Coating apparatus – Projection or spray type – With hood or offtake for waste material
Reexamination Certificate
2003-02-21
2004-11-23
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
With hood or offtake for waste material
C454S050000, C015S301000
Reexamination Certificate
active
06821346
ABSTRACT:
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.
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.
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.
In known arrangements the cyclone separators have been connected 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
It is a still further object of this invention to provide a powder spray b
Ainsworth James
Perillo Luigi
Van Den Bergh Louis
Calfee Halter & Griswold LLP
Crispino Richard
Lazor Michelle Acevedo
Nordson Corporation
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