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POWDER COATING, March 2016 29 S electing the correct infrared (IR) emitter is something that is widely overlooked and undervalued. Every material absorbs IR differently. Choosing the correct emitter will en- sure the most effective heat work that will, in turn, yield the fastest cycle times. The best wavelength for a specific mate- rial will produce test results that show an even heating curve on both sides of the material along with the shortest time needed to get the result. Planck's Law The basics of IR need to be understood in order to improve any process. And, at its core, the IR process begins with Planck's Law. So says the Ceramicx Ire- land research team, which recently pub- lished the technical report titled "Ex- planatory Notes on Plancks Law," which is authored by Dr. Gerard Mc- Granaghan. Ceramicx is represented in North America by IHEA member Weco International. Planck's Law describes the electromag- netic radiation emitted by a black body in thermal equilibrium at a definite temperature. The law is named after Max Planck, a theoretical physicist who originally proposed it in 1900 as the basis for quantum mechanics. According to Planck's Law, as the tem- perature of any emitting surface in- creases, more and more energy will be released as IR energy. The higher the object temperature, the greater the amount of IR energy will be produced. As well as becoming more intense in terms of power, the emitted frequencies become wider and the peak wavelength becomes shorter. At very high tempera- tures, not just IR but also some shorter wavelength visible light will be pro- duced. This is first witnessed as a dull red glow that subsequently turns to or- ange, yellow, and, finally, white. Figure 1 shows typical Planck curves for a range of temperatures that have been plotted from 1,050°C to 50°C (approx- imately 1,922°F to 122°F). The red curve corresponding to 1,050°C ex- hibits the strongest output. It shows the highest power output and its peak is at around 2.5 microns. This is followed by the curve at 850°C where the peak en- ergy is less than half of that produced at 1,150°C. Marek W. Urban, Ph.D. Clemson University IR Curing ShopTalk Infrared Equipment Division of IHEA This column is provided to you by members of the Infrared Equipment Division (IRED) of the Industrial Heating Equipment Association (IHEA). The group includes infrared (IR) curing equipment suppliers from throughout North America. We publish the column three times a year to give you the latest information about IR curing techniques and equipment. Contact information is at the end of the column. Most IR man- ufacturers offer testing for free or for a fee. Any IRED member can assist you in finding solutions to curing problems and best practices for finishing of coatings. This issue's column was submitted by IRED member company Weco International, Clio, Mich., who exclusively represents Ceramicx of Ireland for all of North America. Choosing an infared emitter for your application Figure 1 Planck Distribution, Emissive power and Wavelength with temperature Emissive power (W) Wavelength (µm) 800 700 600 500 400 300 200 100 0 0 5 10 15 20 A depiction of IR distribution for various emitter temperatures from 1,050°C to 50°C.