Patent Publication Number: US-2004055705-A1

Title: Hybrid spray booth for powder coating systems

Description:
RELATED APPLICATIONS  
     [0001] This application is a continuation-in-part of pending U.S. patent application Ser. No. 10/251,930 filed on Sep. 20, 2002 for IMPROVEMENTS IN AND RELATING TO POWDER COATING SYSTEMS, the entire disclosure of which is fully incorporated herein by reference. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] This invention relates to powder spray coating and, in particular, to the recovery of powder which has not adhered to the article to be coated from a powder spray booth.  
       BACKGROUND OF THE INVENTION  
       [0003] The powder which does not adhere to an article to be coated in a powder spray booth is known as the “overspray”. Overspray powder may miss the article to be coated, rebound from a surface of the article, or be deflected by the electrostatic fields in the spray booth away from the article.  
       [0004] It is known to recover overspray powder by exhausting the air from the booth and hence the air-borne overspray powder. The filter elements which have been used to recover overspray from powder spray booth are capable of removing substantially all the overspray from the spray booth exhaust air so that the powder may be reused. It is also known to use cyclone separators instead of, or in conjunction with filter elements for recovery of overspray. Cyclone separators are effective in removing the majority of the overspray from the spray booth exhaust air and are easier to clean than filters because very little powder is deposited inside the cyclone housing.  
       [0005] In known arrangements the cyclone separators have been collected to the powder spray booth by a duct extending from an overspray intake near the floor of the booth to the inlet of the or each cyclone. European Patent Application No. 94929600.8 discloses a powder coating system where the duct is built into the powder spray booth, with one of the side or end walls of the booth forming part of the duct.  
       [0006] In European Patent Application 98940476.9 there is disclosed a further development wherein the portion of the side or end wall which forms part of the duct is removable from the remainder of the wall to allow easy cleaning of the duct. That Application also discloses a system for collecting deposited overspray powder comprising a scraper bar which continuously reciprocates across the booth floor between the end walls to collect powder on the booth floor and move the collected powder towards the end walls of the spray booth adjacent to each of which overspray intakes are provided.  
       [0007] In recent years there has been a growing desire to be able to spray multiple colours in a single booth in rapid succession. However, changing powder colour requires cleaning of the booth to remove powder deposited on the walls, ceiling and floor which was not extracted by air exhaustion. Proper cleaning of the walls and floor of the powder spray booth between colour changes is very important to ensure acceptable production quality. Such cleaning may be carried out manually by an operator using a scraping and/or compressed air jet apparatus. However booths have been proposed which are intended to automate the deposited overspray powder cleaning process including the booth of European Patent Application No. 98940476.9 referred to above with its reciprocating scraper bar.  
       [0008] Whilst many developments have been made, there is a customer driven demand for even more rapid cleaning capability to reduce cleaning time still further. Furthermore, whilst automatic mechanical devices such as the reciprocating scraper bar of European Patent Application 98940476.9 do accelerate the cleaning process, they also increase construction cost and can be vulnerable to mechanical failure.  
       [0009] Cleaning is preferably conducted from one end of the booth to another and so, from the point of view of cleaning, the overspray intake of the powder recovery system would ideally be located at one end of the booth. However, from the point of view of spraying, the best location for the overspray intake is commonly held to be in the lengthwise centre of the booth to give balanced extraction air flow along the booth and therefore even air flow across the openings which are provided for the spray devices. When the overspray intake is provided at one end of the booth, attempts have therefore been made to modify the booth cross-section to produce the desirable air flow balance. In one known system the booth floor has side portions which slope downwards and the region therebetween is vertically offset to define a trough between the sloped side portions. A triangular insert is positioned in the trough during spraying. The combination of the sloped side portions and triangular insert helps balance the air flows along the length of the booth. However difficulties arise when the powder colour is to be changed as the triangular insert has to be removed for cleaning which adds to the cleaning time.  
       [0010] In another arrangement, shown, for example, in U.S. Pat. No. 4,715,314, the booth floor is formed with a slot which extends the length thereof and connects to a duct also running the length of the booth. However the slot can accumulate powder when one colour is sprayed for a long period of time which makes cleaning more difficult.  
       [0011] It is also been proposed to reduce cleaning time by preventing powder from ever depositing on the floor of a spray booth. German Patent 3408014 describes a system where the floor of the booth is formed as a series of descending steps and air is blown across each step from the slot between it and the step thereabove. The aim is to provide an air stream across the width of the booth which will carry all powder falling towards the floor into the overspray intake and prevent the powder reaching the floor and depositing there. The step form of the booth floor however increases the overall complexity of the booth and this, and the fact that air has to be continuously supplied, makes the booth expensive.  
       [0012] German Patent Application No. 19644360 describes a booth which is also intended to prevent overspray powder reaching the floor. The booth has one or more nozzles for creating a generally horizontal airflow across the booth floor. The air flow diverts descending overspray powder towards the inlet of a powder recovery system and prevents the overspray powder from depositing on the floor. In one embodiment, a central baffle positioned above the floor creates an open-sided duct leading to the inlet and a nozzle directs air to each side. As with the system of German Patent 3468014 a continuous air supply is required.  
       [0013] As noted above, booths in which part of the floor is sloped are known. However, according to U.S. Pat. No. 3,905,785, sloping alone is insufficient to cause all the overspray powder to flow by gravity to the recovery system. The Patent proposes a booth in which the floor is constituted by at least one air-permeable inclined plate. Air is sucked from the booth through the plate which acts to filter out air borne overspray. Periodically air is blown up through the plate to fluidise the deposited overspray thereon and cause it to flow to a recovery system. The suction period may be five to twenty times longer than the blowing period. The concept is similar to that of cartridge filters which are periodically purged by reverse air jets.  
       [0014] The majority of known booths are rectangular. However, it is also known to provide circular booths. A circular booth is disclosed in, for example, EPA 0839522. A problem with known circular booths is that these have conical floors leading to a suction duct by which overspray powder is transferred to a recovery system. A pit is generally required to accommodate the cone and duct in order that articles to be sprayed can be received at the same level as other elements in the production line.  
       [0015] In addition to providing air flow improvements to remove overspray powder, new concepts in spray booth construction are being used to reduce the amount of overspray powder that is attracted or adheres to the spray booth interior surfaces. A major advance in this technology of low conductivity wall structures is described in PCT published patent application Ser. No. 01/40524 for POWDER COATING BOOTH CONTAINMENT STRUCTURE (publication number WO 01/78905 published on Oct. 25, 2001) and pending U.S. patent application Ser. No. 09/550,353 filed on Apr. 14, 2000 for POWDER COATING BOOTH CONTAINMENT STRUCTURE, the entire disclosures of which are fully incorporated herein by reference. In brief, cored composite wall structures are used that exhibit extremely low conductivity and electrostatic properties, thereby minimizing the attraction of electrostatically charged overspray powder particles onto the surface of the wall. In contrast to thermoplastic type spray booths, the cored composite walls do not electrostatically attract the overspray powder and are very easy and fast to clean, thereby significantly reducing color change times and improving the transfer ratio of adhered powder to sprayed powder. The cored composite walls are made of resin based materials with reinforcing fibers and a suitable core such as a high density closed cell foam core PVC, for example. Although this wall structure is well suited to making strong, lightweight, easy to clean and self-supporting three dimensional booth structures, the process is high end in terms of cost. In many applications, an end user may not require such strength in the walls and instead needs a lower overall cost spray booth. The present invention then further includes the aspects of providing lower cost cored composite spray booths without compromising overall structural integrity and cleanability.  
       [0016] Some end users may prefer a still lower cost cored composite spray booth especially for spray booth designs that are not directed primarily to quick color change operations. In accordance with another aspect of the invention, a spray booth is contemplated that incorporates a combination of cored composite wall structures in areas of the booth where structural performance and cleanability are important and incorporates thermoplastic components in areas where structural and cleanability factors as less important. Even in cases where color change time is not as important, conventional cartridge style powder coating systems still benefit from the improved application environment established by a cored composite wall spray booth even when fitted with thermoplastic components such as a gun vestibule or ceiling.  
       [0017] It is an object of the present invention to provide a colour spray apparatus in which powder colour can be changed quickly and easily and which, moreover, is of relatively simple construction.  
       [0018] It is another object of the present invention to provide a powder coating system in which both air borne and deposited overspray can be recovered by a system involving a small number of relatively simple parts which are themselves readily cleaned.  
       [0019] It is a further object of the present invention to provide a powder spray booth in which the collection of deposited overspray is facilitated whilst still balancing the extraction air flow along the length of the booth.  
       [0020] It is a still further object of this invention to provide a powder spray booth of generally circular configuration which can be easily incorporated in a production line and which is simple to clean.  
       [0021] The invention will now be summarised with respect to four principal aspects: a diverter plate; sloped floor with cleaning air; pulsed cleaning air apparatus, and pulsed cleaning air method.  
       [0022] In one aspect the present invention provides a powder coating system comprising a powder spray booth with walls and a floor having two side portions and a downwardly offset region therebetween which defines a trough between the side portions, one or more powder spray devices positioned with respect to the booth walls to spray articles passed through the booth via openings in the walls, a powder recovery system having an overspray intake communicating with the interior of the booth, the powder recovery system including suction means for drawing overspray powder from the booth interior via the overspray intake, and, a diverter plate held within the booth between the floor side portions such as to close at least part of the trough and form a floor duct which is in communication with the overspray intake, the diverter plate including at least one aperture for the passage of overspray powder deposited thereon to the duct.  
       [0023] It has been found that with this apparatus it is possible to even out air extraction to give balanced air flow in the booth whilst still providing an arrangement which is easy to clean particularly if, as is preferred, the diverter plate is movable to a second raised position allowing access to the trough. The provision of at least one aperture allows overspray powder deposited on the diverter plate to be drawn therethrough and into the powder recovery system.  
       [0024] Preferably the side portions are sloped down towards the diverter plate. The diverter plate may define a slot between it and each of the side portions.  
       [0025] Deposited overspray powder on the side portions will trickle down towards the diverter plate and be extracted by the air flow to the powder recovery system via the slots between the plate and the side portions. As already noted, deposited overspray powder on the surface of the plate will be extracted via the apertures therein. As a consequence the amount of deposited overspray powder in the booth at the start of the cleaning operation will be reduced so reducing the scale of the cleaning operation and consequently its duration.  
       [0026] The booth may have any desired configuration. It may have the common rectangular shape with the longitudinal axis running generally horizontally. Alternatively, the booth can be circular with the central axis running generally vertically. The provision of an air distribution duct in a circular booth formed by the diverter plate enables limitation of powder build up and optimisation of air distribution and velocities in the booth through control of the size and shape of the apertures in the diverter plate. Advantage can therefore be taken of the easy cleanability of circular booths without requiring that a special pit be provided to position the booth in a production line. This is a significant benefit as is the fact that operators can safely walk into the booth which is not possible with known circular booths having a conical base.  
       [0027] In a rectangular booth, the overspray intake may be provided at or near one end of the booth with the diverter plate extending from that end along part of the length of the booth. In a rectangular booth provided with a plurality of automatic powder spray devices and having slots in the side walls for the automatic powder spray devices, the length of the diverter plate may be the distance between the end and the gun slot furthest from the end plus an offset. The offset can be comparatively small, a suitable value for a common booth design being 200 mm.  
