GB386260A - Improvements in and relating to electric heating units - Google Patents

Abstract

386,260. Wire resistances ; couplings. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Abbott, C. C. ; 240, 2nd Street, Pittsfield, Massachusetts, U.S.A.) July 29, 1932, No. 21480. Convention date, July 30, 1931. [Classes 37 and 38 (i).] A terminal member is secured to a resistance element by forming a longitudinal hole through the terminal, enlarging the hole at one end to form a recess, inserting the end of the resistance element into the hole so that it extends through the terminal into the recess, and then filling the recess with conducting material such as solder. In the construction of heating resistance shown in Fig. 2 the resistance wire 10 is embedded in compacted powdered refractory insulating material 13, such as magnesium oxide, within a metallic sheath 11. Secured to each end of the resistance wire 10 is a terminal 14 passing through an insulator 16 which may be made of green lava. A terminal insulating block 22 of porcelain &c., may be provided at each end of the heater and may have a reduced portion 22a which enters a corresponding recess in the insulator 16. The terminals 14 have threaded ends which project through the insulators 22 and to which are screwed connectors 26 secured to supply leads 28. Protective casing members 30 for the terminals are secured to the end of the sheath, for example, by a screwed connection and a set-screw 31. These members may also be threaded at 30a for mounting in a framework. Each terminal 14 is of tubular form with an enlarged portion 14b and is counterbored at each end to form recesses communicating with the longitudinal hole. A slot 35 extending throughout a considerable part of the length of the terminal also communicates with the axial hole. The straight end portion of the resistance wire 10 is inserted in the axial hole of the terminal 14 and brazed thereto through the end recesses and the slot 35. Silver solder may be employed as the brazing material. The end of the terminal is then threaded and the resistance wire 10 with its terminals is assembled within the sheath 11 which is then filled with powdered magnesium oxide and swaged down. The connectors 26 are secured to the bared ends of the leads 28 by swaging and after the connectors are screwed on to the terminals 14 holes 56 are formed through which silver solder or other brazing material is applied and the connector 26 and terminal 14 are brazed together. In a modification, Fig. 10, both leads 73 are brought out at the same end of the unit. The resistance wire 60 is wound in a double helix on an insulating core 61 and is'supported in cup-shaped insulators 63, 64 at opposite ends of the sheath 65. The terminals 67, 68 project through the insulator 64, and are further insulated from each other by mica sleeves 70, extending into the insulators 64, 72, and by a triangular piece of mica 75, of which the base is held in a slot in the insulator 72 and the apex secured by asbestos thread 77.