AU2008200562A1 - Laminate for use in a flameproof enclosure - Google Patents

Description

.£-1.0-800Z alea L.:8L atU!L :e!leJsny dl Aq pa!aeoaH 90LL I-SOlV :ON 1a SINOO P/00/011 lation 3.2 Regu

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: LAMINATE FOR USE IN A FLAMEPROOF

ENCLOSURE

Applicant: Commonwealth Scientific and Industrial Research Organisation The following statement is a full description of this inv including the best method of performing it known to me: 1 ention, O6tJAfl S'd U1 D ONOW Sdl ]Hd 60: 8006NVrL I.E-L-900 aea .1:81 S aiW! :e!leJ)lsn dl Aq paA!ao8 90cSLLI-SOV :ON 01 SOO I LAMINATE FOR USE IN A FLAMEPROOF ENCLOSUkE Field of the Invention The present invention relates to a laminate for use in a flameproc a panel for a flameproof enclosure including said laminate, and E enclosure including said laminate.

Background of the Invention Hazardous areas, in which potentially explosive atmospheres encountered in a wide variety of industries. In coal mir combustible gases such as methane occur naturally, and in oil chemical plants, gas works, or any other places where a flammi vapour may be present, it is a requirement that safeguards be electrical equipment to prevent ignition of the gas or vapour and explosion or fire.

Flameproof protection essentially refers to the placement of al apparatus within a special enclosure that is capable of con explosion that initiates inside. Flameproof enclosures provide fo protection for electrical equipment, such as lighting and power inst which the enclosure will withstand, without injury, any explo flammable gas that may occur within it. There are a number of Na International Standards which regulate the features and pro flameproof enclosures. In Australia, the relevant standard is set Ex(d) category of the International Electrotechnical Commission the Australian and New Zealand (ANZEx) standards. Importantly, 1 enclosures must prevent the transmission of flame such as will flammable gas which may be present in the atmosphere surrot flameproof enclosure. Accordingly, flameproof enclosures must e any explosion within the enclosure does not create an external expl 2 f enclosure, flameproof exist, are es, where refineries, ible gas or applied to ;onsequent I electrical taining an a type of llations, in sion of a itional and perties of out in the (IEC) and lameproof ignite the nding the isure that :sion.

q 'd 18 'Oki jNOMO SdillIHd 60:Lt GOHVV E' L LE-LO-SO0Z ale( L: aUJL :e!leJlsnV dl Aq pOA!aOaU 90LLL-SOV :ON 11 ShAOO It is therefore essential that the mechanical design of the enclosure is such that, not only can it can withstand the ex further, that it prevents any explosion initiating inside the enc igniting the external atmosphere. This latter requirement is ensuring that joints and other openings (such as bearings) sufficiently long and restricted flame path to prevent external igni designs use special wide flanges that enable any flame escapin joint gap to be quenched before it reaches the potentially atmosphere outside the enclosure.

A flameproof joint corresponds to the position at which correspond a flameproof enclosure come together. It is here that the flame or combustion may be transmitted from the inside to the outs flameproof enclosure. The shortest path through a joint from the ii outside of a flameproof enclosure is known as the length of lar strictly defined gap, being a distance between corresponding su flameproof joint, is provided when the electrical equipment assembled. This gap assists in relieving the pressure inside the caused by an explosion.

Typically, flameproof enclosures are manufactured from metal, su and have a removable flameproof cover enclosing a flameproof Where the flameproof enclosure is constructed solely of a rr necessary to remove the flameproof cover in order to visually ii flameproof chamber and/or its contents. This requiremen cumbersome and time-consuming and requires extreme care by a so as not to damage the flameproof joints in the process.

