Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Patent
1996-07-03
1998-12-22
Walberg, Teresa J.
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
337299, 361105, H05B 368, H01H 3702, H02H 504
Patent
active
058522832
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to electrical heating elements and controls therefor and more particularly, though not exclusively, concerns electrical heating elements for liquid heating vessels such as electric kettles and hot water jugs and associated controls adapted to switch off the supply of electrical energy to the heating element in response to a sensed element overtemperature condition resulting, for example, from the element being switched on when the associated vessel is empty. Whilst the present invention has particular application to electric kettles and hot water jugs and will be described in the following with particular reference to such application, it is however not limited to such application.
BACKGROUND OF THE INVENTION
The conventional electrical heating element most commonly used in electric kettles, hot water jugs and the like comprises a wire-wound resistance heating element contained within a tubular metal sheath with a mineral insulating material packed around the resistance heating element within the sheath. Sheathed heating elements of this kind are often used as immersion heaters and comprise a heating element proper and an element head portion whereby the element is adapted to be fitted in an aperture formed for the purpose in a vessel wall. The heating element proper commonly has a so-called hot return portion where the element is looped back into contact with the element head portion so as to define a location on the other (dry) side of the element head portion whereat the temperature of the heating element proper can be sensed. Element protector controls are well known which are adapted to be fitted on the dry side of the element head with a thermally-responsive actuator, commonly a bimetallic element, in close heat transfer relationship with the aforementioned location. When the heating element proper overheats, as a result for example of the heating element being switched on without the associated vessel containing any water, a thermal signal is transmitted through the element head to the element protector control to cause the control to switch off the element.
An exemplary element protector control of the abovementioned kind is the X1 control manufactured by Otter Controls Limited and substantially as described in GB-A-2194099 with particular reference to FIGS. 3A, 3B and 3C thereof. The X1 control provides a primary level of element protection by virtue of incorporating a bimetallic actuator as aforesaid, and furthermore provides a secondary or back-up level of protection, effective in the event however unlikely of failure of the primary protection, by virtue of the bimetallic actuator being mounted in a synthetic plastics carrier which is arranged to deform in the event of the temperature of the element head portion continuing to rise above the temperature at which the primary level of protection would normally operate, the deformation of the carrier thus caused being arranged to effect a switching off of the heating element.
Planar electric heating elements are also known. Coffee making machines commonly include a hot plate for keeping the coffee hot after it has been made, and such a hot plate commonly comprises a sheathed heating element as aforesaid cast or clenched into an aluminium casting which may itself form the hot plate or alternatively may be secured to a stainless steel hot plate. Another form of planar heating element is described in our British Patent Application No. 9321681.0 and generally comprises a patterned resistance heating element formed on an electrically insulating substrate for example by use of lithographic techniques using electrically-conductive ink or photolithographic techniques as are well known in the field of semiconductor device fabrication, and/or by other deposition techniques such as flame spraying of metals, plasma vapour deposition etc. which per se are well known. More particularly the planar heating element that is described in our British Patent Application No. 9321681.0 comprises a thin sheet of stainless s
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Hochberg D. Peter
Ottes Controls Limited
Paik Sam
Walberg Teresa J.
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