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Chromated zinc plating is oxidizing between Singapore and the East Coast

A) How do I prevent (white) oxidation?

B) How do I clean off white oxidation on chromated zinc plating?

Background:

My company specifies zinc plate per ASTM B633 Type III SC2 on a CRS substrate, used on a large (14 U) chassis (similar to a server or router). The supplier uses trivalent chromate. The supplier is in Singapore (usually 90% humidity & 90 degrees F). The chassis mechanically assembled and integrated and packed in an open air shop. The chassis is packed with a 5 mil plastic VCI film laid on top of the chassis, and a foam "cap" on top of the film. Two units are then placed in a large bag in a corrugated box, with approx. 8 500 gram packs of dessicant, and the bag is sealed. A top is put on the box and it's put in a 40' container along with other units, and is shipped to L.A., then trucked across the country to the east coast (more humidity). We are finding oxidation at the VCI film contact points.

Jon Perdue
telecommunications eqpmt mfgr - San Jose, California, USA
2003

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2003

Jon, I think you aren't asking exactly the right question. You really need to ask how to prevent this problem rather than how to restore the finish after the coating is compromised. While users of galvanized steel-- where the coatings are 10x thicker (and not intended to be decorative) may argue whether white rust can or can't be properly removed, I think in the case of zinc plating which has lost its decorative look, it's different. It's time to strip and replate, and do better next time.

I'm sure it's possible to improve the plating, improve the chromating, improve the post-treatment, and improve the packaging, but if the parts were plated and chromated well, properly dried, and packaged as you described, I don't think you should have had this problem. From this distance it's only a wild guess, but I don't think the chassis were properly dried after plating.

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