SPECIFICATIONPowder spray boothThe present invention relates to powder coating and particularly to a booth in which the spray application of a powder can be carried out.
Powder coating is fairly well known in the coating industry. In general, a powdered resin is applied to a substrate, and then the substrate and powder are heated so that the powder melts and forms a coating on the substrate when it cools. The powder is almost invariably deposited on the substrate by an electrostatic application technique. Electrostatic application techniques generally include some process of imparting an electrical charge to the powder, the substrate, or both in order to aid deposition and retention of the powder on the substrate. Electrostatic techniques are well known, and therefore need not be discussed in detail here.
By and large, powder deposition is performed in a booth which includes some controlled area which functions to contain any oversprayed powder not deposited on the articles to be coated. In many systems, the containment of the powder in the booth is aided by an exhaust system which creates a negative pressure within the booth and causes the oversprayed powder to be drawn out of the booth in a controlled manner to recovery and filtering devices. In some systems, the oversprayed powder which is collected is merely saved for future use, while in others it is recycled to the application device automatically.
In a powder coating installation, there are several critical or desirable aspects which have to be considered, some of which are: safety; efficiency; the size of the equipment; the complexity of the operation and construction; colour change; cleaning; maintenance; and the containment and/or recovery of powder not deposited on the substrate. The spray booth used in these systems, being an integral part of the installation, must also be considered from these standpoints. Therefore, it is a general aim of this invention to provide a spray booth which provides a substantial overall improvement in spray booths in view of these criteria.
In many regards, it is desirable to use static, cartridge type filters of the typical "bag house" type as part of the filter and recovery aspects of the system. These types of filters have no moving parts, and therefore offer simplicity, combined with reliability and efficiency. However, if these filter/recovery units are located in an area remote from the spray booth, the powder laden air is drawn out of the spray booth to the filter/recovery unit through ductwork or some other restriction, or through a confined area. In many systems, if not all, the filter/recovery unit itself represents a confined area. This gives rise to a deficiency in these prior art systems, in that they present a possibility of explosion.
The resins used in powder coating are, as a class, generally flammable. In their powdered form, and within certain air-to-powder ratios, they can burn rapidly. Thus, it can be appreciated that if an air/powder mixture were somehow to become ignited in an enclosed or restricted space, the result could be an explosion. Although burning of the powder even in an open space, can be inconvenient and present safety hazards to both life and limb, an explosion generally gives rise to more dreaded consequences. Thus, because these confined areas in the prior art systems give rise to the possibility of an explosion, we have sought to provide a booth/recovery system without confined areas which could create a potentially explosive condition.The recovery/filter portion of the device of the present invention is located integrally with the booth so that there is no necessity of having ductwork which could create a confined area.
Although some prior art booths did incorporate an integral recovery system with the booth, and although some of them did substantially reduce the "confined areas" these prior art systems were complex and costly to build, operate and/or to maintain. Thus, we have also aimed to provide a powder spray booth/recovery system which is simple in its design, manufacture, maintenance and operation, but yet which eliminates confined areas having explosive air/powder mixtures.
Another important consideration with respect to powder coating booths is the ability to quickly change the powders, or colour of the powder being sprayed. In this regard, it is important that the previous composition be effectively removed from the system, lest it contaminates the powder of a subsequent coating operation. We have therefore further aimed to provide a spray booth/recovery system which is safe, simple and yet which will provide the ability to quickly and efficiently be capable of being changed from one colour or one powder to another, and which further will facilitate maintenance of the system without disabling the spray coating operation.
In general then, the present invention provides a spray booth/recovery system which uses static filters and which provides improved safety and colour change capabilities in a very compact system.
In particular, the present invention provides a booth/recovery device comprising a booth in which to powder coat substrates, the device having a ceiling area, walls, and a floor, and having a recovery unit located underneath the floor of the booth. The recovery unit comprises a powder collector area below the booth, and a clean air chamber sealed from the booth and from the powder collection area, but being provided with an opening from the collection area into the chamber through static filters. The collection area is open to the interior of the spray booth through a hole of substantial cross sectional area in the floor of the booth and leading directly to the collection area.A blower is provided to create a negative pressure in the chamber so that powder laden air is drawn down through the opening in the floor of the booth into the collection area immediately below the booth, and thence upward through filters to the clean air chamber. This filtered air having only traces of fine powder in a nonexplosive proportion, is withdrawn from the clean air chamber through the blower, and passed to an absolute filter for final filtering.
Because of the location of the complete recovery unit under neath the spray booth, the space required for the booth/recovery unit is reduced to the floor space required for the booth itself, whereas prior systems required floor space for both the booth and the recovery unit.
Because of the substantial cross sectional area of the opening in the floor of the booth to the collecting area, there are no confined areas to present explosive conditions. The only confined area in the air flow path is downstream of the filters, where the air/powder ratio is non-hazardous.
The integral collector below the booth can be detachably attached to the booth, mounted on wheels and be provided with detachable fastenings to the ductwork for the blower, so that when colour change is desired, or when filter change is desired, or when maintenance must be done on the collector, another recovery unit can quickly and efficiently be placed under the booth, attached, and started up so that spray coating can continue even during these operations.
