GB2153472A

GB2153472A - Fastening device

Info

Publication number: GB2153472A
Application number: GB08401655A
Authority: GB
Inventors: Edward Victor Byers
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-08-06
Filing date: 1984-01-23
Publication date: 1985-08-21
Also published as: GB8401655D0

Abstract

A fastening device for providing an axial force resistant anchorage to a plain hole in a hard material comprises a tubular metal sleeve 1 which is convoluted around its circumference and which is plastically expanded to fit and grip the hole by the forced passage of a short metal spud of polygonal cross-section or a ball 3 through its central aperture. Figure 3 shows a corrugated sleeve 1 of aluminium or other corrosion resistant metal when used as a replacement cavity wall tie. After the ball 3 has been hammered through it does not matter if it subsequently corrodes away. In another embodiment, a stainless steel sleeve is distended by a number of balls of progressively increasing diameter and may be used as a deeply placed rock anchorage to resist very high tension. The device may be used for anchoring in holes cast in metallic alloys which are too hard to be drilled to tapped. <IMAGE>

Description

SPECIFICATION Fastening device for providing anchorages in holes in hard materials.

The invention relates to a means for providing a firm connection, of great permanence, to a hole in a body of hard material such as rock, masonry, brickwork and concrete or other hard, but friable substance which cannot be tapped with a screw thread and to bodies of materials which it is either infeasible or undesirable to drill or otherwise pierce right through so that a connection might be made by, for instance, a bolt and nut. The device is also of value for making connections to holes cast in metallic alloys which are too hard to be drilled or tapped.

There exists a great variety of methods and devices for providing a connection to a plain blind hole. Some of these utilise wooden pegs or constructions of compressed natural fibres and are quite satisfactory for use in locations where attack by moisture or micro-organisms or a wide fluctuation of temperature is unlikely. There is also a considerable number of devices made in the form of expandable plugs in plastics materials which are totally resistant to attack by dampness of vermin and they ae excellent provided that the force to be resisted is not axial, of substantially so, because the device may then relax its grip over a long period of time owing to creep phenomena, to which plastics materials are notoriously prone.

Accordingly, the invention comprises an expandable plugging means and a co-operating expanding means which are both made of metal. The metal for the plugging means is chosen so asto be resistant to long term attack by corrosion in the particular environment, but the expanding means may usually be made of an ordinary steel. For masonry walls, copper or aluminium or their alloys will generally be satisfactory for the plugging means, but for deep anchorages in rockformations, which may be required to resist high forces, stainless steel will often be preferred.

Although the expandable plugging means, which is hereinafter referred to as the plug, may theoretically take the form of a plain cylindrical tube, such a high degree of precision is necessary in the manufacture of the parts and the drilling of the hole to the correct diameter that it is not feasible, in practice, to use such a simple device as there is then a risk that the plug will not expand far enough to grip the hole or, if it be in masonry, that it will expand too far and burst it. Therefore, the plug is made in a form which permits an initial plastic deformation to occur during expansion to fit the hole, there then still remaining some free space in the annular region between the expander and the sides of the hole into which surplus metal may flow plastically.Such a plug may take the form of a tubular member furnished with longitudinal ribs directed inwardly or outwardly, or both, and the outer surfaces may be provided with circumferentially of spirally arranged fine serrations to improve the grip in the hole. Alternatively, the tubular member may be provided with deep circumferential or spirally arranged grooves, the grooves defining sharp teeth which bite into the sides of the hole when the plug is expanded. In this case, the grooves provide the free space into which surplus metal may be squeezed plastically. Combinations of inwardly projecting longitudinal ribs and external circumferential grooves may also be used.

The expanding means takes the form of one or more hard metal spuds, of larger size than can be accommodated within the interior of the undistended plug, and having rounded surfaces where they engage and expand the plug, being drive therethrough by a removeable drift. For some types of fastener the spuds may be spherical balls.

A notably important application of the invention is as a remedial wall tie for a cavity wall, the stability of which may have become endangered by the corrosive destruction of the wall ties originally employed when the wall was constructed. Such walls have two slender component walls or leaves defining a cavity which is bridged at intervals by metal ties in the mortar joints, these serving to ensure that the leaves are mutually supportive. There is a limit to the unsupported height of a slender wall if it is to be safe against buckling underthe influence of its own weight and any superimposed loads and this is determined by such factors as the quality of the materials used and the skill of the wall builder and the nature of the superimposed loads.If the safe limit be exceeded, as may occur owing to the rotting away oftheties, the leaves will start to buckle and bulge and continue to do so at an increasing rate in the absence of remedial measures. The process is slow, but inexorable and is believed to be a consequence of the fact that mortar exhibits plastic properties over a long time scale. However, quite a small horizontal restraining force in a direction perpendicularto the plane of the wall is sufficient to prevent the onset of buckling or to arrest its progres should it occur. Many walls have been built in the past incorporating steel ties and, no matter how well they are protected by plating or other coatings, they are eventually destroyed by corrosion induced by moisture should this enter the cavity between the leaves and this is not at all unusual in damp localities.The resulting mutual loss of support between the leaves may necessitate very costly repairs if left unremedied, and it is largely in relation to this important, but non-limiting usage, that the invention is hereinafter described.

