Powder coating booth

A powder spray for lengthy parts includes a booth wall structure comprised primarily of doors. A moveable roof may be raised and lowered to clean powder overspray from the interior surfaces of the booth. A cleaning process may be performed with a sideways extraction mode and a downward extraction mode. The mode change occurs when a bulkhead that travels with the moveable roof blocks the inlet duct to the recovery system. The recovery system may be a cyclone system for example. The doors of the booth are hinged so that they can be positioned for spraying operations and cleaning operations. Live hinge designs are provided and hose stress relief designs are also provided. The roof may carry accumulators for pressurized air that feed cleaning nozzles as the roof descends. In addition, exhaust air may be used to assist cleaning the interior surfaces as the roof descends. All of the energy provided for cleaning and color change may be provided by accumulators.

SUMMARY OF THE INVENTION

The invention relates generally to powder coating booths such as may be used with powder coating material application systems and processes. More particularly, the invention relates to powder coating material application systems, booths and processes for elongated objects, such as for example lengthy extrusions.

BACKGROUND OF THE INVENTION

Powder coating materials are typically applied to objects or work pieces by spray application apparatus and processes. These spray application apparatus and processes include electrostatic and non-electrostatic processes as are well known. Spray application of powder coating material often is done in a spray booth that is used to contain and recover powder overspray. Powder overspray may be recovered from the booth and either recycled back to the feed center for re-use or otherwise disposed of. One of the more significant aspects of any powder coating system is a powder change operation and the associated system down time and labor involved in such changeovers. For example, when the color of the applied powder needs to be changed, the entire system must be cleaned and purged of the just used color before the next color can be applied. This involves the clean and purge of spray guns, feed hoses and most importantly the spray booth. Long objects such as extrusions that can be up to about twenty-seven feet in length or more present unique challenges for powder application to those objects because a tall spray booth is required for adequate powder overspray containment.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a powder spray booth is contemplated that accommodates lengthy parts, objects or work pieces. In one embodiment, a spray booth is provided that has a plurality of doors with one or more of the doors being hinged for movement relative to the other doors, and further wherein the doors substantially comprise the booth wall structure. In a specific embodiment the booth includes four hinged doors and a vertical booth height of greater than twenty feet. In accordance with another aspect of the invention tile booth is about three times greater in its vertical dimension than along its lengthwise dimension (wherein lengthwise dimension refers to an axis of travel of parts through the booth during a powder application process.)

In accordance with another aspect of the invention, a powder spray booth is contemplated that incorporates one or more gun slots that may be selectively opened and closed. In one embodiment, a gun slot cover is provided that may be moved between a gun slot open position that may be used during a powder application process, and a gun slot closed position that may be used during cleaning and powder change operations. In a specific embodiment the gun slot cover may be realized in the form of a pneumatically driven flexible member that bends to open the gun slot and relaxes to cover the gun slot.

In accordance with another aspect of the invention, a powder spray booth is contemplated in which the booth interior surfaces may be cleaned by pressurized air provided from a moveable structural member of the booth. In one embodiment, the spray booth includes a roof or ceiling structure that directs pressurized air against the booth interior surfaces as the roof is lowered from a first or raised position used during a powder application process and a second or lowered position used during cleaning and powder change. In a specific embodiment, the roof carries a plurality of pressurized air devices, such as for example nozzles that direct pressurized air at the booth interior surfaces. Air may be provided to such devices for example by one or more accumulators or air tanks carried on top of the moveable roof. In another embodiment that utilizes hinged doors as the booth wall structure, one or more of the doors may also carry pressurized air devices for removing powder off the booth floor.

In accordance with another aspect of the invention, a powder spray booth is contemplated that includes pressurized air devices for removing powder overspray off the booth interior surfaces. In one embodiment, the cleaning energy used to remove powder from the interior surfaces in the form of pressurized air is sourced from one or more accumulators. In a more specific embodiment, the pressurized air source is intermittently triggered so that blasts of air are directed at the interior surfaces of the spray booth. This produces pressure waves that dislodge powder overspray from the spray booth interior surfaces.

