WO1993018312A1

WO1993018312A1 - Fixing means

Info

Publication number: WO1993018312A1
Application number: PCT/GB1993/000497
Authority: WO
Inventors: David Banks-Fear
Original assignee: Southern Springs Limited
Priority date: 1992-03-11
Filing date: 1993-03-10
Publication date: 1993-09-16
Also published as: GB9205467D0

Abstract

A fixing device (6) comprising a fixing screw (18) and a close wound wire spring, each turn of which consists of at least two wire coils (12, 14), the spring pitch being similar to the thread pitch of the fixing screw (18) and the outer diameter of the spring being slightly larger than the outside shank diameter of the fixing screw (18).

Description

FIXING MEANS

This invention relates to a means of securing conventional screw thread type fixings in drilled holes, particularly in hard, non-combustible substrates that will not be affected by, or will at least resist against failure for a substantial period, intense prolonged fire and high temperature conditions.

The invention is particularly useful for the assembly and fixing of fire resisting barriers, bulkheads and linings to contained spaces, such as tunnels or inhabited buildings, but has a wider application as a general means of securing screw thread type fixings in concrete, brick and masonry.

A number of decorative and fire resistant linings and claddings have been proposed or are known, all of which make substantial use of screw thread type fixings to support such claddings from a structural substrate. The substrate usually comprises concrete, reinforced or unreinforced, brick or stone masonry, all incombustible materials in themselves, but which, being hard, do not readily take a thread fixing without some intermediate device being required.

Fixing systems currently in use mostly- require a predrilled hole in the substrate, followed by insertion of a mechanical expander device or make use of a device which self taps its own thread down a predrilled hole or straight in the substrate material.

Mechanical expander devices comprising a spiral member or coil, which is inserted into a pre-drilled hole and thereafter a screw member is inserted into the coil causing the coil to expand to firmly engage the wall of the hole, are known. Examples of such expander devices are disclosed in US-A-906691, US-A-1199674, US-A-3967525, US-A-4309135, US-A-4536115, GB-A-2163510, GB-A-2184808 and EP-A-0702189.

The mechanical expander devices are resistant to intense heat and high temperature but tend to be expensive and are used for the larger diameter high pull out strength fixings. They are rarely formed in stainless steel because the expense and lower load bearing capability of this particular material limits their commercial used.

Chemical resins, which have been used in place of mechanical expander devices, have a limited resistance to intense heat and high temperature, are expensive and can require specialised skills to fix.

Plastics and nylon plugs are in widespread use^* both in industry and for domestic purposes. They have low strength capability but can be used in greater frequency to obtain most normal strength requirements. Because they take standard screw type fixings and are themselves very cheap, their use affords substantial savings in cost. . However they have virtually no resistance to intense heat or high temperature and the plastics or nylon will melt through conduction of heat along the fixing to it at relatively low temperatures, causing the screw thread fixing to fall out.

There is an increasing demand for the fixings to be made of stainless steel because of its claimed long term resistance to corrosion. However it is less strong than many steels and comparatively more expensive, tending only to appear in the smaller proprietary fixings, in conjunction with nylon or plastic plugs for fixing in hard, predrilled substrates.

According to one aspect of the present invention there is provided fixing means for use with a fixing screw comprising a close wound wire spring, each turn of which consists of at least two wire coils, the spring pitch being similar to the thread pitch of the fixing screw and the outer diameter of the spring being slightly larger than the outside shank diameter of the fixing screw.

Another aspect of the present invention provides a combination of a fixing screw and an appropriate close wound spring wire as defined above.

According to a further aspect of the present invention there is provided a method of securing a fixing screw within a hole the effective internal diameter of which slightly exceeds the diameter of the outside shank of the fixing screw, wherein a spring wire close wound, each turn of which consists of at least two wire coils, the spring pitch being similar to that of the fixing screw, is inserted in said hole, and wherein the leading end of the screw is engaged within said spring wire and screwed home, thereby expanding the overall outer diameter of said spring wire by engagement of the inner shank of the screw.with the spring wire, so that the spring wire is pinched tight between the inside of the hole and the outside of the inner shank of the screw.

