GB592049A - Improvements relating to electric heating elements - Google Patents

Abstract

592,049. Electric heating resistances. BULPITT & SONS, Ltd., and ASHTON, F. Dec. 2, 1944, No. 24122. [Class 39 (iii)] In the manufacture of an electric heating element in which a resistance wire, usually coiled, extends through a metal tube filled with an electrically insulating material such as fused magnesia or alundum, the latter is compacted against the tube wall by rotating the tube at high speed. In an example, insulating paste is drawn, by a vacuum device, into a tube 10. Annular plugs are inserted in each end of the tube, and permit the passage, through the tube, of a plunger rod of the same diameter as the resistance coil 22, to be used. This forces the paste against the walls of the tube, as at 23, where it is further compacted by high-speed rotation of the tube about its axis. The paste, which is preferably formed with a volatile liquid, is then slowly and evenly hardened in a muffle furnace. After removing the end plugs, the resistance coil 22 is inserted in the tube, one end of which is closed by an insulating bush 24 and sealing paste 25. A funnel 26 containing insulating powder 27, is screwed into the open end of the tube. This assembly is mounted vertically on a sleeve 33 which engages a rotating eccentric 32 whereby the assembly is vibrated to compact the powder 27 in the coil 22. The open end of the tube is then closed and the element is bent to the required shape.