Powder Coating Over a Chromate Conversion Coating

Ask an Expert From: Products Finishing, , from Powder Coating Consultants, Div. of Ninan, Inc.

Posted on: 8/1/2004

Question: I have seen chemical conversion coating put on aluminum prior to powder coating for 20 years or more.

Question:

I have seen chemical conversion coating put on aluminum prior to powder coating for 20 years or more. I have specified this myself many times. I learned recently that chem film starts to break down at about 70°C. This happens to be the military’s favorite operating temperature requirement. My question then is obvious, is this detrimental to the adhesion of the powder coat over the chem film base? P. M.

Answer:

Chromate conversion coatings on aluminum do have problems when subjected to temperatures above 180°F. However, they need to be exposed to the atmosphere for this to occur. Under a continuous film of powder coating this phenomenon does not happen. Therefore, as my Italian cousins in New York would say: “Don’t worry about it.”

 


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