GB798922A - Improvements in and relating to electrical heating apparatus - Google Patents

Abstract

798,922. Sheathed heating resistors. GENERAL ELECTRIC CO. Dec. 21, 1956 [Dec. 27, 1955], No. 38962/56. Class 39(3) [Also in Groups XIII and XXXVII] A sheathed heater with a coiled wire resistor 2 within a tubular sheath 1 from which it is insulated by magnesium oxide or alumina or magnesia cement has an elongated argon-filled teperature responsive tube 4 extending longitudinally within the sheath, one end of the tube 4 projecting through a washer 6 out of one end of the sheath and communicating externally with a diaphragm or bellows 12 for sensing the inner temperature of the sheath. The tube 4 extends within the heating coil 2 and may be metal, so that current may be supplied to one end of the coil 3 by a terminal 7 at one end of the sheath and to the other end of the coil through the tube 4 connected to the coil by a metal sleeve 9. The bellows 12 carries or operates a movable contact 14 of a switch open-circuiting the heater on rise of temperature. Thermostatic cycling action of the switch may be obtained by mounting its other contact 15 on an over centre device i.e. on a bowed spring 21 with its ends in opposed openings in a casing 11 and passing through opposed slots, 19, 20 in a rectangular contact actuator 18 of non-conducting material mounted on the bellows 12. A spring 17 bears on the lower side of the actuator 18 to oppose the bellows 12, and as the heater cools the spring 17 presses the actuator 18 up so that the bowed spring 21 snaps over centre to engage contacts 14, 15 and so pass current to the heater coil 2 either through the bellows and tube 5 or through a wire connected between the contact 14 and coil 2. When the tube 5 and its exter nal projection 13 are of metal, the part 13 is covered with insulation 16. On rise in temperature of the sheath, the bellows 12 expands to push the spring 21 over centre and open the contacts 14, 15. Spring 17 rests on a collar 22 positioned on a cam 23 actuated by depressing a bush button 24 to push the spring 21 over centre to commence heating. To prevent overheating of the sheathed unit should contacts 14, 15 fail to open, the switch actuator 18 moves down to engage the end of a plunger 17 having on its lower end a contact 25 bearing on a contact 26 on a bowledspring 28, which is thus forced down to over centre position to open the contacts 25, 26 as shown. This spring 28 may be reset by a push button 29 in the bottom of the casing 11. The sheathed heater may be a surface unit on a cooking range. By providing several different cams 23a, 23b each with a separate push-button 24, various temperature settings for the heater may be obtained. The heating is ended by pulling out the push-button.