       [0028] It has been found that it is only necessary to provide the diverter plate in the part of the booth where automatic guns are employed. This is because there are a higher number of guns in the automatic gun portion of the booth and therefore more powder flow into the booth there from the guns. Also, this part of the booth is closest to the extraction fan. Without the diverter plate, the fan can distort the powder spray patterns from the guns and may draw the powder into the collection system before it has a chance to adhere to the part. The effect of the diverter plate is to equalize the suction force of the fan so that powder has more time to adhere to the part and oversprayed powder is drawn evenly towards the fan. In the manual gun section of the booth, there are fewer guns and they are farther away from the fan, so the patterns from those guns are not affected to such a great extent by the fan. Therefore, the diverter plate is not as necessary in the manual gun section of the booth.  
       [0029] In a rectangular booth of the design shown in European Patent Application No. 98940476.9 with an overspray intake at each end, a diverter plate may be provided extending from each end. It has been found that a booth with air intakes at both ends in fact produces the best balancing of the air flow in the booth and actually results in a “dead” zone in the middle of the booth where powder coating is particularly efficient since powder particles have an opportunity to adhere to the part relatively unaffected by the collection system air flows. The plates can be arranged to extend to either side of this “dead” zone.  
       [0030] In a particularly preferred embodiment, the diverter plate is formed in two or more sections, the diverter plate sections being arranged at different vertical spacings from the bottom of the trough such that the duct has different heights along its length. It has be found with this arrangement it is possible to improve still further the air flow balance in the booth and to obtain more even suction.  
       [0031] In this embodiment, the plate section or sections adjacent the or each overspray intake may have the greatest vertical spacing from the trough bottom. With a rectangular booth having an overspray intake at one end, the sections may be arranged in a descending series of steps towards the other end. With a circular booth having a centrally located overspray intake, the section thereabove may be at maximum spacing with one or more lower sections on either side. The narrowing of the duct away from the overspray intake produces the desired even suction and more balanced air flow.  
       [0032] The diverter plate is suitably provided with a plurality of apertures arranged in a pattern. With a rectangular booth, the pattern may be triangular with the apex being at the end of the booth closest to the fan. This pattern has been found to give the best combination of powder collection and air balancing. The total hole cross-sectional area gradually increases from the end towards the middle of the booth.  
       [0033] The apertures in a preferred form are elongate in the lengthwise direction of the plate to give maximum circumference for given cross sectional area and therefore maximum ability to draw deposited overspray from the upper surface of the diverter plate.  
       [0034] In accordance with a second aspect, the present invention provides a powder coating system comprising a powder spray booth having floor, ceiling and walls, one or more powder spray devices positioned with respect to the walls to spray articles passed through the booth via openings in the walls, and a powder recovery system having an overspray intake communicating with the interior of the booth, the powder recovery system including suction means for drawing overspray powder from the booth interior via the overspray intake, wherein at least a portion of the booth floor is sloped and wherein cleaning air supply means is provided for directing air down the sloped portion(s).  
       [0035] Whilst it has been known to make at least a portion of booth floors sloping, the intended result of this, that deposited overspray powder will eventually trickle down the sloped portion, does not always occur. There can be significant build ups of deposited overspray powder on the sloped portion or portions which adds to cleaning time and also gives rise to danger of explosions. By providing a cleaning air supply which directs air down the sloped portion or portions, downward movement of deposited overspray powder is ensured to bring the deposited overspray powder to a region where it can be easily cleaned, either manually or automatically by a mechanical scraper or the like and/or extraction in the exhaust air of the powder recovery system.  
       [0036] The cleaning air supply means may comprise a source of air and at least one plenum extending along at least part of the sloped portion and located at the upper edge of the sloped portion, the plenum having at least one air outlet, preferably plural air outlets.  
       [0037] Very preferably the air source provides periodically pulses of air to the air outlets. It has been found that it is an unnecessary waste of energy to constantly direct air across the slope portion or portions and it suffices just to pulse the air to start movement of deposited overspray powder down the sloped portion or portions. It is currently believed that the best effects are achieved when the cleaning air supply means directs the air generally parallel to the surface of the sloped portion or portions, preferably at an angle of 1-3° to the sloped portion or portions.  
       [0038] In the particularly preferred configuration of the first aspect, the cleaning air supply means of the second aspect may direct air down the side portions along the length of the diverter panel.  
       [0039] In accordance with a third aspect, the present invention provides a powder spray system having a floor, and walls, one or more powder spray devices positioned with respect to the walls to spray articles passed through the booth via openings in the walls, and a powder recovery system having an overspray intake communicating with the interior of the booth, the powder recovery system including suction means for drawing overspray powder from the booth interior via the overspray intake, wherein a cleaning air supply means is provided comprising a source of air and at least one plenum with plural air outlets, the air source providing pulses of air to the air outlets and the plenum being arranged to direct the air pulses across an internal surface of the booth on which overspray powder is deposited.  
       [0040] It has been found that pulses of air may be effective for collection of deposited powder across any internal surface of the booth not just sloped surfaces. The pulses of air cause the deposited overspray powder to collect, either by falling in the case of the ceiling or walls, or by movement along or across the booth in the case of the floor and so facilitate extraction of the deposited overspray powder by the powder recovery system. Good results are achieved without the need for a constant air flow or a complicated structure for directing the air. Thus the system is very economical both as regards manufacture and operation.  
       [0041] The air source may be a compressed air source, one or more fans or an air supply of the powder recovery system. The former has the advantage of cheapness whilst the latter makes for compactness and quietness since fans are relatively noisy.  
       [0042] Very preferably the first aspect is combined with the second and/or third which results overall in a very significant reduction in cleaning time coupled with even air distribution across the booth which produces higher transfer efficiency since the powder particles are given a greater opportunity to adhere to the part. These advantages are accomplished while good powder containment within the booth is also being achieved.  
       [0043] The invention also provides in a fourth aspect a method of operating a powder coating system including a powder spray booth having a floor and walls, one or more powder spray devices and a powder recovery system with an overspray inlet communicating with the interior of the booth, the method comprising periodically directing jets of air across an internal surface of the booth to collect deposited overspray powder thereon.  
       [0044] The method thus involves providing air assist in the booth which facilitates collection and removal of deposited overspray powder.  
       [0045] The internal surface may be the floor and/or one or more walls and/or the ceiling of the booth.  
       [0046] The jets of air are preferably directed sideways across the surface, or lengthwise along the booth. In this way the powder is gathered together and easily collected by a cleaning operation along the booth which may be either manual or automatic.  
       [0047] It has been found that good results are achieved when the air jets are pulsed on for five seconds for every five minutes of spraying of articles in the booth. This prevents any significant build-up of deposited overspray powder by causing removal of the majority of deposited overspray from the booth with the result that the inventory of powder moving around in the system, particularly the quantity within the booth itself, is kept to a minimum.  
       [0048] Alternatively or additionally the jets of air can be pulsed just prior to a colour change so that the amount of deposited powder which has to be removed during the cleaning operation is minimised.  
       [0049] Very preferably this fourth aspect is combined with the second aspect and the air jets are directed across at least part of a sloping portion of the booth floor. For effective movement of deposited overspray powder on the sloping portion(s), the air jets are directed generally parallel the sloping portion(s), preferably at an angle of between 1-3° thereto.  
       [0050] Still a further aspect of the invention relates to the use of pressurized air to blow off overspray powder from the surface of the diverter plate. In one embodiment, the diverter plate has sloping surfaces, and an air plenum is provided along the apex to direct pressurized across the sloping surfaces. Overspray powder is thus blown off the diverter plate and into the floor duct below. The pressurized air may be a continuous flow or pulsed. The use of pressurized air to blow off the diverter plate may be used alone or in combination with the blow off feature of the sloped floor.  
       [0051] Still another aspect of the invention relates to the use of a vertically extending duct having a lower end in communication with the overspray intake and the floor duct. In one embodiment, the vertically extending duct has a removable portion such as doors that form part of the spray booth wall structure. The vertical duct removable portion is provided with one or more holes, slots or other openings to aspirate air from the spray booth during a spraying operation. Preferably the openings are located at an upper region of the vertical duct. Sliding wall sections of the spray booth may also be provided as required.  
       [0052] The invention also contemplates methods for cleaning a spray booth and methods for recovering overspray powder during a powder spraying operation using one or more of the above aspects of the present invention, as set forth in greater detail hereinafter.  
       [0053] Still another aspect of the invention relates to a spray booth having a cored composite wall structure using lower density core materials. The lower density core material does not adversely reduce the wall strength but does significantly reduce material cost. The walls are preferably but not necessarily made as flat panels which simplifies shipping from the manufacturing plant to the end user facility. The use of thermoset resin based composite structures permits the use of two component thermoset resin bonding materials to join structural parts of the spray booth.  
       [0054] In accordance with another aspect of the invention, a process is provided for making cored composite wall structures with lower density core materials. The process may include among other things a vacuum plus heat cure, as well as kerfing, slitting, scoring, thermoforming or otherwise establishing passageways, channels or other suitable paths in the core surfaces to allow air to ventilate from the structure during the process. The process further may include the use of a polyester film or other suitable material or surface as the tooling surface for the functional (i.e. powder exposed) surface of the structure as well as the non-functional (i.e. outside) surface of the structure. Such a tooling surface is “suitable” in the sense that it preferably separates from the composite structure during cure to minimize secondary finishing operations. This further obviates the need for a mold release agent that can compromise the performance of the structure. However, in some processes, it may be desired or necessary to use a tooling surface that does not result in an as molded finished surface. The process may also include the use of a pressure plate to compress the layers together during cure. In contrast to prior processes, in this process the binding resin layers may be laid up prior to application of the vacuum.  
       [0055] Still a further aspect of the present invention contemplates various structural elements used to assemble a complete spray booth, including but not limited to nonconductive fasteners, load bearing bushings, and pultruded non-conductive elements to establish mechanical joints. In accordance with a further aspect of the invention, the nonconductive elements may also be used as a cover or protective layer over otherwise exposed foam core ends of the cored composite wall structures. In accordance with another aspect of the invention, a mechanical joint is provided that is frangible or has a break away feature so as to reduce impact damage if a wall structure such as a cored composite wall structure for example receives an impact that otherwise could break or damage the wall structure.  
       [0056] In some applications, a spray booth may be desired that is still lower in cost even compared to the cost of the lower density cored composite wall structures. In accordance with another aspect of the invention, a hybrid or combination electrostatic spray booth is contemplated that includes the use of cored composite wall structures and thermoplastic wall structures. In one embodiment, the cored composite walls are used for the structural or load bearing members such as the vertical side walls of the spray booth. The thermoplastic wall structures may be used, for example, as a gun extension vestibule or a ceiling. The thermoplastic wall structures can be used to reduce the overall cost of the spray booth, especially by using the thermoplastic wall structure for three dimensional (i.e. non-flat) walls and panels that, depending on the configuration, may be more difficult and expensive to make of cored composite material.  
       [0057] The invention will now be further described by way of example with reference to the accompanying drawings in which:  
       [0058]FIG. 1 is a perspective view partly cut away of a powder booth forming part of a first embodiment of a powder coating system in accordance with the invention;  
       [0059]FIG. 2 is a perspective view partly cut away of part of a powder spray booth forming part of a second embodiment of a powder coating system in accordance with the invention;  
       [0060]FIG. 2A is a perspective view partly cut away of another embodiment of the invention;  
       [0061]FIG. 3 is a sectional detail of part of the booth of FIG. 2;  
       [0062]FIG. 3A is a sectional detail of an alternative embodiment of the booth part of FIG. 3.  
