Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-04-06
2002-12-10
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C126S211000
Reexamination Certificate
active
06492622
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an easy-to-clean glass ceramic cooktop, preferably for use as a cooking surface for a cooktop such as on kitchen stoves, and in particular for self-cleaning ovens or warming stoves. This invention further relates to an easy-to-clean glass ceramic window, preferably for use as a window for oven doors, such as on kitchen stoves, and in particular for windows on self-cleaning ovens or warming stoves.
2. Background of the Invention
Glass ceramic plates for glass ceramic cooking surfaces such as cooktops are typically difficult to clean because the surface contains uneven spots and pits or pores in which spilled or encrusted food gathers during cooking. The food particles are difficult to remove. Even when the cooking surface is cleaned with a scraper, residue is left behind in the pits. The uneven spots on the cooking surface also minimize energy transmission from the heating source of the cooking surface to a cooking utensil such as a pot or pan because air cushions are formed between the cooking surface and the bottom of a cooking utensil. Thus, cooking time is increased, thereby decreasing the efficiency of the cooktop.
Another disadvantage of typically manufactured cooking surfaces of cooktops is that the underside of the cooking surface contains dimples that create distortion. In addition, dimples make the installation of displays and sensors difficult.
The cooking surface can be made smooth by grinding and polishing or by the application of a coating, but these additional steps increase the cost of manufacturing of the cooking surface.
Glass ceramic plates for glass ceramic cooking surfaces such as cooktops are typically manufactured by rolling Li—Al—Si glass (“green glass”), which is then ceramized. The glass ceramic material has a red to red-brown color or is transparent with a non-transparent coating on the underside. As a result of the rolling, the glass ceramic plate acquires a surface that has uneven spots from which it is difficult to remove dirt particles that typically originate from spilled or overflowing food being cooked. When decoration is applied to the cooking surfaces, individual areas of the decor also stick up and are the first parts to be rubbed off when mechanical stress is applied. The surface of the cooking surface is also not flat.
The R
a
of the roughness (arithmetic mean of the absolute height differences from the center plane) is 0.35 &mgr;m to 0.55 &mgr;m. In spite of this roughness, a scraper blade is the most effective cleaning agent. It cleans better than sponges and cleaning agents with abrasive particles. However, it leaves residues behind in the “depressions”.
The glass ceramic plates have a deviation from flatness of up to ±0.4 mm and a size of 300×300 mm. The resulting distortions of the images of long sources of light such as fluorescent tubes are noticeable, however, and adversely affect the high-quality image of the product.
The uneven spots are also disadvantageous with regard to energy transmission. The energy transmission to the pots and pans on cooking units with glass ceramic cooking surfaces is primarily by thermal transmission. Only the transport of heat from the spiral-wound heating coil to the underside of the cooking surface occurs by radiation. As a result of uneven spots, air cushions are formed between the cooking surface and the bottom of the pot that increase the time required for cooking. They also lead to an increase in the surface temperature, as a result of which losses to the environment increase and the efficiency decreases.
Typically, the underside of the cooking surface is provided by means of a patterned roller with a dimpling that has a wavelength of approximately 2 mm and a dimple height of 50 &mgr;m to 200 &mgr;m.
The dimples on the underside also make it impossible to successfully use heating elements that require thermal contact.
As a result of the increased use of electronic controls in cooking devices, an increased number of displays are also being used. To preserve the smooth, flat impression of the unit, these displays are installed under the glass ceramic. On account of the dimpling of the material, these displays are visible only with distortions.
The installation of sensors on the underside is made more difficult by the dimpling, because when the screen printing process is used, it is impossible to achieve a uniform coating thickness. When the sensors on the dimpled side are pressed, the thermal contact is also poor.
A smooth surface of a cooktop made of glass ceramic can be achieved in the manner of the prior art, for example, by grinding followed by polishing. Typically, the preliminary grinding is done with a grain size of approximately 100 &mgr;m. The preliminary grinding is followed by grinding with a grain size of 12-15 &mgr;m. The final polishing is done with an even finer grain size.
A smooth surface can also be produced in the manner of the prior art by means of a coating. For example, there are transparent glass ceramics that have a heat-reflecting coating, e.g. SnO
2
. The prior art also discloses the use of SiO
2
as a protective coating on a glass ceramic cooktop. Both coatings make the surface smooth and facilitate cleaning, among other things.
Although the methods of the prior art described above do produce a cooktop made of glass ceramic that has a smooth surface, they require additional steps after the manufacture of the glass ceramic cooktop that increase the manufacturing costs for the cooktop.
Windows for enclosed heated areas where the temperature exceeds 350° C. are typically made of transparent glass ceramic. When such windows are used as oven door windows for heating stoves or in pyrolysis ovens, combustion residues are deposited on the windows and have to be removed. Commercial cleaning agents, cloths, sponges and scrapers are used to clean the windows.
It is difficult to clean a window of this type. Residue often remains on the window and cannot be removed. This difficulty of removal is caused by the composition of the residues and/or by the surface characteristics of the glass ceramic.
The surface of the transparent glass ceramic that is manufactured using conventional methods is typically structured and uneven. It is similar to an orange peel and generally has a surface with a R
a
(arithmetic mean of the absolute height differences from the center plane) of 0.35 &mgr;m to 0.55 &mgr;m. This macroscopic structure also contains small isolated holes or depressions, pores, or pits, or elevations that have a diameter of up to 0.5 mm. The dirt accumulates in the depressions as well as behind the elevations of the surface and can no longer be removed mechanically. Mechanical cleaning using special cleaning scrapers and sponges is of only limited effectiveness for this purpose. Nevertheless, the best cleaning results are frequently achieved with a sponge and scraper, because, given the composition of the combustion residue, commercial chemical cleaning agents are no longer effective.
These cleaning problems do not occur on a window made of glass ceramic that has a smooth surface on at least one side.
A smooth surface of a window made of glass ceramic can be achieved in the manner of the prior art, for example, by grinding followed by polishing. Typically, the preliminary grinding is done with a grain size of approximately 100 &mgr;m. The preliminary grinding is followed by grinding with a grain size of 12-15 &mgr;m. The final polishing is done with an even finer grain size.
A smooth surface can also be produced in the manner of the prior art by means of a coating. For example, there are transparent glass ceramics that have a heat-reflecting coating, e.g. SnO
2
. The prior art also discloses the use of SiO
2
as a protective coating on a glass ceramic window. Both coatings make the surface smooth and facilitate cleaning, among other things.
Although the methods of the prior art described above do produce a window made of glass ceramic that has a smooth surface, they require additional steps
Melson Sabine
Nass Peter
Schaupert K.
Nils H. Ljungman & Associates
Paik Sang
Schott Glas
LandOfFree
Cooking arrangement for cooking food such as a stove, a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cooking arrangement for cooking food such as a stove, a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cooking arrangement for cooking food such as a stove, a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2986027