Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 213 of 331

tration of flammable vapors or combustible vapors or mists in the exhaust stream below 25% of the lower flammable limit (lfl) of the paint." Lower flammable limit is defined as the concentration level at which a particular atomized solvent will ignite. The volume of air needed to move through the booth and into the exhaust chamber is measured in cubic feet per minute (cfm). Use the following formula to determine the volume of exhaust air: Area x Velocity = cfm of air where area is the cross-sectional area in square feet of all openings in the spray booth. When air input plenums are used the conveyor openings may be ignored. When connecting vestibules are used, the opening between adjacent booths may be ignored. Velocity is the speed or velocity of air required by code. Speed of air move- ment is measured in feet per minute (fpm). Cubic feet per minute (cfm) is the vol- ume of air moving through the booth. This relationship between booth size, the velocity of the air movement, and the volume of air being moved is shown in Fig.11. INDUSTRIAL-TYPE SPRAY BOOTHS Dry-Filter Booths As with any type of paint-arrestor spray booth (see Fig. 12), the booth's main func- tion is to remove the airborne particles from the spray booth exhaust air by means of disposable filters. The standard booth is typically designed to operate at 125 fpm air velocity. The booth normally provides an enclosure to accom- modate a spraying operation. It limits the escape of spray and residue and safe- ly directs them to a filter and exhaust system. Dry-filter spray booths are ideally suited for low- to high-production opera- tions; lighter spray rates; materials that stay wet, such as enamels, high solids, and water-base coatings; materials that do not react chemically with each other; and limited budgets. Some of the styles of dry-filter booths include the floor-type, bench-top, and bench models. While the floor-type booth is avail- able in a wide variety of sizes, this booth is designed for the work place where space is limited. The bench-top booth is perfectly suited to sit on top of an existing work bench. Depending on available space, this booth may fit the re- quirements perfectly. Some booths come with a leg kit for free-stand- ing applications. The bench booth provides greater paint arrestor frontal area for increased capacity Fig. 13. Water-wash spray booth. in comparison to the bench-top booth. It is designed with a table height shelf. Both the bench-top and bench booths are perfect for spraying small objects and 212

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