       [0063]FIGS. 4 and 5 are plan views of a diverter plate for use in the spray booth of FIGS. 1 and 2;  
       [0064]FIG. 6 is an end view of the diverter plate of FIGS. 4 and 5;  
       [0065]FIGS. 6A and 6B are respectively an end view and transverse cross-section view of another embodiment of the diverter plate of FIG. 6;  
       [0066]FIG. 7 is a schematic side view of part of a third embodiment of a powder coating system in accordance with the invention;  
       [0067]FIG. 8 is a perspective view partly cut away of part of a powder spray booth forming part of the powder coating system of FIG. 7;  
       [0068]FIG. 9 is a schematic end view of a fourth embodiment of a powder coating system in accordance with the invention;  
       [0069]FIG. 10 is a plan view of the powder coating system of FIG. 9;  
       [0070]FIG. 11 is a schematic plan view of a fifth embodiment of a power coating system in accordance with the invention;  
       [0071]FIG. 12 is a section along X-X of the powder coating system of FIG. 11;  
       [0072]FIG. 13 is a section along Y-Y of the powder coating system of FIG. 11;  
       [0073]FIG. 14 is a schematic end view showing a cleaning system for use in the powder coating systems of FIGS.  9  to  13 ;  
       [0074]FIG. 15 is a schematic plan view showing the cleaning system of FIG. 14;  
       [0075]FIG. 16 is a schematic end view showing an alternative cleaning system for use in the powder coating systems of FIGS.  9  to  13 ;  
       [0076]FIGS. 17 and 18 are plan views showing possible modifications which can be made to the powder coating booth of the powder coating systems of FIGS.  9  to  13 ;  
       [0077]FIG. 19 is a schematic view of a powder spray booth forming part of a further embodiment of a powder coating system in accordance with the invention;  
       [0078]FIGS. 20 and 21 are schematic views of alternative powder spray booths;  
       [0079]FIG. 22 illustrates layers of a cored composite wall structure in exploded view in accordance with the invention.  
       [0080]FIG. 23 illustrates a cored composite wall structure having pasageways in the core surface to ventilate air during cure;  
       [0081]FIG. 24 illustrates a mechanical joint between angled panel sections using a pultruded reinforcing member;  
       [0082]FIG. 25 illustrates a mechanical joint between angled panel sections using a resin fill;  
       [0083] FIGS.  25 A-F illustrate various alternative embodiments of forming a mechanical joint between two cored composite wall structures at an included angle other than 90 or 180 degrees;  
       [0084]FIG. 26 illustrates a mechanical joint producing an angled connection using a resin fill and optional reinforcing member by partly cutting a single panel;  
       [0085] FIGS.  27 - 29  illustrate uses of pultruded reinforcing or joining members for assembling together cored composite wall sections of a spray booth;  
       [0086] FIGS.  27 A- 27 J illustrate exemplary configurations for joining composite wall structures at about 90 degrees;  
       [0087]FIG. 27K illustrates a breakaway fastener concept in accordance with the invention;  
       [0088] FIGS.  30 - 31  illustrate load bearing bushing embodiments made of non-conducting materials;  
       [0089]FIG. 32 illustrates a pultruded member that forms a mechanical joint between two angled panels;  
       [0090]FIG. 33 is an end view of an alternative floor portion of the spray booth of FIG. 1;  
       [0091] FIGS.  34 - 35  illustrate embodiments of pultruded members used to form air curtains at slot openings in the spray booth of FIG. 1, including gun slot openings and the conveyor slot;  
       [0092]FIG. 34A illustrates a top section view of a pultruded form used as a blow off gun support with an integral air manifold such as for a gun slot;  
       [0093]FIGS. 36A and 36B are isometric views of a hybrid electrostatic powder spray booth using composite and thermoplastic wall structures, and an all composite electrostatic spray booth respectively;  
       [0094]FIGS. 37 and 38 are isometric and top views of a thermoplastic gun vestibule as used in the hybrid spray booth of FIG. 36 in accordance with the invention;  
       [0095]FIG. 39 is an end view of an exemplary ceiling Support structure that may be used with the hybrid booth of FIG. 36;  
       [0096]FIG. 40 is a top sectional view of a cored composite gun vestibule in accordance with the invention; and  
       [0097]FIGS. 41 and 42 are alternative embodiments of a composite wall structure. 
     
    
    
     [0098] It is important to note that this application describes a number of different aspects, features and embodiments of the invention. Although these various aspects and embodiments may illustrate various combinations and uses of these aspects, the invention should not be construed as requiring such combination and uses. Those skilled in the art will readily appreciate that the various aspects of the invention as set forth herein may be used alone or in various combinations and sub-combinations whether explicitly described herein or not.  
     [0099]FIGS. 1 and 2 show a rectangular powder spray booth  2  with side walls  4 , end walls  6  and a floor  10 . The booth  2  further has a conveyor (not shown) from which objects are suspended and conveyed through the booth  2  via openings  12  in the end walls  6  for coating with powder by a number of spray devices (also not shown). The booth  2  shown in FIGS. 1 and 2 has a slot  14  for an automatic spray device and an opening  16  to allow use of a manually operated spray device in each side wall. However it will be appreciated that the number and position of spray devices can be varied depending on the objects to be coated.  
     [0100] The ceiling, walls  4 ,  6  and floor  10  of the booth  2  are preferably made from a non-conducting material such as plastic. By using plastic, the powder sprayed by the spray devices if electrostatically charged will have a reduced tendency to adhere to the ceiling and walls  4 ,  6  since it will not be electrostatically attracted to the walls  4 ,  6  and ceiling and instead will fall under gravity and collect on the floor  10  of the booth  2 . For durability the floor  10  or at least the part or parts on which an operator will walk may instead be made of stainless steel.  
     [0101] The booth  2  will be provided with a powder recovery system which may include filters and/or one or more cyclone separators as further described below with respect to other embodiments of the powder coating system. Whatever form the powder recovery system takes, there will be an overspray intake communicating with the interior of the booth  2  and providing a current of exhaust air within the booth and into the overspray intake. The current of exhaust air will serve to extract airborne overspray powder. The skilled man can readily choose a suitable powder recovery system from those known in the art.  
     [0102] As rectangular powder spray booths are preferably cleaned from one end to the other, for the purposes of cleaning the overspray intake is preferably located at one end of the booth. In the booth depicted in FIGS. 1 and 2, the overspray intake is shown in dotted outline at  18  and is located at one corner of the booth. Rising thereabove is a duct  20  which leads to the powder recovery system which is preferably a powder recovery system of the type styled “close coupled cyclone” as described in European Patent Application No. 94929600.8, now European Patent No. 723,481.  
     [0103] The floor  10  of the booth  2  shown in FIGS. 1 and 2 includes two sloping portions  22  on either side thereof, the sloping portions  22  being spaced and the remainder of the floor  10  being offset therefrom to define a trough  24  between the sloping portions  22 . The wall of the trough  24  is cut away at the end of the booth  2  where the overspray intake  18  is located to provide a connection between the overspray intake  18  and the trough  24  and hence the rest of the interior of the booth  2 .  
     [0104] A diverter plate  26  is positioned in the trough  24  at the end where the overspray intake  18  is located and extends from that end. The length of the diverter plate  26  is preferably equal to the distance from the end of the booth  2  to the centre line of the automatic spray device slot  14  which is furthest from that end plus an offset. The offset may suitably be of the order of 200 mm. The plate  26  is suitably spaced from the side portions  22  to define slots  27  therebetween.  
     [0105] The plate  26  has a pattern of holes  28  therein. Two possible patterns are shown in FIGS. 4 and 5. Both are triangular with the apex being at the end of the booth  2  where the overspray intake  18  is located. The holes  28  are elongate in the lengthwise direction of the plate  26  and hence the booth  2 . As illustrated in FIG. 6 the plate  26  has an upper surface which is slightly peaked for strength and stiffness.  
     [0106] The diverter plate  26  is supported by tabs  29  in the position shown in FIGS. 1 and 2 but is mounted to the end wall  6  via hinges  30  to allow it to be pivoted up and against the end wall  6 . The portion of duct  20  extending above the side floor portions  22  is separated from the interior of the booth  2  by two doors  32  each of which is also mounted by hinges  33  so that the doors  32  can also be pivoted away against the end wall  6  allowing access to the interior of the duct  20 .  
     [0107] With the diverter plate  26  installed over the trough  24 , a floor duct is formed by the diverter plate  26  and the trough structure whereby overspray powder is drawn into the floor duct through the holes  28  and the slots  27 . The overspray powder is drawn by the powder recovery system air flow suction into and through the floor duct and into the vertical duct  20  through the overspray intake  18 .  
     [0108] With reference to FIGS. 6A and 6B, in an alternative embodiment, the peaked diverter plate  26  includes a longitudinally extending diverter plate blow-off air plenum  100 . The diverter plate plenum  100  is preferably positioned along the apex or peak of the sloped sides  102 ,  104  of the diverter plate  26  and extends along all or a portion of the length of the diverter plate  26 . It should be noted that the diverter plate plenum  100  may also be used with a flat, round or other shaped diverter plate such as is shown, for example, in FIGS. 1 and 2 herein.  
     [0109] The diverter plate plenum  100  is an integral cap-like structure having two vertical sides  106 ,  108  and a top  110 . The plenum  100  may be mounted on the diverter plate  26  by any suitable technique. Each vertical side  106 ,  108  is provided with a lengthwise series of openings  112 , in this example a series of air jets. Each air jet  112  extends through its respective plenum side  106 ,  108  and opens to an interior air passage  114  of the plenum  100 . Each air jet  112  is also angled so as to direct a flow of air generally across the outer surface of the diverter plate  26  to blow powder off the plate. The dislodged powder is blown into the floor duct via either or both of the diverter plate holes  28  or the side slots  27  between the plate  26  and the sloped floor portions  22 .  
     [0110] Pressurized air is supplied to the internal air passage  114  and directed out the air jets  112 . The pressurized air is supplied to the plenum  100  via one or more inlet ports  116 . These inlet ports  116  communicate with a suitable source of pressurized air, such as regulated shop air generally available in industrial manufacturing facilities. The plenum  100  may provide continuous or pulsed air. The pulsed air may be provided using a source  36  and a valve  37  such as, for example, those shown in FIG. 2. The use of pressurized air to blow off the diverter plate  26  may be used either alone or in combination with the floor blow off feature described herein below with respect to FIG. 2. The invention thus also provides a method for recovering overspray powder during a spraying operation by providing pressurized air that blows off powder from the sloped floor and/or diverter plate into the floor duct and out to the powder recovery system.  
     [0111] The plenum  100 , as well as the diverter plate  26 , may be made of any suitable material including metal or composite non-metal materials, with the required strength. In an alternative design, a slot or series of slots may be used for the openings  112  rather than a series of air jets. Still further, if the sloped sides  102 ,  104  of the diverter plate  26  are hinged, the plenum  100  may be attached lengthwise to only one of the sloped sides  102 ,  104 . Any suitable structure other than a plenum may alternatively be used to provide a flow of pressurized air along the top center of the diverter plate  26  and to direct air across the surface of the diverter plate.  
     [0112] The booth  2  shown in FIG. 2 differs from that of FIG. 1 in that a plenum  34  is provided at the upper edge of each of the side portions  22 . The plenum  34  on the left-hand of the booth in the sense of the Figures is shown in greater detail in the sectional view of FIG. 3. The plenum  34  comprises a tube mounted within the wall  4  and formed with spaced outlets  35  along the length thereof. The plenum  34  is connected to a source of pressurised air via a valve shown schematically at  36  and  37 , respectively, in FIG. 2. Air from the source  36  is directed out of the air outlets  35  as jets across the side portions  22 .  
