GB2132730A - Improvements relating to expansion bolts - Google Patents

Abstract

An expansion bolt uses one or more coil springs (34, fig. 8) which, as they are axially compressed, are caused to expand radially at their ends to clamp against a bore. The ends of the springs engage over frustoconical abutments (; 33, 35) which are backed by a nut or bolt head and a member whose external formation is such that its engagement with the bore prevents it rotating, but allows it to move axially. A particular application is to a wall tie (Fig. 1) where springs (8) are fitted on threaded portions (3, 4) of opposite hands at opposite ends of a rod. Each spring is twisted in the same way as the associated screw thread. The rod (1) can be turned to cause one spring to clamp first, and then a nut (10) on the other screw threaded portion (4) can be turned to clamp the other spring. It can also be arranged that both springs are compressed and their ends radially expanded simultaneously. In a further alternative one of the springs is replaced by a setting material, and projections 20 (Fig. 6) are provided for keying into this material. <IMAGE>

Description

SPECIFICATION Improvements relating to expansion bolts This invention relates to expansion bolts.

It has been developed primarily for replacement wall ties, but it does have application to bolts for any purpose which have to be secured in masonry or concrete.

Although heavily galvanized, wall ties which span the two leaves of a cavity wall eventually corrode and have to be replaced or at least augmented by further ties. The usual procedure is to drill a hole from the outside through the brick or mortar of the outer leaf and into the inner one. An expansion bolt is then inserted, and an inner section is tightened up to grip the inner leaf, followed by a similar operation on an outer section for an outer leaf. The tightening of the inner section requires a special tool reaching across the cavity. The operation is lengthy, the device is expensive, and since an average semi-detached house will require about two hundred and fifty wall ties, this multiples alarmingly.

Furthermore, the actual gripping elements are not entirely satisfactory. At each end of one such device there is a plastic sleeve-like member, which is radially expanded in the middle when axially compressed. There is therefore only single ring contact in the inner and outer leaf. Also, the effect of prolonged contact with mortar is very likely to have a detrimental effect on the plastics material.

It is the aim of this invention to improve such a replacement wall tie, making it easier and less costly to install and to obtain a firmer grip.

According to the present invention there is provided an expansion bolt having two opposed abutment members on a shank mutually movable axially with respect to each other, and a coil spring surrounding the shank between said members and with its ends cooperating with tapering surfaces on said members that cause those ends to expand radially when the members are moved towards each other by rotation of the bolt or a nut thereon.

Preferably, the tapering surface will be generally frusto-conical and said members will have co-axial bores allowing them to move freely on the shank, their limits of separation being determined by backing members effectively fixed to or having screw threaded engagement with the shank.

In one form, the bolt will be conventional, having a head and a screw threaded end section carrying a nut. One abutment member may co-operate with the bolt head side of the nut, while the other member will be held at an intermediate point of the shank. The nut will have an external formation to resist rotation when inserted in a matching bore, and rotation of the exposed bolt head will draw the nut towards it and radially expand the spring. Alternatively, one abutment member may co-operate with the underside of the head, while the other member will again be at an intermediate point of the shank. The bolt head will have an external formation to resist rotation when inserted in a matching bore, and rotation of the exposed nut will draw the bolt head towards it and radially expand the spring.

When this principle is applied to a wall tie, the bolt preferably comprises a rod with screw threaded portions of opposite hands at opposite ends, each portion having a coil spring between abutments, the rod being rotatable from one end to cause the abutments on the other end portion to move together, and a nut on said one end portion being rotatable to cause the abutments at said one end to move together.

Preferably, the abutments of said other end portion comprise an effectively axially fixed one at or near the extremity, and a movable one backed by a nut threaded on that portion and with an external formation which resists rotation when inserted in a matching bore but which allows axial movement. This nut conveniently has an outer, bore engaging surface which is eccentric with respect to its threaded aperture, since this ensures positive engagement.

The abutments of said one end portion preferably comprise an effectively axially fixed one at the inner end and a movable one backed by the first mentioned nut, this being of smaller external profile than the springs and abutments. This will allow a socket spanner to penetrate the bore for the tie and engage the nut.

It is best to arrange for the springs to be of the same hand as the associated threaded portions. As explained below, this helps ensure radial expansion.

The tie bolt will generally have a central section between the threaded end portions, and this may be provided with a barrier to resist moisture travelling along the rod.

With the tie outlined above, the tightening is carried out in two separate operations, first turning the rod, and then the nut. However, by having the abutment nearest the free end of said one portion effectively axially fixed, and the other abutment on that portion backed by a nut with an external formation which resists rotation when the nut is inserted in a matching bore but which allows axial movement, when the first mentioned nut is turned, both springs will be simultaneously compressed between their abutments and their ends will be forced to expand radially to fix both ends to the tie in one operation.

