Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-07-03
2003-02-04
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S548000
Reexamination Certificate
active
06515263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to improvements in a cooking stove having a smooth-top glass ceramic cooktop, and a smooth-top glass ceramic cooktop with a glass ceramic cooktop cooking surface, to a method for production of stoves with smooth-top glass ceramic cooktops and smooth-top glass ceramic cooktops.
2. Background Information
Smooth-top glass ceramic cooktop cooking surfaces of smooth-top kitchen ceramic or glass ceramic cooktops or a stove having a ceramic or glass ceramic cooktop cooking surface have gained considerable popularity as kitchen appliances.
Thus, cooking appliances having ceramic or glass ceramic cooking surfaces are known.
They provide a substantially smooth upper surface on which the various utensils that are to be heated can be disposed.
In these appliances, the cooking zones can be heated, as a rule, by means of electrically operated or gas operated heating devices arranged below the ceramic or glass ceramic cooking surface in the region of the cooking zones. These devices can be, for example, electrically operated contact-heating or radiant heating elements or else gas-jet burners.
An example of a cooktop comprises an induction heating apparatus having a cooktop including a plurality of induction surface heating units. The cooktop comprises a horizontally disposed planar metal support surface having a plurality of openings therein. A ceramic smooth-top plate is supported in each of the openings and adapted to support a cooking utensil thereon. An induction heating coil is supported subjacent to the ceramic plate in a position to generate a magnetic field which passes through the plate to link the cooking utensil. Each plate is supported by a metallic trim frame, which abuts a conductive layer on the plate, with the frame and layer combining to provide a low reluctance flux path, the low reluctance path operating to reduce the magnetic flux leaked into the space surrounding the heating apparatus during operation thereof.
Another example of a cooktop has a heating unit that includes two tubular tungsten-halogen lamps, each having a tungsten filament. The lamps are supported within a ring of ceramic fibre material and the unit is preferably mounted beneath an infra-red-transmissive cooktop to define a hotplate area of a cooking hob. A control circuit provides a range of discrete power outputs of the lamps, each power output corresponding to a power control setting set by a user of the cooking hob. The circuit includes a phase control circuit for switching power to the lamps at a predetermined phase angle to achieve one or more of the lower power outputs.
Yet another example of a cooktop comprises a burner for a “sealed top” range which has a generally upwardly diverging conical body with radially disposed fuel ports and a generally flat removable cap disposed on the upper periphery of the body this invention is a translucent glass ceramic, a method for its production and its use.
Furthermore, it is known that glass made from the system lithium oxide-aluminium oxide-silicon dioxide can be transformed into glass ceramics (LAS glass ceramics) with high quartz mixed crystals and/or keatite mixed crystals as the main crystal phases. These glass ceramics are manufactured in a number of different stages. After the fusion and hot forming, the material is conventionally cooled to below the inversion temperature. In other words, the material may be cooled to below the transformation temperature. The initial glass is then transformed by controlled crystallization into a glass ceramic item. This ceramization takes place in a multiple-stage temperature process, in which first by nucleation at a temperature between approximately six hundred degrees Celsius to eight hundred degrees Celsius nuclei or seeds, generally consisting of titanium dioxide or zirconium dioxide/titanium dioxide mixed crystals, are generated, although tin dioxide can also participate in the nucleation. During the subsequent temperature increase, at the crystallization temperature of approximately seven hundred and fifty degrees Celsius to nine hundred degrees Celsius, first high quartz mixed crystals form on these nuclei. As the temperature is increased further in the range of approximately nine hundred degrees Celsius to twelve hundred degrees Celsius, these high quartz mixed crystals are further transformed into keatite mixed crystals. The transformation into keatite mixed crystals is accompanied by a crystal growth, i.e. increasing crystallite size, as a result of which there is an increasing diffraction of light, i.e. the light transmission becomes less and less. The glass ceramic item thereby appears increasingly translucent and finally opaque. The glass ceramics with high quartz mixed crystals are usually transparent, and translucent glass ceramics can also be manufactured by reducing the concentration of nucleation agents.
A key characteristic of these glass ceramics is that they are manufactured with materials that have an extremely low coefficient of thermal expansion in the range from room temperature up to approximately seven hundred degrees Celsius of less than one and five tenths millionths per degree Kelvin. With glass ceramics that contain high quartz mixed crystals as the main crystal phase, even materials with almost zero expansion can be realized in a specified temperature range, e.g. between room temperature and seven hundred degrees Celsius.
These glass ceramics are used in transparent form, for example, as fire protection glass, smokestack view windows or cookware. For use as a cooking surface, it is desirable to reduce the light transmission, to make it impossible to see through the surface to the equipment installed underneath. This reduction of light transmission can be achieved, for example, by coloring transparent glass ceramics as well as by using translucent or opaque transformed glass ceramics.
For example, WO 99/06334 describes a translucent glass ceramic of the prior art which has a degree of opacity of at least fifty-percent. WO 99/06334 also claims a corresponding translucent glass ceramic with a transmission in the visible range of five percent to forty percent. The above mentioned translucent glass ceramics thereby contain either beta-spodumene (keatite mixed crystals) as the predominant crystal phase or exclusively beta-spodumene as the only crystal phase.
European Patent 0 437 228 A1 (corresponding to U.S. Pat. No. 5,070,045 issued to Comte et al. on Dec. 3, 1991 and entitled, “Transparent glass-ceramic article,”) describes a transparent glass ceramic with beta-quartz mixed crystals (high quartz mixed crystals) as the predominant crystal phase or a white opaque glass ceramic with beta-spodumene mixed crystals (keatite mixed crystals) as the predominant crystal phase.
The variable-translucence glass ceramic described in European Patent 536 478 A1 (corresponding to U.S. Pat. No. 5,173,453 issued to Beall et al. on Dec. 22, 1992 and entitled, “Variably translucent glass-ceramic article and method for making,”) contains, in addition to areas with beta-quartz mixed crystals, areas with beta-spodumene/gahnite mixed crystals. These gahnite mixed crystals (zinc oxide-aluminum oxide) are formed during the phase transformation of beta-quartz mixed crystals into beta-spodumene mixed crystals and compensate for the change in density that accompanies this phase transformation. The immediate vicinity of transparent, translucent and opaque areas can therefore be transformed in a glass ceramic item. In the translucent and opaque areas, keatite mixed crystals are the main crystal phase. Gahnite crystals have a significantly higher coefficient of thermal expansion than the above mentioned mixed crystal phases (high quartz or keatite) of typical LAS glass ceramics. It can be expected that a variably crystallized product of this type has disadvantages in its impact strength and will develop structural cracks fairly early in actual use on account of the different expansion characteristics.
U.S. Pat. No. 4,211,820 issued to Cantaloupe e
Becker Otmar
Dudek Roland
Mitra Ina
Rodek Erich
Roos Christian
Nils H. Ljungman & Associates
Paik Sang
Schott Glas
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