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topic 59240

Trivalent Plating turns pink when insert molded with phenolic plastic



April 12, 2013

Q. Hello all and I hope that you can help me out with my problem.

I am a screw manufacturer who is selling a plated product to a customer. This part has .0002 zinc with a Hi-Corrosion Trivalent chromate finish. When my customer molds this insert into the finished product it has a pink residue on it. (Please see the photo)

residue on plated screw

I have talked to my local plating houses along with the chemical supplier with no ideas of what is causing this. I did send out the residue to a lab to have it tested and was told that the main chemical in the residue was calcium carbonate.

I have already tried two different chromates from my plater and I am in process of having a third plating lot done at a different plater. My customer has stated that they do not have this issue when they use hexavalent chromate.

I was wonder if anybody has any ideas of what is causing this and a workaround with trivalent chromate.

Thanks for you time.

Ken Janik
- Franklin Park, Illinois


April 18, 2013

A. Hi. It looks to me like a dye to me. Was this chromate originally blue or yellow, or was it clear?

Regards,

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


April 22, 2013

Q. These parts where not dyed. The original finish was .0002 zinc, clear trivalent chromate. The chromate is clear but with a "blue bright" tint.
The pink that you see happened after the parts were molded.

Ken Janik
- Franklin Park, Illinois


April 22, 2013

A. Hi Ken. I'm suggesting that if the color came from the plated and chromate conversion coated screws, it's hard for me to see any source of a pink discoloration other than whatever dye was making the parts blue bright. Good luck.

Regards,

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

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