Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2008

Painting Process Audits

Q: What will be the checkpoints to ensure a good quality powder coating (including chemical pretreatment)? What should an auditor check during powder coating process audit?

A: In my opinion I would do a thorough check of the surface pretreatment process and confirm that you get a good quality phosphate or conversion coating. Your chemical supplier should be able to assist you in setting up an appropriate quality control program.

Adhesion is one of the most important parameters, and I would perform both a dry and wet adhesion test per ASTM 3359 Method B. In addition, you will need to measure dry film thickness of the powder coating. If necessary, look for pin holes and voids, especially if the coated part will be shipped to a corrosive environment. If customers require a Class A finish, I would look for contamination and other defects in the finish. You might need to perform the MEK rub test to insure that you have achieved proper cure and if the coated part eventually will be exposed to sunlight, you might send some samples to a laboratory that can subject the samples to a weather-ometer where UV light (and perhaps also humidity) will accelerate coating degradation. Measurements of gloss and texture might also be necessary.

Good luck,

Ron Joseph

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