GB2191838A - Cavity fixing - Google Patents

Abstract

A cavity fixing has a portion with a screwhole (2) therein and arms (3, 4) extending therefrom. Each arm (3, 4) comprises a flange (5) and arm portions (6, 8, 10) of channel section with weaker portions between the arm portions which weaker portions form bends (7, 9, 11) when the fixing is installed in a cavity behind a partition (18). The bends (9, 11) are closely constrained. Projections (14, 15, 16) prevent reversal of an initial outward set of the arms (3, 4). <IMAGE>

Description

SPECIFICATION Cavity fixing The invention relates to a cavity fixing, that is to say a fixing providing a mounting for a screw within a cavity.

With increased use of plasterboard for forming walls, cavity fixings have become increasingly important since ordinary fibre or plastics expansion wall plugs are generally ineffective in plasterboard for anything other than very light loads.

Our British patent specification 602 218 of 1945 describes and illustrates several embodiments of a fixing device for use as a cavity fixing and such devices have been widely used commercially. Generally such devices comprise a strip having a screwhole at a mid-portion in its length, arms extending in opposite directions from the screwhole and flanges at the ends of the arms, the arrangement being such that when the strip is bent to a U-shape with the screwhole at the curved portion thereof, it can be inserted into a bore in a partition until the flanges at the outer end abut the outer face of the partition. If a screw is then inserted in the bore, engaged in the screwhole and rotated, the portion in which the screwhole is formed is drawn outwardly but the flanges are prevented from moving outwardly by the screwhead so that the arms bend about positions intermediate their lengths.This causes the arms to have, starting from the flanges, first portions which extend through the partition parallel to the screw to first bends, second portions extending from the first bends radially outwardly along the inner face of the panel to second bends and third portions extending from the second bends to the portion in which the screwhole is provided. The second portions extending along the inner face of the partition prevent the fixing device from being pulled outwardly through the bore in the partition. The third portions are longer than the second portions so that the second and third portions form a triangle with the screwhole at its apex and its base lying against the inner face of the partition.

Such fixing devices have, however, only been useful for relatively light loads since if undue torque is applied to the screw, the second bends between the second and third portions can move along the arms to allow the second portions to increase in length and the third portions to decrease in length so that the third portions can be pulled outwardly to lie aganst the second portions and once the third portions have abutted the second portions the first bends can be opened out to cause them to become greater than right angles so that the entire fixing device tends to pull outwardly through the bore since it applies undue pressure to the rim of the bore at the inner face of the partition.

Another disadvantage of fixing devices of specification 608 218 is that a helical set can be imparted thereto whereby the fixing can merely become helically wound around the screw and lose its effectiveness. Fixings have been proposed with four arms rather than two to prevent this but this involves rolling the fixing about a longitudinal axis and welding of a separate nut into an inner end and this greatly increases the manufacturing cost.

According to the invention a cavity fixing comprises a strip of metal formed to present a screwhole, two arms extending in opposite directions from the screwhole and flanges formed at the outer ends of the arms wherein the arms are each formed generally to a channel section, each arm has a first weaker region defining a first bend position, a second weaker region defining a closely constrained second bend position and a third weaker region defining a closely constrained third bend position.

Preferably first portions of the arms, between the flanges and the first weaker region, and second portions of the arms, between the first weaker region and the second weaker region, have projections thereon to abut corresponding projections on the matching ones of the respective first and second portions to prevent the arms being given an inward set.

Thus the arms are manufactured with an outward set such that upon the portion with the screwhole therein being pulled, in use, towards the flanges by a screw, the arms will bow outwardly and not inwardly. The projections on the first and second portions ensure that the outward set is not reversed as the fixing device is pushed into a bore in a partition.

Advantageously, the channel section of a third portion of the arms, between the second weaker region and the third weaker region, is so disposed that upon movement of the portion with the screwhole therein towards the flanges, shoulder portions of the channel shaped third portions of the arms, adjacent the second weaker region, engage between the projections of the second portions to prevent a helical set being imparted to the fixing device.

The screwhole may be tapped with a screwthread or intended to receive a self tapping screw. If tapped the tapping is preferably effected in the die in which the fixing device is pressed by a highspeed tap.

