Metal Finishing Guide Book


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what lower in performance. Do not ignore the necessity of properly selected, cleaned, and operating air-supply components such as extractors, regulators, ball valves, and hoses. Failure to do so only adds to finishing-room difficulties. Pulling back slightly on the trigger opens the air valve to allow use of the gun as a blow gun. In this position the trigger does not actuate the fluid needle and no fluid flows. As the trigger is further retracted, it unseats the needle in Fig. 7. Hold gun perpendicular to surface being the fluid nozzle, and the gun begins to sprayed. spray. The amount of paint leaving the gun is controlled by the pressure on the container, the viscosity of the paint, the size of the fluid orifice, and the fluid needle adjustment. In industrial finishing where pressure tanks or pumps are used, the fluid needle adjustment should normally be fully opened. In a siphon cup operation, the needle valve controls the flow of paint. Fluid Supply The fluid supply can range from siphon cups, to pressure tanks, to material handling pumps for dead-end or circulating systems. Siphon and gravity cups remain popular with refinishers, and those on touch-up lines. Pressure tanks remain popular with those on low- to medium-production lines, using compressed air or HVLP atomization. Pumps are generally used on medium- to high-volume production lines, circulating systems, and airless and air-assisted airless production lines. Pumps may be powered by compressed air, hydraulics, or electricity. Paint Heaters Paint heaters, when used correctly, provide viscosity control, reduced solvent use, sprays of higher solids, reduced flash time, reduced air and fluid pressures, and improved flow. Heaters may be used with pumps on compressed air, HVLP, airless, air-assisted airless, and all types of electrostatic systems. Paint heaters are becoming more prominent in the finishing industry as solvent use is restricted to meet compliance standards. OPERATOR TECHNIQUES More often than not, spray painters are usually improperly trained (if trained at all), allowed to develop many bad habits, and, in many cases, frequently change positions or employers, taking their knowledge and skills with them. On the other hand, management sometimes fails to recognize the importance of training until problems exist. The organization may have the best coating materials and spray equipment mon- Fig. 8. Proper pattern overlap produces an even coating. 213

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