In accordance with another aspect of the invention, a powder spray booth is contemplated that is cleaned by a combination of pressurized air devices and flow of exhaust air into the booth such that the exhaust air assists in removing powder from interior surfaces of the spray booth. In one embodiment, a ceiling structure is provided that has a closely spaced relationship to the interior surfaces of the spray booth. A gap is provided between the ceiling structure and the interior surfaces so that exhaust air is pulled into the spray booth through the gap and applies a shearing force against powder particles on the interior surfaces to dislodge them. The ceiling structure may also carry pressurized air devices that direct high volume pressurized air in the form of pressure waves at the interior surfaces. In a specific embodiment, the ceiling structure may be raised and lowered within the spray booth. The invention further contemplates the cleaning method embodied in such apparatus, in particular a method for cleaning the interior surfaces of a spray booth including the steps of using exhaust air flow into the booth for part of the cleaning energy and intermittently applied pressure waves.

In accordance with another aspect of the invention, a hose strain relief mechanism is provided. The hose strain relief concept has application in any material application system that uses one or more flexible hoses. In the context of a spray booth for elongated parts such as described in the exemplary embodiments herein, the hose strain relief feature is useful due to very long and heavy hose runs particularly to the upper regions of the spray booth.

In accordance with another aspect of the invention, a cleaning arrangement and associated method for a powder spray booth is contemplated that operates in two modes, with one mode being a sideways recovery or extraction mode and the other being a downward recovery or extraction mode. In one embodiment, a spray booth is provided that includes a roof structure that can be raised and lowered within the booth interior, and the booth further includes a powder recovery system that interfaces with the booth interior through a vertical slot and through a floor duct. With the roof in an tipper position, powder overspray is removed from the surfaces and drawn into the vertical slot into the powder recovery apparatus. In one embodiment the recovery apparatus may be a cyclone arrangement. As the roof is lowered, the powder extraction process switches over to powder overspray being extracted through the floor duct. In one embodiment this switch over may be realized by providing a traveling bulkhead within a vertical recovery duct that travels with the roof. When the roof reaches a predetermined position the bulkhead blocks or isolates the recovery duct from the vertical slot and the floor duct is opened. In another embodiment, a floor slot is used adjacent to the recovery duct.

The invention further contemplates various methods embodied in the use of the described structures and or that can be carried out using such structures as set forth in detail hereinafter.

These and other aspects and advantages of the invention will be readily understood and appreciated from the following detailed description hereinafter and the accompanying drawings.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1illustrates a powder coating material application system10that includes a spray booth12, a powder overspray recovery system14, an after filter and blower system16, a plurality of application devices18, a gun mount and mover system20and an overall structural Support framework22(only partially illustrated in the various drawings for clarity.) The application devices18may be selected from any number of spray gun designs, including a SURE-COAT™ spray gun available from Nordson Corporation, Westlake, Ohio. A feed center21may be provided that contains a supply of material that will be applied to objects or work pieces within the spray booth12. The feed center21for example may include any number of hoppers, boxes or other containers of powder, along with suitable pumps and hoses to feed material to the application devices18. A suitable operator interface24to a control system (not shown) may be provided to control operation of the spray guns18, the powder recovery system14, the spray booth12and the gun mover system20. The control system and the operator interface24may be selected from any number of well known control system concepts as are well known to those skilled in tile art, or specifically designed for a particular system. The gun mover system20may be used to both extend and retract the spray guns with respect to the spray booth12and also may be used to produce an up down oscillatory motion of the guns during a spray operation.

In the exemplary embodiment, the powder overspray recovery system14may be realized in the form of a cyclone system15, however, other recovery system designs may be used. The blower and after filter system16provides the energy required for operation of the cyclone recovery system, in the form of a substantial powder entrained exhaust air flow pulled from the spray booth interior to an intake duct of the cyclone15. The air flow produced by the recovery system also produces a substantial flow of air into and through the spray booth12, sometimes referred to as containment air. The containment air flow prevents the loss of powder overspray outside the spray booth12. In the embodiments herein, the cyclone system15is a twill cyclone system, however a single cyclone may alternatively be used. In the exemplary embodiment, powder may either be recovered from the cyclone outlet15a, as is commonly done if the powder will be reused, or alternatively may be extracted from the booth12and pass through to the after filter system16via a bypass outlet or duct arrangement15b.

The cyclone15has a cyclone inlet70(FIGS. 2 and 2A) that communicates with a first or recovery duct or plenum74of a vertical primary duct structure (72, seeFIG. 2). The cyclone15also has a bypass duct inlet76that communicates with the bypass outlet duct15band also communicates with a second or bypass duct or plenum75that is provided in the primary duct72. Alternatively the bypass duct75and the recovery duct74may be separate structures. The bypass arrangement may include a bypass door (see below) that opens and closes depending on where the extracted power is to go. As will be described in greater detail hereinafter, a bullhead is provided within the recovery duct74that under certain conditions blocks the cyclone inlet70so that with the bypass door open the extracted powder goes to the after filter16via the bypass duct75and the bypass outlet15b, thus bypassing the cyclone15.

