GB192386A - Improvements in or relating to electric annealing, hardening and smelting furnaces - Google Patents

Abstract

192,386. Coradi, O. Jan. 24, 1922, [Convention date]. Resistance furnaces.-In an electric furnace for annealing, hardening or smelting, provided with loosely poured in resistance material 7 such as small coal, the current supply electrodes 5, 6 are positioned in the resistance material so that the current path is parallel to the wall of the chamber or muffle 2 to be heated, the shortest path of the current being thus on the outer surface of the chamber and the longest path being on the outer surface of the resistance material. In Figs. 2, 5, 7 the electrodes 5, 6 are of iron or carbon separated by insulation 4. Fig. 2 is a horizontal cross-section of a vertical cylindrical furnace having a crucible 10 located in the muffle 2 and supported by a movable fire-proof support. The furnace may be arranged so as to be tilted if the crucible 10 is not used. In a modification of Fig. 2, without the crucible 10, the resistance is in the form of a truncated cone. The poured-in resistance material may become more tightly packed at the bottom than at the top, so that the reduction of cross-sectional area toward the top is compensated for by the increase in resistance per unit length at that cross-section to produce a uniform temperature over the surface of the muffle. This condition is essential in annealing and hardening furnaces. Fig. 5 is a vertical cross-section of a furnace having vertical partitions 11 dividing the resistance material into a number of independent zones. Figs. 7 and 8 are horizontal cross-sections of further modifications.