Steel Casting Cleaning


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Q. I have a question about cleaning large cast steel parts prior to electroplating. Our plater processes the parts through the standard chemical cleaners (alkaline and HCI) prior to plating, but it doesn’t seem to be sufficient. After the parts are plated, they are powder coated. The parts are baked at 350°F to cure the paint. It’s at this stage we see brown burnt marks that stain the parts, or the paint will blister/bubble. It seems there is some out-gassing through the porosity of the cast, but we aren’t quite sure if that’s the root cause. Have you come across any of the issues described? Is there a standard method for cleaning cast steel prior to electroplating, such as steam cleaning or cleaning the parts with some sort of chemical cleaner agent? Any suggestions would be greatly appreciated. —N.G.
A. What you are experiencing is a common problem with those that paint castings then cure the paint. While casting processes vary in their potential to create porosity, virtually all castings have some level of porosity related to the material and the casting process. As a result, when the casting is heated, these pores will outgas any residues that are in them.
Organic residues from machining lubricants and coolants as well as mold release will tend to turn the part the burnt brown color you describe. I would suggest you first try baking out the part at nearly the same time and temperature of your paint cure operation prior to sending parts to the plater.