WO2000034668A2

WO2000034668A2 - Fixing device and method

Info

Publication number: WO2000034668A2
Application number: PCT/GB1999/004127
Authority: WO
Inventors: Charles Bickford
Original assignee: P A Fixings Ltd
Priority date: 1998-12-08
Filing date: 1999-12-08
Publication date: 2000-06-15
Also published as: GB9826978D0; TW547581U; GB0125655D0; GB2344629A; WO2000034668A3; GB9929130D0; ZA200109220B; AU1668100A; GB2344629B

Abstract

A fixing device comprises a bright zinc-plated steel shank (1) formed by cold forming with a head (2), the shank having formed thereon by thread-rolling a helical bore wall engagement configuration (6). This configuration comprises a pair of spaced apart helical ridges (7, 8) with a helical ridge (9) of larger elevation provided midway therebetween. The device readily self-taps when turned into a bore in a variety of materials. The device holds firmly in timer end grain and on continued turning of its head will perforate and embed in the timber, no amount of torquing causing the device to ream the bore when the device is penetrated into autoclaved aereated concrete.

Description

Improved Fixing Device & Method

The invention relates to an improved fixing device having particular, but not exclusive, application in fixing to timber, plastics materials and friable substrates, such as timber end grain, plywood, blockboard and sterling board edge face, MDF and other particle board (eg chipboard or fibre board), light-weight autoclaved aerated concrete in, for example, block form (eg of the type sold under the trade marks "Thermalite", "Celcon" and "Durox"), plaster, render, soft red brick, breeze (eg breeze blocks) and other friable masonry substrates.

Conventional threaded fixing devices such as screws are difficult to secure in masonry substrates since it is difficult for a conventional thread to find secure location within a bore in such a substrate. Conventional screw threaded fixings are accordingly conventionally secured within bores in masonry substrates by first lining the bore with a lining of relatively soft material into which the threaded fixing can cut its own thread, at the same time compressing the lining against the walls of the bore within the masonry substrate. A typical example of such a lining is that sold under the trade mark Rawlplug. Such linings are available in fibrous and plastics material form and in a wide variety of configurations reflecting a very considerable activity in the art over the years to improve upon the security and ease of use of screw threaded fixing devices used with such liners.

Adopting a somewhat similar principle, alternative forms of fixing device are of metallic material and structured so as to be expansible after introduction into a bore in a masonry material whereby compressive forces against or impingement into the internal surfaces of the bore resist withdrawal of the fixing device from the bore. Reflecting similarly substantial activity in the art, a wide variety of such devices are available. For example, various devices of this kind are available under the above- mentioned trade mark Rawlplug and under the trade marks Fischer and Hilti. The Upat TOP self undercutting anchor compπses an internally threaded cylindrical tubular steel sleeve and a cone received in one open end of the sleeve. A splined lower part of the cylindrical sleeve is in contact with the inclined walls of the cone, these walls being divergent in the direction away from the sleeve. The above described assembly is inserted into a pre-drilled bore until the extremity of the cone (ie the base of the conical portion) comes into contact with the end of the bore. Application of light pressure from a hammer drill causes the splined section to be forced over the conical surface, the splines having tungsten carbide tips which undercut the substrate material. The Upat EXA Express Anchor also operates an expansion fixing but does not operate on the undercutting principle.

Fixing devices somewhat similar to those sold under the trade mark Rawlplug are also sold under the trade mark Fischer, as mentioned earlier. Fixing devices are also made by Fischer which are somewhat similar in structure and operation to the above- described Upat fixing elements. The Fischer Wallbolt comprises a segmented malleable iron expander shield forming a sleeve about an orthodox screw threaded bolt. The combined assembly is in use inserted into a pre-drilled bore in a masonry substrate and the bolt is tightened with a spanner. This draws a terminal conical wedge backwards into the shield and forces four shield segments outwardly against the sides of the bore.

All fixing elements which rely on compression of an associated member into the wall of a pre-drilled bore give rise to structural disadvantages. The walls of the bore are placed under stress and in many substrate materials there is insufficient strength in the substrate structure to prevent cracking. This is particlarly the case with such materials as lightweight autoclaved aerated concrete but also applies to brick structures. It is especially evident adjacent apertures in a masonry structure where on one side at least there will be comparatively small thickness of substrate material. Of course, fixing elements are commonly required in aperture regions for the fixing of window frames, door liners and similar fittings. Equally, a good deal of activity has been focused on improvement of screw threaded members themselves in order that they should find secure fixing in masonry materials without the use of liners and without internal expansion. The driving force in these respects is, of course, the fact that liners do not provide totally satisfactory degrees of security, the fact that the need to insert a liner in a bore represents an additional activity which has associated labour costs and the fact that in the case of expansion bolts and such like the compressive forces necessary for security of fixing can result, as noted above, in rupture of masonry materials particularly when adjacent to extremities of bodies of such materials.

UK Patent Specifications Nos 2 115 511 (ITW III) and 2 152 171 (ITW II) disclose masonry fixings comprising a shank having spaced threads in the form of a helical ridge alternating with a parallel land. The flanks of the threads intersect at an angle of 50° to 65° and exhibit a helix angle of 6° to 8.5°. These features are necessarily combined with special conditions for introduction into a masonry bore and are claimed to provide security of fixing without thread striping upon insertion. Both ITW II and III represent examples of effort in the art to provide threaded devices for direct securement in a bore so as to avoid the disadvantages of expansion-type devices enumerated above.

