bush and the bung are such that, prior to insertion of the bung into said tubular part and prior to the screwing of the elongate member into the bush, the bush can be pressed axially through between the inner ends of said plurality of portions which yield resiliently radially outwards to allow the bush to be received therebetween and then return to hook behind the inserted bush to retain the bush captive.

16. A device according to claim 15, wherein the bung and the bush are such that the bush is only temporarily captive, so as to be removable therefrom during subsequent dismantling of the fastening device.

17. A device according to any one of claims 9 to 16, wherein said plurality of portions is of a material more compressible than spring steel.

18. A device according to any one of claims 9 to 17, wherein the bush is made at least partly of a material more compressible than spring steel.

19. A device according to any one of claims 9 to 18, wherein the bung includes an external peripheral shoulder whereby the bung bears upon the free extremity of said end zone of said tubular part.

20. A device according to any one of claims 9 to 19, wherein the outer end of the bung takes the form of a saddle for receiving another part to be fixed to the tubular part.

21. A device according to any one of claims 9 to 19, wherein the outer end of the bung takes the form of a foot.

22. An expandible bung, substantially as hereinbefore described with reference to the accompanying drawing.

23. A fastening device, substantially as hereinbefore described with reference to the accompanying drawing.