Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Fig. 14. Improper spraying creates paint losses in the form of overspray, rebound, and fallout. ing to get too wide a spray with thin material; or (3) too little spray mater- ial available to pump through the spray apparatus. This situation can be reme- died 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 caused by air entering the fluid sup- ply, and by dried or missing packing around the material needle valve that permits air to get into the fluid pas- sageway. Dirt between the fluid noz- zle 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 materi- al 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 sup- ply. Correct air pressures are discussed elsewhere in this article. 125

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