Coarse deep threads are also disclosed in a fixing for use in masonry-like structures in UK Patent Specification No 1 510 686 (ITW IV), a further example of an attempt to provide a direct-fixture fixing element. In this particular arrangement, the crests of the deep threads are notched in order to assist in the cutting of a thread by the fixture in use and to assist in the transmission of masonry debris within the bore. An intermediate shallower thread ridge appears to be the key to providing a design which enables security of fixture to be achieved whilst at the same time recognizing the need to minimize disturbance of the substrate material. Nevertheless, threads penetrate the substrate at fairly closely spaced positions such that pull-out performance is impaired by the shear resistance of the relatively small sections of substrate material between helical ridge turns. A similar arrangement is disclosed in European Patent Application No 0 133 773 (ITW I).

UK Patent Specification No 466039 (Jasper) discloses a fastening screw having a shank provided with a helical thread groove alternating with a land between the grooves. A longitudinal slot provides self-tapping capacity for the coarse deep thread. Jasper does not disclose the fastening screw for use in masonry structures.

A somewhat similar screw device is described in UK Patent Specification No 274833 (Rosenberg). The entry end screw thread configuration has a groove which penetrates the normal diameter of the fixing device together with raised border ridges, this configuration extending over a short length only of the shank. Rosenberg does not recommend the fixing device for masonry fixing, referring generally to fibrous and non-flowing materials and in particular to metal substrates.

European Patent Specification No 0 225 003 (JSM) and UK Patent Application No 2036227 (Tomoyasu) disclose self-locking screws having a somewhat similar configuration. Helical ridges either side of a small land have their crests grooved. Tomoyasu also refers to a structure in which the ridge crests are not grooved but an intermediate ridge is turned through the land so that there are in fact two parallel grooves forming an overall thread. Both JSM and Tomoyasu relate to self-locking devices reliant on the interaction of male and female threads and there is no disclosure of a use in which the male threaded portion is self-tappingly threadedly into a masonry bore.

UK Patent Specification No 2042120 (Gutshall) discloses a headed screw which incorporates a long-pitch helical thread rolled on a cylindrical blank. The roiling leaves untouched a land between adjacent convolutions of the thread. At each juncture between the root of the thread and the adjacent land a helical crest functioning as an auxiliary thread is provided to improve the holding power of the screw. Gutshall refers to use of the disclosed screw in soft, fibrous or low-density materials which are exemplified as wood and plastics. Gutshall does not appear to recommend the disclosed headed screw for fixture self-tappingly in a masonry substrate.

UK Patent Specification No 1541237 (Oratronics) discloses a threaded device for use as an endodontic stabilizer. The shank of the disclosed device is turned with a helical groove having a sufficiently wide pitch to provide a parallel inter-turn land. The crest of the ridge is grooved. UK Patent Specification No 1519139 (Crock) discloses a simpler structure for use in surgical techniques. The structure disclosed comprises a threaded shank comprising a thread groove somewhat reminiscent of that shown by Rosenberg as mentioned above. Crock refers skirtingly and somewhat speculatively to application in building construction and associated fields but there is no reference specifically to the use of the disclosed device for self-tappingly securing in a masonry bore.

In PCT Application No WO 92/10688, fixing to masonry substrates (eg brickwork, blockwork or concrete) involves forming a bore in the substrate (eg in the tension zone or compression zone of a concrete load-supporting member such as a concrete beam) for a fixing device, introduced into the bore self-tappingly or otherwise, which comprises a shank having a bore entry end and an opposed optionally headed end separated from the bore entry end by the length of the shank, at least a portion of the shank length being configured with a thread rolled helical groove depressed into the blank circumference of the shank so as plastically to displace shank material to at least one of the groove sides, the groove being defined adjacent a helical ridge juxtaposed to a side of the groove or between a pair of parallel helical ridges juxtaposed one either side of the groove and formed in either case of the plastically displaced shank material. The ridges are upstanding from the blank circumference of the shank so as to function in use each as a male thread, at least the leading end of the thread preferably being a female thread-cutting male thread in relation to the masonry. The helical ridges and defined helical groove form a helical configuration whose convolutions are spaced apart by an intervening land in relation to which the ridges are raised and the groove is depressed. The land has a width measured axially with respect to the shank of at least 50% of the land shank diameter and the helix angle of the helical ridge is at least 8° and preferably 10° or more. The fixing device is ordinarily inserted into a slightly oversized bore (and thus the shank of the device will be slightly undersized in terms of diameter relative to the drill diameter used to produce the bore).