In use, the spring wire is expanded in its overall outside diameter and forced out by the inside shank- of the screw, the intensity of the pressure exerted by the screw shank forcing the spring wire outwards in turn forcing the spring wire against the walls of the drilled hole, will cause the substrate material in which the hole is drilled to crush locally and where it is in contact. This will create indentations, in between which is uncrushed substrate, thereby creating mechanical interlock and affording a resistance to pull out of the screw and spring combination. There are at least two wire coils trapped between each screw thread pitch, the shape of which is such to force one coil further out than the other, -by "wedge pitching". The effect of this is to improve the mechanical advantage of the system. The amount of outward movement of the outer coil is increased for the same screw driving effort compared with a spring having a single coil, hence improving the efficiency of localised crushing under pressure points, increasing indentation and mechanical interlock effect.

In some isolated situations, the spring wire may abut very strong material, such as a piece of aggregate, which will not crush. In this situation the metal of the spring wire will deform plastically to assume the shape created by the void between the screw and the material. This will generate very high normal force and in turn, very high local frictional resistance against pull out of the screw and spring combination, not detracting significantly from the mechanical interlock generated resistance.

In all cases, as the screw is rotated, pulling itself into the coils of the spring, expanding the spring into its wedging action, the spring will readily deflect from its undisturbed condition to assume the thread pitch and internal shank diameter of the.screw.

It will be appreciated that different screw diameters will need springs of different internal diameter to match in order to minimise screwing driving resistance.

A further refinement is to turn the ends of the spring wires outwards and to cut them in such a way that they are capable of "digging into" the substrate if the spring tends to rotate on insertion of the screw. In this way, the spring is locked against rotation as soon as the screw is inserted.

When fixed, because the spring material can be selected to be of a non-combustible non-melting material within the design temperature limits, the assumption by the fixing screw of a high temperature and conduction to the fixing spring plug will have no effect on the security of the fixing. Indeed expansion effects under heat are likely to improve the securement.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example some embodiments thereof, and in which:-

Figure 1 shows a fixing means, in accordance with the invention, positioned within a hole drilled in a substrate;

Figure 2 is a similar view to Figure l with a fixing screw inserted in the fixing means;

Figure 3 represents a cross-section through a fixing device, in accordance with the invention, with the screw positioned within the fixing means;

Figures 4 and 5 represent opposite end views of a fixing device, in accordance with the invention. In the Figures, like reference numerals refer to like parts.

Figure 1 shows a substrate 2 having a hole 4 drilled therein. The substrate 2 is generally a hard material such as concrete, brick, stone, etc. A fixing means, generally shown at 6, is positioned within the hole 4. The fixing means comprises a close-wound wire spring having an outer diameter which is substantially the same as that of the inner diameter of the hole so that the fixing means 6 is a close fit within the hole 4. The wire spring is formed from two separate wires 8, 10 which are wound such that each turn of the wire spring consists of two wire coils 12, 14. The inner end 16 of the wire spring 6 projects beyond the diameter of the remainder of the wire spring to firmly engage the wall of the hole 4 preventing rotation of the wire spring when the screw is inserted.

In use, a screw or bolt is passed through an aperture in a bracket or other article which is to be fixed to the substrate and inserted into the aperture within the wire spring 6 and driven home to its desired position by rotation with a screw driver, wrench, etc. Figures 2 and 3 show the shank 18 of the screw. The screw is selected such that the outside diameter of the wire spring is slightly larger than the outside shank diameter of the screw. The pitch of the screw is selected to be similar to that of the wire spring, although the distance between adjacent fights should not be sufficient to accommodate wire coils 12, 14 side by side touching the shank of the screw. The diameter of the wire is preferably slightly greater than the depth of the thread or the flights 20 of the thread.

