DE102019117480A1 - Cover plate, in particular plate for heating food, and device for heating food - Google Patents

Abstract

The present application relates to a cover plate, such as a plate (or surface) for heating food, in particular a cooking, heating, roasting and / or grill surface, and a device for heating food comprising such a cover plate. Another aspect relates to the use of such a cover plate.

Description

Field of invention

The present application relates to a cover plate, such as a plate (or surface) for heating food, in particular a cooking, heating, roasting and / or grill surface, and a device for heating food comprising such a cover plate.

Background of the invention

Cover plates, which are temperature-resistant and serve as separating elements, for example protecting electronic components of a device, such as a device for heating food, and / or serving as viewing windows, for example in chimneys or ovens, are usually made of a glass ceramic with a low coefficient of thermal expansion trained, such as those sold under the CERAN® brand. This is necessary so that the cover plate, which is also referred to as a surface for heating food in a device for heating food, for example as a cooking, roasting, heating and / or grilling surface, can withstand the temperatures that are caused by the currently used heating devices or heating elements are generated.

The highest temperatures of up to 700 ° C occur when using so-called radiant heaters with resistance heating.

Lower temperatures of a maximum of 500 ° C occur when using induction heating elements. Because of these lower temperatures, when using induction heating elements, in addition to glass ceramics with low thermal expansion, special glasses with a somewhat higher thermal expansion can also be used as the material of the cover plate. These are usually around borosilicate glasses with an expansion coefficient of about 3.3 * 10 ^-6 / K, which are commercially available for example as "borofloat 33". Such glasses are sometimes also referred to as "borosilicate glasses of the Pyrex type" or as "borosilicate glasses 3.3".

In the context of the present disclosure, surfaces for heating food, for example for cooking, roasting, heating and / or grilling, are also referred to in simplified terms as “cooking surfaces” or “hob”. In accordance with common usage, a cooking surface can also be referred to as a hotplate or, in general, a surface for heating food as a plate for heating food.

The writings GB 2 079119 A , US 2013/098903 A1 , US 2013/256301 A1 , US 2014/061196 A1 , US 2015/274579 A1 , US 2016/338152 A1 and US 2017/247284 A1 describe cooking appliances, cooking surfaces and / or hobs comprising cover plates made of temperature-resistant glass.

In the international patent application WO 2018/225627 A1 a toughened glass with a coefficient of expansion of 2 * 10 ^-6 / K to 5 * 10 ^-6 / K and a glass transition temperature of 560 ° C or more is described.

However, it has so far been necessary to use an additional process step - chemical or thermal toughening - to give such special glasses the mechanical and thermal stability required for use in heating food, for example for cooking.

1. (a) die Oberfläche der Kochfläche unterliegt im täglichen Gebrauch einer Abnutzung, speziell auf Grund abrasiver Prozesse (Topfbewegung, Reinigung, Gebrauchskratzer)
2. (b) Die Heizzonen haben einen geringen Abstand von ca. 25 mm von der Kochflächenaußenkante. Dieser geringe Abstand ist u.a. bei Herden auf dem europäischen Markt üblich und notwendig, um auf Kochflächen im Einbau-Standardformat vier Kochzonen unterzubringen.

Despite this thermal prestressing, however, tests show considerable weaknesses. Thermally toughened borosilicate glass 3.3 breaks in practical use as a cooking surface if the following common conditions are met:

1. (a) the surface of the cooking surface is subject to wear and tear in daily use, especially due to abrasive processes (pan movement, cleaning, scratches)
2. (b) The heating zones have a small distance of approx. 25 mm from the outer edge of the cooking surface. This small distance is common and necessary for cookers on the European market in order to accommodate four cooking zones on standard built-in cooking surfaces.

In the context of the present disclosure, the heatable areas or zones of a cover plate or plate or surface for heating food are also referred to in simplified form as cooking zones or heating zones.

Under the two conditions mentioned above, the stresses that result from the temperature gradient between the hot cooking zone and the cold outer edge of the cover plate exceed the strength of the cover plate or, in this case, the cooking surface in the outer edge area. This applies even under the prerequisite of a high-grade temperature-monitored cooking device which in overshoot situations only reaches approx. 310 ° during heating. The use of borosilicate glass 3.3 is therefore only possible with the restriction that the distance between the heating zone and the outer edge of the cover plate is at least 45 mm - or that heating elements are used that remain well below 310 ° C due to very low power consumption - but that does also significant losses in parboiling performance.

There is therefore a need for cover plates comprising or at least partially or predominantly consisting of a glass, in particular a thermally toughened glass and / or a borosilicate glass, which can be used as a surface for heating food in a device for heating food and / or as Viewing pane in hot applications, for example as a fireplace viewing pane or stove pane, are suitable, and which can be used in devices with normally powerful heating elements and in which a reduced edge distance is possible compared to known cooking surfaces made of glass.

Object of the invention

The object of the invention is therefore to provide cover plates made of glass, in particular plates or surfaces for heating food made of glass and / or thermally highly resilient viewing panes made of glass, for example for chimneys and / or stoves, which have the aforementioned weaknesses of the prior art the technology overcome or at least mitigate. A further aspect of the invention relates to the provision of a glass which is suitable as an alternative to glass ceramic as a substrate material for a plate or, synonymously, a surface for heating food, in particular a cooking surface (or hotplate), and the weaknesses of the known glasses of the prior art overcomes or at least mitigates.

Summary of the invention

The object of the invention is achieved by the subject matter of the independent claims, preferred and special embodiments can be found in the dependent claims.

The object of the present invention consists in a first aspect in providing a cover plate which overcomes or at least mitigates the aforementioned weaknesses of the prior art, in particular a plate (or surface) for heating food, in particular by cooking, frying, heating and / or grilling, comprising a glass substrate with at least one heatable zone.

A second aspect of the present invention relates to the provision of a device for heating food comprising a cover plate, in particular a plate (or surface) for heating food, comprising a glass substrate with at least one heatable zone, which overcomes the weaknesses of the prior art or at least reduces, preferably a device that can be manufactured inexpensively and / or has improved operator safety.

A third aspect relates to the use of such a cover plate.

The invention consequently relates to a cover plate, in particular a plate (or surface) for heating food, in particular by cooking, frying, heating and / or grilling, comprising a glass substrate with at least one heatable zone, the glass substrate being a glassy material comprising the following components in% by weight comprises: SiO ₂ 60 to 80 Al ₂ O ₃ 0.5 to 25 B ₂ O3 0 to 11 Li ₂ O 0 to 5 Na ₂ O 0 to 8 K ₂ O 0 to 8 MgO 0 to 10 CaO 0 to 10 SrO 0 to 10 BaO 0 to 3 ZnO 0 to 3 TiO ₂ 0 to 3 ZrO ₂ 0 to 6 MnO ₂ 0 to 1 P ₂ O ₅ 0 to 2 Nd ₂ O ₃ 0 to 1 Cs ₂ O 0 to 10 La ₂ O3 0 to 5 SnO ₂ 0 to 1 As ₂ O3 0 to 1 Sb ₂ O ₃ 0 to 1.6 Cl 0 to 0.5 and optionally at least one further coloring oxide from the group Fe ₂ O ₃ and / or CoO and optionally further color oxides, the proportion of the further coloring oxides, including the optionally further color oxides, totaling between 0% by weight to 5% by weight Wt .-% is,
wherein the glass substrate is preferably disc-shaped,
The flexural strength of the thermally toughened glass substrate due to wear of a surface, simulated by sanding with 220 SiC, has a safety characteristic of the flexural strength, defined as the mean value of the strength distribution reduced by three standard deviations, of at least 90 MPa.

• Unter einem färbenden Oxid wird im Rahmen der vorliegenden Offenbarung ein Oxid verstanden, welches in einer Glasmatrix durch färbende Ionen das Glas im Volumen durch Absorption färbt. Die färbenden Ionen des färbenden Oxids liegen dabei in der Glasmatrix verteilt vor, vergleichbar färbenden Ionen in einer Flüssigkeit bzw. Lösung. Durch das färbende Oxid wird also das Volumen des Glases gefärbt, so dass dieses als volumengefärbt bezeichnet wird. Im Gegensatz zu einer Volumenfärbung durch färbende Ionen, insbesondere färbende Metallionen steht beispielsweise die Färbung durch den Zusatz von Pigmenten oder die Farbgebung durch eine Beschichtung. Solche Färbungen durch Pigment und/oder durch eine Beschichtung, welche beispielsweise das Streuverhalten eines Glases verändern können, sind keine Volumenfärbung im Sinne der vorliegenden Offenbarung. Die Volumenfärbung ändert beispielsweise nicht das Streuverhalten des Glases.

In the context of the present disclosure, the following definitions apply:

• In the context of the present disclosure, a coloring oxide is understood to mean an oxide which, in a glass matrix, uses coloring ions to color the glass in volume by absorption. The coloring ions of the coloring oxide are distributed in the glass matrix, comparable coloring ions in a liquid or solution. The volume of the glass is colored by the coloring oxide, so that it is referred to as volume colored. In contrast to volume coloring by coloring ions, in particular coloring metal ions, there is, for example, coloring by the addition of pigments or coloring by a coating. Such colorations by pigment and / or by a coating, which, for example, can change the scattering behavior of a glass, are not volume coloring in the sense of the present disclosure. For example, the volume coloring does not change the scattering behavior of the glass.

