“In Denmark the Powder Coating Companies have problems with yellowing of white coatings in gas fired curing ovens that have direct contact between the exhaust gasses and coated surfaces. We would like to know if this is a common problem in other countries, which parameters in the curing process affects the yellowing tendency, and what has been done to solve the problem? “
“In the US, direct gas fired cure ovens are exhausted at 12 air changes per hour, or higher, to eliminate yellowing of light colored powder coatings. Exhausting of the combustion gases is important for light colored powders used on high quality parts. If the exhaust rate is 12 or more air changes per hour, look to overbaking the powder as the next most contributory cause of yellowing.
Upon occasion, although rare, indirect fired gas ovens, electric convection and IR ovens, or gas fired IR ovens are used to eliminate all problems with combustion gasses. Be aware, that US manufacturers of white powder coated products such as fluorescent lights, appliances, etc. cure their products with direct fired gas combustion ovens without yellowing problems.”