GB2176526A - Security bars - Google Patents

Abstract

A security bar has a plurality of discrete regions 3 of enhanced cut- resistance extending longitudinally of the bar and spaced apart circumferentially around the bar axis, preferably occupying corner regions of the bar in the case of a bar of rectangular or other polygonal cross- section. These cut-resistant regions are formed by melting onto the steel case 1, or onto or comprising the corners of tubular bars, welding wires or rods composed of particles of tungsten carbide or other material of extreme hardness, and a fusible binder therefor. <IMAGE>

Description

SPECIFICATION Security bars The present invention relates to security bars which may be made up into grilles or gratings eg to cover the window openings in security buildings for protection against intrusion or escape, for use as glazing bars or mullions in security applications, or for use more generally in the field of security grilles and shutters.

Bars intended for the kind of service indicated above clearly must possess qualities of resistance to bending and cutting matched to the level of security required of the grille or other structure into which they are to be incorporated. In particular, one aim of the present invention is to provide security bars which are simple to fabricate and capable of resisting for a protracted period of time attacks with the latest generation carbide-coated rod- or hack-saws, which are capable of severing traditional all-steel window bars in an unacceptably short time.

In one aspect, the invention resides in a security bar having a plurality of discrete regions of enhanced cut-resistance each extending longitudinally of the bar and being spaced apart circumferentially around the axis of the bar, where said regions are formed by melting onto supporting structure compound elements composed of particles of a material of extreme hardness and a fusible binder therefor.

The hardness of said regions of enhanced cutresistance is preferably not less than 68 on the Rockwell scale and more preferably considerably in excess of that value.

The invention will be more particularly described, by way of example, with reference to the accompanying drawings, which illustrate respectively five embodiments of the invention each in cross section.

Fig. 1 illustrates a compound security bar structure comprising a steel core bar 1 encased in a steel sheath 2. In order to enhance the cut-resistance of this structure the core bar 1 carries hard weld deposits 3 at four circumferential locations so as to occupy the internal corner spaces of the sheath 2 in the assembled bar. The hard deposits 3 preferably comprise tungsten carbide and may be applied in four stripes along the length of the bar 1 by melting onto the bar welding wires or rods containing powdered tungsten carbide with a mild steel binder. The compound bar is assembled by first applying the hard deposits 3 to the core 1 and then passing the sheath 2 endwise over the bar 1. If desired, the void spaces left between the bar 1 and sheath 2 in this assembly can be filled with a resin or other suitable filler material 4 cast into the voids.

In Fig. 2 a tubular security bar is constructed by welding together the free margins of two steel channel sections 10 and 11.

Prior to this operation, however, hard weld deposits 12 of similar composition to the deposits 3 of Fig. 1 are applied along the two internal corners of each section, to confer a high degree of cut-resistance to the completed bar. By appropriate selection of the material and wall thickness of the two channels 10 and 11 the fabricated tube in this embodiment may exhibit sufficient resistance to bending without further reinforcement. If greater bending resistance than that exhibited by the tube alone is required, however, the tube 10/11 together with its hard deposits 12 can be assembled with a core bar 13, and the voids between the core and tube filled as in the Fig.

1 embodiment if desired.

Fig. 3 shows a variant of the Fig. 2 embodiment in which hard weld deposits 12' are again applied to the internal corners of two channel sections 10' and 11' before the latter are united to form a tubular security bar. In this case, however, the bar is constructed by first depositing the hard material within steel angle sections 14 which latter are then welded to the respective channels 10' and 11'. This process may have the advantage over that described with reference to Fig. 2 of minimising any thermal distortion of the two channels before they are united. In Fig. 2 the channels 10 and 11 may be distorted by the deposition of the hard welds 12 and a subsequent straightening operation could disrupt the bond between the channels and welds. In Fig.

