GB1592092A

GB1592092A - Bolt stud or like tensioning devices

Info

Publication number: GB1592092A
Application number: GB1591878A
Authority: GB
Original assignee: Pilgrim Engineering Developments Ltd
Current assignee: Pilgrim Engineering Developments Ltd
Priority date: 1977-02-02
Filing date: 1978-02-01
Publication date: 1981-07-01

Description

(54) BOLT, STUD OR LIKE TENSIONING DEVICES (71) We, PILGRIM ENGINEERING DEVELOPMENTS LIMiTED, a British Company of Beaufort House, St. Botolph Street, London, EC3A 7DX, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- The present invention relates to tensioning devices for tightening bolts, studs and like tension members and to a method of making a sealing member for such tensioning devices.

Hydraulic tensioning devices such as hydraulic nuts or hydraulic bolts incorporating an annular piston have been employed hitherto in, for example, the tensioning of bolted flange joints. The annular piston is located in an annular recess in the nut or bolt head and surrounds the bolt extending through the flange. The piston is urged out of the recess and against the flange by hydraulic fluid under pressure applied to the recess so as to tensin the bolt. Thereafter, a retaining nut may be screwed down against the flange, or shims in the form of a divided ring may be inserted into the available gap beneath the bolt head or the body of the nut so that the hydraulic pressure may be released.

In such a tensioning device the means for supplying hydraulic fluid to behind the piston means may comprise a feed bore extending through the body of the device into a chamber behind the piston and within the recessed end-face. With suitable sealing means to prevent leakage of fluid from the chamber, fluid can be fed in at high pressure. An expandable sealing member may occupy the or each chamber and a tube, sometimes in the form of a hollow needle, may extend from the feed bore into the sealing member.

Hydraulic fluid is fed into each sealing member to cause it to expand. Lateral expansion is constrained by the side walls of the chamber, and hence axial expansion occurs to urge the piston means outwardly of the body of.the device.

According to the present invention there is provided in a first aspect a tensioning device comprising a body having one or more pistons housed in a recessed end-face of the body and movable parallel to the axis of a shank extending from the body or of a bore extending through the body, an expandable sealing member in the recess behind each piston and comprising a layer of rubber or like resilient deformable incompressible material moulded around and enveloping a former, and means for supplying hydraulic fluid into the or each member to cause its resilient layer to expand and thereby to urge the or each piston in a direction which leads out through the said end-face.

Supply of hydraulic fluid into the or each sealing member e.g. by stem connections, results in expansion of the resilient layer away from the former. Substantial lateral expansion is prevented by the side walls of the recess, and the axial expansion thus ensues with the result that the or each piston is urged outwardly of the end-face.

If desired, channels can be provided in the surface of the former within the sealing member in order to facilitate distribution of injected hydraulic fluid and help ensure even expansion of the resilient layer. To this end, the channels are filled with salt or other sacrificial material prior to moulding on of the resilient layer. After moulding, a suitable solvent (water for salt) can be injected to dissolve the sacrificial material and thereafter the solution formed is withdrawn. In a preferred embodiment, the expandable sealing member has a nitrile rubber layer moulded around a metal former, preferably an aluminium former.

Tbe tensioning device according to the invention may be of the kind with annular pistons of circular outline in plan or they may be of the kind described and claimed in our copending Application No. 4284/77 (Serial No. 1592091) of which this application is a divisional.

As a corollary to the foregoing, the present invention also provides a method of making a tensioning device as previously defined, the method comprising making an expandable sealing member by moulding à layer of rubber or like resilient deformable incompressible material around a former and locating the sealing member in a recess in the end face of a body behind one or more pistons.

An expandable sealing member comprising a resilient layer moulded around a metal former is easier to make than most of the expandable sealing members which have been previously in hydraulic tensioning devices. Hitherto with annular pistons a hollow, annular rubber expandable sealing member has been employed, but some difficulty has been encountered in forming the continuous passage in such members.

Such difficulties are avoided with the expandable sealing members provided in accordance with the second aspect of the invention since the rubber is moulded around the former and the former remains inside the sealing member in use. Hydraulic fluid injected into the sealing member enters between the former and the inside of the sealing member to expand the sealing member away from the former. Furthermore, injection or hydraulic fluid into the present expandable sealing member soon fills any distribution channels and immediately thereafter expansion ensues. This is to be contrasted with the conventional expandable sealing members where the continuous passage represents a substantial dead-space which has to be filled with hydraulic fluid before expansion occurs.