While various concepts, aspects and features of the invention are described and illustrated herein as embodied or used in combination in the exemplary embodiments, these various concepts, aspects and features may also be realized in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such alternative embodiments, combinations and sub-combinations are intended to be within the scope of the present invention. Still further, while various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, arrangements, methods, devices, software, hardware, control logic and so on may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the aspects, concepts or features of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such an arrangement or method is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated.

From the approximate scale ofFIG. 1it is noted that the spray booth12has a height or vertical dimension that is several times its length. In one example, the spray booth12is about twenty-seven feet high and about ten feet in length, wherein by ‘length’ is meant the distance that work pieces, parts and objects W travel through the spray booth12in order to be coated with powder. Thus, the present invention contemplates spray booths that have height to length ratios of at least about two to one and as much as about three to one or greater. This allows the spray booth to be used for powder coating long objects such as extrusions, however, the booth may also be used for spray coating any object that dimensionally can be accommodated through the booth. Due to the height of the booth12, the structural framework22may include platforms (not shown) that can support workers who need to maintain the spray guns18and the gun support and mover system20. An overhead conveyor26(partially shown) may be used to transport parts through the booth during a spraying operation.

While there are a number and variety of aspects and concepts to the present invention as set forth in greater detail herein below, two of these concepts should be particularly noted at the outset. The first concept relates to method and apparatus for cleaning the booth interior surfaces. The basic idea is to utilize not only the application of pressurized air to remove powder overspray, but also to utilize energy provided by the substantial air that is drawn into the spray booth by the recovery system. This air flow may be thought of as the containment air, exhaust air or a combination thereof. In accordance with the invention, during a cleaning operation this air flow is drawn through a somewhat narrow gap adjacent the interior surfaces to create a shear force of the air against the surfaces. This force not only removes powder overspray from the surfaces but also imparts significant kinetic energy and momentum to the dislodged particles which in turn may knock other powder particles from the interior surfaces. In conjunction with the use of the substantial air flow into the booth via the noted gap, pressurized air may also he intermittently applied against the interior surfaces in the form of pressure waves. This energy also removes powder overspray from the interior surfaces. In an exemplary embodiment described below, these two cleaning concepts of using exhaust air and pressure waves are used in combination and realized by using a moveable structure such as a roof that carries pressurized air nozzles and that provides the above noted gap adjacent the interior surfaces. The nozzles are intermittently triggered to create the pressure waves, and the source of the pressurized air in the exemplary embodiment may be one or more storage tanks or accumulators that store a volume of pressurized air.

The second concept to be noted is the idea of removing powder overspray from the booth interior initially by a sideways extraction into a vertical slot that extends along the height of the booth, wherein the slot opens to the intake of a recovery system such as a cyclone. A moveable roof may be used to further clean interior surfaces of the spray booth, and as the roof is lowered the powder overspray extraction transitions from a sideways extraction to a downward extraction through a duct or slot at the bottom of the booth. In the exemplary embodiment this transition occurs by blocking or closing the cyclone intake when the roof reaches a predetermined position, and opening a flow passage for powder overspray to be drawn from the booth into a bypass duct of the cyclone and on to the after filter system.

The spray booth12may be generally diamond shaped although two apexes of the diamond are somewhat truncated as will be apparent fromFIG. 2which is a plan view of the basic system10(the after filter and blower system16being omitted for clarity, as well as the roof and some of the frame work22.)

