High Temperature atmospheres induction furnace

induction furnace

Induction furnaces operating above 3000" c have been previously described. Zaer in 1935 used such a fumace for measurement of the sublimation point of graphite (3500 = 10" c at one atmosphere pressure). In an improvement of this design, a laboratory furnace was constructed in which a graphite crucible with a volume of 150 cm3 could be heated to 3000" c with only a 5 kw generator (Ribaud 1950). The induction furnace has also been developed in industry for use up to 3600" c (Chestnut 1953). However, all these induction furnaces have certain serious disadvantages when stringently controlled conditions are required since they rely on carbon black for thermal insulation. This imposes the limitation that the furnace cannot be evacuated or conveniently used at pressures much greater than one atmosphere, and introduces a high possibility of chemical contamination of the specimen from the gaseous impurities evolved when the carbon black becomes heated. The loading and dismantling of these furnaces is also both dirty and tedious, and they take a considerable time to reach steady operating conditions. The furnace described in this paper can be operated above 3000' c and avoids the above limitations. Moreover, it can be used for extremely rapid heat treatments on graphite and certain refractory carbides, borides and nitrides and for many other operations at high temperature. One disadvantage in this method of heating is that the induction generators have a maximum overall power efficiency of only about 40%. This, however, is acceptable to industrial application as it is nullified by the great increase in operational efficiency. At a given power input the maximum temperature depends solely on the surface area of the heated crucible since heat losses at these very high temperatures are entirely by radiation. The radiation losses can be reduced by employing radiation shields, for example, of polished molybdenum.

induction furnace

High Temperature atmospheres induction furnace.pdf