GB2277289A

GB2277289A - Cut resistant joints

Info

Publication number: GB2277289A
Application number: GB9308121A
Authority: GB
Inventors: Frederick Gerald Forfitt
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-04-20
Filing date: 1993-04-20
Publication date: 1994-10-26
Anticipated expiration: 2013-04-20
Also published as: GB9308121D0; GB2277289B

Abstract

A cut-resistant material 22 such as tungsten carbide is held in the joint location during welding, whereby the cut resistant material is incorporated into the welded joints. A clip holds the cut-resistant material in place during welding and also shields it. The clip is subsequently removed. Such joints are suitable for security structures. <IMAGE>

Description

CUT-RESISTANT JOINTS This invention relates to cut-resistant joints and to methods and apparatus for use in the production of same.

More particularly, but not exclusively, the invention relates to methods and apparatus for use in the construction of security structures such as security windows and the like.

The invention applies particularly to the use of welding for joining structural members, and to the incorporation of cutresistant material into such welded joints. A broader aspect of the invention relates to methods and apparatus for incorporating cut-resistant material in a joint between two members, which joint is formed by melting a joint material around the areas to be joined, and thus this broader aspect is seen to specifically encompass methods of making joints which may not be considered to be "welding".

In my co-pending UK patent application GB 91 14347.9 filed 03.07.91, and in my published European patent specifications EP 0305100 and EP 0304267 there are disclosed structures for use in security assemblies such as security windows, in which the individual bars or members of the structures have embedded therein hardened or cut-resistant material such as tungsten carbide in order that these security members are more resistant to cutting by hacksaws and rodsaws and the like.

As a result of the use of such cut-resistant members in security structures, it has become commonplace for attempts to defeat such structures to be concentrated on the areas in such structure where members are welded together. As a result of this, it has been proposed to use a welding technique in which a hard-facing is provided over the main body of the weld, by the use of tungsten carbide particles dispersed in the weld material of the hard facing.

However, I have discovered that the use of such a hard-facing leads to structural weaknesses in the main body of the welded joint due to the differential rates of contraction of the hard-facing and the remainder of the welded joint.

An object of the present invention is to provide a method of making a cut-resistant joint, a product thereof, and associated apparatus, providing improvements in relation to one or more of the matters discussed above, or to provide a method of enabling a hard or cut-resistant material such as tungsten carbide to be conveniently incorporated into a welded joint, or improvements generally.

According to the invention there is provided a method of making a cut-resistant joint, a product thereof, and associated apparatus, as defined in the accompanying claims.

In a preferred embodiment there is provided a method of making a cut-resistant joint, and products thereof in which discrete elements of tungsten carbide or a similar hard or cut-resistant material are located in a welded joint to render cutting of the joint more difficult. Means is provided for holding the tungsten carbide in the required location during the making of the welded joint. Said means comprises a holding device, such as a clip, which is destroyed and/or removed either during or after the welding process. The pellet or element of hard material is held by the clip or other device long enough to become embedded in the welded joint. This thereby inhibits or prevents cutting from starting at that location. In the preferred embodiment, such pellets are located at each corner of a rectangular welded joint. Corresponding provision is made for joints of other shapes, such as triangular joints. Still further protection may be provided by the provision of hard material throughout the length of, or at intervals along the length of the entire periphery of the welded joint.

In the preferred embodiment, the holding device comprises a spring member of mild steel. This member holds the pellet or element of tungsten carbide by friction in a spring action. One preferred arrangement is that the clip member holds two pellets of the hard material, one at each of two corners of the joint to be welded, and the arrangement is such that as welding progresses, one of the pellets is first incorporated in the welded joint, and then as welding progresses towards the other, the latter is still held by the clip member even though the first pellet has been already incorporated into the joint.

In the preferred embodiment, the mild steel of the clip member serves to, at least in part, cover and shield the hard material such as tungsten carbide, whereby during the welding process, the latter is not subjected to the full rigours of welding, and thereby damaged.

Also in the preferred embodiment, the structure of the two members to be welded is arranged so that a relieved region is provided to receive the pellet of hard material, whereby the latter is conveniently located within the external profile of the assembled joint. This can conveniently be arranged by providing the appropriate chamfers on the members to be welded. However, if circumstances require it, a fillet weld can be adopted.

