EP0189108B1 - Heating device, especially for a cooking plate heated by radiation, and its manufacturing process - Google Patents

Heating device, especially for a cooking plate heated by radiation, and its manufacturing process Download PDF

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Publication number
EP0189108B1
EP0189108B1 EP86100466A EP86100466A EP0189108B1 EP 0189108 B1 EP0189108 B1 EP 0189108B1 EP 86100466 A EP86100466 A EP 86100466A EP 86100466 A EP86100466 A EP 86100466A EP 0189108 B1 EP0189108 B1 EP 0189108B1
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EP
European Patent Office
Prior art keywords
supporting layer
heating
heating coil
heating device
layer
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EP86100466A
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German (de)
French (fr)
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EP0189108A1 (en
Inventor
Hans Kummermehr
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Ceramaspeed Ltd
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Ceramaspeed Ltd
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Priority to AT86100466T priority Critical patent/ATE65150T1/en
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/68—Heating arrangements specially adapted for cooking plates or analogous hot-plates
    • H05B3/688—Fabrication of the plates
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/68—Heating arrangements specially adapted for cooking plates or analogous hot-plates
    • H05B3/74—Non-metallic plates, e.g. vitroceramic, ceramic or glassceramic hobs, also including power or control circuits
    • H05B3/748—Resistive heating elements, i.e. heating elements exposed to the air, e.g. coil wire heater
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
    • H05B2203/017—Manufacturing methods or apparatus for heaters

Definitions

  • the invention relates to a heating device, in particular for a radiation-heated hotplate, according to the preamble of claim 1, and to processes which are particularly suitable for its production according to the preamble of claim 7.
  • the thermal insulation must be carried out on the outside facing away from the heating coil in a very small space with a high temperature gradient. Therefore, a highly disperse insulation material is used for the insulation layer.
  • This insulation material consists of a microporous oxide airgel obtained from flame hydrolysis, in particular silica airgel and / or aluminum oxide airgel, usually with suitable additives such as reinforcing mineral fibers and / or opacifiers and / or binders for hardening.
  • This thermal insulation material is either pressed directly into the receiving shell of the heating device to form the insulating layer, or is pre-pressed as a plate and inserted into the receiving shell.
  • a major problem is the storage of the heating coil on the top of the insulation layer made of the insulation material described. It is known from EP-A-79 076 that the heating coil or other heating element is directly in the thermal insulation material of the insulation layer press in. For this purpose, the heating element is placed in the pressing tool and covered with the still powdery insulation material, after which the heating element is pressed together with the insulation material in order to achieve the desired degree of compression of the insulation material.
  • the upper press-in layer of the thermal insulation material can contain a different consistency than the rest of the insulating layer and, in addition to a high proportion of hardener, can contain an electrically insulating, heat-conducting substance.
  • the heating coil is pressed in, at least one third of its coil diameter, that is to say its overall height, the pressed-in part being completely surrounded by the pressed thermal insulation material and thus anchored.
  • the material of the press-fit layer must contain heat-conducting additives in order to avoid destructive heat build-up in the embedding area by appropriate heat dissipation; as a result, the thermal insulation material of the press-fit layer is stripped of its essential property, namely the outstanding thermal insulation.
  • the thermal insulation material and the heating coil Since in practice it must always be ensured that intimate, direct contact between the thermal insulation material and the heating coil is avoided, a special bearing material is regularly provided for the heating coil. In addition to minimizing the installation effort, the storage of the heating coil must be optimized according to various, sometimes contradicting, aspects. In addition to the best possible thermal insulation with the lowest possible overall height, it is particularly important to ensure that the heating coil can on the one hand radiate upwards as best as possible, but on the other hand is sufficiently securely held in place to withstand short circuits due to mutual contact of the spiral sections, in view of the very considerable thermal expansions during operation exclude and to get a uniform radiation pattern.
  • the heating coil When the heating coil is received in grooves, a substantial part of the outer surface of the heating coil is always covered and can therefore only generate useful radiation to a reduced extent.
  • the storage in grooves especially if these are lined with a closed-surface hard coating, provides a clean positional securing.
  • the radiation can be optimized by anchoring the heating coil on a flat bearing layer, but the heating coil cannot be permanently anchored securely on such a flat bearing layer in view of the considerable temperature changes.
  • the invention has for its object to provide a heating device of the type specified in the preamble of claim 1, in which the heating coil Despite the extreme temperature changes that occur, it is permanently securely stored and at the same time ensures improved, that is to say optimal, heat radiation, the manufacture of the heating device being carried out with a minimum of effort and, furthermore, the greatest possible thermal insulation with the lowest possible overall height being achieved.
  • each individual spiral wire is embedded in the material of the bearing layer only with its lower arch section, i. H. only at most up to about the full wire gauge. This means that the wire of the heating coil is clamped in a quasi-punctiform manner only in the lower apex region of the arch section in the bearing layer, but is otherwise freely available for radiation over its entire length.
  • the entire thermal insulation material is arranged on the side of the heating coil to be insulated, it unfolds fully Insulation effect to the side to be insulated.
  • the material of the insulating layer can be pressed flat or with an uncomplicated shape, so that this reduces manufacturing costs.
  • the bearing layer only needs to have a very small layer thickness, depending on the wire thickness of the heating coil or even less, and thus only makes a minor contribution to the overall height.
  • the material of the bearing layer can be designed, for example by adding opacifying agents or the like, with a view to optimizing its contribution to thermal insulation without fear of disadvantageous heat build-up. Furthermore, since the material of the insulation layer is not mechanically stressed by the storage of the heating coil, its consistency, in particular its degree of compression, can also be optimized with regard to thermal insulation aspects, so that overall the greatest possible thermal insulation results in the smallest possible height.
  • either the bearing layer can be prefabricated as a thin plate with the heating coil anchored thereon and then - optionally at another location - combined with the likewise plate-shaped or also pressed-in insulation layer, or else there is a coating of the insulating layer directly with the material of the bearing layer with subsequent pressing in of the heating coil, in which case a support ring can also be bonded to the material of the bearing layer in a particularly advantageous manner.
  • the heating device shown consists essentially of a receptacle 1 made of metal, in particular aluminum sheet, and thermal insulation material in the form of a thermal barrier layer 2, which is arranged on the inside of the peripheral wall 3 of the receptacle 1 between the bottom 4 and a heating coil 5.
  • the electrically operated heating coil 5 has electrical connections, not shown, which are led out of the area of the receiving shell 1 in a suitable manner.
  • the heating device shown is used for radiant heating of a glass ceramic cover of a hotplate, the glass ceramic plate (not shown in detail) resting on a support surface 10 and thus being kept at a distance from the upper edge of the peripheral wall 3 of the receiving shell 1 and from the heating coil 5.
  • the peripheral wall 3 of the receiving shell 1 and thus the entire heating device has an essentially circular shape in plan view and is concentric with a central axis 9.
  • the insulation layer 2 consists of fine-pored silica airgel with additives. This material is known per se and shows in addition to the silica airgel in all Rule a mineral fiber reinforcement and / or an opacifier and / or a binder as a hardener; Regarding details, reference is made to the relevant DE-OSen 27 47 663, 27 48 307, 27 54 956 and 31 08 816, to which reference is expressly made in this regard.
  • a material is preferably used for the insulation layer 2, which consists of 30 to 50% by weight of pyrogenic silica, 20 to 50% by weight of opacifying agent and 5 to 15% by weight of aluminum fibers and in a density of 200 to 400 kg / m3 is present, but does not need to be organic or inorganic hardened.
  • a special thermal insulation material has a thermal conductivity that is lower than that of still air and, moreover, is only slightly temperature-dependent.
  • the plates or layers pressed from such powdery base materials are not mechanically resistant.
  • the material can also contain aluminum oxide airgel, or a suitable mixture of both aerogels, in order to achieve higher temperature resistance if required.
  • the insulation material of the insulation layer can contain 2 additions of high temperature resistant materials such as manganese oxide, zirconium oxide or titanium oxide. For special purposes you can also work with their airgel.
  • a bearing layer 7 is arranged on the insulation layer 2 and can have a thickness of approximately 1 mm or a little more.
  • the bearing layer 7 may consist of a mixture of materials that contains mineral fibers and a ceramic binder that solidifies at temperatures between about 500 ° C. and 1000 ° C. by ceramic bonding.
  • the proportion of mineral bevels should be as high as possible, since the mineral fibers counteract a tendency of the bearing layer 7 to shrink at elevated temperatures. Therefore, the mineral Fibers are present in a proportion of more than 50% by weight of the dry mixture, but preferably in an even higher proportion of 75 to 95% by weight, a proportion of approximately 80% by weight being selected in the example.
  • the mineral fibers have a softening or melting point of over 1000 ° C, preferably over 1100 ° C, so they are resistant to the temperatures that occur during operation.
  • Such adjustment of the softening or melting point of the fibers is achieved on the one hand by choosing a certain particle size, larger particles softening and sintering later than smaller powder-like particles, and by choosing the additives or fluxes in addition to the main aluminum oxide or silicon oxide component of the mineral fibers.
  • the mineral fibers are drawn from the melt with a thickness between about 0.5 and 3 microns, preferably between 1 and 2 microns and then ground so that they are broken to lengths between 2 and 20 microns, preferably between 5 and 10 microns, whereby however in any case the length of the mineral fibers whose thickness exceeds at least twice, so that there is actually still a fiber character.
  • the additives such as flux in the melt for the production of the fibers, such as Na2O, B2O3, MgO, Fe2O3 and other additives known per se, can then be selected so that the desired temperature resistance up to ranges above 1000 ° C or results in over 1100 ° C, i.e. in areas in which the mineral fibers based on aluminum silicate do not soften or melt at the maximum temperature occurring during operation.
  • the ceramic binder is silica sol, as is known per se for example for coating such a material from EP-A-81 825.
  • the silica sol as a ceramic binder is used together with inorganic fibers such as aluminum silicate fibers or quartz fibers and optionally other inorganic fillers applied in a slurry.
  • Suitable inorganic fibers for the coating material are in principle all correspondingly temperature-resistant fibers such as aluminum silicate fibers, quartz fibers, etc., but aluminum silicate fibers are generally preferred for reasons of cost.
  • the fibers must be so close together that the silica sol forms a connection between them and adheres to neighboring fibers instead of forming their own particles that are not bound to the filler.
  • the fibers thus primarily act as a dispersing agent for the silica sol in order to form a closed surface with it.
  • aluminum silicate fibers are even more expensive than most inorganic granular additives such as ground aluminum oxide, quartz sand, mullite, zirconium oxide, etc., so that these fibers can be stretched by granular fillers which are similar to the fibers, albeit to a lesser extent, than for cost reasons Dispersants can serve for the silica sol.
  • Clays and kaolin continue to be considered as inorganic granular additives.
  • Aluminum oxide, optionally with an admixture of kaolin, is preferred, which improves the suppleness of the bearing layer 7.
  • the amount of silica sol essentially results from the need for binders for the closed surface coating with regard to the desired caking of the fillers with one another.
  • the amount of the silica sol has a lower limit where the abrasion resistance of the surface is too low due to the binder content being too low.
  • the proportion of the silica sol as a solid must not be less than about one tenth of the fillers and fibers to be bound therewith in the surface coating, so that the silica sol in the closed surface coating is present in any case in a solids content of 10% by weight or more.
  • An increase in the proportion of silica sol initially gives one Increased abrasion resistance through better integration of the fibers and granular fillers as well as a shiny and smooth surface.
  • the proportion of the silica sol based on the amount of fillers in the coating composition may only be approximately 1: 1, so that at least as many parts by weight of fillers as dry parts by weight of silica sol are present in the closed storage layer 7.
  • the proportion of the fillers present in fiber form should not be less than a third of the fillers of the bearing layer 7 in order to allow the fibers to act sufficiently as network formers to form a closed film.
  • the above information relates to the proportions by weight in the finished bearing layer 7, so that the dry mass of the silica sol is taken into account.
  • the aqueous silica sol i.e. the colloidal silica
  • This can be supported by adding wetting agents, as is known per se, although mechanical support by doctor blades or rollers is of course also possible.
  • aqueous silica sol (30% solids content) 23.5% by weight aluminum silicate fibers 11.8 wt% alumina 5.9% by weight kaolin
  • aqueous silica sol (30% solids content) 13.3% by weight aluminum silicate fibers 6.7% by weight of aluminum oxide 10.0% by weight kaolin
  • aqueous silica sol (30% solids content) 25.53% by weight aluminum silicate fibers 12.75 wt% alumina 12.75 wt% clay
  • the masses are applied moist with a liquid to paste-like consistency corresponding to the type of application by spraying, knife coating, brushing, dipping, screen printing or the like.
  • the heating coil 5 has previously been stress-free annealed in the desired shape and is thus pretreated by means of a magnet with a temperature of, for example, 200 ° C. and pressed into the still moist bearing layer 7.
  • the indentation is preferably only carried out until about two thirds of the wire thickness of the lower arc section of each helix ring is immersed in the mass, due to the increased temperature of the heating coil, a certain solidification of the mass already occurs during the pressing in and thus the heating coil is attached. If necessary, a small proportion of organic additives can be added to the mass to achieve an adhesive effect.
  • the material When the heating coil is in operation, the material then ceramizes completely under the action of heat and cementes the embedded arch section of the heating coil to a certain extent.
  • the immersion depth should be kept as low as possible to minimize the radiation to hinder. The immersion depth of approximately 2/3 of the wire thickness shown in FIG. 2 is therefore optimal.
  • the radially outer peripheral region 6 of the receiving shell 1 or the insulating layer 2 and thus also the bearing layer 7 is bent upwards in the example shown in the example, so that the heating device as a whole has an approximately plate-like appearance in cross section.
  • a support ring 8 made of bonded fibers, for example a material such as that sold under the name Fiberfrax (registered trademark), is placed on the cranked peripheral region 6 and forms the support to the underside with the upper support surface 10 in the manner already described the glass ceramic plate.
  • the heater can be manufactured in various ways. First of all, the material of the insulating layer 2 can be pressed against the bottom 4 of the receiving shell 1 in a manner known per se and can thus be formed as a compressed insulating layer 2 directly above the bottom 4 of the receiving shell 1. The mass for forming the bearing layer 7 can then be applied to the surface of the insulating layer 2 formed in this way by spraying, brushing or the like, and the heating coil can be pressed in. Then the support ring 8 can also be expediently placed as long as the mass for forming the bearing layer 7 is still moist, and is thus held in place by adhesion. In such a case, the illustrated heating device is either prefabricated in one stage or - with an interruption and, if necessary, a change of location after the insulation layer 2 has been pressed in - in two stages.
  • the insulation layer 2 can also be prefabricated as a plate and thus pre-pressed and prefabricated into the receiving shell 1. In this case too, without the presence of the receiving shell 1, the formation of the bearing layer 7, the fitting thereof with the heating coil 5 and possibly the bearing ring 8 in the above described manner.
  • the bearing layer 7 can also be prefabricated separately and fitted with the heating coil 5, optionally also with the support ring 8, and thus dried or hardened.
  • This assembly unit can then be used together with a separately prefabricated plate-shaped insulating layer 2 in a receiving shell 1, or in a receiving shell 1 with pressed-in insulating layer 2.
  • the heating device according to the invention thus allows a large number of manufacturing options with great freedom of movement with regard to the manufacturing locations.
  • the production is in any case simple and problem-free, especially since the effort to produce grooves can also be dispensed with in view of the planar design of the surface of the bearing layer 7 according to the invention.
  • heating up to a desired temperature can take place immediately after embedding the heating coil 5, so that in any case sufficient drying and hardening of the mass for the bearing layer 7 takes place in the local storage areas.
  • Mineral pigments may also be present in the bearing layer 7, in particular in the form of TiO2 or TiO2-containing substances.
  • the mineral pigments which are not absolutely necessary, serve to scatter or reflect part of the IR radiation and to increase the abrasion resistance.
  • a TiO2-containing substance for example, a mixture of Al2O3 and TiO2 can be chosen, the TiO2 serving as a pigment and also as an opacifier against IR radiation.
  • suitable pigments include rutile, ilmenite, iron oxide, chromium oxide and the like. It is sufficient if the mineral pigments are present in the storage layer 7 in a proportion of up to a maximum of about 20% by weight of the dry mixture, but preferably in a proportion less than 10% by weight.
  • the storage layer may contain 7 5 wt .-% mineral pigments in the form of TiO2.
  • the use of pigments or opacifiers in the bearing layer 7 is therefore possible relatively easily because, due to the very slight embedding of the helix wire, there is no fear of a noticeable build-up of heat.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Resistance Heating (AREA)
  • General Preparation And Processing Of Foods (AREA)
  • Baking, Grill, Roasting (AREA)
  • Formation And Processing Of Food Products (AREA)

