CN1496233A - Hobs with non-planar multidimensionally shaped cooking surfaces made of glass or glass ceramics - Google Patents

Abstract

On the inner surface of such a cooking surface, food is cooked directly or indirectly. On the outer surface of the cooking surface is arranged a food heater, typically formed by a planar radiant heating device. In order to optimize the heat input over the entire cooking surface, the invention provides that the heater consists of a resistive electric heater which is coated directly in contact with the cooking surface made of glass or glass ceramics. Cover the outer surface of the cooking surface. The resistance heater can be formed as a surface heater (4) or as a coiled conductor track.

Description

Hobs with non-planar multidimensionally shaped cooking surfaces made of glass or glass ceramics

technical field

The invention relates to a cooker with a non-planar multidimensional cooking surface made of glass or glass ceramics, on the inside of which food is cooked and whose outer surface is equipped with a heating device for heating the food .

Background technique

Cooktops with cooking surfaces made of fragile materials typically comprise a flat cooking plate made of glass or ceramic or glass-ceramic, on the upper surface of which cooking utensils are placed, the cooking plate has cooking zones, the cooking zones Heating is performed from below with a flat heating body.

In known manner (EP0853444 A2, DE19835378 A1), oxide ceramics and non-oxide ceramics such as Si ₃ N ₄ or SIC are used as cooking plate material, but it is also known to use glass or glass ceramics with a low coefficient of thermal expansion , preferably a glass-ceramic cooking plate, known under the trademark CERAN. These glass or glass-ceramic cooking plates are heated from below with flat radiant heating elements. Radiant heating devices are generally in the form of electric heating; but can also be in the form of gas radiant burners.

During this time, methods have been disclosed which enable three-dimensional formation of glass-ceramic plates. Thus, using these methods, it is also possible to form a cooking plate made of glass ceramics as a three-dimensional concave cooking surface, which as a whole functions as a cooking zone, ie in which the food is cooked evenly. Trough-shaped devices are known under the trademark Cook-In, hemispherical devices are known under the trademark CERAN WOK and from DE 19906520 A1, and therefore belong to the prior art. Furthermore, food can be cooked directly on the inner surface of the cooking recess. But in the Wok device as mentioned in the above-mentioned German document, the food is usually cooked directly with a metal Wok cooking utensil, which is placed in the hemispherical concavity of the glass-ceramic face.

The above cookers are also heated by planar radiation heating devices, and these heating devices are located below the heated cooking surface at a certain interval. Here, heat conduction takes place in the form of radiation and conduction.

However, a flat radiant heating device under a trough cooker operates much less efficiently than a flat cooking plate due to the average distance from the food being cooked. Therefore, in order to achieve the same cooking efficiency, heating must be performed at a higher power and at a higher temperature, thereby reducing economic benefits. This is especially the case with hemispherical WOK cookers, where very fast cooking times are of high RMS value for meaningful operation. In a WOK cooker, for example, short-fried food can be cooked, which cannot be done for a long time. Therefore, the function of such WOK cookers is generally problematic in the case of slow heating. In order to improve the heating of the three-dimensional shape of the cooker in this respect, it is necessary to design a heater geometrically matched to the shape of the groove for each groove body, and its cost is often significantly increased due to the small number of production pieces, thus making this Kinds of cookers are uneconomical.

Contents of the invention

The object of the present invention is to provide a cooker of the above-mentioned type with a non-planar multidimensional cooking surface made of glass or glass ceramics, wherein food is cooked on the inner surface of the cooking surface and the outer surface of the cooking surface is provided with food heating Appliance, cooker of the present invention is so designed aspect heater, promptly it can work effectively. Here, the heater can be manufactured cost-effectively and installed easily. Furthermore, the heater can be easily adapted for heat distribution and controllability according to the specific purpose of use of the hob.

According to the invention, the above object is solved by the fact that the heater consists of a resistive electric heater which is coated in direct contact with a cooking surface made of glass or glass ceramics on its outer surface.

Therefore, the heater proposed by the present invention no longer consists of conventional radiant heating devices. Precisely, the heating takes place by direct contact with the cooking concavity made of glass ceramic or glass.

