WO1991019109A1

WO1991019109A1 - Securing devices

Info

Publication number: WO1991019109A1
Application number: PCT/GB1991/000899
Authority: WO
Inventors: David Arthur Evans
Original assignee: Strachan & Henshaw Limited
Priority date: 1990-06-05
Filing date: 1991-06-05
Publication date: 1991-12-12
Also published as: GB9012519D0; AU7952991A

Abstract

A securing device in the form of a bolt or screw or dowel (1 or 1a) comprises a body (2 or 2a) into which a coaxial aperture extends from one end. An intermediate portion of the body through which the aperture extends has a tapering inner wall (14) and is provided with axial slots (16). A tapered pin (20) fitting the wall (14) is force fitted into the aperture to deform the intermediate portion outwards. The slots facilitate the deformation to cause the body to grip the sides of an aperture in which the securing device is inserted. Using such a device in the form of a bolt, the bolt shank can be held in engagement with the sides of the hole through which it passes while the shank is tensioned by the clamping load. Using such a device as a dowel makes it possible to accept a greater tolerance in the intended fit in a dowel hole.

Description

SECURING DEVICES

This invention relates to securing devices for connecting parts together, particularly but not necessarily exclusively, bolts, set screws and dowels. Bolts (and set screws) are subjected to a loading which is a combination of a tensile force clamping the parts together and a lateral shear force resisting sliding of one part on another. In most cases, the tensile loading is not a critical factor, particularly as stresses can usually be limited by increasing the number or size of the bolts making the connection. On the other hand, lateral loads generate shear stresses at the connection that may be more difficult to resist because of the problem of lack of fit between the bolts and the holes in the parts through which they pass. The problem is sometimes circumvented by providing a separate connection between the parts to resist shear, eg. a spigot and socket connection, but in many cases that is not possible.

As a result, for demanding applications, in heavy engineering in particular, where the tensile load is close to the capacity of the bolts and increases in the size or number of bolts are either impractical or too expensive, it is usual to employ high tensile or high strength friction grip bolts (HSFG bolts) or fitted bolts. The HSFG bolt functions by being tightened to the very high tensile loading, close to the yield point of its material, and the parts bolted together are held against lateral or shear loads by the high friction between them that results from the tensile forces. This is a common technique for structural steelwork. It is eminently suitable for spliced joints, for example, using multiple bolts in clearance holes; the parts do not require to be lined up exactly to share the load among all the bolts. The technique succeeds, however, only if the parts bolted together are relatively thin so that they deform sufficiently to give good contact at the friction surfaces in the region surrounding each bolt.

In contrast, the fitted bolt is intended to fit tightly in its hole and so absorb lateral forces as a shear load in its shank. The connection must be specially prepared, eg. by reaming the hole and grinding the bolt shank, so that they fit as closely as possible without making assembly impossible. It is often difficult in practice to ensure a tight fit on assembly; there is always the temptation to loosen the fit to make assembly easier, which means that close supervision and control is needed. Apart from that, however, there is also a technical flaw that limits the efficiency of fitted bolts.

Because of the near impossibility of ensuring that a tight enough fit is obtained for the bolt to act in the manner required in theory, it is usual to tighten a fitted bolt on its thread to apply quite a high tension load, so that friction between the parts will supplement the resistance to lateral shear forces. However, the elastic deformation of the bolt under tension also reduces its diameter, so that the initial tight fit is inevitably lost. The result is that a connection will usually be provided with only so many fitted bolts as are sufficient to locate parts accurately on pre-assembly, without fully tightening these bolts, so that the parts can later be refitted exactly in final erection, and bolts in clearance holes, in particular HSFG bolts, are used for the greater proportion of the holes of a connection. The fitted bolt in that case functions as a removable spigot rather than a tension-carrying member.

The minor deflections and movements resulting from these deficiencies in the conventional forms of bolt described may not be directly harmful. In structural steelwork, for example, in which the joints are subjected to a constant loading, bolted connections may be entirely satisfactory. However, if the connected parts are subjected to fluctuating loads over a period of time, particularly if there is some shock loading, the bolts tend to loosen, which will eventually lead to joint failure. To keep tight a bolted joint for a machine component, such as a bearing plummer block, that is subjected to varying loads, often presents problems. Dowels may be employed additionally as a palliative but they do not offer a universal solution and they add further complication, especially as they do not contribute to clamping the parts together.