Many modern and some traditional construction materials are friable in nature and do not support high pull-out strengths for fixing devices fixed in them. The reasons for this are manifold. For example, in many friable materials a fixing will not self-thread into a predrilled bore because the initial turns of the fixing do not start a helical channel in the bore, but simply enlarge the outer extremity of the bore by abrasion of substrate mateπal. Many devices which can be threaded into a bore self-tap, but have a propensity for overtorque damage, the bore increasing in cross-section over its length to that of the circumference of the threaded surface of the fixing. These problems are particularly prevalent in autoclaved aerated concrete such as in building block form, but are also found when fixing to such traditional materials as soft red brick (and bricks made of differently coloured fired clays) and plasters and renders made of eg lime plaster/render mixes. Timber substrates pose different problems, but in many cases pull-out strength requirements mean that a fixing must pass through a timber member and be secured by a nut on a face opposed to the face through which the fixing is introduced, the latter normally being engaged by a head of the fixing. This means certain constraints when fixing together two members where one face is inaccessible for securement of a nut. Timber end grain is notoriously poor as a fixing base for a fixing device. This is indeed so much so that it is rare to rely solely on screw thread engagement in timber end grain in any real life situation; of course, nut securement is usually precluded in the case of fixings in timber end grain. According to the invention, there is provided in a first aspect a shanked fixing device for fixing together a first member and a second member, the second member having a body portion for receiving said shank of said device in a preferably preformed bore of the body portion, said body portion being composed of timber end or side grain or comprising friable masonry material (eg having a crush resistance of 10N/mm² or less eg 6N/mm² or less), the fixing device comprising the shank and an optional head and the shank of the fixing device being configured with a bore wall engagement configuration wherein helically extending first, second and third parallel threads are upstanding from a helically extending land to define by said threads first and second helically extending grooves laterally contained in the case of the first groove by the second thread and the first thread and in the case of the second groove by the second thread and the third thread, the second thread preferably being sized (and arranged) so as in use of the fixing device to penetrate the wall of the bore in the body portion of the second member at least to the same extent as the, or the smaller of the, extents of such penetration by the first and third threads, preferably at least to the same extent as the larger of the extents of such penetration by the first and third threads, and most preferably more deeply than either of said first and third threads. The circumferential diameter of the second thread is thus in a preferred form of the invention the largest of the above three threads but it may not be, and indeed could be the smallest or could be substantially equal to that of another thread or might be of intermediate size relative to two other unequal threads. The second thread is conveniently disposed, in an approximate sense at least, midway between the first and third threads but the second thread may optionally be disposed eg at any position in a central band occupying the central third of the spacing between the first and third threads.

In an embodiment of the invention, a shanked fixing device for fixing together a first member and a second member, the second member having a body portion for receiving said shank of said device in a bore of the body portion, and said body portion being composed of timber end or side grain or comprising friable masonry material, comprises the shank and an optional head and the shank of the fixing device being configured with a helical bore wall engagement configuration and a helical land, said helical bore wall engagement configuration comprising a first helical thread upstanding from the land circumference of the shank, a second helical

7a thread upstanding from the land circumference of the shank and spaced from and generally parallel to said first helical thread, said second helical thread having an apical circumference greater than that of said first helical thread, a first helical groove defined between said first and second helical threads, a third helical thread upstanding from the land circumference of the shank and spaced from and generally parallel to said second helical thread, said third helical thread having an apical circumference less than that of said second helical thread, and a second helical groove defined between said second and third helical threads. Conveniently, the third helical thread has an apical circumference (ie the circumference of the shank around the thread crest, eg the apex of the helical thread or the summit of the helical thread if it is truncated as in the case of a thread having a frustoconical cross- section) substantially equal to that of the first helical thread.

In an embodiment of the fixing device, the threads have a helix angle of from 30° to 55°. Within this range of helix angles, one group of fixing devices conveniently has threads which have a helix angle of from 37° to 55° whilst the helix angle of the threads in another group is from 30° to 45°, a third group having a helix angle of from 35° to 40°. Preferably, the threads have a helix angle of from 30° to 45°, advantageously a helix angle of from 37° to 45°.

A preferred embodiment of a fixing device according to the invention is one in which the helix angle of the threads is approximately 37°.

Conveniently, the thread angle of the threads is, each independently, from 30° to 70°, for example from 30° to 60° or from 35° to 70°, preferred thread angles being in the range from 35° to 50° (eg from 37° to 45°). The preferred thread angle is about 40°. Preferably, the thread angle of the first and third threads is substantially the same; that of the second thread may differ, but is conveniently the same as that of the first and third threads. In a preferred embodiment, the first thread, in use of the fixing device in a bore substantially equal in diameter to the diameter of the shank land, penetrates the bore wall in the body portion of the second member such that a first channel is formed helically therein and such that the so-penetrated bore has a diameter in helical cross-section through the first channel equal to F in the equation below (the diameter in "helical cross-section" of the bore refers to the diameter of a right circular cylinder described about the threaded shank and having the first thread in contact therewith at the thread radial outer extremeties), the second thread in use penetrating the bore wall in the body portion of the second member such that a second channel is formed helically therein and such that the so-penetrated bore has a diameter in helical cross-section (see above) through the second channel equal to E in the following equation and the third thread in use penetrating the bore wall in the body portion of the second member such that a third channel is formed helically therein and such that the third channel has a diameter in helical cross-section (see above) through the third channel which is equal to or greater than F but less than E:-

E = F + K,

in the above equation, E and F being as defined above and K, being a constant having a value of from F x _±_ to F x _ . K preferably has a value of from F x

1 00 1 00 to F x j _ . In preferred fixing devices according to the invention, E has a

1 00 1 0 0 value which is about 10% greater than that of F.