However, it is also possible and can be preferred for the glass, according to embodiments, to be transparent and uncoloured, that is to say, apart from unavoidable traces, it does not contain any coloring oxides. Such inevitable traces are typically 500 ppm or less.

The preparation of food by means of heating is understood in particular to mean cooking, for example using cookware such as a saucepan, frying, for example using roasting utensils such as a frying pan or roaster, grilling and / or heating food. Food includes, in particular, solid but also fluid substances, such as water, or mixtures of solid and fluid substances, such as dough.

A device for heating food can be, for example, a cooking device which comprises a so-called cooking surface. This cooking surface in turn comprises a vitreous substrate or glass substrate and optionally coatings which are arranged on a surface of the surface and / or can furthermore be refined and / or reworked, in particular, for example, have machined and / or faceted edges and / or bores. In addition to the surface for heating food, the device can comprise further components, in particular electronic components. In general, a surface for heating food therefore comprises a vitreous substrate or glass substrate and optionally coatings which are arranged on a surface of the surface or the substrate and / or can furthermore be refined and / or reworked.

In the context of the present disclosure, a substrate is understood to mean a product which can be reworked and / or refined, in particular by treating surfaces and / or edges, such as, for example, the faceting of edge surfaces and / or the application of coatings.

In the context of the present disclosure, a cover plate is understood to mean a refined substrate.

The heatable zone of a cover plate, for example a surface for heating food, is preferably an area of the substrate. If the surface for heating food is a cooking surface, such a heatable zone can also be referred to as a “cooking zone”.

A disk-shaped design of a product, such as a substrate, is understood to mean that the spatial extent of the product in two spatial directions of a Cartesian coordinate system is at least one order of magnitude greater than in the third spatial direction. This third, hence the smallest spatial dimension, is usually also referred to as the thickness of the product, for example a substrate or a surface for preparing food by heating, the other two spatial directions are usually referred to as its length or width. In the sense of the present disclosure, a disk-shaped substrate can be designed both flat or flat and also curved and can also be designed as a flat or flat disk or as a curved disk.

The main surfaces or main surfaces of the substrate and, accordingly, also of the cover plate or area are determined by the length and the width of the plate. These are the top and bottom of the substrate or surface. The upper side of the substrate or the cover plate or surface is that main surface of the substrate, the cover plate or the surface which faces a user during operational use, for example for heating food. The underside is that main surface of the substrate or of the cover plate or of the surface which faces away from the user in operational use of such a plate. If a “surface” of the substrate or the surface for heating food is spoken of in the context of the present application, this means a main surface (also main surface), that is the top or the bottom of the surface or the substrate.

In general, the top can also be understood as the side of a substrate or the cover plate or surface that has or can have markings, for example cooking zone markings or functional coatings, which are intended to improve the operability of a device, for example haptic coatings. The underside is the side of the substrate which, for example, can face electronic components. Coatings on the underside therefore generally have different properties than coatings on the upper side.

Depending on the exact storage of the panel in operational use, the underside can also be referred to as the back and the top as the front.

The term “T _g ” refers to the transformation or glass transition temperature of a material. The transformation temperature T _g is determined by the point of intersection of the tangents to the two branches of the expansion curve when measured with a heating rate of 5K / min. This corresponds to a measurement after ISO 7884-8 or. DIN 52324 .

In the context of the present disclosure, the linear thermal expansion coefficient α is given in the range from 20-300 ° C., unless stated otherwise. The terms α and 020-300 are used synonymously in the context of this invention. The specified value is the nominal mean thermal coefficient of linear expansion according to ISO 7991, which is determined in static measurements.

In the context of the present disclosure, a vitreous material or a glass is understood to mean an amorphous material which is obtained from a melting process, preferably with subsequent hot shaping such as rolling, floating or drawing.

• Da die Festigkeit wesentlich auch durch die Oberflächenbeschädigungen bestimmt wird, wie sie im täglichen Gebrauch an einer Oberfläche, insbesondere der Oberseite, einer Fläche zum Erhitzen von Lebensmitteln und/oder eines Glassubstrats, welches von einer solchen Fläche umfasst wird, typischerweise nach einiger Benutzung auftreten, wird ein praxisrelevanter Gebrauchszustand vor der Inbetriebnahme durch Schmirgelung des Bereichs der Fläche bzw. des Glassubstrats, welches mindestens den Bereich zwischen den Heizzonen und der Außenkante der Abdeckplatte umfasst, mit gebundenem SiC-Korn der Körnung 220 nach DIN ISO 6344 hergestellt. Hierbei erfolgt die Schmirgelung senkrecht zur Außenkante der Platte. Anschließend wird die dem geschmirgelten Bereich benachbarte beheizbare Zone in Betrieb genommen.

If in the context of the present disclosure the temperature difference resistance of a surface and / or a substrate is used, this has been determined as follows:

• Since the strength is also essentially determined by the surface damage that occurs in daily use on a surface, especially the top, a surface for heating food and / or a glass substrate that is covered by such a surface, typically after some use, a practically relevant state of use before commissioning is achieved by sanding the area of the surface or the glass substrate, which includes at least the area between the heating zones and the outer edge of the cover plate, with bonded SiC grains of grain size 220 DIN ISO 6344 manufactured. The sanding is done perpendicular to the outer edge of the plate. The heated zone adjacent to the sanded area is then put into operation.

• Ein Schmirgelblatt der Größe 65 mm x 30 mm wird durch ein Gewicht mit ebener Unterseite derart gleichmäßig belastet, dass die Anpresskraft pro Fläche 2 N/cm2 beträgt. Das derart beschwerte Schmirgelblatt wird senkrecht zur Außenkante der Abdeckplatte mit einer Geschwindigkeit von 0,3 m/s ± 0,1 m/s bewegt, beginnend innerhalb der beheizbaren Zone und endend, sobald das Schmirgelblatt in seiner Gänze über den Außenrand (bzw. die Außenkante) der Abdeckplatte hinaus bewegt worden ist. Um den Schmirgelvorgang bis über den Außenrand (bzw. die Außenkante) der Abdeckplatte, beispielsweise über den Kochflächenrand, hinaus ausführen zu können, kann erforderlichenfalls eine geeignet dimensionierte Platte direkt am Außenrand der Abdeckplatte positioniert werden, die den Höhenunterschied zwischen der Abdeckplatte und der Umgebung der Abdeckplatte ausgleicht. Das Schmirgelblatt ist dabei so orientiert, dass seine längere Seite von 65 mm parallel zur Plattenaußenkante (also der Außenkante der Abdeckplatte bzw. dem Außenrand der Abdeckplatte) liegt. Der so beschriebene Schmirgelvorgang wird mit einem zweiten, ebenfalls noch unbenutzten Schmirgelblatt wiederholt.

The sanding is done as follows:

• An emery sheet measuring 65 mm x 30 mm is loaded evenly by a weight with a flat underside in such a way that the contact pressure per area is 2 N / cm2. The emery sheet weighted down in this way is moved perpendicular to the outer edge of the cover plate at a speed of 0.3 m / s ± 0.1 m / s, starting within the heatable zone and ending as soon as the emery sheet in its entirety over the outer edge (or the Outer edge) of the cover plate has been moved out. In order to be able to carry out the sanding process beyond the outer edge (or the outer edge) of the cover plate, for example beyond the edge of the cooking surface, a suitably dimensioned plate can be positioned directly on the outer edge of the cover plate, if necessary, which reduces the height difference between the cover plate and the surroundings Cover plate compensates. The emery sheet is oriented such that its longer side of 65 mm is parallel to the outer edge of the plate (i.e. the outer edge of the cover plate or the outer edge of the cover plate). The sanding process described in this way is repeated with a second, also unused sanding sheet.

Commissioning takes place by installing the surface or illustrative plate in a device for heating food or placing the surface or illustrative plate for heating food on a heating element of a device for heating food, with the distance between the in the latter case Radiator and the underside of the plate corresponds to the distance that is usually found in devices for heating food. Furthermore, the start-up with the maximum power setting of the radiator and using an empty vessel which is used for heating food, for example a cooking or roasting utensil or vessel, which has a flat base and a base diameter of at most 5 mm of deviates from the diameter of the heatable zone.

The bottom diameter of the vessel used can therefore be up to 5 mm larger or up to 5 mm smaller than the diameter of the heatable zone.

Flat in the bottom of a crockery or a vessel is defined as when the surface of the bottom is within a tolerance range of 0.1 mm at most, even in a heated state, i.e. in particular also achieved or achievable by heating the crockery or vessel during commissioning as stated above, in particular also with the maximum power setting and regardless of the filling level of the dishes or vessels.

An empty vessel or crockery is used for the commissioning test, as detailed below.

After putting the heater or heating element into operation, the heatable zone heats up and runs through a temperature-time curve at the hottest point on the upper side of the surface or, more clearly, the plate, which is also shown schematically in 2 is shown. The upper side is the side of the surface or, more clearly, the plate which is in contact with the dishes or vessel. 2 it can be seen here that the temperature-time curve reaches a first maximum within a maximum of 5 minutes, which is also referred to as the overshoot temperature. By intervention of the sensor control of the heating element or Radiator, the heating process is automatically canceled at this point, which leads to a subsequent drop in temperature, as in 2 can be seen.

The temperature difference between the overshoot temperature and the outer edge of the plate, which is still at room temperature, leads to tensile stresses in the vicinity of the outer edge, the magnitude of which depends on the level of the temperature difference, the material parameters of the substrate and the distance between the edge of the heated zone and the outer edge of the plate . The relevant material parameters are in particular the linear thermal expansion coefficient, the modulus of elasticity E and the Poisson's ratio µ.

