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topic 8878

Powder Coat Contamination, Dirt, and Dust


Q. We coat our product with a glossy black paint and seem to be having problems with dirt and dust contaminating the paint after it is recycled through the collection hopper after being purged from the filter packs. Is there a way to clean dust and dirt out of the recycled paint? It shows up in the cured paint as little specks, bumps and fibers. Any help would be great!

Steve Scholle
- Lincoln, Nebraska, USA


A. We use a Sweco sieve with a magnet to remove contamination, and have pretty good luck. It's a 3 screen system to remove the larger particles first. I'm not sure that the magnet is doing much, however.

Kim Pendelberry
- Webster, New York


A. We use a air agitated sieve, three screen, but it has not been successful with the powder removed from the blower system, just the powder from the booth.

Joe Deamicis
Academy - Edison, New Jersey

July 26, 2013

Q. Recently our company has seen a sharp increase in paint defects relating to Dirt, Debris/ foreign material in our finished product. So you know what equipment we are working with: TTX 11 stage pretreatment system with e-coat followed by a Nordson Colormax spray booth with Auto guns, followed by a TTX preset/gelling oven prior to the final curing oven. While following the parts through our process we observed that the e-coat only parts prior to powder seem too look pretty good, however after powder the defects seem to appear. While these defects are small (.001"-.003") typically they seem to cluster on parts, mostly on the larger flat surfaces. Our first though was a cleanliness issue, so our team updated our clean color change over procedure, and shortened the interval between over clean outs, yet this has shown little or no benefit. At this point we unsure of what to look to change or improve to help lessen this problem, or experiments which might help lead us to our problem so I'm hoping to get some advice on what experiments to try or items we should investigate next.
Thank you

Steven Ross
- Hartford, Wisconsin, USA

August 13, 2013

A. As your E-coat only components are satisfactory you can almost certainly discount anything down-line.
I guess the only things you are adding up-line are Powder & Air.
The defects at 25 microns are not going to be sieved out if related to contaminants in the powder.
If Powder contamination is the cause this could be isolated by using new batch virgin powder only for a period and checking.

Should the issue disappear then obviously you are picking up contaminants through your booth / reclaim system.

Should the issue persist then it would be time to look at every air introduction.
Check that your air supply to guns is adequately filtered.
Check that your input oven air is adequately filtered.

Some dust within the oven itself can re-circulate.
A simple method to reduce this impact is to coat the oven walls with odourless fish oil.
This entraps rogue dust particles.

Hope these suggestions help.

William Doherty
Trainer - Salamander Bay, Australia

August 14, 2013

A. I neglected to mention that in amongst the air potential sources of contamination there is of course the possibility that your convection oven is not tuned well.
Incomplete combustion related to over rich fuel / air mixtures would produce soot.
That might be an additional avenue to investigate.
Hope this helps.

William Doherty
Trainer - Salamander Bay, Australia

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