Volcanoes in the Coating

Q. We are seeing a defect primarily in one of our smooth gray powder coatings. It looks like little volcanoes and is in no repeatable pattern. It does however show up more prevalent in the areas that are metal finished. The parts are welded boxes and metal finished with 50 grit, then run thru a seven stage iron phosphate washer system. We ran some Bonderite panels through the system after the washer and the defects showed up on the panels. Do you have any ideas on the cause of the defect?  J.V.

A. There could be several causes. It sounds like you have some type of contamination that is airborne or in the powder material. Look for sources of moisture or lubricants. If the volcanoes go through to the substrate it may be caused by silicone. Look for lubricants and release agents used inside the facility for maintenance, molding or die-casting. Check maintenance products, sweeping compounds, or cloth items used to clean around the spray area. Check your compressed air system for oil, water or contamination. Have some powder sprayed in another location to rule out the powder.