A reduced distance between the edge of the heatable zone and the outer edge of the plate at the same temperature increases the tensile stresses near the edge and thus the risk of breakage.

In the context of the present disclosure, the temperature differential resistance denotes that maximum temperature on the upper side of the plate at which the plate breaks for the first time under the condition of a minimum distance of the edge of the heatable zone from the outer edge of the plate of 25 mm.

It has been shown that a cover plate which has a correspondingly sufficient resistance to temperature differences in such a start-up test is generally not only suitable as a cover plate in a device for heating food, but can also be used, for example, as a heater cover.

In the present case, a glass is referred to as volume colored in particular when it is colored by coloring metal ions. In the context of the present disclosure, a transparent glass is understood to mean, in particular, a glass which comprises no or only slightly scattering components. In particular, a glass can thus be designed to be transparent, volume-colored, but of course also be transparent and uncolored.

In the context of the present disclosure, a lighting device is understood to mean, in particular, a device or a product which is designed as a lighting means or comprises a lighting means, for example an LED.

In the context of the present disclosure, a display element is understood to mean an electronically controlled element which outputs optical signals. For example, the display element can be designed as a matrix or segment display, in particular as a graphic display.

The chemical resistance of glasses is generally given in three classes, a distinction being made between the hydrolysis, acid and alkali resistance of the glass.

The determination of the hydrolysis resistance of a glass and the specification of a hydrolytic class takes place in the context of the present disclosure according to the regulation DIN ISO 719. Depending on the amount of extracted glass components, correspondingly examined glasses are divided into classes, class 1 denoting the class in which only a few Material was extracted, and the class number increases with increasing leaching of the glass by hydrolytic attack.

The acid resistance of a glass or the acid class is determined in the context of the present disclosure in accordance with the regulation of DIN 12116. Here, too, the class is classified according to the amount of extracted glass components, the best class again being class 1.

The alkali resistance of a glass or the alkali class is determined in the context of the present disclosure in accordance with ISO 695. Here, too, the best class, that is to say the one with the highest alkali resistance, is again class 1.

According to one embodiment, the chemical resistance of the glass is given by an indication of the class of hydrolytic resistance H, acid resistance S and alkali resistance L of at least 2, 3, 3.

Such a design of a cover plate has a number of advantages.

By designing the cover plate in such a way that it comprises a glass substrate comprising the aforementioned components, the glass substrate is designed as a thermally toughenable glass substrate. In particular, the glass substrate is designed in such a way that it can be thermally pre-stressed to a high degree and that sufficient durability of the cover plate can be achieved through thermal pre-stressing. This is particularly important in the event that the plate is intended as a surface for heating food and therefore sufficient operational safety of a device for heating food should be ensured including such a surface. Such a configuration thus increases the user safety of both the cover plate or the surface and the device for heating food. At the same time, the glass substrate can be manufactured inexpensively. Thus, both the cover plate or surface and the entire device for heating food can be produced more economically in this way.

Furthermore, the glass substrate is designed in such a way that the flexural strength of the thermally pre-stressed glass substrate due to wear of a surface, simulated by sanding with 220 SiC, has a safety characteristic of the flexural strength, defined as the mean value of the strength distribution reduced by three standard deviations of at least 90 MPa

The sanding with 220 SiC simulates in a reproducible way scratches that arise from the use of the cover plate. For example, it is known that the tops of surfaces or plates for heating food by hard-grained contaminants that are rubbed over the top of the plate, for example by contaminants on the bottom of a vessel or dishes for heating food, or by cleaning, for example with a scraper and / or with abrasive cleaning agents and / or utensils, for example abrasive sponges, often can and also have scratches as signs of use.

In other words, the glass substrate is designed such that it is a glass substrate that is resistant to mechanical abrasion. This resistance of the glass substrate to mechanical abrasion is to be understood here in such a way that the glass substrate may still have scratches, for example, but these do not critically reduce the strength of the glass substrate, in particular the flexural strength.

This has the advantage that a cover plate comprising such a glass substrate or even consisting of such a glass substrate is less prone to failure due to breakage in the application case, the glass substrate generally being in the form of a thermally prestressed glass substrate in the application case. The application here includes, for example, the operation of a cooking device or, more generally, a device for heating food, if the cover plate is designed as a surface for heating food and is used in such a device.

However, the use of the cover plate is by no means limited to its use as a surface for heating food, for example as a cooking surface, but the use of the cover plate is generally conceivable for areas of application in which a significant temperature gradient occurs in the edge area of the cover plate. Possible areas of application therefore include, for example, covers for lamps and / or radiators, inner panes of pyrolysis ovens or the like.

According to one embodiment of the cover plate, the glass substrate is thermally prestressed, the thermal surface compressive prestress being at least 65 MPa.

According to a further embodiment, the substrate has a coefficient α · E / (1-μ) which is between at least 0.28 MPa / K and at most 0.53 MPa / K, where α is the mean coefficient of thermal expansion in the temperature range between 20 ° C and 300 ° C, E the modulus of elasticity and µ the Poisson's ratio of the glass. The Poisson's ratio µ is also known as the Poisson's number.

This is advantageous because in this way applications of the cover plate are made possible in which, for example, normally powerful heating elements can be used in a device for heating food, so that in particular the parboiling performance is not very low, for example in the case of a cooking surface or a cooking device. In particular, with a cover plate or cooking surface configured in this way, a design is possible in which the at least one heatable zone has a minimum distance of only 25 mm from the outer edge of the cover plate or plate (or surface) for heating food or cooking surface.

According to one embodiment, the cover plate is preferably designed such that the glass substrate has a temperature difference resistance of at least 310 ° C. with a minimum distance of 25 mm from the edge of the at least one heatable zone to the outer edge of the cover plate.

Such a configuration is particularly advantageous for the use of the cover plate as a surface or plate for heating food, especially when heating elements (or radiators) with a specific power of at least 8 W / cm ² are used in the device for heating food and the distance between the heating zone and the outer edge of the cover plate or surface for heating food is at most 25 mm. In this way the available surface can namely be optimally used, ie there are no large cold areas and edge distances on the surface of the surface for heating food. This is of particular relevance for the European domestic appliance market, since here usually four heating elements - corresponding to four heating zones of the glass substrate or the cover plate or surface - are arranged in the appliance.

The specific power of the heating element or heating element is preferably limited to a maximum of 15 W / cm ² .

Also for devices in which there are no longer any fixed heating zones, as they are known from classic cooking devices, but rather heating up depending on the position of the dishes, for example cooking or roasting utensils such as a pot or pan (so-called "Cook anywhere" function), such a design of the cover plate is advantageous. This is because it is precisely with such a configuration of a device for heating food that the dishes are pushed from a hot area to the edge in order to interrupt the heating process, so that here a hot dish comes into contact with a cold area of the cover plate. In order to prevent the formation of cracks and thus breakage of the cover plate or surface for heating food in such a case, a configuration of the cover plate as described above is particularly advantageous.

It is also possible for the heating element of a heatable zone to be operated in two or more circuits. It is thus possible for a heatable zone to be adapted to the size of the dishes used for heating food. For example, it is possible that a heatable zone comprises a first, smaller zone and a second heatable zone which surrounds the first, the first, smaller zone being heated first and the second zone being able to be switched on if necessary.

Induction heating elements are particularly preferred as heating elements.

The preloading process consists of three sections. In the first section, the glass substrate is heated to a temperature T which is 100 K to 150 K above the glass transition temperature T _g . The second section consists of a holding time after which the temperature T is homogeneously present in the entire glass substrate due to temperature equalization. In the third section, the glass substrate is cooled on both sides, usually by blowing a gaseous medium or a mixture of gaseous and liquid phases, which results in a surface compressive stress of at least 65 MPa in the entire glass substrate after room temperature has been reached.

A fundamentally high temperability of the glass substrate or the cover plate or the surface or plate for heating food is therefore necessary to deal with the temperature differences that occur during the operation of the device for heating food, such as those between the heatable zone and the outer edge of the plate to withstand without breaking.

The ability of the material to withstand the temperature difference ΔT between the heated zone in the heated state and the adjacent cold outer edge of the cover plate without breaking determines the maximum permissible temperature Tmax in the heated zone. This capability assumes that the tensile stresses occurring in the cold edge area of the cover plate due to the temperature difference between the hot, heatable zone and the adjacent cold outer edge of the cover plate are lower than the strength at the same point.

In the context of the present disclosure, the maximum permissible temperature Tmax of the heated heatable zone is in particular the surface temperature of the cover plate, specifically the temperature of the top of the cover plate. The top of the cover plate is the side of the cover plate that faces the user during operational use, that is to say the side that is designed to hold dishes for heating food in it Contact occurs. For example, this top side can be designed in such a way that it has further elements, such as the marking of the edge of the heatable zones (which, for example, in the case of a hotplate or cooking surface, are also referred to as cooking zone markings).

It can be assumed that the surface temperature of the cover plate in the heated heatable zone is usually the highest temperature. This is particularly the case when the heating element of a device for heating food is designed as an induction heating element, because in this case the heating takes place in particular using appropriate cookware.

In general, however, without being restricted to this embodiment, it is also possible that other forms of heating elements are selected. In this case, too, within the scope of the present disclosure, Tmax is described as the maximum permissible temperature on the surface, namely the upper side of the cover plate, of the heated heatable zone.