Abstract

A flat bearing coating (7) for the heating coil (5) of a heating device is formed from an inorganic mass with a binding agent and fillers, especially based on silica sol with a fibre additive. The mass for the bearing coating (7) is applied moist onto a substrate or directly onto an insulating coating (2), and the heating coil (5) is pressed into the still moist mass to a depth between a half and a complete wire thickness of the coil wire. In this way, each lower curved section of the heating coil is held individually in the hardening (and, if required, ceramising) material of the bearing coating. In this manner, any opposing movements of the coil sections, which could lead to a short-circuit, are reliably prevented and, nevertheless, a maximum useful radiation is ensured. The production is simple and allows great flexibility with respect to a step-by-step prefabrication. <IMAGE>

Description

Die Erfindung betrifft eine Heizvorrichtung, insbesondere für eine strahlungsbeheizte Kochplatte, nach dem Oberbegriff des Anspruchs 1, sowie für ihre Herstellung besonders geeignete verfahren nach dem Oberbegriff des Anspruches 7.The invention relates to a heating device, in particular for a radiation-heated hotplate, according to the preamble of claim 1, and to processes which are particularly suitable for its production according to the preamble of claim 7.

Bei derartigen Heizvorrichtungen muß die Wärmedämmung auf der der Heizwendel abgewandten Außenseite auf sehr geringem Raum mit hohem Temperaturgradienten erfolgen. Daher wird für die Dämmschicht ein hochdisperses Dämmaterial verwendet dieses Dämmaterial besteht aus einem aus der Flammenhydrolyse gewonnenen mikroporösen Oxidaerogel, insbesondere Kieselsäureaerogel und/oder Aluminiumoxidaerogel, in der Regel mit geeigneten Zuschlagstoffen wie verstärkenden Mineralfasern und/oder Trübungsmittel und/ oder Bindemittel zur Härtung. Dieses Wärmedämmaterial wird entweder zur Bildung der Dämmschicht unmittelbar in die Aufnahmeschale der Heizvorrichtung eingepreßt, oder aber als Platte vorgepreßt und in die Aufnahmeschale eingelegt.In such heating devices, the thermal insulation must be carried out on the outside facing away from the heating coil in a very small space with a high temperature gradient. Therefore, a highly disperse insulation material is used for the insulation layer.This insulation material consists of a microporous oxide airgel obtained from flame hydrolysis, in particular silica airgel and / or aluminum oxide airgel, usually with suitable additives such as reinforcing mineral fibers and / or opacifiers and / or binders for hardening. This thermal insulation material is either pressed directly into the receiving shell of the heating device to form the insulating layer, or is pre-pressed as a plate and inserted into the receiving shell.