Using in the following description, the term "helical cross-section" in the above sense, the first thread, in use of the fixing device in a bore equal in diameter to the diameter of the shank land conveniently penetrates the bore wall in the body portion of the second member such that a channel is formed helically therein and such that the so-penetrated bore has a diameter in helical cross-section through the channel equal to F in the following equation in which F is as defined above, C is shank land diameter and K₂ is a constant having a value of C x j_o_ to C x j _ , for example a

1 00 1 0 0 value of from C x _ to C x 27.5 1 00 1 00

F = C + K,

Preferably, K₂ has a value of from C x _2o_ to C x j _ . in one particularly preferred

1 0 0 1 0 0 embodiment, F has a value which is about 20% greater than that of C whilst in another F has a value which is about 25% greater than that of C.

The first thread, in use of the fixing device in a bore equal in diameter to the diameter of the shank land, penetrates the bore wall in the body portion of the second member such that a channel is formed helically therein and such that preferably the so-penetrated bore has a diameter in helical cross-section through the channel equal to F in the following equation:-

F = c

+ C

100

In the above equation, C is shank land diameter and K₃ is a constant having a value of from 25 to 30. K₃ conveniently has a value of 26 to 28 and is preferably a value of 27.

Conveniently, the spacing of the first and third threads measured as the distance between the apices or summits thereof in a single turn of the bore wall engagement configuration is from 25% to 40% of the spacing between the turns of the second thread measured between the apices thereof. Preferably, the spacing between the first and third threads is from 28% to 35% of the spacing between the turns of the second thread. Particularly preferred is that the spacing between the first and third

10 threads is from 28% to 33% of the spacing between the turns of the second thread. Most advantageously, the spacing between the first and third threads is about 30% of the spacing between the turns of the second thread.

One or both of the first and second grooves of the bore wall engagement configuration may have its floor depressed relative to the shank land, preferably both being so depressed, advantageously to the same level as one another.

One or both of the grooves of the bore wall engagement configuration may have its floor sufficiently depressed relative to the apex or summit of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross-section through the apex of said thread by a margin 25% to 45% relative to the latter. Conveniently, one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross-section through the apex of said thread by a margin 27% to 40% (eg 30% to 38%) relative to the latter, preferably a margin of 32% to 37%.

In a particular embodiment, one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross-section through the apex of said thread by a margin of 33% to 36% relative to the latter, preferably by a margin of approximately one third relative to the latter.

Conveniently, the apices of the threads are flattened so that the threads in practice have a frustoconical form.

11 In a second aspect, the invention provides a fixing method which comprises turning into a bore in a substrate a fixing device as defined earlier according to the invention, the bore having a diameter less than the diameter of the fixing device shank in helical cross-section through the apex (or non-apical summit) of the one of the threads having the smallest diameter, the substrate being a substrate of a member to which another member is to be fixed by use of the fixing device and the substrate being composed of timber or comprising friable masonry material, such as autoclaved aerated concrete, a cured plaster or render coat, plasterboard or soft red or other soft brick.

In particular, the friable masonry material may be masonry material having a crush resistance of less than 5N/mm², for example a crush resistance of less than or equal to 3.5N/mm².

The friable masonry material may be cementitious or clinker-based.

In the case of timber substrates, the timber substrate is in particular timber end grain. In such cases, the fixing device is turned into the bore in the substrate by application of axial force. The application of axial force may be application of intermittent dynamic force along the axis of the shank of the fixing device. In particular, the axial force may be a percussive force applied by hammering.

In preferred methods, the diameter of the fixing device in helical cross-section through the apex or other crest of the second thread is equal to 115% to 145% of the nominal diameter of the bore in the substrate. For example, the diameter of the fixing device in helical cross-section through the apex of the second thread is equal to 120% to 135% of the nominal diameter of the bore in the substrate, preferably 125% to 130% of the nominal diameter of the bore in the substrate.

12 Conveniently, the pitch between the first and third threads in each turn of the bore wall engagement configuration is from 40% to 90% of the nominal diameter of the bore, the diameter of the land of the fixing device shank corresponding to the nominal diameter of the bore less minimal clearance. Preferably, the pitch between the first and third threads in each turn of the bore wall engagement configuration is from 50% to 80% (eg 60% to 70%) of the nominal diameter of the bore, the diameter of the land of the fixing device shank corresponding to the nominal diameter of the bore less minimal clearance.

In a preferred embodiment, the diameter of shank of the fixing device in helical cross-section through the apex of the first thread and the diameter of said shank in helical cross-section through the shank land are such that the material of the wall of the bore is penetrated by said first thread to a depth equal to at least 5% of nominal bore diameter, preferably to a depth equal to at least 10% of nominal bore diameter.

Embodiments of the invention will now be described, by way of example only, reference being made to the accompanying drawings in which:-

Figure 1 shows a first embodiment of a fixing device according to the invention;

Figure 2 is a view of the fixing device of Figure 1 in the direction of the arrow X shown in Figure 1 ;

Figure 3 is a portion, on an enlarged scale, of a cross-section of the fixing device shown in Figure 1 , the cross-section being taken along the line Ill-Ill shown in Figure 1 ;

Figure 4 shows a second embodiment of the fixing device according to the invention;

13 Figure 5 is a portion, on an enlarged scale, of a cross-section of the fixing device shown in Figure 4, the cross-section being taken along the line V-V shown in Figure 4;

Figure 6 shows schematically a screw heading station forming part of a screw production line for producing a headed blank from which to make by thread rolling a fixing device according to the invention, the production procedures being arranged to form a fixing device with a countersink head for screwdriver engagement, but readily adaptable to form a device as shown in Figures 1 to 5;

Figures 7(a), 7(b) and 7(c) show various stages in the plastic deformation of a cut-off blank wire section in a screw heading process using the apparatus shown in Figure 6;

Figure 8 shows schematically a thread-rolling station forming part of a screw production line for use in forming a helical bore wall engagement configuration according to the invention;

Figures 9(a) and 9(b) show the dye construction relative to Figure 8 in greater detail; and

Figures 10(a) and 10(b) show two stages in the installation of a fixing device according to the invention in a building block made of autoclaved aerated concrete.

