GB2156413A - Mounting for security glazing - Google Patents

Abstract

Improved resistance to spalling is achieved with security glazing in which the glazing, pane is able to move by at least 1 mm with respect to this figured frame on receiving an impact, before returning to its original position. The pane 1 is mounted in frame 2 having spigots 20 which engage in recessed portions 18 in the fixed frame 4 with resilient damping means 17 being placed between the spigot and the fixed frame. Appropriate relative dimensioning of the recessed portions with resilient damping means and the spigot enables the pane of glass to move on impact during criminal attack. <IMAGE>

Description

SPECIFICATION Improvements in or relating to mountings for security glazing This invention relates to mountings for security glazing, and in particular to mountings for that type of security glazing commonly known as anti-bandit glazing.

Laminated anti-bandit and bullet resistant glazing has been used for many years in security screen in stallatiobs in for example post offices, banks, building societies, shop and display windows, warehouses, offices, museums, showcases and art gallerys. The common feature of such glazing is the laminated glass construction by which is meant a construction formed of sheets of float glass bonded by intermediate layers of flexible bonding materials of which polyvinylbutyral (pvb) is the most commonly used.

It is primarily to glass specified as "anti-bandit" that this invention is directed. By "anti-bandit" is meant in particular resistance of the glass to sustained manual attacks from hammers, pick-axes, crowbars, bricks and other heavy implements likely to be employed by criminals. Such glass is subject in the United Kingdom to British Standard 5544.

For many purposes it is indeed desirable that anti bandit glass meets a higher standard which allows it to be termed "bullet-resistant" glass. For this purpose it will need to be able to withstand ballistic attack, the grade of glass chosen being matched to specific weapons likely to be employed. British Standard 5051 covers bullet resistant glass laminates ranging in thickness from 25mm to 78mm.

Glass is known to be an extremely brittle material having relatively little tensile strength. This property has a highly damaging effect on the performance of glass laminated security glazing. When the glazing receives a sharp blow to its front face, as can be expected in attacks with havey implements such as hammers etc, fragments and slivers of glass known as "spall", break off from the rear face of the glazing.

This spall can travel at high velocity and for a considerable distance, posing a danger to personnel behind the glass.

Spall can be responsible for lacerations to the face and for damage to eyesight. Hence a reduction in the amount of spall produced from a blow to security glazing has been previously attempted in so called spall-resistant security glasses. These normally include an additional very thin layer of glass bonded to the rear face of the security glass. Although decreasing the amount of spall produced, none of these spall resistant glasses have eliminated completely the problem of spall.

It is an object of the present invention to provide a mounting for security glazing which further reduces the spall produced during an attack on the glazing.

Accordingly there is provided a resilient mounting for a pane of glass comprising a frame having one or more recessed portions in which may closely be received an edge of a pane of glass, and resilient damping means between the frame and the pane of glass such that on the application of a blow to the pane of glass the edge of the pane is laterally movable with respect to the frame through at least 1 mm, the resilience of the damping means being such that the edge of the pane is subsequently returned to its original position.

According to a further aspect of the invention there is provided a resilient mounting for a pane of glass comprising a pane of glass; a frame havine one or more recessed portions in which an edge of the pane may be received, the one or more recesses being of a width substantially greater than that of the pane; and resilient damping means between the frame and the pane such that on the application of a blow to the pane of glass the edge of the pane is movable with respect to the frame through at least 1 mum, the resilience of the damping means being such that the edge of the pane is subsequently returned to its original position.

The present invention is based on observations by the applicant that the performance of panes of security glass which are relatively small in area is adversely affected due to the absence of the natural resilience present in relatively large panes of glass. Counter positions in offices where space is at a premium may be as narrow as only 0.5m across. Panes of glass for use in such counter positions will have very little natural resilience and hence the spall produced therefrom will be unacceptably high in the event of an attack. Resilient mountings according to the present invention at least partly compensate for this lack of natural resilience, thereby reducing the amount of spall which is produced.

It should be pointed out that although the improvement in the spall characteristics of the glass is most apparent in the case of relatively small panes of glass, mountings according to the present invention may also be advantageously employed in the siting of panes of larger area. Even where the glass is of such a size as to possess a considerable degree of natural resilience, mountings according to the present invention will further improve its resistance to spall.

The glass employed is preferably a laminated security glass. The applicant's co-pending UK patent application 8321555 describes a laminated security glass especially suited for use with the resilient mountings of the present invention.

