Preparing for Stainless Steel

Question:

It has been suggested that my company’s powder coat department paint stainless steel. I’m wondering if my pretreatment and powder coat are capable of preparing the stainless substrate? We are evaluating this on 304 No. 4 brushed Stainless Steel. Our paint system consists of the appropriate cleaning and rinse stages as well as a zinc phosphate and hexavalent chrome sealer. We are using an acrylic powder for our topcoat. I have concerns about the capability of the zinc phosphate to properly etch the 304 substrate, which would affect adhesion. Could you please comment on the capability of my system? D. W.

Answer:

Your pretreatment system will remove the organic soils (oils, waxes, etc.) on your product but will not provide any surface etching or conversion coating on 304 stainless steel. In fact, you may only want to operate your first and second stages, as these are the ones used to clean and rinse the organic soils from your product. Zinc phosphate and chrome sealers will not react with 304 stainless steel and therefore will provide no direct benefit. The number four brushed surface may have sufficient roughness to provide adequate adhesion, but I would test it first. If it does not provide adequate adhesion, you have two choices. First you can scuff sand the surface to provide “tooth” for the powder coating. Alternately you can apply an adhesion promotion chemistry called Silane used to prepare glass for powder coating.