Alternative materials for the cut-resistant elements include carbon derivatives such as diamond, and Stellite (a trade name for a product based on nickel). The method of the invention is applicable to any welded joint, including any cross-sectional shape of members to be joined, including round sections. For example, where a round section is to be joined to a flat section, the device for holding the tungsten carbide or like material may be in the form of a washer having inwardly curled portions to hold the pellets of hard material at intervals around the periphery of the round section member.

Mild steel sheet may be employed for the holding device, and in the embodiments the structures are formed by a pressing operation in steel sheet of thickness 30 x iO3 inches (0.76 millimetres). Alternative materials for the holding device need to have the characteristics that they do not affect the quality of the welded joint while holding the tungsten carbide or the like until the joint is made. It is thought likely that plastics materials would unacceptably affect the quality of the welded joint.

The holding device may be arranged to hold more than one element of hard material, or longer such elements.

Typically, a normal size element will be of 1 to 5 millimetres in width or diameter, and 3.5 to 10.5 millimetres in length.

By providing means for holding the cut-resistant material in the required location during the making of the joint, the invention enables hard or cut-resistant materials to be incorporated in otherwise conventional welded joints, thereby protecting such joints against attack of the kind discussed above, while avoiding the technical shortcomings of previous proposals for hard-facing such joints. To put it another way, the invention enables the joints in welded structures and the like to be protected against the use of cutting tools, to an extent comparable with that of the structural members of grills, bars and the like.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which : Fig 1 shows a typical front elevation of a security grill made from a hollow structural steel section, a triangular steel section, a rolled steel section, or a flat steel section; Fig 2/A shows a section through a welded connection or joint in Fig 1, the section being taken on the line II-II in Fig 1, and the drawing showing the use of generally square section structural members in the grill; Fig 3/A shows a view on arrow III in Fig 2/A providing an elevation view of the joint; Figs 2/B and 3/B show views corresponding to those of Figs 2/A and Fig 3/A but showing the use of triangular steel sections; Figs 2/C and 3/C, and 2/D and 3/D show further views corresponding to the above and illustrating the use of a rolled steel section and a flat steel section for the construction of the grill of Fig 1; Fig 4 shows a section on the line IV-IV in Fig 1, showing attachment of a mounting bracket to a grill bar; and Fig 5 shows an elevation view of the assembly of Fig 4, the direction of viewing being indicated by arrow V in Fig 4.

Fig 6 shows a perspective view of a clip for holding hardened material in the joint region during welding; Figs 7 and 8 show modifications of the clip of Fig 6 for use in joining flat plate and triangular sections, respectively, to another structure; Figs 9 and 10 show modifications of the clips of Figs 8 and 6 respectively showing the use of clips generally similar in form to those of Figs 8 and 6 but cooperating with several adjoining sides of one of two members to be joined, Fig 9 showing a triangular section and Fig 10 showing a square section being joined to another member; and Figs 11 and 12 show axial end elevation and longitudinal sectional views through a clip member in use for joining a round section to a flat section.

As shown in Fig 1, a security structure in the form of a security grill 10 comprises vertical elements or bars 12 and horizontal elements or bars 14. The grill 10 is in the form of a metal fabrication having welded joints between the vertical and horizontal bars.

Brackets 16 are likewise welded to the outermost vertical bars 12 for mounting purposes. Corresponding brackets 18 are provided on the lower horizontal bar 14.

The melt joints with which the invention is principally concerned are formed at the interfaces between the bars 12 and 14 and the brackets 16 and 18, as more fully described below.

As shown in Fig 2/A, upper horizontal bar 14 is in the form of a generally square box-section. Each of the vertical bars 12 is in the form of a corresponding box-section member.

All these structural members incorporate cut-resistant material as described in my above-mentioned prior European applications.