The strength in the cold edge area of the cover plate, σ _R , is made up of the flexural strength σ _G defined by typical usage injuries and the additional strength due to the thermal surface compressive prestress σ _V : $${\mathrm{\sigma }}_{\text{R.}}={\mathrm{\sigma }}_{\text{G}}+{\mathrm{\sigma }}_{\text{V}}.$$

With regard to product safety, it is necessary to consider the strength in the edge area σ _R in a statistical sense, since it is subject to a certain random scatter. It is therefore the mean value reduced by three standard deviations (3 s) ( x ) to choose the strength as a practical benchmark: $${\sigma }_{\mathrm{R.}}\stackrel{yields}{\to }\overline{x}\left({\sigma }_{\mathrm{R.}}\right)-3\cdot s\left({\sigma }_{\mathrm{R.}}\right)$$

The strength in the cold edge area of the cover plate must be greater than the thermally induced tensile stresses σ _Z occurring there. These are defined by the material parameters modulus of elasticity (E), thermal expansion coefficient (α) and Poisson's ratio (µ) as well as the spatial distribution of the temperature on the cover plate and there in particular the distance between the edge of the heatable zone and the adjacent cold outer edge of the cover plate. This distance is referred to as a.

The maximum possible tensile stress σ _Z based on the material parameters results from the common formula $${\sigma }_Z=\frac{\alpha \cdot \mathrm{E.}}{1-\mathrm{\mu }}\cdot \Delta T.$$

Measurements show that at a distance a of the heatable zone from the cold outer edge of the cover plate of 25 mm, the actually induced tensile stress σ _{Z reaches} this theoretical maximum value. The condition that there is no thermally induced break due to the temperature difference between the hot, heatable zone and the adjacent cold outer edge of the cover plate can be summarized as follows: $$\overline{x}\left({\sigma }_{\mathrm{R.}}\right)-3\cdot s\left({\sigma }_{\mathrm{R.}}\right)>{\sigma }_Z=\frac{\alpha -\mathrm{E.}}{1-\mathrm{\mu }}\cdot \Delta T$$

This condition limits the maximum possible temperature difference ΔT between the hot, heatable zone and the adjacent cold outer edge of the cover plate. The maximum possible absolute temperature of the heated heatable zone Tmax results directly from the addition of the temperature of the cold edge of the cover plate T _edge , which is at room temperature of approx. 25 ° C in the rapid heating process, and the temperature difference ΔT just described: $$T_{max}=\Delta T+\mathrm{25th}°\mathrm{C.}$$

This is the value for Tmax, which was determined for a distance a of the edge of the heatable zone from the outer edge of the cover plate of 25 mm. This distance a is also referred to below as “edge distance” or “distance” for short.

If the distance a between the hot, heatable zone and the adjacent cold outer edge of the cover plate increases, the tensile stress in the cold edge area σ _Z decreases accordingly: $${\sigma }_Z\left(a>\mathrm{25th}mm\right)<{\sigma }_Z\left(a=\mathrm{25th}mm\right)={\sigma }_Z$$

verstanden werden. D.h., bei einem Abstand a, welcher größer als 25 mm ist, beispielsweise 50 mm beträgt, ist eine heißere Maximaltemperatur Tmax möglich.The maximum temperature of the heatable zone can therefore also be used as a function of the distance a, ie $${\text{T}}_{\text{Max}}=\text{f}\left(\text{a}\right),$$

be understood. That is to say, at a distance a which is greater than 25 mm, for example 50 mm, a hotter maximum temperature Tmax is possible.

The person skilled in the art can readily calculate the influence of the edge distance a numerically; a formulaic description of this relative influence is possible to a good approximation using a radially symmetrical model; so e.g. after Goodier; J. N .:

L bezeichnet hier den Abstand vom Mittelpunkt der beheizbaren Zone bis zum Außenrand der Platte. Die Integration erfolgt hier über den Weg von r = 0 in der Mitte der beheizbaren Zone bis r = L. Dieser Abstand L ist in zwei Abschnitte unterteilbar: der Radiusstrecke der beheizbaren Zone R und dem Abstand a des Randes der beheizbaren Zone von der Plattenaußenkante: $$L=R+a$$

Thermal Stress On: Soc. Mech. Eng., Jour. Appl. Mech., Vol 4, No. 1, March 1937 . According to this, the tangential tensile stresses on the cold outer edge of the plate are: $${\sigma }_Z=\alpha \cdot \mathrm{E.}\cdot \left(-T_{\mathrm{R.}and}+\frac{2}{{\mathrm{L.}}^2}\cdot {\displaystyle {\int }_0^{\mathrm{L.}}T\left(r\right)\cdot rdr}\right)$$

L denotes the distance from the center of the heatable zone to the outer edge of the plate. Integration takes place here via the path from r = 0 in the middle of the heatable zone to r = L. This distance L can be divided into two sections: the radius of the heatable zone R and the distance a of the edge of the heatable zone from the outer edge of the plate: $$\mathrm{L.}=\mathrm{R.}+a$$

If one introduces this subdivision into sections in (8), one obtains for the tangential tensile stress at the cold outer edge of the plate, σ _Z (a), an integral component, which depicts the temperature profile of the heatable zone, and an integral component, which depicts the edge area: $${\sigma }_Z\left(a\right)=\alpha \cdot \mathrm{E.}\cdot \left(-T_{\mathrm{R.}and}+\frac{2}{{\left(\mathrm{R.}+a\right)}^2}\cdot {\displaystyle {\int }_0^{\mathrm{R.}}T\left(r\right)\cdot rdr}+\frac{2}{{\left(\mathrm{R.}+a\right)}^2}\cdot {\displaystyle {\int }_{\mathrm{R.}}^{\mathrm{L.}}T\left(r\right)\cdot rdr}\right)$$

The edge distance a thus appears in the prefactors of the integrals, namely quadratically in the denominator, which directly illustrates the stress-reducing effect of a larger edge distance. The first integral component, which depicts the temperature profile of the heatable zone, is to be regarded as a constant regardless of the edge distance and when the edge distance is varied. The second integral component, which maps the edge area, depends on the temperature profile in the edge area, which in principle has an exponentially decreasing characteristic and can usually be resolved with simple means.

For the tensile stress σ _Z (a) described in (10) and dependent on the edge distance a, the breakage criterion according to (4) applies again: $$\overline{x}\left({\sigma }_{\mathrm{R.}}\right)-3\cdot s\left({\sigma }_{\mathrm{R.}}\right)>{\sigma }_Z=\frac{\Delta T\left(a\right)}{\Delta T}\cdot {\sigma }_Z\left(a\right)$$

It is immediately plausible that the maximum possible temperature difference ΔT (a) between the hot, heatable zone and the cold plate outer edge a increases to the same extent as the Tensile stress σ _Z (a) in the cold edge area decreased with an increased edge distance a. The corresponding information for the absolute maximum temperature of the hot, heatable zone, Tmax, results accordingly.

The relationship between the maximum temperature of the hot, heatable zone, Tmax, and the edge distance a is shown in 4th illustrated for different materials.

bevorzugt unterhalb der Grenzgeraden, gegeben durch die Formel: $$a=\frac{1}{3}\cdot \left(T_{max}-235\right).$$

Glass compositions which are suitable for cover plates according to the present disclosure are distinguished by the fact that they follow in the distance-temperature diagram 4th lie below a limit straight line, which is given by the following formula: $$a=\frac{1}{3}\cdot \left(T_{max}-215\right),$$

preferably below the limit straight line, given by the formula: $$a=\frac{1}{3}\cdot \left(T_{max}-235\right).$$

Here, a again denotes the minimum distance between the edge of the heatable zone and the outer edge of the cover plate in millimeters and Tmax the maximum temperature in the heated heatable zone.

The so-called position in the distance-temperature diagram ensures an improved break resistance compared to the prior art with regard to temperature differences that occur between the heated heatable zone and the adjacent cold outer edge of the cover plate.

If a cover plate is used as a plate for preparing food, these materials for induction cooking appliances with sufficiently good temperature control, which do not exceed a maximum temperature of 290 ° C and preferably 310 ° C, allow increased design freedom with regard to the arrangement of heatable zones on the Plate for preparing food, as required, for example, in European models with a minimum distance of 25 mm between the heated zone and the outer edge of the cover plate.

According to one embodiment of the cover plate, the glass substrate comprises a glassy material comprising the following components in% by weight: SiO ₂ 63 to 79, preferably 64 to 79 Al ₂ O ₃ 3 to 22, B ₂ O3 0 to 11, Li ₂ O 0 to 4.1 Na ₂ O 0.1 to 7.1, K ₂ O 0 to 8, preferably 0 to 0.2 MgO 0 to 9.8, preferably 0 to 1.1 CaO 0 to 9.8, preferably 0 to 0.2 SrO 0 to 8.9, preferably less than 0.01 BaO 0 to 2.8 ZnO 0.4 to 1.6 TiO ₂ 0 to 2.4 ZrO ₂ 0 to 4.5, preferably 0 to 1.9 MnO ₂ 0 to 0.3 P ₂ O5 0 to 1.3 Nd ₂ O ₃ 0 to 0.25 Cs ₂ O 0 to 3, preferably free of CsO except for unavoidable traces La ₂ O3 0 to 0.5, preferably free of La ₂ O3 except for unavoidable traces SnO ₂ 0 to 1, preferably 0 to 0.5 As ₂ O3 0 to 0.85 Sb ₂ O ₃ 0 to 1.6, preferably 0 to 0.6 and optionally at least one further coloring oxide from the group Fe ₂ O ₃ and / or CoO and optionally further color oxides, the proportion of the further coloring oxides, including the optionally further color oxides, totaling between 0% by weight to 5% by weight Wt .-%.

