GB2124119A - A hydraulic bolt tensioning tool with power drive for rotating a nut - Google Patents

Abstract

The piston rod 15 of a hydraulic actuator is pivotally connected to a collar 7 which engages the nut 6 whilst the cylinder 16 is pivotally connected to a link 20 rigid with the body 3 of the bolt tensioning tool. <IMAGE>

Description

SPECIFICATION Improvements in and relating to hydraulic tools This invention relates to apparatus for rotating screw-threaded members, particularly, but not exclusively, screw-threaded fasteners such as nuts and bolts.

The problems encountered in the controlled tightening of screw-threaded fasteners are well known. It has been proposed in the case of a bolt that a stretching force should be applied to extend the bolt and to develop thereby a controlled stress in it, prior to the tightening an associated nut and then removing the force. A hydraulic bolt tensioner for this purpose is illustrated in British Patent No. 1,590,131.

Another, quite different approach is illustrated in British Patent No. 1554272 or in US Patent 3706244.

A power driven ratchet device is used to forcibly rotate a nut or other fastener until a desired torque is developed. This approach suffers from the serious disadvantage that the final tightening to the desired torque is carried out against progressively increasing frictional resistance, not only between the interengaged screw threads, but also between the face of the nut (or the bolt head) and the abutting hardware.

In the case of apparatus arranged to stretch a bolt, it is normal to tighten the associated nut either by hand or with the aid of a simple lever such as a tommy bar before removing the stretching force.

Even though the stretching force may have developed the desired stress in the bolt, some of that stress is lost through thread distortionideflection on removing the force. The magnitude of the stress loss cannot be readily measured and compensated for, except on a trial and error basis.

According to the present invention, a hydraulic bolt tensioning tool includes power driven means for rotating a nut engaged on a bolt which the tool is to tension. Preferably the power driven means comprises a hydraulic actuator having one end thereof operably connected to rotate the nut and the other, relatively displaceable end pivotally connected to the body of the tool. Preferably the nut is rotated by means of a co-operating collar relatively loosely fitted around the nut and operably connected to the actuator. The connection may be a lever extending from the collar, pivotally connectable to said one end of the actuator and displaceable in a plane normal to the axis of the bolt. The actuator is preferably disposed to operate in that same plane.The pivotal connection between the actuator and the body of the tool may take the form of a rigid extension piece attached at one end to the body of the tool and having the pivotal connection at its opposite end.

The length of the extension piece and its point of attachment to the tool body will naturally reflect the geometry of the system, since it is desirable that the actuator shall be so disposed as to exert as much rotational force on the nut as possible. The collar may be provided with a plurality of attachment prints for the operable connection to the actuator, or it may have a single attachment point. In the latter case, it is preferred that the collar be readily detachable from the actuator and that it should be axially displaceable out of engagement with the nut, to facilitate re-positioning relative to the latter for successive operating strokes, i.e. for stepwise, progressive rotation of the nut.Where plural attachment points are provided disconnection and re-connection at a different attachment point may prove to be less convenient than a collarwhich can, for example be lifted, turned and dropped back into engagement with the nut. An example of this will be described later.

It will be appreciated that the collar may equally have some suitable form of ratchet mechanism built into it for the same purpose.

An important feature of the invention lies in the fact that the actuator is preferably double-acting. It may therefore be used to tighten or to loosen a nut, or other fastener. Because it will normally only be used when the associated bolt tensioning tool is energised, it is not necessary to provide any anchoring means to prevent the actuator turning the tool body instead of the nut. The clamping force exerted by an energised bolt tensioning tool is normally more than adequate to lock the latter, and with it the extension piece and pivotal connection, firmly in place so that only the nut is turned. It will be noted that the tensioner itself will hold the associated bolt firmly in place against rotation by the nut.

It will be appreciated from the foregoing that a tool according to the invention can be used to precisely stress bolts; it can also be used to free rusted or corroded nuts. The latter are a major problem in many industries and the ability to both stretch the bolt and then to apply great force to the nut will often avoid any need to remove the nut and/or bolt by more risky and/or destructive methods such as flame cutting.

In order that the invention be better understood a preferred embodiment of it will now be described by way of example with reference to the accompanying drawing in which Figure 1 is a composite side view, partly in section, of part of a tool according to the invention, Figure 2 is a plan view of the tensioner of Figure 1, but shown without the hydraulic piston and associated bolt puller, Figure 3 is a plan view (partly cut-away) of another tool according to the invention and Figure 4 is a side view of the tool of Figure 3.

Referring to all four Figures the bolt tensioner comprises a bridge portion 3 placed over the free end of a bolt 5, the latter having a nut 6 engaged thereon. The nut is fitted with a relatively loose fitting collar 7, which is a clearance fit inside the bridge. The bridge has a cut-away portion 4 which gives access to the collar (and thereby to the nut).

Referring to Figure 1, the collar is provided with a set of apertures, only one of which is shown, at 8. These apertures are radially directed and spaced-apart around the collar so that at least one aperture is always accessible through the cut-away portion 4.

Again referring to Figure 1, a second set of smaller apertures 9, (only one of which is shown) is provided immediately below the apertures 8.

These apertures enable the collar/nut of Figures 1 and 2 to be turned by a hand tool, as necessary.

The following descriptionm specifically refers to Figures 1 and 2, although like parts in Figures 3 and 4 bear like reference numerals.

The aperture 8 is screw-threaded to receive a complementary peg 37 which carries a locknut 10.

