Good Atomizing with an Airless Air-Assist Spraygun
Advice on how to get a good spray pattern and prevent striping with an AAA gun. January 14, 2008
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Question
Our finish guy has been having problems with SW CV. We use a Graco air assist model 50 with a #15 gun. Salesman set us up. The product goes on flat and smooth, but when it dries, lines appear, and some orange peel. I know everyone has their own favorite settings for air pressure and fluid flow. Any info would help. Also, is there anywhere we could send him for some education on finishing? He seems worth it and would like to learn.
Forum Responses
(Finishing Forum)
From contributor R:
We will need to know which Graco pump you have. Is it a 10:1 pump or higher ratio? If it were a 10:1 pump, then 50 psi on the fluid would be 500 after the pump. Usually 650 is a good number for Graco air assist pumps depending on the viscosity of your coating. Next is atomizing air which most people set way too high. It should be just high enough to make the "horns" in the spray pattern go away. Spray on a piece of cardboard with the atomizing air off and you will see what the horns are. The orange peel is caused by improper atomization, so the fluid pressure is probably too low.
From contributor G:
Does your finish guy have a computer? Info is better communicated directly as opposed to second hand.
From contributor C:
Check out AWFI, who advertise here for courses. I have found them very valuable.
From contributor J:
Is this a pigmented product? I've seen this problem with pigmented coatings. The G15 gun comes with a carbide seat or acetyl seat. The carbide is for pigmented, waterborne, and higher viscosity materials. The acetyl is for acid-catalyzed, low viscosity lacquers and stains. I found for the extra dollars, the 20:1 pump is better for all the different materials out there. It sounds like you need more fluid pressure.
From the original questioner:
Thanks for the info. It helped a lot. He doesn't need a computer - he reads over my shoulder. It's a 15:1 pump. Pigmented and not. Clear over pigmented.
From contributor J:
15:1 should be plenty because the gun is only rated for 1500 psi. Start at 40 psi to your pump (600psi fluid pressure) and no atomizing air. Spray a quick burst at a piece of cardboard. You should have an oval pattern with round dots on each end. Increase your pump air 10 psi and repeat until the dots blend into the pattern. This is like airless now. You don't want to spray at this pressure. Back off 5 psi until the dots reappear. Use your atomizing air to blend the dots back into your pattern. Start at 5 psi. The atomizing air shouldn't need to be over 10 psi.
