Coatings for Stainless Steel

Ask an Expert From: Products Finishing, ,

Posted on: 3/1/2005

Question: My company manufactures steel doors.

Question:

My company manufactures steel doors. We want to adhere acetate images to stainless steel doors. What can we use as a top-coat sealant for the acetate and long term protection for the doors? Thanks. M. S.

Question:

I want to apply a hard transparent coat on stainless steel products, having failed on adhesion. Is there any surface treatment or adhesion promoter for use on stainless? We need a transparent coating and we could not apply a pigmented primer. Thanks for the help! S. K.

Question:

We are an interior design firm specializing in supermarkets. We would like to do decorative painting on stainless steel surfaces. Is this possible? J. P.

Answer:

Here is an opportunity to get three for the price of one; three questions that is. Stainless steel is relatively inert, hence adhesion of paints and coatings is often a problem. The first step is to remove any oily soils. Adhesion to stainless steel is enhanced by using pretreatments. Acid etching is a pretreatment. Surface abrasion is a pretreatment. Primers are also pretreatments. In your case, you don’t want to use a pigmented primer because it would cover up the stainless steel substrate. You can successfully coat your product by following these directions:

1. Degrease the stainless steel using a hot alkaline or detergent cleaner. 2. Rinse completely with clear water and dry. 3. Pretreat the surface using acid or abrasion.

Although it is effective, I don’t like to recommend hydrofluoric acid etches because of the extreme safety hazard. It must always be used under controlled conditions. Instead, muriatic acid may be just as effective. Another possible problem with using acids on certain grades of stainless is pitting and stress corrosion cracking. You can eliminate the acid and roughen the surface by abrading. This can be done by using sandpaper, plastic abrasive pads, wire wheels, wire brushes or media blasting. It is important to note that wire brushing stainless steel is not always a good choice because it may leave iron particles embedded in the surface. Again, it is important to note that the first step in any pretreatment is surface degreasing. After degreasing and pretreating, apply the coating as soon as possible.


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