Q: I work at an OEM shop running three batch booths and three ovens. The current issue we are experiencing is a lot of contamination showing up on a lot of our parts. The contamination seems to be powder specks from some of the other colors we spray. For example, spraying a midnight blue and clear on a part and then seeing white specks all over it. The contamination we are finding seems to just be on the surface and not under the powder.
Our booths are separated into what type of colors we spray, one booth does light colors, one does grey, and the other does dark colors. We have tried other batches of the same color to eliminate the powder contamination theory with no success. We have also done deep cleaning in the ovens daily to try and eliminate that option.
Although all of our booths are enclosed, I have a gut feeling that just the trip from the booth to the oven might be causing this. My other thought is with the weather we have here in the Northwest United States during the fall season, the ambient air has an extra charge, creating more particles in the air to want to stick to our parts. Have you heard of any studies that might suggest this? What are the steps of elimination we should do to narrow this down?
A: Isolating a source of contamination is always a monumental task. Here is what I would suggest.
Isolate the coated products from potential sources of contamination. To isolate parts, I would spray small parts (or perhaps better yet, 4 in. x 6 in. [100 mm x 150 mm] test panels) and isolate them from various environments. To do this, place the test panel in a metal paint can (2.5 liter) secured with a lid. Specifically, place coated panels just after they exit your spray booth into a metal can. Allow some other panels to traverse from the spray booth to the oven, then place them in a metal can. Also run coated parts/panels through the oven outside of the metal cans.
If there are any other environments you would like to isolate the coating from, include coated test panels accordingly. Please note it is a good idea to put a few small holes in the metal cans to allow any fumes/vapor emanating from the curing powder to escape.
Run all the panels (in metal cans and not) through the oven concurrently. Collect all the panels and inspect for defects. If all the test panels exhibit white (or other color) specks on the surface, then either the powder coating is contaminated or contaminants exist in the powder booth or powder delivery system (including the hoses, hoppers, etc.).
If the panels isolated upon exiting the oven are clean, then the powder and booth are clean and the contamination is occurring outside the spray booth. If the test panels isolated from the oven that traversed through the area between the booth and oven are clean, then the oven environment is suspect.
If all the test panels are clean except those that were exposed to the oven atmosphere, then your oven is contaminating your product. Interestingly, a deep clean of an oven can sometimes exacerbate a contamination issue. Deep cleaning can dislodge dirt that would be otherwise adhered to the oven interior.
Once the contamination source is identified, you’ll have to go to work to either eliminate the source or isolate your parts from the source. If your finishing operation is open to the rest of your plant, I strongly recommend that you build an enclosure around the finishing process (including leading into your oven).