Material Build-Up Problem on Spray-Gun Tip

      Advice on correcting a spray-gun performance issue: build-up of material on the spray tip, causing "fingers" in the wet finish. February 15, 2009

I am looking for help for a customer of mine that is spraying ICA urethane. He is experiencing a buildup of material on the outside bottom of his tip when he is spraying which is causing fingers. He is running 280 lbs. fluid pressure and anywhere from 10 to 25 lbs. of atomization air. Any suggestions on how to avoid this problem or at least slow down the frequency of the issue?

Forum Responses
(Finishing Forum)
From contributor D:
I have the same gun shooting the same material, thinned 10-15%. I use 300lbs on the material- 11-13 lbs for atomizing air. I am also using .09 tips. Larger tip orifice may require higher material pressure, but atomizing air should be in same range.

The most common reason for fluid buildup on the tip is too much atomizing air.
Also the cleaning routine is important when using a catalyzed finish. When finished with session, I flush the pump and lines with 3 changes of MEK and also special attention to tips and nozzles.

From contributor M:
Finish on the tip is not normally associated with fingers. Fingers are viscosity related, tails are not enough atom air. Tails are single dots at the outside of the pattern, top and bottom if you will. Fingers are all through the pattern and tend to wave up and down as you spray. Try replacing the seat insert and hitting the coating with some reducer to eliminate fingers.

From contributor B:
Depending on the ICA product being sprayed, some are quite high in volume solids and would require higher fluid pressure to properly atomize. I do agree with contributor M on his suggestions though.

From contributor W:
What I would first do is confirm that the atomization (fluid) pressures are correct. Typically you do not want to go below 300psi. Second I would say that fingers are due to low fan air pressures - 10-25psi of fan air is a very large range. Tip boogers can be a variety of things but first would be too high of fan air. What is the tip size? How old is the tip? Warn or not cleaned properly? Start with new tip, then run through the standard Kremlin start up process.

From contributor L:
We have a Kremlin mvx, and always have all kinds of problems with it. It has been the least reliable finishing system i have ever used in 20 years of spraying wood. I used to have a Husky gravity feed that worked every time you picked it up. My biggest issue with it is that there is no control over the fluid output except with the tip. Any little burning on or inside that tip will screw up your pattern, as well as a small piece of dried finish or other contaminant.

From contributor S:
For the Kremlin there are several issues that might help with very little cost. The seat insert is normally supplied as a SS seat. These are great for long life, but can leak a little. Replace the insert with a 129-679-904 Delrin insert. This will solve a lot of little problems like a buildup of coating on the air cap. This is much better then installing a heavier fluid spring. The tip needs to be kept clean. I think the best cleaner is an ultrasonic cleaner.

From contributor S:
I recommended the ultrasonic cleaner for the end of the day clean up. If the gun has a slight leak when it is not in use, the recommendation for the Delrin insert works every time to eliminate leakage, and it is a lot cheaper too.

The Airmix guns are designed for finishing shops, and last a long time. The fluid tips are rates at about 3,000 liters, or about 750 gallons of coating before replacement. The Transfer Rates are about 82% on flat parts, which mean the gun will pay for itself in a short period of time.

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