IMPROVEMENTS RELATING TO ELECTRICALLY HEATED WATER BOILING VESSELS

摘要

An electrically heated water boiling vessel has a planar heating element incorporated into the base of the vessel, the planar heating element comprising a stainless steel plate having a printed heating element formed on the underside thereof, the printed heated element being sandwiched between electrically-insulating layers of glass. A control for switching off the element in an overtemperature situation has a primary actuator in the form of a bimetal which directly accesses the printed heating element through a window formed in the outermost glass insulating layer, and the bimetal is held in a secondary actuator in the form of a thermally-collapsible carrier for the bimetal which contacts the glass insulation around the window; by this means the primary and secondary actuators are subjected to different temperatures. An enclosure is provided on the opposite (wet) side of the planar heating element at a location corresponding to the window location, the enclosure being apertured to admit water when the vessel is filled and serving to simulate an overtemperature situation sensible by the bimetal when water boils in the vessel and the steam generated in the enclosure expels the water therefrom; by this means a signal control can achieve automatic switching off upon boiling and also provide element overtemperature protection.