GB2241549A - Fastener anchor - Google Patents

Abstract

A cavity fastener anchor with self-cutting effect has a bore (B) to receive a fastener (F), and is as a tapered core (C), with a tapered thread (T) having a starter spike (P) and an anchor portion nearer to the head (H), the head (H) being bigger than the thread (T). The anchor is formed of plastics by injection moulding and has a drive recess R. <IMAGE>

Description

FASTENER ANCHOR This invention relates to fastener anchors for fixings in sheet material and walls, partitions and similar structures including sheet material. The sheet material is generally plasterboard. Such fastener anchors are commonly called cavity anchors as they are widely used on plaster board structures which produce a cavity.

Fastener anchors for such usage of various types are known.

Among these are anchors which are put through an existing hole in the sheet material into a cavity where some alteration or deformation of anchor shape takes place to trap the anchor to the material so that the anchor can retain a screw or the like fastener to the sheet material and in turn hold an object in place on the material. Other anchors are known which are of metal and formed like a coarse threaded machine screw with a parallel core and are inserted into an existing hole formed in the sheet material to engage the sides of the hole with the thread and hold the anchor in place. Such anchors can have a cutting part on the distal end to cut-away material to form the hole for the rest of the anchor to enter. The anchor can have a bore for a fastener and a head to receive a screwdriver bit to drive the anchor.

With the increasing use of plasterboard and similar dry construction of techniques for internal walls and partitions in buildings, both in new construction and alteration, there is a need for quick and easy provision of fixing points in the sheet material, which points can be anywhere in the sheet, without the need to be located on to supports behind the sheet, and which can permanently and reliably support substantial loads.

While anchors of the type described above can be effective they have shortcomings. All require a hole to be made first. If the hole is made with a separate tool, such as a drill, an operative has to carry out two actions, making the hole and inserting the anchor to produce the fixing. Where the anchor has a cutting part on the distal end this increases the cost of the anchor. This type of anchor is of metal and is therefore expensive and the metal has to be chosen to avoid corrosion, while being easily breakable so that a fixing screw can dislodge the cutting part once the anchor is installed. Anchors which form a thread in an existing hole distort the sheet material.

It is an object of the invention to provide a cavity fastener anchor which does not have such shortcomings.

According to the invention there is provided a cavity fastener anchor with self-cutting effect having between a tip and a driving head a body having a bore to receive a fastener, the body being formed as a tapered thread core with a tapered thread on the core, the thread having a starter portion at the tip and an anchor portion nearer to the head, the head being bigger than the thread.

Conveniently the tip is formed as a spike extending from the starter thread portion. There may be a gap between the thread and the head.

According to the Invention there is also provided a self-cutting twist-drivable hollow-wall or cavity fastener anchor including a tapered core and a tapered thread on the core and in the core a bore to receive a fastener.

According to the invention there is provided a method of producing a fastener anchorage in a sheet material including, providing an anchor insert of a pointed, headed, tapered core with a tapered thread thereon and a fastener bore therein, forcing and turning said anchor point against sheet material at an anchorage position to drive said anchor into the sheet material to radially consolidate material as a threaded hole, continuing to drive said anchor to a stop into said material, consolidating displaced material against the anchor taper, whereby an anchorage with a bore to receive a fastener is produced in a single operation.

The anchor is conveniently of plastics such as ABS or a hard NYLON (RTM), and formed by Injection moulding. For plasterboard of some 10 millimetres to 20 millimetres thickness an anchor about 35 millimetres long is suitable. Thus one size of anchor is suitable for both the common plaster board thicknesses. Such an anchor has a core tapering from a point to some 7 millimetres diameter carrying a thread tapering from nothing to an overall diameter of 12 millimetres and a head of 14 millimetres diameter. The head is conveniently shaped to receive a cross-point driving bit. However other bit-forms may be provided for either the simple blade or the more specific types now in use. A bore in the core is sized to receive a No.6, approximately 3.5 millimetre, screw of wood screw, chipboard, SPEED DRIVE (TM) or other suitable type.The thread need not reach the head, a gap of about one millimetre is convenient.