The tie bolt may be modified by having no abutments and spring on said other end portion, and forming that portion with a nonsmooth surface for keying into a hard setting material such as resin.

Also, in place of one spring there can be two or more springs in tandem, and between each adjacent pair of springs there will then be an intermediate abutment member, freely movable on the shank with tapered ends that engage the respective adjacent ends of the springs. Thus, as compression is carried out, there are more spring ends to expand radially, and the gripping area is increased.

For a better understanding of the invention, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a replacement wall tie, Figure 2 shows face views of nuts, either of which may form part of the tie of Fig. 1, Figure 3 shows a screw key, partly in longitudinal section, for tightening the tie, Figure 4 is a diagram for explaining the sequence of operations in fitting such a tie, Figure 5 is a side view of part of a modified tie, Figure 6 is a side view of another modified tie, Figure 7 shows axial section and end views of an alternative to the nuts of Fig. 2, Figure 8 is a side view of an expansion bolt, and Figure 9 is a side view of another expansion bolt.

It will be understood that, except where specified, the various components of the ties or bolts will preferably be made of a noncorrosive metal, in particular stainless steel, although it may be acceptable in some circumstances to have a less expensive metal, such as mild steel, with an anti-corrosive coating.

In Fig. 1, the tie has a straight rod 1 of stainless steel with a plain middle section 2 and screw threaded end portions 3 and 4, these being of opposite hand. The portion 3 will be referred to as the inner end portion and will be assumed to have a left-hand thread. It is terminated by a fixed head 5, which may be a smooth-headed cap nut which uses the screw thread. Threaded up to the other end of the portion 3, where it merges into the section 3, there is an eccentric nut 6 (Fig. 2) which has projections whose envelope equals the diameter of the head 5, and this will move axially of the rod when the latter is rotated as described below.

On the facing sides of the cap 5 and nut 6 there are spigots 7 of generally frusto-conical form tapering towards each other. These could each be integral with the respective cap 5 or not 6, but preferably they are separate members which are sleeved over the rod, without any internal screw threading. A coil spring 8 surrounds the end portion 3, and its ends abut the frusto-conical surfaces of the spigots 7. Its external diameter in the relaxed state is equal to or very slightly less than that of the head 5 and nut 6, and its twist is of the same hand as that of the threaded portion 3.

The arrangemerit at the other end of the rod on portion 4 is similar, and corresponding parts have the same references. However, the coil spring is handed in the same way as the thread of the portion 4 and so is not identical with the other spring 8. Also, instead of the eccentric nut 6 there is a non-eccentric nut 9 which has a plain cylindrical outer surface matching that of the head 5, and at the outer end there is nut 10, smaller than elements 5, 6 and 9, which provides a grip for a socket spanner. A length of threaded portion 4 is left exposed beyond this nut.

On the plain central section 2 there is a drip washer 11 of rubber or plastics, preferably polyvinylchloride (PVC) which servies as a barrier to condensation moving along the rod.

Referring to Fig. 2, two examples of the nut 6 are shown in face view, that on the left having six projections 12, and that on the right having eight all circumferentially evenly spaced. The eccentricity is small. If the projections 1 2 are proud of a base cylinder of 10.1 6 mm diameter, say, and their circular envelope is 12.32 mm in diameter, then the eccentricity of the threaded hole (a 6 mm lefthand thread as the portion 3 is left-handed in this example) would be 0.51 mm from the common axis of the base cylinder and envelope. That is of the order of 4% in relation to the envelope.

The nut is formed by sintering or is machined from bar, and will have an easy fit on the threaded portion 3. There may be one or two less projections 12, or even a few more, but generally the range 6-8 should be satisfactory. Preferably, they have pointed profiles as shown, but rounded or square ones could serve as well.

Fig. 3 shows a screw key 1 3 which will be used in fitting the tie as described below. It has a cylindrical body whose outer diameter matches that of the head 5 and nut 9. Its working end is co-axially drilled and tapped to form a socket 14 which will thread onto the outer end portion 4. At the blind end of this socket there is seated a ball bearing 15, whose fit is such that, with a light coating of grease, it will remain in that position.

At the outer end, there is a transverse arm 1 6 push fitted through a cross bore in the body, and the end face is provided with a square or hex socket 1 7.

For installation, as shown in Fig. 4, a bore matching the diameter of the head 5 and nut 9 is drilled through the outer leaf of the wall into the inner one (stage 1). The drill is removed and the hole is blown clear of dust and particles (stage 2). The key 1 3 is screwed on to the outer end portion 4 of a tie, which is then inserted, cap 5 end first, into the hole.