Flameproof enclosures with transparent windows are known in th However, due to limitations on the size of non-metallic sections of i enclosures imposed by the Australian and International standard, risk of ignition by static electricity the acceptable window size is small. Typically, the maximum acceptable window size is 500 3 flameproof )losion, but osure from chieved by provide a ion. Some 1 through a flammable ng parts of )roducts of de of the 'side to the iepath. A faces of a has been enclosure ;h as steel chamber.

ietal, it is ispect the is both i operator industry.

lameproof i, and the relatively

I

m 2 The 9 'd Z18 *ON 9NOMO SdIlI[Hd 60 Ll 200Z 'NV E 1E- 0-800s ale .9:81. (tu:H) awLU :e!lejsnV dl Aq pa' !Oa 909LLL-SOEIV :ON 1I SIAIO transparent materials used in the prior art are principally tougF and polycarbonate. Toughened glass is often used for relativ windows where heat is generated, for example a headlight Polycarbonate is typically used for relatively larger windows, such panels for computer screens and controllers. Desirable prope window material are that it is clear, tough and impact resist preferred properties are low combustibility, heat resistance, resistance, abrasion resistance, mechanical strength, durability, inert, and grease and oil inert.

Smaller transparent windows, particularly those of polycarbonate, to have less static electricity risk associated with them in atmospheres than larger ones given their small surface area.

larger windows would allow for greater visual inspection of t workings of the flameproof chamber while the electrical power is Fault finding in potentially explosive atmospheres is usually perfk the power de-energised and the cover open. This means tha finding procedure relies on intuitive guesswork, experience, an( knowledge of the equipment. The effectiveness of the repair p only proved by closing and bolting the cover and re-ener equipment. Clearly, this creates an expensive maintena particularly if the fault persists.

The above discussion of background art is included to explain the the present invention. It is not to be taken as an admission that material referred to was published, known or part of the comm knowledge at the priority date of any one of the claims of this speci It would therefore clearly be desirable to provide means for enhan inspection of a flameproof chamber without compromising properties, while minimising the likelihood of static electricity bui thus the risk of explosions.

4 ened glass ely smaller enclosure.

as viewing ties of the .nt. Other corrosion chemically are known explosive However, e internal energised.

rmed with t the fault I a sound )cedure is 3ising the ce effort, context of any of the n general ication.

ced visual lameproof Id up and t 'd Zt8 'ON CNOM0O Sdl Hd 60'Lt 800'NVr"E L:-L-900Z (P-4-jk) alea 1L:8. auLL :e!lJlsnv dl Aq paAO3ajl 9OSLLL-SOIV :ON (I SIf00 The inventors have now surprisingly found that it is possible to ms visual inspection panel, having static dissipative properties, for e enclosure which is significantly larger than that of the prior ad retaining the necessary mechanical strength and explosio properties. The panel enables the visual examination of the chamber of the flameproof enclosure when in use when in th state) to allow for more effective fault diagnosis. The developmen laminate by the inventors has enabled the production of suc Moreover, the replacement of a significant portion of steel in tl panels with the novel laminate results in weight savings an( improves handleability and reduces risk of injury.

It is therefore an object of the present invention to provide a lamir in a flameproof enclosure which overcomes, or at least alleviat more disadvantages of the prior art. It is another object to provii inspection panel including said laminate. It is a further object tc flameproof enclosure including said laminate.

Summary of the Invention According to the present invention, there is provided: a transparent laminate for use in a flameproof enclosure, th including at least two layers of a transparent material laminated to( laminate having first and second major outer surfaces, wherein at of the outer surfaces has static dissipative properties.

The thickness of the laminate should be such as to confer mechanical strength and explosion resistant properties, suct necessary for a flameproof enclosure, without unduly compron transparency of the laminate.

nufacture a flameproof whilst still i resistant flameproof energised of a novel la panel.

e prior art therefore ate for use is, one or e a visual provide a laminate ether, the least one sufficient as are ising the S'd L88 'ON ONOW Sdll]Hd di:L 800']NVri E alea 1. :8L (uJ:H) awuj :e!lejlsnv dl Aq paA!aoaO 909LL L-SOfvl :ON al SVOO The inventor has found that there are two principal laminate prope need to be considered for determining the optimum thickness of th The first is the maximum bending stress, which should not excee strength of the laminate. The second is the desired maximum d the laminate when subjected to pressure from an explosion. Ea( properties is dependent on the dimensions (width and height) of tias well as on the test pressure which is determined from the maximum pressure exerted on the laminate by an explosion pli margin. In accordance with industry practice, the test pressure particular laminate size and design is typically determined by the c authority during the flameproof testing and accreditation process. F Manufacturers need to rely on previous accreditation data or I enough with flameproof design to estimate the likely test pres particular design. The value of the test pressure includes a sg which is applied in accordance with the relevant design standard.

