Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2004

Solvent Fumes Condensing at the Entry & Exit of a Baking Oven

Q. I face a problem of oil drops falling on the painted body at the exit end of the baking oven. Fumes inside the oven condenses at a low temperature of 28°C. Oil drop analysis reflects it is s.o. alkyd used in paint. How does this happen? Can resin parts evaporte? Is there any perfect oven balancing formula that can be checked? What should be exhaust opening ratio? What will happen in the oven to the paint film if the paint is baked at a higher temperature than specified? Say about 30-35 deg. more for 4-5 min.

A. What is evaporating in the oven is some of the lower boiling resin or other organics, such as plasticizers. In all probability the alkyd resin itself is unlikely to be evaporating, at least not at 30-35 degrees C. In any case, it might be necessary to redesign the oven exhaust ducting so that the condensate doesn't fall onto the painted parts. By the way, it is not unusual for condensate to collect in an oven and for it to form a dark amber, brown or black film or lining on the oven ducting and walls.

Since I don't know anything about the coating, the best way to test the effect of temperature is to take a few test panels, such as Q-panels and coat them in the same way that the product is normally coated. Then subject the coated panels to the higher temperature for the period you are examining. After allowing the panels to condition at room temperature for several days, conduct simple tests on the coating to determine if it has lost any of its properties, such as adhesion, flexibility, impact resistance and color. All of these tests are very easy to perform yourself. No matter what resins are being used, practical tests are the best methods for predicting how the coating will perform under extreme conditions.

Good luck with your project.