Powder Clinic: Pinholes Mentioned in July Issue

Q. Just read the article in most recent issue of PF about our problem and wanted to respond with what we found out. We sent a sample panel to a powder manufacturer and they had their chemist look at it. Their response was that the micro pores did not go to the surface of the part and it was moisture in the powder in combination with the moisture in the oven air that was on the surface of the part too long before evaporating, causing imprints. We had our gas company test the moisture content of the supply gas. They said it was at the maximum level allowed. This then led us to verify the volume of exhaust gas being expelled by the fan. We did the drive calculations and found it was at the minimum recommended level. We increased the pulley ratios by 30 percent and the problem has almost disappeared. Thanks again for your help.

A. You make a couple of important points. Using your vendors to analyze a defect can be very helpful. They often have expertise and analytical equipment that can be used to evaluate problems. Also, looking at the depth of a defect helps to understand the source. For example, a pinhole that exists at the surface but does not penetrate to the substrate is most likely an airborne contaminant. Your process of detecting the source was great. I’m sure you're glad to have it resolved.