Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 125 of 331

TROUBLESHOOTING SPRAY GUNS If fluid is leaking from the needle packing nut, check for a loose packing nut or dried-out packing. Tighten the nut un- til leaking stops, or replace packing, if required. If air is leaking from the front of the gun, check for Fig. 11. Split spray pattern caused by too much atomiz- ing air pressure and/or trying to widen the spray pattern too much. Remedy the prob- lem by opening the fluid con- trol knob (D) to the full posi- tion and turning the spray control knob (C) down to nar- row the spray pattern width. foreign matter on the air valve stem or seat, a broken air-valve spring, or a bent air-valve stem; check the air valve packing nut to see if it is too tight, the air-valve assembly to see if is tight enough, and the air valve as- sembly gasket for leaks; and check to see if the gun is a bleeder-type spray gun. If fluid is leaking from the front of gun, check for a worn or damaged needle or fluid nozzle, dirt in the flu- id needle seat, and a broken fluid control spring; check to see if the fluid packing nut is too tight, and if the wrong size needle is being used. FAULTY PATTERNS AND HOW TO CORRECT THEM Fig. 12. Spitting, caused by air bubbles in the fluid supply, can be remedied by sce- curing all fittings and connections. Loosen nut (E) and place two drops of machine oil on the packing. Replace the nut and fin- ger-tighten. In aggravated cases, replace the packing. Remove the air and fluid noz- zles (F) and clean the back of the fluid noz- zle and nozzle seat in the gun body using a rag soaked with thinner. Replace and tighten fluid nozzle with the wrench sup- plied with the gun. Replace the air nozzle. Tighten or replace swivel nut (G). Dried material in a side port of a spray nozzle restricts passage of air through the port on one side resulting in full air pres- sure coming from the clean side of the part in a "C" or fan pattern in the direction of the clogged side (see Fig. 9). This situation can be remedied by dissolving the materi- al with thinner. Do not use metal devices to probe into the air nozzle openings. Dried material also gets stuck around the outside of the fluid nozzle tip re- stricting passage of atomized air to a point at the center of the air nozzle opening caus- ing an inverted tear-drop-shaped spray pat- tern (see Fig. 10). This faulty pattern can also be caused by a loose air noz- zle, or a bent flu- id nozzle or nee- dle tip. If dried material is caus- ing the trouble, remove the air nozzle and wipe off the fluid tip using a rag soaked with thinner. Tight- en the air nozzle and replace the fluid nozzle and/or the needle, if it is bent. A split spray pattern — heavy on each end of a fan pattern and weak in the middle — is usually caused by (1) too much atomizing air pressure; (2) attempt- 124 Fig. 13. Fan spray pattern caused by low atomizing air pressure or too much spray material being fed through the gun. To correct the prob- lem, increase air pressure from air supply.

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