When a part with a coating of powder enters the cure oven, its temperature begins to increase. When the part/powder temperature reaches the melt temperature of the powder, the powder melts and flows, forming a continuous liquid film. If a thermoplastic paint system is being used, this is all that happens in the cure oven.
However, if thermosetting materials are used, an additional important reaction takes place. The part, now coated with a continuous liquid film continues to increase in temperature as it approaches oven temperature.
When the cure temperature is reached, the heat latent hardeners become active and the curing reaction begins. When the part is maintained at the cure temperature for the proper length of time, the film becomes 100 percent cured. A 100 percent cured film is tough and impact resistant.
There are important differences between cure ovens designed for liquid coatings and those designed for powder. Powder ovens should bring the part up to temperature quickly, to allow maximum flow out before the curing reaction gels the film. Liquid ovens require slow heat-up to avoid boiling of the solvent in the paint.
Because of this difference, powder ovens can normally be much shorter and less costly than liquid ovens. In addition, powder ovens consume much less energy than liquid ovens because powder ovens require no exhaust air to carry away solvent. Heating the air that must be exhausted is a major BTU user in liquid ovens.