GB249858A - Improvements relating to electric heaters - Google Patents

Abstract

249,858. Metropolitan-Vickers Electrical Co., (Assignees of Keene, A. D.). March 26, 1925, [Convention date]. Void [Published under Sect. 91 of the Acts]. Wire resistances, embedded.-The resistors of electric heating units in ovens, furnaces, &c. are embedded directly, or with interposed insulation such as alundum, in carborundum or other material which conducts heat and electricity to a similar extent to carborundum. A helicallywound wire with the turns spaced apart before or after winding may be dipped in, or otherwise coated with, moistened, powdered electric-insulating material such as alundum and, when the coating has dried, bent to the form shown in Fig. 1 on a former such as a wooden plate with pegs, and lightly pressed into moistened, powdered heat- and -electric conducting material such as carborundum in a rectangular mould. Alternatively, grooves in the powdered carborundum may receive the wire, which is afterwards covered with powdered carborundum. In either case, a high pressure and heat are applied to press the carborundum into intimate contact with the insulated wire and to form a plate unit 14 which may act also as a muffle. The carborundum is mixed with 5 to 10 per cent of clay acting as a binder. Terminals 15, 16 of michrome or other refractory material extend into the plate 14, have the ends of the resistance wire 12 wrapped around them, and are covered with insulation 17 such as alundum. In a modified unit of rod form, Fig. 5, a wire helix 12 is embedded in a rod 18, 19 of carborundum &c., terminals similar to those in Fig. 1 or formed by doubling the wire 12 on itself being employed. In this form, the insulation 13 about the wire may be omitted, the carborundum itself conducting a small current. The helix 12 may be embedded in the rod by the process used for the rectangular plate or by extrusion of plastic material through a nozzle.