Ein wesentliches Problem besteht in der Lagerung der Heizwendel auf der Oberseite der Dämmschicht aus dem geschilderten Dämmaterial. Zwar ist es aus der EP-A-79 076 bekannt geworden, die Heizwendel oder ein sonstiges Heizelement unmittelbar in das Wärmedämmaterial der Dämmschicht einzupressen. Hierzu wird das Heizelement im Preßwerkzeug vorgelegt und mit dem noch pulverigen Dämmaterial überschichtet, wonach das Heizelement zusammen mit dem Dämmaterial zur Erzielung des gewünschten Verdichtungsgrades des Wärmedämmateriales gepreßt wird. Die obere Einpreßschicht des Wärmedämmaterials kann dabei eine gegenüber dem Rest der Dämmschicht unterschiedliche Konsistenz und neben einem hohen Härteranteil eine elektrisch isolierende, wärmeleitende Substanz enthalten. Die Heizwendel wird, dabei mindestens zu einem Drittel ihres Wendeldurchmessers, also ihrer Bauhöhe eingepreßt, wobei der eingepreßte Teil vollständig von dem gepreßten Wärmedämmaterial umgeben ist und so verankert wird.A major problem is the storage of the heating coil on the top of the insulation layer made of the insulation material described. It is known from EP-A-79 076 that the heating coil or other heating element is directly in the thermal insulation material of the insulation layer press in. For this purpose, the heating element is placed in the pressing tool and covered with the still powdery insulation material, after which the heating element is pressed together with the insulation material in order to achieve the desired degree of compression of the insulation material. The upper press-in layer of the thermal insulation material can contain a different consistency than the rest of the insulating layer and, in addition to a high proportion of hardener, can contain an electrically insulating, heat-conducting substance. The heating coil is pressed in, at least one third of its coil diameter, that is to say its overall height, the pressed-in part being completely surrounded by the pressed thermal insulation material and thus anchored.

Zweifellos ergäbe eine solche Vorgehensweise minimalen Herstellungsaufwand bei - jedenfalls anfangs - bestmöglicher Lagesicherung der Heizwendel. Jedoch ist ein solches Vorgehen nicht praktikabel, da die Heizwendel infolge der im Betrieb entwickelten hohen Temperaturen nicht unmittelbar mit dem Wärmedämmaterial in Berührung kommen darf; denn im Dämmaterial, insbesondere in den Mineralfasern, die zur Verstärkung gerade der Lager- oder Einpreßschicht erforderlich sind, enthaltenes Eisenoxid verbindet sich mit dem Chrom-Nickel-Draht der Heizwendel, so daß das Metall der Heizwendel seine Hochtemperaturbeständigkeit verliert und durchbrennt. Überdies wird durch die zumindest weitgehende Einbettung der Heizwendel die Abstrahlung nach oben, also die eigentliche Nutzstrahlung, erheblich vermindert. Abgesehen von der angestrebten herstellungstechnischen Vereinfachung durch Verpressung in einem Arbeitsgang ergeben sich auch keine dämmtechnischen Vorteile, wenn das Material der Einpreßschicht gut wärmeleitende Zusätze enthalten muß, um in jedem Falle zerstörende Wärmestaus im Einbettungsbereich durch entsprechende Wärmeableitung zu vermeiden; hierdurch wird das Wärmedämmaterial der Einpreßschicht gerade seiner wesentlichen Eigenschaft, nämlich der überragenden Wärmedämmung, wieder beraubt.Such a procedure would undoubtedly result in minimal manufacturing effort with - at least initially - the best possible securing of the heating coil. However, such a procedure is not practical, since the heating coil must not come into direct contact with the thermal insulation material due to the high temperatures developed during operation; Because in the insulating material, especially in the mineral fibers, which are required to reinforce the bearing or press-fit layer, iron oxide contained connects with the chrome-nickel wire of the heating coil, so that the metal of the heating coil loses its high temperature resistance and burns out. Moreover, due to the at least extensive embedding of the heating coil, the upward radiation, that is to say the actual useful radiation, is considerably reduced. Apart from the desired simplification of the manufacturing process by pressing in one work step, there are no insulation advantages if the material of the press-fit layer must contain heat-conducting additives in order to avoid destructive heat build-up in the embedding area by appropriate heat dissipation; as a result, the thermal insulation material of the press-fit layer is stripped of its essential property, namely the outstanding thermal insulation.

Da in der Praxis stets darauf geachtet werden muß, daß ein inniger unmittelbarer Kontakt zwischen dem Wärmedämmmaterial und der Heizwendel vermieden wird, wird regelmäßig ein besonderes Lagermaterial für die Heizwendel vorgesehen. Neben einer Minimierung des Montageaufwandes ist hierbei die Lagerung der Heizwendel nach verschiedenen, zum Teil einander widersprechenden Gesichtspunkten zu optimieren. Neben bestmöglicher Wärmedämmung bei geringstmöglicher Bauhöhe ist dabei insbesondere zu gewährleisten, daß die Heizwendel einerseits bestmöglich nach oben abstrahlen kann, andererseits aber ausreichend sicher an Ort und Stelle gehalten ist, um auch im Hinblick auf die sehr erheblichen Wärmedehnungen im Betrieb Kurzschlüsse durch gegenseitige Berührungen von Wendelabschnitten auszuschließen und ein gleichmäßiges Strahlungsbild zu erhalten.Since in practice it must always be ensured that intimate, direct contact between the thermal insulation material and the heating coil is avoided, a special bearing material is regularly provided for the heating coil. In addition to minimizing the installation effort, the storage of the heating coil must be optimized according to various, sometimes contradicting, aspects. In addition to the best possible thermal insulation with the lowest possible overall height, it is particularly important to ensure that the heating coil can on the one hand radiate upwards as best as possible, but on the other hand is sufficiently securely held in place to withstand short circuits due to mutual contact of the spiral sections, in view of the very considerable thermal expansions during operation exclude and to get a uniform radiation pattern.

Eine Maximierung der Abstrahlung wird ersichtlich dann erzielt, wenn die einzelnen Abschnitte der Heizwendel auf einer planen Unterlage aufliegen und somit abgesehen von den im wesentlichen punktförmigen Auflagestellen keine Berührung mit dem Lagermaterial besitzen, insbesondere nicht in merklichem Umfange in dieses eingebettet sind. Hierzu ist es beispielsweise aus der US-A-38 33 793 bekannt, die einzelnen Wendelabschnitte der Heizwendel auf eine ebene Platte aus gebundenen Keramikfasern aufzulegen und mittels Metallklammern lagezusichern, welche an im Abstand voneinander liegenden Stellen der Heizwendel einen unteren Bogenabschnitt des Heizdrahtes übergreifen und durch die Platte aus Keramikfasern hindurch in das Wärmedämmaterial hineingesteckt sind. Eine solche mechanische Verankerung an in relativ großem Abstand voneinander liegenden Stellen ermöglicht jedoch Relativbewegungen der Wendelabschnitte zwischen den Verankerungspunkten, die sich überdies im Laufe der Zeit lockern können. Durch die tief im Wärmedämmaterial steckenden metallischen Klammern ergeben sich erhebliche Wärmebrücken, so daß bei gegebener Wärmedämmfähigkeit die Bauhöhe erheblich vergrößert werden muß.A maximization of the radiation is evidently achieved when the individual sections of the heating coil lie on a flat surface and thus apart from the essentially punctiform support points have no contact with the bearing material, in particular are not embedded to a noticeable extent in this. For this purpose, it is known, for example, from US-A-38 33 793 to place the individual coil sections of the heating coil on a flat plate made of bonded ceramic fibers and to secure them by means of metal clips which overlap and pass through a lower arc section of the heating wire at points of the heating coil which are spaced apart from one another the plate made of ceramic fibers are inserted into the thermal insulation material. Such mechanical anchoring at locations that are at a relatively large distance from one another, however, enables relative movements of the helical sections between the anchoring points, which can moreover loosen over time. The metal brackets inserted deep in the thermal insulation material result in considerable thermal bridges, so that, given the thermal insulation capacity, the overall height is considerably increased must become.

Ähnlich ist es aus der DE-A-27 29 930 bekannt, die Heizwendel auf eine ebene Keramikfaserplatte aufzulegen, die jedoch mit sternförmigen Erhebungen versehen ist. Die Wendelabschnitte werden dabei in die noch weichen Erhebungen der Keramikfaserplatte hineingedrückt, wenn die Fasermatte zur Bildung der Platte gepreßt wird, und sind nach Trocknung oder Aushärtung durch diese lokalen Einbettungen auf der ansonsten planen Oberfläche der Keramikfaserplatte verankert. Hierdurch sind zwar Wärmebrücken durch Metallklammern oder dergleichen vermieden, jedoch erfolgt ebenfalls eine Verankerung nur an in relativ grossen Abständen voneinander liegenden Stellen der Heizwendel; an diesen Stellen ist die Abstrahlung erheblich behindert, so daß die Anzahl der Verankerungspunkte relativ gering gehalten werden muß. Zwischen den Verankerungspunkten kommt es zu freien radialen Wärmedehnungsbewegungen, die entsprechende Kräfte in die Verankerungen einleiten, so daß diese im Laufe der Zeit gelockert werden können oder die Heizwendel ganz frei kommt.Similarly, it is known from DE-A-27 29 930 to place the heating coil on a flat ceramic fiber plate, which, however, is provided with star-shaped elevations. The spiral sections are pressed into the still soft elevations of the ceramic fiber plate when the fiber mat is pressed to form the plate, and are anchored to the otherwise flat surface of the ceramic fiber plate after drying or curing by means of these local embeddings. As a result, thermal bridges through metal clips or the like are avoided, but anchoring also only takes place at points of the heating coil which are at relatively large distances from one another; At these points, the radiation is significantly impeded, so that the number of anchor points must be kept relatively low. There are free radial thermal expansion movements between the anchoring points, which introduce appropriate forces into the anchors so that they can be loosened over time or the heating coil is completely free.