As the screw is driven into the wire spring, the taper of the screw shaft expands the coils of the spring. Two coils 12, 14 are trapped between adjacent flights 20 of the screw and the walls of the flights force one coil 12 further outwards than the coil 14 by "wedge pitching". The outermost portions of the coil are forced against and into the wall of the hole creating localised indentations 22 and causing crushing of the substrate 2 in regions where the hole is bounded .by particularly hard material, such as aggregate, the wire will deform. The wedge pitching arrangement provides a considerable mechanical advantage over a spring formed from a single wire.

The leading end of the wire spring to be inserted into the hole preferably comprises a tangential tail 24 which extends beyond the diameter of the wire spring. The tail is preferably provided with a sharp end which may be formed from a single oblique cut or two cuts forming a tapered portion. In use, the tangential tail is inserted first into the drilled hole and the wire spring hammered into position. The wire spring is prevented from turning when the screw is rotated by the tangential tail digging into the wall of the substrate, as shown at 16 in Figure 1.

The trailing end of the wire spring is equipped with a short tangential leg which facilitates the start of the thread when the screw is inserted.

It will be appreciated that many modifications of the fixing means of the invention are possible. For example, the screws and springs may be made of various materials, stainless steel screws and springs being particularly preferred. The wire spring may also be formed of three or more separate wires and the thread pitch selected to accommodate each of the wires and to provide a wedge pitching action employing three or more wires between adjacent flights of thread.

Claims

1. A fixing means for use with a fixing screw comprising a close wound wire spring, each turn of which consists of at least two wire coils, the spring pitch being similar to the thread pitch of the fixing screw and the outer diameter of the spring being slightly larger than the outside shank diameter of the fixing screw.

2. A fixing means as claimed in Claim 1, wherein the ends of the spring wires are turned outwards away from the spring axis.

3. A fixing device comprising a fixing screw and a close wound wire spring, each turn of which consists of at least two wire coils, the spring pitch being similar to the thread pitch of the fixing screw and the outer diameter of the spring being slightly larger than the outside shank diameter of the fixing screw.

4. A fixing device as claimed in Claim 3, wherein the inner diameter of the spring is slightly less than the inside shank diameter of the fixing screw.

5. A fixing device as claimed in Claim 3 or Claim 4, wherein each spring turn comprises two wire coils and wherein the screw threads are so shaped that, upon insertion of the screw in the spring and engagement of the spring turns with the screw threads, one coil of each turn is forced out further from the spring axis than the other.

6. A method of securing a fixing screw within a hole, the effective internal diameter of which slightly exceeds the diameter of the outside shank of the fixing screw comprising inserting into the hole a fixing means comprising a close wound wire spring, each turn of which consists of at least two wire coils, the spring pitch being similar to that of the fixing screw, engaging the leading end of the screw within the wire spring and screwing the screw home thereby expanding the overall outer diameter of the wire spring by engagement of the inner shank of the screw with the wire spring.

7. A method as claimed in Claim 6, wherein the fixing means is as outlined in Claim 1 or Claim 2.

AMENDED CLAIMS

[received by the International Bureau on 3 August 1993 (03.08.93); original claims 1,5,6 and 7 cancelled; claims 2,3 and 4 amended and renumbered as claims 2,1 and 3 (1 page)]

1. A fixing device comprising a fixing screw and a close wound wire spring, each turn of which consists of at least two wire coils, the spring pitch being similar to the thread pitch of the fixing screw and the outer diameter of the spring being slightly larger than the outside shank diameter of the fixing screw, wherein the screw threads are so shaped that, upon insertion of the screw in the spring and engagement of the spring turns with the screw threads, one coil of each turn is forced out further from the spring axis than the other.

2. A fixing device as claimed in Claim 1, wherein the ends of the spring wires are turned outwards away from the spring axis.

3. A fixing device as claimed in either Claim 1 or Claim 2, wherein the inner diameter of the spring is slightly less than the inside shank diameter of the fixing screw.