White Spots on Dark Powder Coatings
Q. I am having a problem with white spots (particles) showing on my dark colors, black, blue, red. Some of these particles can be wiped away or blown off but many are curing onto the parts. It appears to be coming from inside the oven. I dipped a piece of hot steel in some black powder and sent it through the oven (bypassing the booth and guns), feeling this would eliminate possibility of guns or booth being the problem, which I think it did. The part had the white spots (particles) on it. The longer runs of black we do, the less the problem occurs. J. F.
A. The answer to your question is simple. You have contaminants in your cure oven. This is proven by the fact that you have similar problems in all your dark colors and not just one. This eliminates your powder coating formulator as the culprit. I am sure you have the problem in your lighter colors, as well. You just don’t see it. Lastly, your test using a hot part proves that the powder application and recovery equipment is not to blame.
Now we can talk about how to fix this common problem. First, you have to clean your oven every month. The best cleaning method is to vacuum the oven walls, ductwork (in and out), and fire box chamber using a vacuum with fine filtration. There are several suppliers which make vacuums that can service powder coating operations. DON’T USE A SHOP VAC SINCE THE FILTERS THAT COME WITH THESE UNITS WILL NOT STOP FINE PARTICLES AND THEY WILL JUST SHOOT THEM ALL OVER THE OVEN AND YOUR PLANT. After vacuuming all oven surfaces, you must damp mop them to remove the finer particles. DO NOT USE TOO MUCH WATER IN YOUR OVEN—AS IT WILL RUIN THE INSULATION.
After you clean your oven, you must take steps to reduce this contamination from returning. Obtain a combustion air filter to eliminate contaminants from entering the oven through the burner. Secondly, clean the area surrounding the oven to eliminate this source of dirt. Lastly, do not store dirt-laden items, boxes, parts, and so on near the oven.
Remember: Cleanliness is next to Godliness and is essential for high-quality appearance powder coating operations.
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