Reducing Cure Time with a Hybrid Oven

Q. We use a 20-m-long convection oven to cure powder coatings. The current curing time for a standard aluminum part is about 18 min. Is it possible to decrease the curing time to fewer than 9 min if we change the oven to a hybrid system with combined infrared (IR) and convection heating? S.A.

A. Infrared heating uses a direct transfer of light energy to rapidly provide significant heat rise and molecular activity in the coating. Properly applied, it can reduce the cure time. How much it reduces the cure time depends on several variables, including part geometry. If the part has a lot of surface exposed to the infrared emitters and limited mass and depth, then the gain is significant and the cure can be much shorter. The gain will be less profound and the cure will not be shortened as much if the part has a lot of depth and mass, and many areas that are hard to directly access with the radiant energy from the emitter.

Another variable is the type and position of the emitter. Long-wave IR is relatively cool compared with medium-wave or short-wave IR. It will not accelerate cure the way medium- or short-wave will. Short-wave IR is the most intense and may actually be too intense for some applications, providing so much energy so quickly that the coating is over-cured or non-uniform. It can be effective, but care should be exercised. A more intense energy supply requires more precise control of the position and dwell time inside the IR oven area. Medium-wave is often the best option because it supplies significant benefit and is somewhat less intense.

It is not possible to say what you can do in terms of changing the time of cure in a general operation. I strongly recommend testing to determine how your particular part will work with a hybrid oven arrangement. I am not optimistic that you can cut your overall cure time in half by adding IR. More often, IR is effective for one or two minutes, and the overall oven time is reduced by around 25 to 30 percent. A flatter surface that provides a lot of easy exposure with few hidden surfaces could reduce your time a lot, but a complex shape with a lot of mass and poor access to the radiant energy will not reduce the time as much. Testing will help answer your question more accurately and help ensure you get the right oven.