     [0113] With reference to FIG. 2A, in an alternative embodiment the optional hinged or otherwise optionally removable doors  32  of the vertical duct  20  are provided with one or more holes  120 , suitably spaced along the vertical length of the doors  32  to aspirate air from the spray booth  2  to further optimize air flow patterns within the booth. For example, in the example of FIG. 2A, more holes are provided near the top of the door  32  than at the middle or bottom portions thereof. This produces higher aspiration near the upper portion of the vertical duct  20  in order to produce a Suction that draws in powder entrained air in the upper regions of the booth  2  interior before the powder descends to the floor area. Although a cyclone separator  42  is illustrated in FIG. 2A, other powder recovery systems may be used, as noted hereinbefore.  
     [0114] The vertical duct  20  may be used alone or in combination or various sub-combinations with other aspects of the invention described herein. For example, the vertical duct may be used with a booth that has a sloped floor and/or floor duct, or may simply be an additional feature to a conventional spray booth that does not have the floor duct and sloped floor features. The vertically extending duct  20  thus also may be used to enhance powder recovery methods during a spraying operation by aspirating air and overspray powder from upper regions of the spray booth before the powder alights on any of the booth interior surfaces.  
     [0115] Additional optional features illustrated in FIG. 2A include providing sliding doors  122  as part of one or both of the end walls  6 . The doors  122  are shown in an open position, with the closed position shown in phantom lines. The sliding doors provide selectable access to the booth  2  interior for conveying parts there through, without the need for a permanent opening in the end wall  6 . This provides a more enclosed spray booth to further improve and control air flow patterns within the booth.  
     [0116] Another optional feature illustrated in FIG. 2A is to provide a lengthwise slope to the floor  10  that forms part of the trough  24 . The floor  10  may be sloped so as to further contribute to a balanced air flow and suction within the spray booth. The floor is preferably sloped downward towards the overspray extraction intake duct  18  end so as to provide greater suction in the region of the automatic spray guns. A dual sloped floor may be used in those situations where an overspray intake is used at each end of the spray booth  2 .  
     [0117]FIG. 3A shows an alternative arrangement for providing pulsed air flow across the side portions  22 . The arrangement has a number of features in common with that illustrated in FIG. 3 and where appropriate like reference numerals will be used for like parts.  
     [0118] In the arrangement of FIG. 3A, a plenum  34  again extends the length of the side portion at its upper edge. The plenum is formed in two parts  34   a,    34   b,  the forwardmost part  34   b  being formed with spaced outlets  35  which extend to a generally v-shaped groove  38  which is milled in the forwardmost part  34   b.    
     [0119] The plenum is supplied by a series of air feed tubes  39  spaced along the length of the booth. The feed tubes  39  are in turn supplied by a valved pressurised air source as in the arrangement of FIG. 3 but not shown in FIG. 3A, the connections being via threaded inlet fittings  40 .  
     [0120] Whichever arrangement is employed, that of FIG. 3 or that of FIG. 3A, the air outlets  35  are preferably arranged to direct the air jets at an angle of 1-3° to the side portions  22 . Therefore if the angle (a) of the side portions  22  is  37   o  with respect to the horizontal floor of the booth, the air outlets  35  will direct air at an angle (b) of 38-40° to the horizontal. This orientation of air outlets  35  will cause the air jets to impinge on side portion  22  at an angle of 1 degree to 3 degrees. In the arrangement of FIG. 3A where the groove  38  is provided, the lower wall of the groove may be at an angle (c) of 135° to the vertical, that is, 45° to the horizontal.  
     [0121] The plenum  34  of the arrangement shown in FIG. 3 may be a PVC extrusion which is bonded to the inner panel  41  of wall  4 . Alternatively, as is illustrated by FIG. 3A, the plenum can be attached externally of the wall  4 . The plenum  34  can also take other forms from those illustrated in FIGS. 3 and 3A.  
     [0122] In use, the booth  2  is employed to spray powder on to objects passing therethrough either from automatic guns extending through the slots  14  and/or by manual guns directed through the openings  16 . Air born overspray powder is extracted from the interior of the booth  2  on the current of exhaust air produced by the powder recovery system via the overspray extract  18  and duct  20 . Overspray powder which falls out of the transport air provided by the powder recovery system will be deposited on the floor  10  of the booth  2  and so on the side portions  22 , the bottom of the trough  24  and the plate  26 . The flow of exhaust air caused by the air recovery module along the trough  24  will tend to draw deposited overspray powder on the upper surface of the diverter plate  26  down into the trough  24  therebelow either through the holes  28  or the slots  27  between the side portions  22  and the diverter plate  26 . It has been found that the elongate shape of the holes  28  maximises the area therearound from which deposited overspray powder is drawn into the holes  28  and thence to the overspray intake  18  on the current of exhaust air. The peaking of the upper surface  29  of the plate  26  assists the passage of deposited overspray powder not drawn through the holes  28  into the slots  27  and so again to the overspray intake  18 .  
     [0123] Deposited overspray powder on the side portions  22  will to an extent by gravity naturally trickle down the side portions due to their sloping and into the trough  24  and so into the current of exhaust air produced by the powder recovery system. The booth  2  of FIG. 2 however provides an air assist to this process through the plenums  34 . The jets of air produced from the air outlets  35  of the plenums  34  increase the movement of the deposited overspray powder down the side portions  22 . With short runs between colour changes, an air pulse may be provided just prior to the colour change. With longer runs, an air pulse is provided periodically to prevent deposited overspray powder build-up and so reduce the inventory of powder within the system, particularly the amount of powder in the booth  2 . Whilst the air assist could be provided constantly, it has been found that in fact suffices to provide periodic pulses of air to set in motion the deposited overspray powder oil the side portions  22 . In one successful experiment, a pulse of five seconds every five minutes served to keep the side portions  22  reasonably clear of deposited overspray powder. Pulsing the air, as opposed to constantly supplying compressed air, reduces system energy costs.  
     [0124] The air assist provided by the plenums  34  not only helps keep the side portions  22  clear but also increases the collection of deposited overspray powder on the upper surface from the diverter plate  26 .  
     [0125] The great majority of deposited overspray powder which is collected off the side portions  22  and the diverter plate  26  is re-entrained in the exhaust air flow of the powder recovery system and so extracted as, in effect, air borne overspray powder from the booth  2 .  
     [0126] The diverter panel  26  could extend the full length of the booth  2 . However it has been found that it suffices for it to extend just past the slots  14  for automatic guns by an offset which, as noted above, can be in the order of 200 nm. This is because the higher number of guns in the automatic gun portion of the booth produces more powder flow, and this greater powder flow is closer to the fan than the manual guns. The effect of the diverter plate is to equalize the suction force of the fall so that the powder has more time to adhere to the part and oversprayed powder is more evenly drawn into the collection system. Since the manual guns are farther from the fan, their spray patterns are not as greatly affected by the fan and the need for the diverter plate is therefore reduced with respect to those guns.  
     [0127] The diverter plate  26  functions to even out air distribution along the booth  2  to give an air balance in the powder booth which leads to higher transfer efficiency while ensuring good powder containment. Thus it serves to reduce the amount of deposited overspray powder and so increase the amount of air borne overspray powder. This balancing effect is achieved in part by the pattern of holes  28 . As the diverter plate  26  is an air flow restrictor, the size, number and pattern of the holes determines the air velocity through the overspray intake  18 . As an example, the diverter plate  26  may be arranged so that in combination with the input air velocity of the powder recovery system and the cubic feet per meter rating of the booth  2 , the air velocity through the overspray intake  18  is 2000 ft/min.  
     [0128] The booth  2  shown in FIGS. 1 and 2 has a single diverter plate  26  which is used in conjunction with the single overspray intake  18 . However in a booth with two overspray intakes such as that shown in European Patent Application No. 98940476.9, a diverter plate  26  could be provided at both ends extending towards the middle of the booth  2 . The diverter plates  26  would preferably stop short of the “dead” zone in the middle of the booth which it has been found is created by the provision of two overspray intakes, one at each end of the booth. The dead zone is a relatively quiet area of the booth, in that the air flows caused by the collection system are not as strong in that area of the booth as in the remainder of the booth.  
     [0129] During spraying, air is periodically supplied to the plenums  34  to produce air jets down the side portions  22  and so cause movement of deposited overspray powder thereon into the trough  24  and on to the diverter plate  26 . The air jets will also assist in keeping the diverter plate  26  clean. In one working embodiment, the plenums  35  had 0.5 mm diameter holes set at a 15 mm spacing and powder collection was achieved by blowing air at  4  bar pressure for five seconds every five minutes. As will be appreciated, the air assist parameters given for any given booth will depend on various parameters such as the type of powder coating material, the configuration Oil the booth, and in particular, the angle of sloping of the side portions  22 . The provision of air assist means that if desired the angle of sloping can be reduced which makes it easier for operators to move around within the booth  2  and facilitates construction of the booth  2 .  
     [0130]FIGS. 7 and 8 illustrates schematically a further embodiment which has many features in common with those of FIGS. 1 and 2 and therefore like reference numerals will be used for like parts. in the embodiment shown in FIGS. 7 and 8, the diverter plate  26  extends the length of the booth which is provided at one end with a powder recovery system having a cyclone separator  42 . The plate  26  need not extend the full length of the booth and could instead stop short of the end distant from the powder recovery system like the plate  26  of the powder spray systems illustrated in FIGS. 1 and 2. However, unlike those systems, the plate  26  is formed in a plurality of sections  44  each of which may be considered as a separate diverter plate, the plural sections being arranged as a series of steps descending away from the powder recovery system. The sections  44  may be integral or separate. As illustrated in FIG. 8 they may be arranged such that a slot  46  is provided between each section  44  and the next section down the booth.  
     [0131] The advantage in embodiments illustrated in FIGS. 7 and 8 is that it has been found to give even more balanced airflow throughout the booth because of the narrowing powder suction duct below the diverter plate  26  as the diverter plate sections  44  step down in the direction away from the cyclone separator  42 . In addition, the diverter plate sections  44  are kept almost free of powder due to the airflow striking their surfaces in an almost parallel manner and drawing powder through the slots  46  formed between the plate sections  44 .  
     [0132] Whilst rectangular booths as shown in FIGS. 1, 2 and  7  are very common, it is also known to use cylindrical or circular booths. With many known circular booths there is a problem which is that, for effective overspray powder extraction, it has been found necessary to provide a conical floor. In order to accommodate the conical floor the booth has either to be very tall or, in order that articles may be received at the same level as at other stations of a conveyor line, a pit has to be provided for the conical floor.  
     [0133] It has now been found that it is possible to obtain good overspray powder recovery with a circular booth having a flat base by incorporating therein a diverter plate and using this in conjunction with a powder recovery system which exhausts air from the booth.  
     [0134]FIGS. 9 and 10 illustrate a circular booth  2  with a centrally located overspray intake leading via a duct  20  to a cyclone separator  42 . A diverter plate  26  extends diametrically across the booth  2  below the path taken by articles to be sprayed which enter and leave via openings which may be closed by doors  48 . On either side of the plate  26 , the booth floor  10  slopes upwards towards the booth wall  4  in each side of which three slots  14  are provided for automatic gulls shown schematically at  50  together with the gun mounts shown schematically at  52 . As in the embodiment of FIGS. 1 and 2, the diverter plate  26  may be hinged along one edge so that it can be raised up to the side for cleaning of the trough  24 , as is illustrated in dot-dash lines in FIG. 9.  
     [0135] The circular booth  2  has a low height and so no pit or platform is required. An operator can easily walk into the booth  2  so that it can be cleaned of any residual powder when changing colours by wiping. There is no safety issue as in current commercial booths since the operator cannot fall into a deep conical floor as there is none.  
