TECHNICAL FIELD

A method for fastening an attachment or suspension device to a porous support surface, preferably a plasterboard sup¬ port surface, and an attachment device for carrying out the method.

BACKGROUND PRIOR ART

Because present day building materials are required to be resistant to both fire and mould., woodfibre board and chip¬ board is being replaced to an ever increasing extent with primarily plasterboard (gypsum) .

Several methods and devices for fastening electric ca¬ bles, paintings etc., to porous support surfaces, such as plasterboard panels, or for suspending devices on such sur¬ faces are known to the art. Those methods which afford the most reliable attachment are based on the use of attachment devices comprising fasteners which pass through the panels, or on the use of special duty plaster screws or plugs . One drawback with such attachment devices is that they are dif¬ ficult and time consuming to attach. Furthermore, such de- vices are relatively expensive. The quickest way of securing articles to such porous support surfaces is to use, inter alia, conventional attachment and suspension devices, such as nail clamps and X-hooks . Although these attachment devices are able to take up transversely acting loads in an accept- able manner, they are less than satisfactory with regard to taking up loads which act in _. a fastener-withdrawing direc¬ tion. In order to obtain reliable attachment to the best possible extent when using attachment devices of this kind, it is endeavoured to locate the attachment devices in posi- Lions in which the fasteners used therewith will enter into

an underlying stud work or nogging-piece. When the articles to be attached in this way are electric cables, it is found necessary in some cases to extend the cables farther than would otherwise be required and, moreover, often in a manner which is less pleasing from an aesthetic point of view.

In order to enhance the ability of conventional attachment and suspension devices to take up such fastener-withdrawing forces satisfactorily, it has been proposed to skew-nail such devices to the support material, skew-nailing being a method in which nails are driven into the support material while inclined thereto. When skew-nailing,there has been used either two separate nails or a U-shaped fastener whose legs are caused to diverge or converge through the action of guides provided in the attachment device and/or are formed at their extremities in a manner which will ensure that the legs converge or diverge when driven into said support ma¬ terial. Both of these variants are disclosed in the German Offenlegungsschrift Number DE 3115914 A1 , for example Figure 9 of this publication illustrates an attachment device which is secured with the aid of two nails, whereas Figure 3 and 5 of the publication illustrate an attachment device which is fastened with the aid of a U-shaped fastener, this fastener being shown separately in Figure 6.

Both of these fastener types have the drawback of relaxing their grip slightly when subjected to relatively small with¬ drawing forces, such that the attaching device will no longer abut the support surface. This is due to the fact that the bearing surface of the fastener means which takes up the withdrawing forces is relatively small in area, and conse¬ quently the surface pressure thereon becomes so high as to crush the underlying brittle support material. As the at¬ tachment device moves, this crushed material becomes packed forwardly of the fastener means in the withdrawing direction

thereof and forms cushions or crushed-zones which are able to withstand the withdrawing forces to a greater extent than the unaffected material and therewith prevent continued withdrawal of the fastener means used to fasten the attach- ment device. When these withdrawing forces cease, the attachment device will return, either partially or fully, to its original position. Furthermore, the crushed material in the fastener holes of the attachment device is often re¬ distributed so that upon the reoccurrence of such withdrawing forces further material is crushed. Should these withdrawing forces be repeated intermittently, the fastener means will gradually work out of the support surface and the attachment will become progressively looser,, until it falls away. These intermittently occurring forces which tend to withdraw the fasteners may be caused as a result of cleaning or dusting externally fitted cables of various kinds, for example. When the attachment device is used to hang paintings, pictures, or mirrors in the vicinity of doors, such withdrawing forces may occur intermittently as a result of closing the door. For example, the surges of air generated when closing the door are liable to cause the painting, etc., to rock and therewith subject the fasteners to withdrawing forces.

SUMMARΪ OF THE INVENTION The object of the invention is to provide a method and a de¬ vice therefor which will overcome the aforedescribed diffi¬ culties. This object is achieved with the aid of fastener means which are so formed that when applied they are caused to expand within the support surface, such as to create crushed zones which improve the ability of the fastener means to take-up load. The characteristic features of the present invention are set forth in the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with ref-

erence to the accompanying drawings, in which Figure 1 is a sectional view of an attachment device and co-acting fastener means, shown in various stages when securing the device to a support surface; Figure 2 illustrates in perspective an em- bodiment which has the form of a cable clip with associated

V-shaped fastener means; Figure 3 is a plan view of a further embodiment, in the form of an attachment device provided with a hook; Figure 4 is a bottom plan view of a three-legged fastener means; and Figure 5 illustrates in side view and partially in section the suspension device of Figure 3 in cooperation with the fastener means of Figure 4.

DESCRIPTION OF EMBODIMENTS

Figure 1 illustrates in section an attachment or suspension device which is preferably made of a plastics material and which co-acts with a V-shaped fastener means 2 _r the fastener means being shown in its various stages when securing the attachment device to a support surface 3. For space reasons, Figure 1 has been divided into two halves, which have been displaced relative to one another. The left-hand part of

