Q: I work at a metal company, and we are dealing with a finished powder coating issue that we really need help with. We are powder coating our cabinets with black powder, and the surface of the side cabinet is not equally black. It has a band of slightly white color on it instead.
The root cause we suspected was due to the heat distribution differentiation (after the chemical washing oven process and just before entering powder coating process) because the parts’ thickness is different. The area where the parts are 0.8 mm, the color looks just fine. However, the areas where the parts have additional reinforced plates (making the thickness higher) are getting the slightly white bands.
What solutions can we use to solve this troublesome issue?
A: From what you describe, this is a problem associated with the cure of the powder coating. Much depends on what the chemistry and gloss are. What I think is happening is the coating is experiencing much higher temperatures over the thin metal and much lower temperature and less cure at the thicker areas.
If this is a polyester powder coating, the problem may be blooming. Some polyesters exude a hazy material when exposed to low oven temperatures. At higher temperatures, the material essentially sublimes into the oven atmosphere. If it is another chemistry, it may involve a different gloss due to inconsistent cure.