GB2245326A

GB2245326A - Expansion bolt assembly

Info

Publication number: GB2245326A
Application number: GB9013968A
Authority: GB
Inventors: Martin Nigel Walsh
Original assignee: Pilgrim Moorside Ltd
Current assignee: Pilgrim Moorside Ltd
Priority date: 1990-06-22
Filing date: 1990-06-22
Publication date: 1992-01-02
Anticipated expiration: 2010-06-22
Also published as: GB9013968D0; GB2245326B

Abstract

An expansion bolt assembly comprises a bolt 1 having a tapered intermediate portion 4 on which is mounted an expansible cylindrical sleeve 5 having a corresponding internal taper, the sleeve having at least two axially extending slots 7, 9 and 8, 10 formed in it from each end. The sleeve 5 may be located centrally of a shaft coupling (not shown) by means of a washer provided with a tubular extension. <IMAGE>

Description

Improvements in and relating to bolts This invention relates to expansion bolts. Such bolts are well-known; in general terms, they usually have some means whereby their diameter can be increased in a radial direction to grip the inside of a bolt hole.

For large, heavy duty applications, this means may take the form of a shank region of the bolt having a shallow taper, onto which a correspondingly internally tapered metal sleeve is placed. The outer diameter of the sleeve is cylindrical and sized to be an easy fit in the bolt hole. Hydraulic tools are used to draw bolt through the sleeve thereby expanding the latter to grip the inner surface of the bolt hole.

For less strenuous and/or less precise applicatios, a number of loose collet portions may be located on the bolt shank with spring wire grips, the free end of the bolt having a wedge member disposed to spread the collet portions apart when the bolt is tightened. This latter device will be recognised as the sort of expansion bolt commonly used in masonry, concrete and the like.

It is an object of the present invention to provide an expansion bolt suitable for relatively precise, moderately severe duty 3nplicstlons and .hi ch does not reou-rc hydraulic tools to install it.

According to this invention, an expansion bolt comprises a bolt having a tapered portion intermediate its ends and a one piece tubular sleeve having a cylindrical outer surface of substantially constant diameter and an inner surface having a taper corresponding to that of the tapered portion of the bolt, wherein the sleeve has at least two axially extending slots formed in it from each end. Each slot preferably extends at least half way along the sleeve; a slot length of approximately two thirds to three quarters of the length of the sleeve has proved satisfactory in practice. A particularly preferred arrangement is one in which the slots of a pair are diametrically disposed.It will be appreciated that if the sleeve is to remain in one piece, then the slots from the respective opposite ends must not meet and accordingly it is preferred that the slots at one end are displaced through 900 from those at the other end. This applies where two slots are used; if three or even four slots were to be employed at each end of the sleeve, then the preferred between adjacent slots from both ends would be 600 or 450, respectively. This assumes a symmetrical t i r, i;hich i c h I s p r e Li 1 01; tne g r o u n d of achieving symmetrical pressure distribution, in a radial direction in use.

The slots may be formed in any convenient manner, for example by sawing or machining. In order to reduce the stress concentration at the bottom of each slot, it is preferred to drill a small hole at this point. Manufacture of the sleeves is thus relatively straightforward.

It has been found that the expansion bolt construction just described is particularly suitable for application where the use of hydraulic tools is either impracticable, or inconvenient. This is particularly true in the case of relatively small diameter bolts. Use of a slotted sleeve has other advantages, for example it is possible to get a greater degree of radial expansion than would be possible with a conventional sleeve and without using very high forces to achieve it. Bolts constructed in accordance with this invention can be used to replace conventional relatively small diameter cla,pino bolt in a1.? tanner of flanged coupling.In particular t is possible to replace conventional "fitted" bolts, which are notoriously difficult to remove after an extended period of service and which when removed, frequently cause damage to the internal bore of the hole from which thev came. In contrast with this, a bolt according to the invention will @@@@@@@@@ be re-usable in many instances.

In order that the invention be better understood an embodiment of it will now be described by way of example with reference to the accompanying drawing in which: Figure 1 is an exploded perspective view of a bolt in accordance with the invention, Figure 2 is a cross-sectional side view of another bolt according to the invention, and Figure 3 is another cross-sectional side view of the bolt of Figure 2.

