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Powder Coat Paint issues

Q. Any chance you have an idea on the root cause pertaining to the attached pics. These are aluminum parts (K-Alloy) that are originally Powder Painted with PA006QF 20-1028HY Wet White.
They are then re-painted with 243QF 22-7001 Tuxedo Black.

61658-1d 61658-1c 61658-1a 61658-1b

Powder Coat supplier is Akzonobel if that helps.

Bill V.
- Nesconset, New York
April 16, 2024

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A. Hi Bill.
Sorry, I don't have enough experience with powder coating to know what went wrong, but I do have some questions ...
1. Are you speaking of a rework to make white parts black, or are you speaking of a two-coat system where he first coat is partially cured before applying the second coat? If that is the case, how could the illustrated parts be accepted to go on to the second coat with powder missing -- or is that not the case?
2. What is the pretreatment for the aluminum? Any chance a solvent is causing those fisheyes?

Luck & Regards,

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

Q. It's rework to re-coat parts that we're previously powder coated white and now are being re-coated black. Pictures represent those that we're re-coated black.

Bill V. [returning]
- Nesconset, New york
April 16, 2024

A. What did you do to the white parts before recoating to ensure adhesion? As the original coat would be fully cured, no cross coat bonding (cross linking) would occur, leaving the 2nd coat in black with poor adhesion to the original. Sanding to get a "key" might have been one method of gaining adhesion.
For any coat the presence of anything that can emit a gas under heat can lead to pimpling, bubbling, fish eyes etc Such things can be oils (even the natural oil of human skin is enough, did they wear gloves?), marker pens, fats greases etc.
What was the pretreatment system for the original coat? Application of thermosetting powders onto metals that have no pretreatment has a far lower success rate than those with conversion coatings, crystal deposition coatings and more.

Geoff Crowley
Galvanizing Consultant - Bathgate, Scotland
June 8, 2024

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