GB2291155A - Hydraulic bolt or stud tensioning apparatus - Google Patents

Abstract

A hydraulic bolt or stud tensioning apparatus 20 of the tandem-piston type has mechanically coupled inboard and outboard pistons 27, 31 defining with inboard and outboard cylinder bodies 25 and 30 piston extending chambers 40 and 41. An axially extending puller bar 21 having an inboard end adapted to engage with bolt 11, mechanically couples the pistons 27 and 31 and contains a fluid passage 50 joining the chambers 40 and 41. A retraction spring 43 between the inboard piston 27 and outboard cylinder body 30 acts to retract both pistons with respect to their respective cylinder bodies by virtue of the coupling with the puller bar. A handle 55, (or lifting eye or lugs) connected to the outboard piston 31 enables the apparatus to be disposed on the end of the bolt and rotated as a whole to thread the puller bar onto the bolt and to be removed after tensioning. One or more further pistons may be located intermediate the inboard and outboard pistons 27, 31. <IMAGE>

Description

Hydraulic bolt tensioning arranaement This invention relates to hydraulic bolt or stud tensioning arrangements and in particular to such arrangements of the socalled multi-layer or tandem-piston type in which a plurality of piston and cylinder arrangements have their pistons coupled to apply a large tensile stress to such a bolt or stud.

Arrangements of this type are described for example in GB-A-1,418,508, US-A-3,837,694 and DE-A-26 48 722.

In such arrangements a plurality of annular piston and cylinder defining bodies are arranged in operation to surround coaxially an individual bolt anchored at some point thereof and able to be stretched by the arrangement at a free end, the bodies being coupled mechanically and hydraulically to each other, essentially forming a stack from an inboard piston and cylinder body, closest to an anchored part of the bolt, to an outboard piston and cylinder body furthest from the anchored part of the bolt and coupled to said free end thereof.

In each of the publications mentioned above, each piston extends axially to, and bears on, the next-inboard piston in addition to defining with an associated cylinder body a piston-extending chamber to which hydraulic fluid is supplied at elevated pressure to displace the piston in an outboard direction. The outboard piston is mechanically coupled to said free end of the anchored bolt to which tensile stress is to be applied, directly or by way of a separate puller supported on the outboard piston, so that when hydraulic fluid is supplied to each of said piston-extending chambers the cumulative force exerted on the bolt is substantially proportional to the sum of the individual piston/chamber means.

Such a tandem piston arrangement enables an effectively large piston area to be provided without unduly large piston dimensions or fluid pressure when a large force is to be exerted.

When such a stressed bolt has been secured by means of a nut to retain some of the tensile stress, to ease disassembly of the tensioning arrangement hydraulic fluid is supplied to a pistonretracting chamber defined outboard of the outboard piston whereby an inboardly directed force acts on the outboard piston and is likewise transmitted by abutment against each successively inboard piston in turn until they are all retracted with respect to their respective cylinder bodies.

It will be appreciated that such arrangements are frequently used in relation to imparting tensile stress to a plurality of large, adjacent bolts where space is minimal and where unfettered access for, and to all parts of, the tensioning arrangement is limited.

In such arrangements, it is frequently necessary to have cylinder bodies with lateral dimensions large enough to surround and operate on a bolt of the order of 100-250mm diameter making such an assembly for even one bolt heavy and unwieldy.

However, such tandem arrangements permit increased tensile stresses to be applied for a particular fluid pressure without even greater increase in lateral body dimensions, or for a lower fluid pressure to be usod than would be the case without such tandem arrangement.

Notwithstanding this, it is often necessary to constrain design, manufacture and/or usage in some way that affects, or is affected by, the requirement to supply fluid to various piston-extending chambers.

It is known to provide a fluid supply passage to each chamber by way of the surrounding cylinder body, each passage either leading to a discrete supply pipe and pipe coupling at the exterior of the body or being aligned and communicating with corresponding ducts within the separate cylinder bodies that lead to a common supply pipe and pipe coupling for each functional chamber type.

Whereas the tandem arrangement is essentially modular in respect of its major components, and may appear suited to final assembly, or partial dis-assembly and re-assembly, on site, the fact that in the former case, it is necessary to have sufficient clearance about the cylinder bodies to allow for such supply pipes and couplings and even confine them to a specific orientation with respect to the bolt axis, as well as with respect to each other, whilst in the latter case, there is a requirement for alignment of, and sealing between, duct interconnections between cylinder bodies both effectively inhibit assembly to the manufacturing environment.

In practice therefore, a conflict exists providing a tandem piston tensioning arrangement for increased force in a smaller crosssection and in handling, disposing it and in operating it in a confined space where access to the side of the arrangement at different levels is restricted, such as when required to operate at the bottom of a hole or recess.