Since the high pressure pumps usually employed for injecting hydraulic fluid are of low capacity, this saving of dead-space represents a considerable saving in the time needed to tension the hydraulic tensioning device.

The present invention will now be described further by way of example with reference to the accompanying drawings, of which: Figure 1 is a vertical cross-section of a flange bolt with a hydraulic washer-like device which embodies the present invention; Figure 2 is a horizontal cross-section of the bolt and hydraulic device of Figure 1; Figure 3 is a horizontal cross-section similar to Figure 2 of an alternative hydraulic device embodying the present invention; Figures 4a and b show plan and side views of a former; Figures Sa, b and c show end, side and opposite end views of a former fixing pin; Figure 6 shows a plan view of a mould; Figure 7 shows a section on the line VII VII of Figure 6; Figure 8 shows a section in the direction VIII of Figure 6; Figure 9 shows a plan view of a piston; Figure 10 shows a section on the line X X; and Figure 11 shows a section on the line XI XI.

Referring first to Figures 1 and 2, a bolt 10 extends through a flange 12 and is being tensioned by a hydraulic washer-like device 14 embodying the present invention and retained on th bolt by a nut 15. The hydraulic device 14 has a smooth central bore 16 for the bolt and comprises an oblong body 18 of high tensile steel having a recessed endface 20 which houses piston means 22 in the form of a single piston surrounding the bolt 10. The recess in the end-face 20 is dimensioned such that the piston means 22 is movable parallel to the axis of the bore 16.

As can be seen in Figure 1, an expandable sealing member 24 occupies a chamber within the recessed end-face 20 and behind the rear face of the piston means 22. This sealing member 24 comprises a layer 26 of nitrile rubber moulded on to a metal former 28 conveniently of aluminium. A bore 30 extends through the oblong body 18 and houses a stem connection 32 for supplying hydraulic fluid into the expandable sealing member 24 to urge the piston means 22 in a direction which leads out through the said recessed end-face.

In order to facilitate distribution of hydraulic fluid within the sealing member 24, hollow channels 34 are provided. Such hollow channels are formed in the sealing member during moulding by the use of sacrificial cores of soluble material such as common salt. During the manufacture of the sealing member the channels are filled with salt before the reslient layer 26 is moulded on. Thereafter water is injected to dissolve the salt and the solution thus formed is withdrawn.

The shape of the piston means 22 will be apparent from Figures 1 and 2; the horizontal cross-section is the same as for the sealing member 24. The piston means 20 has a circular-cylindrical inner side-face 36 of radius slightly greater than that of the bore 16 and an extended outer side-face 38. The outer side-face 38 is dimensioned such that the piston means 22 has a minimum overall transverse dimension less than the least possible overall diameter of an annular piston giving the same piston face area, and a maximum overall dimension less than the least possible for a pair of circular pistons having spaced parallel axes on opposite sides of the bore 16 and giving the same piston face area. Furthermore, the two piston face areas of the piston means on either side of the body's transverse plane 40 have centroids collinear with the point of intersection of the axis of the bore 16 with a common plane transverse thereto, and equispaced therefrom.

In use, hydraulic fluid will be supplied via a manifold to a series of like tensioning devices arranged similarly to the hydrauic device 14. As this is done, the fluid will cause the reslinet layer 26 to expand and tend to force the piston means 22 out of the recessed endface 20. The load transferred by the piston means 22 to the face of the flange 12 creates an upward force acting against the nut 15 which in turn will cause a tensile strain in the bolt 10. With increasing fluid pressure so the tensile strain will increase, until at say 30,000 psi the reslient layer 26 has expanded to the relative position 261 shown by chain lines in Figure 1. The body 18 will then have moved to the relative position 18' with the result that the end-face 20 is at x-x instead of y-y.

Thereupon a pair of split shims can be inserted into the available gap and the fluid pressure released. Preferably the shims are split by the transverse plane 40 of the body, each having a profile subtended by the points a to g, and are of thickness xy.

