GB2223075A - Bolt tensioners - Google Patents

Abstract

An L-section piston 12 is interposed between a bridge 1 and a puller 20 so as to define a hydraulic cylinder between the arms of the L-section, one arm of the L-section constituting a piston head and the other arm constituting a relatively thin skirt portion which in use is supported by the puller. When the appropriate strain has been developed in the stud 2, the nut 4 is run down against the hardware 3. The L-section piston may be made of aluminium alloy or plastics such as carbon-loaded polyetherkeytone. In Fig. 2 (not shown) both the piston head and skirt taper and the bridges is divided to form a spherical washer to accommodate misalignment between the stud and hardware. <IMAGE>

Description

Improvements in and relating to bolt tensioners This invention relates to bolt tensioners of the kind comprising an annular piston and cylinder device. The cylinder is usually machined into a bridge piece which is mountable over and in encircling relation to a bolt (or stud) which is to be tensioned, a retaining nut on the bolt being accessible through an aperture in the bridge.

Such tensioners are well-known.

In a typical instance, the annular cylinder contains an annular ram, the head of which is arranged to bear against the underside of a puller member which is screwed down the shank of the bolt or stud. Because the free end of the bolt often projects only a short distance from the associated hardware, the puller usually extends down into the bridge. The cylinder may be constituted by an annular recess machined into the top of the bridge, or it may be defined between the puller and the immediately adjacent region of the bridge.

Whilst the latter configuration reduces the outside diameter of the tensioner to a minimum, it does so at the expense of making the puller an essential part of the hydraulic system. The puller cannot simply be unscrewed from the bolt without at the same time causing a fluid leak and/or risking damage to the hydraulic seals.

Alternatively, the whole tool has to be screwed down onto the bolt, which is generally inconvenient.

GB-A-1321398 discloses a construction in which the above problem is overcome by fabricating the piston as a ring with an annular skirt which extends axially of the puller into a gap defined between the latter and the tool body.

The arrangement is such that in use, the abutting cylindrical faces of the piston and the tool body together constitute or define a radially-innermost wall of the piston/cylinder device which acts on the puller.

It is an object of the present invention to improve on such a construction and make possible an even greater reduction in tool diameter and/or weight than it permits.

According to this invention, a bolt tensioning tool comprises a bridge mountable invencircling relationship to a fastener which is to be tensioned and in abutting relation to hardware through which said fastener extends, puller means engageable with said fastener together with hydraulic piston and cylinder means operable to displace said puller means relative to said bridge to tension the fastener, the piston being constituted by a generally L-section member interposed between the puller and the bridge, one arm of said section comprising a skirt portion extending axially between the bridge and the puller, an annular chamber for hydraulic fluid being defined between said arms, characterised in that at least said skirt portion is made from an elastic, non-structural material (as herein defined) which is relatively thin so that, in use, it is incapable of acting in a structural capacity without internal support from the puller.

"Elastic, non-structural material" means in the present context a material such as an aluminium alloy or an engineering plastics material such as PEEK, a poly ether ketone material, carbon-loaded versions of which have a quoted compressive strength in excess of 30,000 psi.

Given the extremely high working pressures of bolt tensioners, such materials would be in the ordinary course of events quite unsatisfactory because of the likelihood of deformation and/or extrusion.

Also, because of internal support from the puller, the radial thickness of the skirt portion can be made very much thinner than would be otherwise possible, even using a structural material for the piston skirt. In view of this, the skirt portion need not necessarily be integral with the piston crown, nor need it be made from the same material.

Because there is the skirt portion between the puller and the bridge, the overall outside diameter of the tool must be slightly greater than in the case where the cylinder is defined directly between the puller and the bridge, but less than in a conventional tensioner. However, the use of the elastic member ensures that the puller can be removedXinserted without causing fluid leakage and without disturbing the associated seals. For easy insertion of the puller, it is preferred that the abutting faces of the elastic member and puller should be slightly angled or tapered with respect to the major axis of the tool. The use of the tapered profile for the abutting faces ensures that the puller can be easily screwed down a bolt shank until it seats against the elastic member even if the respective parts are not completely clean.