For special applications, proprietary bolting systems exist to avoid the deficiencies of conventional bolts but they are elaborate and generally applicable only to bolts of a very large size, eg. above 40mm shank diameter- In the Morgrip (Trade Mark) bolt, the head of the bolt is threaded to receive an operating head having a chamber containing a piston by means of which hydraulic pressure is applied to a plunger extending along a hollow shank of the bolt. The bolt is put in place with the plunger under hydraulic load to extend the bolt shank and so reduce its diameter. The hydraulic pressure is released once the bolt has been put in position. The diameter of the shank when not under tension is an interference fit with the bolt hole so releasing the pressure causes the shank to grip the bolt tightly. Final tightening of the nut on the bolt can follow without releasing the lateral grip of the bolt on the parts connected by it. The hydraulic pressure must be applied again to remove the bolt, of course. A particular disadvantage of this arrangement is that it has a very limited tolerance band in the diametrical sense, quite apart from its complicated nature.

In the Pilgrim (Trade Mark) bolt, another large- size device, a taper-bored sleeve is slid onto a tapered shank threaded at both ends. The shank, with the sleeve on it, is located loosely in the hole in the parts to be connected and a hydraulic pump applies pressure fluid through one end of the shank, through passages in the shank, to the interface between the shank and the sleeve. The sleeve is expanded by hydraulic pressure to grip the sides of the hole, while at the same time the tapered shank can be drawn further into the sleeve to lock it in its expanded position. When nuts are threaded onto both ends of the shank to clamp the parts tightly between them with a measured axial load, the hydraulic pressure can be released. It will be seen that this is also a complex arrangement. Furthermore, the use of the tapered sleeve and the presence of a complicated series of passages in the shank for the hydraulic fluid reduces the tension- carrying capacity of the shank necessitating a securing device of larger overall diameter than would otherwise be the case.

According to the present invention, there is provided a securing device comprising an elongate body having an aperture extending axially from one end of the body through an intermediate portion of the length of the body, said portion being formed by a circumferential wall of non-homogeneous form facilitating deflection of said portion outwards under radial loading, within the length of said portion the axial aperture having a tapered face and receiving a fitting tapered pin for applying said radial loading to deform said intermediate portion of the body outwardly.

Such an arrangement allows close fitting to a hole in a relatively simple manner and is capable of being applied to devices of relatively small diameter. Especially in the smaller diameter range of bolts, the insertion of the tapered pin to deform the shank radially can be carried out manually without the need for a hydraulic pump or other like power source.

The invention is also applicable to set screws, which may be required to be substituted for bolts when the access from only one side of the parts being secured together.

A further application of the invention is to dowels which secure parts together against shearing loads. A dowel formed in accordance with the invention may not require a tapered reamed hole to be prepared for its insertion, as is the case with conventional dowels.

The invention will be described further by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side view of a bolt according to the invention,

Fig. 2 is an axial section of the bolt in Fig.

1,

Figs. 3 to 6 are axial sections illustrating some modifications of the bolt in Figs. 1 and 2,

Figs. 7 and 8 are axial sections of further examples of bolt according to the invention,

Fig. 9 is an axial section of a set screw according to the invention, Figs. 10 to 12 are axial sections of examples of dowel according to the invention, and

Fig. 13 illustrates a spacing washer for use with a securing device according to the invention. Figs. 1 and 2 illustrate the body 1 of a bolt with a shank 2, head 4, screw portion 6 at the opposite end of the shank. A nut 8 and washer 10 are mounted on the threaded end 6. The bolt body is hollow with an axial aperture 12 extending through it. The walls of the aperture comprise a conically tapered intermediate portion 14 spaced from the head 4 and the threaded portion 6. On each side of intermediate portion the aperture has a slightly larger diameter cylindrical wall extending to its opposite ends.

Four axial slots 16 are formed in the shank at equiangular spacings. Each slot begins close to the head 4 and extends into the threaded portion 6. These slots thus pass right through and beyond both ends of the tapered intermediate portion 14. Extending through the aperture and tapered to fit the portion 14 is a taper pin 20. The taper engagement between the pin 20 and the portion 14 is self-locking; in this example there is a diametrical taper of 1:50. To use the bolt, the shank is passed through aligned holes in the parts Pi,P₂ "to be connected together. The washer 10 and nut 8 are then attached to the bolt, the nut being threaded on to place the shank under a relatively light tension loading. The pin 20 is next inserted into the aperture 12 and is hammered down to bear against the slotted taper portion 14. As a result, the central section of the bolt shank is expanded radially to grip the hole through which it runs. If required, the nut can be further tightened and the pin hammered in further, this process being repeated until the parts are left gripped both axially and laterally by the bolt. Although the taper angle ensures the pin remains permanently locked in place, it can be hammered out to release the connection.

