IR Curing Shoptalk
Infrared Equipment Division of IHEA
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Curing in a limited space
Q: We are considering changing from liquid coating to powder coating but have limited space. Because we want an in-line process, is it possible to use IR for a full cure rather than a long convection oven?
A: The simple answer is yes, but that doesn’t address the many issues that need to be considered.
First, if your parts are reasonably thin (up to 1/4 inch thick) and reasonably flat, they could be racked and run through an IR oven and cured. Of course, the IR vendor you select to work with should test your parts with the powder coating that you plan to use to determine heater intensity (temperature and wavelength) and dwell time to get full cure and proper color and gloss.
Heavy parts such as castings or weldments present a different set of problems. In many cases, however, heavy parts can be fully cured with IR alone. What needs to be considered in these instances are part geometry, part presentation, heater intensity, heater zone control, and finish desired. The good news is that vendors can apply their experience to your application and properly configure an oven for you.
Another key factor to consider is the powder coating to be used. Experience has shown that most powder coatings, even metallic ones, flow and cure well when using only IR energy. Most powder coatings manufacturers can make minor modifications to powders to help with gloss (or lack of gloss), surface finish, and temperature.
Curing methods go beyond line of sight
Q: It’s commonly stated that IR heats along a line of sight. If this is true, how can it heat parts that are in the center of racked parts?
A: To answer this question, we have to first assume that we aren’t racking things like engine blocks or propane tanks. If parts are racked on tree-style hangers, it may be as simple as putting a twist in the hook to change the presentation of the parts to the IR heaters. The key element here is the configuration of heaters within the oven chamber. If heaters can surround the parts, chances are good that uniform heat can be delivered to your parts.
The next consideration should be adding control zones within the oven. The good thing about this small initial investment is that it gives the equipment flexibility to handle future products as well as the present products.
Some vendors use air recirculation within the oven chamber to help deliver more uniform heat to the products. Others have made installations without recirculating air, which work very well because of the efficiency and type of IR emitters they use.
As always, it’s recommended that the vendor test your parts to prove the process. In saying this, we by no means want to sound as if you have to run tests when using IR because it’s a complicated process. This is not the case! The reason for testing is that heating processes are a function of time and temperature. With IR, there are many emitter types and wavelengths, and construction methods for the finished oven. It takes only a few quick tests to begin to zero in on the proper time and temperature combination for your parts.