     [0136] FIGS.  11  to  13  illustrate a circular booth  2  where a central, diametrically extending, diverter plate  26  is arranged in stepped fashion similarly to the embodiment illustrated in FIGS. 7 and 8. The diverter plate  26  is formed in three sections  44 , the two side sections being lower than the central section which is above the extraction point. The result again is balanced air flow through the booth  2  and even suction across the booth base because the duct  24  is narrowest in the regions most remote from the extraction point.  
     [0137] As can be seen in FIG. 11, the diverter plate sections  44  may be slightly peaked which, as noted above with respect of FIG. 6, enhances strength and stiffness. FIG. 11 also shows that the diverter plate sections  44  may be hinged to one of the side portions  22  to allow them to be moved up to the position shown in dotted outline and thereby give access to the trough  24  which extends through the booth.  
     [0138] The circular booths  2  of FIGS.  9  to  13  can be manually cleaned such as by blowing them down with an air wand or wiping. Alternatively, automatic cleaning devices could be used. FIGS. 14 and 15 illustrate an automatic cleaning arrangement with a double “D” profile cleaning air ring  54  shown in both an upper position and a lower position. The ring  54  directs air towards the walls  4  of the booth  2  as it is lowered and raised therein. As cleaning ring  54  is lowered from the ceiling, it blows any powder which has collected on the walls down the walls of the booth and into the collection system housed in the lower portion of the booth. The ring  54  may be retracted into the booth roof for normal cleaning.  
     [0139]FIG. 16 illustrates an alternative system for automatic cleaning which comprises an air cleaning frame  56  which rotates inside the booth  2  whilst blowing air onto the walls  4  and floor  10  to remove deposited overspray powder which is collected through the trough in the bottom of the booth. The cleaning frame  56  could be partial as illustrated or could be double-sided or mirrored to speed cleaning. The frame  56  would preferably be parked outside the booth  2  when the booth is in normal operation. To clean the booth  2 , the frame  56  would be attached to the conveyor and moved into the booth  2 .  
     [0140] In order to allow manual powder coating guns to be used in combination with automatic powder spray guns, the circular configuration shown in FIGS.  9  to  16  may be modified to provide at least one station for an operator. FIGS. 17 and 18 illustrate modified booth shapes which accommodate manual spray guns. The illustrated configurations allow manual spray guns to be used from both sides of the booth  2  but manual guns used from one side alone may suffice in which case the other side would preferably be smoothly curved to prevent accumulation of powder therein. It will be appreciated that other shapes are possible. For example, rather than being indented as shown in FIG. 18 the booth walls may be straight between the sides of the article entrance slot  12  and the automatic gun slots  14 .  
     [0141] All of the circular booths embodiments may be provided with air assisted overspray collection by fitting plenums to direct air jets down the floor side portions  22  and so cause movement of deposited overspray thereon into the trough  24  and onto the diverter plate  26 . As with the rectangular booth embodiments, the provision of air assist will mean that the sloping of the side portions  22  may be reduced which will make it easier for operators to move around within the booth  2  and facilitate its construction.  
     [0142] The air assist need not be used in conjunction with a diverter plate  26 . FIGS. 19.to  21  illustrate arrangements in which air assist is employed simply in combination with a sloped floor portion. In the arrangement of FIG. 19 nearly the whole of the floor  10  is sloped and the air assist is provided across the complete upper edge of the sloped floor  10 . This Figure also serves to show schematically the withdrawal of air borne overspray powder via duct  20  and into a cyclone separator  42  of a powder recovery system.  
     [0143] In a circular booth, the whole of the booth floor  10  may be sloped. This is illustrated in FIG. 20 which shows a circular booth  2  having a sloped floor  10 . As also illustrated the floor may be perforated and formed in three sections with the outer sections being hinged or otherwise raisable to facilitate cleaning. In the FIG. 20 embodiment, the center section of the diverter plate would remain stationery and the outer two sections could be hinged upwardly to allow the operator to enter from either side of the booth.  
     [0144]FIG. 21 shows a further alternative in which the floor  10  has a triangular cross-section and the air assist is provided at the apex thereof. As shown by the arrows, the air assist moves deposited overspray powder down each side of the floor to prevent build-up on the floor  10  and to collect the deposited overspray at the sides of the booth  2 . The booth  2  may have side inlet ducts for receiving the collected overspray powder and directing it to the powder recovery system.  
     [0145] In still further alternatives, the air assist is provided across other non-sloped internal surfaces of the booth  2 , for example, one or more of the walls or the ceiling. Air assist can also be provided to an advantage with a non-sloped floor. A particular embodiment which may have great utility is to provide air assist centrally of the booth disclosed in European Patent Application No. 98940476.9 such that the jets of air are directed towards the ends of the booth and thus to each of the overspray intakes provided at those ends. The air assist will facilitate collection of deposited overspray powder on the floor and movement thereof towards the overspray intakes for recovery by the powder recovery system.  
     [0146] In all these alternatives, the air assist may be continuous or pulsed. The latter has the advantage of economy due to reduced energy requirements for the air source and therefore cost savings.  
     [0147] With a long run between the colour powder changes, it is desirable that an air pulse be provided periodically, whilst with short runs, it can suffice to provide a pulse just prior to the colour change.  
     [0148] Reverting to FIGS. 1 and 2, the cleaning operation which is performed when the colour of the powder is to be changed will now be described. It will be appreciated that the description applies equally to the other embodiments provided with a diverter plate  26  and a powder recovery system which provides for air exhaust. The powder spray devices are shut off and doors closed across the access openings  12  in the end wall  6 . The diverter panel  26  is pivoted up against the adjacent end wall  6  as too are the doors  32  to the vertical duct  20 . An operator preferably using all ail hose, begins at the opposite end of the booth  2  from the vertical duct  20  and moves along the booth blowing the deposited overspray powder which remains therein from all wall and floor surfaces including the sloped floor surfaces and the surfaces of the diverter panel  26 , the floor duct, the vertical duct  20  and the overspray intake  18 . The operator may open each diverter panel individually as he walks along the length of the booth so that the floor duct will still transport the blown off powder to the overspray intake, the vertical duct and the powder recovery system. These last two operations are simplified because of the hinged mounting of the diverter panel  26  and the doors  32  of the vertical duct  20 . As the powder is blown off of the surfaces of the booth, it is drawn into the extraction duct  20  by the fan.  
     [0149] The amount of deposited overspray powder which has to be removed in this operation is much less than with known booths because a significant proportion of the deposited overspray powder will have already been removed due to the action of the diverter plate  26 , sloped side portions  22  and the air plenums  34 . Consequently the amount of recycling work to be done during the cleaning process is reduced which reduces labour costs. Also, in some prior systems, powder has to be collected in a dust pan or waste container and thrown away because recycling has not been completed by the time the cleaning process is over. This waste of powder coating material will not occur in the present system due to the reduced time and effort required to clean the booth.  
     [0150] In tests with this booth, it has been found to be possible to reduce booth cleaning time to below fifteen minutes.  
     [0151] These improvements in colour change capability are achieved whilst at the same time improving the actual performance of the booth since the diverter plate  26  acts to even out, or balance across the length of the booth the air flows which draw oversprayed powder into the system. This has the effect of improving the transfer efficiency of the guns because the powder particles have a better opportunity to attach to the part being coated. In addition, oversprayed powder is more effectively contained within the booth by mans of this design.  
     [0152] In accordance with another aspect of the invention, spray booth cleaning and color change times can be significantly reduced by using spray booth wall structures made of non-conductive cored composite materials. The non-conductive nature of the cored composite wall structure eliminates electrostatic attraction between the overspray powder particles and the interior or functional surface of the spray booth walls. This improves the powder application environment by improving the transfer of powder sprayed from the spray gun to the object being sprayed (improved transfer ratio) because the spray booth itself does not significantly attract powder particles. Thus, the benefits of a cored composite wall structure may be realized with spray booths that are designed for quick change color operations as well as spray booth designs wherein color change times are not a primary focus.  
     [0153] As used herein the term “wall” is used in its broadest sense to include but not be limited to vertical walls, panels, doors, plates, ducts, covers, floors, ceilings and so on. The cored composite wall structure and manufacturing processes and assembly techniques hereinafter described may be used with any desired spray booth configuration, not just the exemplary designs described herein. The cored composite structures described herein are especially useful in making enclosures and structures used with electrostatic application systems such as electrostatic powder spray booths as described herein; however, such description is intended to be exemplary in nature and should not be construed in a limiting sense. For example, the invention may also be used for non-powder application systems as well as non-electrostatic application systems.  
     [0154] Although the described embodiments herein relate to a spray booth enclosure and structural panels and walls therefor, the cored composite structures may be used for many different parts of such an enclosure, including but not limited to spray booth walls, feed hoppers, color module housings such as for powder recovery systems, cyclones, after filters and so on.  
     [0155] In accordance with one aspect of the invention, a cored composite wall structure is provided that is characterized by a first skin layer made of fiber reinforced thermoset resin materials, a second skin layer made of fiber reinforced thermoset resin materials, and a core sandwiched or positioned between the first and second skin layers. One of the skin layers forms a functional side or surface of the cored composite wall, meaning that the functional side is exposed to overspray powder such as occurs within a spray booth interior. The opposite skin layer forms a non-functional side or outer surface of the spray booth.  
     [0156] By “composite” structure is meant that the structure includes a generally homogenous material created by the synthetic assembly of two or more materials (typically a selected filler, hardener or reinforcing elements and a compatible matrix binder) to obtain specific characteristics and properties. Typical examples and not by way of limitation would be a two part resin based encapsulating material such as an epoxy resin (unreinforced) and glass fiber reinforced resins such as fiberglass materials.  
     [0157] By “cored” composite structure simply means that the structure includes a structural core material disposed between two composite skins or layers. Typically the core will be integrally bonded to the skins or layers with a suitable thermoset encapsulating or bonding material. Preferably but not necessarily the encapsulating material comprises a resin that is the same as the composite layer resin.  
     [0158] By “thermoset” is meant that the material when cured by the application of heat or chemical reaction, changes into a substantially infusible and insoluble state. An epoxy resin is again a typical example of a thermoset material by which the epoxy resin and the hardener cure when brought into contact with each other into a hardened matrix that is not reversed by application of heat.  
     [0159] With reference to FIG. 22, an exemplary embodiment of a cored composite wall structure  200  in accordance with the invention is illustrated in exploded form.  
     [0160] The layers are illustrated as they would be laid up in a suitable tooling arrangement as will be described further herein. Many of the materials and alternative materials used in the cored composite wall structure  200  are fully described in the above referenced PCT publication WO 01/78905 and reference may be made to that document for additional details.  
     [0161] The cored composite wall structure  200  has a first or inner skin layer  201 , a second or outer skin layer  203  and a sandwiched core  212 . The inner skin layer  201  includes a first layer  202  that forms the inner surface of a wall section that is part of a spray booth, and hence is referred to as being on the functional side of the wall structure  200 . The first layer  202  is an unreinforced two component resin layer Such as a polyester gelcoat which forms a smooth interior surface. The gelcoat layer  202  may be any suitable thickness, in this illustrated case 0.02 to 0.03 inches. The gelcoat layer  202  may also be suitably pigmented for aesthetic appearance. The smooth hard white surface is easier for workers to see oversprayed powder that is adhering to booth interior canopy surfaces which must be cleaned during a color change operation. The gelcoat layer  202  forms a durable interior surface that is impervious to moisture adsorption and does not degrade over time or due to ultraviolet light. In addition, it is impact and scratch resistant and scratches that do form can be easily buffed out. Suitable resins for the gelcoat layer  202  in an electrostatic powder spraying environment are those that cure into non-conductive, resilient, moisture impervious layers, such as an epoxy based resin system, polyester or a vinylester resin system. Derakane 441 400 from Dow Corporation, and COREZYN VEX 169 540, from Interplastic Corp. of St. Paul, Minn., are exemplary of suitable vinylester resins for this purpose. A pigmented version may also be suitable for the gelcoat layer.  
