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Brown spots on powder coated brass substrate

Brown spots on powder coated brass substrate

Brown spots on powder coated brass substrate

(OP)
We are having an issue where polyester powder coated brass samples are developing brown spots (almost certainly corrosion) after being powder coated and sitting for a while. The technicians claim they do not see this phenomenon during salt spray and humidity testing. Pinholes? Contamination?

I appreciate any feedback. Thanks.

RE: Brown spots on powder coated brass substrate

What is the product form of the brass; what is the pre-treatment process prior powder coat?

RE: Brown spots on powder coated brass substrate

(OP)
They are brass doorknobs. The pretreatment is either vapor degreasing or ultra-sonic cleaning.

RE: Brown spots on powder coated brass substrate

Is buffing performed on these pieces prior to coating? If so, how do you verify that all traces of buffing compound have been removed?

RE: Brown spots on powder coated brass substrate

It looks like typical contamination.  Any residue on the part surface runs the risk eventually sucking up water and then corroding.  Just because it looks clean doesn't mean that there isn't any residue.  

Take a serious look at your cleaning and rinsing process.  Also look at how the parts are stored between the cleaning process and the painting process.  Contaminants can redeposit from the air and you'll never seem them until they "pop".

RE: Brown spots on powder coated brass substrate

If the powder coating exhibits pinholes or holidays due to improper temperatures or flowout, then moisture/air going thru these holidays may trigger the substrate underneath to oxidize and possibly leach out these pinholes.  

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