Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 208 of 331

ceiling as would be the case of a normal downdraft booth. The air flow is from the ceiling of the booth down and out through each side plenum. No pit or el- evated platform is required for this booth. SPRAY BOOTH DESIGN AND SIZING Selecting the booth and sizing it for an application requires review of several areas. Knowledge about the facility and production process are important in choosing the right equipment. Take the time to understand the application, and do not forget future plans that may influence the choice of spray booth de- sign. The following are some general guidelines for selection and sizing. 1. Maintenance: All booths require regular maintenance for optimum perfor- mance. As a first step, determine the capability of the maintenance depart- ment or maintenance contractor. This will determine the sophistication lev- el of the equipment required. 2.Budget: Always take the budget into consideration when choosing the spray booth. Balancing the application requirements and available funds will help identify the most effective exhaust chamber, air flow, and booth options for the job. 3.Selecting the Booth Design: The first step in selecting an appropriate booth de- sign for an application begins with an investigation of the finish quality lev- el and the production requirements. This step will help determine the direction of air flow through the booth, as well as the appropriate filtration method, either dry filter or water wash. Production Requirements Part Size and Configuration The size and style of the part, the carrier that conveys it through the booth, and the relationship of the spray gun to the part, all play a role in determining the di- rection of air flow as well as the velocity or speed of air through the booth. Air flow and velocity are needed to transport paint overspray into the filters. There are three types of air flow through a booth as discussed above: cross-draft, semi- downdraft, and downdraft. Production Rate and Transfer Efficiency Fig. 7. Manual booth sizing. Production rate is a measure of the number of parts that can be finished within a cer- tain time frame, usually per hour or per shift. Transfer efficiency is the percentage of material being sprayed that adheres to the part; the remainder is overspray. The type of application equip- ment—conventional, elec- trostatic, or HVLP (high vol- ume, low pressure)—deter- 207

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