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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

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, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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April 18, 2013

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

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, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
April 22, 2013

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