In the drawings accompanying this specification: Figure 1 gives cross-sectional views of various types of tubular members which may be used for plugs, together with the shapes which they assume when plastically deformed in a confining hole and a view of one of them when furnished with fine circumferential serrations on its outermost surfaces: Figure 2 gives a side elevation and cross-sectional view of a tubular member with deep, tooth-defining circumferential grooves on its outer surface, and with inwardly projecting longitudinal ribs: Figure 3 shows how a plug may be used to stabilise a cavity wall, using a single ball as an expanding means, together with other types of expanding spud: Figure 4 shows a cavity wall section stabilised buy a plug expanded by two balls:: Figure 5 shows how a shaped pin may be used instead of the two-ball arrangement of Figure 4.

Figure 6shows a plug provided with a flanged head at one end: Figure 7shows an anchorage in a rock formation.

Figures la, band c show suitable cross-sectional plug shapes for manufacture in malleable metals such as copper, aluminium and zinc ortheir alloys, the lower views showing how the plugs 1 become deformed when confined in a hole in a distortionresistant material 2 and subjected to the effect of an expanding means 3, which is of larger diameter than can be accommodated in the undistorted section. All these shapes are characterised by the fact that there is at all times during the expanding process some free space into which plastically deformed metal may flow after the section has been expanded sufficiently to encounter the sides of the hole and any alternative section must have this property.

These must be not less than three longitudinal ribs on either the inner, or the outer, or both surfaces of the section and the preferred number for, for instance, a remedial wall tie, is six. Shapes 1a and 1b may be made by extrusion processes. Shape 10 may be made from a plain cylindrical tube by forcing it through an appropriately shaped die and this method is particularly suitable for stainless steel plugs because this metal is very difficult to extrude in complicated shapes. Figure 1 d gives a view of shape lofurnished with fine circumferential serrations along its outermost surfaces.These serrations 4, with may also be in the form of an interrupted fine screw thread, may be fashioned buy a cutting process or bythe forced passage of plug 1 through the appropriate number of inwardly directed radially arranged knurling wheels. In a hole in a hard material which has some degree of friability the gripping power of the plug may thereby be improved.

Figure 2 shows a side elevation of a plug provided with deep circumferential grooves which define at least moderately sharp teeth at regular intervals along at least the hole-engaged portions of the plug.

The grooves 5, which may also be in a spiral, may be formed by a cutting process, or, provided that a removeable central mandrel is inserted to prevent collapse, by thread rolling techniques. Crosssectional view 2b shows how the plug may also be provided with internally projecting longitudinal ribs; three are shown. This type of deeply grooved plug is of value for engaging holes in low-strength concretes or shales, both hole material and teeth becoming mutually crushed to some extent by the expanding process, there then still remaining a quantity of viably strong msterial between the teeth.

The proportions are chosen so that there is at all times some free space between the teeth into which surplus metal may become squeezed in the longitudinal directions from each tooth.

Figure 3 depicts the use of the device as a remedial wall tie for cavity walls, the plug 1 being placed in a hole in wall 2 which is drilled right through one of the leaves and part of the way into the other towards the face which it is not wished to disfigure, which will often bear a plastered finish. After insertion, the plug is expanded bytheexpanding means 3, which is a hard metal ball and which is driven right through the plug by a metal drift 6, the end of the drift being furnished with a re-entrant cone or spherical seating to engage the ball centrally. In field conditions, the dirftwill usually be driven in buy a pneumatically or electrically powered hammering machine, and is made of a small enough diameter to be readily withdrawable when the operation is complete.The end of the drift may be magnetised to control the ball during insertion. Alternatively, the device may be supplied with the ball already driven in a short retention distance at the manufacturing point, the plug body being temporarily confined in a die to prevent the expansion of the plug end. Ball 3 is shown approximately half way along its journey and shows how the plug becomes over-expanded where it is unconfined in the region of the cavity. It is found that the ball not only causes the required deformation, but also leaves the plug section with a permanent and substantial approximately circumferential compression stress which serves to keep the engaged surfaces of the plug in elastically stressed contact with the sides of the hole. Once the ball has been forced right through the plug its purpose has been served and it does not matter if it subsequently rots away.