With reference then toFIG. 2andFIGS. 2A-2C, the exemplary spray booth12includes four doors30,32,34and36that may be hinged or otherwise mounted to the structural framework so as to be easily opened and closed. The spray booth12is substantially defined by these foul doors, a floor38and a moveable roof or ceiling structure40. The right front door30is hinged to one side of a gun slot panel42and the left front door32is hinged to one side of a recovery duct intake panel44. The right rear door36is hinged to an opposite side of the gun slot panel42and the left rear door34is hinged to an opposite side of the recovery duct panel44. The terms front and rear are used as a convenience to refer to the lengthwise ends of the booth that the traveling parts enter and leave respectively it being understood that direction of travel through the booth may be reversed. The terms left and right are also merely a convenience when referring to the drawings. Due to their length, the doors may be multi-piece construction having an upper section and a lower section as best illustrated in FIGS.1and2A-2C. Thus, other than the short (lengthwise) gun slot panel42that truncates one apex of the diamond and the short (lengthwise) intake panel44that truncates an opposite apex of the diamond, the booth12has a vertical wall structure that is defined in large measure by four hinged doors with each door comprising two (upper and lower) sections. This is in distinct contrast to prior booths that typically have a door structure at the booth ends but otherwise have fixed vertical walls that define the booth configuration.

The hinged doors30,32,34and36may each be made of composite materials including a foam core panel and gelcoat inner surface such as sold by Nordson Corporation as an Apogee panel structure. Other door structures may alternatively be used as required. The doors may be removably mounted using lift off hinges46as will be further described herein, or other suitable hinge designs as required. The spray booth vertical wall structure is thus primarily defined by the doors.

The roof40may also be made of composite panels and has a generally conforming diamond shape perimeter (generally conforming to the plan shape of tile booth when the doors are closed) but with a conveyor slot48provided (FIG. 2A). The roof40includes an upper frame (404,FIGS. 14A,14B) that is supported by a series of cables or other suitable mechanism so that the roof can be raised and lowered in a level manner within the spray booth. The roof40is in its uppermost position (FIG. 2A) during a material application or coating operation and can be lowered nearly to the floor (seeFIG. 4A) during a cleaning or color change operation. The roof40is dimensioned so that the generally conforming perimeter has a narrow lateral clearance or gap with the door surfaces, for example about two inches, when the doors are fully closed (FIG. 13). This narrow clearance helps to contain powder overspray while at the same time providing a source of exhaust air drawn into and through the booth by the powder recovery system14. This substantial air flow through the roof/door gaps is also used to clean the door interior surfaces as will be further explained.

FIG. 3illustrates a plan view of the roof40panel structure. The roof40carries a series of air nozzles50that may extend around the entire periphery of the roof (inFIG. 3not all of tile nozzles are illustrated) or at least at enough intervals and positions to thoroughly clean the interior surfaces of the doors. The roof40also includes a conveyor slot cover52that preferably is hinged so that it can be raised and lowered either manually or by operation of a suitable actuator. The cover52is raised to its upright position for a spraying operation so that the conveyor hangers can pass through the slot48. During cleaning and/or color change operations, however, the cover52is lowered to its closed position.FIG. 3Afurther illustrates that the roof may include two air ducts54and56that extend lengthwise along either side of the conveyor slot48and provide an air flow down into the booth so as to prevent powder from escaping through the conveyor slot48. As explained below, the ducts54,56may be coupled to a suitable source of pressurized air.

As noted herein above, the roof40may include a frame structure (404, seeFIG. 14) that may be supported by winch driven cables400so that the roof40can be raised and lowered during a cleaning operation. Since the roof is basically a two section structure, the closed cover52helps to stabilize the roof sections as it travels up and down the booth, especially when the nozzles50are intermittently triggered. The roof frame404further supports a source or reservoir of compressed air such as air tanks (86,FIG. 14A) or accumulators that provide high volume pressurized air to the ducts54,56and the nozzles50. The tanks86thus provide an energy/volume storage system to deliver high volume pressurized air when the nozzles50are triggered, thus producing a pressure wave of high volume air directed at the interior surfaces of the booth12. Supply hoses are connected to the tanks86to replenish them during a cleaning operation.

As best illustrated inFIGS. 2A-2CandFIGS. 4A-4B, the latter which are a simplified schematic of the cyclone/booth interface, the cyclone15interfaces with the spray booth12via the primary duct72that extends the height of the booth12. The duct72is multi-sectional and includes an interior recovery plenum74that communicates with a booth intake slot62formed in the intake panel44. The plenum74also communicates with the cyclone inlet70. Powder overspray is drawn sideways into the plenum74from the spray booth12via the slot62and passes into the cyclone15via the cyclone intake duct70. During spray coating operations, the roof40is positioned at the top of the booth12. The intake slot62extends vertically along the entire height of the booth12.