     [0162] The second layer  204  is an optional surface veil made of nonwoven E-glass reinforcing fibers. The surface veil  204  is used primarily for improving aesthetic appearance by preventing print through of underlying layers. The surface veil  204  typically is about 0.01 inch thick though any suitable thickness may be used, and is available from Owens Corning. The glass fibers in a veil are longer in general and are dispersed in a swirled fashion within the veil and typically are held in a binder that is soluble in the encapsulating resin of the composite structure.  
     [0163] The third layer  206  is an optional non-woven chopped strand mat. Chopped strand mat is a well known random orientation glass fiber composition. Although the chopped strand mat material is a commodity product with various weight densities and manufacturers, a 1.5 ounce E-glass chopped strand mat from Owens Corning is suitable. The chopped strand mat layer  206  also reduces print through, but further is used as a non conductive reinforcing layer to increase impact and shear resistance strength. The glass fibers in a chopped strand mat are typically shorter than in a veil but are also held in a binder that is soluble in the encapsulating resin.  
     [0164] The fourth layer  208  is optional and is a woven roving of E-glass reinforcing fibers, such as for example, 17 ounce woven roving available from Brunswick Technologies, Inc. The woven roving layer  208  may be used for added shear strength and impact resistance.  
     [0165] It is noted that the various glass reinforcing layers used in the exemplary embodiment may be chosen based on their weight and fiber orientations in order to have a desired property. For example, the nonwoven veil and chopped strand mat are weakest in terms of reinforcing strength, but are primarily used for appearance and less expensive. The woven roving layer is stronger, but additional options include knitted unidirectional, bidirectional, tridirectional, 45° bidirectional or drop stitched E-glass layers which exhibit increasing degrees of reinforcing strength as listed but also are more expensive. The designer may thus choose the reinforcing layer materials based on the strength, cost and appearance requirements for a specific application.  
     [0166] Besides glass reinforcing fibers, alternatively other reinforcing fiber materials may be used such as S-glass and poly-para-phenylene-terephthalamide, sold under the trade name KEVLAR by DuPont. Carbon fibers, although conductive, may be suitable in some applications since they have very high strength to weight ratios. The reinforcing layers will be chosen based on the booth design, for example, a cored composite wall that will be used as a floor for walking on may require higher reinforcement than a ceiling wall.  
     [0167] For low cost, lower strength applications it may be suitable simply to omit the veil  204  and the reinforcing layer  208 . Though not the strongest reinforcing layer materials, the chopped strand mat layer  206  may provide adequate strength in some applications.  
     [0168] A fifth layer  210  of a suitable encapsulating material is provided, prior to cure, between the woven roving layer  208  and the sandwiched core  212 . The encapsulating material layer  210  is preferably a two component thermoset polyester, vinylester or epoxy resin system. The encapsulating layer  210  is used to encapsulate the fiber reinforcing layers (in this example, the veil layer  204 , the chopped strand mat layer  206  and the woven roving layer  208 . The encapsulating layer  210  also establishes bonds between the reinforcing layers and an inner surface  202   a  of the gelcoat layer  202  and one surface  212   a  of the core  212 .  
     [0169] The encapsulating layer  210  is initially laid up as a separate layer of resin such as polyester. As will be described herein, the resin flows under pressure, vacuum and heat to encapsulate the reinforcing layers, and bond the first skin  201  elements together and to the core  212 .  
     [0170] On the non-functional side of the wall structure  200 , the second or outer skin  203  includes similar layers as the inner skin  201 , except that the chopped strand mat layer is not used since the aesthetic appearance and texture of the outside surface does not require the same surface finish as the functional side. The gelcoat layer may also be made with a reduced thickness.  
     [0171] Accordingly, the outer skin  203  includes a gelcoat layer  214 , a surface veil layer  216 , a layer of woven roving  218 , and an encapsulating layer  220  such as, for example, a polyester resin. These layers may be the same or different as the materials used for the layers in the inner skin  201 . Since appearance and surface finish features of the outer skin  203  are less stringent than the inner skin  201 , the gelcoat layer  214  and the surface veil  216  may be thinner. The resin layer  220  encapsulates the various layers of the outer skin  203  and bonds the structure to an opposite surface  212   b  of the core  212 .  
     [0172] The core  212  may be selected from any number of a wide variety of materials. Preferably, the core  212  comprises a non-conductive material such as polyvinylchloride (PVC) foam. A suitable material is a semi-rigid, closed cell PVC foam. With the process described below, a lower density PVC foam may be used as compared to the density of the core used in the above referenced patent applications. The ability to use lower density PVC foam represents a significant cost reduction. For example, a PVC foam density as low as about 2.5 pounds/ft 3  available from BALTEC may be used. Presently, 2.5 pounds/ft 3  is the commercially available minimum foam density, and it may be that in the future suitable lower density foams will be available. Different wall structures of a spray booth may use different density cores for added strength, such as floor sections. Use of lower density cores allows for use of thicker core dimensions without increasing cost. Also, the gelcoat layer may be thinner when a lower density core is used. For example, in FIG. 22 when a core density of about 2.5 pounds/ft 3  is used, the gelcoat layer  202  may be about 12-14 mils thick. Still further, within a single wall structure the cored composite material may include a variable density distribution. For example, in a panel that will include an opening such as for a door and having to support a hinge, it may be desired to use a higher density core at that location in the panel.  
     [0173] Other suitable core materials include but are not limited to end grain balsa, glass reinforced polyisocyanurate, polyisocyanurate, polyurathane, plywood, polystyrene, syntactic foams, or paper based honeycombs. The selected material will depend on various requirements of a particular application as to moisture content, strength requirements, degree of nonconductivity needed, and so on.  
     [0174] It is noted that for lower cost booth requirements, the first and second skins  201 ,  203  may be minimalized in terms of the encapsulated layers. The minimum structure for a reinforced inner skin  201  would include the gelcoat layer  202 , a chopped strand mat layer  206  and a bonding layer  210  such as a polyester resin. Such a minimal reinforced structure would exhibit an inner surface having a comparatively reduced surface quality and structural strength, but may be appropriate in some low cost applications. The outer skin  203  may similarly be minimized to three layers including the gelcoat layer  214 , a chopped strand mat and an encapsulating layer  220 .  
     [0175] Still further, the gelcoat layers  202 ,  214  may optionally be molded directly to the core, although this will reduce the strength of the wall structure compared to a less minimal skin structure, but which still may be suitable in some low cost, low strength applications. In such a case, the core would be relied upon to carry all the mechanical loads with the gelcoat serving as a smooth sealed finished surface.  
     [0176] An exemplary process for forming a cored composite wall structure such as, for example, illustrated in FIG. 22 will now be described. Although this process is described in terms of producing flat panel type wall structures, it is contemplated that appropriate tooling can be provided so as to used the process to produce non flat wall structures.  
     [0177] In the exemplary process, the various layers are laid up manually. A platform mold of selected dimensions is used to support the layers. After the various layers are laid up, a pressure plate or other suitable mechanism for applying a compressive load to the layers is positioned over the layers.  
     [0178] In accordance with another aspect of the invention, the tooling surface used for the functional side is realized using a sheet of polyester film, such as, for example, film sold under the trade name MYLAR by DuPont, or other suitable material. First, a gelcoat layer is applied to a MYLAR sheet, partially or fully cured, and then the MYLAR/gelcoat material can be rolled up as a layer for subsequent use.  
     [0179] The MYLAR/gelcoat layer is first placed onto the tooling platform, then the rest of the layers of the cored composite structure are laid up. Note that the encapsulating layers are applied during the lay up steps. An additional MYLAR layer is positioned between the top gelcoat layer and the pressure plate.  
     [0180] After the layers are in place, the pressure plate is positioned on top of the layers, and a vacuum bag is used to enclose the materials and tooling. A vacuum is pulled, for, example 25 inches of mercury, which results in the generation of an evenly distributed compressive load on the materials via the pressure plate. The amount of compression applied will depend on the materials used for the various layers of the cored composite structure. The compressive load and vacuum helps to uniformly distribute the resin bonding material throughout the structure. The vacuum also is used to draw entrapped air from the structure.  
     [0181] Heat may be applied during the vacuum and compression time. Typical temperatures may be about 80° F. to about 140° F. although the actual temperatures will depend on the materials being used and the desired cure time. The use of heat decreases the viscosity of the resin bonding material so that the resin flows more easily throughout the composite structure. Heat also accelerates the curing time for the resin. As a consequence, lower density cores can be used as compared to prior processes because the shorter cure time lessens the effect of styrene attack on the core.  
     [0182] It should be noted that under this process the gelcoat layers  202 ,  214  separate from the MYLAR tooling surface as it is bonded to the composite structure, because thermoset resins do not bond or adhere to thermoplastic materials such as MYLAR without special additional treatments. The gelcoat layers thus become part of the finished composite structure and the MYLAR separates there from. The MYLAR sheets can then be reused as a tooling surface to produce additional composite structures. MYLAR also produces an exceptionally smooth surface to the gelcoat layer thereby eliminating post cure secondary finishing operations. This smooth micro-finished gelcoat surface produced by the MYLAR tooling surface improves cleanability of the resultant spray booth functional surface as well as the aesthetics and cleanability of the non-functional surface. The process thus produces a cored composite wall structure that has two as molded finished outer gelcoat surfaces, one on the functional side and one on the non-functional side. By “as molded” means that the surfaces are suitable for use as is upon removal from the mold.  
     [0183] The present invention further contemplates a cored composite wall structure or product made by the above described process. Additionally, the flat panels produced provide for easy assembly and shipment. The result is a significantly lower cost cored composite spray booth compared to prior known processes.  
     [0184] Because the cure times for this process are substantially shortened compared to prior processes, there may not be sufficient time for entrapped air to be ventilated out of the cored composite structure. The core itself is substantially impermeable to air. Entrapped air is undesirable in some applications as it can produce surface irregularities and also can cause overspray powder attraction as well as reduce structural integrity. In order to eliminate this problem, the core  212  may be ventilated to provide air passageways or channels  250  that allow entrapped air to be ventilated. The core may be ventilated, for example, by cutting, thermoforming, pressing or otherwise establishing channels, slits, kerfs or other suitably shaped air passageways in the core surfaces. Resin encapsulating material eventually flows during cure into these core surface channels or kerfs  250 . The passageways  250  can be laid out in any desired pattern, with one example being from end to end along the short side of the composite wall. FIG. 23 illustrates such an example. A typical kerf may be about {fraction (1/16)}″ wide by {fraction (3/32)}″ depth at one inch center to center spacing, however, these values are only exemplary and may be changed as required for a particular application.  
     [0185] With reference again to FIG. 1, the use of composite thermoset resin based wall structures for the spray booth  2  provide various options to form mechanical joints to assemble the booth, particularly when the composite structures are generally flat rectangular walls. Of particular note is that the composite resin walls allow use of two component epoxy resin bonding materials at various lap joints and corner joints. Two component resin based bonding materials are both very low in conductivity and also provide very strong structural bonds, particularly in contrast to solvent based adhesives or thermowelding commonly used with thermoplastic wall structures. Since the composite walls are thermoset resin based structures, preferably although not necessarily the mechanical joint members are made of a thermoset resin that can be resin bonded to the composite wall structures. Alternatively, however, for example, the mechanical joint members may be made of suitable thermoplastic materials with appropriate adhesive technology for bonding the members to the composite walls, although this may in some cases reduce the load bearing properties of the joint. Thermoset resin members will provide exceptional strength at the load bearing mechanical joints.  
