We have a customer who wants to electrocoat stainless steel parts (grade 430 or 436). Can we expect adhesion problems with normal pre-clean treatments? R.W.
Stainless steel can be electrocoated just like any other conductive substrate. Most pretreatment for steel or aluminum (zinc or iron phosphate) will not deposit much, if any, phosphate, which enhances adhesion. However, normal pretreatment cleaners should clean the stainless parts adequately. The only adhesion concerns you may want to test would be impact or bend tests if the parts are of a very light gauge and/or the stainless is highly polished.
You did not indicate why your customer wants the parts electrocoated. Assuming it is for color only, adhesion should not be a problem. Be sure to ask your pretreatment and electrocoat material suppliers if they have any concerns. Stainless contains a fair amount of chromium in it and could be a waste concern if you have a highly acidic pretreatment and tough environmental state or local standards.
If the parts are stainless for corrosion resistance, maximum corrosion is obtained if the parts are passivated prior to coating. Passivation should not affect adhesion of the electrocoat to the parts.
The only other concern would be if the parts were made from stainless powder metal. Powder metal concerns (regardless of metal type) were addressed in Electrocoating Powdered Metal Parts from the September 2001 issue.