Multi-Metal Pretreatment

Q. I need to clean steel, aluminum and steel castings, steel forgings, electrogalvanized and galvanneal sheet, and aluminum sheet metal parts for an e-coat application. Presently, we use Parco 305 (Henkel), but results are variable. The finish on the galvanized parts is especially variable. What chemistries do you have for this range of materials? C.M.

A. Since e-coat is a conveyorized system, I am assuming that you do not have many options or alternatives in your current cleaning and pretreatment system to add a separate tank to segregate some of your materials to a different cleaner. The cleaner you mention (Parco 305) is a highly alkaline, liquid concentrate containing hydroxides and complex phosphates. Given the elevated pH and use with aluminum, I would also assume the cleaner is silicated to prevent attack or etching of the aluminum and galvanized components. This is a fairly complex formulation of builders and would also likely have an equally complex surfactant package.

I don’t want to be pessimistic, but considering the wide variation of alloys being processed in your cleaning system, possibly with an equally impressive range of soils and contaminants, it is unlikely you will find an aqueous cleaner formulation that would provide significantly improved performance.

One thing that I have found that is particularly unique to galvanized sheet is the variation of coating types that may be on the surface. There are “paint grip” formulations in a variety of chemistries that come from the mill already pretreated and ready for paint. There are others that are simply oiled for medium-term corrosion resistance. Your supplier is likely a service center receiving material from a variety of different mill sources. It may be this variability that causes more of your headaches than your cleaner. I would suggest focusing on understanding what is different about the problem batches before searching for a new cleaner.