IR-SPECIFIC POWDER?

Q. We have an IR convection curing station on our powder line instead of the conventional curing ovens, and we continue to experience difficulty in getting powders that are compatible with our process. Since the curing process temperature is so high and quick, we continue to experience all sorts of issues. We have two sources now, but they continue to struggle as well.

Is there a powder manufacturer you are aware of that specializes in providing powders that cure in this fashion? G.H.

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A. You do not mention just what problems you are having. It would help to know some specific details. Chances are you are having some problems with the degree of cure (under and over) and inconsistency in appearance of the powder, gloss in particular. The infrared energy may behave differently when you run different geometry and masses and the resulting cure may be inconsistent.

There is no special powder for curing in an infrared oven. You can make some minor adjustments to the flow and gel cycle of a powder to match it up to a particular oven and possibly get improved results, but the real problem is the cure technology, not the powder.

IR can be an advantage when used correctly. It can accelerate the cure cycle and provide flexibility for different masses of substrate when used in front of a convection cure oven. An infrared oven is excellent for full cure when the parts run in the oven are consistent in size and mass. However, any technology that delivers more rapid and intense result has a narrower process window and less margin for error. Convection is slower but more forgiving of process variables such as shape and mass.

The behavior of infrared energy on the part surface is heavily dependent on consistent profiles, position, mass to surface ratio and other production variables. This is why IR is seldom a good fit for 100% of the cure when part shapes and sizes vary. If the line runs one part only or very similar parts, then IR can be effective for 100% cure, but if a variety of parts have to be processed, it is usually better to have some convection along with the IR to provide more uniform cure across the different masses and geometries.

The combination of the two technologies is used in many operations to provide the benefits of the IR (shorter cycle time and more rapid cure on heavy masses) while using the convection oven to open up the process window and avoid too much or too little cure.

If you can add convection to the process, you should. Less IR will avoid over-cure and an addition of convection will help you attain more uniform and predictable results over a wider variety of parts.?