EP1980135A1

EP1980135A1 - Flat radiation-heated heating element

Info

Publication number: EP1980135A1
Application number: EP07700492A
Authority: EP
Inventors: Maravic Dusko; Keith Campbell Hilton
Original assignee: Nuveco AG
Current assignee: Nuveco AG
Priority date: 2006-01-17
Filing date: 2007-01-16
Publication date: 2008-10-15
Also published as: RU2008133387A; WO2007083217A1

Abstract

The invention relates to a radiation-heated hotplate which is made of a dimensionally stable, flat, non IR-permeable material which is heated by a radiation heating body. To date, all radiation heating bodies are exclusively used in conjunction with glass ceramics. They are constructed for that reason. The inventive method also enables hotplates, which are not made of a IR-permeable material, to be heated by means of a radiation heating system. All materials used for constructing a hotplate must have characteristics ensuring excellent dimensional stability when used as a flat hotplate. The hardness and the visual aspect of the surfaces of the hotplate do not contain the necessary characteristics of the hotplate but are still greatly welcomed. The inventive hotplate is only advantageous when it is used in conjunction with a special cooking utensil (see description). Only then can optimum results, such as lower energy requirement, lower temperatures and precise temperature-guided controls, be obtained. In order to obtain all of said advantageous characteristics, the hotplate must be in permanent contact with the base of the cooking utensil and on the entire surface thereof.

Description

Even radiation-heated heating element

The term "planar radiant-heated heating element" is understood to mean a dimensionally stable, flat heating plate which is not made of IR-permeable material and which is heated by a radiant heater.It is preferably used as a hotplate, but in principle wherever an optimum heat transfer between the heat source (heating plate) and the heat sink (with a permanent, full-surface contact) is sought.

General information on the topic of cooking plate heating

There are various hotplates on the market. They differ among themselves either in the design, the material or in their type of heating. For example, you know a mass cooking plate, which is usually made of cast iron. Such a plate is heated by a tube spiral, which is firmly connected to the cast iron plate. It also uses steel or stainless steel as cooking plate material. The heating of both systems is the same in the physical sense: indirect contact heating. With steel plates you can even realize a barbecue. Whether such heat sources are used more for cooking or more for grilling can not be clearly defined. But one thing is certain: a cast iron mass cooking plate is not usually used as a grill plate.

The glass ceramic, which has proven in the last 10 years clearly as the most commonly used cooking, can be difficult to call a hotplate. Nevertheless, it is defined as such, at least in the sense of its functionality. A so-called hotplate made of glass ceramic is primarily no heat source, but a mechanical carrier of the cookware. Because it largely transmits infrared rays, the cookware it carries is mostly heated by radiation. This technology is called radiant heating. As a result of absorption of the radiation energy, the glass ceramic hob is "plate" very hot. Usually, your surface temperatures be kept below 570 ⁰ C. The mass hotplates they are kept at a slightly lower temperature level, but often around 500 ° C.

Heat technology exist between the mentioned versions of hot plates huge differences. A mass hot plate or a steel hot plate is heated convectively, so by a physical contact. The heat transfer is purely by heat conduction. The differences in temperature that occur in the hotplate, which occur as a result of the heat transfer, create thermally induced stresses which then deform the hotplate. A curvature of the hotplate is therefore inevitable. The glass ceramic is fairly flat and does not bulge significantly thanks to its very small size. Although the heat is mainly transported by radiation to the bottom of the cookware, the cooking pots with dimensionally stable flat bottoms (see patent application CH 00016/06) have a significant Lower temperature of the glass ceramic surface than when using conventional cookware. This proves that a not exactly negligible part of the heat transfer between the floor and the glass ceramic takes place by contact (heat conduction).

Induction cooking is not at all comparable to cooking on a hotplate for heat transfer reasons. With the glass ceramic, however, there is a small similarity in that the majority of the heat that heats the bottom of the pot, not by contact between the bottom of the pot and the substrate (glass ceramic), but by radiation or induction. In the case of induction, the floor is exclusively heated inductively, in glass ceramic occur simultaneously at different heat transport mechanisms.

As a rule, radiant heating is recommended only and exclusively in conjunction with the glass ceramic. The inventors are not aware that a combination of radiant heating and non-glass related materials is used as cooking surfaces. The heating of a metallic hotplate has hitherto been carried out exclusively by a contact heating such as tubular heating coils, etc.

The present invention provides a solution with the aim of heating a non-glass-related hotplate with radiant heating.

