Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Zinc Plated Part became rusty after powder coating
Q. I am from metal fabrication company. Recently we have a product which need the parts to be zinc plated (5 micron with clear chromating) and powder coated with masking on area 300 mm x 300 mm. (Part size 1000 mm x 500 mm). Yet after powder coating process, we found the masked area became rusty after a few days. My question is,
1. Does high temperature 180 - 200 degree affect the zinc plated life span?
2. We do recommend to apply lacquer after powder coating process to the masking area yet are facing the problem for conductivity. Is there any chemical suitable to be used?
Hope that anyone with experience will help to give some advice. Thanks.
Regards,
Assistant Operation Manager - Johor, Malaysia
2007
A. There are three or four different matrixes used for depositing zinc. Then from shop to shop there are many different kinds of additives and impure contaminants which co-deposit with the zinc.
A clean iron-free, low organic added zinc solution should produce deposits that can stand you 200 degrees if you mean F-degrees. If you mean C-degrees - then the organics in the codeposited brighteners, and/or the iron impurity are going to move around in the deposit and possibly cause lack of adhesion and/or lack of corrosion protection. Further the chromate, if too thick, is a "gel" which dehydrates at your 180-200 °F.
Also 5 microns (0.0002 inches), is not very much protection, and part of it is removed in the chromate.
Go find a clean zinc electrolyte, apply 0.0003 to 0.0004 inches thick, and a very thin chromate.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
2007
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