As will be further explained herein below, the floor38may include a bypass opening78that may be selectively opened and closed with a slide cover80. During a cleaning operation, as the roof40is lowered towards the cyclone inlet region, powder overspray is removed from the interior surfaces of the booth12and drawn into the intake slot62and into the cyclone for recovery. As the roof40is lowered to a point at which the cyclone inlet70is blocked by a bulkhead82(seeFIG. 4A), the bypass opening78is opened and communicates with the vertical bypass duct75which connects to the bypass inlet76above the cyclone15(seeFIG. 4a) so that the powder entrained exhaust air bypasses the cyclone and is transported to the after filter and blower system16. The bulkhead82travels vertically within the recovery duct74at the same speed as the roof40during a cleaning operation. But, when the bulkhead82reaches a position in which it faces and blocks off the inlet to the cyclone15, positive stops prevent the bulkhead82from being lowered further even though the roof40continues to descend during a cleaning operation. When the cyclone inlet is blocked by the bulkhead82, the bypass opening78is opened and powder flows through the opening80and into the bypass recovery duct75and on to the after filter and blower system16via the cyclone bypass duct15b.

The doors30and36that generally extend away from the gun slot panel42and toward the recovery intake slot62may be provided with air jets (not shown) along their bottom edge so us to direct powder that falls on the floor toward the intake slot62of the recovery system. Compressed air tanks or accumulators (not shown) may be disposed below the floor of the booth or other convenient location to supply high volume compressed air to the door air jets. In accordance with an aspect of the invention, all of the energy needed to remove overspray coating material—from the booth interior surfaces via nozzles on the roof, the doors, gun blow off nozzles and so on—may be provided by accumulators so that the energy in the form of high volume pressurized air can be stored and ready to use. The accumulators may be replenished during spray coating operations although the accumulators86on the roof40are periodically replenished during a cleaning operation as will be further explained below.

The doors30,32,34and36are fully closed as inFIG. 2during a cleaning mode of operation. When the doors are fully closed, the doors closely surround the roof40perimeter (for example with about a lateral two inch gap), and the roof conveyor slot cover52is closed so that powder overspray can be removed from the interior surfaces of the booth and will be contained and not escape the booth but rather collected into the recovery system. A gun slot cover arrangement60(FIG. 2and the discussion below referencingFIGS. 7-9) is also closed to prevent powder escaping through the gun slots61. Prior to and/or after the conveyor slot cover52is closed, the roof nozzles50may be triggered to remove powder at the top of the booth surfaces.

The roof40is lowered and the air nozzles50that travel with the roof are used to remove powder off the interior surfaces of the doors. In this exemplary embodiment, the nozzles50are intermittently triggered to direct pressure waves along the booth surfaces, for example about a 1.5 second blast of air at about 100 psi. The accumulators86are sized to permit them to be mounted on the roof frame and travel with the roof40, therefore, the accumulators86are not particularly large. For example, the accumulators86may be sized at about sixty gallons so that each discharge cycle through the nozzles50substantially reduces the stored amount of compressed air energy in the accumulators86. In the exemplary embodiment, it takes about eight seconds to replenish the accumulators86so that the nozzles50are intermittently triggered or cycled at about 1.5 second on and about eight seconds off as the roof is lowered. The descent rate of the roof is balanced with the replenish rate of the accumulators so that there is no loss of pressure or volume to maintain effective cleaning of the surfaces throughout the descent of the roof40.

During a cleaning as well as a coating operation, the after filter system16is constantly drawing exhaust air into the booth12via the cyclone15. During a cleaning operation, this exhaust air primarily enters the booth12via the gap between the roof40perimeter and the door interior30,32,34,36surfaces throughout the descent of the roof. With reference toFIG. 4A, this high velocity air flow produces a shearing force that dislodges powder particles from the door interior surfaces. This shear force is the only cleaning force applied to the interior surfaces during each eight second interval that the accumulators86are being replenished. The nozzles50create a pressure wave that is effective for a distance of about two feet with each 1.5 second trigger of high pressure air. Therefore, the rate of descent of the roof40during a cleaning operation may be selected to balance the effective use of the nozzles50to blast powder from the surfaces and the high velocity exhaust air to also dislodge powder from these surfaces. In one embodiment the roof may descend at about 8-10 feet/minute, and the roof retracted back to the top at about 30 feet/minute.