Um Relativbewegungen der Wendelabschnitte zueinander trotz der ständigen Temperaturwechsel zu vermeiden, ist es andererseits bekannt, die Heizwendel in Nuten der Lagerschicht zu lagern und dort zu verankern. So ist es aus der DE-A-27 28 776 bekannt, die Heizwendel in im Querschnitt halbkreisförmigen Nuten erheblich größeren Durchmessers zu lagern und hierzu in eine feuerfeste Klebemasse einzudrücken, welche die Lagernut ausfüllt, so daß die Heizwendel mit ihrer gesamten unteren Bogenhälfte eingebettet und nach entsprechender Trocknung und Aushärtung der Feuerfestmasse gewissermaßen einzementiert ist. Hierdurch sind jegliche Relativbewegungen zwischen den einzelnen Wendelabschnitten mit Gewißheit unterbunden. Jedoch ist auch die Nutzabstrahlung durch die Einbettung der Heizwendel bis auf halbe Höhe stark vermindert. Die bei Temperaturwechseln auftretenden Wärmedehnungen führen durch die Einbettung des gesamten unteren Bogens jeder Drahtwendel zu ganz erheblichen Spannungen, die zu einem allmählichen Lockern der Einbettung der Drahtwendel in der Feuerfestmasse und/oder einem Ausarbeiten der Nut durch die Feuerfestmasse führen.In order to avoid relative movements of the coil sections in spite of the constant temperature changes, it is known, on the other hand, to store the heating coil in grooves in the bearing layer and to anchor it there. Thus, it is known from DE-A-27 28 776 to store the heating coil in semicircular grooves of considerably larger diameter and for this purpose to press it into a refractory adhesive which fills the bearing groove, so that the heating coil is embedded with its entire lower half of the arch and after appropriate drying and hardening of the refractory mass is cemented to a certain extent. As a result, any relative movements between the individual spiral sections are prevented with certainty. However, the useful radiation is also greatly reduced by embedding the heating coil up to half the height. The thermal expansions that occur during temperature changes lead by embedding the entire lower arch of each wire coil to very considerable tensions, which lead to a gradual loosening of the embedding of the wire coil in the refractory mass and / or a working out of the groove by the refractory mass.

Letzteres ist bei einem Stand der Tecknik nach der EP-A-57 252 dadurch vermieden, daß die Oberfläche der Dämmschicht mit einer geschlossenflächigen Lagerschicht überzogen ist, die ein anorganisches temperaturbeständiges Bindemittel und einen anorganischen Füllstoff insbesondere in Form von gemahlenen Mineralfasern enthält. Hierdurch ist eine mechanisch stabile, durchgehende Lagerschicht gebildet, die auch die Bereiche zwischen den Nuten erfaßt und wie eine dünne stabile Platte wirkt. Die Wendelabschnitte der Heizwendel werden klebend in den Nuten befestigt.The latter is avoided in a Tecknik stand according to EP-A-57 252 in that the surface of the insulation layer is covered with a closed-surface bearing layer which contains an inorganic temperature-resistant binder and an inorganic filler, in particular in the form of ground mineral fibers. In this way, a mechanically stable, continuous bearing layer is formed, which also covers the areas between the grooves and acts like a thin, stable plate. The coil sections of the heating coil are adhesively attached in the grooves.

Bei der Aufnahme der Heizwendel in Nuten ist immer ein wesentlicher Teil der Außenoberfläche der Heizwendel abgedeckt und kann daher nur vermindert Nutzstrahlung erzeugen. Andererseits ergibt aber die Lagerung in Nuten, insbesondere wenn diese mit einem geschlossenflächigen harten Überzug ausgekleidet sind, eine saubere Lagesicherung. Umgekehrt läßt sich mit der Verankerung der Heizwendel auf einer ebenen Lagerschicht die Abstrahlung optimieren, jedoch läßt sich die Heizwendel auf einer solchen ebenen Lagerschicht im Hinblick auf die erheblichen Temperaturwechsel nicht bleibend sicher verankern.When the heating coil is received in grooves, a substantial part of the outer surface of the heating coil is always covered and can therefore only generate useful radiation to a reduced extent. On the other hand, however, the storage in grooves, especially if these are lined with a closed-surface hard coating, provides a clean positional securing. Conversely, the radiation can be optimized by anchoring the heating coil on a flat bearing layer, but the heating coil cannot be permanently anchored securely on such a flat bearing layer in view of the considerable temperature changes.

Es ist auch bereits versucht worden (EP-A-31 514 oder BE-A-464 026), die einzelnen Windungen der Heizwendel nur punktweise direkt im Material der Wärmedämmschicht zu verankern; dies führt jedoch bei Dämmaterial auf der Basis von Oxidaerogel, wie es im Rahmen der vorliegenden Erfindung verwendet werden soll, im Hinblick auf die geringe Bruchfestigkeit dieses Materials zu einer zu labilen Lagerung.Attempts have also already been made (EP-A-31 514 or BE-A-464 026) to anchor the individual turns of the heating coil only at certain points directly in the material of the thermal insulation layer; In the case of insulating material based on oxide airgel, as is to be used in the present invention, however, this leads to an unstable storage in view of the low breaking strength of this material.

Aus der EP-A-71 048 schließlich ist es bekannt, die Heizwendel an einer auf der eigentlichen Wärmedämmschicht angeordneten Lagerschicht ebenfalls auf der Basis des Materials der Dämmschicht, jedoch mit besonderer Anpassung an die Lagerungsfunktion zu befestigen. Die Anpassung an den Lagerungszweck kann in einem Härterzusatz des Materials der Lagerschicht, oder aber auch in einer Behandlung der Oberfläche der Lagerschicht mit wässrig aufgebrachtem Kieselsol bestehen. In dieser Lagerschicht aus behandeltem Dämmaterial wird die Heizwendel dadurch verankert, daß in Abständen einzelne Windungen der Wicklung verzogen und in das Dämmaterial der Lagerschicht tief eingedrückt werden, während die dazwischenliegenden Wicklungen der Heizwendel nur an der Oberfläche der Lagerschicht anliegen. Damit wird zwar die Abstrahlung von den ungestörten Wicklungen fast ungeschmälert erhalten, jedoch führt die tiefe Verankerung der verzogenen Windungen zu Wärmebrücken und die stark verminderte Wärmeabfuhr an den von behandeltem Dämmaterial umschlossenen verzogenen Windungen zu einem Wärmestau mit der Gefahr eines frühzeitigen Ausfalls der Heizwendel an diesen Stellen. Im Bereich zwischen den verzogenen Windungen fehlt eine wirksame Lagesicherung der Heizwendel. Die infolge der Aufnahme der verzogenen Windungen erhebliche Bauhöhe der gegenüber der darunterliegenden Dämmschicht schlechter wärmedämmenden Lagerschicht führt zu einer größeren Bauhöhe des Lagerkörpers für die Heizwendel, wenn eine bestimmte Wärmedämmfähigkeit erreicht werden muß.Finally, it is known from EP-A-71 048 to fasten the heating coil to a bearing layer arranged on the actual thermal insulation layer, also on the basis of the material of the insulating layer, but with special adaptation to the storage function. The adaptation to the storage purpose can consist in an addition of hardener to the material of the bearing layer, or else in a treatment of the surface of the bearing layer with aqueous silica sol. In this bearing layer made of treated insulating material, the heating coil is anchored in that individual turns of the winding are distorted at intervals and pressed deep into the insulating material of the bearing layer, while the intermediate windings of the heating coil lie only on the surface of the bearing layer. This means that the radiation from the undisturbed windings is almost undiminished, but the deep anchoring of the warped windings leads to thermal bridges and the greatly reduced heat dissipation from the warped windings enclosed by treated insulating material leads to heat accumulation with the risk of premature failure of the heating coil at these points . In the area between the warped turns there is no effective securing of the position of the heating coil. The considerable height due to the inclusion of the warped turns of the poorly insulating bearing layer compared to the underlying insulation layer leads to a greater height of the bearing body for the heating coil if a certain thermal insulation capacity has to be achieved.

Der Erfindung liegt die Aufgabe zugrunde, eine Heizvorrichtung der im Oberbegriff des Anspruchs 1 angegebenen Gattung zu schaffen, bei der die Heizwendel trotz der auftretenden extremen Temperaturwechsel dauerhaft sicher gelagert ist und gleichzeitig eine verbesserte, das heißt optimale Wärmeabstrahlung gewährleistet, wobei die Herstellung der Heizvorrichtung mit einem Minimum an Aufwand erfolgen soll und weiterhin auch größtmögliche Wärmedämmung bei geringstmöglicher Bauhöhe erzielt wird.The invention has for its object to provide a heating device of the type specified in the preamble of claim 1, in which the heating coil Despite the extreme temperature changes that occur, it is permanently securely stored and at the same time ensures improved, that is to say optimal, heat radiation, the manufacture of the heating device being carried out with a minimum of effort and, furthermore, the greatest possible thermal insulation with the lowest possible overall height being achieved.

Die Lösung dieser Aufgabe erfolgt durch die kennzeichnenden Merkmale des Anspruchs 1.This object is achieved by the characterizing features of claim 1.

Dadurch, daß die Oberfläche der Lagerschicht eben ausgebildet ist, entfällt eine Einbettung in Nuten oder dergleichen, welche eine Abstrahlung behindern könnten. Die erforderliche Verankerung ist gleichwohl dadurch gegeben, daß jeder einzelne Wendeldraht nur mit seinem unteren Bogenabschnitt im Material der Lagerschicht eingebettet ist, d. h. nur höchstens bis zu etwa der vollen Drahtstärke. Dies bedeutet, daß der Draht der Heizwendel quasi punktförmig nur im unteren Scheitelbereich des Bogenabschnittes in der Lagerschicht eingespannt ist, im übrigen aber auf seiner ganzen Länge frei zur Abstrahlung zur Verfügung steht. Diese geringe Verankerungstiefe reicht für eine sichere Verankerung aus, da jeder untere Bogenabschnitt des Wendeldrahtes auf diese Weise einzeln in der im Betrieb durch keramische Bindung züstatzlich verfestigenden Kieselsolschicht gehalten ist, und Wärmedehnungen ohne wesentliche Spannungen durch Expansionen im Bereich der oberen Bogenabschnitte der Heizwendel aufgenommen werden können. Hierdurch werden in zwei benachbarte Verankerungspunkte, zwischen denen lediglich ein einziger Ring des Wendeldrahtes liegt, allenfalls ganz geringe Biegespannungen eingeführt und so jegliche Lageänderungen der Heizwendel insgesamt, etwa im Sinne einer zu starken gegenseitigen Annäherung von Wendelabschnitten, vermieden.Because the surface of the bearing layer is flat, there is no need for embedding in grooves or the like, which could hinder radiation. The required anchoring is nevertheless given by the fact that each individual spiral wire is embedded in the material of the bearing layer only with its lower arch section, i. H. only at most up to about the full wire gauge. This means that the wire of the heating coil is clamped in a quasi-punctiform manner only in the lower apex region of the arch section in the bearing layer, but is otherwise freely available for radiation over its entire length. This low anchoring depth is sufficient for secure anchoring, since each lower arch section of the filament wire is thus individually held in the silica sol layer, which is additionally strengthened during operation by ceramic bonding, and thermal expansion can be absorbed without significant stresses due to expansions in the area of the upper arch sections of the heating coil . As a result, only very slight bending stresses are introduced into two adjacent anchoring points, between which there is only a single ring of the filament wire, and any changes in the position of the heating filament as a whole, for example in the sense of excessive mutual approximation of filament sections, are avoided.