Because the cooking surface and heater are fixedly connected, efficiency is increased, control is greatly improved and cooking time is shortened. In this way, the functionality of the entire cooking system is improved.

In the case of direct heating, both the low material cost and low processing cost of the heating device are beneficial to the product yield. Uniform heat input throughout the heating zone is another important advantage of the heater of the present invention.

Since the resistance heater can have a structure of any size and whose geometry can cover any desired cooking surface area, different heat inputs can be realized on the cooking surface.

Resistance heating can be realized in different ways.

According to a further development of the invention, the hob can be formed particularly simply when the resistance heater is made of at least one electrically conductive layer of a resistive material with a positive temperature coefficient, which is coated including the associated connecting electrodes. Cover the outer surface of the cooking surface.

The conductive layer, the thermistor, can be designed in different ways.

A first embodiment of the invention provides that an electrically conductive layer in the form of a surface heater covers the outer surface of the cooking surface and that it consists of a thin layer of tin oxide and is equipped with connecting electrodes made of a thick layer of metal.

It is known (WO 00/18189) that such a thin-layer heating element made of tin oxide (SnO ₂ ) is coated on a glass substrate. They can be applied simply by spraying, dipping or by CVD (Chemical Vapor Deposition). The thick layers of metal forming the electrodes are preferably printed on. Furthermore, the resistors are preferably arranged in such a way that a homogeneous field distribution and thus uniform heating can be set, if the cooktop in question is generally intended to do so.

A heating possibility with purposefully adjustable heat distribution can be achieved with a cooker design in which the conductive layer is formed by conductor tracks, which are coated on the outside of the cooking surface according to a predetermined geometry and including the associated connecting electrodes On the surface, wherein the contact surface is on both ends of the printed conductor.

With the printed wire structure, the heat input can be limited very precisely locally, which may be of great benefit to certain shapes of cooking recesses.

In this embodiment of the conductor tracks, the conductor tracks are preferably in the form of thick-layer circuits, which are produced from conductive pastes with a substantial metal content, such as silver-containing alloys. It is also known (EP 0069298 A1, EP 0861014 A1) to coat the above-mentioned thermistor on the lower surface of a flat cooking surface.

Furthermore, the conductor tracks are preferably applied by screen printing. Printed wires can also be deposited directly as metal conductors by methods such as wire metal spraying.

To obtain the geometrical structure, the underside of the cooking surface needs to be masked accordingly in order to obtain the conductor layout. Here, such wiring can be arranged almost freely at the selected cooking zone location.

Significant advantages are obtained, especially for trough-shaped cooking cavities, if the conductor tracks are applied in a meandering shape.

In order to specifically fine-tune the heat distribution in the conductor track structure, the conductor track structure is designed in such a way that the conductor tracks have different widths and/or thicknesses in predetermined sections. In this way, as in the case of grooved cooking surfaces with a meandering conductor track structure, a narrow conductor track section can be formed in each case at the deepest point in order to take into account the maximum heat input there.

According to a further development of the invention, it is particularly advantageous if the electrically conductive layer is divided into heating circuits which can be operated separately from one another.

Depending on the heating power variation of the individual sections, different parts of the cooking zone can be locally assigned different heat inputs and can be adjusted independently of one another.

The resistance of glass ceramics has NTC characteristics (negative temperature coefficient characteristic), that is to say, the electrical conductivity increases significantly with increasing temperature. In order to suppress the current flow between the metal pan or glass ceramic surface and the heating conductor, an electrical insulation layer is a prerequisite for the cooker to work. For this purpose, according to a configuration of the invention, an insulating layer is applied between the underside of the cooking surface and the resistance heater. The insulating layer can consist of a ceramic material such as _SiO2 , according to WO 00/19774, or of Al2O3 or ZrO2, according to FR 2744116. Furthermore, enamel layers can also be used, according to EP 0222162 B1, DE 19845102 A1 and EP 0381792.

Feasible methods for insulating layer coating include: melt glue method (sol suspension method), vapor deposition method (CVD, PVD method), sputtering method and thermal spraying method such as flame spraying method or plasma spraying method.