The two embodiments depicted in Figures 1 to 5 of the drawings are somewhat similar in configuration and the differences between the two will appear from the following description. In the Figures, like parts are designated by like reference numerals.

The fixing device shown in Figure 1 of the drawings comprises a bright zinc plated steel shank 1 of solid right circular cylindrical form. The shank is formed by cold forming with a head 2 shown best in Figure 2 of the drawings from which it will be seen that this is in conventional hexagonal form comprising six faces 5 intended for

14 location in the jaw of an open spanner of complementary size and shape or by a suitable socket or ring spanner. Obviously, however, the head 2 may be formed with a different type of head such as a countersink head (as exemplified in Figure 7) conventionally slotted as for conventional blade screwdriver engagement or formed with a Posidrive screw engagement depression.

The end 3 of shank 1 opposed to head 2 is formed with an annular cant or bevel 4 intended to assist in introduction of the tip of the shank into an appropriately sized and configured bore in a substrate.

Shank 1 is formed by thread rolling with a helical bore wall engagement configuration designated generally in Figures 2 and 4 by reference numeral 6. This configuration compπses a pair of spaced apart helical ridges 7 and 8. Mid-way between ridges 7 and 8 is a helical ridge 9 of larger elevation. All three helical ridges are formed on shank 1 with identical helix angles with the result that the ridges are, of course, parallel one to another and separated by the same pitch throughout the extent of the helix. All three ridges serve as a screw thread for fixing the fixing device in a bore in an appropriate substrate. All three ridges are of frusto-conical form in cross-section. Each ridge has an upstand from the surrounding basal surface of the shank 1 which is uniform throughout the helix. Ridges 7 and 8 have the same upstand as one another whereas ridge 9, as previously mentioned, has a greater upstand.

The turns of helical bore wall engagement configuration 6 are separated by the turns of helical land 13.

Ridge 7 defines with ridge 9 a helical groove 11 forming part of helical engagement configuration 6. Similarly, ridge 8 forms with ridge 9 a groove 12 which is identical to groove 11.

15 The embodiment shown in Figure 4 is broadly similar to that shown in Figure 1 as already mentioned. However, in the embodiment shown in Figure 4 a groove 11a is defined between ridge 7 and ridge 9 and similarly a groove 12a is defined between ridge 9 and ridge 8. It will be noted that both grooves 11 a and 12a are depressed relative to land 13 whereas in the embodiment shown in Figure 1 , land 13 and the floors of each of grooves 11 and 12 have a common level.

The fixing devices shown in the Figures may be made in a range of sizes. The particular parameters of a fixing device other than diameter (ie M size) will vary according to the M size of the fixing device. With reference to the embodiment of fixing device shown in Figure 4 of the drawings. Table 1 below indicates suggested dimensions, in some cases minima and maxima, for the dimensional parameters signified by the letters A to J shown in Figures 4 and 5.

16

17 Fixing elements according to the invention can be manufactured by the steps of cold-forging and thread-rolling, bright zinc plating and heat treatment without resort to complex assembly operations such as are normally associated with an expansion bolt. This produces economies in terms of materials and manufacturing costs as well as the economies associated with relative ease of installation and use noted below.

In Figures 6 to 9, the manufacture of fixings according to the invention is depicted schematically. Referring to Figure 6, a screw heading station comprises a solid metallic block 15 formed with a right circular cylindrical uniform diameter bore 16. Steel wire 17 passes along bore 16 and is urged until its end abuts against stop 20. A cut-off 19 is mounted for reciprocatory motion radially against the mouth of bore 16 so as to sever the wire 17 to form a blank 18. A transfer finger 21 mounted for reciprocatory motion parallel to that of the cut-off 19 is provided for transferring cut-off blank 18 a stage further in the heading operation as depicted at two points in Figure 6 in broken lines. At the maximum displacement of transfer finger 21 blank 18 is transposed in register with a bore 23 in solid metallic block 22, bore 23 being identical with bore 16 in block 15 except that bore 23 has a blind end represented by the crown of a piston 27 movable axially of bore 23 to provide for different desired lengths of fixing element. Whilst retained by transfer finger 21 , a blank 18 is displaced into bore 23 in block 22 by means of the first of two punches 25 mounted for reciprocatory motion in the directions of double- headed arrow Y shown in Figure 6.

The mouth 24 of bore 23 is depressed into the body of block 22 and has the configuration of a countersink. The first of punches 25 drives blank 18 fully into bore 23 and produces the partial plastic deformation shown in Figure 7(b). The first punch 25 is provided with a plain punch face 28. The second punch 25 is provided with a punch face 28 having a structure 26 disposed thereon for forming in the head of the fixing device a screw engagement depression 29 having a so- called Posidrive configuration. The action of the second of the two punches 25

18 completes plastic deformation of the terminal end of blank 18 to form the head 30 shown in Figure 7(c).

