Metal Finishing Guide Book

2012-2013

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ing to get too wide a spray with thin material; or (3) too little spray material available to pump through the spray apparatus. This situation can be remedied by (1) reducing the air pressure; (2) opening the fluid control knob to the full position; and (3) turning the spray pattern control down to narrow the spray pattern width. This reduces the width of spray but will correct the split pattern (see Fig. 11). Spitting is Fig. 14. Improper spraying creates paint losses caused by air entering the fluid supin the form of overspray, rebound, and fallout. ply, and by dried or missing packing around the material needle valve that permits air to get into the fluid passageway. Dirt between the fluid nozzle seat and body, or a loosely installed fluid nozzle, can also contribute to the problem, as well as a loose or defective swivel nut, siphon cup, or material hose. To stop the spitting, be sure all fittings and connections are tight. A fan spray pattern that is heavy in the middle, or a pattern that has an unatomized (salt-and-pepper) effect, indicates that the atomizing air pressure is not sufficiently high or that there is too much material being fed to the gun. This problem can be solved by increasing the pressure from the air supply. Correct air pressures are discussed elsewhere in this article. 216

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