Troubleshooting Airless Air-Assist Overspray

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Clogged ventilation filters in the spray booth or static in the air could cause overspray to occur underneath panels. May 17, 2005

We have a Kremlin 20:15 pump that we have been using regularly for about 2 years, spraying PU. Just recently, when spraying any flatish panel or say a fielded door, the underside is getting a buildup of overspray. I have replaced all the gaskets at the fluid tip, etc. and thoroughly stripped and cleaned the pump, but still the problem is there. I have not altered the viscosity of the product.

In theory it has to be a turbulence problem or something to actually coat the underside of the panel when, say, spraying a door edge and face and some have had quite a heavy coat of overspray! It is very frustrating. I even sprayed a simple frame yesterday and found the underside coated in dry spray.

Forum Responses
(Finishing Forum)
From contributor J:
Check the possibility of ventilation problems, if you are spraying in a spray booth. Also, make sure your atomizing air isn't set too high. This could be putting unnecessary material into your spray area.

From contributor R:
Are your booth's exhaust filters clogged? Sounds like you're not getting enough air movement.

From contributor W:
We had a problem like this that we solved by grounding the pump to our spray booth (which is bolted through the concrete). A bit of wire and an alligator clip make it simple to hook up or disconnect. Amazing how a little cold weather and increased relative humidity can get those electrons misbehaving! Please let us know if this fix works.

From the original questioner:
The pump has an earthing strap which I just clip onto the regulator on the booth wall, but maybe it isn't actually grounding properly. I think I will grind an area to bare metal to get a better earth, as at least that eliminates one potential problem.

I have replaced the filters and given the booth a birthday today. So again I can see if that helps. I am also going to spray a similar item out in our open ended booth to see if I get the same results, as this will take another element out of the equation.

From contributor D:
Are you entirely sure you are getting overspray and not bounce back? How are you spraying these panels? On horses, on pin boards, on rack system?

If you are using too high atomization and are spraying on any type of board, whether the panels are raised above the board or not, you will most likely get bounce. If this is the case, try suspending the doors from a rack system or horses to eliminate this from happening.

From the original questioner:
I am spraying them raised up on nails (10" minus thickness of board) on my turntable. I have used this method for 2 or 3 years (with no problems), and have not changed anything.

From the original questioner:
I totally cleaned my booth down and replaced the inlet filter, as even though I thought I was getting decent airflow, in fact it wasn't really that good. I suppose a buildup of dust, etc. over a long period...

I also cleaned up an area of bare metal on the booth to provide a good earth, as I don't think where I was earthing from before was any good (but something I hadn't really thought about).

So far the results seem positive, as I did a quick test panel with no problems at all. Many thanks for all your responses.