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Letter 21052
Painting and heating of zinc-plated
details
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WE are currently processing assemblies using cold rolled sheet
material. These require plating per ASTM
B-633 [link is to spec at TechStreet]-85 TYPE IIFe/Zn
8. After this process one side of the details is masked for powder
coat painting, cure tempature for the powder coat is 400 degrees.
With this tempature the zinc plating gets cloudy and has a white
tint.This is not acceptable to our customer.What can we do to avoid
this situation.
RICK CARTER
- ROUND ROCK, TEXAS, USA
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Perhaps I'm missing something, but I would have thought it would
be more practical to do the powder coating before the plating.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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Sounds to me like you are dehydrating the chromate in your baking
of the powder paint. The gold color is imparted in a post plating
operation called chromating. The chromates are what really provide
your corrosion resistance by forming a hydrous (spelling?) chromium
barrier on the zinc. Heating above a certain temperature will
dehydrate the coating and the chromate will no longer protect the
parts. Visually it appears as you have described.
Bill Grayson
- Santa Cruz, CA
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WHAT WILL HAPPEN TO THE PAINT WHEN IT GOES THRU THE ZINC PLATING
PROCESS? WILL IT DEGRADE THE FINISH AND DURABILITY OF THE POWDER
PAINT? THANK YOU
RICK CARTER
PARADIGM METALS INC. - ROUND ROCK, TEXAS USA
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That depends on a number of factors, and may require some
development work. But what I can tell you is that people do make
products like this by doing the powder coating first and then
plating. Powder coating can be very resistant to all plating
chemicals.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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