Description of drawings

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the accompanying drawings. The accompanying drawings show:

Figure 1 is a perspective view of a cooktop having a Wok cooking surface and a planar resistive heater consisting of a thin conductive layer coated on the outer surface of the cooking surface;

Fig. 2 is a cross-sectional view of the cooker shown in Fig. 1;

Figure 3 shows the cooker shown in Figure 1, but it has two separately controllable planar heating circuits;

Fig. 4 represents the Wok cooking range shown in Fig. 1 in a perspective view, but it has a resistance heater made of printed wires, and the printed wires are coated around the concave surface of the Wok cooking range in the form of heat coils;

Fig. 5 shows a stove similar to Fig. 4, but it has two separate heating circuits;

FIG. 6 shows a schematic diagram of a cooker with a trough-shaped cooking concavity and a circuit arranged in a meandering manner.

Detailed ways

Figures 1, 2 show a first embodiment of the invention in two different views. In the present exemplary embodiment, a hemispherical cooking concavity 1 is formed of glass ceramic as the cooking surface, which has the configuration of a wok container, on which the food to be cooked 2 is located. Before the resistance heater proposed by the present invention is applied on the cleaned outer surface of the cooking concave surface 1, a metal mask must be applied on the outer surface, the thickness of which is about 2 mm. By means of vapor plasma spraying, an insulating layer 3 of Al ₂ O ₃ is applied, the layer thickness of which is selected such that a dielectric strength of approximately 3750 V is obtained. This insulating layer 3 ensures electrical insulation between the glass-ceramic cooking surface, which is electrically conductive at higher temperatures, and the resistance heater, which will be described below.

According to the exemplary embodiment shown in FIGS. 1 and 2, a surface heater 4 is applied over the entire surface of the underlying insulating layer 3, for example in the form of a thin conductive layer 4 of tin oxide (SnO ₂ ). This coating is preferably carried out by CVD, although other methods of producing thin layers are of course also possible. Subsequently, an electrode layer 5 or 6 , for example made of silver, is applied circumferentially to the central point of the cooking cavity or to the edge of the conductive layer 4 by means of screen printing or spraying. The electrodes are then connected via compressed springs 7 and 8 to load leads 9 and 10 , which are themselves connected to a power source 11 .

A uniform radial field distribution and thus also uniform heating is ensured by the electrode arrangement shown.

In the embodiment of the surface heater shown in FIGS. 1 and 2, the entire surface is designed as a single heating circuit. FIG. 3 shows an embodiment similar to that shown in FIGS. 1 and 2 , however, the surface heater is divided, that is to say, two separate thin resistive layers 4 a and 4 b are provided surrounding each other. the heating circuit. In order to connect the two heating circuits, in addition to the electrode layers 5 , 6 a central ring electrode 12 , ie a center tap, is provided which is led via a central load line 13 to a power distributor 14 .

If the voltage is connected to the poles a) and b) of the distributor 14, the upper heating circuit, that is, the thin layer area 4a is activated; if the voltage is connected to the poles b) and c), the lower heating circuit, that is, the thin layer area 4b is activated.

By varying the layer thickness and/or the material composition on the two heating circuits, the electrical energy input can be designed differently.

If the bottom of the Wok cooker concave surface 1 is provided, for example, with a lower-resistance resistive layer 4b, then the heat here can be supplied alone with a higher intensity, as desired in Wok cooker.

Instead of the surface heaters shown in FIGS. 1 to 3 , the cooking concavity 1 of the Wok cooker can also be heated by means of resistive conductor tracks with a predetermined geometry.

Such a second embodiment is shown schematically in FIGS. 4 , 5 . A metal conductor track 15 is respectively applied in the form of a heating coil on the bottom of the cooking recess or on the insulating layer applied thereto, wherein, in FIG. 4 , according to the embodiment shown in FIGS. 1 and 2 Only one integral heating circuit is provided, whereas in FIG. 5 two separately operable heating circuits 15 a , 15 b are provided in accordance with the embodiment shown in FIG. 3 .