In the example of Fig. 3, the construction is largely identical with that shown in Figs. 1 and 2 and, as in the later figures also, the same parts are indicated by the same reference numbers. In this second example the slots 16, and the internal voids between the aperture 12 and the pin 20, are filled with a sealant material 30 to protect against corrosion. 0-rings (not shown) may be provided between the pin and the aperture to contain the sealant. The sealant material may be an elastomer, such as a silicone polymer, applied after the pin has been hammered home. It is alternatively possible to prefill the slots with a material, eg. a solder. In each case the material should have a relatively low elastic modulus, and therefore a high compliance, on account of the widening of the slots during the radial expansion of the shank, whether metallic or non-metallic.

In the example of Fig. 4, the smaller end of tapered pin 20a is given a cylindrical screw thread 42. A clamping nut 44 is threaded onto it and bears on the end of the shank through a washer 46 to draw the pin into the aperture to expand the bolt shank. In other respects the pin 20a is identical to the pin 20 and as in that earlier example it can be hammered out when the connection is to be released.

In Fig. 5, in an analogous manner to Fig. 4, a necked spigot 52 is formed on the end of pin 20b to attach a pulling tool, eg. hydraulic or mechanical, to draw the pin into the aperture to expand radially the shank of the bolt body 1.

The example of bolt shown in Fig. 6 employs the tapered pin 20a of Fig. 4, with the screw thread 42. The bolt body la is similar to the body 1 already described but its shank 2a has a tapered end 6a with a smooth outer wall in place of the threaded end shown in the body 1 of the preceding examples. Washer 46 rests on a collar 52 which surrounds and is radially located by the end 6a. When the nut is tightened, the clamping load is transmitted through the pin 20, nut 8, washer 46 and collar 52 onto the face of the part P₂ being clamped. The action of drawing the pin into the bolt body thus also determines the clamping force of the bolt. Because the end 6a is not threaded to receive a tightening nut, the slots 16 may extend right through this end of the bolt body.

Figs. 7 and 8 show examples of the invention as applied to a proprietary securing device of Huck Manufacturing Co. , Irvine, California, USA, known as the Huckbolt (Trade Mar ) . The Huckbolt has a shank with a necked extension which is intended to be gripped by a hydraulic pulling tool, in a similar manner to that described with reference to Fig. 5. Preceding the extension and in place of a screw thread on the end of the main part of its shank, there is a series of annular grooves. A collar is swaged onto this grooved portion while the bolt shank is held under tension by the pulling tool, the collar thus assuming the role of a conventional nut but the fixing being shake-proof because there is no screw thread.

In the example of Fig. 7, there can be seen the bolt body lb with a blind aperture 12a having the tapered portion 14 and the slots 16 of the previous examples. On the end further from the bolt head 4a, the main portion of the shank 2b is formed with a series of annular grooves 62 and a terminal extension 64, joined to the main portion of the shank by a rupturable neck 66, has a series of larger annular ribs 68. In the same manner as the example of Fig. 1, the pin 20 is driven into the aperture 12a to cause the bolt shank to grip the parts P^P_j. A loosely fitting collar 70 is placed over the opposite end of the bolt and tension is applied to the shank by a pulling tool (not shown) holding the extension 64. The pin 20 is then forced further in, to such extent as may be required. The collar 70 is now swaged onto the grooves 62 while being held tightly against the part P₂, to leave the parts Pi,P₂ permanently secured together with the shank of the bolt gripping the side faces of the bolt hole firmly. The extension 64 can now be broken off at the neck 66 by increasing the force of the pulling tool. In the modified form shown in Fig. 8, the tapered pin 20c is formed with the annular grooves 62 and the necked extension 64. The pin 20c extends through bolt body lc, the shank 2c of which does not project from the parts P₁,P₂. The collar 70 is swaged onto the end of the pin 20c to grip the grooves 62 while the pin is held at the required tension by the hydraulic pulling tool gripping the extension 64. In other respects, this embodiment has the same features as those described with reference to Fig. 7.

The invention is also applicable to the Huckfit (Trade Mark) fastener, also a product of Huck Manufacturing Co, in the same manner.

In Fig. 9 the invention is applied to a set screw. The screw body Id is similar to the bolt body 1 of Figs. 1 to 3 and like parts are indicated by the same reference numbers. The threaded portion 6 engages the threads of a tapped hole T in the part P₂ The manner of insertion is also similar to that of the example of Figs. 1 to 3 and needs no further description.

Figs. 10 to 12 are examples of the invention in the form of dowels. In each of the examples illustrated the dowel body la comprises a shank 2d, a head 4b and a tapered end portion 6a at the end of the shank remote from the head. As with the bolt bodies already described, there is an aperture 12 extending through the dowel body with a tapered intermediate portion 14 and axial slots 16 passing through the portion 14. In Fig. 10, similarly to the first example of bolt described above, the tapered pin 20 is hammered into a tubular dowel body, the shank 2d of which is formed in the same manner as the bolt shank of that example, except that its end is of course not threaded. The head 4b sets the position of the slotted portion of the shank relative to the depth of the parts through which the dowel passes.