Embodiments of the invention will now be described with reference to the accompanying drawing of a fastener anchor (Fig. 1) and a representation (Figures 2a, 2b, 2c) of the installation of an anchor as shown in Figure 1.

The shape of the anchor will be considered first. It is seen from Figure 1 that the anchor has a core tapering from a tip to a head. There is a tapering thread on the core. While at first sight the anchor is the same shape as a conventional wood screw (known in the U.K. as an Art. 1). This is not the case, in fact experiments with anchors of such shape showed that no satisfactory result could be produced. Similarly a cylindrical core causes substantial disturbance of the board material axially of the anchor.

By producing the anchor with the deep thread and tapering thread and core form shown an effective anchor is produced.

Figures 2a, 2b, 2c show three stages in the installation of an anchor A.in a plaster board PB, followed by the insertion of the fastener F, here the preferred twin-start fastener, using a conventional screw driver BL. The anchor when driven into a sheet of plaster board does not cause significant displacement of material outward of the sheet in the axial direction (Figures 2b, 2c). It is believed that the material Is consolidated (as shown at M) by movement radially of the anchor which movement might be described as a "flow". To ensure a quick and accurate drive of the anchor a tip P is provided, preferably as a spike or other sharp extension from the thread. If required a mark can be made in the surface of the sheet material to aid the starting of the anchor drive.Such a mark is often made when setting out the positions for anchors so no extra action is needed. With a suitable "spike" the anchor can be driven into an unmarked surface. The thread can start with a rapidly-rising cutter edge.

It is believed that by making the thread depth about one-third of the local core diameter the anchor is of effective form.

The anchor is made from plastics material chosen to meet various requirements. Firstly the plastics material must be strong enough to support the action of a screwdriver CP (preferably a cross-point type) engaged with the head to drive the anchor. Secondly the plastic material must be strong enough to "cut" into the sheet material. Thirdly the plastics material should be soft enough for a fastener inserted to the bore to make a suitably retaining thread and other grip.

Examples of the anchor made from ABS material on a hand operated prototyping injection moulder at about 18000 psi have proved effective. The thread form here is as shown in the drawings. In the specific example the anchor has an overall length of about 35 millimetres, the head H is about 13.5 millimetres in diameter and about one millimetre thick with a chamfered lower edge. The core C tapers from a point at tip P to a diameter near the head of about 7 millimetres while the thread T tapers from the negligible initial amount I just back from the tip to have an overall diameter of about 12 millimetres. There is a gap G between the thread and the head. The thread form is significantly different from that of conventional (Art. 1) woodscrews and screws designed for chipboard and like materials.

In such screws the core is about 80X of the overall diameter compared with the 601. core diameter in the present device, while the thread here is of coarser pitch. The anchor has a bore B to receive a fastener and a recess R to receive a cross-point, as shown in Figure 2b.

While careful choice of material characteristics is clearly needed it is not expected that only one material alone will be suitable. In particular different sheet material types or expected duty, such as ambient temperature, may lead to choice of different materials. For example polypropylene appears to be too soft to resist damage by a screwdriver. Hard NYLON (RTM) has proved suitable. One use for the cavity anchors is providing fixings for radiators. Here a higher ambient temperature and possibly heat conduction to the fastener may require a material with a higher temperature rating than that for an anchor intended for an unheated object.The choice of different grades and mixtures of plastics materials, with fillers, fibres and the like and the use of different moulding techniques, to achieve particular performances well-known to those skilled in the art and such choice is not dismissed here nor beyond general guidance. One way of expressing a suitable material characteristic is "ductility", usually a property of metals but appropriate in the present situation.

The form, using a thread of substantial depth and a taper, is considered to be a significant feature in the effectiveness of the anchor compared to the other forms tried and found to be ineffective. For example using an anchor with the distal part of the form of a very short drill bit, with angled sloping opposed cutting faces, moulded in the plastics material integrally with the thread and core, was not very effective. Again a distal part where the thread starts at the very extremity, while starting effectively, can "wander" or tilt and cause the anchor to be misplaced in the sheet material.

