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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Iridite and chromate treatment Q&A's

Q. Hi, I have a question about Yellow Iridite and Chromate treatments.

My print reads: the finish of the part (a washer) should be "Chromate treated bright zinc electroplate, chromic acid". Now, my supplier's spec is "Zinc/cadmium plating with a yellow Iridite finish". Can I consider these finishes to be equivalent?

What would be the difference, if any, between Zinc chromate finish, clear Iridite finish and yellow Iridite finish?

Thanks,

OSCAR A ESPINOZA
QE - TULSA, OKLAHOMA
2004

A. Iridite is a trade name for a line of chromate finishes for a variety of metals. It was the first, back in the 1940's and has in some places become a generic term, like Band Aid.
Chromate conversion coatings come in a variety of colors. Generally, the darker the color, the greater the corrosion resistance to white salts. I would interpret this specification of your client to mean a yellow chromate on zinc plate which will withstand 96 hrs CASS Test to white corrosion. You really should have your client tell you what they want specifically and/or quote a MIL spec or ASTM standard. By having different nomenclature on the print and on other paperwork you run the risk of making a mistake, especially if the customer doesn't really know what they want.

Gene Packman
chemical manufacturer - Syosset, New York
2004

A. The two processes are not equivalent. The zinc/Cadmium or Cadmium alone with Iridite is better for corrosion protection. Yellow chromate is very good, olive drab is even better.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2004

A. Hi. Gene's warning that ambiguous or contradicting specs must be fixed before you agree to them should be heeded. As a quick example, Gene is correct that "Iridite" was sometimes used in generic fashion, but where does that leave you if you apply a different brand and then the customer says your work doesn't comply?

Luck & Regards,

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

Multiple threads merged: please forgive chronology errors and repetition 🙂

Q. I have a customer who wants a fastener plated "Iradite Zinc" , He Calls it "Quad Triple Odd 2 plating thickness". Is there such a thing available?

Russell Baker
Quest Fastener - Kent, Washington, USA
2005

2005

A. Hi Russell. It's actually "Iridite" -- a Macdermid trade name for a chromate conversion process on top of zinc plating. It's important to get a real specification in writing, not just guess at the specification. But to help you with the lingo, 'triple odd 2' probably is '0002', that is,: two ten-thousandths of an inch thickness of zinc plating followed by an Iridite brand chromate conversion process (of essentially non-detectable thickness).
This would be thin zinc plating, but serviceable -- for "mild service condition" per ASTM B633, or what some people call "commercial thickness" (although I think that's a dangerously imprecise way to talk). A minimal specification would still have to include the 'color' of the Iridite: clear, yellow, olive drab, black. Unfortunately, I don't know what 'quad' means and can't think of anything meaningful at the moment that sounds similar; hopefully another reader will ... but someone in the delivery chain has to offer an actual specification for what will be required or offered or delivered and get it included :-)

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

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