GB653139A - Improvements in or relating to thermally operated electric load controlling devices - Google Patents

Abstract

653,139. Thermal switches. GENERAL ELECTRIC CO., Ltd., HUNT, M. H., and HUMPHREY, R. Sept. 2, 1948, No. 23167. [Class 38(v)] A snap-action switch suitable for regulating an electric hotplate comprises a thermally-responsive rod (or tube) 7 of anodized aluminium or alloy, heat-treated for stability, and heated by a coil 12 of bare resistance wire or strip connected in series or parallel with the hotplate, the rod 7 being additionally insulated by mica and fibre-glass tape when the coil 12 is in parallel. The rod 7 is supported at a reduced end 11 by a porcelain thimble 17 passing through an aperture in the part 19 of a leaf-spring 18 and engaging the latter at a projection 20 therein, the other reduced end 10 of the rod 7 engaging a recess 22 in a lever 21 pivoted at 26. A frame 27 providing the pivot 26 is secured to a shelflike part 3, which together with the front plate 2, constitutes a copper silicon aluminium alloy casting heat-treated for stability. The spring 18 urges the rod 7 against the lever 21 and the projection 20 co-operates with the centre limb 36 of an E-shaped spring whose outer limbs 37 are located in notches 38 in an insulated conducting member 39 integral with a terminal 6 carried by the shelf 3. A rivet 40 secures the spring 18 and limb 36 to the member 39. The switch contacts 8 are carried respectively by the spring 36, 37 and a member 41 integral with the terminal 5, and the coil 12, if in parallel, is energized across the hotplate terminals 4, 6, the supply being connected to the terminals 4; 5. On expansion of the rod the projection 20 engages the limb 36 to open the contacts 8. The operating temperature is adjustable by rotation of a cam 29 which co-operates with a screw 28 on the lever 21, the cam being axially biassed, by a spring 32 whereby a stop (Fig. 3, not shown), engages a recess in the cam plate 33 to locate the cam in the " off" position, continuous rotation of the cam being prevented by a lug 35. According to the Provisional Specification the rod 7 is provided at the lever end with a steatite button whereby it is slidably supported in a mica plate secured to the shelf 3 and the other end has a reduced section supported in an insulated brass bracket, the rod being biassed by a coiled spring interposed between the bracket and the shoulder on the rod. The member 39 is a U-shaped brass plate, the notches 38 being formed on, and the rivet 40 being secured to, one arm of the U, and the fixed contact-carrying member 41 being fixed to the other arm. Other details are also described.