If, within the scope of the present disclosure, a glass substrate comprises a glassy material, this particularly includes the case that the glass substrate predominantly, i.e. at least 50% by weight, or essentially, i.e. at least 90% by weight, or even entirely consists of this material. In particular, the cover plate can be designed as a plate or disk made of the vitreous material, optionally provided with refinements such as coatings.

With such a composition, particularly good strength values can be achieved.

According to a further embodiment of the cover plate, the glass substrate has a thickness between 2.8 mm and 6.3 mm.

If the glass substrate is less thick, sufficient strength is no longer guaranteed. The strength can in principle be achieved by using a greater thickness of the glass substrate and corresponding to the area. However, this not only has the disadvantage that more material has to be used in this way and therefore the costs of the substrate increase accordingly, but a greater thickness also leads to more weight. Therefore, the maximum thickness of the glass substrate is limited and is preferably not more than 6.3 mm.

According to a further embodiment of the cover plate, the glass substrate has a chemical resistance H, S, L of at least 2, 3, 3 or better, the chemical resistance as hydrolytic class H according to DIN ISO 719 , the acid class S according to DIN 12116 and alkali class L according to ISO 695 is determined.

Such a design of the cover plate as a chemically resistant cover plate is advantageous because in this way damage to the cover plate surface, which can be kept as low as possible from abrasion of the surface due to corrosion by food, such as water or vinegar or the like. It is also advantageous if, especially in the case of direct contact of a food with the cover plate, for example when using the cover plate as a surface for heating food, for example when grilling a food directly on the surface, as far as possible no substances from the glassy material of the cover plate or Surface can be detached.

According to a further embodiment of the cover plate, the glass substrate is transparent and uncolored, characterized by a transmission in the visible wavelength range of the electromagnetic spectrum τ _vis of at least 85.0%, based on a glass thickness of 4.0 mm. τ _vis is understood here as the standard color value Y in the wavelength range 380 nm to 780 nm, based on standard light D65, observer 2 ° and a glass thickness of 4.0 mm. The glass substrate preferably has a neutral transmission characteristic.

According to yet another embodiment, the glass substrate is transparent, volume-colored, the glass substrate preferably having a neutral transmission characteristic.

The person skilled in the art will adjust the composition of the glass substrate in such a way that the desired degree of transmission is achieved, in particular by setting the amount of coloring components accordingly.

A design of the glass substrate as a transparent, uncolored glass substrate can be advantageous if, for example, the arrangement of display elements and / or lighting devices, for example as a display of the status of a surface for heating food or the device for heating of food, is desired below the surface or below the glass substrate and display elements and / or lighting devices are thus viewed by the operator through the surface or the glass substrate. In particular, in the event that a high resolution of the display elements and / or a color-true perception of display elements and / or lighting devices is necessary, for example for temperature display via the setting of a color location of a lighting device and therefore to increase user safety, transparent, uncolored glass substrates can be advantageous be.

However, it is also possible and may even be preferred for the glass substrate to be transparent, volume-colored. For example, by designing a glass substrate in this way as a volume-colored glass substrate, the view of components of the device that are arranged below the glass substrate or the surface for heating food can be reduced.

bezogen auf Normlicht D65, einen Beobachter unter Betrachtungswinkel 2° und eine Glasdicke von 4,0 mm. Die Beschreibung des bevorzugten unbunten Farborts kann gleichermaßen über die Angabe der CIE-Farbkoordinaten x und y erfolgen mit den Grenzen 0,26 < x < 0,38 und 0,27 < y < 0,42.The glass substrate is preferably designed in each case in such a way that it has a color-neutral transmission characteristic. This means in particular that colors are falsified as little as possible when viewed through the glass substrate or the cover plate or surface for heating food, both in the case of an embodiment as transparent, uncoloured glass and as transparent, colored glass. In other words, the glass preferably has an achromatic color point, ie the saturation value C * of the CIEL * a * b * color space is a maximum of 10.0 and preferably less than 4.0, where C * is defined as $${\mathrm{C.}}^{\ast }=\sqrt{a^{\ast }{}^2+b^{\ast 2}},$$

based on standard light D65, an observer at a viewing angle of 2 ° and a glass thickness of 4.0 mm. The description of the preferred achromatic color point can also be made by specifying the CIE color coordinates x and y with the limits 0.26 <x <0.38 and 0.27 <y <0.42.

According to yet another embodiment of the cover plate, the glass substrate has a quotient α · E / (1-μ) which is between at least 0.28 MPa / K and at most 0.53 MPa / K, where α is the mean coefficient of thermal expansion in temperature between 20 ° C and 300 ° C, E is the modulus of elasticity and µ is the Poisson's ratio of the glass.

According to a further embodiment of the cover plate, at least one coating is arranged in at least one area of at least one surface of the cover plate.

For example, a coating can be arranged in at least one area of the top and / or the bottom of the cover plate. The coating can be, for example, a so-called decorative layer or decoration arranged on the upper side of the surface, which can be in the form of a logo and / or in the form of a marking of the at least one heated zone, or alternatively or additionally a masking layer arranged on the underside of the cover plate, which is designed in particular with a transparent, uncoloured cover plate to cover or hide components arranged below the cover plate, for example a device for heating food, especially when the cover plate is used as a surface for heating food.

A second aspect relates to a device for heating food, in particular by cooking, frying, heating and / or grilling, which comprises a cover plate, such as a plate (or surface) for heating food, according to the preceding embodiments, and at least one of the at least one heatable zone of the cover plate or the plate or surface for heating food associated heating element, in particular an induction heating element, wherein the heating element has an edge distance to the edge of the cover plate of at most 25 mm and wherein the heating element has a specific heating power of at least 8 W / cm ² and preferably of a maximum of 15 W / cm ² .

It has been shown that induction heating elements in particular are particularly suitable, since in this way only low temperature loads occur on the glass substrate or cover plate or surface. The use of induction heating elements therefore also increases the operator safety of the surface and thus also of the device for heating food which is equipped with such a cover plate or surface.

Furthermore, such a configuration of the device for heating food, for example a cooking device, is advantageous because it allows a large part of the cover plate to actually be heated. In other words, by designing the cover plate according to embodiments, a larger area of the cover plate is available as a heatable zone or zones. This allows in particular the integration of four heating zones or in particular cooking zones for a cover plate which corresponds to the usual dimensions of a cooking surface, for example. It is also possible to use powerful heating elements at the same time, so that sufficient parboiling performance is guaranteed.

According to yet another embodiment of the device for heating food, the device comprises a sensor, such as a touch sensor on a capacitive or optical basis and / or a temperature sensor, and / or the device comprises a lighting device, such as an LED, and / or a display element, like an electro-optical display element. This is advantageous because in this way the user safety of the device is further improved by suitable lighting devices and / or display elements, which for example can transmit information about the state of the device, for example the temperature in the heated state, to the operator via preferably optical or electro-optical signals is.

In order to enable the transmission of optical signals in the IR range, in particular the functionality of touch sensors, in a satisfactory manner, the substrate and / or the surface for heating food has an IR transmission over the entire surface or in areas preferred for this purpose, which for each of the Wavelengths 950 nm and 1600 nm is between 25 and 80%, each based on a thickness of 4.0 mm.

According to a further embodiment of the device for heating food according to embodiments, the device comprises a means with which one can be connected to an IT means, such as a computer, a tablet PC, and / or a smartphone, the means preferably configured in this way is that a wireless connection can be established, and particularly preferably the IT means can be connected to the device in such a way that the cooking appliance can be controlled with the IT means, and / or the means is designed as an IT means which is designed to be connectable, and wherein the cooking appliance is controllable with the IT means.

In this way, the operation of the device is simplified in a particularly advantageous manner for the user of the device.

Yet another aspect of the invention relates to the use of a cover plate according to embodiments as a surface for heating food, as a lamp or radiator cover, as an inner pane of a pyrolysis oven, as an oven pane, as a fireplace viewing window or as an oven viewing pane or as a heat shield to shield hot environments.

Examples

The invention is explained in more detail below using examples.

The relevance of the resistance to temperature differences is explained further on the basis of the following exemplary embodiments 1 to 4 and the comparative example. The composition of the glass and its material properties are first described. A cover plate, here a plate or surface for heating food, made of the corresponding glass is then considered, the plate or surface comprising a glass substrate which is thermally pre-stressed.

• Ausführungsbeispiel 1 beschreibt eine Ausführungsform einer Abdeckplatte sowie eines Geräts zum Erhitzen von Lebensmitteln umfassend eine Fläche bzw. Platte zum Erhitzen von Lebensmitteln umfassend ein Glassubstrat.

Embodiment 1:

• Embodiment 1 describes an embodiment of a cover plate and a device for heating food comprising a surface or plate for heating food comprising a glass substrate.

