Electric heating – Microwave heating – With diverse-type heating
Reexamination Certificate
2000-08-31
2001-11-27
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With diverse-type heating
C219S754000, C219S395000, C219S397000, C219S478000, C219S537000
Reexamination Certificate
active
06323472
ABSTRACT:
BACKGROUND TO THE INVENTION
It is known to provide microwave ovens with heating devices additional to the microwave heating means. In particular, radiant electric heating devices are known to be located at the top of the oven cavity to provide high power density for grilling or browning food items or moderate power density for baking food items.
At present, products are available which can achieve either baking or browning cooking effects but cannot provide both from the same heater. Either the baking element would operate at too low a power density to grill or the grilling element would be too hot to bake without burning. A grilling heater cannot be arranged to cover the entire area of an underlying turntable in the oven as it would require far too high power and smaller grilling heaters can result in uneven heating of the underlying turntable.
It is also necessary to locate a heater used for high power grilling as far away from the oven door as possible, to prevent damage to the door and to reduce the temperature experienced by a user of the oven.
OBJECT OF THE INVENTION
It is an object of the present invention to overcome or minimise these problems.
SUMMARY OF THE INVENTION
According to the present invention there is provided a radiant electric heater for a microwave oven, the oven comprising an oven cavity having therein a rotatable turntable for supporting one or more items to be heated, the radiant electric heater being arranged for location above the turntable and comprising at least one first heating element and at least one second heating element, the at least one first heating element being adapted and arranged to overlie only a proportion of the total upper surface area of the turntable to the extent that in operation alone, for each complete rotation of the turntable substantially all parts of the upper surface of the turntable are heated for substantially the same duration of time, the at least one first heating element providing a first power density, and the at least one second heating element being adapted and arranged such that it, or a combination thereof with the at least first heating element, overlies substantially the total upper surface area of the turntable, and such that the at least one second heating element operated alone, or an operating combination of the at least one second heating element with the at least one first heating element, provides a second power density lower than the first power density.
The at least one first heating element may be located within the confines of the at least one second heating element.
The at least one first heating element may be provided to occupy a substantially rectangular, or part-annular, or arcuate, region of the heater. Such part-annular or arcuate region of the heater may subtend an angle of about 180 degrees.
A single first heating element and a single second heating element may be provided.
Alternatively a single first heating element and two further heating elements may be provided, one of the further heating elements being arranged substantially complementary to the first heating element, a plurality of second heating elements being provided in operation comprising the other of the further heating elements connected in series with a parallel combination of the first heating element and the one of the further heating elements.
As a further alternative, at least one first heating element and first and second further heating elements may be provided, a plurality of second heating elements being provided in operation comprising the first of the further heating elements connected in parallel with a series combination of the at least one first heating element and the second of the further heating elements.
The at least one first heating element may be located in the heater such as to be as remote as possible from a door of the microwave oven.
The first power density may be such as to provide grilling and/or browning of one or more food items located in the oven cavity.
The second power density may be such as to provide baking of one or more food items located in the oven cavity. The at least one first heating element and the at least one second heating element may comprise any of the well known forms such as coiled wire, metal ribbon, metal foil or lamp forms, or combinations thereof.
The at least one first heating element and the at least one second heating element may be supported relative to a base of thermal insulation material, such as microporous thermal insulation material.
A dish-like supporting means may be provided for the heater.
By means of the invention a single radiant heater is provided for installation in a microwave oven and which will achieve quick, efficient and even grilling and browning, when the oven turntable is used. The same heater provides a baking facility of lower power density and which provides an even baking effect over the entire oven cavity at a reasonable baking position. Advantages are low cost with high functionality and efficiency since the best cooking element for the purpose is always available.
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patent: 4020323 (1977-04-01), Dills
patent: 4326113 (1982-04-01), Toyoda et al.
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patent: 5504310 (1996-04-01), Bae
patent: 6172347 (2001-01-01), Lee
patent: 4027777 (1992-05-01), None
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patent: 30 40 113 (1982-05-01), None
patent: 2 380 682 (1978-09-01), None
Ceramaspeed Limited
Dorman Ira S.
Leung Philip H.
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