In order to estimate the minimum thickness of a laminate required below its yield stress, the present inventor has produced a firsl curves which are shown in Figure 1. Each curve in Figure 1 re constant yield stress parameter which has been plotted as a the dimensions, (width and height) of the laminate. In order to ca required minimum thickness of a laminate having a width an the yield stress parameter is read from Figure 1. The thickr mm of the laminate required to keep the laminate below its yield str application of the test pressure P in MPa is calculated using equatic ty fUP An alternative way of calculating the desired minimum laminate th using the maximum allowable deflection of the laminate when su the pressure exerted on the laminate by an explosion. The prese has produced a second series of curves, illustrated in Figure 2, w represent a deflection parameter plotted as a function of the.d 6 rties which s laminate.

d the yield .flection of :h of these e laminate anticipated s a safety S(P) for a ertification lameproof )e familiar sure for a fety factor to keep it series of )resents a unction of culate the Sa height ess (ty) in ss during n (1) ckness is ajected to it inventor hich each mensions [:LN 800 'NVr 'L 0 6 'd U~8 'ON CNOMO SdIllLHd L.£-1O-800Z aea awLL :e!lejsnv dl Aq paA!aoa8 90SLLL-SOaV :ON C1 SYLOO (width and height) of the laminate. The minimum thickness (td) laminate required to achieve a particular maximum deflection exerted by the test pressure P in MPa is determined from equatioi td 3(g.Pd) (2) For given laminate dimensions and pressure, typically ty and similar values. However, if restrictions are placed on one of the I for example the maximum deflection d, then one value may pr Typically, both ty and td are calculated for a particular lamina greater value is used for the actual laminate thickness.

Suitable materials for the laminate should be transparent and coml appropriate Standard for construction of flameproof enclosures.

currently recognises two Standards, which are very similar in con are ANZEx (the Australian and New Zealand Standard) and International Standard). Both Standards describe flameproof eqt Ex(d) protection. The materials are typically explosion and, resistant, with low combustibility. The material may be a t polymer, such as polycarbonate or polymethyl methacrylal (toughened) glass. Preferably the transparent material is a pol) due to its high transparency, strength, relatively low combustibility of lamination. In a preferred embodiment, the laminate includes one layer of clear PC-300 T M Polycarbonate from SciCron Technolo( The lamination process used will depend on the materials use laminate. In the case of a laminate of polycarbonate layers, the i process may involve adhering together a number of sheets of poly preferably using polyurethane as the adhesive between adjacer Preferably, the assembly of polycarbonate and polyurethane are su a vacuum treatment to remove any air from between adjacent poly sheets. This promotes the migration of gas molecules from around the polyurethane material and thereby prevents gas bubbles from 1 the final product. The evacuated assembly is then subjected to 7 in mm of a in mm, <i will yield arameters, edominate.

:e and the )ly with the Australia :ent. They ECEx (an lipment as or impact ansparent e, and/or carbonate and ease is at least lies, LLC.

d for the amination arbonate t sheets.

Djected to ,arbonate nd within arming in eat, and 01 'd U8 'ON ONOM~O Sdl ]Hd 01:11 800'NVr l 1E-.0-800 aleG 1LL:8 (rw:H) awLL :eejsnv dl Aq paA!aOal 909LL.-SOaV :ON (l SVIOO possibly also pressure, in order to bond the sheets together. Ty temperature of lamination is in the range of 110 to 120"C. The y lamination is usually around 1 atmosphere.

It has been found by the inventors that lamination imparts ad.

mechanical properties not present in a monolithic sheet of equal Furthermore, thick monolithic sheets often must undergo fabrication processes to avoid structural stresses therein whici significantly higher costs as compared to a laminate of thinner addition, commercially available static dissipative treatments are available for application to thick polycarbonate sheets. Specialis treatment of the thick sheets in small batches would also add sigr the cost.