The thread-rolling station shown in Figures 8 and 9 comprises a fixed dye 31 and a displaceable dye 32. The two dyes are spaced apart to form jaw 33, the gap therebetween being equal to the core diameter of the product being rolled. Dye 32 is displaceable in reciprocatory fashion according to the arrow 2 shown in Figure 8. In use, headed blank 18b is inserted into jaw 33 and thus between the fixed and moving dyes 31 , 32 by manual or mechanical means (eg a mechanical feed-finger) as is known in the thread-rolling art. The vertical position of the blank in relation to the fixed and moving dye is governed by a work rest on which the blank 18b rests prior to introduction to the dyes by the feed-finger. In accordance with the operational sequence, the moving dye first moves clear of being parallel with the fixed dye 31 in the direction of arrow C. Blank 18b is then transferred by the feed-finger into the work rest and pushed against and between the leading edge of moving dye 32 and the back edge of fixed dye 31. The reciprocating action of the moving dye 32 then carries the blank 18b between them. During this time, the blank 18b is plastically deformed to the face of the dyes as the blank rolls along the faces thereof. This gives rise to formation of the helical bore engagement configuration 6 shown in the embodiments in Figures 1 to 5 of the drawings. Die grooves corresponding to ridges 7, 8 and 9 on the fixing element are shown at 7a, 8a and 9a in Figure 9(a) whilst die ridges corresponding to device grooves 11 and 12 (referring to Figures 1 to 3) or 11 a and 12a (referring to Figures 4 and 5) are depicted at 11 b and 12b in Figures 9(a) and 9(b).

As previously noted, Figure 10 shows diagramatically a light-weight autoclaved aerated concrete substrate 42 whose surface 43 is punctured by a right circular cylindrical bore 44 drilled into the substrate 42 using a low speed power-driven masonry drill bit without hammer action. The substrate may be eg a Celcon block or a Durox block. Tarmac Topblock and Clinker Topblock are examples of other firable construction materials with which the invention is concerned.

19 A fixing device according to the invention, such as that shown in Figures 1 to 5 of the drawings (although an alternative embodiment having a countersink head is depicted in Figures 10(a) and (b)), is offered up to the bore 44 and its tip is inserted into the mouth of the bore 44. The fixing element is then rotated manually a number of times until the threads 7, 8, 9 start to engage by tapping a corresponding female thread in the outer portions of the wall of the bore 44. This practice is continued until finger turning becomes impractical. A screwdriver or spanner as appropriate is then taken by the operator, engaged with the head of the shank 1 and further turning then effected. The threads represented by the three ridges 7, 8, 9 continues, with this motion, to form its own female thread with gradually increasing extent along the length of the internal surface of bore 44 until the shank 1 is completely received in the bore 44. This stage is depicted in Figure 10b.

It will be appreciated from the foregoing that the invention is simple to use in practice, the device readily self-tapping when turned into a bore in a variety of materials. The device holds firmly in timber end grain and on continued turning its head, if any, will perforate and embed in the timber. No amount of torquing will cause the device tested below to ream the bore of an autoclaved aerated concrete block, but rather self-threading penetration continues. Over-torquing is per se impossible in soft red bricks. Under ultimate tensile loads in all substrates the product does not fail or cone out the substrate. As the tensile load is increased the bolt starts to withdraw but as each convolusion of the thread emerges the following convolusion takes the tensile load back to its ultimate. This gives the product a fail safe characteristic. When hammered into a predrilled hole into end and cross grained timber the bolt turns on impact and cuts its own thread perfectly into the timber. The clamping force timber to timber is excellent in both end and cross grain situations. It will replace the necessity to use standard nuts and bolts. The product can be removed by unscrewing even though it has been hammered in.

20 Tensile load performance tests were carried out using 8mm fixing devices referred to in Table 1 with Parameters D, G, H and I as set forth in that Table and the minima for Parameters A, B, C, E, F and J as set forth in that Table, the helix angle shown in Figure 4 of the drawings and a thread angle of 40°. The tests were carried out according to the protocol set forth below. The results are shown in Table 2 below.

Testing Protocol

The fixing device in each load performance test was offered up to pre-drilled bores of depth 80mm and diameter equal to Parameter C plus minimal clearance relative thereto in the substrates referred to in Table 2. Embedment depth of the fixing devices was as set forth in Table 2. Hydrajaws portable tension tester Model 0087C was deployed in combination with a load spreading bridge and a Master tension tester (gauge 0-5 KN) Model No PA12A.3776). Axial pull-out force was applied to head 2 of the fixing device to determine static tensile load supported, and other observations made.

TABLE 2

Substrate Embedment Static Tensile Comments

Depth Load Supported

2.5NM Celcon Blocks 75mm 2.5KN Block cracked

2.5NM Durox Blocks 75mm 1.1 KN

7NM Topblock (Tarmac ) 30mm 3.5KN

3.5NM Clinker Tarmac

Topblock 75mm = 4KN

21

Claims

1 . A shanked fixing device for fixing together a first member and a second member, the second member having a body portion for receiving said shank of said device in a bore of the body portion, said body portion being composed of timber end or side grain or comprising friable masonry material, the fixing device comprising the shank and an optional head and the shank of the fixing device being configured with a bore wall engagement configuration wherein helically extending first, second and third parallel threads are upstanding from a helically extending land to define by said threads first and second helically extending grooves laterally contained in the case of the first groove by the second thread and the first thread and in the case of the second groove by the second thread and the third thread, the second thread being arranged and sized so as in use of the fixing device more deeply to penetrate the wall of the bore in the body portion of the second member than either of said first and third threads.