The present invention is further illustrated in the accompanying drawings, wherein:Figure 1 is a perspective view of a spray coating booth having a recover/collection unit in its base; andFigure 2 is a fragmentary view of the interior construction of the recover/collection unit in the base of the booth of Fig. 1.
Referring first to Fig. 1, the device comprises generally a spray booth 1, having a base 2 which comprises the filter/recovery unit for powder, and an absolute filter 5 connected to the base 2 through ductwork 3.
The ductwork 3 connects on either:side of one end of the base 2 by means of quick-disconnect connections 30 to holes 22 (see Fig. 2) in the base. This ductwork 3 links the interior of the base 2 to a blower 4 which creates a negative.pressure in the base 2 as will be more fully discussed later. The blower 4.exhausts into a plenum 29 having filters 28 which clean any air discharged therethrough.
The blower 4 can be mounted on a base 10 for convenience.
The spray booth 1 defines a controlled area for spraying and comprises generally a ceiling portion 6, opposed side wall portions 7, opposed end walls 32 and a floor area 8. The floor area 8, in this embodiment, actually comprises the top of the recovery/collector unit 2 and hence the two elements are designated by a common reference numeral herein.
The booth 1 is supported by legs over the base 2. An opening is provided in one of the side walls 7 of the booth 1 and both end walls 32. The opening in the side wall 7 provides access into the interior of the booth1 1 for spraying equipment, or for access for a man to enter the booth himself. Openings are provided in each end wall 32 for product to be transported through the booth 1 for spraying. A slot 9 in the ceiling portion 6 of the booth allows the passage of conveyor hooks from an overhead conveyor to carry the articles to be coated through the booth 1.
Referring now to Fig. 2, the details of the recovery/filter unit in the base 2 of the booth 1 1 can be seen. Fig. 2 is a fragmentary view of the collector/recovery unit 2 showing the interior details of the unit.
The base 2 is generally comprised of opposed exterior side walls 21, end walls 33, an upper wall 8, and a bottom portion 13. As noted above, the upper wall 8 also forms the floor of the booth. Along each of the opposed side walls 21 of the base 2 is a clean air chamber 19 below the floor 8 of the booth 1, defined between part of an exterior side wall 21 of the base, the upper wall 8 of the base, part of an inner side wall 11 and a bottom chamber wall 20.
There are holes 22 in one end wall 33 for each clean air chamber 19 to connect the ductwork 3 (see Fig. 1), in order to create a negative pressure in the clean air chamber 19 and to draw air thereinto.
The interior side wall 11 extends downward from the floor 8 and forms a centrally located air flow passage 12 directly from the booth to a powder collection area 14 below the clean air chambers 19. The centrally located air flow passage 12 is elongated in the direction of travel of the articles to be coated and extends across the whole length of the booth 1. It is of substantial cross sectional area so as not to present a restriction which would result in a "confined area" subject to explosion.
Each chamber 19 is provided with multiple holes 17 on the underside through the bottom walls 20. Each of these holes 17 is capped by a static cartridge type filter 16. The filters 16 can be removeably attached to the chamber 19 by any suitable means. In this embodiment the holes in the bottom wall 20 of the clean air chamber 19 and associated filter elements 16 are arranged in three banks of six filters on each side of the unit making a total of six filter banks. Each bank consists of two rows, three deep. In the plane of Fig. 2, four filters 16 can be seen, two on each side.
Below each of the six banks of filters, the bottom 13 of the base 2 tapers downward in the shape of an inverted pyramid, each pyramid defining one of six powder collection areas 14 where powder filtered out of the air by the filters 16 is collected. At the apex of each "pyramid" is a venturi pump 15 or other suitable means to transport the collected powder to a recycling bin, or storage for future use or discarding. There is an opening (not shown) at the apex of each pyramid communicating with a respective venturi pump 15.
Interiorly of the clean air chamber 1 9, venturi throats 18 are situated above and around each of the holes 17 through which filtered air passes. A series of pipes 25 extend across the base 2, one each in alignment with all four of the venturi throats 18, and hence the filters 16, across in a row. Each of the pipes 25 has four holes 26 in its underside which are aligned on each with a respective venturi throat 18. An air solenoid 24 associated with each pipe 25 and mounted exteriorly of the outside wall 21 is effective to discharge a burst of air into a respective pipe 25, and thus out of the holes 26 in the underside of the pipe 25 into each venturi throat 18. The burst causes momentary reverse air flow through the filters 16, and dislodges collected powder from the filter material. The dislodged powder falls into a respective "pyramid" collection area 14. The solenoids 24 are sequentially operated through any suitable control mechanism well known in the art, so that only one bank or row is cleaned at a time. Therefore, there is no net interruption of the air flow through the filter/collector unit 2. Access doors 27 are mounted on the exterior side walls 21 for servicing or replacing the filters 16. The whole base 2 is mounted on wheels 23 to allow it to be easily removed from underneath the spray booth 1, so that a new base 2 can be substituted therefor in order to facilitate the spraying of a new powder or colour, or to service the unit.
If necessary, a rubber gasket can be used to seal the periphery of the base unit to the booth.