As zinc-coated steels gain popularity in metal-stamping processes—this has also increased concerns and complaints of zinc staining and corrosion. Zinc-coated steels pose many challenges for lubricant formulators and for stampers. Not only must you provide ferrous corrosion protection for the underlying steel substrate—but you must also prevent the dreaded white and black staining so problematic to these materials.
It’s for this reason that many stampers will rely on oil-based lubricants—even though they may forfeit tool life, part finish and add process costs to downstream processes. Even emulsifiable oil stamping fluids can stain and corrode zinc coated metals, and the mere contact of water itself can stain or discolor zinc-coated steels. This is where air knives can have a significant impact.
Using air knives to remove excess fluid from part surfaces can dramatically reduce or eliminate white and/or black staining and corrosion of zinc-coated steel. Shortening the contact time the metal surface and freshly deformed substrate has with aqueous solutions lessens the chances of generating white and/or black surface staining. Drier parts can also lengthen storage time between stamping and pretreatment as the parts have less fluid pooling on parts in hoppers and less chance for contact point corrosion with other parts. This reduction in part residue can likewise be a great benefit to lower temperature and/or lower pH cleaning processes.