The second embodiment shown in Figure 3 is much the same as that described above except that the piston means comprises two separate pistons each with a kidney-shape piston face. The faces are the same configuration as the horizontal cross-section through the respective expandable sealing members 50 shown in Figure 3. Once again the tensioning device exemplified is a hydraulic washer-like device 52 with a central bore 54 for a bolt. Separate feed-bores with stem connections 56 are provided for supplying hydraulic fluid into the two sealing members, though a minifold or other arrangement is used to ensure that fluid at the same pressure is supplied to both. Operation of the device is otherwise the same as that for the device of Figures 1 and 2, and shims or a working nut can be used to take up the gap obtained by use of the device.

Both the two hydraulic devices described above have the advantage that the body is less wide than a comparable conventional device with an annular piston, which thereby makes possible the simultaneous tensioning of adjacent bolts pitched close together.

Furthermore, bending moments within the devices are minimised using either of the piston means illustrated. Compared with the design shown in Figures 1 and 2, that of Figure 3 has the further advantage of having piston means with no relatively thin sections which might be subject at extreme pressures to slight flexing or bending.

The procedure for manufacturing the sealing member will now be described with reference to Figures 4 to 11.

An aluminium former 101 of thickness 3/8" is drilled and tapped in three positions as shown at 102 on Figures 4a and 4b. Into these holes are fitted three former fixing pins 103 see Figures 5a, b and c made from mild steel bar, externally threaded at one end 104 to screw into the former 101 and internally drilled and tapped for example 8BA at the other end 105. The former fixing pin 103 is of sufficient length to give the required thicknes of the upper and lower face of the nitrile rubber tyre.

The mould 106 is shown in Figure 6 having a cavity 120 with three teat holes 107 at the bottom of it, each teat hole first reducing to a hole 111 small enough in diameter to support the former fixing pin.

This further reduces to a dimaeter to accommodate the shank of an 8BA bolt at 108 and then increases to accommodate the head of the same 8BA bolt at 109.

Two sheets of uncured nitrile rubber of a shore hardness of 60 and a thickness of 3/16" are cut to shape to be slightly oversize of the mould cavity 120 and are then degreased.

One sheet is laid into the bottom of the mould which has also been degreased.

The aluminium former 101 with the fixing pins 103 now fitted is presented to the mould 106 the pins being passed through the bottom layer of nitrile rubber and locating in the teat holes 107 where the assembly is made secure in the mould by the use of the 8BA bolts.

It is thus seen that the former fixing pins mount the former very securely in the mould thus giving the uniform wall thickness of the completed cured tyre.

A strip of the correct length of the same uncured nitrile rubber of width say 3/8" is degreased and placed around the sides of the mould between the mould and the sides of the aluminium former and on top of the bottom layer of rubber.

The second sheet of nitrile rubber cut to size is placed on top of the former and kneaded on to the side walls methodically in order to exclude any air which may be trapped in the uncured assembly.

A piston 111 (Figures 9 to 11) with a recess 114 on its underside is placed on top of the assembly and a thick flat plate is placed over the whole assembly to provide uniform heat distribution and also to alleviate any unevenness of the plattens of the hydraulic press used for the curing process.

After curing, the tyre assembly is removed from the mould and allowed to cool. When cool, one former fixing pin 103 can be removed and the tyre can be tested using a standard workshop airline at 100psi. As the tyre is unconstrained in this test, it will be subjected to far greater strains than will ever be incurred in practice. Immersion of the inflated tyre in water will determine any leakage. The pressure can now be released and the two remaining former fixing pins can be removed. X-ray examination of the tyre can be used to indicate a constant wall thickness.

Note that the aluminium former remains in the tyre throughout its use. In use, the holes of the two unused teats in the tyres are blanked off using mild steel probe fittings which can be interference fitted into the teats or fitted using Araldite (Araldite is a Registered Trademark) as required.

Perhaps the main advantage of using these former fixing pins for holding the former apart from the obvious one of the former not moving during the curing process, is that in use on the tensioner the holes drilled in the former allow the fluid which is inlet on one side of the tyre to rapidly transfer through to the other side thus enabling uniform inflation of the tyre during the application of the pressure cycle, and similarly and perhaps more important on removal of the pressure, the fluid returns to the hydraulic reservoir (i.e. pump) uniformly thus enabling the load cell assembly and, in this case tensioning device, to return to its initial position quickly and uniformly.