Preferably the flanges are so shaped that together they form a complete but divided annulus and outer edge portions thereof are pressed out to form anti-rotation spikes to engage in the outer face of the partition.

The third weaker regions comprising closely constrained third bend positions, curve upon the portion with the screwhole therein being pulled towards the flanges by a screw, thereby to reinforce the portion in which the screwhole is provided, which portion is preferably formed as a collar Some latitude regarding the thickness of partitions which a particular cavity fitting of the invention is suitable for use in can be provided by not closely constraining the first bend position, but the partition must be thick enough to prevent the first bend regions being so positioned that the lengths of the second portions approach the lengths of the third portions.

Additional projections may be provided on the second portions to prevent the space between the projections on the first portions and the projections on the second portions being of a size such that flanges of other fixings could engage therein, for example during transit in a box, since this could make it difficult to separate the fittings one from the others.

The fitting is preferably die cut and pressed from sheet steel of 0.8mm (0.032 inches) thickness.

The invention is diagrammatically illustrated by way of example in the accompanying drawings in which: Figure 1 is a view showing an initial die cut strip of metal from which a cavity fixing according to the invention is formed; Figure 2 is a front elevation of a formed fixing; Figure 3 is a side elevation of the fixing of Fig. 1; Figure 4 is a front end view of the fixing of Fig. 3; Figure 5 is a sectional view taken on line V-V of Fig. 3; and Figure 6 is a view corresponding to Fig. 3 but showing the fixing installed in position in a cavity.

Referring to the drawings and firstly to Fig.

1, a blank 1 from which a cavity fixing is formed is die cut and has a screwhole 2 at its midportion and arms 3 and 4 extending in opposite directions therefrom, the arms 3, 4 being identical and each comprising, considered from the free end thereof, a portion 5 to form an annular flange, a first portion 6 extending to a first bend region 7, a second portion 8 extending from the first bend region 7 to a closely constrained second bend region 9 and a third portion 10 extending from the second bend region 9 to a third closely constrained bend region 11 adjacent the screwhole 2.

From the configuration of Fig. 1 the blank 1 is deformed into a cavity fixing 12 having the configuration of Figs. 2 to 5 and in use the cavity fixing 12 is deformed to have the configuration of Fig. 6.

As shown in Figs. 2 to 5, the flanges 5 after formation have cutaways bent to form spikes 13.

The first portions 6 inciude projections 14 which are bent to semi-circular form so that the projections 14 of the two arms 3, 4, form almost a complete annulus. Projections 15 are provided in the first bend region 7 but the base of the projections 15 is necked at 15a so that the projections 15 have little if any effect on the bendability of the first bend region 7. The second portions 8 have projections 16 similar to the projections 14 on the first portions 6. The third portion 10 is curved to a channel form and the semi-circular form of the projections 14 and 16 on the first and second portions 6 and 8 respectively and the channel shape of the third portion 10 effectively preclude bending of the first portion 6, second portion 8 and third portion 10.Bending is thus limited to the first bending region 7 which can be bent at almost any position between the inner end of the projections 14 and the outer end of the projections 16, the closely constrained bending region 9 where bending is only possible at the narrowest portion and the closely constrained bending region 11 where bending is only possible at the narrowest portion.

It can be seen from Fig. 3 that the body of the fixing 12, that is to say excluding the flange 5, is widest at the location of the second bend region 9. It can be narrowed from this width by pressing the arms 3, 4 together but such pressing together is limited by abutment of the projections 16 and 14 and the resilience of the material will cause the arms 3, 4 to spring apart again when released. The arms 3, 4 thus have a permanent outward set which cannot be reversed by normal handling.

In the embodiment shown the screwhole 2 has a tapped thread 2a.

