Patent GB-203463-A (GB)
Title: Improvements in and relating to electric heating devices
IPC: H05B3/48
Filed: 1922-07-07
Abstract: 203,463. British Thomson-Houston Co., Ltd., (General Electric Co.). July 7, 1922. Wire resistances, embedded and encased. - A heating unit of the kind described in Specification 144,767 and consisting of a wire surrounded by an insulating powder within an outer metal sheath which is swaged to convert the powder into a compact mass is provided with terminals projecting from the sheath and insulated therefrom bv a tubular insulator having one end secured within the sheath. The insulating powder surrounds the terminals and a portion of the tubular insula. tor. In the form shown in Fig. 7 both terminals are at one end of the sheath and consist of a metal rod 11 and a surrounding metal tube 15. The tube 15 is threaded at its inner end 16 and the resistance wire 25 is secured thereto by screwing some of the turns on to the said screwed part, the other end of the wire being secured in a similar manner to a metal collar 26 screwed on the inner end of the rod 11. The rod 11 is insulated from the tube 15 by a filling of insulating powder such as magnesium oxide which is converted into a compact mass by subjecting the tube 15 to a swaging operation, temporary washers being first introduced into the ends of the tube 15 and surrounding the rod 11, these washers being removed after the swaging operation. The tubular terminal 15 is surrounded by an insulating tube 20 consisting of layers of mica and asbestos coated with china wood oil. The layers are formed by winding the mica and asbestos in a spiral form round a rod. A metal tube 22 is then slipped over the insulating layers and the whole swaged and then baked. The rod is removed and a groove 23 formed in the tube 22 which is secured in the sheath 30 by spinning the latter into the groove 23. The sheath 30 is closed at the other end by a member 32 and filled with an insulating powder such as magnesium oxide. The entire unit is then swaged and the terminal end of the sheath threaded to receive a threaded bush 85 as shown in Fig. 1. The sleeve 22 is next cut off level with the end of the sheath leaving a portion of the insulator 20 exposed. An insulating piece 36 as shown in Fig. 1 is placed over the exposed part of the insulator 20 and secured by a nut 37. Nuts 40, 41, 45 and 46 are screwed to the tubular and rod terminals 15, 11 to facilitate connection to the supply leads. Fig. 14 shows a modification in which the terminals 60, 61 project from opposite ends of the sheath 64. In assembling the parts, terminal 61 is held centrally within the sheath by an insulator 65, washer 66 and a clip 67 as shown in Fig. 12. Terminal 60 is held in position by a tool 68 having a number of slots 69 through which powdered magnesium oxide is introduced into the sheath. After filling, the tool 68 is removed and the sheath closed by an insulator 75 as shown in Fig. 14. The whole is then swaged and metal connectors 76, 77 fixed to the ends of the terminals by swaging, the metal of the connectors being forced into notches 78 formed in the terminals. Nuts are then screwed on to the terminal ends. The insulators 75 65 may be made of bakelite or of asbestos and mica layers as described with reference to Fig. 7.