Pinholes in Powder Finish

Q. We apply powder coating on aluminum panels, and are facing a problem with pinholes. Our pretreatment is acid etching and chrome-free coating. Please give me a solution for the pinhole problem. D.K.

A. The pinholes could be from several sources:

• The metal surface: The aluminum could have porosity or fractures that are outgassing.
• The treatment: The treatment process could be leaving some contamination on the part surface.
• The powder: The powder may be defective or it may be applied too thickly.
• People: Someone may have lotion or something on their hands that is getting onto the parts.

To find the problem you will need to work through a process of elimination. Do you bend or weld the aluminum? If so, are the pinholes located around the bend or the weld? If it is around a stressed area in the metal, that could be the source of the problem. Try the same powder on a different source of aluminum and coat those parts on your line. Have some parts treated by another facility and coat them on your line. If the problem goes away, you will know it is your pretreatment. Treat the aluminum at your plant and coat it in a different location. Try a different powder and try applying the powder thinner. You should be able to find the problem by systematically eliminating different sources.