The size of the gap between the roof and the interior door surfaces may be used to control the air flow and shear force created by the exhaust air. The after filter system16can draw a substantial volume of exhaust air, so the gap cannot be made so small that the head pressure on the roof creates too much strain or stress on the roof assembly. A typical gap range may be about 1.5 inches to about 2 inches. The actual gap used will be determined by the booth size, the exhaust air flow characteristics, required cleaning time, the effectiveness of the pressure wave created periodically by the nozzles50and the desired rate of descent.

The use of the exhaust air to perform a significant portion of the cleaning operation has a significant cost benefit as it allows the amount of required pressurized air to be reduced. In one embodiment, the shear forces applied by the exhaust air passing through the gap between the roof and the doors provides about half of the energy needed to clean the booth12interior surfaces. This represents a substantial savings of pressurized air that would otherwise have to be used (or other cleaning techniques such as wiping actions).

The brief but high velocity pressure wave that is periodically applied via the nozzles50not only dislodges the powder particles from the surfaces being cleaned, but also imparts sufficient energy to the dislodged particles that they impact other particles to dislodge them. In the exemplary embodiment herein, the pressure waves have about a two foot effective zone so that the nozzles50may be intermittently triggered and need not produce a constant flow of pressurized air. The pressure waves do not cause static charging or impact fusion.

The powder entrained exhaust air is drawn into the recovery system14, such as the cyclone intake duct70, for example, via the intake slot62which extends vertically from the floor to the top of the booth. Since in this example the cyclone intake duct70is positioned about halfway between the floor38and the top of the booth, the intake slot62may vary in width along its length, being narrower near the cyclone intake duct70and wider at the top and bottom (seeFIGS. 4A,4B and4C). This achieves a fairly uniform flow of air into the intake slot62along the entire height of tile booth. For example, the intake slot62may be about two inches at the intake duct and taper in width to about four inches near the top and bottom of the intake panel44.

During a cleaning operation, which may be part of a color change operation for example, the doors are fully closed, the guns are retracted from the booth (powder is removed from the gun exterior surfaces by air nozzles positioned at the gun slots) and the gun slot cover mechanism60is used to close the gun slots (as will be described hereinafter.) The conveyor slot cover52is also closed after all conveyor hooks have cleared the slot. The roof40is then lowered and powder is removed and directed downward off the surfaces of the doors and is drawn sideways into the intake slot62and the cyclone15. Prior to lowering the roof, the nozzles50may be triggered.

As the roof40is lowered, the effective size of the booth changes. This changes the dynamics of the air flow into the cyclone15. In order to efficiently continue to draw powder out of the booth interior, the operation is changed from a sideways recovery mode via the intake slot62to a downward or down draft recovery mode via the floor duct78(seeFIGS. 4A and 4B). This changeover is accomplished by providing a recovery duct bulkhead82that travels within the plenum74. The bulkhead82travels at about the same rate as the roof40while the roof is being lowered. The bulkhead82in one embodiment is a closed box-like structure or frame that generally conforms to the interior shape of the recovery duct plenum74. Any suitable means may be used to move the bulkhead such as cables for example. As the bulkhead82reaches the intake inlet duct70of the cyclone15, it blocks the inlet to the cyclone15. Mechanical stops84may be provided inside the plenum74to limit further lowering of the bulkhead82within the plenum74. When the inlet70to the cyclone is thus blocked, the floor bypass duct78is opened by sliding the cover80. This allows powder that is directed down towards the floor38to be exhausted from the booth through the floor, into the bypass duct75and into the bypass inlet duct76of the cyclone (sometimes referred to as a banjo) to the after filter and blower system16. After the roof has been lowered to or near the floor, it is then raised back up to the top of the booth and the bulkhead82also returns to the top of the plenum74.

In an alternative embodiment illustrated inFIGS. 4A and 4B, in place of the floor opening78, or in combination therewith, a slot79may be provided between the bottom of the primary duct72and the floor38. This slot79communicates with the recovery duct plenum74so that downward moving exhaust air and powder enters the plenum74via the slot79. Since the slot79will always be open, the exhaust air with powder may also be selectively recovered through the bypass duct75into the bypass inlet76of the cyclone15. For example, when the roof40and bulkhead82are still in the upper portion of the booth12, the slot79will communicate with the cyclone inlet70via the recovery duct74. However, when the inlet70is blocked, the bypass duct door81may be opened so that the powder entrained exhaust air flows into the bypass duct75, into the bypass outlet15band on to the after filter system16. The door81may be realized in any convenient manner such as a simple plate valve the closes and opens the bypass outlet. A pneumatic cylinder or other motive means, including manual operation, may be used to open and close the cyclone bypass.

