Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Adhesion of Powder Coating to Stainless Steel

Q. What is stopping the adhesion of powder coatings to stainless steel? Does it have to do with surface tension, hardness, chemical compostion, etc of the metal? We have had success on 304, and limited on 430 but no success on 316. What is causing this adhesion problem? Is it something in the powders or the metal? We have researched the metal and found that there is only minimal difference between grades of stainless (Rockwell, Chemical content) so is it the powder itself with poor characteristics? I appreciate any help that you can provide.

A. Surface preparation is probably the cause of the poor adhesion of the powder coating. Not all stainless steels accept phosphate pretreatments to the same extent; some being more reactive to the chemicals in the pretreatment process, and others being more inert. What you have written makes perfect sense. If you want better success with 316 stainless you might need to change the pretreatment chemicals to more aggressive reactants, or you might need to provide some physical profiling of the surface so that the powder coating can adhere chemically and physically.

Best wishes,

Ron Joseph