Da - anders als bei einer Einbettung der Heizwendel in Nuten - das gesamte Wärmedämmaterial an der zu dämmenden Seite der Heizwendel angeordnet ist, entfaltet es volle Dämmwirkung zu der zu dämmenden Seite hin. Durch den Wegfall von Nuten oder sonstigen Vertiefungen kann das Material der Dämmschicht eben oder mit unkomplizierter Form gepreßt werden, so daß hierdurch Herstellungsaufwand vermindert wird. Die Lagerschicht braucht nur sehr geringe Schichtdicke, entsprechend der Drahtstärke der Heizwendel oder sogar weniger, besitzen und trägt somit zur Bauhöhe nur geringfügig bei. Da nur der im wesentlichen punktförmige Scheitelbereich des Wendeldrahtes eingebettet ist, kann das Material der Lagerschicht, etwa durch Zusatz von Trübungsmittel oder dergleichen, im Hinblick auf die Optimierung seines Beitrags zur Wärmedämmung ausgelegt werden, ohne daß nachteilige Wärmestaus zu befürchten sind. Da weiterhin das Material der Dämmschicht nicht mechanisch durch die Lagerung der Heizwendel beansprucht ist, kann es in seiner Konsistenz, insbesondere in seinem Verdichtungsgrad, ebenfalls hinsichtlich Wärmedämmgesichtspunkten optimiert werden, so daß sich insgesamt größtmögliche Wärmedämmung bei geringstmöglicher Bauhöhe ergibt.Since - unlike when the heating coil is embedded in grooves - the entire thermal insulation material is arranged on the side of the heating coil to be insulated, it unfolds fully Insulation effect to the side to be insulated. By eliminating grooves or other depressions, the material of the insulating layer can be pressed flat or with an uncomplicated shape, so that this reduces manufacturing costs. The bearing layer only needs to have a very small layer thickness, depending on the wire thickness of the heating coil or even less, and thus only makes a minor contribution to the overall height. Since only the essentially punctiform apex region of the helix wire is embedded, the material of the bearing layer can be designed, for example by adding opacifying agents or the like, with a view to optimizing its contribution to thermal insulation without fear of disadvantageous heat build-up. Furthermore, since the material of the insulation layer is not mechanically stressed by the storage of the heating coil, its consistency, in particular its degree of compression, can also be optimized with regard to thermal insulation aspects, so that overall the greatest possible thermal insulation results in the smallest possible height.

Die Unteransprüche haben vorteilhafte Weiterbildungen der Erfindung zum Inhalt.The dependent claims contain advantageous developments of the invention.

Beim erfindungsgemäßen Verfahren kann entweder die Lagerschicht als dünne Platte mit darauf verankerter Heizwendel vorgefertigt und anschließend - gegebenenfalls an einem anderen Ort - mit der ebenfalls plattenförmigen oder auch eingepreßten Dämmschicht vereinigt werden, oder aber es erfolgt eine Beschichtung unmittelbar der Dämmschicht mit dem Material der Lagerschicht mit nachfolgendem Eindrücken der Heizwendel, wobei dann auch ein Auflagering besonders vorteilhaft klebend mit dem Material der Lagerschicht verbunden werden kann.In the method according to the invention, either the bearing layer can be prefabricated as a thin plate with the heating coil anchored thereon and then - optionally at another location - combined with the likewise plate-shaped or also pressed-in insulation layer, or else there is a coating of the insulating layer directly with the material of the bearing layer with subsequent pressing in of the heating coil, in which case a support ring can also be bonded to the material of the bearing layer in a particularly advantageous manner.

In der Zeichnung ist eine Ausführungsform der Erfindung veranschaulicht.An embodiment of the invention is illustrated in the drawing.

Es zeigtIt shows

  • Fig. 1 einen Schnitt durch eine erfindungsgemäße Heizvorrichtung undFig. 1 shows a section through a heating device according to the invention and
  • Fig. 2 die Einzelheit aus Kreis II in Fig. 1 in stark vergrößerter Darstellung.Fig. 2 shows the detail from circle II in Fig. 1 in a greatly enlarged representation.

Die veranschaulichte Heizvorrichtung besteht im wesentlichen aus einer Aufnahmeschale 1 aus Metall, insbesondere Aluminiumblech, und Wärmedämmaterial in Form einer Wärmedämmschicht 2, welche an der Innenseite der Umfangswand 3 der Aufnahmeschale 1 zwischen deren Boden 4 und einer Heizwendel 5 angeordnet ist. Die elektrisch betriebene Heizwendel 5 weist nicht näher dargestellte elektrische Anschlüsse auf, die auf geeignete Weise aus dem Bereich der Aufnahmeschale 1 herausgeführt sind. Die dargestellte Heizvorrichtung dient zur Strahlungsbeheizung einer Glaskeramikabdeckung einer Kochplatte, wobei die nicht näher dargestellte Glaskeramikplatte auf einer Auflagefläche 10 aufliegt und damit Abstand vom oberen Rand der Umfangswand 3 der Aufnahmeschale 1 sowie von der Heizwendel 5 erhält. Die Umfangswand 3 der Aufnahmeschale 1 und damit die gesamte Heizvorrichtung hat in Draufsicht im wesentlichen Kreisform und liegt konzentrisch zu einer Mittelachse 9.The heating device shown consists essentially of a receptacle 1 made of metal, in particular aluminum sheet, and thermal insulation material in the form of a thermal barrier layer 2, which is arranged on the inside of the peripheral wall 3 of the receptacle 1 between the bottom 4 and a heating coil 5. The electrically operated heating coil 5 has electrical connections, not shown, which are led out of the area of the receiving shell 1 in a suitable manner. The heating device shown is used for radiant heating of a glass ceramic cover of a hotplate, the glass ceramic plate (not shown in detail) resting on a support surface 10 and thus being kept at a distance from the upper edge of the peripheral wall 3 of the receiving shell 1 and from the heating coil 5. The peripheral wall 3 of the receiving shell 1 and thus the entire heating device has an essentially circular shape in plan view and is concentric with a central axis 9.

Die Dämmschicht 2 besteht aus feinporigem Kieselsäureaerogel mit Zuschlagstoffen. Dieses Material ist an sich bekannt und weist neben dem Kieselsäureaerogel in aller Regel eine Mineralfaserverstärkung und/oder ein Trübungsmittel und/oder ein Bindemittel als Härter auf; hinsichtlich Einzelheiten Wird auf die einschlägigen DE-OSen 27 47 663, 27 48 307, 27 54 956 und 31 08 816 verwiesen, auf die insoweit ausdrücklich Bezug genommen wird. Bevorzugt wird ein Material für die Dämmschicht 2 verwendet, welches aus 30 bis 50 Gew.-% pyrogener Kieselsäure, 20 bis 50 Gew.-% Trübungsmittel und 5 bis 15 Gew.-% Aluminiumfasern besteht sowie in einem Raumgewicht von 200 bis 400 kg/m³ vorliegt, jedoch nicht organisch oder anorganisch gehärtet zu sein braucht. Ein solches Spezial-Wärmedämmaterial besitzt eine Wärmeleitfähigkeit, die geringer ist als diejenige ruhender Luft, und ist darüber hinaus nur wenig temperaturabhängig. Allerdings sind die aus derartigen pulverförmigen Grundstoffen gepreßten Platten oder Schichten mechanisch wenig widerstandsfähig. Anstelle von Kieselsäureaerogel kann das Material auch Aluminiumoxid-Aerogel aufweisen, oder eine geeignete Mischung beider Aerogele, um bei Bedarf höhere Temperaturbeständigkeit zu erreichen. Zur weiteren Erhöhung der Temperaturbeständigkeit kann das Dämmaterial der Dämmschicht 2 Zuschläge an hochtemperaturbeständigen Stoffen wie Manganoxid, Zirkonoxid oder Titanoxid enthalten. Für Spezialzwecke kann auch mit deren Aerogelen gearbeitet werden.The insulation layer 2 consists of fine-pored silica airgel with additives. This material is known per se and shows in addition to the silica airgel in all Rule a mineral fiber reinforcement and / or an opacifier and / or a binder as a hardener; Regarding details, reference is made to the relevant DE-OSen 27 47 663, 27 48 307, 27 54 956 and 31 08 816, to which reference is expressly made in this regard. A material is preferably used for the insulation layer 2, which consists of 30 to 50% by weight of pyrogenic silica, 20 to 50% by weight of opacifying agent and 5 to 15% by weight of aluminum fibers and in a density of 200 to 400 kg / m³ is present, but does not need to be organic or inorganic hardened. Such a special thermal insulation material has a thermal conductivity that is lower than that of still air and, moreover, is only slightly temperature-dependent. However, the plates or layers pressed from such powdery base materials are not mechanically resistant. Instead of silica airgel, the material can also contain aluminum oxide airgel, or a suitable mixture of both aerogels, in order to achieve higher temperature resistance if required. To further increase the temperature resistance, the insulation material of the insulation layer can contain 2 additions of high temperature resistant materials such as manganese oxide, zirconium oxide or titanium oxide. For special purposes you can also work with their airgel.

