by Ron Joseph
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