Spectrally Tuned Emissivity Surfaces for Optimal Glass Heating and Bending

George Neuman, Anthony V. Longobardo, Daniel Prone

Radiation furnaces typically heat products by electrically heating wires or elements that then emit radiation with some spectral distribution. The energy emitted over a given wavelength range is a function of the temperature of the material and its emissivity. The energy absorbed by a material is closely related to its emissivity. Heating inefficiencies occur when the spectral emissivity of a heating element and a substrate are not well matched. The presence of a low emissivity coating on a glass substrate presents additional challenges. If the substrate is transparent to wavelengths where the heaters have a high output and the coating absorbs energy we can preferentially couple to the coated surface. Under certain circumstances this could lead to an overheating of the coating and subsequent coating
damage. A method is described whereby the energy from heaters is optimally matched to a glass substrate leading to improved heating efficiencies, better bending control and protection of low-e coatings.

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