Glass with the following composition is used (in% by weight; Tab.1a): Tab.1a SiO ₂ 67 Al ₂ O ₃ 20th As ₂ O ₃ 0.85 Li ₂ O 3.7 Na ₂ O 0.1 K ₂ O 0.2 MgO 1.1 CaO 0.03 SrO 0.01 BaO 0.84 ZnO 1.6 TiO ₂ 2.4 ZrO ₂ 1.8 P ₂ O ₅ 0.03 Nd ₂ O ₃ 0.06

This glass has the following material properties (Tab. 1b): Tab. 1b T _g [° C] 661 Density [g / cm ³ ] 2.45 CIE color coordinate x 0.3108 CIE color coordinate y 0.3178 Tvis (D65 / 2 °) 89.7% C * (D65 / 2 °) 0.9 Quotient α · E / (1-µ) [MPa / K] 0.41 Young's modulus E [GPa] 82 Thermal linear expansion coefficient α (20-300) [10 ^-6 / K] 3.9 Poisson's ratio µ 0.217

bezogen auf Normlicht D65, einen Beobachter unter Betrachtungswinkel 2° und eine Glasdicke von 4,0 mm. τ_vis wird hier verstanden als Normfarbwert Y im Wellenlängenbereich 380 nm bis 780 nm, bezogen auf Normlicht D65, Beobachter 2° und eine Glasdicke von 4,0 mm.Here and in the following, T _g denotes the glass transition temperature, measured in accordance with DIN 52324. C * denotes the saturation value of the CIEL * a * b * color space, where C * is defined as $${\mathrm{C.}}^{\ast }=\sqrt{a^{\ast }{}^2+b^{\ast 2}},$$

based on standard light D65, an observer at a viewing angle of 2 ° and a glass thickness of 4.0 mm. τ _vis is understood here as the standard color value Y in the wavelength range 380 nm to 780 nm, based on standard light D65, observer 2 ° and a glass thickness of 4.0 mm.

A glass substrate is produced with this glass and thermally toughened. The cover plate according to embodiment 1 comprises this glass substrate with at least one heatable zone.

The strength characteristics are summarized in Tab.1c: Tab. 1c Safety value of the flexural strength, defined as the mean value of the strength distribution of the thermally prestressed plate reduced by three standard deviations after use damage 136 MPa Maximum temperature of the heatable zone, T _max (a = 25 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 25 mm) 357 ° C Maximum temperature of the heatable zone, T _max (a = 50 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 50 mm 440 ° C

The maximum possible or permissible surface temperature of the upper side of the substrate or the plate in the heatable zone, also referred to in Table 1c as the maximum temperature of the heatable zone, T _Max , is therefore a function of the minimum distance a of the edge of the heatable zone from the outer edge of the cover plate can also be referred to as T _Max (a), as is done in Table 1c. This maximum permitted surface temperature in the heatable zone then indicates the temperature difference resistance of the cover plate for this edge distance.

This maximum temperature is therefore to be understood as a temperature limit value, i.e. the maximum permissible temperature.

The temperature difference resistance of 357 ° C, determined under the conditions of a conventional, damaged top of a cover plate, such as the top of a hotplate or cooking surface or more generally a plate for heating food, and with a minimum distance of the edge of the heated zone from the outer edge of the plate 25 mm is sufficient to allow the desired design freedom. This means that the technical design of a device for heating food, for example, with a space-saving integration of four heatable zones in a format common in the European market, for example, of a conventional cover plate for a device for heating, also known as a "cooking surface" for short of food in this way is possible.

In supplementary embodiments of embodiment 1, the composition according to Table 1a was changed by adding small amounts of further elements to such an extent that volume-colored variants resulted, which decisively reduced the transparency, although a desirable color neutrality was retained. The admixtures are listed in Table 1d (in% by weight): Table 1d Example 1, variant A Example 1, variant B Ex. 1, variant C Fe ₂ O ₃ 2.25 0.7 0.7 CoO 0.86 0.0615 0.03 SnO ₂ 0.59 0.0 0.3

The optical properties of these variants of Example 1 are listed in Table 1e: Table 1e Example 1, variant A Example 1, variant B Ex. 1, variant C CIE color coordinate x 0.3642 0.2948 0.3114 CIE color coordinate y 0.3999 0.3214 0.3354 τ _vis (D65 / 2 °) 1.85% 28.9% 42.8% C * (D65 / 2 °) 9.95 5.7 3.4

The strength characteristics according to Table 1c due to the basic composition according to Table 1a proved to be unaffected by the admixtures according to Table 1d.

• Ausführungsbeispiel 2 beschreibt eine weitere Ausführungsform einer Abdeckplatte und eines Geräts zum Erhitzen von Lebensmitteln umfassend eine Abdeckplatte, hier eine Fläche oder Platte zum Erhitzen von Lebensmitteln, umfassend ein Glassubstrat.

Embodiment 2:

• Embodiment 2 describes a further embodiment of a cover plate and a device for heating food comprising a cover plate, here a surface or plate for heating food, comprising a glass substrate.

Glass of the following composition is used (in% by weight; Tab. 2a): Tab. 2a SiO ₂ 66 Al ₂ O ₃ 22nd Li ₂ O 4.1 Na ₂ O 0.6 K ₂ O 0.2 MgO 1.0 CaO 0.2 BaO 0.015 ZnO 0.4 TiO ₂ 1.5 ZrO ₂ 1.9 P ₂ O ₅ 1.3 Nd ₂ O ₃ 0.25 SnO ₂ 0.5

This glass has the following material properties (Tab. 2b): Tab. 2b T _g [° C] 691 Hydrolytic class according to DIN ISO 719 1 Acid resistance class according to DIN 12116 3 Alkali resistance class according to ISO 695 1 Quotient α · E / (1-µ) [MPa / K] 0.44 Young's modulus E [GPa] 82 Thermal linear expansion coefficient α (20-300) [10 ^-6 / K] 4.2 Poisson's ratio µ 0.22

A glass substrate is produced with this glass and thermally toughened. The cover plate according to Example 2 comprises this glass substrate with at least one heatable zone.

Strength parameters are summarized in Tab.2c: Tab. 2c Safety value of the flexural strength, defined as the mean value of the strength distribution of the thermally prestressed plate reduced by three standard deviations after use damage 130 MPa Maximum temperature of the heatable zone, T _max (a = 25 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 25 mm) 321 ° C Maximum temperature of the heatable zone, T _max (a = 50 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 50 mm 395 ° C

The temperature difference resistance of 321 ° C, determined under the conditions of a conventional, damaged top of a cover plate, such as the top of a hotplate or cooking surface or more generally a plate for heating food, and with a minimum distance of the edge of the heated zone from the outer edge of the plate 25 mm is sufficient to allow the desired design freedom. This means that the technical configuration of a device for heating food, for example with a space-saving integration of four heatable zones, is possible in this way.

• Ausführungsbeispiel 3 beschreibt eine nochmals weitere Ausführungsform einer Abdeckplatte sowie eines Geräts zum Erhitzen von Lebensmitteln umfassend eine Abdeckplatte, hier eine Fläche oder Platte zum Erhitzen von Lebensmitteln, umfassend ein Glassubstrat.

Embodiment 3:

• Embodiment 3 describes yet another embodiment of a cover plate and a device for heating food comprising a cover plate, here a surface or plate for heating food, comprising a glass substrate.

Glass of the following composition is used (in% by weight; Tab. 3a): Tab. 3a SiO ₂ 64.3 Al ₂ O ₃ 21.4 Li ₂ O 3.6 Na ₂ O 0.6 K ₂ O 0.15 BaO 2.3 ZnO 1.2 TiO ₂ 2.3 ZrO ₂ 1.6 MnO ₂ 0.29 CoO 0.23 NOK 0.29 Sb ₂ O ₃ 1.54

This glass has the following material properties (Tab. 3b): Tab. 3b T _g [° C] 675 Hydrolytic class according to DIN ISO 719 1 Density [g / cm ³ ] 2.50 Quotient α · E / (1-µ) [MPa / K] 0.43 Young's modulus E [GPa] 82 Thermal linear expansion coefficient α (20-300) [10 ^-6 / K] 4.1 Poisson's ratio µ 0.22

A glass substrate is produced with this glass and thermally toughened. The cover plate according to embodiment 3 comprises this glass substrate with at least one heatable zone.

Strength characteristics are summarized in Tab. 3c: Tab. 3c Safety value of the flexural strength, defined as the mean value of the strength distribution of the thermally prestressed plate reduced by three standard deviations after use damage 123 MPa Maximum temperature of the heatable zone, T _max (a = 25 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 25 mm) 310 ° C Maximum temperature of the heatable zone, T _max (a = 50 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 50 mm 410 ° C

The temperature difference resistance of 310 ° C, determined under the conditions of a conventional, damaged upper side of a cover plate, such as the upper side of a hotplate or cooking surface or more generally a plate for heating food, and with a minimum distance of the edge of the heated zone from the outer edge of the plate 25 mm is sufficient to allow the desired design freedom. This means that the technical design of a device for heating food, for example with a space-saving integration of four heatable zones, is possible in this way.

• Ausführungsbeispiel 4 betrifft eine weitere Abdeckplatte und ein weiteres Gerät zum Erhitzen von Lebensmitteln umfassend eine Abdeckplatte, hier eine Fläche bzw. Platte zum Erhitzen von Lebensmitteln, umfassend ein Glassubstrat.

Embodiment 4:

• Embodiment 4 relates to a further cover plate and a further device for heating food comprising a cover plate, here a surface or plate for heating food, comprising a glass substrate.

