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Dirt specs in powder coated finish

We have a considerable problem with dirt specs showing up in our powder coated parts. Especially the larger flat panels. Most appear as hard specs and some occasional lint or fibers.

We have a reclaim powder coat booth and are reclaiming our powder along with adding clean virgin powder at about a 70-30% ratio. We shoot primarily a hybrid TGIC polyester/ acrylic blend. The booth is in a warehouse style shop with welding and fabrication on one side, and assembly on the other. The booth is in the middle of the shop with no environmental or positive air room around it. We keep everything very clean in and around the booth and ovens, and regularly clean out the ovens. We have a three stage phosphate, rinse, seal pre-treatment system which are dumped and re-charged once a month.

Tim Magnuson
- Aberdeen, Washington
2002

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2002

Unfortunately, we all seem to have this problem from time to time. Usually though, contaminated surface are fairly easy to diagnose and correct. The most widely abused area that brings contamination in is improper cleaning of the booth and feed hoppers between color changes. If you happen to be painting black and then switch to a lighter or white color, ANY residual microns of black powder left in the system, have the ability to apply themselves onto your parts and be cured as contamination or in the case...specs in the paint. The amount of specs will be decided upon how efficient you clean your system and nowadays, it seems that every company pushes for faster color changes. The pretreatment system can possibly leave Total Dissolves Solids or (TDS) that will produce contaminated surfaces or water spots depending if the pretreatment system has sufficient filtration and pure enough rinse water (1000mHmos) or cleaner. Usually pretreatment is not the source of specs in topcoats. Poor oven housekeeping can produce contamination and in your case you said you regularly clean your oven. Oven cleaning on a regular basis can be a blessing if the oven is cleaned immaculately and wiped with damp rags after. If you simply vacuum and wipe the oven, you will simply disturb the contamination accumulating within the oven and you would be better off reserving the cleanings for time when it can be done properly. Conveyors can deliver debris upon the tops of your parts. This is the easiest way to tell if your contamination is coming from and conveyor or not. Conveyors, depending upon each specific paint operation may or may not need to be cleaned regularly. Environmental rooms are excellent ways to help eliminate foreign debris from accessing into the powder application system.

In most cases, taking the time to properly clean the application system including the pumps and the airlines attached to them will eliminate powder spec contamination. Many times, employees blowout the pumps, but fail to clean inside the venturis and lines where backed up powder remains. Keeping good cleaned cartridge filters will also help from having foreign debris floating within the booth itself. Each person that applies powder should make sure they don't bring other powders and/or dirt into the booth area on their person or shoes. And lastly, some "paper" cartridge filters themselves will contribute fibers from the element when pulsed. When adding powder to the hopper, make sure you don't have cardboard fibers from the box clinging to the plastic bag when dumping the powder in the hopper.

Bob Utech
Benson, Minnesota