The roof40may carry with it one or more accumulators86that contain pressurized air and provide the energy and air needed for the air nozzles50that are mounted on the roof as well as the conveyor slot air plenums54,56. Separate accumulators may also be used to provide the pressurized air for the air jets mounted on the bottom edges of the doors as well as the blow off nozzles for the spray guns18. In this manner all energy needed to clean the booth interior surfaces is provided from accumulators so that shop air need not always be applied to the cleaning apparatuses. The accumulators can be replenished during a coating or cleaning operation. This allows the cleaning energy to be maintained at a constant pressure as it is being discharged through the various cleaning nozzles including but not limited to the nozzles50on the roof40. The various cleaning nozzles for the guns, the floor and the roof nozzles may be intermittently triggered at appropriate intervals such as every second and a half for example as described above.

FIG. 5illustrates schematically the door positions for cleaning and spraying operations (tile doors in the closed position for cleaning are shown in solid line). During cleaning the doors are fully closed. During spraying, the doors may be opened to any convenient dimension to maintain adequate flow of containment air to contain the powder overspray. In one embodiment the doors are opened to an eighteen inch gap. The doors may be opened and closed with any suitable actuator mechanism. In the embodiment ofFIG. 2, pneumatic cylinders90and92are used to open and close the left side doors and pneumatic cylinder driven arms94,96are used to open and close the right side doors. Proximity sensors (not shown) or other suitable position monitors may be used to control positioning of the doors. For larger booths in which the doors include two or more sections, each section may have its own pneumatic drive member as illustrated inFIG. 2A. A door for example having an upper section32aand a lower section32bwill have two actuators90aand90bthat can be operated together to move the two sections as a single door unit. Similarly, the front right side doors30aand30bmay be moved by actuators96aand96b.

FIG. 6illustrates an example of a lift off hinge46that may be used to mount the doors but other hinge designs may be used as required. In this example, the hinge46is realized in the form of a structural steel lift off hinge that includes a pivot pin100. One plate102of the hinge is mounted to a door while the other hinge plate104is mounted on a suitable support structure. A piece of polypropylene106or other suitable material may also be installed on the inside surface of the hinge joint46that faces the booth interior to function as a live gap seal and prevent powder from escaping the booth.

FIGS. 7,8and9illustrate an embodiment of the gun slot cover mechanism60. The gun slot cover mechanism60is used to open and close the gun slots61. When the gun slots are open, the spray guns can be moved into and out of the spray booth. When the guns have been retracted for a cleaning and/or color change operation, the gun slot cover60is positioned so as to prevent powder from escaping through the gun slots. Due to the vertical length of the gun slots, a plurality of covers may be used as required.

The gun slot cover mechanism60includes a flexible cover member112that is mounted on a frame114using a ball and track arrangement116. A central portion118of the cover member is attached to one end of a piston120that may be translated, for example, by a pneumatic cylinder122. A plate124supports two ball arms126which carry a guide ball128thereon. The guide ball128slides within a channel130attached to the cover member112. In order to open the gun slots, the piston120is pushed outward so as to displace the central portion118into the booth interior. The cover member112includes two side portions132that bend inward as the balls128slide along the positionally fixed channels130. This position is shown in phantom inFIG. 7. When the piston is retracted, the cover member112returns to the position illustrated inFIG. 7, which closes the gun slots and forms a smooth sealed gun slot panel42. Due to their length, as shown inFIG. 8, more than one drive mechanism may be used for each cover.

With reference toFIG. 10, because the spray guns are positioned on only one side of the spray booth, it may be necessary to double spray the parts.FIG. 10illustrates an exemplary layout for a material application system that uses two spray booths200and202. The conveyor26transports parts through both booths. Note that in this example there are two after filter/blower systems16, one for each cyclone system15. As an alternative embodiment, a motor or other suitable drive mechanism may be provided with the conveyor system so as to rotate parts during a coating operation. This would allow parts to be fully coated within a single booth. Parts may also be manually repositioned for complete coating.

With reference toFIGS. 1,11A and11B, the spray guns18typically include one or more hoses and cables305, including, for example, material feed hoses, air hoses and in the case of electrostatic guns, electrical cables. The material feed hose extends from the gun all the way to the feed center21. The electrical cables may have to run a substantial distance to an electrical control console (not shown) and the air hoses will typically run a length to a supply manifold or other compressed air source. Particularly in the case of powder feed hoses, for the guns located above normal human height, the hose runs can be quite lengthy. This is especially the case for guns near the top of a twenty-seven foot booth. These hose lengths can be quite heavy and represent a significant load for the gun movers and oscillators.

