Patent GB-168128-A (GB)
Title: Improvements in or relating to automatic cut-out devices for electrically heated appliances for heating or boiling liquids
IPC: H05B1/02
Filed: 1920-05-19
Abstract: 168,128. Johnston, E. W. May 19, 1920. Automatic circuitbreakers etc.; mechanically t r i p p e d and released switches; thermal cut-outs. -Appliances for heating and boiling liquids are provided with a cut-out or current - reducing device comprising a tube, containing a movable actuating- member held by solder &c., which is located between the heating-elements and the liquid, either on the surface with which the heating elements are in contact, on the surface in contact with the liquid, or formed integrally with the appliance. The actuating-member may be rotatable or longitudinally movable in the tube, and preferably means are provided to reset it into normal position after movement before the solder has set. Fig. 1 shows a plug consisting of inner and outer metal tubes separated by insulating material. The inner contact tube has a spring 10 which engages the top of the contact pin 5 and the outer tube a tongue 12 with an inclined rear face. The tubular member 1 is flattened for the greater part and a rod 11 is slidably mounted therein and embedded in solder or other fusible material of low melting point. A spring 14 may be included which tends to retain the head 13 of the rod 11 in a retracted position. The plug when applied is engaged with the rod by means of the tongue 12 and head 13. On overheating of the vessel the plug flies off and with the spring 14 the rod 11 is immediately re-set. Modifications in regard to the number of contact elements, the position 10 and the nature of the latch connection are referred to. According to one Provisional Specification the outer tube of the plug may have an earth connection. Figs. 4 and 5 show the invention applied to an electric switch which may have several positions for regulating the heat supply. The switch 31 is enclosed in a rotatable casing 19 which has an arm 20 adapted to be engagred by the head 13 of a thermal device, and is biassed towards the ' off ' position of the switch by a spring 21. The head 13 of the thermal device is normally in engagement with an abutment 17, and a re-setting spring 18 tends to maintain it in this position when the solder melts. The switch knob 28 carries a spring ring 27 which has a radial arm 26. The arm 26 may be engaged between facing ratchet teeth 29, 30, of unequal height, on the casing 19 in any position thereof other than the " full out " position shown in Fig. 5, where it is in engagement with the face of the higher tooth 29 only. The switch can thus be operated from the " full on " position by the knob 28 to reduce the current supply, independently of the casing 19, but if the cut-out device be not set, cannot be moved towards the full on position without turning the casing, whereupon it will automatically be moved to open the circuit if the arm 20 be not first engaged with the thermally controlled member 13 to set the cut-out. The tooth 30 prevents the switch being moved clockwise from the " off " to the " full on " position, means being provided to prevent the arm 26 from being lifted over that tooth. On the operation of the cut-out the projection 20 slips past the head 13 and the tooth 29 sweeps the switch to the " off " position from whatever position it may occupy. A stop 25 engages the projection 26 in the " off " position, and a similar stop may be used to hold the switch in a position of reduced current flow, instead of interrupting the circuit, upon the operation of the thermal device. The thermal device may comprise a star wheel and a flattened rotary spindle within the tube 1, the member 20 engaging the arms of the star in turn and a spring-resetting device being unnecessary; or a single rotary arm may be employed on a spring-controlled rotary spindle. The release device described in connection with the switch may be adapted to the control of a plug.