To deal with minor misalignment of the bolt relative to the hardware, the tensioner preferably includes a spherical washer or the like, to minimize friction.

In order that the invention be better understood, two preferred embodiments of it will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a cross-sectional side view through a bolt tensioner in accordance with the invention, and Figure 2 is a cross-sectional side view of another bolt tensioner in accordance with the invention.

In Figuie 1, a cylindrical bridge 1 surrounds the free end of a stud bolt 2 , which extends from hardware 3. Further details of the hardware 3 are not material and will therefore not be discussed further in this specification.

The stud carries a nut 4 which is inside a cylindrical recess 5 defined in the bridge. The nut is accessible through an aperture (not shown) in the wall 6 of the bridge. Immediately above the recess 5 there is an oppositely directed recess, the inner wall 11 of which constitutes one wall of an annular cylinder. The recess 10 contains a piston comprising an elastic member 12. This has an upper ram part 13 and a lower side wall or skirt part 14.

A fluid chamber 15 is defined between the wall 11 and the parts 13 and 14, a fluid port 16 being provided in order to enable the piston/cylinder device to be pressurised with hydraulic fluid. 0-ring (or other) seals 17,18 are provided to prevent leakage from the piston/cylinder.

In use,a steel puller 20 is screwed down the stud 2 until the underside of its head 21 seats against the top of the ram part 13. The piston/cylinder device is then energised to tension the stud 2. When the appropriate strain has been developed in the stud, the nut 4 is run down tight against the hardware 3. The energising pressure is released, leaving the bolt stressed to the desired level.

The tool may then be removed.

In Figure 2, like parts bear like reference numerals, in the interest of clarity. However, the puller 20 and elastic member 12 are profiled so that mating surfaces 40, 41 are tapered for ease of assembly. The puller head 42 has a bore 43 extending transversely through it, so that a bar can be inserted to facilitate screwing it up/down the stud 2. To reduce weight the upper, radially outwardly part of the puller is relieved, at 44. The lower part 45 of the bridge is a separate piece retained (loosely) by a grub screw 46 so that it is free to rotate and tilt about the major axis of the bridge. To facilitate this the abutting surfaces of the lower part 45 and the main body 1 of the bridge immediately above it are machined to constitute a spherical washer surface 48. The tool can thus accomodate a degree of misalignment between the stud and hardware. The risk of binding and/or excessive friction is thereby minimised.

The elastic member may be made from a hard, anodised aluminium alloy, or from a carbon-loaded PEEK plastics material. Other materials may also be used.

Claims (6)

1. A bolt tensioning tool comprising a bridge mountable in encircling relationship to a fastener which is to be tensioned and in abutting relation to hardware through which said fastener extends, puller means engageable with said fastener, together with hydraulic piston and cylinder means operable to displace said puller means relative to said bridge to tension the fastener, the piston being constituted by a generally L-section member interposed between the puller and the bridge, one arm of said section comprising a piston crown and the other arm of said section comprising a skirt portion extending axially between the bridge and the puller, an annular chamber for hydraulic fluid being defined between said arms, characterised in that at least said skirt portion is made from an elastic, non-structural material (as defined) which is relatively thin so that, in use, it is incapable of acting in a structural capacity without internal support from the puller.

2. A bolt tensioner according to claim 1 characterised in that the abutting faces of the L-section member and puller are angled or tapered with respect of the major axis of the tool.

3. A bolt tensioning tool according to claim 1 or claim 2 characterised in that at least the skirt portion is made from a plastics material.

4. A bolt tensioning tool according to claim 3 characterised in that the plastics material is a poly ether ether ketone material.

5. A bolt tensioning tool according to claim 1 or claim 2 characterised in that the L-section member is made from an aluminium alloy.

6. A bolt tensioning tool substantially as herein before described with reference, to and illustrated by the accompanying drawings.