Q. Are there any new methods other than or in addition to phosphating which act as bonding media between powder and a metal surface? A.L.
A. Powder will bond effectively on a mechanically clean surface that has been abraded or roughened with a blast media or other surface preparation method. It is important to be sure that the media used to roughen the surface is clean and that it cuts the surface. Spherical shot may peen the surface and leave some oils imbedded in the metal. A grit blast media like aluminum oxide is usually better because it cuts into the surface more effectively. Many automated blast systems use a blend of shot and grit. Grinding or sanding can be effective, but they are not suitable for a higher-volume operation. There are also chemical conversion coatings that will enhance adhesion. In addition to iron phosphate, zinc phosphate, manganese phosphate and chrome, new pretreatments such as zirconium oxide will enhance adhesion to a metal. These newer treatments do not require heat and they do not generate the sludge that is a normal byproduct associated with phosphate solutions. Phosphates have been connected to eutrophication in fresh water lakes, while the zirconium-based products have not been a problem.