Upon engagement of the fitting 12 in a bore 17 in a partition 18, for example piece of plasterboard, engagement of a screw with the thread 2a of the screwhole 2 and rotation of the screw, the fitting 12 changes from the configuration of Figs. 2 to 5 to the configuration of Fig. 6. It can be seen that the arms 3, 4 have bent in the first bend region 7 at a position, due to the particular thickness of the plasterboard 18, between the projections 14 and 15. The second portion 8 has however remained rigidly straight and lies against the inner face of the partition 18, the arms 3, 4 have each bent at the second bend region 9, the portions 10 have remained rigidly straight and the arms 3, 4 have each bent at the third bend regions 11. Ears 1 0a at the outer ends of the third portions 10 have engaged within the projections 16 of the second portions 8 thereby preventing a helical set being imparted to the fixing and the fixing is rigidly and immovably fixed in the partition 18. The curve imparted to the third bend regions 11 reinforces the collar defining the screwhole 2. Although some tolerance for the precise location of the bend in the first bend region 7 is permitted, the locations of the bends in the second bend region 9 and third bend region 11 are closely constrained and it is thus impossible for the bend region 9 to migrate along the third portion 10 which, if it was allowed to happen, could allow the portion with the screwhole therein to move closely against the inside face of the partition.If this did happen then the arms 8 could move upwardly as viewed in Fig. 6 to lie with the arms 10 alongside the screw so that the fixing could be pulled out through the aperture 17 in the partition 18. Maintaining the precise location of the second bend region 9 can ensure that the third portions 10 are always longer than the second portions 8 and thus that the portion with the screwhole 2 therein cannot move closely adjacent the inner face of the panel. The triangular configuration of Fig. 6 which is highly desirable is thus maintained.

The screwhole 2 may be of a self-tapping kind or of a kind which can receive an ordinary woodscrew, as shown it has the screwthread 2a formed by highspeed screw tapping while the fixing is still in the die in which it is formed so that it can receive a machine screw.

The projections 15 project into what would otherwise be a large opening between the projections 14 and 16, as best seen in Fig. 3, which large opening could, if the projections 15 were not provided, receive the flange 5 of another fitting, for example in box of fittings being transported, whereby two fittings could become interengaged causing separation problems at the point of use.

Claims (9)

1. A cavity fixing comprising a strip of metal with a portion formed with a screwhole therein, two arms extending in opposite directions from the screwhole and flanges formed at the outer ends of the arms wherein the arms are each formed generally to a channel section and each arm, considered from the end at which the flange is provided has in succession, a first arm portion, a first weaker region defining a first bend position, a second arm portion, a second weaker region defining a closely constrained second bend position, a third arm portion and a third weaker region defining a closely constrained third bend position.

2. A cavity fixing according to claim 1, in which the first arm portions, between the flanges and the first weaker region, and the second arm portions, between the first weaker region and the second weaker region, have projections thereon to abut corresponding projections on the matching ones of the respective first and second arm portions to prevent the arms being given an inward set.

3. A cavity fixing according to claim 2, in which the arms are manufactured with an outward set such that upon the portion with the screwhole therein being pulled, in use, towards the flanges by a screw, the arms will bow outwardly and not inwardly and the projections on the first and second arm portions ensure that the outward set is not reversed as the fixing device is pushed into a bore in a partition.

4. A cavity fixing according to claim 2 or claim 3, in which the channel section of the third arm portion, between the second weaker region and the third weaker region, is so disposed that upon movement of the portion with the screwhole therein towards the flanges, shoulder portions of the channel shaped third arm portions adjacent the second weaker region, engage between the projections of the second arm portions to prevent a helical set being imparted to the fixing device.

5. A cavity fixing according to any one of claims 1 to 4, in which the flanges are so shaped that together they form a complete but divided annulus and outer edge portions thereof are pressed out to form anti-rotation spikes to engage in the outer face of the partition.

6. A cavity fixing according to any one of claims 1 to 5, in which the third weaker regions comprising the closely constrained third bend positions, curve upon the portion with the screwhole therein being pulled towards the flanges by a screw, thereby to reinforce the portion with the screwhole therein, which portion is preferably formed as a collar.

7. A cavity fixing according to claim 2 or any one of claims 3 to 5 when appendant to claim 2, including additional projections on the second arm portions to prevent the space between the projections on the first arm portions and the projections on the second arm portions being of a size such that flanges of other similar cavity fixings could engage therein, for example during transit in a box, since this could make it difficult to separate the fittings one from the others.

8. A cavity fixing according to any one of claims 1 to 7, formed by die cutting and pressing from sheet steel of 0.8mm (0.032 inches) thickness.

9. A cavity fixing substantially as hereinbefore described and illustrated with reference to the accompanying drawings.