Letter 39029

Alternative to zinc and colour customer asking for trivalent finish on future orders  

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please can you help?. we are a enginering company supplying mild steel studs to varios industries.Some customers who currently we supply zinc & colour are requiring trivalent finish on future orders.What does this meen and what colour is it.
Thanks in advance .

KL Smith
skm products - Leleicester, England

Okay, K L, the main purpose of "colour" on top of zinc plating is corrosion protection by application of chromate, rather than aesthetics. So when you say you supply "zinc and colour" what you really mean is that you provide a coating that includes zinc plating and color chromating. The color is usually yellow (actually more like amber or honey).

These yellow chromates have traditionally been based on hexavalent chromium which is a toxic compound now forbidden by RoHS and other standards. So what you now need to do is have your plater apply "hexavalent-free" passivation processes after the zinc plating. These are usually inherently colorless, but proprietary coatings are available that are yellow in color if that is essential.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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