Auf der Dämmschicht 2 ist eine Lagerschicht 7 angeordnet, die eine Dicke von etwa 1 mm oder wenig mehr haben kann. Im Beispielsfalle möge die Lagerschicht 7 aus einem Stoffgemisch bestehen, welches mineralische Fasern und ein keramisches Bindemittel enthält, das bei Temperaturen zwischen etwa 500°C und 1000°C durch keramische Bindung verfestigt. Der Anteil an mineralischen Fasen sollte möglichst hoch sein, da die mineralischen Fasern einer Tendenz der Lagerschicht 7 zum Schrumpfen bei erhöhten Temperaturen entgegenwirken. Daher sollten die mineralischen Fasern in einem Anteil von über 50 Gew.-% am trockenen Gemisch enthalten sein, vorzugsweise jedoch mit einem noch höheren Anteil von 75 bis 95 Gew.-%, wobei im Beispielsfalle ein Anteil von etwa 80 Gew.-% gewählt sein möge. Die mineralischen Fasern besitzen einen Erweichungs- bzw. Schmelzpunkt von über 1000°C, vorzugsweise von über 1100°C, sind also gegenüber den im Betrieb auftretenden Temperaturen beständig. Eine solche Einstellung des Erweichungs-oder Schmelzpunktes der Fasern gelingt einerseits über die Wahl einer bestimmten Partikelgröße, wobei größere Partikel später erweichen und sintern als kleinere pulverartige Partikel, sowie über die Wahl der Zuschlagstoffe oder Flußmittel zusätzlich zum Aluminiumoxid- oder Siliziumoxid-Hauptbestandteil der Mineralfasern. Die Mineralfasern werden aus der Schmelze mit einer Dicke zwischen etwa 0,5 und 3 µm, vorzugsweise zwischen 1 und 2 µm gezogen und anschließend gemahlen, so daß sie auf Längen zwischen 2 und 20 µm, vorzugsweise zwischen 5 und 10 µm gebrochen werden, wobei jedoch in jedem Falle die Länge der Mineralfasern deren Dicke um wenigstens das Doppelte übersteigt, so daß tatsächlich noch ein Fasercharakter vorliegt. Unter Berücksichtigung dieser Faserabmessungen können sodann die Zusatzstoffe wie Flußmittel in der Schmelze zur Herstellung der Fasern, wie Na₂O, B₂O₃, MgO, Fe₂O₃ und andere, an sich bekannte Zuschlagstoffe so gewählt werden, daß sich die gewünschte Temperaturbeständigkeit bis in Bereiche über 1000°C oder über 1100°C ergibt, also in Bereiche, in denen die Mineralfasern auf Aluminium-Silikat-Basis bei der im Betrieb auftretenden Maximaltemperatur nicht erweichen oder erschmelzen.A bearing layer 7 is arranged on the insulation layer 2 and can have a thickness of approximately 1 mm or a little more. In the example, the bearing layer 7 may consist of a mixture of materials that contains mineral fibers and a ceramic binder that solidifies at temperatures between about 500 ° C. and 1000 ° C. by ceramic bonding. The proportion of mineral bevels should be as high as possible, since the mineral fibers counteract a tendency of the bearing layer 7 to shrink at elevated temperatures. Therefore, the mineral Fibers are present in a proportion of more than 50% by weight of the dry mixture, but preferably in an even higher proportion of 75 to 95% by weight, a proportion of approximately 80% by weight being selected in the example. The mineral fibers have a softening or melting point of over 1000 ° C, preferably over 1100 ° C, so they are resistant to the temperatures that occur during operation. Such adjustment of the softening or melting point of the fibers is achieved on the one hand by choosing a certain particle size, larger particles softening and sintering later than smaller powder-like particles, and by choosing the additives or fluxes in addition to the main aluminum oxide or silicon oxide component of the mineral fibers. The mineral fibers are drawn from the melt with a thickness between about 0.5 and 3 microns, preferably between 1 and 2 microns and then ground so that they are broken to lengths between 2 and 20 microns, preferably between 5 and 10 microns, whereby however in any case the length of the mineral fibers whose thickness exceeds at least twice, so that there is actually still a fiber character. Taking into account these fiber dimensions, the additives such as flux in the melt for the production of the fibers, such as Na₂O, B₂O₃, MgO, Fe₂O₃ and other additives known per se, can then be selected so that the desired temperature resistance up to ranges above 1000 ° C or results in over 1100 ° C, i.e. in areas in which the mineral fibers based on aluminum silicate do not soften or melt at the maximum temperature occurring during operation.

Das keramische Bindemittel ist Kieselsol, wie dies beispielsweise für eine Beschichtung eines derartigen Materials aus der EP-A-81 825 an sich bekannt ist. Das Kieselsol als keramisches Bindemittel wird zusammen mit anorganischen Fasern wie Aluminiumsilikatfasern oder Quarzfasern sowie gegebenenfalls weiteren anorganischen Füllstoffen in einer Aufschlämmung aufgebracht. Als anorganische Fasern für die Beschichtungsmasse kommen grundsätzlich alle entsprechend temperaturbeständigen Fasern wie Aluminiumsilikatfasern, Quarzfasern usw. in Frage, wobei jedoch Aluminiumsilikatfasern aus Kostengründen in der Regel bevorzugt sein werden. Die Fasern müssen so eng beieinanderliegen, daß das Kieselsol dazwischen eine Verbindung zu benachbarten Fasern bildet und an diesen haftet, statt eigene, nicht an Füllstoff gebundene Partikel zu bilden. Die Fasern wirken somit primär als Dispergierungsmittel für das Kieselsol, um mit diesem eine geschlossene Oberfläche zu bilden.The ceramic binder is silica sol, as is known per se for example for coating such a material from EP-A-81 825. The silica sol as a ceramic binder is used together with inorganic fibers such as aluminum silicate fibers or quartz fibers and optionally other inorganic fillers applied in a slurry. Suitable inorganic fibers for the coating material are in principle all correspondingly temperature-resistant fibers such as aluminum silicate fibers, quartz fibers, etc., but aluminum silicate fibers are generally preferred for reasons of cost. The fibers must be so close together that the silica sol forms a connection between them and adheres to neighboring fibers instead of forming their own particles that are not bound to the filler. The fibers thus primarily act as a dispersing agent for the silica sol in order to form a closed surface with it.

Auch Aluminiumsilikatfasern sind jedoch noch teurer als die meisten anorganischen körnigen Zuschlagstoffe wie gemahlenes Aluminiumoxid, Quarzsand, Mullit, Zirkonoxid usw., so daß diese Fasern aus Kostengründen durch körnige Füllstoffe gestreckt werden können, die ähnlich wie die Fasern, wenn auch in geringerem Umfange, als Dispergierungsmittel für das Kieselsol dienen können. Als anorganische körnige Zuschlagstoffe kommen weiterhin Tone und Kaolin in Frage. Bevorzugt ist Aluminiumoxid gegebenenfalls mit einer Zumischung aus Kaolin, welches die Geschmeidigkeit der Lagerschicht 7 verbessert.However, aluminum silicate fibers are even more expensive than most inorganic granular additives such as ground aluminum oxide, quartz sand, mullite, zirconium oxide, etc., so that these fibers can be stretched by granular fillers which are similar to the fibers, albeit to a lesser extent, than for cost reasons Dispersants can serve for the silica sol. Clays and kaolin continue to be considered as inorganic granular additives. Aluminum oxide, optionally with an admixture of kaolin, is preferred, which improves the suppleness of the bearing layer 7.

Die Menge an Kieselsol ergibt sich im wesentlichen aus dem Bedarf an Bindemittel für die geschlossene Oberflächenbeschichtung im Hinblick auf die gewünschte Verbackung der Füllstoffe miteinander. Die Menge des Kieselsol hat eine Untergrenze dort, wo sich eine zu geringe Abriebfestigkeit der Oberfläche durch zu geringen Bindemittelanteil ergibt. Aus diesem Gesichtspunkt darf der Anteil des Kieselsol als Feststoff nicht geringer sein als etwa ein Zehntel der damit zu bindenden Füllstoffe und Fasern in der Oberflächenbeschichtung, so daß das Kieselsol in der geschlossenen Oberflächenbeschichtung jedenfalls in einem Feststoffanteil von 10 Gew.-% oder mehr vorliegt. Eine Erhöhung des Kieselsolanteils ergibt zunächst eine Erhöhung der Abriebfestigkeit durch bessere Einbindung der Fasern und der körnigen Füllstoffe sowie weiterhin eine glänzende und glattere Oberfläche. Eine Obergrenze für den Kieselsolanteil in der geschlossenen Oberflächenbeschichtung liegt da, wo das Kieselsol dazu neigt, sich in körniger Form zu partikulieren und auf diese Weise brüchig zu werden. Dies wird durch einen ausreichend hohen Füllstoff-, insbesondere Fasergehalt des Kieselsol vermieden. Daher darf der Anteil des Kieselsol bezogen auf die Menge der Füllstoffe in der Beschichtungsmasse nur etwa bei 1:1 liegen, so daß also mindestens ebenso viele Gewichtsanteile Füllstoffe wie Trockengewichtsanteile Kieselsol in der geschlossenen Lagerschicht 7 vorhanden sind. Hierbei sollte jedoch der Anteil der in Faserform vorliegenden Füllstoffe nicht unter einem Drittel der Füllstoffe der Lagerschicht 7 liegen, um die Fasern ausreichend als Netzwerkbildner zur Bildung eines geschlossenen Films wirksam werden zu lassen.The amount of silica sol essentially results from the need for binders for the closed surface coating with regard to the desired caking of the fillers with one another. The amount of the silica sol has a lower limit where the abrasion resistance of the surface is too low due to the binder content being too low. From this point of view, the proportion of the silica sol as a solid must not be less than about one tenth of the fillers and fibers to be bound therewith in the surface coating, so that the silica sol in the closed surface coating is present in any case in a solids content of 10% by weight or more. An increase in the proportion of silica sol initially gives one Increased abrasion resistance through better integration of the fibers and granular fillers as well as a shiny and smooth surface. There is an upper limit for the silica sol content in the closed surface coating where the silica sol tends to particulate in a granular form and thus become brittle. This is avoided by a sufficiently high filler, in particular fiber, content of the silica sol. Therefore, the proportion of the silica sol based on the amount of fillers in the coating composition may only be approximately 1: 1, so that at least as many parts by weight of fillers as dry parts by weight of silica sol are present in the closed storage layer 7. Here, however, the proportion of the fillers present in fiber form should not be less than a third of the fillers of the bearing layer 7 in order to allow the fibers to act sufficiently as network formers to form a closed film.

