GB767501A - Improvements in or relating to temperature-responsive means - Google Patents

Abstract

767,501. Thermal switches. BEST, F. L., and BEST PRODUCTS, Ltd. April 23, 1954 [Jan. 29, 1953], No. 2637/53. Class 38(5) A thermal switch, e.g. for controlling an immersion heater 10 in a kettle, has a shaft 14 held against rotation in a casing 12 by a fusible alloy in the closed end 13 of the casing until the alloy softens on temperature rise to allow an operating spring 28 to swing a switch-operating arm 23, e.g. from stop 37 to stop 38, Fig. 2, to move a contact spring 34 to open position by means of a disc abutment 36 on the arm. A few turns 29 of the operating spring 28, near its anchored end 30, are located around a screw 20 secured in an extension 19 of the shaft 14 and are compressed against the end of the extension to urge the shaft into the casing 12 so that the space containing the alloy and head 16 of the shaft is sealed by the abutting of shoulders formed on the shaft and casing respectively. The arm 23, loosely pivoted on the screw 20 (which acts as a bearing for the shaft and its extension 19 in a bracket 21) is connected to the shaft by a one-way clutch, e.g. a helical spring 24 which normally binds on a reduced portion of the extension 19 but is released when the arm is reset, by being pushed by hand against the action of the spring 28, from stop 38 to stop 37, where the arm is held by the clutch action of the spring 24 on the shaft. The arm 23 may be constituted by the radially-extending end 26 of the clutch spring 24 instead of being attached to it as shown. The Provisional Specification describes also a switch having contacts on leaf springs which are forced apart by an operating member passing between them and having a shaft held by solder in a non-circular part of a casing bore.