The actual diameter of the bore will allow easy insertion of the head 5 and of the nut 6 through the outer leaf, and the latter's eccentricity will not be such as seriously to impede entry into the inner leaf as the nut 9 and other elements on the portion 4 enter the outer leaf. In practice, a bore in brick or mortar is seldom perfect, and a bit of turning and joggling of the tie will find a free passage. When the tie is pushed right home (stage 3) and perhaps the head of the key 1 3 tapped with a hammer to ensure this, the key is turned to rotate the rod 1 in the normal clock-wise direction. The nut 6 may already have positive engagement with its section of the bore, and its projections 1 2 will stop it rotating.Even if it does not, just part of a turn will bring the positively eccentric projections into firm contact with the bore and stop rotation thereafter. However, the mechanical advantage given by the screw thread as the rod 1 rotates will cause the nut 6 to move axially further into the bore, the projections 1 2 scoring the brick or mortar. The associated spring 8 will therefore be compressed, and the action of the frusto-conical spigots 7 will be to expand its ends radially. This will bring them into contact with the interior of the bore and as the rod 1 is rotated further, so this expansion grip becomes tighter.Because the spring is coiled in the same sense as the associated left-hand screw thread, which is being turned right-handed, should there be any tendency for the spigot 7 nearest the end to be frictionally entrained by the head 5 and in turn to twist the coil, this twist will be in the direction to unwind it and help the radial expansion. Since the nut 6 does not rotate the other spigot 7 has no tendency to turn. There will therefore be two axially spaced expansion zones, and a more stable and comprehensive grip than with the devices normally used hitherto. When tightened to a set torque measured by applying a tool to the socket 17, the key 1 3 is withdrawn, the ball bearing 1 5 ensuring that the mutual screw disengagement is easily started. A sharp tap with a hammer may assist this.

The key 1 3 is replaced (stage 4) by a socket spanner 18 which engages the nut 10.

Turning this spanner in the normal clock-wise direction moves the nut 10 axially into the bore and produces expansion of the ends of the associated spring 8 in the manner described. Again, the hand of the coil spring aids its expansion. The rod 1 is held fast by the completed inner leaf grip while this fourth stage is carried out. When the nut 10 is tightened to asset torque, the spanner 1 8 is removed and the mouth of the bore plugged.

Instead of a single spring at each end, there could be one or more intermediate frustoconical members 7a at each end, with a corresponding greater number of springs, as shown diagrammatically in Fig. 5. This increases the gripping zones to four.

A modification of this tie is shown in Fig.

6, where similar parts have the same references as before.

In some circumstances, it may be appropriate to anchor the inner end of the tie in a different way. The head 5, nut 6 and spring expansion device between these are discarded and a collar 1 9 replaces the nut 6. Lugs 20 are then struck up from the screw-threaded portion 3, or perhaps formed by weld metal deposits. The bore in the wall is formed as before, but prior to insertion of the tie, the bore in the inner leaf is injected with a plug of stiffly viscous resin. The tie is driven home into this, and it permeates around the~ portion 3 to set hard and hold the inner end of the tie. The lugs 20 ensure that it cannot be unscrewed. The outer end of the tie is then secured to the outer leaf as before.

It would of course be possible to have the inner end of the tie with other resin gripping formations, but it will probably be easier in practice to take the normal production rod and adapt it as shown.

A further possibility is to make the rod tubular and to inject the resin down it from the outer end, providing apertures along the inner end portion for it to escape into the bore in the inner leaf.

An alternative to the nut 6 is shown in Fig.

7. This is of composite construction, having a stainless steel core 21 to thread onto the portion 3, and a surrounding plastics moulding 22 positively keyed to it. The moulding has a frusto-conical skirt 23 split along evenly spaced generatrix lins to form, in this example eight leaves 24 with external knurling, although there could be a few more or less. The taper of the skirt will be into the bore, and while the smaller end which leads may match or be slightly less than the bore diameter, the larger end in its relaxed state will be somewhat greater, say about 2.5 mm if we keep to the other dimensions mentioned above. The leaves 24 therefore form springy barbs which deform inwardly to allow entry, but which will inhibit withdrawal.The compressed fit within the bore and the knurling will prevent rotation, and so as the rod is turned, this nut will be forced to move axially further into the bore.

Referring to Fig. 8, the expanding spring principle is applied to a bolt 25 which is to secure a base plate 26 to a concrete foundation 27. A blind hole 28 is drilled in this, to register with an aperture 29 in the plate 26.

The bolt has a head 30 and a washer 31 intermediate the head and the upper side of the plate 26. Below the plate 26 and within the hole 28 there is, in descending order, acylindrical spacer 32, a spigot member 33, a coil spring 34, another spigot member 35 and a nut 36 threaded on the shank and having an external cylindrical surface which is knurled to grip the cylindrical interior of the hole 28. The spigot members 33 and 35 have frusto-conical formations which enter the ends of the coil spring 34.

