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What about yellow Iridite and WEE?

Hi,

I'm Lisa Kirk. I am not an engineer, but have been given the task of writing a WEEE Treatment Document for our next toll gate.
What I'm finding is that our sheet metal is described as a few different substances.
Can anyone tell me the difference between Yellow Chromate, Yellow Iridite, and Zinc Plate type II Yellow? Are any of these RoHS compliant?

I am a Document Specialist at an engineering company in the Northeast.

Thanks!

Lisa Kirk
Documentation Control - Peabody, Massachusetts
2007

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Hello, Lisa. Iridite is a trade name owned by Macdermid, but otherwise the 3 descriptions are equivalent. You are describing a finish that consists of zinc electroplating (RoHS compliant), followed by chromate conversion coating (the chrome coatings that have been applied traditionally are not RoHS compliant).

Traditionally, hexavalent chromium conversion coatings exhibited far better corrosion resistance than other conversion coatings, but hexavalent chromium is now RoHS regulated. Great improvements have been made in the last several years to where trivalent chromate conversion coatings (which are RoHS compliant) can now be acceptable.

I would not specify "yellow" unless absolutely necessary because it's not a good idea to dye "environmentally green" products to make them look like they are toxic (the yellow color is the natural color of hexavalent chromium). Then you need to quote an ASTM or MIL spec, and specify "RoHS compliant". And I believe, since they are sheet metal, you probably are painting or powder coating the parts after the plating and conversion coating.

This project may not be as easy as you hope, because you are actually changing the specification and the product when you add the RoHS-complaint proviso and, while the new trivalent chromates are the equivalent of the old hexavalent chromates in corrosion resistance, there can be conductivity issues and paint adhesion issues. And, since there are several proprietary approaches to this (thick film chromates, thin film with topcoat, etc.), one shop may process your parts to your satisfaction and the next shop may process them such that paint will not stick to them reliably.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007