Basics about temperature control

A huge majority of cooking systems that are in use to date have no temperature control. There are systems that have such, but they are only limited use and also still quite inaccurate. An attempt to control the cooking and frying temperature was made with EP 0783830 in connection with EP 0802756. It has been shown that a fairly accurate temperature control of hotplates resp. of the food is possible.

With CH 00016/06 it is shown that a further, equally good temperature control is also possible.

Both o. G. Inventions have in common that they have the same type of hotplate heating, namely a direct Kontaktheizunq the hotplate and a dimensionally stable, flat pan bottom construction. Only under the condition that both the cooking plate and the pot bottom can guarantee a high level of flatness and dimensional stability, it is possible to achieve a degree of temperature control of the cooking or roasting.

It is true that the glass-ceramic, regardless of whether it is used in conjunction with radiation heating or magnetic induction, basically does not require planar, dimensionally stable pot bottoms. Even if one would use such floors, so that a useful temperature control can not be achieved. All attempts in this direction are still far from guaranteeing reasonably usable results. To date, this applies both to the radiation heating and for the magnetic induction. Description of the invention

Summary of the invention

In order to exclude any misunderstandings, it should be said that the proposed invention leads to meaningful results only when a cup base construction according to EP 0802756 or CH 00016/06 is used as the heat sink. The use of conventional cookware (with Bodeneinzug!) Does not lead to the desired results. The main difference between the proposed invention and the aforementioned solutions is that here the heat source does not consist of a direct contact heating but of a heat radiation. The cooking plate and the cookware, especially their base plate, must remain permanently flat and dimensionally stable so that a temperature control of the food is possible. If you want to use the hob as a grill, then flatness and dimensional stability are not mandatory. From the o. G. For reasons, only those materials are selected which can meet these requirements. The surface finish and the choice of coating materials merely serve to fulfill the conditions mentioned above with regard to evenness and dimensional stability.

Detailed description of the invention

The heat source is therefore a radiant heater, as a heat sink, a light-impermeable heating plate, s. Fig. 1.

According to FIG. 1, a heating element consists of a heating plate (1), which consists of a material which is not permeable to IR or otherwise denoted by a material which is not light-transmissive. The heating plate is warmed up by IR radiant energy, which the heat source (2) emits. The heat source (2) usually consists of a heating coil, a heating tape or a halogen lamp, which is preferably integrated in a heat insulation (3) so as to experience a mechanical stability. An insulating ring (4) serves as a thermal wall (to prevent the heat flow to the outside) and as a further measure to increase the mechanical stability. All components are housed in a holding plate (5). This does not necessarily have to be made of steel, other materials such as plastics can also be used because the outside wall temperatures of the thermal insulation (3) or the insulating ring (4) will not be excessively warm / hot.

The back of the heating element is thermally insulated to avoid unnecessary heating of the heating element or its surroundings and to increase the energy efficiency of the system. The radiation power follows the radiation law (Kirchhof law) and is known to be defined by the fourth power of the temperature. Such radiant heaters, used as cooking plates resp. Cooking zones or so-called cooking zones are produced millions of times and used only in conjunction with glass ceramics. The heat source (2) resp. the radiant heat source, be it as conventional radiant heating (steel wire or heating spiral or so-called Quick Light (steel strip, or heating strip) or halogen spotlight or a combination of both is absolutely standard.

Ceramaspeed / UK, E.G.O / BRD u.e.a., are among the world's leading manufacturers of radiant heaters for the ceramic hobs.

Note: Basically, the term heating element in the case of use as a hotplate with the name hotplate is the same. For this reason, from this point only the name hot plate is used.

The amount of heat absorbed by the hotplate to be heated depends on the IR absorbency of the selected plate material. As a rule, good heat conducting materials should be chosen. Their surfaces should be able to absorb radiation well. Materials that are also characterized by a high heat penetration coefficient are also beneficial.

From a mechanical and thermal point of view, only those cooking plate materials should be selected which do not buckle during heating or during cooling. They must always remain flat during their mission. Neither a thermoindicated bending stress nor an uneven warming resp. Cooling, z. B. caused by poor positioning of the cookware, may cause the hotplate deformation.

If the cooking plate loses its flatness, that is to say its dimensional stability, this leads to the loss of many advantages which a cooking system, which uses the cooking plate according to the invention, has. Low energy consumption, low temperatures, and the exact temperature control can no longer be guaranteed.

From o. G. For reasons, preferably materials with good heat conduction, high flexural strength, low expansion and sufficient hardness are recommended. It is irrelevant whether they are metals such as suitable steels, copper and aluminum alloys or composite materials. It is only important that the thermoindicated bending stresses that have occurred do not deform the flat hotplate. Less important is the reason why they do not deform. Because of low thermoindicated bending stress or because of high bending stress of the hotplate material or because of low residual stresses in the hotplate material. Also insignificant is the origin of the material hardness. Some materials have sufficient hardness, for example, hard or tempered low alloy steels, composites such as MMC (AISiC, CuSiC), etc. Others, such as aluminum and copper alloys, must be coated with a hard coat.