The application of the circuit 15 is preferably achieved by screen printing through silver conductive paste, followed by firing at 500°C-600°C, or by masking and direct CNC support (Computerized Numerical Control Supported) Wire metal spraying of metals or alloys such as NiCR to implement. Here, the two ends of the conductor track extend out in a triangular shape and contact the load conductors 9 , 10 and 13 by means of spring contacts.

The conductor tracks 15 can be applied with different track densities. Thus, for example, as shown in FIG. 4 , with a high conductor density of many windings, more heat is supplied to the base of the cooking cavity than to the edge.

This unequal heat input can also be achieved by varying the conductor width.

In the embodiment shown in FIG. 5, the conductor track row is divided into two heating circuits 15a, 15b, the conductor track density (distance and width) being equal in both parts. The lower heating circuit 15b has a lower electrical resistance due to the proportionally smaller track length (due to the smaller upper circumference of the bottom) and thus has a higher power than the upper heating circuit 15a. When the two heating circuits operate simultaneously, the entire cooking zone is heated very uniformly over the entire surface, but with different heat inputs.

In this case, a variation of the heat input can also be achieved by different conductor widths and/or different resistive materials in the two heating circuits.

FIG. 6 shows an embodiment of the invention in relation to a trough-shaped cooking well 16 . The heating circuit in the form of a conductor track 17 is applied, for example, in a meandering manner. In this embodiment, a different heat input can also take place over the groove periphery, for example by means of different widths of the conductor tracks 17 . The reduction of the circuit width in the center, ie in the deepest part of the cooking cavity, results in a reduction in electrical resistance. Therefore, the bottom is heated more strongly.

Claims (13)

1. kitchen range, it has the cooking surface of the on-plane surface multidimensional shape made from glass or glass ceramics, cooking food is equipped with the heater that is used for heat food also for the outer surface of this cooking surface on the inner surface of this cooking surface, it is characterized in that: this heater is made up of a resistance-type electric heater, and this resistance heater is directly to contact on the outer surface that is applied to this cooking surface with the cooking surface made from glass or glass ceramics.

2. by the described kitchen range of claim 1, it is characterized in that this resistance heater is by at least one conductive layer made from the resistance material with positive temperature coefficient (4,15,17) form, connect electrode (5 under this conductive layer comprises, 6,12) on the interior outer surface that all is applied to this cooking surface.

3. by the described kitchen range of claim 2, it is characterized in that: this conductive layer becomes the form of face heater and covers the outer surface of this cooking surface in the face mode, this conductive layer is made of a kind of thin layer of tin oxide (4) and has a connection electrode (5,6,12) that is made of the metal thick-layer.

4. by the described kitchen range of claim 2, it is characterized in that: this conductive layer is formed by printed conductor (15,17), and these printed conductors are by the prespecified geometric structure and comprise that the described affiliated electrode that connects is applied on the outer surface of this cooking surface interiorly.

5. by the described kitchen range of claim 4, it is characterized in that: described printed conductor becomes thick-layer printed conductor form, and they are formed by the conductive paste that contains a large amount of metal ingredients.

6. by the described kitchen range of claim 5, it is characterized in that: this conductive paste is made of a kind of alloy of argentiferous.

7. by one of claim 4-6 described kitchen range, it is characterized in that: described printed conductor is coated with up with silk screen print method.

8. by one of claim 4-7 described kitchen range, it is characterized in that: described printed conductor (17) is coated with up according to serpentine structure.

9. by one of claim 4-8 described kitchen range, it is characterized in that: described printed conductor has different width and/or different thickness in predetermined segment.

10. by one of claim 2-9 described kitchen range, it is characterized in that: this conductive layer is divided into heater circuit (4a, the 4b that can work apart from each other; 15a, 15b).

11., it is characterized in that: between the bottom surface of this cooking surface and this resistance heater, scribble an insulating barrier (3) by the described kitchen range of one of claim 1-10.

12. by the described kitchen range of claim 11, it is characterized in that: this insulating barrier (3) is made of a kind of ceramic material.

13. by the described kitchen range of claim 11, it is characterized in that: this insulating barrier (3) is formed by a kind of enamel layer.

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