Pretreating Stainless Steel

Question:

I just read through your answer to J. A. on painting stainless steel in the October 2002, Products Finishing. In it you mention abrading the surface of the stainless steel to improve paint adhesion. One of the methods suggested was wire brushing the stainless.

I would avoid using a wire brush on stainless steel, especially if it is passivated, because it will embed iron in the surface that can then cause the stainless steel to red rust. When stainless steel is passivated, it is treated with acid to remove any iron from the surface and establish a chrome oxide layer that is resistant to corrosion. Wire brushing will leave iron on the surface and defeat any benefits from passivating the stainless. Any other method, such as the media blasting, should be done with materials that will not contaminate the stainless steel with iron. The media should not be steel shot, nor should it be any recycled media that was previously used for blasting parts made of mild steel. Just my two cents worth. T. D.

Answer:

T.D., your two cents could be worth dollars to someone pretreating stainless steel using a method that causes more harm than good. Thanks for bringing the possible contamination and subsequent corrosion problem to my attention. The same caveat applies to the Sealant Adhesion to Stainless Steel question by M. S., also on page 28 of the October 2002, Products Finishing. “Pay no attention to that man behind the curtain.” The great and wonderful Oz led you down the wrong color brick road.