48057

Zinc plated passivated and sealed zn-foundry parts  

March 5, 2008

I work in a foundry that produces zinc parts. One of our customers requires zinc part that are zinc plated with a white passivation. They do not specify whether the parts should be sealed or not. For passivation we use Tridur Blue 3 Liquid N2. Our goal is not protecting the parts against corrosion, but instead assure that the parts have a nice, as white as possible, look, that should last for at least some months (hereby our doubt as to whether the parts should be sealed or not). However, all of our parts turn blue within two weeks. Some blue color is accepted by our customer, but the results we obtain are simply not good enough. We would be very happy if we could get some help on getting an as white and homogeneous possible looking parts.

Jon Sevillano
foundry / plating shop employee - Spain

Atotech lists this process under their "blue" chromates as opposed to their "white/clear" chromates, Jon. So if your objection is that it is too blue you should work with Atotech, or other vendor of your choice, to select a chromate which is marketed as being less blue rather than trying to tinker with this one to make it less blue. Good luck.

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

Dear Sir,
The problem is coming from the copper content of zamak parts that you are plating. You have to plate al least 6-7 micrometers of zinc before blue passivate the parts.

I hope this helps

Emrah INÇAL
- Istanbul Turkey