In principle, all hotplate materials should be coated for some reason (food compatibility, corrosion, oxidation, visual appearance, etc.). Various layer materials are available for this purpose, such as DLC, Cr-Ni, TiC, TiN, etc. etc. A range of layer materials that are used here in Hessen are state-of-the-art and should therefore not be given more prominence here , Temperature control of a hotplate

Fig. 2 shows an example of a temperature control of a hotplate again.

For temperature detection of the hotplate (1) different temperature sensors (6) such as Pt-100, Pt-1000 or thermocouples, etc. can be used. They are very reliable and have already been used successfully millions of times. A temperature-controlled controller (7), preferably electronically controlled, is used to implement the measured values and to specify or maintain the setpoints. The control is usually done mechanically, by push button or toggle on the one hand or - as many times done - touchless (touch control). A signal line (6.1) sends the measured values to the controller. In principle, the controller (7) can be positioned in the immediate vicinity of the cooking plate (1). The signal line (6.1) can be shortened very much. In particular, where not so great demands are placed on the temperature accuracy, other types of controllers can be used, for. B. so-called. Thermo-mechanical temperature controller or limiter.

A temperature sensor (6) initially serves once to detect the temperature of the cooking plate (1). A hotplate can also have several T-probes. Temperature detection is necessary to comply with legal standards. Finally, the maximum temperature must not destroy the hotplate (1) resp. lead to accidents as a result of overheating.

Since the hotplate serves as a source of heat for heating cookware by contact or allows cooking, frying and grilling, the knowledge about the cooking, roasting and grill food must be guaranteed. In terms of a healthy food preparation, the temperature detection is primarily the control of the cooking or roasting process.

If you want to use the hob as a grill, then flatness and dimensional stability are not mandatory.

In order to influence the acrylamide formation in starchy foods such as potatoes, etc., the maximum temperature is preferably limited to 175 ⁰ C. This is not a mandatory limitation on the cooking system, but rather an empirical value gained from an infinite variety of practical cooking experiments.

applications

The cooking plate according to the proposed invention can be used both individually and as an integrated hob, consisting of several individual hotplates. As a single hotplate speak hotplate module, you can in a countertop stone, stainless steel or in one of the many high temperature resistant plastics, preferably thermosets, integrate.

If you want to produce a hob, then there are the same installation conditions as they prevail today in conventional hobs. In this solution The manufacturer of the hob can perform the entire assembly in his production because the actual installation in the kitchen worktop by the kitchen builder or a third party takes place.

As a countertop material, all materials that are in use, can be taken. The temperature of the cooking plate edge is below 175 ° C. When using a kitchen worktop made of wood or wood-like materials, a small modification must be made to prevent direct contact between the hotplate and the worktop. Finally, the hot plate is up to 175 ⁰ C warm and this temperature level is clearly too high for the wood. For this reason, a thermal "wall" is built in. An intermediate ring made of a temperature-resistant material with low thermal conductivity is recommended.High-temperature resistant plastics, in particular thermosetting plastics, as well as various hard glasses are also suitable for this.When using glass, its light transmission can be of particular use Thus, for example, one can achieve an optical signaling of the operating state or of the cooking plate temperature.

The choice of hotplate material:

As a material of the hotplate (1) different materials come into question. Preferably, however, will be

1. High-tech ceramics, such as a densely sintered silicon nitride,

2. Low alloy steel (1.2067, 1.8159, 1.7225, 1.2311, 1.xxxx u.e.a)

3. Low alloyed copper (K-55 and others)

4. Intermetallic phases (MoSi2 and e.a.)

5. MMC (AISiC, et al.)

6. other (suitable) compound materials of ceramic and / or metallic origin

7. Composite materials (SGL materials, etc.) used.

All proposed materials should have sufficiently hard surfaces. Some of them are included as base material (silicon nitride, low alloy steels, AISiC, composites), others must be coated with hard materials (K-55). The coating of the surface is also for other reasons, so to avoid corrosion and oxidation. And last but not least, the coating materials are optically selected. The eye buys known with.

Claims

claims

1. A plane radiant-heated heating element, according to claim 1, characterized in that it consists of a, formed from a non-IR-permeable material, heating plate (1) and a heat source (2), which is characterized by radiation.

P.S .: further claims will be defined later.