Conveniently the resilient damping means is contained within the one or more recessed portions. The resilient damping means preferably comprises one or more elastomeric members disposed between the frame and the pane. Conveniently the one or more elastomeric members are formed of a soft rubber material of between 45 degrees and 55 degrees shore hardness. By rubber is meant any natural or synthetic elastomer.

At this point the distinction should be drawn between the elastomeric members of the above described arrangement and certain known types of mountings incorporating strips of rubber employed as a sealant.

Such rubber strips will impart a degree of resilience to the pane of glass but which is insignificant compared with that achieved by the arrangement according to the present invention. The oversized recesses and the thickness of rubber contained therein allow for movement of the edge of the pane through at least imm and more usually through more than 2mm should the pane of glass receive a blow. In sharp contrast the maximum movement of the edge of a pane clamped in previously known mountings is of the order of 25 lim (0.001 inch). Thus the movement allowed by the present invention is of the order of 40 times that achieved by mountings with simple rubber sealant strips.

In one convenient arrangement the resilient damping means comprises four elastomeric members disposed one at each corner of the pane with spaces therebetween. This arrangement allows the glass to be securely mounted whilst facilitating the transference of sound from one side of the glass to the other via the spaces provided.

In this way the provision of additional speech transferring means such as a speech grille or microphone, is rendered unnecessary. Alternatively, for extra security, the elastomeric members may be continuous throughout the entire circumference of the glass pane, further hindering any attempt to lever the pane from its mounting.

One embodiment of the invention will now be described in further detail, by way of example only, with reference to the accompanying drawings, in which; Figure 1 is a front elevation of a security screen suitable for use in a counter position incorporating a resilient mounting according to the invention, Figure 2 is a perspective view of the resilient damping means of Figure 1, and Figure 3 is a perspective view of a portion of the glass pane of Figure 1 which engages the damping means of Figure 2.

Referring to Figure 1, there is shown a security screen suitable for use in a counter position comprising of pane of laminated security glass 1, which pane is reinforced by a stainless steel border 2 in which the pane is secured by means of a sealant 3 (Figure 3). The pane 1 is constrained within a frame shown generally at 4 and comprising 2 upright members 5 and 6, and an overhead cross member 7. Each of members 5, 6 and 7 contains a longitudinal recess 8 in which the edge of the pane 1 and its associated border 2 is received.

The bottom edge of the pane 1 and its stainless steel border 2 are flush against a serving counter 9.

The counter 9 contains a service tray shown schematically at 10. Adjacent counter positions are shown attached to the frame 4 at 11 and 12 respectively.

Contained within the recesses 8 adjacent each corner of the pane 1 are resilient damping means shown generally at 13. Figure 2 depicts in more detail one of the damping means 13. A metallic cup 14 is supported on a false floor 15 firmly secured to the frame 4. The cup 14 is recessed to form a cavity 16 of rectangular cross section in which is contained a block of rubber 17, typically a soft rubber having a shore hardness of between 45 and 55 degrees. The block 17 is provided with a laterally disposed aperture 18 of generally square cross section, and one face of the cup 14 is slotted as shown at 19 to allow access thereto. The dimensions of the slot 19 are such that it is of a slightly greater width than that of the aperture 18.

Figure 3 shows that part of the glass pane which cooperates with the damping means 13. The stainless steel border 2 at each corner of the pane 1 extends to form a spigot 20. The spigot is of a square cross section, and, in use, is received within the aperture 18 in the rubber block 17 of Figure 2. If the pane 1 receives a sharp blow, for example from a sledgehammer or pick-axe, the spigot 20 is forced against the rubber block 17, causing it to to deform and compress. The edge of the pane therefore moves relative to the frame 4, typically through about 2mm. After the impact the rubber block 17 causes the spigot to return to its equilibrium position.

Resilient damping means 13 are provided in each of the 4 corners of the pane 1. This allows either independent movement of any particular corner of the pane (eg when a blow is directed towards one corner of the pane) or alternatively movement of all 4 corners simultaneously (eg when a heavy central blow is received). In addition to providing a location for the damping means, the recesses 8 provide a small gap around the edge of the pane through which sound can be transmitted from one side of the pane to the other. This method of sound transference allows speech to be understood behind the counter without the introduction of a direct path through the screen, through which an attack may be made.

Other methods of speech transference such as grilles and microphones may be used in addition to the recesses 8, but generally the use of such methods will be deemed unnecessary.