It is an object of the present invention to provide a hydraulic bolt tensioning device of the multi-layer or tandem-piston type which is of simple construction and mitigates complexity and constraints in handling and operation.

According to the present invention a hydraulic bolt or stud tensioning arrangement of the tandem piston type in which a plurality of annular pistons within cylinder defining bodies, dimensioned to surround in operation an individual anchored bolt axis, are coupled mechanically and hydraulically in tandem from an inboard piston and cylinder body operationally closest to an anchored part of the said bolt to an outboard piston and cylinder body furthest from said anchored part of the bolt, with each said piston defining with its associated cylinder body a pistonextending, bolt-stressing fluid chamber, is characterised by a puller bar extending along a axis common with said bolt axis, adapted at its inboard end for connection to the bolt and outboard thereof to support said inboard and outboard pistons for transmission of forces in both axial directions therebetween having a fluid passage therein extending from its outboard end to each piston-extending chamber, and piston retracting spring means disposed between said inboard piston and next outboard cylinder body operable to exert force on the inboard piston in an inboard axial direction.

Such piston retraction spring means acts to dispose both pistons fully retracted in their cylinder bodies in the absence of high fluid pressure in the chambers formed thereby, serving not only to expel superfluous fluid but also to facilitate the provision of carriage means affixed to the accessible outboard piston so that the tensioning arrangement may be lifted intact by way thereof and independently of side access.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which the single Figure is a sectional elevation through an end portion of a bolt extending from a machine part to which it is anchored, and a tandem piston bolt tensioning arrangement in accordance with of the invention in operational disposition with respect thereto, the embodiment having only inboard and outboard pistons.

Referring to the Figure a bolt 11 extends from a machine casing, such as a flange 12 and terminates at an end portion 13. In conventional manner the other end of the bolt (not shown) is, or may be, anchored with respect to the flange 12 to resist axial and rotational motion of the bolt per se. As shown, the end portion 13 is short in a direction measured along the longitudinal axis 14 of the bolt having such length as is necessary to engage with a nut 15 and a threaded extension piece, or puller bar, of a hydraulic tensioning arrangement.

Conventionally a tensile stress imparted by the tensioning arrangement to the bolt along its longitudinal axis 14 stretches the bolt and permits the nut 15 to be rotated into abutment with the flange with relatively little torque and thereafter, upon removal of the tensioning arrangement and the extension piece, apply the stress axially compressively to the flange.

A hydraulic bolt tensioning arrangement in accordance with the invention is shown at 20 and disposed operationally in relation to bolt 11. The arrangement includes a puller bar 21 and an annular bridge member 22 which is arranged to straddle the nut 15 and bolt end 13 to support the tensioning arrangement on the flange 12. The bridge member may include a lateral aperture 22' providing access to the nut, and possibly containing all or part of a nut turning device 23.

The arrangement further includes a plurality of annular pistons within cylinder defining bodies surrounding the puller bar 21 and thus, in operation, the bolt axis 14. The pistons and cylinder bodies are coupled mechanically and hydraulically in tandem as will be described.

An inboard cylinder body 25 is formed integrally with, or mounted on, the bridge member 22, and contains, in an annular recess 26 therein, an inboard piston 27. The inboard piston and cylinder body are thus operationally closest to an anchored point of the bolt, or alternatively, the flange 12.

An outboard cylinder body 30, containing an outboard piston 31 is mounted on, and secured to, the inboard cylinder body, therefore being furthest away in a direction along axis 14 from the anchored part of the bolt.

The terms 'inboard' and 'outboard' and derivatives thereof as used in this specification are indicative of operations and directions with respect to position along the bolt axis at which such bolt in operating is anchored within the flange and irrespective of the position of a bolt end 13.

The outboard cylinder body 30 is mounted on the inboard cylinder body 25, with a lower portion 32 of the outboard body being supported coaxially within the recess 26 in the inboard body and secured thereto at annular interface 33 by screw thread engagement.

The puller bar extends along the axis of the tensioning arrangement through the inboard and outboard pistons, which pistons surround the puller bar and interengage therewith by means of screw threads 35, 36, or the like, respectively, thereby forces are transmitted between the pistons and puller bar in both axial directions, that is, a force exerted on any one piston is transferred into the puller bar and other piston irrespective of the axial direction of that force.

The inboard cylinder body 25 defines, with the inboard piston 27 a piston-extending, bolt-stressing fluid chamber 40, whilst the outboard cylinder body 30 defines, with outboard piston 31 a corresponding piston-extending chamber 41.

