I have heard that in the polishing of zinc and aluminum castings it is necessary to keep the polishing "dust" from these two metals separate. Is this for safety reasons or for economic reasons of selling a pure "dust"?Scott MacDonald
I have not run into too many people who have had problems with mixing the aluminum polishing and zinc casting polishing. However, remember that zinc is one of the most active metals we deal with on a daily basis. It is so incredibly active, that finely divided particles can react with oxygen in the air we breath and combust. If that happens, you will risk a fire or worse. Old time polishers will tell you of their experiences with exhaust stack flare-ups. Some have had tragic consequences. Safety will dictate that polishing or grinding of the metals be kept separate in the name of safety.
Now for an answer to a question that you did not ask. Always keep the buffing of steel parts separate from the buffing of aluminum parts. The mixing of steel powder and aluminum powder all through the exhaust system is setting you up for a flash fire that can travel pretty quickly. When the iron oxidizes, the resulting Iron Oxide plus the aluminum powder will form "Thermite," which burns at an incredibly hot temperature. All it takes is one spark to set it all off. And sparks abound during the buffing of steel, as you know. Most buffing equipment designers will never plan to use the same buffing jack for both aluminum and steel.