Advantageously, polycarbonate sheets are available in a thicknesses and accordingly, laminates of many thicknesses produced. The total number of layers in the laminate will be depenc desired thickness of the laminate and on the thicknesses of the transparent material used to make the laminate. Typically the includes more than two layers of a transparent material laminate( The laminate may include three or more layers of a transparent ma preferred embodiment, the laminate includes four layers of ti material.

Typically the thickness of the laminate is between 16 and 60 mm.

range of thickness for the laminate material is between 20 mm ar Where the laminate is intended to include apertures therethrough operating means (eg push buttons or the like) for operation of eqi the enclosure, the laminate thickness is preferably greater than 2 more preferably is a minimum of 32 mm. In a preferred embod laminate is a laminated polycarbonate sheet which has a thickness and which further has an anti-static coating applied to at least surface, or the at least one outer surface is treated so as to h 8 pically, the )ressure of antageous thickness.

specialised i leads to sheets. In rot readily 3d surface ificantly to range of may be ent on the sheets of laminate I together.

:erial. Ina ansparent A suitable id 50 mm.

to receive jipment in mm and ment, the of 32 mm one outer ave static I I 'd ZL8 'ON HOM~tO Sdl [Hd 0d:L[ 800S'NVr Vl I L£-LO-800Z aeo L .:81 awJ :e!lejlsnv dl Aq paA!aoaN 909SLL-SOIV :ON (I Sn0OO dissipative properties. Preferably, the at least one outer surface is treated to have static dissipative properties.

The static dissipative surface prevents charge buildup on th surface, thereby preventing electrostatic discharge events. Wh one major surface of the laminate should have static dissipative p is preferred that both major surfaces have static dissipative Furthermore, the static dissipative outer surfaces of the laminate e essential to obtain certification for use with flameproof enclosure ii atmospheres. The outer major surfaces of the laminate may be treated (surfaced) so as to produce the static dissipative Preferably the surfacing comprises a hard cured polymeric coatir preferably, the surfacing is thin, such as less than 10 microns, f( about 1 micron thick. Alternatively, an anti-static coating may be example by spraying or painting, to the surfaces of the lamir composition of such a coating may be one based on tin and ind While any of a number of antistatic treatments may be used, a prel static surface is one which has been treated with a composition b tin and indium oxide. In a preferred embodiment, the laminate i least one layer of clear PC-300M Polycarbonate from SciCron Tec LLC. PC-300 Polycarbonate is a polymer sheet product de control static electricity and is comprised of a polycarbonate sheet been treated with SciCron Technologies' proprietary, clear, C-3( dissipative surfacing. The static dissipative surface is a result c treatment of the surface, rather than a simple applied co consequently, is more permanent and scratch resistant. It is impe the static dissipative surface is properly grounded when in use.

According to the present invention there is also provided a transpa for a flameproof enclosure, said panel including a transparenl including at least two layers of a transparent material laminated to, laminate having first and second major outer surfaces, wherein at of the outer surfaces has static dissipative properties, and conducti 9 chemically e laminate ile at least "operties, it properties.

re typically 1 explosive chemically properties.

g. More )r example ipplied, for ate. The ium oxide.

erred antiased upon icludes at hnologies, 'signed to which has 0TM static f a curing ating and rative that rent panel laminate ether, the least one pg means 'd 7tS 'ONi CNOMO SdlllHd I[LI 800 'NVn'E I LE-LO- 00 ae LL..:8 awL :e!leilsnVdlAq paA!aoa 90ZgLI.-SOV :ON I SIAYO dissipative for conducting electrostatic charge away from the surface/s.

said static According to the present invention there is further provided a enclosure including: at least one explosion resistant side wall; one or more transparent panels including a transparent laminate i least two layers of a transparent material laminated together, th having first and second major outer surfaces, wherein at least major outer surfaces has static dissipative properties; and conduc for conducting electrostatic charge away from the said static surface/s; and means for connecting said panel(s) to said at least one side wall.

Iflameproof Preferably, the both outer surfaces of the panel have static properties.

The panel may comprise an integral part of a wall of a flameproof or may comprise a flameproof cover for a flameproof enclosure. Ty panel comprises a flameproof cover for a flameproof enclosure.