In all three Figures, corresponding parts have been given the same reference numbers, in the interest of simplicity.

In Figure 1, a bolt 1 has a screw threaded portion 2, 3 at each end. Intermediately the ends, there is a tapered portion 4. An expansion sleeve 5 engageable upon the tapered portion 4 is provided. The outer diameter of the sleeve 5 is substantially constant; the inner surface 6 has an internal taper corresponding to that of the bolt portion 4.

The sleeve is provided with two pairs of axially extending slots, 7, 8 and 9, 10 respectively. It will be appreciated Lhat u..l; te of these can bc scen In their etirct; slct 9 is only partially visible and slot 10 is completely concealed by the rest of the sleeve. Each slot extends over approximately two-thirds of the length of the sleeve and the two pairs of slots are displaced through 900 relative to one another, as shown. The bottom of each slot terminates in a circular drilling 11, only one of which is seen in the figure. Each end of the bolt is provided with a suitable nut, 12 and 13 respectively. Each nut is provided with an integral washer, 14 and 15 respectively.

A hexagonal socket 18 is provided in each end of the bolt 1 so that a wrench or key can be inserted to prevent rotation on tightening the nut(s).

A typical application for this bolt would be in a shaft coupling. Its installation and removal will now be described with the aid of Figures 2 and 3 which will show a similar bolt, on an enlarged scale.

Figure 2 illustrates a typical method of installing the bolt of Figure 1 into a bore 20 defined in hardware 21.

The latter could be a flanged shaft coupling, for example, but precise details are irrelevant to present purposes and will not be further discussed here.

Prior to installation, the sleeve 5 is slid loosely onto the ta@@@@ portion 4; the assembly is then s@@d into the bore 20. To ensure that the sleeve 5 is centred relative to the two outer forces of the hardware 22, 23, a washer 24 having a tubular, axially directed flange 25 Is placed on the bolt end, with the flange extending into the bore 20 to abut against the end of the sleeve 5. Nut 12 is then run down the threaded portion 2, to engage the washer24.

On further tightening the nut 12, the bolt is pulled through the sleeve, which is restrained from moving by the interaction of the washer 24, the sleeve end and the flange 25. The sleeve is therefore expanded radially to grip the inside of the bore 20. The degree of expansion/tightness achieved is readily controlled by means of the torque applied to nut 12; any initial risk of the bolt rotating can be controlled by a key inserted into the socket 18. Once an initial grip has been achieved, the latter is normally not needed, of course. When the bolt is suficiently tight, the nut 12 can be released and the flanged washer 24 removed. Nut 12 is then replaced; nut 13 is applied at the opposite end of the bolt and both are tightened to lock the whole assembly in place.

The removal of the thus installed bolt is illustrated in figure 3. Nut 12 is slackened a couple of turns; nut 13 is replaced by a washer 26 with an axially extending tubular flange 27. Nut 13 is run down the threads to engage this washer 26 and on further tightening, the bolt is drawn through the sleeve in the opposite direction, thereby releasing the sleeve, which is prevented from nov in with the bolt by the interaction of the nut flange 15, the washer 26 and the end of the sleeve against which flange 27 abuts. Once again, a key can be used in socket 18 to prevent bolt rotation.

It will be appreciated that in most cases the sleeve will be formed from a metal such as steel, which has good elasticity and a high resistance to creep. It is generally undesirable to use soft, extendable materials such as aluminium, although for some applications, engineering plastics may be satisfactory.

Claims

1. An expansion bolt comprising a bolt having a tapered portion intermediate its ends and a one piece expansion sleeve having a cylindrical outer surface of substantially constant diameter and an inner surface having a taper corresponding to that of the tapered portion of the bolt, wherein the sleeve has at least two axially extending slots formed therein from each end of the sleeve.

2. An expansion bolt according to claim 1 wherein said slots have a depth in the axial direction of the sleeve of between a half and three quarters of the length of the sleeve.

3. An expansion bolt according to claim 1 or claim 2 wherein pairs of slots are disposed diametrically of the sleeve and are equally spaced around the circumference thereof.

4. An expansion bolt according to any preceding claim, further comprising washers having axially extending portions which in use serve to locate said sleeve relative to the faces of components which are to be joined by the bolt.

5. An expansion bolt substantially as herein described with reference to and as illustrated by the accompanying drawings.