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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Chromate coat being swabbed off aluminum

Our company uses alumimum outer covers that are "chem film" coated, Class 1A. Recently, several parts were checked for coating stability using Q-tips ⇦ this on eBay or Amazon [affil links] soaked in IPA. The operator noticed that a significant amount of brown-gold color was transferred to a swab. Does this indicate that the chem film was not properly applied or insufficiently dried, or other? Thanks for your help!

Rick Burkholder
infrared technologies - Dallas, Texas

My first guess would be over dried rather than under dried. Chromates are gels which need drying below 150 degree F in order to not dehydrate and get powdery.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Just a guess here, Rick.. but it almost sounds like the final rinse your coater was using wasn't very clean. Was the chromate coming all the way off? Or.. was just some residue coming off?

Marc Green
anodizer - Boise, Idaho

Another possibility: Too long immersion time in the chem solution.

Dado Macapagal
- Toronto, Ontario

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