Preferably, the conducting means includes a supporting frame i contact with the static dissipative surface/s. However, it is not es the flameproof cover to include a frame. The laminate may be directly to the flameproof enclosure, as long as it has sufficient strength and there is an electrical pathway from the static dissipati to the flameproof enclosure. Such an electrical pathway may be simply by bolts extending through the laminate for connecti flameproof enclosure, whereby the bolts provide electrical contac the static dissipative surfaces and the flameproof enclosure.

contact may be enhanced by grounding wires between the bolt static dissipative surfaces.

ii r cluding at e laminate one of the ing means dissipative dissipative enclosure pically the electrical sential for onnected echanical e surface provided n to the between Electrical and the E~l 'd i18 'ON ONOWO SdIllIHd 11:11 2001NVVLe L-1-800 aea W.LB awL :esIwsnv dl Aq PaA!aOa8 90SLL--SOV :ON (I SIAOO Where the panel comprises a flameproof cover, typically, the fram incorporation of the transparent laminate panel into the flameproc in a manner which provides for a flamepath between the flame and the side wall of the flameproof enclosure. The panel alsc includes connecting elements for attaching the panel to the flameproof enclosure (typically bolts).

Typically the frame is constructed from metal, preferably steel.

steel may be used, alternatively mild steel (grade 250) or stainle brass could also be used.. The laminate is preferably retained in the frame by retaining means, typically comprising one or mor strips or a retaining ring which can be attached to the frame by a means (such as by screws or bolts). An adhesive may also I further secure and seal the joint between the laminate and frame.

It should be noted that the use of an adhesive (dependi composition), may result in some electrical insulation between the the laminate, thereby hindering the antistatic properties of the or laminate surfaces. Should this be the case, the panel advantage include secondary conducting means located in direct electrical c one or more static dissipative surfaces of the laminate. The conducting means preferably comprises a metal strip, such as a cc band or braid, which is retained in a groove in the frame awal adhesive joint. Preferably the groove is located in an upper sec frame so as to minimize collection of dust/debris therein whe Alternatively, the secondary conducting means may simply ci conduction (earth) wire for establishing an electrical pathway fr each static dissipative surface to the frame.

e allows for f enclosure )roof cover preferably N'all of the Grade 360 ss steel or a rebate in a retaining iy suitable ie used to ,ig on its frame and e or morn ously may )ntact with secondary pper or tin from the ion of the n in use.

)mprise a )m the or The connecting means should conform with the appropriate construction of flameproof enclosures (in Australia, IEC Ex(d)).

11 stAindard for t 'l UL8 'ON ONOO Sdfl1LHd [:LI 900'VC'LE I LE-LO-0 alea W SL:8 ew!li :e!lwejsnv di Aq pa!woaj 90SZLL.-SOV :ON al SINOO Where the panel is a flameproof cover, typically the connecing means comprises detachable connecting elements provided on one or ore of the panel and the wall of the flameproof enclosure. Preferably, the connecting elements comprise holes in the frame of the panel which are ali nable with corresponding holes provided on the wall of the flameproof enclos re through which may be received bolts or screws.

Alteratively, where the panel comprises part or all of said al least one sidewall, the means for connecting the panel to the flameproof e nclosure is permanent and may be, for example, welded joints.

As previously noted, the transparent panel may include aperture, extending therethrough for receiving, pushbuttons, switches mechanical lev rs and the like. Typically such apertures are provided in the laminate and if so, are reinforced and sealed so as to not undermine the integrity of the ameproof enclosure.

Detailed Description of Preferred Embodiments The invention will now be described in greater detail with refere ice to the Examples and accompanying drawings in which: Figure 1 is a graph of the yield stress parameter plotted as a unction of laminate width and height (both in mm).

Figure 2 is a graph of the deflection parameter (g x 106) plotted as a function of laminate width and height (both in mm).

Figure 3 shows a perspective view of a first embodiment of a tr nsparent panel in accordance with the present invention, comprising a fameproof cover.

Figure 4 shows a cross-sectional view taken along line A-A of Figure 3.

12 718 'ON NOMO SdIlllHd :11 800i 'NVf 'lE LE-10-800 aea 11:81 awU!l :e!leJlsnv dl Aq paA!aOaH 90SZLLL-SOHV :ON (l SnYOO 00 0 SFigure 5 shows a front view of a flameproof enclosure including a second embodiment of a transparent panel, in accordance with an embodiment of the invention.

cO I 5 Figures 6a and 6b show rear views of the transparent panel shown in Figure O 00 0 Figure 7 is a partial cross sectional view along the line VII-VII of Figure 6b.

