GB755971A - Improvements in electric kettles and the like - Google Patents

Abstract

755,971. Thermal switches. RUSSELL, W. M. Nov. 23, 1954 [Dec. 1 1953], No. 33408/53. Class 38(5) [Also in Group XI] An electric kettle, coffee percolator or like electrically heated vessel is provided with a circuit breaker which is actuated when steam generated in the vessel impinges on a heat responsive element mounted on the vessel. As shown, a bimetal strip 56 is secured at its lower end to a partition wall 53 formed integrally with a handle 12 which also houses a circuit breaker lever 58 which is urged to operating and non-operating positions by an over-centre spring 67. A steam vent 48 is formed above a baffle 45 near the top rim of the body of the kettle and in a handle cover plate 51, a further aperture 52 is formed opposite the vent 48. A safetyswitch is mounted in a terminal housing 13 and consists of a bell-crank lever 29 of electrically insulating material which is urged in an anticlockwise direction by a coiled spring 31. Normally, rotation of the lever 29 is limited by a bimetal strip 33 secured to the housing 13 and to the heating element 14. In using the kettle the switch lever 58 is pressed in and an arm 71 of the lever moves clear of a contact arm 72 thus allowing contacts 74, 75 in the circuit of the heater 14 to be engaged. Hot air and vapour rising from the water before it boils will be shielded from the vent 48 by the baffle 45 but when the water boils, steam passes through the vent and aperture 52 into contact with the bimetal strip 56 which is deformed and moves the top of the switch lever 58 outwardly of the handle to the position shown at 58<SP>1</SP>. Contacts 74, 75 are thus disengaged and current supply to the heater is broken. In the event of the circuit breaker failing or the kettle being switched on when containing no water the bimetal strip 33 bends outwardly and clears a detent 36 in the hell-crank lever 29 which moves anticlockwise to the position shown in Fig. 5, a nose 37 of the lever 29 causing a contact 21 connected to a contact pin to be disengaged from a heater element stud 22 and the current supply to be interrupted. When the bimetal strip 33 has cooled down the lever 29 is reset by turning a spindle 28 secured to the lever, clockwise. There may be two heater elements connected in parallel; the circuit breaker being connected in the circuit of only one of them. According to the Provisional Specification an auxiliary resistance may be automatically connected in circuit to reduce the heat supplied by the heater element after the water has boiled. Alternatively. the heat responsive element may cause the supply current to a single heater element to be periodically opened and closed so as to reduce the mean rate of production of heat by the heater.