While the present invention has been described in detail with reference to embodiments which have an unthreaded bore, other forms are possible. Thus, for example, the tensioning device provided could be in the form of a hydraulic bolt, with the piston means in an end-face form which projects the shank of the bolt. Likewise, a more conventional form of sealing member can be employed.

It will also be appreciated that while the expandable sealing members employed have been described in the context of particular tensioning devices, the use of such a member comprising a resilient layer on a metal former should find wider applicability. One example would be in devices more akin to the known hydraulic nuts and hydraulic bolts, and employing a single annular piston.

WHAT WE CLAIM IS: 1. A tensioning device comprising a body having one or more pistons housed in a recessed end-face of the body and movable parallel to the axis of a shank extending from the body or of a bore extending through the body, an expandable sealing member in the recess behind each piston and comprising a layer of rubber or like resilient deformable incompressible material moulded around and enveloping a former, and means for supplying hydraulic fluid into the or each member to cause its resilient layer to expand and thereby to urge the or each piston in a direction which leads out through the said end-face.

2. A tensioning device according to claim 1 in which the body is a bolt head, the shank of the bolt extending from the bolt head in the same direction as the piston.

3. A tensioning device according to claim 1 in which the body is a washer with a cylindrical bore extending through it parallel to its axis.

4. A tensioning device according to claim 1 in which the body is a nut with a screwthread bore extending through it parallel to its axis.

5. A tensioning device according to any of claims 1 to 4 in which the means for supplying hydraulic fluid comprises a feed bore extending through the body of the device into the expandable sealing member in a chamber or chambers behind the piston or pistons.

6. A tensioning device according to any of claims 1 to 5 in which distribution channels are provided in the surface of the former.

7. A tensioning device according to any of claims 1 to 6 in which the former is of metal.

8. A tensioning device according to claim 7 in which the metal is aluminium or an alloy of aluminium.

9. A tensiong device according to any of claims 1 to 8 in which the resilient layer is of nitrile rubber.

10. A method of making a tensioning device as defined in any of claims 1 to 9 comprising making an expandable sealing member by moulding a layer of rubber or like resilient deformable incompressible material around a former, and locating the sealing member in a recess in the end face of a body behind one or more pistons.

11. A method according to claim 10 in which distribution channels are provided in the surface of the former and are filled with a sacrificial material prior to moulding, the sacrificial material being removed after moulding.

12. A method according to claim 11 in which the sacrificial material is removed by dissolving it in a solvent.

13. A method of making tensioning devices, substantially as hereinbefore described with reference to Figures 4a to 11 of the accompanying drawings. ~ ~~

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Perhaps the main advantage of using these former fixing pins for holding the former apart from the obvious one of the former not moving during the curing process, is that in use on the tensioner the holes drilled in the former allow the fluid which is inlet on one side of the tyre to rapidly transfer through to the other side thus enabling uniform inflation of the tyre during the application of the pressure cycle, and similarly and perhaps more important on removal of the pressure, the fluid returns to the hydraulic reservoir (i.e. pump) uniformly thus enabling the load cell assembly and, in this case tensioning device, to return to its initial position quickly and uniformly. While the present invention has been described in detail with reference to embodiments which have an unthreaded bore, other forms are possible. Thus, for example, the tensioning device provided could be in the form of a hydraulic bolt, with the piston means in an end-face form which projects the shank of the bolt. Likewise, a more conventional form of sealing member can be employed. It will also be appreciated that while the expandable sealing members employed have been described in the context of particular tensioning devices, the use of such a member comprising a resilient layer on a metal former should find wider applicability. One example would be in devices more akin to the known hydraulic nuts and hydraulic bolts, and employing a single annular piston. WHAT WE CLAIM IS:

1. A tensioning device comprising a body having one or more pistons housed in a recessed end-face of the body and movable parallel to the axis of a shank extending from the body or of a bore extending through the body, an expandable sealing member in the recess behind each piston and comprising a layer of rubber or like resilient deformable incompressible material moulded around and enveloping a former, and means for supplying hydraulic fluid into the or each member to cause its resilient layer to expand and thereby to urge the or each piston in a direction which leads out through the said end-face.