Examples: Example 1; Method of Manufacturing Laminate In this preferred embodiment, the laminate of the invention comprises a polycarbonate laminate which is manufactured by laminating together commercially available polycarbonate sheets of desired thick ess. In particular, it is formed from four thinner polycarbonate sheets. Two outer sheets, each having a thickness of 6 mm, and comprising PC-300TM Polycarbonate are placed on either side of two inner sheets of untreated/uncoated polycarbonate, each having a thickness o 9.5 mm (LEXAN 9034 clear 112 PE purchased from Mulford Plastics). Po yurethane bonding medium comprising a heavy film of polyurethane, is place between adjacent polycarbonate sheets. Accordingly, the inner ayers of polycarbonate do not have static dissipative properties on t eir outer surfaces. The outer layers each comprise a sheet of the PC-300

T

M

polycarbonate having static dissipative properties on one major surface thereof. These outer layers are arranged such that their respective static dissipative surfaces are facing outermost on the laminate. The f ur layers are then laminated together using an industrial lamination techni ue. The polycarbonate layers were arranged with a thin (less than 1mm thick) sheet of the polyurethane between adjacent layers. The assembly was then mechanically secured, so that the layers remained aligned, while the 13 9 'd 718 'Ohl flNOMO Sdll1IHd OI:L[ 800 NVr l I Ic-O--OOZ (PI al I:L (Uw:H) aIlu :eq!ejsnv dl Aq paA!aMa j 90LLL-SO8V :ON OI SIA OO surrounding air was evacuated. The temperature of the assembly slowly to a temperature sufficient to melt the polyurethane sheet, approximately 120°C and maintained for a sufficient period of tir bonding. The temperature was then slowly lowered to room te The final thickness of the laminate, according to this embi therefore approximately 32 mm.

was raised typically to ne to effect ,mperature.

diment, is Examples 2 and 3: Determining Optimal Thickness of Laminate Example 2: A polycarbonate laminate with a height of 650 mm an 480 mm is intended to withstand a test pressure of 1.1 MPa (16C Figure 1, the thickness parameter, f, for a laminate having those is approximately 40. Using equation the laminate thicknes! therefore be at least: ty= 40 x 41.1 42 mm.

Example 3: A polycarbonate laminate with a height of 650 mm ane 480 mm must be able to withstand a test pressure of 1.1 MPa (1t a deflection of less than 54 mm. From Figure 2, the deflection pa; for a laminate having those properties is approximately 1.6 x equation the laminate thickness td is calculated to be: td 3(1.6 x 10x 1.1 54) 32 mm.

Description of Drawings Figures 1 and 2 have been described in detail in the discussion of 2 and 3. Embodiments of a transparent panel according to the in% now be described in detail with reference to Figures 3 to 7.

Figure 3 illustrates a transparent panel according to one embodirr invention, wherein said transparent panel comprises a flameproo: for a flameproof enclosure. The flameproof cover 10 includes a tr laminate 12, shown being supported within a frame 14 comprisin 14 i a width of psi). From Jimensions ty should a width of 0 psi) with ameter, g, 106. Using Examples ention will ent of the cover ansparent 3 first and II 'd LS 'ONi CNOMO SdIllHHd Z 20H *NVr 'LE IS-LO-900 ale(] .:8L awLu :elejsnv dl Aq paA!aOaH 90SLLl.-SOUV :oN (1 S"1tOO second frame members 14a and 14b. The transparent laminate and second major outer surfaces 12a and 12b, both of which, the present embodiment have static dissipative properties.

members 14a and 14b are each constructed from steel and there conducting means for conducting electrostatic charge awa\ respective static dissipative surfaces 12a and 12b. The laminate position within the frame 14 by means of bolts 16. The bolts used to fix the flameproof cover 10 to a flameproof enclosure (not Figure 4 shows a cross-sectional view taken along line A-A of the cover 10 of Figure 3. The laminate 12 of the flameproof cover four layers and is manufactured in accordance with Example 1 above. The laminate comprises two outer layers 13a, 13b eac thickness of 6 mm and comprising a sheet of PC 300T m Polycarb two inner layers 13c, 13d are each 9.5 mm thick and comprise ai polycarbonate sheet.

