Fixing Fish Eyes When Powder Coating Over Electrocoat

Q. We powder coat wheels that come into our facility with an e-coat finish already applied. Recently, we have started getting fisheyes in every batch after we apply the powder coat over the e-coat. We have gone through troubleshooting exercises for every possible cause that we have experienced in the past, but this seems to be a new issue that we have not ever experienced. We have flushed airlines, performed many tests, cleaning and preventing on every avenue, but we are still at a loss. A.N.

A. Fisheyes occur when there is something in the coating or on the surface that is incompatible with the powder coating in the melt and flow stage. The powder cannot mix or flow out with a contaminant, so it leaves a void in the film. Fisheyes are a unique-looking defect that form a nearly perfect circle with a raised edge around the offending contaminant. In your case, the most likely cause is something on the electro-coated finish that is difficult to remove by any normal cleaning method. Spray out the powder on test panels with no e-coat. If they have fisheyes, the problem is in the powder or your plant. If they do not have fisheyes, it probably indicates an issue with the e-coat finish. Try panels that have been e-coated by your supplier alongside panels e-coated by another supplier. This will give you additional insight into the root cause if the panels from another supplier do not fisheye while your supplier’s do. Have some panels with the suspect e-coat finish powder coated in another facility. Try different powders. Conduct testing that will help isolate the source of the contamination. You will probably find that the electro-coated parts are being exposed to silicone.