The piston 27, inboard cylinder body 25 and outboard cylinder body 30 contained thereby also define a piston-retracting chamber 42 in which is contained piston retracting spring means 43. The spring means is provided conveniently and compactly by a stack of belleville washers. The spring means 43 exerts an axial force on the inboard piston to bias it with respect to the cylinder body 30 to attempt to retract it into its cylinder body 25. Because of the coupling to the puller bar, the outboard piston is likewise biased to retract with respect to cylinder body 30 and the puller bar with respect to the bridge/cylinder bodies.

A fluid passage 50 is defined axially through the puller bar 21 from the inboard piston-extending chamber 40 to the outboard piston-extending chamber 41. Coupling port 51 disposed on the longitudinal axis of the puller bar is connected by way of passage 50 and cross drillings 52, 53 to the piston-extending chambers 40 and 41 respectively.

Carriage means 55, shown as a lifting handle although lifting eyes or lugs could be substituted, is secured to the outboard piston 31 at 56 and by way of which the tensioning arrangement may be carried and lowered onto, or lifted from, the bolt 11. In particular it will be appreciated that the retracting spring means 42 causes the cylinder bodies and bridge to be biased with respect to the puller bar towards the outboard piston, whereby the tensioning arrangement remains intact and readily moved and disposed. It will be seen that, for preference, the arrangement is substantially symmetrical about the longitudinal axis of the puller bar.

Thus in operation, the tensioning arrangement is lifted by way of the carriage means and disposed with the inboard end of the puller bar adjacent the end part 13 of the bolt, whereupon the whole arrangement is rotated by way of the carriage means to thread the end of the puller bar onto the bolt and bring the bridge 22 into abutment with the flange 12. Thereafter, fluid supplied under pressure to the coupling 51 enters chambers 40 and 41, the fluid pressure in each chamber acting on the respective piston to cause it to move in an outboard axial direction against the resistance of the bolt exerted by way of puller bar 21.

When sufficient force is applied by way of puller bar 21 to stretch the bolt along its axis and the nut rotating means 23 is operated to move the nut 15 into contact with machine part 12, fluid pressure is vented and, if appropriate, a subsequent tensioning operation is performed or the arrangement 20 is removed.

When the bolt 11 is supported in tension by the nut 15, and fluid pressure in passage 50 reduced, the spring retracting means 43 acts to retract the pistons with respect to their respective cylinder bodies; however, as the pistons are fixed with respect to the puller bar and bolt, the cylinder bodies and integral bridge are lifted clear of the flange to effect said retraction and excess fluid expelled from the chambers 40 and 31.

The tensioning arrangement is thereafter unthreaded from the bolt and lifted away by way of the carriage means 55.

The embodiments described require access to only one end thereof for both transporting, engaging (rotating) and supplying hydraulic operating fluid, which compact arrangement makes it suited to use in environments where access to other parts is severely limited, or non-existent, such as at the bottom of a blind hole or recess. The embodiments described above with reference to the Figures includes only inboard and outboard pistons and cylinder bodies. It will be appreciated that if desired the concept of defining fluid passage along a piston may be extended to a tandem piston arrangement including one or more further pistons intermediate said inboard and outboard pistons.

Clearly other forms of fluid passage consistent with axial load transfer between pistons may be defined without departing from the invention and the usage of fluid passage by way of piston or pistons to join piston-extending chambers hydraulically, and, as mentioned above other forms of spring retraction means and/or carriage means may be provided.

Claims (4)

1. A hydraulic bolt or stud tensioning arrangement of the tandem piston type in which a plurality of annular pistons within cylinder defining bodies, dimensioned to surround in operation an individual anchored bolt axis, are coupled mechanically and hydraulically in tandem from an inboard piston and cylinder body operationally closest to an anchored part of the said bolt to an outboard piston and cylinder body furthest from said anchored part of the bolt, each said piston defining with its associated cylinder body a piston-extending, bolt stressing fluid chamber, the arrangement being characterised by puller bar, extending along an axis common with said bolt axis, adapted at its inboard end for connection to the bolt and outboard thereof to support said inboard and outboard pistons for transmission of forces in both axial directions therebetween and having a fluid passage therein extending from its outboard end to each piston-extending chamber, and piston retracting spring means disposed between said inboard piston and next outboard cylinder body operable to extend force on the inboard piston in an inboard axial direction.

2. An arrangement as claimed in claim 1 in which the piston retracting spring means comprises a stack of belleville washers.

3. An arrangement as claimed in claim 1 or claim 2 in which the outboard piston has secured thereto carriage means arranged to permit the arrangement to be lifted thereby.

4. An arrangement as claimed in claim 3 in which the carriage means is arranged to permit the arrangement to be rotated about the bolt axis thereby.