The bolt is entered through the aperture 29 and all the elements 32 to 36 are placed on the shank before the plate 26 is lowered into position. When it is there, the head 30 is rotated. The nut 36 is held against rotation by frictional grip of the hole 28, and so it is forced to move axially upwards. The spigot member 33 is held fixed by the spacer 32, and so the ends of the spring 34 are radially expanded to clamp against the inside of the hole 28.

Fig. 9 shows a corresponding arrangement with the bolt reversed. It is placed head first in the hole so that its thread end projects proud from it. The plate can then be lowered over it, and the washer fitted and then the nut tightened. Here, the nut 37 will be "ordi nary', while the bolt head 38 will be knurled to fit the hole and resist rotation.

The knurling of the nut 36 and bolt head 38 will preferably be serrations extending parallel to the axis of the respective bolt. This will make insertion into the bore and subsequent axial movement fairly easy while providing maximum resistance to rotation. They could be formed with profiles similar to those of Fig.

2.

In the example of Fig. 1, the expansion of the springs was described as being carried out in separate operations. That is perhaps the safer method, but it is slow compared with doing both simultaneously. For this, the nut 9 would be replaced by one similar to nut 6 (or the one of Fig. 6 reversed to point outwardly) and there would be a cap nut on the outer end of the rod 1 instead of the nut 6. Turning this cap nut would rotate the rod, and while the inner nut 6 would move further in as before, its equivalent on the outer portion 4 would be drawn outwards to expand the outer spring at the same time as the inner one. To ensure simultaneous and uniform expansion of both springs they should preferably be set by a ring gauge before starting the operation.

Claims (11)

1. An expansion bolt having two opposed abutment members on a shank mutually movable axially with respect to each other, and a coil spring surrounding the shank between said members and with its ends co-operating with tapering surfaces on said members that cause those ends to expand radially when the members are moved towards each other by rotation of the bolt or a nut thereon.

2. A bolt as claimed in claim 1, wherein said tapering surfaces are generally frustoconical and said members have co-axial bores that allow them to move freely on the shank, their limits of separation being determined by backing members effectively fixed to or having screw threaded engagement with the shank.

3. A bolt as claimed in claim 1 or 2, having a head and an end threaded section carrying a nut, wherein one said abutment member co-operates with the bolt head side of the nut and the other said abutment member is at an intermediate point of the shank, the nut having an external formation to resist rotation when inserted in a matching bore.

4. A bolt as claimed in claim 1 or 2, having a head and an end threaded section carrying a nut, wherein one said abutment member co-operates with the underside of the head and the other said member is at an intermediate point of the shank, the bolt head having an external formation to resist rotation when inserted in a matching bore.

5. A bolt as claimed in claim 1 or 2, wherein the bolt is a wall tie and comprises a rod with screw threaded portions of opposite hands at opposite ends, each portion having a coil spring between abutments, the rod being rotatable from one end to cause the abutments on the other end portion to move together, and a nut on said one end portion being rotatable to cause the abutments at said one end to move together.

6. A bolt as claimed in claim 5, wherein the abutments of said other end portion comprise an effectively axially fixed one at or near the extremity, and a movable one backed by a nut threaded on that portion and with an external formation which resists rotation when inserted in a matching bore, but which allows axial movement.

7. A bolt as claimed in claim 6, wherein the nut on this other end portion has an outer, bore-engaging surface which is eccentric with respect to its threaded aperture.

8. A bolt as claimed in claim 5, 6 or 7 wherein the abutments of said one end portion comprise an effectively axially fixed one at the inner end, and a movable one backed by the first mentioned nut, this being of smaller external profile than the springs and abutments.

9. A bolt as claimed in any one of claims 5 to 8, wherein the springs are of the same hand as the associated threaded sections.

10. A bolt as claimed in any one of claims 5 to 9, wherein a central section between the threaded end portions is provided with a barrier to resist moisture travelling along said rod.

11. A bolt as claimed in claim 5, wherein the abutment nearest the free end of said one portion is effectively axially fixed, and the other abutment on that portion is backed by a nut with an external formation which resists rotation when the nut-is inserted in a matching bore, but which allows axial movement, whereby when said first mentioned nut is turned, both springs are simultaneously compressed between their abutments and their ends are forced to expand radially.

1 2. A modification of the bolt as claimed in claim 5, wherein the other end portion has no abutments or spring, but is formed with a non-smooth surface for keying into a hardsetting material such as resin.

1 3. A bolt as claimed in any preceding claim, wherein, in place of one spring, there are two or more springs in tandem, and between each adjacent pair of springs there is an intermediate abutment member, freely movable on the shank, with tapered ends that engage the respective adjacent ends of the springs.

1 4. An expansion bolt substantially as hereinbefore described with reference to Figs.

1 to 4, alone or as modified by any of Figs. 5, 6 and 7, or with reference to Fig. 8 or 9.