     [0186]FIGS. 24, 25 and  26  illustrate various mechanical joint techniques in accordance with the invention for joining the sloped floor panel  22  to a vertical wall portion  260  of the trough or floor duct  24  (area N circled in FIG. 1) using two generally flat panels. These angled joints may also be used to form non-rectangular structures such as spray gun vestibules (discussed below).  
     [0187] In FIG. 24, a non-conductive pultrusion  264  may be shaped generally as a knee joint. The pultrusion  264  may be made of any suitable non-conductive material such as fiberglass having good structural strength. The knee joint  265  includes a contoured surface  266  on the functional side of the panels  22 ,  260  to minimize overspray powder entrapment. On the non-functional side, the knee joint  264  includes appropriately angled support legs  268 ,  270  which are bonded to the outside (non-functional) surfaces  272 ,  274  of the joined panels  22 ,  260  respectively. Bonding areas are identified by the letter B and may be bonded, for example, with a two component epoxy resin bonding material or other suitable bonding material. The knee joint  264  also includes bonding surfaces  276 ,  278  that are bonded to the edges  280 ,  282  of the panels  22 ,  260  respectively. The pultruded knee joint  264  may include a hollow channel  284  to reduce material or to provide pressurized air.  
     [0188] Those skilled in the art will readily appreciate that the pultruded knee joint  264 , as well as other pultruded support members described herein, may be manufactured by techniques other than pultruding, such as for example, by molding although this would typically be at a higher cost.  
     [0189] The knee joint  264  is contemplated to be a single piece that runs the length of the spray booth  2  along the joint between the joined floor panels  22 ,  260 , however, sectional pieces may also be used as required.  
     [0190]FIG. 25 illustrates an alternative technique for joining the sloped and vertical flat panels  22 ,  260 . In this example, an epoxy-resin fill  284  is applied at the joint and allowed to cure in place.  
     [0191]FIG. 26 illustrates another alternative technique to form the sloped floor/vertical wall mechanical joint. In this example, a single flat panel  290  is cut as at  292  up to about 90% or so through the panel, starting the cut from the non-functional side through the outer skin  203  and the core  212 . This allows the panel to be bent at the cut area to form the sloped floor portion  22  and a vertical wall portion  260 . Note that the inner skin  201  has sufficient strength to hold the partially cut sections together. When the cut portions are bent away from each other, a void  294  is present that is then filled with a suitable two component resin  296 . If additional reinforcement is needed, a pultruded tube  298  may be bonded to the resin file  296 . This tube  298  is on the non-functional side of the floor. In this embodiment, due to the strain placed on the inner skin  201 , it is preferred that the inner skin  201  include a woven roving layer as described hereinbefore.  
     [0192] FIGS.  25 A-F illustrate a number of many alternative embodiments for forming angled joints other than at about 90° or 180°. In FIG. 25A, a first composite wall  400  is coped as at  402  and joined to a reinforcing member such as a rectangular hollow pultrusion  404  using an appropriate bonding material such as an epoxy resin layer  406 . A second composite wall  408  may be face mounted as at  410  to a side  412  of the pultrusion  404 , again using an appropriate bonding material such as an epoxy resin layer  414 . The pultrusion  404  is preferably hollow to allow the pultrusion  404  to function as a pressurized air manifold if so desired. The shape of the pultrusion  404  may be selected as required for the required included angle.  
     [0193] In FIG. 25B a first composite wall  416  is coped as at  418  to join with an end of a second composite wall  420  without an intermediate reinforcing member. In this case, the walls  416  and  420  are bonded with a suitable material such as an epoxy resin layer  422 . The coping may be shaped to achieve a desired included angle α′.  
     [0194]FIG. 25C is a modification of the structure of FIG. 25B. In this example, reinforcing members  424   a  and  424   b  may either be used alone or together as shown on the inside and outside surfaces of the mechanical joint to provide additional structural support of the joint. The reinforcing members  424  may be pultruded elements such as fiberglass for example, formed at an appropriate angle so as to be easily bonded to the composite walls. The reinforcing members  424  may be single pieces that run tile entire length of the joint (into the plane of the drawing) or may be sectional.  
     [0195]FIG. 25D illustrates an alternative to the FIG. 25C embodiment. In this example, the wall edges  426  and  428  are not coped but rather are bonded to the reinforcing members  424   a  and  424   b,  and a suitable filler  430  is provided between the facing edges. The filler may be, for example, an epoxy resin that is applied before or after the walls are bonded to the reinforcing members  424   a  and  424   b.    
     [0196]FIG. 25E illustrates another embodiment that is similar in some respects to FIG. 26 hereof in that a round or tubular pultrusion  432  is used. In this case, however, both edges of the composite walls  400  and  408  are coped as at  434  and  436  and bonded to the tubular pultrusion  432 . Any appropriate bonding material may be used such as an epoxy resin. An advantage of the embodiment of FIG. 25E is that the included angle α′ may be selected at the time the panels  400 ,  408  are assembled, rather than having to make a pultrusion with a predetermined angle. FIG. 25F is still a further embodiment in which the ends of the composite wall  400  and  408  are mitred and bonded by an appropriate binding material such as for example an epoxy resin layer  434 .  
     [0197] In accordance with one aspect of the invention, it will be noted from FIGS.  25 ,  25 A-F and  26  that the structural mechanical joints are formed so that there is no exposed foam core edge of any of the composite wall structures. This is desirable in may applications because the foam core is susceptible to environmental influences such as moisture. Also, when the foam core edge would otherwise be exposed to powder, it would be very difficult to clean.  
     [0198]FIGS. 27 and 28 illustrate exemplary uses of a pultruded angle  300  used to join two composite panels  302 ,  304  together. In FIG. 27, the pultruded angle  300  is resin bonded to one of the panels  302 , and a threaded fastener (not shown) is used to attach the angle  300  to the other panel  304 . A plastic end cover  301  may be used to cover the otherwise exposed foam core edge  304   a.    
     [0199] The angle  300  may alternatively be bonded to both panels or fastened to both. Fasteners and bonding material may both be used for added structural support. FIG. 28 illustrates the use of two angles  300   a  and  300   b  used to vertically join or stack two cored composite panels  306   a, b  together, for example, for assembling a higher spray booth. Again, the angles are bonded to their respective panels and either fastened or bonded together. FIG. 29 illustrates a T-bar pultrusion  308  that can be used for a ceiling or door attachment. The T-bar  308  may also be used a illustrated on the left side of FIG. 29 to mount a gunslot extension panel  310  to a vertical wall panel  312 . Alternatively, the T-bar may instead be replaced with a simple straight flat bar or slat. The support pultrusion designs described herein typically will extend substantially along the length of the mechanical joint.  
     [0200] FIGS.  27 A- 27 H illustrate a number of the many different configurations that may be used to form 90 degree mechanical joints between two cored composite wall structures W 1  and W 2  using one or more reinforcing members R. This is by no means intended to be an exhaustive list of the various available options, but rather are provided in an exemplary manner to illustrate how the use of preformed reinforcing members may be used to establish mechanical joints between two cored composite wall structures. The elements may be joined by a suitable bonding material such as for example an epoxy resin B.  
     [0201] In the embodiment of FIG. 27A, we have found that sometimes a near  90  degree joint is difficult because when the wall sections are forced into the recess, the edges of the wall cause a flaring of the reinforcing member. This can be exacerbated by hydraulic pressure from the squeezed epoxy resin layer B. FIGS. 27I and 27J illustrate an alternative reinforcing member  450  having first and second legs  452 ,  454  formed at right angles to each other. The legs  452  and  454  are joined by a relief portion  456  which provides a pocket  458  into which the bonding material B may flow. This allows near perfect right angle assembly of the two walls, and also may be used to provide a further reinforcing filler of bonding material at the corner joint.  
     [0202]FIG. 30 illustrates a load bearing non-conductive bushing  314 , such as may be made of glass filled NYLON or DELRIN, for example. The bushing  314  includes an enlarged head  316  and may be used to distribute load stresses against a panel. The bushing  314 , for example, may be used in connection with threaded fasteners and through bolts. FIG. 31 illustrates a blind tapped mushroom cap bushing  318 . The cap  320  forms a smooth surface that minimizes overspray powder retention inside the spray booth  2 .  
     [0203] Both the bushing  314  and the bushing  318  include an indentation or other recess  319  formed in the shank  321  of the bushing. When the bushing is installed into a hole formed through a cored composite wall, the bonding resin is applied to the shank  321 , especially in the area of the indentation  319 . As the resin cures, it strongly bonds to the core but will tend not to bond to the bushing itself. However, the resin will cure into a shape that conforms to the indentation and thus will function as a resin type lock ring to retain the bushing in the wall structure.  
     [0204]FIG. 32 illustrates another type of pultrusion  350  that may be used to form an angled mechanical joint between two panels  352  and  354  (corresponding, as an example, to the wall portions  22  and  260  of the spray booth  2 ). In this example, the pultrusion  350  includes a preferably hollow central body  356  having a passageway  358  therein that may be in fluid communication with a source of pressurized air. Even if pressurized is not used, the hollow body  356  saves weight and material. A first support leg or flange  360  extends from the main body  356  and is bonded or otherwise attached to the vertical booth wall  352 . The first support leg may include an extension  362  that in combination with a generally parallel wall  356   a  of the main body, forms a channel or rail  364 . This channel  364  may be used to mount the pultrusion  350  (and the supported walls thereon) onto a booth support frame (see FIG. 33). An additional angle pultrusion  300  (for example, as in FIG. 27 hereof) may be used as a brace to further support the vertical wall attachment to the angled joint pultrusion  350 . A series of air jets  357  may be formed in the body  356  and appropriately angled so as to direct a flow of air from the air passageway  358  across the functional surface of the booth floor panel  354  to reduce powder collection thereon during a spraying operation.  
     [0205] A second support leg or flange  366  extends from the main body  356  and is bonded or otherwise attached to the sloped floor panel  354 .  
     [0206]FIG. 33 is an end view of an exemplary floor portion of the spray booth  2  illustrating use of the wall mount protrusion  350 . Note that the sloped floor panel  354  is shown but the vertical booth panel is omitted for clarity. A separate pultrusion  350  is used on each side of the spray booth. A suitable frame structure  368  is used to allow the booth to be moved about a shop floor if needed and also supports the spray booth on the shop floor. The frame  368  includes a series of vertical legs  370  that are secured to the rail portions  364  of the mounting pultrusion  350 . A series of gussets  372  may be provided to further support mechanical joint between the sloped floor  354  and the vertical wall  260  (FIG. 1) of the floor duct  24 . These gussets  372  are preferably non-conductive and may be, for example, made of fiberglass.  
     [0207]FIG. 34 illustrates another pultruded form in the form of an air knife  380  that may be used to provide an air curtain at the conveyor slot (centerline  381 ) along the ceiling of the spray booth. In this example, the air knife pultrusion includes a support leg  382  that may be bonded or otherwise attached to the non-functional side  384  of the spray booth ceiling panel (it should be noted that FIG. 33 only illustrates one half of the air knife, that there will be a mirror image structure on the other side of the conveyor slot). The air knife pultrusion  380  includes a hollow body  386  that forms an air passageway  388  therein that is in fluid communication with a source of pressurized air. An air jet  390  extends through one wall of the body  386  so as to direct a flow of air downwardly into the spray booth interior. The pultrusion  380  preferably extends lengthwise along the entire length of the conveyor slot and includes a sufficient number of air jets  390  spaced along the length thereof to produce a curtain of air that helps contain overspray powder within the booth and not escape through the conveyor slot. FIG. 35 illustrates a simpler embodiment of an air knife for the conveyor slot. In this example, a simple rectangular (illustrated) or square or round or other suitable shaped pultrusion  392  is bonded to the inner side  384   a  of the ceiling panel at the conveyor slot. Again, the pultrusion includes an air passageway  394  and a series of lengthwise extending airjets  396 .  
