Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 206 of 331

Fig. 4. Cross-draft air flow. TYPES OF SPRAY BOOTHS A spray booth consists of a work compartment where spraying takes place, an ex- haust chamber for collecting particulate, an exhaust fan and motor, and an ex- haust duct to the exterior of the building. Paint booths are categorized by the method of collecting the overspray and the direction of air flow in the booth. There are subcategories in each case. Dry-Filter Booths There are several types of dry filters available for use in spray booths. The rec- tangular pad type is available in many grades and types. The roll media type is also available in many sizes, grades, and types. This designation is a slight misnomer as the media is rolled for ease of shipment but is unrolled and applied as a large rectangular block of filter media. Roll media filters should not be confused with continuous roll. Continuous roll media come on spools in large, long rolled coils. As the filter becomes contaminated, the clean section is advanced. This can be hand or motor operated. Cardboard baffle and light density Styrofoam filters are also available; how- ever, dry baffle exhaust systems have al- most entirely disappeared, except when used with paint filters as prebaffles. A single or double row of baffles is placed vertically in front of a normal paint ar- restor bank. This provides the primary collection surface for overspray and ef- fectively protects the filters from rapid loading; however, they now become part of the collection system and must be cleaned and maintained. This applica- tion originated with the collection of high solids paints that caused heavy loading and forced rapid change of filter media. The physical characteristics of the high solids materials allow collection through a trough at the base of the baffles. In some cases, this reclaimed mate- rial is reusable or it can be returned to the manufacturer. Fig. 5. Downdraft air flow. Water-Wash Booths 205 Unfortunately efficiency factors have at times been misrepresented as pro- viding an assurance that a spray booth will meet EPA requirements. Although some spray booth designs are more efficient than others at preventing material from entering the environ- ment, high-efficiency factor ratings do not automatically ensure EPA com- pliance.

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