GB785911A - Improved electrical heater elements - Google Patents

Abstract

785,911. Sheathed electric heating resistors. GENERAL MOTORS CORPORATION. April 18, 1956 [May 4, 1955; June 3, 1955], No. 11824/56. Class 39(3) [Also in Group XXII] The heater comprises an outer tube 20 filled with compacted insulation, e.g. magnesium oxide, and containing two or more heating resistance wires 34 extending longitudinally and connected to terminals 22, 24 protruding through one end of the tube, and a resilient plug 26 of heat-resistant synthetic rubber is gripped by compressing the end of tube to locate the terminals, part of the plug protruding from the tube. In Fig. 9 three resistor wires 128 are connected to spaced terminal pins 122 passing through the resilient plug 134 and a second resilient plug 138 is spaced within the tube from the first plug 134 by a ceramic bushing 136, which, on compressing the end of tube, e.g. to a square shape, is crushed. A second ceramic bushing 140 bearing against the inner end of the inner resilient plug is also crushed. The part of the synthetic plug protruding from the end of the chromium steel tube 20 is formed with integral radial or diametral fins 63, 142 extending out between the terminal pins. The plug may be of silicone rubber or Buna N synthetic rubber and its exposed surface and adjacent parts of the pins may have a water repellent coating, e.g. a 2 per cent solution of linear methylpolysiloxanes applied thereto by brushing. The heater is made by supporting by a hook 48 a coiled resistance wire 34 in the tube 20 and pouring powdered magnesium oxide powder through a funnel 50 into the tube, which is vibrated by a mechanical shaker 53. The terminal pins 22 passing through the resilient plug 26 and ceramic bushing 27 are held against sliding by a cup-shaped clamp 28 carrying set screws 30. When the tube is full its top end is compressed by transverse dies to a square shape to hold the wire loop firmly. A cap placed in the open end of the tube is then sealed by turning in the end of the tube and welding it to the cap. The plugged end is then swaged to decrease its diameter from 0.5" to 0.45" or to give a 25 per cent reduction. The tube between the ends is then pressed between dies to a triangular cross-section, preferably after bending the tube to a spiral to form a hot-plate.