2. A shanked fixing device for fixing together a first member and a second member, the second member having a body portion for receiving said shank of said device in a bore of the body portion, and said body portion being composed of timber end or side grain or comprising friable masonry material, the fixing device comprising the shank and an optional head and the shank of the fixing device being configured with a helical bore wall engagement configuration and a helical land, said helical bore wall engagement configuration comprising a first helical thread upstanding from the land circumference of the shank, a second helical thread upstanding from the land circumference of the shank and spaced from and parallel to said first helical thread, said second helical thread having an apical circumference greater than that of said first helical thread, a first helical groove defined between said first and second helical threads, a third helical thread upstanding from the land circumference of the shank and spaced from and parallel to said second helical thread, said third helical thread having an apical circumference less than that of

22 said second helical thread, and a second helical groove defined between said second and third helical threads.

3. A fixing device as claimed in Claim 2 wherein the third helical thread has an apical circumference substantially equal to that of the first helical thread.

4. A fixing device as claimed in any one of Claims 1 to 3 wherein the threads have a helix angle of from 30° to 55°.

5. A fixing device as claimed in Claim 4 wherein the threads have a helix angle of from 35° to 50°.

6. A fixing device as claimed in Claim 4 wherein the threads have a helix angle of from 30° to 45°.

7. A fixing device as claimed in Claim 5 wherein the threads have a helix angle of from 37° to 45°.

8. A fixing device as claimed in any one of Claims 1 to 4 wherein the helix angle of the threads is from 37° to 55°.

9. A fixing device as claimed in any one of Claims 1 to 3 wherein the helix angle of the threads is approximately 37°.

10. A fixing device as claimed in any preceding claim wherein the thread angle of the threads is, each independently, from 30° to 70°.

11. A fixing device as claimed in Claim 10 wherein the thread angle of the threads is, each independently, from 30° to 60°.

12. A fixing device as claimed in Claim 10 wherein the thread angle of the threads is, each independently, from 35° to 70°.

23

13. A fixing device as claimed in Claims 10 to 12 wherein the thread angle of the threads is, each independently, from 35° to 50°.

14. A fixing device as claimed in any one of Claims 10 to 13 wherein the thread angle of the threads is, each independently, from 37° to 45°.

15. A fixing device as claimed in any preceding claim wherein the thread angle of the threads is about 40°.

16. A fixing device as claimed in any preceding claim wherein the first thread, in use of the fixing device in a bore equal in diameter to the diameter of the shank land, penetrates the bore wall in the body portion of the second member such that a first channel is formed helically therein and such that the so-penetrated bore has a diameter in helical cross-section through the first channel equal to F in the equation below, wherein the second thread in use penetrates the bore wall in the body portion of the second member such that a second channel is formed helically therein and such that the so-penetrated bore has a diameter in helical cross-section through the second channel equal to E in the following equation and wherein .the third thread in use penetrates the bore wall in the body portion of the second member such a third channel is formed helically therein and such that the third channel has a diameter in helical cross-section through the third channel which is equal to or greater than F but less than E:-

F + K,

wherein E and F are as defined above and K. is a constant having a value of from F x ___ to F x _1_ .

100 100

24

17. A fixing device as claimed in Claim 16 wherein K, has a value of from

F x ⁹ to F x » ,

100 100

18. A fixing device as claimed in Claim 16 wherein E has a value which is about 10% greater than that of F.

19. A fixing device as claimed in any preceding claim wherein the first thread, in use of the fixing device in a bore equal in diameter to the diameter of the shank land, penetrates the bore wall in the body portion of the second member such that a channel is formed helically therein and such that the so- penetrated bore has a diameter in helical cross-section through the channel equal to F in the following equation:-

F = C + K,

wherein F is as defined above, C is shank land diameter and K₂ is a constant having a value of C x -i- to C x ------ .

100 100

20. A fixing device as claimed in Claim 19 wherein K₂ has a value of from C x A__ \o C _l_i .

100 100

21. A fixing device as claimed in Claim 20 wherein K₂ has a value of from C x ²⁰ to C x 25 ,

100 100

22. A fixing device as claimed in Claim 19 wherein F has a value which is about 20% greater than that of C.

23. A fixing device as claimed in Claim 19 wherein F has a value which is about 25% greater than that of C.

25

24. A fixing device as claimed in any one of Claims 1 to 18 wherein the first thread, in use of the fixing device in a bore equal in diameter to the diameter of the shank land, penetrates the bore wall in the body portion of the second member such that a channel is formed helically therein and such that the so- penetrated bore has a diameter in helical cross-section through the channel equal to F in the following equation:-

C

+ C

100

wherein F is as defined above, C is shank land diameter and K₃ is a constant having a value of from 25 to 30.

25. A fixing device as claimed in Claim 24 wherein K₃ has a value of 26 to 28.

26. A fixing device as claimed in Claim 25 wherein K₃ has a value of 28

27. A fixing device as claimed in any preceding claim wherein the spacing of the first and third threads measured as the distance between the apices thereof in a single turn of the bore wall engagement configuration is from 25% to 40% of the spacing between the turns of the second thread measured between the apices thereof.