In accordance with an aspect of the invention, a strain relief arrangement may be provided. This concept contemplates a mechanism that limits the load carried by the gun mover and oscillator while at the same time allowing full range of gun movement during a powder coating operation.

Positioned behind the guns18are one or more hose cabinets300that extend vertically about to the top of the spray booth12. Mounted on the cabinets300are a plurality of strain relief devices302. In the exemplary embodiment, there is a single strain relief device302for each spray gun, however, one alternative would be to make the strain relief devices of an appropriate size that each could accommodate more than one gun.

Each strain relief device302includes a support cylinder304and a hose clamp bar306. A hose and, when used, electrical cables and air hose extend from the associated spray gun, are provided a predetermined slack length between the gun18and the cylinder304so that the gun mover and oscillator can freely move the guns as desired. The hoses/cables are positioned over the top of the cylinder304and then the clamp bar306is secured by any convenient means such as bolts308. The clamping action isolates the hoses and cable weight from the gun and gun mover except for the portion that extends from the gun18to the clamp bar306. In this manner, a fixed predetermined load can be maintained on the gun mover independent of the overall length of the hoses and cables. This also reduces force applied to the back end of the gun and stress on the hoses and cables.

The hoses and cables run from the relief device302into the hose cabinet300and down to the floor area for further routing as needed. The cylinder302should be of sufficient diameter to prevent the hoses from collapsing under their own weight. Note that multiple cabinets may be used as needed depending on the number and size of hoses and cables being routed.

FIG. 12is a simplified schematic of another feature of the invention. We have found that in some cases, eddy currents and other flow effects can cause entrapment areas or pockets within the recovery duct interior plenum74. In an alternative embodiment, the interior plenum350, which it will be recalled is the duct through which powder entrained exhaust air enters the cyclone15via the recovery slot62and cyclone inlet70, is provided with an offset or shifted slot opening352, meaning that the slot is not centered on the central axis X of the plenum350. In addition, the slot352opens to a tangential or tapered surface354that joins to the main plenum cylinder356. This geometry produces a swirling, somewhat cyclonic action within the plenum350to reduce eddy currents and entrapment areas or “dead spots.”

Even with the embodiment ofFIG. 12, or with other configurations, there may be surfaces360that are not fully cleaned by air flow within the duct work.FIG. 13illustrates one solution to this possible anomaly. An air blow off manifold370is mounted at one end to the ceiling or roof40so that it travels with the roof during a cleaning operation. The blow off manifold370may be realized, for example, in the form of a hollow composite extrusion372and may be provided with one or more air jets, slots or ports374that direct pressurized air376at the surfaces360of concern.

Pressurized air may be supplied to the blow off manifold370from one of the accumulators86that are carried by the roof40, or any other suitable source. A pressure regulator378and solenoid valve380may be used to control flow of air to the manifold370. The blow off manifold may be on continuously as the roof40travels down and tip the booth12during a cleaning operation, or may be pulsed.

FIGS. 14A and 14Billustrate some additional features that may be used with the roof40structure. In some cases when the roof40is fully raised, such as during a spraying operation, it may be desired to pulse the nozzles50before the conveyor slot cover52is closed. In order to maintain stability of the roof40that is primarily supported on the cables400, stabilizers402are provided that extend generally vertically from the roof frame404. These stabilizers402may be in the form of stanchions, bars or other suitably strong and rigid members that are slideably received in a stabilizer channel406when the roof40is raised. The stabilizer channels406are rigidly mounted to the overall framework22and thus hold the roof40stable even against the impulse forces of the nozzles50.

The roof40structure also carries rollers410. These rollers410bridge the narrow gap between the roof40and the interior surfaces of the booth doors as the roof40is raised and lowered, thereby stabilizing the roof40, keeping it centered and preventing extreme movement during nozzle50pulses. The closed cover52(FIG. 3) also helps stabilize the roof40during cleaning operation. The rollers410may be provided with brushes (not shown) to prevent powder from adhering to the rollers. Since the rollers410are positioned above the nozzles50, the Sur faces they contact are clean so that powder is not pressed against the wall surfaces.

It is intended that invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.