Miniseptor—A Modular Approach to Susceptor Design

Abstract

MINISEPTOR is a susceptor for vacuum hear-treat and melting applications which is made up of a number of multisided polygons, (almost circular rings) primarily of graphite, stacked concentric with the axis of an induction coil. Its modular construction makes feasible hot zones, as large as 11 ft in diameter by 1712 ft high, for operating temperatures to 2750 °C (5000 °F). The reduced mass of the susceptor greatly reduces the stored energy in the susceptor resulting in brisk, temperature cycling. In addition, initial costs and operating costs are lower than for conventional systems. The modular construction of the susceptor and its thermal insulation allows replacement in sections as required, without complete removal, which simplifies maintenance and lowers the required minimum stock of spare parts. Variable configuration of the bars, pins, fit, and grade of the graphite used affect the overall resistance of each ring, the number and configuration of rings determining the power delivered to the susceptor at any given voltage and frequency. The multiplicity of independent concentric “rings” permits altering the spacing between “rings” so that it is possible to control the temperature gradient by distribution of the power along the length of the hot zone. Performance characteristics observed on a hot zone 35 in. in diameter and 51 in. tall are discussed. Uniformity of the temperature gradient across the hot zone and holding temperatures observed on this scale model of the large hot zone described above are reviewed.