     [0208] It should be noted that a similar arrangement may be used at the gun slots  14  (FIG. 1). In such a case, the wall panel  384  in FIG. 33 would be a vertical wall panel of the booth  2 , and the “slot” would be a gun slot  14  rather than the conveyor slot. The pultrusion  380 ,  392  would thus be used to provide an air curtain at the gull slot  14  to prevent overspray powder from escaping through the gun slot  14 .  
     [0209] With reference to FIGS.  36 A, in accordance with another aspect of the invention, spray booth cost can be further reduced by providing a hybrid spray booth. In accordance with this aspect of the invention, thermoplastic walls or sections of the spray booth may be used in place of cored composite wall structures, especially although not necessarily for structures that would be difficult or costly to make with cored composite panels. As noted hereinabove, the lower density cored composite wall structure is particularly although not exclusively suited to making flat panels. As a consequence, non-rectangular structures or structures that cannot be fabricated from flat panels are not as well suited to the lower density cored composite structures. The present invention contemplates that such structures may be formed from thermoplastic material. In addition, cost may further be saved by using thermoplastic material for non-structural (i.e. lower load bearing) structures, such as a ceiling. The load bearing wall structures, however, such as for example the vertical side and end walls of the spray booth, may be made of the higher strength cored composite wall structures.  
     [0210] In the exemplary embodiment of FIG. 36A, a hybrid booth  500  comprises a plurality of vertical side walls  502  or other load bearing walls that are made from cored composite materials as described hereinabove. In addition, optional end vestibules  504  may be provided that are also, although not necessarily, made of cored composite material since these structures tend to receive heavy loads and impact during normal use (because the parts being sprayed enter and exit the spray booth through the end vestibules via the overhead conveyor). The end vestibules  504  may include flared ends or fairings  504   a,  which may be made of either composite material or, more preferably, thermoplastic material. When end vestibules are not used, end walls such as wall  502   a  may be provided made of cored composite wall structures. In some booth designs, an optional gun vestibule  506  with associated gun slots  508  is provided so that larger parts can be conveyed into the booth  500  and sprayed. In accordance with the invention, the gun vestibule  506  may be made of thermoplastic material and mounted to the cored composite side walls  502 . Still further, the gun vestibule may, if required, be made of cored composite wall structures (as in FIG. 36B wherein like components include similar reference numerals with a prime ′). The hybrid booth  500  may further include a ceiling  510  made of thermoplastic material with a conveyor slot C provided between the two ceiling half sections. The present invention is not limited to a spray booth as configured in FIG. 36A however and may take on many different sizes, shapes and so on. Note that the side walls  502  typically will be made up of a plurality of subsections.  
     [0211] In accordance with this aspect of the invention, the thermoplastic material may be any material suited to the particular structural requirements of the spray booth  500 . An exemplary material is polycarbonate, well known to those skilled in the art. One example of a suitable material is multi-wall polycarbonate available from GE which may be used for higher strength structures such as the ceiling  510 , whereas regular single layer polycarbonate may be used for structures such as the gun vestibule  506 . Other suitable materials include but are not limited to the following: co-polymer, polypropylene, PVC, PETG, acrylic, polyethylene and ABS.  
     [0212]FIGS. 37 and 38 illustrate the gun vestibule  506  in greater detail. The gun vestibule  506  is either preformed into the desired shape, such as during a molding process, or formed from sheet stock. Typically a gun vestibule  506  includes a front wall  512  having one or more gun slots  514  therein and integral flared side walls  516 . A ceiling and floor panel  511   a  and  511   b  may be included as well and attached to the vestibule  506  as required.  
     [0213] The spray booth in this example is of the type that uses a cartridge filter style powder recovery system, therefore, an enlarged opening  513  is provided in a side wall to accommodate the powder recovery system. Additional openings  515  may be provided such as for a manual spray station. The present invention, however, may be used with cyclone style booths and other powder recovery system designs. A significant advantage of the present invention as noted herein above is that the used of the composite wall structures improves the spraying environment by reducing the attraction of powder to the booth components thus improving transfer efficiency and optimizing powder flow patterns within the spray booth.  
     [0214] The side walls  516  include extended end flanges  518  that overlap the edges  520  of the corresponding cored composite vertical side walls  522  of the spray booth  500 . Because it is difficult to bond thermoplastic material to thermoset material, the vestibule  506  is bolted or otherwise attached to the side walls of the spray booth  500 . In the embodiment of FIG. 3. The end flanges  518  thus include a mounting flange  524  that is bolted to the vertical side walls  522  of the booth, such as with a series of non-conductive nut and bolt arrangements  526 . The bushings of FIGS. 30 and 31 may be used, for example. Note that the overlapping portions of the flanges  518  provide a cover or protective layer over the otherwise exposed foam core of the side wall edges  520 .  
     [0215] The ceiling  510  may be installed using any convenient ceiling support structure. Reinforcing members such as fiberglass pultruded members described hereinabove may be bonded to the cored composite vertical side walls and end walls with the ceiling  510  supported thereon. The ceiling may be bolted, bonded or simply laid onto the roof support structure as required for a particular booth design. For larger booths, reinforcing beams or braces may be provided to prevent the ceiling from sagging under its own weight.  
     [0216]FIG. 39 illustrates in section one embodiment of a ceiling support structure  530 . The ceiling support structure  530  in this example is a cantilevered design because of the provision of a conveyor slot  532  having a centerline  534  (note that only one half of the ceiling is illustrated in FIG. 39). A right angle pultrusion  536  is bonded to the outside of the vertical side walls  502 a. The ceiling  510  overhangs the booth and may be bonded or otherwise attached to the support angle  536 . Along the inner edge  510 a of the ceiling  510 , an end cap  538  may be provided. Attentively, an air knife such as in FIGS.  34  or  35  for example may be mounted at the conveyor slot  532 . A reinforcing beam  540  or series of such beams may extend transversely across the ceiling  510  to add rigidity and strength if required.  
     [0217]FIG. 40 illustrates an alternative embodiment of a gun vestibule  550  (corresponding to the gun vestibule  506 ′ in FIG. 36B in which the gun vestibule is made from cored composite wall structures. The pultruded knee member  264  of FIG. 24 may be used to join the various wall sections together, including a front wall  552  and flared side walls  554  joined to vertical side walls  556  of the spray booth  500 . The front wall  552  may include one or more gun slots  558 . The vestibule  550  may be installed simply by bonding the knee joints  264  to the vertical side walls of the booth, or bolted or otherwise releasably installed if a removable vestibule is desired. A ceiling and floor may be provided on the top and bottom of the vestibule and may be made of cored composite or a thermoplastic material. All exposed foam core edges, as described hereinabove, are preferably covered.  
     [0218] With reference to FIG. 34A, we illustrate an embodiment where the air knife pultrusion  380 ′ (see FIG. 34) is used in an alternative embodiment at a gun slot  560 . The pultrusion  380 ′ in this case however does not need to be provided with air jets. Rather, the pultrusion  380 ′ is attached to a booth or vestibule wall  562  along one edge  382 ′ thereof so that a flange  564  faces generally towards the gun slot  560 . This may be done with a suitable bonding material such as a thermoset resin. The pultrusion  380 ′ extends vertically along the gun slot  560 . A series of blow off guns or nozzles  566  are mounted on the flange  564 . An appropriate air line  568  provides fluid communication between an air inlet  570  to each nozzle  566 , as well as to pressurized air supplied to the air manifold  572  within the pultrusion  380 ′ via an air hose fitting  574 . The pultrusion  380 ′ thus serves as both a mounting bracket for the blow off nozzles  566  and an integral air manifold  572  therefor.  
     [0219] With reference to FIGS. 41 and 42, the manufacture of cored composite wall structures may be realized in different ways. In FIG. 41, the cored composite wall structure  580  is formed by a cold press or cold laminating process. The structure  580  includes a closed cell foam core  582  such as described hereinabove. Other foam core materials may be used as appropriate. On either side of the core  582  is a composite reinforcing layer or skin  584   a  and  584   b.  One example of the skin  584  layers is a pultruded glass mat/polyester resin skin with a gelcoat outer surface. A suitable bonding material such as a bonding layer  586  of epoxy resin is disposed between the outer surfaces of the core  582  and each inner surface of the skins  584   a,b.  Any bonding material may be used so long as it does not adversely affect the foam core during the curing process. A cold press is then applied to complete the cure, or heat may also be added during the press time.  
     [0220] In the embodiment of FIG. 42, the foam core is omitted from the structural composite wall  587 . For structural strength, a structural core  588  is disposed and bonded to each of the skin layers  590   a  and  590   b,  which may be the same as any of the skin layers disclosed herein or other suitable reinforced resin layer. Again, an epoxy resin may be used to bond the core  588  to the skins  590   a,b.  In the embodiment of FIG. 42, the structural core is realized in the form of a pultrusion made of a suitable material such as the pultrusion materials described herein above, including but not limited to fiberglass. The structural core  588  may include one or more pneumatic channels or passageways  592  therethrough for connection to a source of pressurized air that could be tapped into for any of the various air curtain/wash and blow-off features described herein. The structural core elements  588  may be positioned around the outer periphery of the wall structure  587 . Additional structural cores  588  or other suitable reinforcing elements such as pultruded braces and so on may be appropriately positioned to support the skins  590  within the perimeter of the wall structure.  
     [0221] With reference to FIG. 27K, some of the wall structures of a spray booth may be exposed to impact damage, such as for example the end walls and end vestibules near openings for the moving parts or any panel that could be impacted by workers. In order to minimize damage to the booth, the present invention contemplates the use of a frangible or breakaway mounting arrangement between panels or wall structures. Not all of the wall structures need to be break away although they could be. More common will be the provision of a break away mounting for panels that can be expected to incur impact type damage. In the embodiment of FIG. 27K two panels or wall sections  302  and  304  are joined at a mechanical joint that includes a right angle  300  that on one leg is bonded to the first wall  302  and on the second leg is bolted or fastened to the second wall  304  (fasteners may alternatively be used for the bonded joint as well). The fastener joint  600  in the exemplary embodiment includes a bushing  602  such as the bushing  314  in FIG. 30 hereof. A threaded fastener  604  extends through the bushing  602  and may include a hex head  606  on one end and a threaded end  608  on the other that receives a nut  610  which secures the fastener  604  to the angle  300 . A blind bushing such as illustrated in FIG. 31 herein may alternatively be used. Note that the bushing  602  is provided with an outer notch  612  as described herein above. In order for the mechanical connection  600  to be frangible or breakaway, in accordance with the invention it is contemplated that the bolt  604  be made of a lower strength material such as an unreinforced nylon material or other suitable plastic that will break under impact. The fastener may alternatively be made to have a spring action. Still another alternative is to core out a portion  614  of the bolt  604  to increase its breakability.  
     [0222] While the invention has been described with reference to various embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof.  
     [0223] Therefore, it is intended that invention not be limited to the particular embodiments disclosed herein, but that the invention will include all embodiments falling within the scope of the appended claims