3 the angles 14 with the deposits 12' can be straightened, if need be, prior to their attachment to the channels 10' and 11'. Subsequent welding of the angles 14 to the channels requires significantly less heat input than the deposition of equivalent welds directly to the channels, and once the angles are attached the contained deposits 12' are securely retained against disruption.

In Fig. 4 a tubular security bar is formed from four steel flats 20 united by a cut-resistant hard weld 21 at each corner of the fabrication. The deposits 21 may be of similar composition to the deposits 3, 12 and 12' in the previously described embodiments although in this case an outer surface layer of ordinary, softer weld material will be applied over the hard welds so that the corner regions of the bar can be more readily dressed to conform to the desired external profile. Depending upon the performance required of the bar structure an internal core bar and/or further hard weld deposits at the internal corners of the completed structure might also be provided.

Fig. 5 shows a tubular steel security bar 30 of a profiled cross-section similar to that shown in UK Patent Application No.

2129859A. In this case the cut-resistance of the bar is enhanced by hard weld deposits 31 of similar composition to those described above, which are applied to longitudinal grooves machined in the external bar surface at several circumferential positions. Such a bar may be finished eg by painting or may be clad in an external stainless steel sheath to improve its appearance. If still greater resistance to cutting should be required, the tube should be filled with a composite comprising nuggets of alumina or similar hard material within a polymer matrix, also as described in GB 21 29859A.

Although we have referred above to tungsten carbide particles in a mild steel matrix as the material of the hard deposits 3, 12, 12' and 21, alternative materials may be employed to confer the desired level of cut-resistance to the illustrated structures, it being appreciated that the effective resistance to cutting through a hard weld deposit is a function not only of the absolute properties of the hard material included but also of the deposition technique which might predicate different binder phases.

Particular alternatives which may be found useful in structures according to the invention include tungsten carbide in nickel and/or cobalt matrices and chromium boride in a nickel matrix.

Claims (10)

1. A security bar having a plurality of dis Crete regions of enhanced cut-resistance each extending longitudinally of the bar and being spaced apart circumferentially around the axis of the bar, where said regions are formed by melting onto supporting structure compound elements composed of particles of a material of extreme hardness and a fusible binder therefor.

2. A bar according to claim 1 comprising a tubular structure of polygonal cross-section and where said regions of enhanced cut-resistance are located at corner regions of said tubular structure.

3. A bar according to claim 2 comprising an outer tube of generally rectangular crosssection within which is a core bar of generally circular cross-section onto the external surface of which said regions of enhanced cut-resistance are deposited, by melting elements as aforesaid, so as to lie adjacent to the internal corner regions of the tube in the assembled structure.

4. A bar according to claim 2 comprising a tube of generally rectangular cross-section which is fabricated by uniting two channel sections which bear said regions of enhanced cut-resistance at the internal corner regions thereof.

5. A bar according to claim 4 which said regions of enhanced cut-resistance are formed by melting elements as aforesaid onto the surface of said channel sections at the internal corner regions thereof, prior to uniting those sections.

6. A bar according to claim 4 wherein said regions of enhanced cut-resistance are formed by melting elements as aforesaid onto supporting members which are then attached to said channel sections at the internal corner regions thereof, prior to uniting those sections.

7. A bar according to claim 2 comprising a tube which is fabricated from a plurality of flat elements welded together at positions corresponding to the corners of the completed tube wherein the welds which lie at said corners define said regions of enhanced cut-resistance.

8. A bar according to claim 1 or claim 2 comprising a tubular structure having said regions of enhanced cut-resistance deposited, by melting elements as aforesaid, into grooves provided in the external surface of said tubular structure.

9. A bar according to any preceding claim wherein said regions of enhanced cut-resistance are formed by melting compound elements composed of particles of tungsten carbide and a mild steel, nickel or cobalt binder therefor, or particles of chromium boride and a nickel binder therefor.

10. A security bar substantially as hereinbefore described with reference to Fig. 1, Fig.

2, Fig. 3, Fig. 4 or Fig. 5 of the accompanying drawings.