plating, anodizing, & finishing Q&As since 1989
Tri Chrome Coating For FE/ZN 12
My customer needs to replace a cadmium plate coating with an equivalent coating for corrosion protection but doesn't need the lubrication properties. I have talked to two platers who are reluctant to make a recommendation other than zinc. From online research I think I need Fe/Zn 12 Type 3 class 2 per ASTM B633 [affil link] . Does that sound reasonable? How do I ensure that trichrome is used rather than hexavalent chrome?Dale Neff
Hi, Dale. As you already know, zinc and zinc alloys are not cadmium and do not offer the exact combination of properties that cadmium offers including corrosion resistance, freedom from gummy corrosion products, lubricity, crimpability, toxicity to certain funguses and molds, radiation adsorbtion, etc. So a plater (or an internet responder) simply can't accept responsibility for recommending an equivalent coating; the designer is stuck with that job. But yes, zinc-iron is a good coating.
As far as I know, Mil specs and ASTM specs have not yet been written for trivalent conversion coatings, so I think you need to write something like: "Conversion coating to be applied from proprietary hex-chrome free baths designed for WEEE/RoHS compliance, and coating to be compliant with WEEE/RoHS requirements". That's just an off-the-cuff attempt; I haven't written such a spec myself yet.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Thank you for your comment. RoHS compliant has greatly aided my getting the information I need.Dale Neff
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