Sanding Defects

Q. What type of defects would you expect to see in a powder coat finish on 6061 aluminum forgings that have been heavily sanded to remove parting lines, etc.?

A. If the sanding is too aggressive or the grit size too large it could create lines in the metal that would be visible after the coating is applied. Such defects can be avoided by using the right grit size and proper technique to avoid leaving obvious cuts in the metal. That could mean using a progressively less aggressive grit size to get a smoother finish.

Another potential defect could come from dirt, oil or other contamination on the sanding disk or paper. The act of aggressive sanding could leave deposits of that contamination, which would be revealed after the coating was applied and cured. It could also cause some outgassing if materials were embedded in the metal and released during cure.

Sanding seems like a logical way to remove oxidation or visible mechanical defects. That said, you should keep in mind that sanding can be inconsistent and hard to control. If you must abrade the surface it may be better to use a blasting operation, which will be more uniform and effective than sanding.