Concealing of Al2(SO4)3 Stain by Spray Coating Process

In hard anodizing process which requires an aluminum part soaked in the electrolysis solution in order to form anodic (aluminum oxide) film on the aluminum part so that it will be harder and durable for work. Although, this part will be drained afterwards by ionize water to eliminate impurities from it, aluminum sulfate stain may be traceable from the part. It is especially for cookware products that require clear coating on an anodized part for aesthetic purpose. It can be imagined that the trace mark from aluminum sulfate can scrap this part or it has to be reworked. However, in coating process, there are three coating steps named prime, middle, top that may aid to conceal the mark as long as the required coating thickness is within specification. However, only middle level is concerned in this work. Therefore, the objective of this paper is two folds. One is to investigate the relationship of spray coating parameters to dry film thickness (DFT) and the other is to determine DFT which is able to conceal the abovementioned trace on the hard anodizing part.