28. A fixing device as claimed in Claim 27 wherein the spacing between the first and third threads is from 28% to 35% of the spacing between the turns of the second thread, all measurements of spacing being on the basis set forth in Claim 27.

29. A fixing device as claimed in Claim 27 wherein the spacing between the first and third threads is from 28% to 33% of the spacing between the turns of

26 the second thread, all measurements of spacing being on the basis set forth in Claim 27.

30. A fixing device as claimed in Claim 27 wherein the spacing between the first and third threads is about 30% of the spacing between the turns of the second thread, all measurements of spacing being on the basis set forth in Claim 27.

31. A fixing device as claimed in any preceding claim wherein one or both of the first and second grooves of the bore wall engagement configuration has its floor depressed relative to the shank land.

32. A fixing device as claimed in any preceding claim wherein one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross- section through the apex of said thread by a margin of 25% to 45% relative to the latter.

33. A fixing device as claimed in Claim 32 wherein one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross- section through the apex of said thread by a margin of 27% to 40% relative to the latter.

34. A fixing device as claimed in Claim 32 wherein one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the

27 floor of said groove is less than the diameter of the shank in helical cross- section through the apex of said thread by a margin of 30% to 38% relative to the latter.

35. A fixing device as claimed in Claim 32 wherein one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross- section through the apex of said thread by a margin of 32% to 37% relative to the latter.

36. A fixing device as claimed in Claim 32 wherein one or both of the first and second grooves of the bore wall engagement configuration has its floor sufficiently depressed relative to the apex of the adjacent one of the first and third threads that the diameter of the shank in helical cross-section through the floor of said groove is less than the diameter of the shank in helical cross- section through the apex of said thread by a margin of approximately one third relative to the latter.

37. A fixing device as claimed in any preceding claim wherein the apices of said threads are flattened.

38. A fixing device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

39. A fixing method which comprises turning into a bore in a substrate a fixing device as claimed in any preceding claim, the bore having a diameter less than the diameter of the fixing device shank in helical cross-section through the apex of the one of the threads having the smallest diameter, the substrate being a substrate of a member to which another member is to be fixed by use

28 of the fixing device and the substrate being composed of timber, plastics or comprising friable masonry material.

40. A method as claimed in Claim 39 wherein the friable masonry mateπal is autoclaved aerated concrete, a cured plaster or render coat, plasterboard or soft red brick.

41. A method as claimed in Claim 39 or Claim 40 wherein the friable masonry material is masonry mateπal having a crush resistance of less than 5NM.

42. A method as claimed in Claim 41 wherein the friable masonry material is masonry material having a crush resistance of less than or equal to 3.5NM.

43. A method as claimed in Claim 41 or Claim 42 wherein the friable masonry material is cementitious or clinker-based.

44. A method as claimed in Claim 39 wherein the timber substrate is timber end grain.

45. A method as claimed in Claim 44 wherein the fixing device is turned into the bore in the substrate by application of axial force.

46. A method as claimed in Claim 45 wherein the application of axial force is application of intermittent dynamic force along the axis of the shank of the fixing device.

47. A method as claimed in Claim 42 wherein the axial force is a percussive force applied by hammering.

48. A method as claimed in any one of Claims 39 to 47 wherein the diameter of the fixing device in helical cross-section through the apex of the second

29 thread is equal to 115% to 145% of the nominal diameter of the bore in the substrate.

49. A method as claimed in any one of Claims 39 to 48 wherein the diameter of the fixing device in helical cross-section through the apex of the second thread is equal to 120% to 135% of the nominal diameter of the bore in the substrate.

50. A method as claimed in any one of Claims 39 to 49 wherein the diameter of the fixing device in helical cross-section through the apex of the second thread is equal to 125% to 130% of the nominal diameter of the bore in the substrate.

51. A method as claimed in any one of claims 39 to 50 wherein the pitch between the first and third threads in each turn of the bore wall engagement configuration is from 40% to 90% of the nominal diameter of the bore, the diameter of the land of the fixing device shank corresponding to the nominal diameter of the bore less minimal clearance.

52. A method as claimed in any one of claims 39 to 51 wherein the pitch between the first and third threads in each turn of the bore wall engagement configuration is from 50% to 80% of the nominal diameter of the bore, the diameter of the land of the fixing device shank corresponding to the nominal diameter of the bore less minimal clearance.

53. A method as claimed in any one of claims 39 to 52 wherein the pitch between the first and third threads in each turn of the bore wall engagement configuration is from 60% to 70% of the nominal diameter of the bore, the diameter of the land of the fixing device shank corresponding to the nominal diameter of the bore less minimal clearance.

30

54. A method as claimed in any one of Claims 39 to 52 wherein the diameter of shank of the fixing device in helical cross-section through the apex of the first thread and the diameter of said shank in helical cross-section through the shank land are such that the material of the wall of the bore is penetrated by said first thread to a depth equal to at least 5% of nominal bore diameter.

55. A method as claimed in Claim 54 wherein the diameter of shank of the fixing device in helical cross-section through the apex of the first thread and the diameter of said shank in helical cross-section through the shank land are such that the material of the wall of the bore is penetrated by said first thread to a depth equal to at least 10% of nominal bore diameter.

56. A method as claimed in any one of Claims 39 to 55 wherein the second thread is disposed midway between said first and third threads.

57. A method substantially as hereinbefore described with reference to the accompanying drawings.

31