Figure 1 shows, in full lines, the V-shaped fastener means 2 positioned in the attachment device 1 prior to driving the fastener means into the support surface 3, which may comprise plasterboard or some like material. The fastener means is made from a hard material, preferably steel, whose hardness has been further enhanced by cold working when bending the fastener means to its V-shape. The distance between the points of the legs of the fastener means 2 is adapted to the length of the base of a trapezium shaped part 4 incorporated in the attachment device 1 , said trapezium shaped part 4 being intended to cause the fastener legs to diverge progres¬ sively still further as the fastener means is driven into the support surface. As the fastener legs diverge and the angle therebetween increases, the legs will enlargen or widen the holes caused by preceding leg parts during the entry of the

legs into the support surface 3. The fastener parts shown in broken lines in the two halves of the Figure illustrate the positions of respective fastener legs during different stages of a fastener driving operation. In the right hand half of the Figure, one fastener leg is shown in full lines fully driven into the support surface 3. As illustrated in Figure 1 , the lateral movement executed by the fastener leg causes the hole 6 made by the leg to widen considerably. In this way, the material located in the wall of the hole 6 is crushed in the aforesaid direction of lateral movement, such as to form a crushed zone 5 in which the material is packed together so as to create a cushion which transfers the laterally acting force from the fastener means 2 to the support surface 3 and spreads the force to a larger area around the fastener means and therewith produce the same effect as that which would be produced if the force take-up surface of the fastener means was enlarged. When compared with a fastener means of the kind in which the fastener legs are replaced with nails which are of the same length and diameter and which are skew-nailed into the support surface at angles corresponding to fully driven-in legs, the force required to loosen the inventive attachment device and fastener means, i.e. the withdrawing force, is several times greater.

The reference 7 in the right half of Figure 1 identifies the tip of the leg of a fastener means which has been driven fully into the support surface and illustrates the position which the fastener leg would have taken if the leg had not encountered a progressively increasing resistance from the crushed zone during lateral movement of the leg as it is driven into said support surface. As a result of this re- sistence the part 4 of the attachment device is deformed to some extent and the fastener leg undergoes a certain degree of elastic deformation and therefore becomes pre-stressed,

such as constantly to hold the crushed zone under pressure and therewith also to hold the attachment device 1 in close abutment with the support surface 3. This pressure is not found in the case of devices which are skew-nailed, which is the reason why the fastener means of such devices tend to

"eat" their way out of the support surface when subjected to intermittent loads, as beforementioned. Neither is this effect obtained with known attachment devices of the kind which are intended to co-act with slender and relatively soft U-shaped fasteners, whose legs are guided in holes or grooves in the attachment device so as to enter the support surface at an inclined angle, corresponding to skew-nailing, or with which the end surfaces of the fastener legs are formed so as to produce a corresponding effect.

Figure 2 is a perspective view of a cable clip 8 which is preferably made of a plastics material and which is intended to be fastened to the support surface with the aid of a V- shaped fastener 2. The clip includes an attachment part 9 which has an essentially flat undersurface for abutment with the support surface, and also an arm 10 which extends from the attachment part 9 and which is intended to grip around a cable or the like to be attached to the support surface. The fastener 2 is placed in a rectangular, through-passing hole 11 which has located centrally therein a trapezium shaped part 4 which is arranged in the manner illustrated in Figure 1 , such that the upper surface of said part is located beneath the upper surface of the attachment part 9 to such an extent that when the fastener means 2 is brought into abutment with the upper surface of the part 4 ^* as the' fastener means is driven into the support surface, the upper edge of the fastener 4 will lie parallel with the upper surface of the attachment part 9. These cable clips are suited for use with any kind of fastener applicator or nail driving pistol, the clips, in this case, preferably being produced in a long,

continuous strip. In this regard, the fastener means are placed in respective clips prior to inserting the clips into the pistol ^* magazine, or alternatively the fastener means can be placed in a separate magazine and inserted in the clips in conjunction with firing the clips from the applicator or pistol.

The V-shaped fastener means is preferably manufactured from spring steel and the fastener part joining the fastener legs preferably has a radius of curvature which is equal to or smaller than the diameter of the wire from which the fastener means is made. The trapezium-shaped part 4 has an upper surface which is essentially flat. When the fast¬ ener means is driven into the support surface, and therewith into abutment with said upper surface, the corners of the trapezium-shaped part are subsequently deformed to some ex¬ tent, therewith exerting a gentle retardation force to the fastener means.

Figure 3 is a plan view and Figure 5 a side view, partly in section, of an embodiment of the invention comprising a suspension device 12 which includes a circular attachment part 13 having a centrally located circular hole 14, in which a hub 15 in the shape of a truncated cone is arranged with the base surface of the cone in plane with the surface of the attachment part 13 intended for abutment with the support surface and connected to the defining wall of the hole by means of three spokes 16, and which further includes an arm 17 which extends from the attachment part 13 and which is also intended for abutment with the support surface, the end part of the arm 17 merging with a hook 18. Figure 5 illus¬ trates the suspension device 12 in co-action with a fastener means 19 which comprises a base part 20 having extending therefrom three legs 21 which are placed in the openings lo- cated between respective spokes 16 when fastening the sus-

pension device 12 to a support surface 3. When the fast¬ ener legs 21 are driven into the support surface 3, the legs are caused to diverge within the confines of the support surface, such as to create crushed zones on mutually op- posing sides of the legs 21, in the manner aforedescribed. Figure 4 is a bottom plan view of the fastener means 19, separate from the attachment device. The fastener means concerned is punched from sheet steel and the fastener legs are then bent while simultaneously cold working or bossing the device.

The fastening reliability of the described suspension device and attachment device, and the method applied therewith, is greatly superior to the fastening reliability of convention- al methods and devices when the length of the fastener means is at least 2*5, preferably 3-5 - 4 times the height of the trapezium-shaped part, and when the angle defined by the fastener legs with the symmetry line of the attachment de¬ vice is greater than 8 , and if possible at least 11°. The length of the fastener means in relation to that part of the device which causes the device to expand in the support sur¬ face, and also the extent of such divergence, can be varied within relatively wide limits without departing from the scope of the invention.