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topic 5279

Wax Coat Affecting Yellow Chromate


I am having a yellow chromate adhesion problem. Every measure has been taken to ensure proper adhesion, I.E. pre nitric dip 1%, Acetic Acid pre dip(acetic acid chromate), lowering brightener adds, monitoring proper concentrations, but nothing seems to work.

The rub off never occurs in plant it is only after the customer receives the plated chromated parts back and applies a wax coat which is then baked at 180 degrees, when the parts are returned it looks as if they were never chromated. My belief is that the film is being dehydrated by the 180 degree bake, but the customer does not want that to be the answer. Any comments and/or suggestions will be greatly appreciated.

P.S. Acid Chloride Zinc Plating bath.

Brad Hackney
- Cleveland, Ohio, Cuyahoga


Brad - Well, the good news is that you are correct(that's bad for the customer). Yellow chromate can be significantly degraded at 180 °F -- sometimes even lower temps can cause failures. I would suggest looking into alternative coatings at your end since it is probable that the customer is pretty set on their coating. Good Luck.

Dan Brewer
chemical process supplier - Gurnee, Illinois


It could possibly be an ingredient in the wax that causes the problem. My wife's shop found that there was one hand lotion that would strip yellow chromate from chloride zinc and also from purple dyed anodize in a matter of seconds.

James Watts
- Navarre, Florida


Give up the Chloride Zinc as you will never win this battle of the bond. Yellow will invariably tend to rub off particularly if the surface condition is smooth before plating but lasts better if the surface is rough. The only process which will work is Cyanide Zinc or if you're lucky then alkaline Zinc may also work.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

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