Liquid heating vessels

Details Liquid heating vessels Liquid heating vessels

1996-08-09

1999-06-22

Walberg, Teresa

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

219436, H05B 304, A47J 2721

Patent

active

059140631

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to liquid heating vessels, and in particular to liquid heating vessels in which an electric heating element is mounted to or provided on the underside of a metallic vessel base.
Whereas in the United Kingdom, water heating vessels such as kettles and jugs have traditionally been provided with immersion heaters extending into the lower part of the vessel to heat the liquid therein, in Europe, the market has been more for vessels having underfloor heating elements. Particularly the vessels have a smooth inside, and are of a corrosion resistant metal such as stainless steel. Such arrangements have the advantage that the inside of the vessel may be easily cleaned after use. However, the cost of manufacturing a heating vessel completely in stainless steel is very high.
To reduce costs, it has been proposed to mount a metallic heating plate in the base of a plastics walled vessel. Whilst this does considerably reduce costs, there are problems associated with mounting a hot metallic plate to a plastics vessel wall, in particular in relation to providing a satisfactory seal between the two components.
The present invention seeks to overcome this problem, and from a first aspect provides a liquid heating vessel comprising a plastics wall and a heated metallic plate forming at least a part of the base of said vessel, said plate having a peripheral channel grippingly receiving a depending portion of the vessel wall, and sealing means arranged and clamped between a wall of said channel and said depending portion of the vessel wall.
The invention also extends to a metallic plate forming or for forming at least a part of the base of a liquid heating vessel comprising an upwardly open peripheral channel to receive a depending edge of a wall of said vessel.
With an arrangement in accordance with the invention, the depending portion of the vessel wall is clamped between the respective side faces of the channel, so as to compress the plastics material, preventing thermal tensile creep. Furthermore, the sealing means acts not only to provide a water-tight seal between the baseand the vessel wall, but also acts to further thermally insulate the plastics material of the vessel wall from the base and to provide a resilient clamping force on the vessel wall.
The plastics vessel wall may be the side wall of the vessel in which case the channel may engage over the lower edge of the wall. However, the outer wall may also extend inwardly to constitute part of the base of the vessel as well. In this case a lip or the like may depend from the radially inner periphery portion of the base portion of the vessel wall for engagement with the channel of the metallic plate. Such arrangements have the advantage of cost reduction, since the amount of metal required in forming the base of the vessel is reduced.
Preferably, the metallic plate is of a relatively low thermal conductivity and, most preferably is of stainless steel. This has the advantage of reducing thermal conduction radially outwardly through the base, thereby avoiding overheating, and thus damage to, the lower part of the plastics wall. This is very important, in a dry switch on or boil dry situation, since a plastics material such as polypropylene, which may be used for the vessel wall, will melt at about 140.degree. C., while the element may reach a temperature several hundred degrees higher.
To reduce radial thermal conduction further, one or more circumferential grooves or other formations which locally reduce the plate thickness may be provided in the base between the element and the wall. This reduces the cross-sectional area of the base through which heat may flow radially, effectively `choking` the flow of heat radially outwardly from the element.
From a yet further broad aspect, therefore, the invention provides a liquid heating vessel comprising a plastics wall portion, a metallic plate having an electric heating element on the underside thereof the plate being mounted, at its periphery, to said plastics wall portion, means being provided

REFERENCES:
patent: 5176856 (1993-01-01), Takahashi et al.
patent: 5657532 (1997-08-01), Alexander et al.
patent: 5702623 (1997-12-01), Sharples

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