Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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systems and equipment INFRARED DRYING AND CURING SYSTEMS CASSO-SOLAR CORP., POMONA, N. Y. Today's finishes require precise control of color, gloss, texture, surface finish, and cure. Cured organic coatings must perform well in the environments in which the product will be used. Infrared curing and drying can provide these properties con- sistently, with easy operator control, fast curing times, precise control, a conta- minant-free environment, low maintenance costs, and a savings in floor space. Infrared radiation can be used in a variety of different applications, from dry- ing and curing to preheating before a convective oven or post curing after a con- vective oven. It can be used with many substrate materials such as metal, glass, plastic, paper, textiles, and wood. Combination systems that utilize infrared to flow out a powder or liquid coating to be cured with UV are providing coatings with new strengths and characteristics. Whether infrared radiation is used in the finishing process of organic coatings on products, such as light fixtures, furniture, hot water tanks, shelving units, kitchen cabinets, or insulated doors, line speeds can be drastically increased and cost savings can be realized. How a convective oven differs from an infrared oven is like night and day. At night, if a car remains outside in a driveway, it eventually becomes the same temperature as the sur- rounding air. The air slowly exchanges energy with the outside of the car body dur- ing molecular collisions of the air molecules with the surface of the car. During the day, the air temperature could be ex- actly the same; however, the car rapidly heats up well be- yond the air temperature be- cause the sun's radiation can heat the car body faster than the air can cool it. This applies to finishing systems as well. Radiation can transfer heat energy to a prod- uct at a much greater rate than convective air. Much time is spent in bringing a product up to its curing temperature in a convective oven. Infrared radiation drastically shortens the time necessary to get the coating to its curing tempera- ture and then holds it there for its curing cycle. Figure 1 compares product tem- perature with time for curing a powder-coated product in a convection oven versus an infrared oven. Fig.1. Product temperature versus time for curing a powder coated product in a convection oven compared with an infrared oven. INFRARED THEORY Every organic coating has a particular energy spectral absorption curve. There will be peak wavelengths, where the coating absorbs very well at and near its sur- face, and valley wavelengths (off-peak wavelengths), where the energy penetrates 224

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