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Trivalent Chromate Conversion for EMC properties

I manage a mechanical and systems engineering group responsible for the design of high speed document scanning equipment. Currently we often specify sheet steel with galvannealed finish. We specify this for moderate corrosion protection but more importantly for Electromagnetic Compliance. Our products have very high speed electronics within them and a finish that provides good surface conductivity for EMC enclosures is critical. We currently use a zinc plate with clear chromate conversion process. Due to environmental pressures to eliminate all sources of hexavalent chromium from our products, we are looking to specify Trivalent plating processes for future projects. I am looking for information that describes the electrical properties of zinc plating with "chromate conversion" utilizing trivalent chromium in contrast to hexavalent chromium.

Robert M. Westcott
- Rochester, New York, US
2002

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I suppose that if chrom-"ate" is read as CrO3 then 'trivalent chromate' would actually be an oxymoron. But if you have been using clear chromates all this time, your salt spray requirements are minimal and your platers could well have been using clear trivalent chrome conversion coatings all along. I believe that the surface resistance of clear chromates is lower than yellow chromates. As long as you don't use the new "topcoats" that have been designed to help trivalent chromates approach the corrosion resistance of traditional yellow hexavalent chromates, I don't see any change.

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

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adv.
WE SUPPLY A HIGH CORROSION TRIVALENT CHROMATE(ENVIRONMENTALLY FRIENDLY) IN EITHER CLEAR OR YELLOW. DEPENDING ON THE CHROMATE AND APPLICATION WE ACHIEVE 40-200 HOURS OF NEUTRAL SALT SPRAY RESISTANCE TO WHITE RUST (WHITE RUST MEANS THAT THE ZINC IS STARTING TO CORRODE. PLEASE CONTACT US.

REGARDS,

Steve Cornwell
ACCU-LABS

Chicago, Illinois

2003

Hi, I'm a student from Mexico, and got a work to do about cleaning methods for metallic and organic contaminants on trivalent chromate conversion baths. Could anyone tell me some advise or at least where should I look for that information? Thanks

Julio
- Quer´taro, Mexico
December 7, 2008