Metal Finishing Guide Book

2013

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also be high enough above the floor to allow the operator room to spray the lower edges and the underside easily. Sufficient working depth will allow at least 3 ft between the rear of the part and the water-wash tank or filter pads, at least 3 ft between the front of the part and the booth face or intake filters, and allow for automatic machines, such as reciprocators, in conveyorized applications. Working depth should be sufficient for the part, including the fixture or pallet, to be entirely within the booth enclosure during finishing, plus allow for clearance at the rear. There should be a minimum of 3 ft between the part and the tank in a water-wash booth or the filters in a dryfilter booth. Conveyor openings are required when a conveyor moves parts through the spray booth. Conveyor openings should allow 6-in. minimum clearance around the part. A vestibule is a protected entry into the booth (see Fig. 9). It provides better air flow control through the booth by effectively blocking the tunnel leading into and out of the booth with the product. The vestibule length should be a minimum of the gap between parts so the vestibule always contains a part. Booth Air Requirements The final step in selecting the booth is establishing the minimum air velocity and volume requirements. The spray booth should be located to allow for proper air entry and flow through the booth. An open-faced booth should be located with the face at least booth height dimension from any wall (see Fig. 10). When this placement is not possible, air input plenums will provide adequate air flow. A spray booth requires a minimum air draft or velocity, measured in lineal feet per minute (fpm), to carry overspray through the booth, past the operator or the automatic equipment, and deposit it into either the water curtain or filter pads. As a rule, OSHA inspectors rely on the guidelines specified in NFPA-33 requirements in the booth during spraying operations. Although the NFPA-33 guideline covers most spray operations, greater air flow may be required when specific types of finishing equipment are used. The high-pressure atomization equipment used to break up higher solids materials, for example, produces high atomization pressures and consequently high fluid stream velocity at the tip of the spray gun. This 779

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