Die vorstehenden Angaben beziehen sich auf die Gewichtsanteile in der fertigen Lagerschicht 7, wobei also die Trockenmasse des Kieselsol berücksichtigt ist. Das wässrige Kieselsol, also die kolloidale Kieselsäure, besitzt jedoch einen Wasseranteil von zwischen 60 und 70 Gew.-%, der gegebenenfalls zusammen mit einer zusätzlichen Wasserzugabe zur Verdünnung dazu dient, durch Einstellung der Viskosität oder allgemein des Fließverhaltens das Bindemittel mit den Füllstoffen zu vermischen und einen geschlossenen Auftrag zu ermöglichen. Dies kann unterstützt werden durch eine Zugabe von Netzmitteln, wie dies an sich bekannt ist, wobei natürlich auch eine mechanische Unterstützung durch Rakeln oder Walzen in Frage kommt.The above information relates to the proportions by weight in the finished bearing layer 7, so that the dry mass of the silica sol is taken into account. However, the aqueous silica sol, i.e. the colloidal silica, has a water content of between 60 and 70% by weight, which if necessary together with an additional addition of water serves for dilution by mixing the binder with the fillers by adjusting the viscosity or generally the flow behavior and enable a closed order. This can be supported by adding wetting agents, as is known per se, although mechanical support by doctor blades or rollers is of course also possible.

Nachfolgend werden vier Beispiele für eine solche Überzugsmasse angegeben:Four examples of such a coating composition are given below:

Beispiel 1example 1

58,8 Gew.-% wässriges Kieselsol (30 % Feststoffanteil)
23,5 Gew.-% Aluminiumsilikatfasern
11,8 Gew.-% Aluminiumoxid
5,9 Gew.-% Kaolin58.8% by weight aqueous silica sol (30% solids content)
23.5% by weight aluminum silicate fibers
11.8 wt% alumina
5.9% by weight kaolin

Nach Herausrechnung des Wasseranteils der kolloidalen Kieselsäure der obigen Masse ergibt sich eine Feststoffverteilung in der Lagerschicht 7 von etwa 30 Gew.-% Kieselsol, 40 Gew-% Aluminiumsilikatfasern, 20 Gew.-% Aluminiumoxid und 10 Gew.-% Kaolin.After deducting the water content of the colloidal silica of the above mass, there is a solids distribution in the bearing layer 7 of approximately 30% by weight of silica sol, 40% by weight of aluminum silicate fibers, 20% by weight of aluminum oxide and 10% by weight of kaolin.

Beispiel 2Example 2

70,0 Gew.-% wässriges Kieselsol (30 % Feststoffanteil)
13,3 Gew.-% Aluminiumsilikatfasern
6,7 Gew.-% Aluminiumoxid
10,0 Gew.-% Kaolin70.0% by weight aqueous silica sol (30% solids content)
13.3% by weight aluminum silicate fibers
6.7% by weight of aluminum oxide
10.0% by weight kaolin

Nach Herausrechnung des Wasseranteils der kolloidalen Kieselsäure der vorstehenden Masse ergibt sich eine Feststoffverteilung von etwa 41 Gew.-% Kieselsol, 26 Gew-% Aluminiumsilikatfasern, 13 Gew.-% Aluminiumoxid und 20 Gew.-% Kaolin.After calculating the water content of the colloidal silica of the above mass, a solids distribution of about 41% by weight of silica sol, 26% by weight of aluminum silicate fibers, 13% by weight of aluminum oxide and 20% by weight of kaolin results.

Beispiel 3Example 3

48,97 Gew.-% wässriges Kieselsol (30 % Feststoffanteil)
25,53 Gew.-% Aluminiumsilikatfasern
12,75 Gew.-% Aluminiumoxid
12,75 Gew.-% Ton48.97% by weight aqueous silica sol (30% solids content)
25.53% by weight aluminum silicate fibers
12.75 wt% alumina
12.75 wt% clay

Nach Herausrechnung des Wasseranteils der kolloidalen Kieselsäure der vorstehenden Masse ergibt sich eine Feststoffverteilung von etwa 23 Gew.-% Kieselsol, 39 Gew.-% Aluminiumsilikatfasern, 19 Gew.-% Aluminiumoxid und 19 Gew.-% Ton.After calculating the water content of the colloidal silica of the above mass, a solids distribution of about 23% by weight of silica sol, 39% by weight of aluminum silicate fibers, 19% by weight of aluminum oxide and 19% by weight of clay is obtained.

Beispiel 4Example 4

48,94 Gew.-% wässriges Kieselsol (30 % Feststoffanteil)
44,66 Gew.-% Aluminiumsilikatfasern
6,40 Gew.-% Ton48.94% by weight aqueous silica sol (30% solids content)
44.66% by weight aluminum silicate fibers
6.40% by weight of clay

Nach Herausrechnung des Wasseranteils der kolloidalen Kieselsäure der obigen Masse ergibt sich eine Feststoffverteilung von etwa 22 Gew.-% Kieselsol, 69 Gew.-% Aluminiumsilikatfasern und 9 Gew.-% Ton.After calculating the water content of the colloidal silica of the above mass, a solids distribution of about 22% by weight of silica sol, 69% by weight of aluminum silicate fibers and 9% by weight of clay is obtained.

Die Massen werden feucht mit einer der Art der Aufbringung durch Spritzen, Rakeln, Streichen, Tauchen, Siebdruck oder dergleichen entsprechenden flüssigen bis pastenartigen Konsistenz aufgebracht. Die Heizwendel 5 ist in der gewünschten Form zuvor spannungsfrei geglüht worden und wird so vorbehandelt mittels eines Magneten mit einer Temperatur von beispielsweise 200°C aufgenommen und in die noch feuchte Lagerschicht 7 eingedrückt. Die Eindrückung erfolgt dabei bevorzugt nur soweit, bis etwa zwei Drittel der Drahtstärke des unteren Bogenabschnittes jedes Wendelringes in die Masse eintaucht, wobei infolge der erhöhten Temperatur der Heizwendel bereits beim Einpressen eine gewisse Verfestigung der Masse und so eine Anheftung der Heizwendel erfolgt. Bei Bedarf kann der Masse auch ein geringer Anteil an organischen Zuschlagstoffen zur Erzielung einer Klebewirkung beigefügt werden. Bei Betrieb der Heizwendel keramisiert das Material dann unter der Wärmeeinwirkung vollständig aus und zementiert den eingebetteten Bogenabschnitt der Heizwendel gewissermaßen ein. Wie ohne weiteres ersichtlich ist, ergibt sich eine besonders gute Haltewirkung dann, wenn der untere Bogenabschnitt der Heizwendel über mehr als die Hälfte der Drahtstärke eintaucht, da dann beim Aushärten der Masse durch die oberen hintergreifenden Oberflächenschichten der Masse eine formschlüssige Halterung erfolgt. Andererseits sollte die Eintauchtiefe so gering wie möglich gehalten werden, um die Abstrahlung möglichst wenig zu behindern. Daher ergibt sich die in Fig. 2 dargestellte Eintauchtiefe von etwa 2/3 der Drahtstärke als optimal.The masses are applied moist with a liquid to paste-like consistency corresponding to the type of application by spraying, knife coating, brushing, dipping, screen printing or the like. The heating coil 5 has previously been stress-free annealed in the desired shape and is thus pretreated by means of a magnet with a temperature of, for example, 200 ° C. and pressed into the still moist bearing layer 7. The indentation is preferably only carried out until about two thirds of the wire thickness of the lower arc section of each helix ring is immersed in the mass, due to the increased temperature of the heating coil, a certain solidification of the mass already occurs during the pressing in and thus the heating coil is attached. If necessary, a small proportion of organic additives can be added to the mass to achieve an adhesive effect. When the heating coil is in operation, the material then ceramizes completely under the action of heat and cementes the embedded arch section of the heating coil to a certain extent. As can easily be seen, there is a particularly good holding effect when the lower arc section of the heating coil is immersed by more than half the wire thickness, since then when the mass hardens, a positive locking takes place through the upper, engaging surface layers of the mass. On the other hand, the immersion depth should be kept as low as possible to minimize the radiation to hinder. The immersion depth of approximately 2/3 of the wire thickness shown in FIG. 2 is therefore optimal.

Der radial äußere Umfangsbereich 6 der Aufnahmeschale 1 bzw. der Dämmschicht 2 und damit auch der Lagerschicht 7 ist im Beispielsfalle in der dargestellten Weise nach oben hin abgekröpft, so daß die Heizvorrichtung insgesamt im Querschnitt etwa tellerförmiges Aussehen erhält. Auf den abgekröpften Umfangsbereich 6 ist ein Auflagering 8 aus gebundenen Fasern, etwa einem Material, wie es unter der Bezeichnung Fiberfrax (eintr. Warenzeichen) im Handel ist, aufgesetzt, und bildet mit der oberen Auflagefläche 10 in der bereits geschilderten Weise die Abstützung zur Unterseite der Glaskeramikplatte.The radially outer peripheral region 6 of the receiving shell 1 or the insulating layer 2 and thus also the bearing layer 7 is bent upwards in the example shown in the example, so that the heating device as a whole has an approximately plate-like appearance in cross section. A support ring 8 made of bonded fibers, for example a material such as that sold under the name Fiberfrax (registered trademark), is placed on the cranked peripheral region 6 and forms the support to the underside with the upper support surface 10 in the manner already described the glass ceramic plate.

