Summary for powder coat paint issues Discussion
Powder coat paint issues on re-coated aluminum parts centered on why previously white powder-coated K-Alloy parts developed defects after being recoated black. Bill V. said the parts were originally finished in PA006QF 20-1028HY Wet White and then re-painted with 243QF 22-7001 Tuxedo Black. Geoff Crowley replied that the key question is what was done to the white coating before recoating to ensure adhesion, because a fully cured first coat will not crosslink with the second coat. He suggested sanding or otherwise creating a mechanical key as one possible fix. He also noted that pimpling, bubbling, and fish eyes can come from anything that outgasses under heat, including oils, skin contamination, marker ink, fats, and grease. Crowley added that the original pretreatment matters too, since powder on untreated metal performs much worse than on properly pretreated surfaces.
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.
Powder Coat supplier is Akzonobel if that helps.
Bill V.
– Nesconset, New York
April 16, 2024
This is a meeting place for camaraderie & sharing, not a free consultancy. So some readers don’t engage with anonymous posters.
SUGGESTED POWDER COATING BOOKS
for Shops & Engineers
“Industrial Powder Coating: Basics, Methods, Practical Application” by Judith Pietschmann (2023)
avail from
eBay,
AbeBooks, or
Amazon
“User’s Guide to Powder Coating” by Nicolas Liberto (2003)
avail from
eBay,
AbeBooks, or
Amazon
“High Performance Powder Coating” by Bob Utech (2002)
avail from
eBay,
AbeBooks, or
Amazon
“Powder Coating. The Complete Finisher’s Handbook” by Nicolas Liberto (1994)
avail from
eBay,
AbeBooks, or
Amazon
“Powder Coating Systems” by William Lehr (1991)
avail from
eBay,
AbeBooks, or
Amazon
“The Technology of Powder Coatings” by S.T.Harris (1976)
avail from
<!–UTL eBay, –>
AbeBooks, or
Amazon
“Fundamentals of Powder Coating by Emory Miller & David Taft (1974)
avail from
<!–UTL eBay,–>
AbeBooks, or
Amazon
(as an Amazon Associate & eBay Partner, we earn from qualifying purchases)
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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
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