The head of the anchor can be formed to have a part extending radially of the anchor core which is of the same thickness as a typical plaster finish coat (about one millimetre) now commonly used to "skim" dry partitions and wall surfaces. Thus when the anchor is driven to a stop in the sheet material (Figure 2c) the head does not enter the sheet material but does become flush with the surface of the "skim" finish coat (not shown), producing a tidy effect and appearance. In particular the absence of disturbance of the structure of the sheet material by the anchor enhances the usefulness of the anchor.

The anchors described can be reused. The use of a controlled torque to drive the anchors is advantageous to avoid damage to either anchor or sheet material by overdriving while ensuring a tight fixing. Clearly anchors of various size can be made to suit various fasteners, even large ones such as coach screws.

Colour coding for size, material, etc. is appropriate. It is possible to drive a serrated nail or similar fastener if this is required, although care is needed.

The use of a wholly plastic anchor avoids risk of damage to cables and metal pipes or thin metal cable capping or that of electrical conduction. The anchor is however strong enough to penetrate the plaster "dabs" sometimes used to fix plaster board.

The techniques described above provide an effective, economic cavity anchor which is quickly and easily installed to provide a strong anchor for a fastener for many duties. Typical of these in structures using plaster board for walls are the fixing of radiators, handrails, cupboards and other items requiring a secure fixing which resists loading stresses.

Claims (15)

1. A cavity fastener anchor with self-cutting effect having between a tip and a driving head a body having a bore to receive a fastener, the body being formed as a tapered thread core with a tapered thread on the core, the thread having a starter portion at the tip and an anchor portion nearer to the head, the head being bigger than the thread.

2. A fastener anchor according to Claim 1 in which the tip is formed as a spike extending from the starter thread portion.

3. A fastener anchor according to Claim 1 in which there is a gap between the thread and the head.

4. A self-cutting twist-drivable hollow-wall or cavity fastener anchor including a tapered core and a tapered thread on the core and in the core a bore to receive a fastener.

5. A fastener anchor according to any one of the preceeding Claims which is of plastics material, such as ABS or a hard NYLON (RTM), and formed by Injection moulding.

6. A fastener anchor according to any one of the preceeding Claims for plasterboard of some 10 millimetres to 20 mIllimetres thickness which anchor is about 35 millimetres long.

7. A fastener anchor according to Claim 6 which has a core tapering from a point to some 7 millimetres diameter carrying a thread tapering from nothing to an overall diameter of 12 millimetres and a head of 14 millimetres diameter.

8. A fastener anchor according to Claim 6 which has a head with a chamfered edge to match a skim plaster coat.

9. A fastener anchor according to any one of the preceeding Claims in which the thread has a rapidly-rising cutter edge starter portion.

10. A fastener anchor according to any one of the preceeding Claims in which the head is shaped to receive a cross-point, simple blade or other specific type of driving bit.

11. A fastener anchor according to any one of the preceeding Claims in which a bore in the core is sized to receive a No.6, approximately 3.5 millimetre, screw of wood screw, chipboard, SPEED DRIVE (TM) or other suitable type.

12. A fastener anchor according to Claim 3 in which the gap is about one millimetre.

13. A method of producing a fastener anchorage in a sheet material including, providing an anchor insert of a pointed, headed, tapered core with a tapered thread thereon and a fastener bore therein, forcing and turning said anchor point against sheet material at an anchorage position to drive said anchor into the sheet material to radially consolidate material as a threaded hole, continuing to drive said anchor to a stop into said material, consolidating displaced material against the anchor taper, whereby an anchorage with a bore to receive a fastener is produced in a single operation.

14. A cavity fastener anchor with self-cutting effect substantially as herein described with reference to the accompanying drawings.

15. A method of producing a fastener anchorage in a sheet material substantially as herein described with reference to the accompanying drawings.