Cure Problems

Q. We recently acquired a business that included a powder coating system. The cure oven is a gas-fired infrared system. We are having problems with getting full cure on different part shapes and masses and we cannot seem to get the oven properly adjusted to stop having under-cured parts. We also have problems with the oven stopping due to a programming issue. Is there anything we can do to get the oven to cure everything without a lot of headache? How can we get around a long bring-up time when we start the oven back up after it shuts down? R.R.

 

A. You clearly have the wrong oven for the products that you need to cure. In addition, the program is faulty and that causes more problems. You are going to need to add to your oven or change the oven completely. Infrared ovens can offer great advantages in management of different metal masses and surfaces, and they can speed up the curing process. However, any technology that is more reactive and faster is also going to require more precision in application. In addition, gas fired IR can work well for powder cure, but you must have a good control system and you need to recognize that one of the advantages of IR—instant on and off capability—is not the same with a gas system. Gas takes longer to react and to light. Different gas-fire emitters may not be as uniform or efficient as some electric arrangements. Type of reflector and the position of the emitters are also a factor.

Convection ovens are a different way to apply thermal energy for curing. Convection heating uses warm air to heat the substrate and the hot substrate transfers energy into the coating for cure. This technology is slower and less precise. It offers a larger process window with a better margin for over-exposure. A combination of IR and convection is often the best option. The IR accelerates the overall cure and the convection contributes to uniformity of cure and reliability across different masses. You should test different cure options and then retrofit your current oven with one that will work across the broad group of parts you are trying to process.