The peg and aperture are best seen in the right hand portion of composite Figure 1. The peg has at its free end a bifurcated portion 11, 12 which in conjunction with a nut and bolt (13, 14 respectively), constitutes a pivotal connection to the operative portion 15 (the ram) of a double-acting hydraulic actuator. The portion 15 has an extra aperture 17 to which the peg can be connected, if need be. The fixed (cylinder) portion 16 of the hydraulic actuator is pivotally connected bya nut and bolt 18, 19to a pair of bars 20, 21 which are rigidly attached to the bridge by an assembly comprising another nut and bolt 22,23, a bracket 24 and set screws 25.

This attachment of the bars 20,21 to the bracket 24 is not of course a pivotal attachment, but simply provides for the length of bar to be selected to suit a particular actuator, co-operating regions of the bars and the bracket being keyed together (not shown) to prevent rotation about bolt 23. Should bending and/or rotation be a problem a Figure 3-type bracket 34 may be modified to reinforce the connection.

It will be appreciated that so far the other operative parts of the bolt tensioner itself have not been described. However, they are conventional and accordingly only parts of them are shown (and only in Figures 1 and 4). Thus the bridge carries an annular hydraulic cylinder 26. This contains a circular piston (not shown) which acts on a screwthreaded puller 27 engaged on the bolt 5. (Only part of the puller is shown in Figure 1). The effect of the circular piston when the associated cylinder is energised is to displace the puller axially away from the bridge and thereby away from a surface 28 on which the bridge stands. This latter surface may be on a flange or other member through which the free end of the bolt 5 projects. Pressure applied to the bolt by the puller will, therefore tend to stretch the bolt axially.

The operation of the bolt tensioner will now be explained further with particular reference to Figure 2. In Figure 2 the hydraulic actuator is in its retracted or minimum length state. The bolt tensioner is operated to put the bolt under axial stress.

At the same time the bridge is firmly clamped against the surface 28, thereby preventing rotation of the bridge and tensioner around the axis of the bolt. Operation of the actuator will now rotate the nut anticlockwise a fraction of a turn, thereby unscrewing it slightly (assuming a conventional right hand thread). If the nut still cannot be turned by hand or by means of a bar inserted into aperture 9 then the peg can be disconnected, removed and inserted in the next adjacent aperture 8, prior to retracting the actuator ram and re-connecting itto the peg. The converse procedure is used on tighten ing a nut, the extra aperture 17 being used in either case as is necessary to obtain a full range of movement of the peg within the cut-away portion 4, for a given range of travel of the ram 15.

The arrangement of Figures 3 and 4 differs from that of Figures 1 and 2 in a number of respects. The collar has a fixed projection 30 (corresponding to the peg 9 in Figures 1 and 2) which has a notch 31 (Figure 3) adjacent its free end. The projection includes an operating handle 32 and the collar is internally relieved at 33, so that by lifting the handle upwards (Figure 4) the collar can be freed from engagement with the nut and turned, as will be further discussed later.

Also the bar and bracket assembly 20,21 and 24 is replaced by two simple welded brackets 34 provided with a pivotal connection 35 to the body of a double acting hydraulic actuator. The piston 15 of the latter carries at its free end a follower 36 which seats in the notch 31.

Also shown in Figure 4 are the hydraulic head 26 and related parts described earlier, of course.

The operation of the tool of Figures 3 and 4 is generally the same as that of the tool of Figures 1 and 2. However, it is much easier to re-position the collar after each stroke of the piston 15. It will be appreciated that in this particular embodiment it is only possible to unscrew a right-hand threaded nut.

The previous embodiment described can also be used to tighten a nut and when tightening a nut, the bolt tensioner is first used to develop a desired axial stress in the bolt. The actuator is then used to tighten the nut down onto the surface 28 hard enough to prevent significant thread deflection on release of the stressing force.

Either embodiment can be used to loosen a seized nut. The bolt tensioner is used to stretch the bolt to the point at which the actuator only has to overcome the seizure. If that is not practicable, then the tensioner is used to reduce the frictional force between the nut and the surface 28 as much as possible. The final dislodgement of the nut is then accomplished by use of the actuator. In practice, the apparatus will frequently loosen severely seized nuts with relative ease, due to the considerable mechanical advantage of the arrangement.

Claims (10)

1. A hydraulic bolt tensioning tool including power driven means for rotating a nut engaged on a bolt which the tool is to tension.

2. Atool according to claim 1 wherein the power driven means is a hydraulic actuator connected between the body of the tool and a member operable to rotate the nut.

3. A tool according to claim 2 wherein the hydraulic actuator has one end thereof pivotally connected to the body and the other end is pivotally connected to said member.

4. A tool according to claim 2 or claim 3 wherein the member comprises a collar co-operating with the nut and having fulcrum means projecting in a plane normal to the axis of the bolt, said means being pivotally connected said other end of the actuator.

5. A tool according to claim 4 wherein the collar is internally relieved whereby raising the collar relative to the nut enables the collar to be turned without also turning the nut.

6. A tool according to claim 5 wherein the collar is provided with handle means operable to raise and/or turn the collar relative to the nut.

7. A tool according to claim 4 wherein the collar has a plurality of points of attachment for said fulcrum means spaced around it radially of the bolt.

8. A tool according to any preceding claim wherein the connection between the actuator and the body of the tool comprises a rigid extension piece attached to the body at one end and pivotally attached to the hydraulic actuator at the other end, or vice versa.

9. A tool according to any preceding claim wherein the power driven means is operable to rotate the nut in either a clockewise or counterclockwise direction.

10. A hydraulic bolttensioning tool substantially as herein described with reference to and as illustrated by the accompanying drawings.