The authoritative public forum
  for Metal Finishing since 1989
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Better Understanding of Zinc Plating

2002

I would like to know more about:-
1). What is 'Bluish colour' Zinc plating?
2). What is 'Clear white colour' Zinc Plating?
3). What is 'Rainbow colour' Zinc plating?
4). Which of zinc plating has a better corrosive resistance in the normal room temp.(25C)with humidity 55-60 %
5). What is JS 500 Corrosion-Resistant Finish.
6). When will Zinc plating with average of 10-12 µm coating start to corrode in the normal room temp.(25C)with humidity 55-60 %.

Tan Cher Peng
- Dongguan city, Guangdong Province, China

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Dear Mr. Peng:

Thank you for visiting www.finishing.com, but on your next visit please tell us about yourself, what you do, and why you want to know the answers to these questions. And please tell us something that the readers can learn something from reading. I don't mean to be rude, but we're not all standing around here, eager to expedite the transfer of our knowledge, experience, and technology to a stranger with a hotmail address in China. Rather, we're here to help each other as peers.

Zinc plating protects steel from rusting through sacrificial protection, but is itself prone to quickly corroding with white rust. To delay that white rust, the zinc plating is topcoated with a chromate conversion coating. That chromate conversion coating can be rather clear to bluish, or it can be yellow iridescent. The yellow has more hexavalent chromate and therefore offers more corrosion resistance. JS500 is a proprietary topcoat system that includes another step in addition to chromate conversion coating, and therefore reportedly offers greater corrosion resistance.

Your last question is a difficult one to answer, but this thickness of zinc is considered a quality thickness for interior exposure, and the best answer may be that it should be adequate for the life of the component--again interior exposure.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002