Figure 3a and 3b show short spuds of hard metal which may be used as expanding means. 3a is cylindrical and 3b has a polygonal section having a like number of sides of any inwardly projecting ribs within the plug. Both are smoothly curved towards their axes over the region which causes deformation of the plug. The parallel-sided length of the body of the spud depends on what force can reasonably be used for driving it through the plug because this force must not only provide the distending force, but also that which is required to overcome frictional effects along the length of the spud and this increases with length. It will generally only be possible to use a spud which is the same length as the plug for quite shallow holes such as may be found cast in bodies of unmachinable metals.In this latter case, the spud may then be furnished with an enlarged head as shown at 3c, permitting the attachment of other articles to the casting. Otherwise, the choice between a machined spud or ball is governed only by economic considerations. In small sizes, it will usually be cheaper to use a ball because there are made in very large numbers for other purposes, but for diameters of plug of several centimetres, such as may be required for rock anchorages, the reverse will usually be the case.

When the plug is also made to serve as the connecting means between the anchorages provided by both of its ends into two separate bodies, as in a remedial wall tie, the driving distance and the length of the drift required may both be reduced by the artifice shown in Figure 4. The first ball, 7 is followed by a second ball 8, or larger diameter, a loose-fitting rod 9 being used to keep the balls apart and transmit driving force to ball 7. This arrangement may be forced into the plug body at the manufacturing point, the plug being confined in a die to prevent expansion during the process. The proportions are chosen so that ball 7 is in a position where it is about to enter the section of the plug within the remote wall leaf and ball 8 has just entered the plug body.

Figures 5 shows a shaped cylindrical pin 10, bearing two enlargements 11 and 12, corresponding to the diameters of balls 7 and 8 in Figure 4 may be used to produce the same effect as the balls, the factory assembly process being the same. If desired, the near end of the pin may, as shown, be of sufficient length greatly to reduce the required length of driving adrift.

Figure 6 shows a plug with a flanged or otherwise enlarged end which is used to retain and attach other articles to the plugged body. Such a feature may also be used at one end of a remedial wall tie for a cavity wall in which one of the leaves is of very weak material, the enlarged head providing a more positive retention that a frictional grip. The head may be accommodated in a drilled recess of appropriate size. It is also possible to use a plug with its end flush with or slightly below the surface of the plugged body as an attachment point for, for instance, a self-tapping screw.

Figure 7 shows the use of the fastener as a rock anchorage. The expandable portion is then integral with or otherwise firmly attached by any known method to a cylindrical tubular part 13 provided with any desired end attachmentfitments and having a sufficient internal diameter to allow the passage, without hindrance, to the expanding spuds to the expandable portion. The tubular end piece 13 may be of considerable length so that the expandable portion which establishes the connection is deeply buried therein, enabling advantage to be taken of a great weight of overburden, this being important in weak rock formations.Rock anchorages of this type will usually be made of a corrosion-resistant, strong material such as a stainless steel and the preferred shape of the rock gripping portion is that of Figure 1c, the corrugations being made by the hydraulic distension of a plain tube confined in a suitably shaped constraining die.

With a strong stainless steel anchorage of this kind, an inordinately large force may be required to induce the necessary degree of expansion by the passage of a single spud. In such a case, a number of spuds 14, of progressively increasing diameters may be driven through, one after the other: three such spuds are shown, the last one being part of the way along its journey. In field conditions, the hole for such an anchor will usually be made by a pneumatically powered drilling machine and the latter may also be used to drive the spuds when equipped with a suitable drift.

In general, with the invention it is possible to design the device to caterforthe appreciable variations in hole diameter which are unavoidable when drilling such materials as rock and brickwork and which are much greater than can be readily achieved when drilling a metal. The radial pressure of the plug surfaces against the sides of the hole is controlled by the proportions and shape of the plug body and the yield stress of the metal from which it is made, no special skill or judgment being required ofthe operator, this being a matter of importance when making connections to easily burstable objects such as bricks or masonry blocks. For a given combination of plug features and hole material, the capacity of the fastener to resist axial force is, otherwise, proportional to the engaged length of the plug and can be arranged to exceed the tensile strength of the plug body.

Claims

1. A fastening device for making an axial force resistant connection to a circular hole in a body of hard material comprising an expandable plugging means made of a malleable metal and an expanding means consisting of one or more hard metal spuds which are driveable through a central aperture in the plugging means to cause itto increase in external size to engage and grip the sides of the hole.