Welded joints 20 are formed at the interfaces between the main structures 12, 14 of window 10, as mentioned above, and within these welded joints is incorporated material in the form of hardened and thus cut-resistant elements, such as tungsten carbide. This is the same material which is incorporated in the actual structure of the main members of the window structure itself. These elements or short rods of tungsten carbide are indicated at 22, and are shown positioned in generally V-shaped recesses defined between chamfered edge faces 24 of the bars 12, 14. Corresponding reinforced joints are provided wherever security considerations require that the joint needs to be reinforced against attack by cutting implements.

Figs 2/B, 3/B and 2/C, 3/C and 2/D, 3/D adopt the same reference numerals as Figs 2/A, 3/A, but with suffixes B, C and D respectively. These figures illustrate respectively triangular and rolled steel and flat sections.

Figs 4 and 5 show the corresponding joint area details for the joints between the bracket 16 and the vertical bars 12. Reference numerals in Figs 4 and 5 correspond to those of Figs 2/A and 3/A with suffixes "E". The vertical bar 12 is shown as a rolled steel section corresponding to that of Figs 2/C and 3/C but the method of joining the bracket 16 applies also to the other sections, as illustrated above.

Turning now to the drawings illustrating the method for actual incorporation of the reinforcing material in the joint, namely Figs 6, 7 and 8, it will be seen that these show in each case means for holding the tungsten carbide cut-resistant elements in the required location during the making of the welded joint.

Thus, in Fig 6, the means 26 for holding is in the form of a clip 28 of mild steel having a generally rectangular shape so as to fit round a square tube 30 which is to be joined to a corresponding rectangular section 32.

The clip 28 has a main strip section 34 extending across the width of tube 30, and flanges 36 extending along the adjoining two faces of tube 30, and dimensioned and constructed so as to have a spring-action thereon whereby the clip is firmly held in the position shown during use.

Depending from flanges 36 are a pair of holding formations 38. Each formation 38 is produced by rolling the lower end of its respective flange 36 so as to produce a generally cylindrical recess to receive and hold the rods 22 of tungsten carbide.

In use, the holding device 26 holds the tungsten carbide elements 22 in the joint location as welding proceeds. The welding process actually destroys the lower portion of flanges 36, so that the tungsten carbide rods 22 are disconnected from the remainder of clip 28. However, the rods 22 are held long enough to become embedded in the welded joint. Moreover, the mild steel of the clip member serves, during welding, to cover and shield the tungsten carbide so as to prevent it being damaged by the heat of welding. The welding process commences with one of the rods 22, and then proceeds across to the other, so that they are incorporated into the welded joint in sequence.

In the embodiment of Fig 7, the welding method is substantially as described above, but the clips 40 have been modified so as to accommodate flat plates 42, 43 to be welded together. For this purpose, clips 40 have parts 44, 46, 48 corresponding to those 34, 36, 38 described above.

The embodiment of Fig 7 is used and operates in substantially the manner described with respect to Fig 6. In Fig 7 there is shown cut-resistant material on one side only of each of the clips 40, but if cut-resistance is needed on both sides, then the hardened material is provided on both sides of the joint.

Likewise, in the embodiment of Fig 8, a clip 50 is shown for cooperating with a triangular-section member 52, and has parts 54, 56 and 58 corresponding to the parts 44, 46 and 48 of the preceding embodiment, whereby the rods 22 of tungsten carbide are held in the appropriate location with respect to a joint between the triangular member 52 and an adjoining metallic structure 60. The method of making a joint is as described previously.

In the embodiment of Fig 9, the same reference numerals have been adopted as in Fig 8, with the addition of a suffix "A". The clip 50A is in the form of a single structure fitting round two full adjoining sides of the triangular section member 52A and locating the cut-resistant material 22 in an analogous manner.

Likewise, in Fig 10 the same convention with respect to reference numerals has been adopted as in Fig 9, but this time in relation to Fig 6.

Both the embodiments of Figs 9 and 10 correspond closely in function and use to those described above in relation to Figs 6 and 8.

In the embodiment of Figs 11 and 12 a round section member 70 in a form of a rod is joined to a flat section member 72 by insertion through an opening 74 therein. Cutresistant material in the form of discrete elements 76 of tungsten carbide are incorporated into the welded joint between the two members 72, 70 by means of a clip 78 providing an outer annulus 80 from which inwardly extending arms 82 extend and are formed with curled inner ends 84 to receive the cut-resistant material.