Figure 5a shows a flameproof enclosure 100 including a second e of a transparent panel according to the invention, comprising a cover 110. The flameproof cover 110 includes a transparent lar supported within an electrically conductive metal frame 114. Figurn a front perspective view of the flameproof cover per se. The frs comprised of a mechanically strong and explosion resistant matc comprised of the same material as the main body of the flameprool 100, which in this case is steel.

The flameproof enclosure 100 also includes explosion resistant si4 which only side wall 115 is shown. The flameproof cover 110 is to the side wall 115 by connecting means comprising a series of which are located at regular intervals along the periphery of the f The bolts 116 extend through the frame 114 of the flameproof cove into the side wall 115 of the flameproof enclosure 100 to hold the 1 cover 110 in position. A small gap 117 exists between the fram 12 has first iccording to The frame bre provide from the 12 is held in 16 are also shown).

flameproof 10 includes discussed h having a nate. The 1 untreated "nbodiment flameproof ninate 112 5b shows me 114 is rial and is enclosure e walls of onnected bolts 116 ame 114.

r 110 and ameproof 114 and 81 'd L 'ON CNOM~O SdIIIHd Oi:L[ 800 'NVr IE Lk-LO-800O (P-I4-A) ale L1:81 (wL:H) awJ :etlejwsnv dl q paAlaoaN 909LLL-SOdV :ON l SINOO side wall 115. In operation under explosive conditions) escape via the gap 117, at which time the flames are extinguishec The frame 114 includes a visor 118 which provides for shiel flameproof cover 110 from falling debris, thus preventing the cover 110 from becoming scratched or damaged.

Apertures 122 are provided in the laminate 112 to receive opera and/or a control panel (not shown). In the embodiment shown, th means include push buttons 124 and switches 126 which may operate machinery (not shown) inside the flameproof enclosure 10 For comparison purposes, to the right of the flameproof cover 110 conventional flameproof cover 110'. It includes a small window t constructed from polycarbonate. Because of the inherent lack of strength and risk of static electricity buildup, the window 112' is f smaller than the laminate 112 of the invention, thereby seriousl visual inspection of the flameproof chamber.

Turning now to Figures 6a and 6b, there is shown a rear elevatio perspective view, respectively, of the flameproof cover 110 show Figure 6a shows the rear side of the frame 114 in which is rebate 126 for receiving the laminate 112 (not shown for simplicity) is adhered using a suitable cement comprising a silicone sealant.

of suitable silicone sealants include those sold under the tra Silglaze N-10 and RTV 1608. Given that the cement can result ir insulation between the frame 114 and the front static dissipative sul of the laminate 112, secondary conducting means in the form ol braid 128 is also provided (see Figure The copper braid 128 is a recess 125 provided in the upper part of the frame 114. It i therein by a retaining element comprising a steel bar 127 which is a the frame 114 by means of recessed screws 129. The braid 12 16 gases may ding of the flameproof ting means e operating be used to 0.

is shown a lerein 112' nechanical ignificantly r hindering n and rear i in Figure 3rovided a wherein it Examples le names Selectrical face 112a a copper located in retained ttached to Sprovides 61 'd Zt8 'ON CNOMO SdlllHd EI:L l 80H r' E a;G L:SL aW!j :eijelsnV dl Aq paA!aOaHj 90LL L-SOV :ON 0I SIrOO conduction means to conduct static electricity from the front surface 1 12a of the laminate panel 112 to the steel frame 114.

Figure 6a also shows a series of securing means comprising s 130 for securing a retaining ring 136 to the frame 114.

Figure 6b shows a rear perspective view of the flameproof cover 1 can be seen that the retaining ring 136 is provided for assisting in laminate panel 112 in position within the frame 114.