In Figs. 11 and 12, the dowel body is secured in the same manner as the examples of bolt shown in Figs. 4 and 5 respectively, employing the tapered pins 20a and 20b of those examples. Further description of the device and its mode of installation is therefore not necessary.

It will be understood that individual features of the different embodiments can be combined where required and that no further description is required to permit the person skilled in the art to form such combinations from the embodiments disclosed.

The number of slots in the shank of a securing device body can be varied, although it is generally desirable to arrange them in a symmetrical pattern to avoid eccentric loading. The length of the tapered portion of the shank aperture can also be varied within quite wide limits; it should always terminate clear of the ends of the slots. For optimum effect, the tapered portion 14 of the aperture 12 should extend into the axial length of both holes in the parts to be connected and through which the securing device passes. Packing means may be arranged under the head of the device to ensure this, preferably so that centre of the length of the engaging regions of the tapered faces lies approximately at the middle of the combined thickness of the parts at the holes through which the device passes. Fig. 13 shows a preferred form of washer 70 to be used as packing, having an oversize central hole 72 to accommodate the radial deformation of the bolt shank, but with three or more spaced ribs 74 projecting inwards from the wall of the hole to hold the washer concentrically on the shank. Where the device also comprises a securing nut, packing may be placed above the nut and a preferred form of packing comprises an integral skirt on the nut.

Claims

1. A securing device comprising an elongate body having an aperture extending axially from one end of the body through an intermediate portion of the length of the body, said portion being formed by a circumferential wall of non-homogeneous form facilitating deflection of said portion outwards under radial loading, within the length of said portion the axial aperture having a tapered face and receiving a fitting tapered pin for applying said radial loading to deform said intermediate portion of the body outwardly.

2. A securing device according to claim 1 wherein said circumferential wall is divided by at least one axial slot for facilitating said deflection under radial loading.

3. A securing device according to claim 2 wherein there is a plurality of said slots at equiangular spacings around the wall.

4. A securing device according to claim 2 or claim 3 wherein the or each slot extends beyond the ends of said tapered face of the aperture.

5. A securing device according to any one of claims 2 to 4 wherein the or each slot is sealed by a material having a substantially lower elastic modulus than the material of said intermediate portion of the body.

6. A securing device according to any one of the preceding claims wherein said aperture extends through the length of the body.

7. A securing device according to claim 6 wherein the tapered pin is provided with engagement means at its smaller end for connecting a pulling device to cause the pin to apply said radial load to said portion of the body.

8. A securing device according to claim 7 wherein the engagement means comprises a screw thread to receive a nut for pulling the pin into said aperture of the body.

9. A securing device according to claim 7 wherein the engagement means comprises a protuberance for attaching a fluid power pulling device for the pin.

10. A securing device according to claim 7 wherein the engagement means comprises a plurality of radial protuberances for gripping engagement with an annular locking element.

11. A securing device according to any one of claims 2 to 10 in the form of a bolt or set screw and wherein said slot or slots extend from adjacent a head of the bolt at one end of a shank of the bolt or screw into a threaded region at the opposite end of the shank.

12. A securing device according to any one of claims 1 to 10 in the form of a dowel.

13. A securing device according to claim 11 or claim 12 when dependent to claim 8, wherein the screw thread is formed on an end of the tapered pin projecting from the body of the securing element and the nut on said screw thread bears on annular abutment means which surrounds the adjacent end of the securing element body and through which an axial load on the nut can be transmitted to the parts connected by the element.

14. A securing device according to any one of claims 1 to 4 in the form of a bolt and wherein a shank position of the bolt is provided with a peripherally profiled region on which a clamping collar can be engaged, and the bolt body or the pin is provided with engagement means for connecting a pulling device.

15. A securing device according to claim 15 wherein said engagement means is provided on the bolt body and the aperture for the pin terminates short of said engagement means.

16. A securing device according to claim 15 wherein said engagement means and said peripherally profiled region are both provided on a portion of the pin projecting from the bolt body.

17. An assembly of parts having a releasable connection comprising at least one securing device according to any one of the preceding claims.

18. An assembly of parts according to claim 15 wherein said at least one securing device passes through aligned apertures in a plurality of parts and spacer means are disposed on said intermediate portion of said device at least at one end of the combined apertures, whereby to locate the centre of the combined length of said apertures at least approximately midway along the length of said tapered face cooperating with the tapered pin.