2. Afastening device as in Claim 1 in which the plugging means is a metallic extrusion of tubular form provided with three or more outwardly protruding longitudinal ribs.

3. Afastening device as in Claims 1 and 2 in which the plugging means is additionally provided with three or more inwardly projecting longitudinal ribs.

4. Afastening device as in Claim 1 in which the plugging means is formed from a plain cylindrical metal tube which is forced to assume a circularly corrugated shape of not less than three lobes by forced passage through a shaping die, or other procrustean method.

5. Afastening device as in all preceding Claims in which the outermost plugging means surfaces which engage the hole are provided along the whole or part or parts of their lengths wth circularly of spirally enveloping fine serrations.

6. Afastening device as in Claim 1 in which the plugging means is a plain cylindrical metal tube provided over the whole or part or parts of its length with grooves which define circularly or spirally enveloping outwardly projecting sharp teeth.

7. Afastening device as in Claims 1 and 6 in which the plugging means is additionally provided with three or more inwardly projecting longitudinal ribs.

8. A fastening device as in all preceding Claims in which the plugging means is so proportioned that there is at all times during the expansion process some free space in the annular region between the sides of the hole and the expanding means to accept plastically displaced metal.

9. Afastening device as in all preceding Claims in which the plugging means is of sufficient length to pass through and connect two or more bodies of which the outermost two at least are provided with holes of suitable diameter to be gripped by the plugging means when an expanding means is driven right through it from one of its ends or when two expanding means are driven one from each end towards the centre of its length.

10. Afastening device as in all preceding Claims in which the plugging means is provided at one end with an integrally connected tubular member at one end and through the interior of which an expanding means may be passed to the expandable portion of the plugging means without impediment.

11. Afastening device as in Claim 10 in which the said integrally connected tubular member is provided with an internal or external screw thread or any other known means of attachment for other articles.

12. Afastening device as in Claims 1 to 9 inclusive in which the plugging means is additionally provided at one end with an enlarged head outwardliy flanged from the central aperture to retain other pierced articles.

13. Expanding meansforfastening devices as in Claim 1 and all hitherto subsequent Claims in which the spud or spuds are short stumpy hard metal bodies having insufficient length for induced friction seriously to impede their forced passage through the plugging means and having a cross-sectional shape which is either circular or of polygonal form having a number of sides which corresponds to the number of internally projecting ribs within the plugging means and on which the advancing ends are curvaceously convexly shaped from their outermost peripheries towards their central axes over at least the region which induces expansion of the plugging means.

14. Expanding means as in Claim 13 in which the spud or spuds have driven ends which areeitherflat or inwardly or outwardly curvaceously or conically shaped so as to engage centrally with the correspondingly inverse shaped end of a force applying tool.

15. Expanding means as in Claim 13 in which the spud or spuds are hard spherical metal balls.

16. Expanding means as in Claims 13to 15 inclusive in which the spuds or balls are of successively increasing plugging means engagement sizes to induce increasing amounts of expansion when used in pluarlity.

17. Expanding means as in Claim 16 consisting of a plurality of spuds or balls of successively increasing sizes which are driven through the plugging means one by one.

18. Expanding meansfora lengthyfastening device as in Claim 9 comprising two spuds of differing plug engagement sizes and a loose rod in between the spuds to keep them a finite distance apart and transmit force from the second and larger spud to the first and smaller spud and which arrangement is inserted forcibly into the plugging means priors to use until the second spud has just entered the the plugging means which is confined in a die to prevent external expansion during the process.

19. Expanding meansfora lengthy fastening device as in Claim 9 consisting of a rod of insufficient size to engage the interior of a plugging means and which is provided with a curvaceously fronted enlarged short portion at one end and is also provided with a curvaceously blended short enlargement of greater size at some point on the rod and which is forcibly driven into the plugging means prior to use until the second enlargement has just entered the plugging means which is confined in a die to prevent expansion during the process.

20. Afastening device as in Claims 1 to 8 inclusive in which the first or only spud is forcibly inserted a short retention distance into the end of plugging means which is confined in a die to prevent external expansion during the process.

21. An expanding means in the form of a short spud with an enlarged pierced article retaining head for use with short fastening devices as in Claims 1 to 8 inclusive.

22. Aforce applying tool or drift having one end which is magnetised and shaped to engage centrally an expanding means in the form of a spud and having a shaped at the other end adapted to receive blows from a hammer or to be attached to a power driven hammering machine.