In order to test the integrity of the flameproof enclosure 100, the chamber is filled with either hydrogen gas (H 2 or methane gas ignited. The expanding gases are released from the flameproo but the flameproof enclosure must be able to contain the flames, would ignite the atmosphere outside, thereby causing an explosior Although the discussion of preferred embodiments described abo on embodiments in which the laminate panel forms a cover of the enclosure, the laminate panel could also form part of a or an enti of the flameproof enclosure. Where the laminate panel forms sidewall of the flameproof enclosure it is envisaged that the lami would be welded to the main body rather than being bolted (as above).

It will be appreciated that various alterations and/or additions in th construction and arrangement of parts previously described ma, without departing from the spirit or ambit of the present invention.

17 najor outer crew holes 10 where it holding the flameproof

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4 and enclosure therwise it ye focuses flameproof re sidewall part of a nate panel described particular be made OZ ZL9 'ON *NOMO SdI]N[Hd E:Ll 8006'NVU'LE

Claims (12)

1. A transparent laminate for use in a flameproof enclosure, t[ e laminate Sincluding at least two layers of a transparent material laminated to gether, the I D 5 laminate having first and second major outer surfaces, wherein a least one 0 of the outer surfaces has static dissipative properties. 00 0 2. The laminate of claim 1, wherein said transparent material is 0 polycarbonate.

3. The laminate of claim 1, wherein both major outer surfa ,es of the laminate have static dissipative properties.

4. The laminate of claim 1, wherein said at least one outer s rface has been treated to have a hard, cured, polymeric static dissipative coa ing. The laminate of claim 4, wherein said hard, cured, polyme ic coating comprises a SciCron Technologies C-300T M coating.

6. The laminate of any preceding claim, wherein the thickness of the laminate is the greater of the two values ty and td which are calculated according to equations and ty f P (1) td =3 (2) where f yield stress parameter determined from Figure 1, g deflection parameter determined from Figure 2, P test pressure in MPa, and d maximum deflection in mm.

7. The laminate of claim 1, wherein the thickness of the IE minate is between 16 and 60 mm, preferably between 20 and 50 mm. 18 \l 'd Q'No L dN NOWO sdlin[Hd 1iL1 800H 'NV'LE I.C-LO-00 aeO L.:81. aW!l :e!giJsnvdl Aq paA!aoal 90LLL-SOV :ON 1I SfIlOO

8. A transparent panel for a flameproof enclosure, said panel ir transparent laminate including at least two layers of a transparent rr laminated together, the laminate having first and second major oute wherein at least one of the outer surfaces has static dissipative pror: conducting means for conducting electrostatic charge away from the dissipative surface/s.

9. The transparent panel of claim 8 comprising a flameproof flameproof enclosure. The transparent panel of claim 8 wherein said conducting m( includes a supporting frame in electrical contact with the static dissip surface/s.

11. A flameproof enclosure including: at least one explosion resistant side wall; one or more transparent panels including a transparent laminate i least two layers of a transparent material laminated together, th having first and second major outer surfaces, wherein at least one c outer surfaces has static dissipative properties; and conducting conducting electrostatic charge away from the said static dissipative and means for connecting said panel(s) to said at least one side wall.

12. A transparent laminate for use in a flameproof enclosure, s as herein described with reference to the accompanying drawings.

13. A transparent laminate for use in a flameproof enclosure, si as herein described with reference to any one of the Examples.

14. A transparent panel for a flameproof enclosure, substantiall, described with reference to the accompanying drawings. cluding a aterial surfaces, erties, and Ssaid static cover for a hans ative icluding at e laminate f the major means for surface/s; ibstantially jbstantially as herein Xj>lMak6f!W2 CSmQWCAP Mutu.ed itah pg 1.doo E l 800 'NVF 'i S'd IL2 'ON GNO O SdlllHd LC4O-9O&Z (P-n4-fl 0120 LVSL (wi-i) awi eqewsny di Aq paA!8oaH 9O9LLVSONV :aN (1 SINOO A transparent Panel for a flameproof enclosure, substantiall described with reference to any one of the Examples.

16. A flameproof enclosure, substantially as herein described wit to the accompanying drawings. ,as herein reference x-vMfi~e79=t5 maRC" -cuevd d ,*A 86'd 6(8 'ON MMO Sdl ][Hd CNOV~O SIV]Id Ll g006'NVr %8