Glass of the following composition is used (in% by weight; Tab. 4a): Tab. 4a SiO ₂ 79 Al ₂ O ₃ 4th B ₂ O3 10 Na ₂ O 5 K ₂ O 1 CaO 1

This glass has the following material properties (Tab. 4b): Tab. 4b Tg [° C] 575 Hydrolytic class according to DIN ISO 719 1 Acid resistance class according to DIN 12116 1 Alkali resistance class according to ISO 695 1 Density [g / cm ³ ] 2.28 Quotient α · E / (1-µ) [MPa / K] 0.34 Young's modulus E [GPa] 69 Thermal linear expansion coefficient α (20-300) [10 ^-6 / K] 4.0 Poisson's ratio µ 0.2

A glass substrate is produced with this glass and thermally toughened. The cover plate according to embodiment 4 comprises this glass substrate with a heatable zone.

Strength parameters are summarized in Tab. 4c: Tab. 4c Safety value of the flexural strength, defined as the mean value of the strength distribution of the thermally prestressed plate reduced by three standard deviations after use damage 114 MPa Maximum temperature of the heatable zone, T _max (a = 25 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 25 mm) 361 ° C Maximum temperature of the heatable zone, T _max (a = 50 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 50 mm 450 ° C

The temperature difference resistance of 361 ° C, determined under the conditions of a conventional, damaged top of a cover plate, such as the top of a hotplate or cooking surface or more generally a plate for heating food, and with a minimum distance of the edge of the heated zone from the outer edge of the plate 25 mm is sufficient to allow the desired design freedom. This means that the technical design of a device for heating food, for example with a space-saving integration of four heatable zones, is possible in this way.

• Das Vergleichsbeispiel betrifft eine Abdeckplatte und ein Gerät zum Erhitzen von Lebensmitteln umfassend eine Abdeckplatte, hier eine Fläche bzw. Platte zum Erhitzen von Lebensmitteln, umfassend ein Glassubstrat.

Comparative example:

• The comparative example relates to a cover plate and a device for heating food comprising a cover plate, here a surface or plate for heating food, comprising a glass substrate.

Glass of the following composition is used (in% by weight; Tab. 5a): Tab. 5a SiO ₂ 80.7 Al ₂ O ₃ 2.5 B ₂ O3 12.5 Na ₂ O 3.5 K ₂ O 0.6

This glass has the following material properties (Tab. 5b): Tab. 5b T _g [° C] 525 Hydrolytic class according to DIN ISO 719 1 Acid resistance class according to DIN 12116 1 Alkali resistance class according to ISO 695 2 Density [g / cm ³ ] 2.22 Quotient α · E / (1-µ) [MPa / K] 0.26 Young's modulus E [GPa] 63 Thermal linear expansion coefficient α (20-300) [10 ^-6 / K] 3.3 Poisson's ratio µ 0.2

A glass substrate is produced with this glass and thermally toughened. The cover plate according to the comparative example comprises this glass substrate with a heatable zone.

Strength characteristics are summarized in Tab. 5c: Tab. 5c Safety value of the flexural strength, defined as the mean value of the strength distribution of the thermally prestressed plate reduced by three standard deviations after use damage 62 MPa Maximum temperature of the heatable zone, T _max (a = 25 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 25 mm) 272 ° C Maximum temperature of the heatable zone, T _max (a = 50 mm) (with the minimum distance between the edge of the heatable zone and the outer edge of the plate at a = 50 mm 350 ° C

The temperature difference resistance of 272 ° C, determined under the conditions of a conventional, damaged upper side of a cover plate, such as the upper side of a hotplate or cooking surface or more generally a plate for heating food, and with a minimum distance of the edge of the heated zone from the outer edge of the plate 25 mm is not sufficient to withstand the overshoot temperatures of at least 310 ° C without breaking. In order to avoid breakage, the minimum distance between the edge of the heatable zone and the outer edge of the plate would have to be increased significantly, namely by at least another 20 mm. As an alternative or in addition, a heating element with a significantly lower output would have to be used. However, this would lead to an undesirable impairment of the cooking or heating performance. The freedom of design in terms of the technical configuration of the device is therefore significantly limited. Especially for the European market, where the most efficient possible integration of as many heatable zones as possible in as little space as possible is desired, such cover plates are not suitable or lead to undesirable or at least very unusual designs.

Figure list

• 1 eine Abdeckplatte mit vier beispielhaften beheizbaren Zonen
• 2 einen Temperatur-Zeit-Verlauf der Oberseite der Abdeckplatte in einer beheizbaren Zone nach Inbetriebnahme,
• 3 eine Darstellung der Biegefestigkeit für das Beispielglas 4,
• 4 ein Abstands-Temperatur-Diagramm für verschiedene Abdeckplatten aus unterschiedlichen Materialien.

The invention is explained in more detail below with reference to drawings. Show it

• 1 a cover plate with four exemplary heatable zones
• 2 a temperature-time curve of the top of the cover plate in a heatable zone after commissioning,
• 3 a representation of the flexural strength for the example glass 4,
• 4th a distance-temperature diagram for different cover plates made of different materials.

In 1 a cover plate according to the present disclosure is shown by way of example schematically and not true to scale. This cover plate 100 has four heatable zones as an example 102 on. The edge 103 the heatable zone 102 is shown here as an example by black circles. Furthermore, the distance a is _lo between the edge 103 the one in the upper left area of the cover plate 100 arranged heatable zone 102 and the outer edge 101 the cover plate 100 drawn. The distance a _lo is the distance a for the heatable zone 102 "Top left" (lo).

The distance a is generally the shortest connection between the outer edge in the context of the present disclosure 101 (or synonymous outer edge) of the cover plate 100 and the edge 103 a heatable zone 102 .

Like this one 1 can be seen, the distance a for each heatable zone 102 be different, for example in the present case the distance a _lu - not shown - for the heatable zone 102 , which is shown here on the lower left, is greater than the distance a _lo. . Provided the Tmax for all heatable zones 102 is the same - this can be the case, for example, if all the heating elements used have the same performance characteristics - the smallest distance a is decisive.

2 is a schematic representation of the temperature-time curve for the surface temperature of the cover plate in a heatable zone. The temperature is plotted on the y-axis, the time on the x-axis. After the heater or heating element is put into operation, the heatable zone heats up and runs through a temperature-time curve at the hottest point on the upper side of the surface or, more clearly, the plate, as shown schematically in the curve here 200 is shown. The upper side is the side of the surface or, more clearly, the plate which is in contact with the dishes or vessel. 2 it can be seen here that the curve 200 of the temperature-time curve a first maximum within a maximum of 5 minutes, here denoted by 201 , which reaches a temperature also known as the overshoot temperature. When the sensor control of the heating element or radiator intervenes, the heating process is automatically interrupted at this point, which leads to a subsequent drop in temperature, as in 2 can be seen.

3 FIG. 4 shows, for exemplary embodiment 4, the determination of the flexural strength after sanding a thermally prestressed substrate with 220 sandpaper. The x-axis denotes the flexural strength in MPa, measured in the double ring test. The y-axis indicates the probability of failure (cumulative frequency). For example, the mean flexural strength (failure probability = 50%) here is 120 MPa.

4th shows a distance-temperature diagram. The distance a in mm is plotted on the y-axis and the maximum surface temperature Tmax in the heated heatable zone is plotted on the x-axis. Furthermore, the limit line is 300 drawn. The curve is also designated 301 for embodiment 1, the curve 302 for embodiment 2, the curve 303 for embodiment 3, the curve 304 for embodiment 4 and the curve 305 for the comparative example. The curve 305 for the comparative example is above the limit straight line 300 . The straight line 300 is given by equation (11), preferably by equation (12).

bevorzugt die Ungleichung $$25\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right),$$

und insbesondere bevorzugt die Ungleichung $$20\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

insbesondere besonders bevorzugt die Ungleichung $$20\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right)$$

erfüllt.The present disclosure also describes a device for heating food according to embodiments comprising a cover plate according to embodiments, in particular comprising at least one heatable zone, the cover plate being characterized by a permissible maximum temperature Tmax, preferably a permissible maximum surface temperature, after use-simulating sanding with 220 SiC , preferably a permissible maximum temperature of the top of the cover plate, the probability of breakage of the cover plate being less than 0.13%, the minimum distance a between the outer edge of the cover plate and the edge of the at least one heatable zone, given in millimeters, the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

prefers the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right),$$

and particularly prefers the inequality $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

the inequality is particularly preferred $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right)$$

Fulfills.

bevorzugt die Ungleichung $$25\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

und insbesondere bevorzugt die Ungleichung $$20\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

insbesondere besonders bevorzugt die Ungleichung $$20\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right)$$

erfüllt.The present disclosure also relates to a cover plate according to embodiments, wherein the cover plate is characterized after a use-simulating sanding with 220 SiC by a maximum permissible temperature Tmax, preferably a maximum permissible surface temperature, preferably a maximum permissible temperature of the top of the cover plate, with the probability of breakage failure Cover plate is less than 0.13%, the minimum distance a between the outer edge of the cover plate and the edge of the at least one heatable zone, given in millimeters, the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

prefers the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

and particularly prefers the inequality $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

the inequality is particularly preferred $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right)$$

Fulfills.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• GB 2079119 A [0006]
• US 2013098903 A1 [0006]
• US 2013256301 A1 [0006]
• US 2014061196 A1 [0006]
• US 2015274579 A1 [0006]
• US 2016338152 A1 [0006]
• US 2017247284 A1 [0006]
• WO 2018/225627 A1 [0007]