More than four arms 82 may be provided if desired.

Interestingly, the above embodiments provide a simple and inexpensive and conveniently-used method for incorporating cut-resistant material into a welded joint between two metallic structures. Protection for the tungsten carbide is provided during the welding operation, and the holding and protecting structure is automatically removed or released by the welding operation itself.

Amongst other modifications which could be made in the above embodiments are modifications to the shape and form and the dimensions and materials of the means for holding the cutresistant material in position during the welding operation, and likewise for the slugs or pellets or elements of cut resistant material themselves. Obviously, for this purpose, clips can be devised for use with any desired section of material to be welded.

Claims

1 A method of making a cut-resistant joint between two members, which joint is formed by melting a joint material around the areas to be joined, the method comprising a) incorporating a cut-resistant material in the joint material, which cut-resistant material is harder than the joint material; characterised by the steps of b) incorporating said cut-resistant material in the form of a discrete element in the joint material; and c) said step of incorporating comprising providing means to hold the element of cut-resistant material in the joint region during making the joint.

2 A method of making a cut-resistant melt joint comprising incorporating a cut-resistant material by holding an element of reinforcing material in the joint region during making the joint.

3 A method according to claim 1 or claim 2 characterised by employing a holding device, such as a clip, which is destroyed and/or removed either during or after the making of the joint.

4 A method according to any one of the preceding claims characterised in that one of said elements of cut-resistant material are provided in the joint made by the method, at each corner of the joint.

5 A method according to any one of the preceding claims characterised by providing said elements of cut-resistant material at intervals along the length of the entire extent of the joint.

6 A method according to any one of the preceding claims characterised by said means to hold the element of cut resistant material in the joint region comprising a spring member of mild steel which holds the element of cut-resistant material during the making of the joint either by friction or by a spring action.

7 A method according to any one of the preceding claims characterised by said step of incorporation comprising providing an element of said cut-resistant material at each of two corners of a joint to be welded, and by first incorporating one in the joint, and then the other, the latter of these being held by the holding means even though the former has been already incorporated into the joint.

8 A method according to claim 7 characterised by said holding means serving, during the making of a joint, to cover and shield the cut-resistant material so that the latter is not subjected to the full effect of the melt process.

9 A method according to any one of the preceding claims characterised by said two members to be joined defining a relieved region to receive the element of cut-resistant material.

10 A method according to any one of the preceding claims characterised by said means to hold the element of cutresistant material comprising a washer having inwardly curled portions to hold elements of reinforcing material at intervals around the periphery of a round section member to be joined.

11 A method of reinforcing a joint between two members, substantially as described herein with reference to the accompanying drawings.

12 A fabricated structure comprising a joint between two members formed by a method according to any one of the preceding claims.

13 Apparatus for use in a method of making a cut-resistant joint between two members, which joint is formed by melting a joint material around the areas to be joined, the apparatus comprising a holding device to hold an element of cutresistant material in the joint region during making of the joint.

14 Apparatus according to claim 13 characterised by said holding device being in the form of a clip which is destroyed and/or removed either during the period when the joint is made, or thereafter.

15 Apparatus according to claim 13 or claim 14 characterised by said holding device comprising a spring member of mild steel or the like.

16 Apparatus according to any one of claims 13 to 15 characterised by said holding member being adapted to hold said cut-resistant material either by friction or by a spring action.

17 Apparatus according to any one of claims 13 to 16 characterised by said holding device being adapted to hold an element of said cut-resistant material, one at each of two corners of a joint to be made.

18 Apparatus according to any one of claims 13 to 17 characterised by said holding device comprising a material adapted to serve, during the making of the joint, to cover and shield the cut-resistant material.

19 Apparatus according to claim 13 characterised by said holding device being in the form of a washer having inwardly curled portions to hold an element of cut-resistant material at intervals around the periphery of a round section member.

20 Apparatus for use in a method of making a cut-resistant joint between two members, substantially as described herein with reference to the accompanying drawings.

21 A security structure, such as a security window, comprising a melt joint between two members of the structure, characterised by said melt joint containing within the joint material a discrete element of a cut-resistant material embedded therein.