In order to illustrate the effectiveness of the present invention, the following non-limiting example is a comparison of the performance of the security glass of UK Patent Application 8321555 when rigidly mounted, and when resiliently mounted according to the invention. Similar panes of glass, measuring approximately 1m by 0.5m were mounted in frames and resiliently struck by a 71b sledgehammer. Suitably positioned trays behind the glass collected any spall produced which was periodically weighed. The amount of spall was determined; a. after the first blow, b. after a sustained attack for 20s, and c. after a further 40s attack.

Table 1 shows the results of such tests carried out on security glass which was rigidly mounted at each corner. Table 2 shows similar tests carried out on the same composition of security glass when resiliently mounted as in Figures 1 to 3. As can be seen from the Tables, the spall produced on the first blow is practically salved by the provision of the resilient mounting. This is a very important reduction as when the first blow of a bandit attack takes place a counter clerk is very often still in position close to the security glazing. In addition, the average amount of spall per blow throughout the 20 second attack was reduced by around 30%, and throughout the 40 second attack by around 50%. Thus not only in the resilient mounting seen to reduce spalling from the first blow, but throughout a sustained attack as well.

Table 1 - Results of Tests on Rigidly mounted Security class

Test no Spall on 20s attack 40s attack lse blow spall wt nc, of blows giblow pall wt no of blows s/blow 1 2.4g 49.2g 16 1 3.08g 121.6g ) 34 3.58g 2 1.2g 30.9g 16 1.93g 43.8 32 I.37g 3 3.3g 49.3g 18 2.74g 99.3 35 2.84g 4 2.0g 171.0g 18 9.50g 259.9 35 1 7.43g 5 2.7g 64.6g 19 3.40 94.8 34 2.79g ave 2.32g ave 4.13g ave 3.60g Table 2 - Results of Tests on Resliently mounted Security class

Test no Spa11 on 20s attack 40s attack |lst blow spall wt no of blows g/blow spall we no of blows1g!blow 1 O. lg 91.7g 21 4.37 75.4g 36 2.09g 2 4.0g 49.4g 24 2.06 40.6g 29 1.40g 3 1.8g 60.3g 24 2.51 51.lg 31 1.65g 4 Og 50.9g 20 2.55 20.4g 32 0.64g 5 0.3g 64.4g 19 3.39 88.3g 27 : 3.278 ave 1.24g ave 2.98g ave

Claims (13)

1. A resilient mounting for a pane of glass, which mounting comprises a frame having one or more recessed portions for receiving an edge of a pane of glass and resilient damping means to be placed in the frame between the frame and the pane of glass, which recessed portion(s) and resilient damping means are so dimensioned and the damping means possesses such compressibility that when a pane of glass is received loosely in said frame it will be laterally movable with respect to the frame through at least 1 mm and the resilience of the damping means will be such that the pane is subsequently returned to its original position.

2. A mounting as claimed in claim 1, wherein the resilient damping means is contained within the one or more recessed portions.

3. A mounting as claimed in claim 1 or 2, wherein the resilient damping means comprises one or more elastomeric members for disposition between the frame and a said pane.

4. A mounting as claimed in any preceding claim, wherein the one or more elastomeric members is/ are formed of an elastomer having a Shore hardness of from 450 to 55dg.

5. A mounting as claimed in claim 4, wherein the elastomer is a natural or synthetic rubber.

6. A resilient mounting for a pane of glass, substantially as hereinbefore described with reference to the accompanying drawings.

7. A window which comprises a pane of glass housed within the one or more recessed portions of the frame of a mounting as claimed in any preceding claim, which recess(es) is/are of greater with than the thickness of the pane so that the pane is held loosely in the frame and the damping means acting on the pane to permit its movement by at least 1 mm with respect to the frame on receiving an impact and its return to its original position.

8. A window as claimed in claim 7, wherein the pane is formed of laminated security glass.

9. A window as claimed in claim 7 or 8, wherein the resilient damping means comprises four elastomeric members disposed one at each corner of the pane, with a space existing between the pane and the elastomeric members.

10. A window as claimed in claim 9, wherein the elastomeric members are formed with recesses therein entered by edge regions of the pane.

11. A window as claimed in claim 10, wherein the pane is formed with projecting portions at corner regions which enter the recesses.

12. A window as claimed in claim 11, wherein the projections are carried on a border of non-glass material extending around the edges of the pane.

13. A window, substantially as hereinbefore described with reference to the accompanying drawings.