GB348119A - Improvements in electric furnaces - Google Patents

Abstract

348,119. Electric furnaces. ROBERTSON, W. I., 70, Leigham Vale, Tulse Hill Park, London. Feb. 7, 1930, No. 4234. [Class 39 (iii).] A furnace for dental work and small scale chemical and metallurgical operations comprises an electrically heated tube 11, a surrounding casing 6, lagging 7, such as kieselguhr, in powder form filling the space between the tube and casing, and a hearth 12 movable to and adapted to close the mouth of the tube. The tube may constitute the heating resistance or it may be formed of corundum or alundum and heated by a wire 15 arranged in a helical groove on the tube. The wire may be held in the groove by fine wire passing around it and through holes in the tube, or perforated lugs 14 through which the wire 15 passes may be formed on the tube. Alternatively a heating wire may be arranged in zig-zag form in quartz tubes on the inner walls of the tube 1. For work at 2500‹ C., a heating wire of a platinum-iridium alloy or rhodiumiridium alloy is used. The tube 1 and casing are arranged on a base 4 of uralite or sindanyo and at the top of the tube and casing is arranged a table 5 of the same material. The hearth 12, of quartz or corundum, is detachably mounted on a movable rod 11 resting on a metal block 13. The furnace is mounted on a box having perforated sides and containing a transformer 22 and an adjustable resistance 24. A panel on the box carries a switch 20 and an ammeter 21. An intermediate tapping on the-transformer enables regulation to be effected. A hole is formed in the top of the box to carry the closure plug 27 of the furnace.