Patent GB-1470364-A (GB)
Title: Water boiling vessel
IPC: A47J27/21
Filed: 1973-02-13
Abstract: 1470364 Electric kettles OTTER CONTROLS Ltd and J C TAYLOR 13 May 1974 [13 Feb 1973 25 April 1973] 7069/73 and 19682/73 Heading A4A [Also in Divisions H1 and H3-5] In order to be able to dispense with the conventional boil dry control device of an electric kettle and rely only on a steam switch, the kettle 1 is so designed that it cannot be wholly emptied of water so that, if the kettle immersion heating element 4 is energized without the kettle being filled, the element 4 will be in contact with the retained water and will cause it to boil to actuate the steam switch. As shown the spout 2 is formed of a pipe whose inner end is spaced from the wall of the kettle and the lid opening 13 has a depending lip which prevent the entire liquid content being expelled from the kettle. A steam vent 15 to the steam switch also has a depending lip and the base of the kettle has projections Fig. 2 (not shown) extending into the loops of the heating element, this last means ensuring that the retained water is largely confined to immersing the heating element 4. Instead of the spout being formed from a pipe, the wall about the spout may have an inwardly projecting lip to prevent all the water being emptied from the kettle. As an alternative measure the base of the kettle may have an upstanding lip surrounding the heating element, the top edge of the lip being bent inwardly and then towards the element to form a water trap. The steam switch comprises a trifurcated snapacting bi-metallic actuator 34, the free end of whose central tongue engages a lever 36 pivoted at 37. A U-shaped spring 39 between a fixed support 40 and a recess in lever 36 provides a bi-stable overcentre mechanism. A hammer portion 44 of lever 36 co-operates with the movable contact blade 45 of the switch to move it from fixed contact 47 when the bi-metal 34 is heated by steam from vent 15. To prevent steam escaping from the vent 15 once the switch has opened a stopper 38 is forced over the vent by the switch mechanism. As shown the stopper 38 is carried by the lever 36. Alternatively, the switch mechanism may trip a manually charged spring mechanism to actuate the stopper 38. The steam switch is reset by a pushbutton 43 on the lever 36. The neutral pin of a three pin connector of the kettle is connected to a cold end of the heating element by a spring strip. If desired the spring strip may be soft soldered to the neutral pin so that if the switch fails to function, the solder will melt and the spring strip will move away from the neutral pin to de-energize the kettle. The immersion heater comprises an element 4 mounted on a flat metal head plate 5. The sheath ends of element 4 are secured in the plate 5 by crimping the edges 22 of apertures 20 therein about the element. Connecting studs 23 are brazed or welded to the plate 5 and a disc 24 of resilient sealing material, provided with suitable holes for the element ends and the studs is interposed between the kettle wall and the plate 5. Annular beads 26 about the apertures through which the element ends pass are forced into the recesses 27 when nuts 29 are tightened to draw the switch unit and heater together. A resilient sealing ring 25 is disposed between the kettle body and an annular rim 33 of the switch body. Alternatively, the head plate 5 can be mounted on the outer wall of the kettle and the seal 24 can be positioned between the outer wall and the head plate.