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infrared heating[¦in·frə¦red ′hēd·iŋ]
the heating of materials by electromagnetic radiation having a wavelength of 1.3−4.0 microns (infrared radiation). It is based on the ability of materials to absorb a certain part of the spectrum of such radiation. Deep or superficial heating of the irradiated body, as well as local drying without heating the entire object, can be accomplished with appropriate selection of the emission spectrum of infrared radiation. Infrared heating was first used on an industrial scale in the 1930’s in the United States at Ford plants to bake enamel onto automobile bodies.
Infrared radiators, which consist of the energy source itself (a heated body) and a reflector, are the source of energy for infrared heating. Depending on the degree to which the sources are heated, they are arbitrarily divided into low-temperature sources, which are heated to a temperature of less than 700°C; medium-temperature sources, from 700° to 1500°C; and high-temperature sources, above 1500°C. Tubular electrical heaters, reflector drying lamps, and electrical heaters (which consist of a tungsten filament housed in a hermetically sealed quartz pipe filled with inert gas and iodine vapor) are used as heat sources. Infrared heating units are chambers, tunnels, or domes whose size and shape correspond to the size and shape of the items being processed. The radiators are attached to the inside of the unit; the distance between them and the surface of the objects being heated is usually 15–45 cm. In industry infrared heating is used extensively for heating to comparatively low temperatures with low heat fluxes (for drying dyes and lacquers, vegetables, and fruits; for heating thermoplastic materials prior to molding; and for vulcanizing rubber).