Metal Finishing Guide Book


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are conveyorized and where automatic coating equipment is used or large amounts of coating material are sprayed; and high-production applications. Features of water-wash booths include up to 99.6% collection efficiency, depending on paint formulation; continuous ventilation rate (constant static pressure); and agitation systems for more effective paint-killing action. The water-wash action removes the liquid from most paints and reduces it to extremely small particles. It is a nonflammable, nonsticky waste, which may be nonhazardous. The sludge formed is skimmed from the tank top, or scooped from the tank bottom, and placed in drums. There are several potential challenges associated with water-wash systems such as maintenance downtime, operating costs, and sludge disposal costs. The addition of a sludge removal system can greatly minimize these problems. The benefits of a proper sludge removal system are numerous and include reduction in the overall volume of disposed material because the end product is a drier sludge; the final water content, with some systems, may be low enough to permit the dried sludge to be classified as nonhazFig. 18. Paint mixing room. ardous; the result of cleaner booth water can eliminate nozzle clogging in the air-wash section of the booth; and higher production due to increased up time. AUTOMOTIVE, TRUCK, AND TRAILER BOOTHS, PREP STATIONS, AND PAINT MIX ROOMS There are a variety of vehicular spray booths available, including cross-draft, downdraft, and semidowndraft, which were discussed above. Figures 14, 15, and 16 show models of these three types of vehicular spray booths. The prep work station (see Fig. 17) is a filter exhaust system that traps sanding dust at the source, returning a clean, even flow of air to the work areas around the part. They are also used to exhaust paint overspray on some light painting applications. They come in semidowndraft and downdraft designs. During sanding or prep work, the overhead plenum recirculates clean, filtered air to the work station. During priming, the inside/outside damper vents solvent vapors to the outside. The advantages of utilizing a prep work station include a quick return on investment; a cleaner work area because a prep work station can be equipped to control both dust and vapors; increased productivity due to lower maintenance and easy cleanup; and lower energy costs (shop air is recirculated after filtering, so heating and air conditioning bills are lower). A paint mix room (see Fig. 18) is designed to provide a bright, clean, wellventilated area for mixing paints and related materials. These ���clean-air��� rooms help provide a contaminant-free mixing operation and a safe work environment. The paint mix room downdraft ventilation system pulls in air from around 835

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