Non-patent literature cited

• ISO 7884-8 [0030]
• DIN 52324 [0030]
• DIN ISO 6344 [0033]
• Thermal Stress On: Soc. Mech. Eng., Jour. Appl. Mech., Vol 4, No. 1, March 1937 [0084]
• DIN ISO 719 [0099]
• DIN 12116 [0099]
• ISO 695 [0099]

Claims (19)

Cover plate, in particular plate for heating food, in particular by cooking, frying, heating and / or grilling, comprising a glass substrate with at least one heatable zone, the glass substrate comprising a glassy material comprising the following components in% by weight: SiO ₂ 60 to 80 Al ₂ O ₃ 0.5 to 25 B ₂ O3 0 to 11 Li ₂ O 0 to 5 Na ₂ O 0 to 8 K ₂ O 0 to 8 MgO 0 to 10 CaO 0 to 10 SrO 0 to 10 BaO 0 to 3 ZnO 0 to 3 TiO ₂ 0 to 3 ZrO ₂ 0 to 6 MnO ₂ 0 to 1 P ₂ O5 0 to 2 Nd ₂ O ₃ 0 to 1 Cs ₂ O 0 to 10 La ₂ O ₃ 0 to 5 SnO ₂ 0 to 1 As ₂ O3 0 to 1 Sb ₂ O ₃ 0 to 1.6 Cl 0 to 0.5 and optionally at least one further coloring oxide from the group Fe ₂ O ₃ and / or CoO and optionally further color oxides, the proportion of the further coloring oxides, including the optionally further color oxides, totaling between 0% by weight to 5% by weight % By weight, the glass substrate is preferably disk-shaped and the flexural strength of the thermally pre-stressed glass substrate due to wear of a surface, simulated by sanding with 220 SiC, a safety characteristic of flexural strength, defined as the mean value of the strength distribution reduced by three standard deviations, of is at least 90 MPa. Cover plate after Claim 1 , wherein the glass substrate is thermally toughened, wherein the thermal surface compressive prestress is at least 65 MPa, wherein preferably the substrate has a coefficient $$\mathrm{\alpha }\cdot \text{E /}\left(1-\mathrm{\mu }\right)$$

which is between at least 0.28 MPa / K and at most 0.53 MPa / K, where α denotes the mean thermal coefficient of linear expansion in the temperature range between 20 ° C and 300 ° C, E the modulus of elasticity and µ the Poisson's ratio of the glass. Cover plate according to one of the Claims 1 or 2 , wherein the glass substrate has a temperature difference resistance of at least 310 ° C with a minimum distance of 25 mm between the edge of the at least one heatable zone and the outer edge of the cover plate. Cover plate according to one of the Claims 1 to 3 , wherein the glass substrate comprises a glassy material comprising the following components in% by weight: SiO ₂ 63 to 79, preferably 64 to 79 Al ₂ O ₃ 3 to 22, B ₂ O3 0 to 11, Li ₂ O 0 to 4.1 Na ₂ O 0.1 to 7.1, K ₂ O 0 to 8, preferably 0 to 0.2 MgO 0 to 9.8, preferably 0 to 1.1 CaO 0 to 9.8, preferably 0 to 0.2 SrO 0 to 8.9, preferably less than 0.01 BaO 0 to 2.8 ZnO 0.4 to 1.6 TiO ₂ 0 to 2.4 ZrO ₂ 0 to 4.5, preferably 0 to 1.9 MnO ₂ 0 to 0.3 P ₂ O ₅ 0 to 1.3 Nd ₂ O ₃ 0 to 0.25 Cs ₂ O 0 to 3, preferably free of CsO except for unavoidable traces La ₂ O ₃ 0 to 0.5, preferably free of La ₂ O ₃ except for unavoidable traces SnO ₂ 0 to 1, preferably 0 to 0.5 As ₂ O ₃ 0 to 0.85 Sb ₂ O ₃ 0 to 1.6, preferably 0 to 0.6 and optionally at least one further coloring oxide from the group Fe ₂ O ₃ and / or CoO and optionally further color oxides, the proportion of the further coloring oxides, including the optionally further color oxides, totaling between 0% by weight to 5% by weight Wt .-%. Cover plate according to one of the Claims 1 to 4th wherein the glass substrate has a thickness between 2.8 mm and 6.3 mm. Cover plate according to one of the Claims 1 to 5 , the glass substrate having a chemical resistance H, S, L of at least 2, 3, 3 or better, the chemical resistance being determined as hydrolytic class H according to DIN ISO 719, acid class S according to DIN 12116 and alkali class L according to ISO 695 is. Cover plate according to one of the Claims 1 to 6th , the glass substrate being transparent and uncolored, characterized by a transmission in the visible wavelength range of the electromagnetic spectrum τ _vis of at least 85.0%, based on a glass thickness of 4.0 mm, the glass substrate preferably having a neutral transmission characteristic. Cover plate according to one of the Claims 1 to 6th , the glass substrate being transparent, volume-colored. Cover plate according to one of the Claims 1 to 7th , the glass substrate being transparent and uncolored, the saturation value C * of the CIEL * a * b * color space being at most 10.0 and preferably less than 4.0, where C * is defined as $${\mathrm{C.}}^{\ast }=\sqrt{a^{\ast }{}^2+b^{\ast 2}},$$

based on standard light D65, an observer at a viewing angle of 2 ° and a glass thickness of 4.0 mm. Cover plate according to one of the Claims 1 to 6th or 8th , the glass substrate being volume-colored, the saturation value C * of the CIEL * a * b * color space being a maximum of 10.0 and preferably less than 4.0, where C * is defined as $${\mathrm{C.}}^{\ast }=\sqrt{a^{\ast }{}^2+b^{\ast 2}},$$

based on standard light D65, an observer at a viewing angle of 2 ° and a glass thickness of 4.0 mm, and the transmission in the optical range τ _vis between the wavelengths 380 nm and 780 nm is less than 5% Cover plate according to one of the Claims 1 to 6th or 8th , the glass substrate being volume-colored, the saturation value C * of the CIEL * a * b * color space being a maximum of 10.0 and preferably less than 4.0, where C * is defined as $${\mathrm{C.}}^{\ast }=\sqrt{a^{\ast }{}^2+b^{\ast 2}},$$

based on standard light D65, an observer at a viewing angle of 2 ° and a glass thickness of 4.0 mm, and the transmission in the optical range τ _vis in at least partial areas of the cooking surface between the wavelengths of 380 nm and 780 nm is between 25% and 50%. Cover plate according to one of the Claims 1 to 11 , the glass substrate having an IR transmission over the entire surface or in areas preferred for this purpose, which is between 25% and 80% for each of the wavelengths 950 nm and 1600 nm, in each case based on a thickness of 4.0 mm. Cover plate according to one of the Claims 1 to 12 wherein at least one coating is arranged in at least one area of at least one surface of the area. Cover plate after one he Claims 1 to 13th , wherein the cover plate is characterized after use-simulating sanding with 220 SiC by a maximum permissible temperature Tmax, preferably a maximum permissible surface temperature, preferably a maximum permissible temperature of the top of the cover plate, the probability of breakage of the cover plate being less than 0.13%, with the minimum distance a between the outer edge of the cover plate and the edge of the at least one heatable zone, given in millimeters, the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

prefers the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right),$$

and particularly prefers the inequality $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

the inequality is particularly preferred $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right)$$

Fulfills. Device for heating food, in particular by cooking, frying, heating and / or grilling, comprising a cover plate according to one of the Claims 1 to 14th and at least one heating element assigned to the at least one heatable zone of the cover plate, the heating element being at an edge distance from the edge of the cover plate of at most 25 mm, and the heating element having a specific heating power of at least 8 W / cm ² and preferably a maximum of 15 W / cm ² . Device for heating food after Claim 15 , wherein the cover plate is characterized after use-simulating sanding with 220 SiC by a maximum permissible temperature Tmax, preferably a maximum permissible surface temperature, preferably a maximum permissible temperature of the top of the cover plate, the probability of breakage of the cover plate being less than 0.13%, with the minimum distance a between the outer edge of the cover plate and the edge of the at least one heatable zone, given in millimeters, the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

prefers the inequality $$\mathrm{25th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right),$$

and particularly prefers the inequality $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-215\right),$$

the inequality is particularly preferred $$\mathrm{20th}\le a\le \frac{1}{3}\cdot \left(T_{max}-235\right)$$

Fulfills. Device for heating food according to one of the Claims 15 or 16 , wherein the device comprises a sensor, such as a touch sensor on a capacitive or optical basis and / or a temperature sensor, and / or wherein the device comprises a lighting device, such as an LED, and / or a display element, such as an electro-optical display element. Device for heating food according to one of the Claims 15 to 17th , wherein the device comprises a means with which one can be connected to an IT means, such as a computer, a tablet PC, and / or a smartphone, the means preferably being designed so that a wireless connection can be established, and wherein the IT means can be connected to the device in such a way that the cooking device can be controlled with the IT means, and / or wherein the means is designed as an IT means which is designed to be connectable, and the cooking device can be controlled with the IT means . Use of a cover plate according to one of the Claims 1 to 14th as a surface for heating food, as a lamp or radiator cover, as the inner pane of a pyrolysis oven, as an oven pane, as a fireplace viewing window or as an oven viewing pane or as a heat shield to shield hot environments.

Images