Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 122 of 331

which it is made or through the ap- plication of a conductive pretreat- ment. Recent equipment developments Fig. 5. Gun should be moved parallel to surface being sprayed. now make it relatively simple to ap- ply water-reducible coatings with elec- trostatic equipment. Both hand-held and automatic systems are available. Since the material is highly conduc- tive, it is necessary to isolate the ma- terial supply. The fluid supply will be highly charged, and it is, therefore, necessary to erect barricades to pre- vent physical contact with this portion of the system. Sometimes the added expense to apply this coating may not justify the material savings. Also, added maintenance — cleaning the hangers, supports, or convey- ors — to assure conductivity to ground is necessary. All electrically conductive items, such as containers and spray equipment, within 10 ft of the spray area should be grounded to prevent static buildup. Operators grounding out any static buildup may experience a severe shock. COMPONENTS OF A SPRAY SYSTEM A spray finishing system consists of the following components: a spray gun, a com- pressed air supply, a fluid supply, and other necessary items such as hoses, fittings, regulators, and proper respiratory equipment Spray Gun Spray guns (see Fig. 4) are available in a wide variety of performance capabilities and costs. The three factors in order of importance are function, service, and price. As with anything, you pay for quality. Cheap spray guns, which may look like the expensive guns they imitate, have no place in a production finishing shop. Consult your spray gun supplier for correct air and fluid nozzle recom- mendations. After all, this is the part of the spray gun that develops the atom- ization desired. Compressed Air Supply The compressor you use does not make air, it only compresses it. The condition of your air supply usually tells a lot about the compressor and the air-supply lines. A compressor is rated for its volume, measured in cubic feet per minute (cfm), and its pressure, measured in pounds per square inch (psi). To assure maxi- mum performance of any spray finish- ing system, the compressed air supply should always exceed the required psi and cfm requirements of its compo- nents. This is especially true when using HVLP spray guns. The rule of thumb is to expect about 4 cfm for every 1 horsepower at 100 psi with an electric compressor. Gas compressors are some- Fig. 6. Fanning will result in an uneven coating. 121

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