Die Herstellung der Heizvorrichtung kann auf verschiedene Weise erfolgen. So kann zunächst das Material der Dämmschicht 2 in an sich bekannter Weise gegen den Boden 4 der Aufnahmeschale 1 verpreßt werden und somit als verdichtete Dämmschicht 2 direkt über dem Boden 4 der Aufnahmeschale 1 ausgebildet werden. Sodann kann die Masse zur Bildung der Lagerschicht 7 durch Spritzen, Streichen oder dergleichen auf die Oberfläche der so gebildeten Dämmschicht 2 aufgebracht und die Heizwendel eingedrückt werden. Dann kann zweckmäßig auch der Auflagering 8 aufgesetzt werden, solange die Masse zur Bildung der Lagerschicht 7 noch feucht ist, und so durch Haftung gehalten werden. In einem solchen Falle wird die veranschaulichte Heizvorrichtung entweder einstufig oder - mit Unterbrechung und gegebenenfalls Ortswechsel nach dem Einpressen der Dämmschicht 2 - zweistufig vollständig vorgefertigt.The heater can be manufactured in various ways. First of all, the material of the insulating layer 2 can be pressed against the bottom 4 of the receiving shell 1 in a manner known per se and can thus be formed as a compressed insulating layer 2 directly above the bottom 4 of the receiving shell 1. The mass for forming the bearing layer 7 can then be applied to the surface of the insulating layer 2 formed in this way by spraying, brushing or the like, and the heating coil can be pressed in. Then the support ring 8 can also be expediently placed as long as the mass for forming the bearing layer 7 is still moist, and is thus held in place by adhesion. In such a case, the illustrated heating device is either prefabricated in one stage or - with an interruption and, if necessary, a change of location after the insulation layer 2 has been pressed in - in two stages.

Alternativ kann die Dämmschicht 2 auch als Platte vorgefertigt und so vorgepreßt und vorgefertigt in die Aufnahmeschale 1 eingesetzt werden. Auch in diesem Falle kann, ohne Anwesenheit der Aufnahmeschale 1, die Ausbildung der Lagerschicht 7, deren Bestückung mit der Heizwendel 5 und gegebenenfalls dem Auflagering 8 in der vorstehend geschilderten Weise erfolgen.Alternatively, the insulation layer 2 can also be prefabricated as a plate and thus pre-pressed and prefabricated into the receiving shell 1. In this case too, without the presence of the receiving shell 1, the formation of the bearing layer 7, the fitting thereof with the heating coil 5 and possibly the bearing ring 8 in the above described manner.

Es kann jedoch auch die Lagerschicht 7 separat vorgefertigt und mit der Heizwendel 5, gegebenenfalls auch mit dem Auflagering 8 bestückt und so getrocknet bzw. gehärtet werden. Diese Montageeinheit kann dann anschließend zusammen mit einer separat vorgefertigten plattenförmigen Dämmschicht 2 in eine Aufnahmeschale 1 eingesetzt werden, oder in eine Aufnahmeschale 1 mit eingepreßter Dämmschicht 2 eingesetzt werden.However, the bearing layer 7 can also be prefabricated separately and fitted with the heating coil 5, optionally also with the support ring 8, and thus dried or hardened. This assembly unit can then be used together with a separately prefabricated plate-shaped insulating layer 2 in a receiving shell 1, or in a receiving shell 1 with pressed-in insulating layer 2.

Die erfindungsgemäße Heizvorrichtung läßt somit eine Vielzahl von Fertigungsmöglichkeiten mit großer Freizügigkeit bezüglich der Fertigungsorte zu. Dabei gestaltet sich die Fertigung in jedem Falle einfach und problemlos, zumal auch Aufwand zur Herstellung von Nuten im Hinblick auf die erfindungsgemäß ebene Ausbildung der Oberfläche der Lagerschicht 7 entfallen kann.The heating device according to the invention thus allows a large number of manufacturing options with great freedom of movement with regard to the manufacturing locations. The production is in any case simple and problem-free, especially since the effort to produce grooves can also be dispensed with in view of the planar design of the surface of the bearing layer 7 according to the invention.

Da in jedem Falle die Heizwendel 5 auf der Lagerschicht 7 montiert und verankert wird, bevor der Auflagering 8 aufgebracht werden muß, eignet sich die Fuge zwischen der Unterseite des Auflageringes 8 und der dortigen Lagerschicht 7 besonders gut für die Durchführung der elektrischen Anschlüsse der Heizwendel 5. In jedem Falle kann bei Bedarf unmittelbar nach Einbettung der Heizwendel 5 eine Aufheizung bis auf eine gewünschte Temperatur erfolgen, so daß jedenfalls in den lokalen Lagerbereichen eine ausreichende Trocknung und Härtung der Masse für die Lagerschicht 7 erfolgt.Since in each case the heating coil 5 is mounted and anchored on the bearing layer 7 before the bearing ring 8 has to be applied, the joint between the underside of the bearing ring 8 and the bearing layer 7 there is particularly suitable for making the electrical connections of the heating coil 5 In any case, if necessary, heating up to a desired temperature can take place immediately after embedding the heating coil 5, so that in any case sufficient drying and hardening of the mass for the bearing layer 7 takes place in the local storage areas.

In der Lagerschicht 7 können weiterhin mineralische Pigmente enthalten sein, und zwar insbesondere in Form von TiO₂ oder TiO₂-haltigen Stoffen. Die mineralischen Pigmente, die nicht unbedingt erforderlich sind, dienen dazu, bereits einen Teil der IR-Strahlung zu streuen oder zu reflektieren sowie die Abriebfestigkeit zu erhöhen. Als TiO₂-haltiger Stoff kann beispielsweise ein Gemisch aus Al₂O₃ und TiO₂ gewählt werden, wobei das TiO₂ neben seiner Funktion als Pigment auch als Trübungsmittel gegenüber IR-Strahlung dient. Weitere Beispiele für geeignete Pigmente sind etwa Rutil, Ilmenit, Eisenoxid, Chromoxid und dergleichen. Es genügt, wenn die mineralischen Pigmente in einem Anteil von bis zu maximal etwa 20 Gew.-% des Trockengemisches, vorzugsweise jedoch in einem geringeren Anteil als 10 Gew.-% in der Lagerschicht 7 enthalten sind. Im Beispielsfalle möge die Lagerschicht 7 5 Gew.-% mineralische Pigmente in Form von TiO₂ enthalten. Eine Verwendung von Pigmenten bzw. Trübungsmitteln in der Lagerschicht 7 ist deshalb relativ problemlos möglich, weil infolge der nur ganz geringfügigen Einbettung des Wendeldrahtes ein merklicher Wärmestau nicht zu befürchten ist.Mineral pigments may also be present in the bearing layer 7, in particular in the form of TiO₂ or TiO₂-containing substances. The mineral pigments, which are not absolutely necessary, serve to scatter or reflect part of the IR radiation and to increase the abrasion resistance. As a TiO₂-containing substance, for example, a mixture of Al₂O₃ and TiO₂ can be chosen, the TiO₂ serving as a pigment and also as an opacifier against IR radiation. Other examples of suitable pigments include rutile, ilmenite, iron oxide, chromium oxide and the like. It is sufficient if the mineral pigments are present in the storage layer 7 in a proportion of up to a maximum of about 20% by weight of the dry mixture, but preferably in a proportion less than 10% by weight. In the example, the storage layer may contain 7 5 wt .-% mineral pigments in the form of TiO₂. The use of pigments or opacifiers in the bearing layer 7 is therefore possible relatively easily because, due to the very slight embedding of the helix wire, there is no fear of a noticeable build-up of heat.

Claims (9)

  1. Heating device, especially for a radiantly heated hot plate

    with a heating spiral (5) operated by electric current and

    with a supporting arrangement for the heating spiral (5),
    - with a supporting layer (7) applied with a closed surface and having a flat surface and
    - with an insulating layer (2), arranged on the side of the supporting layer (7) opposite the heating spiral (5) and based on a microporous oxide aerogel, especially one of silicon and/or aluminium obtained by flame pyrolysis, especially with mineral fibre reinforcement and/or opacifier, which is arranged together with the supporting layer (7) and the heating spiral (5) in a mounting dish (1) fastened to the underside of the hot plate,

    characterized in that

    the supporting layer (7) has an inorganic temperature-resistant binder as base material together with inorganic fillers which are applied with the base material in a suspension to the insulating layer,

    the inorganic binder, which consolidates at temperatures between about 500 °C and 1000 °C by ceramic bonding, is silica sol, which is included at a ratio to the inorganic fillers of not more than 1:1 and not less than 1:9, the inorganic fillers being inorganic fibres, in a fraction of preferably at least one-third, and the remainder granular fillers, and

    that each arc-shaped portion of the heating spiral (5) facing the supporting layer (7) is embedded to not more than about the full wire thickness of the heating spiral (5) in the material of the supporting layer (7) in such a way that the heating spiral (5) is secured along its entire length against excursions in the direction of the surface extension of the supporting layer (7) and held by adhesion to the supporting layer (7).
  2. Heating device according to Claim 1, characterized in that the supporting layer (7) contains mineral pigments.
  3. Heating device according to Claim 2, characterized by TiO₂ or TiO₂-containing substances as mineral pigments.
  4. Heating device according to Claim 2 or 3, characterized in that the content of mineral pigments is up to 20 weight %, and preferably up to 10 weight %, of the dry mixture.
  5. Heating device according to one of Claims 1 to 4, characterized in that the supporting layer (7) has a thickness of about 1 mm or a little more.
  6. Heating device according to one of Claims 1 to 5, characterized that the depth of immersion of the spiral wire of the heating spiral (5) is more than half the wire thickness, and especially about 2/3 of the wire thickness.
  7. Process for the production of a heating device according to one of Claims 1 to 6, characterized in that the composition for forming the supporting layer is applied to a base and the preformed and stress-free annealed heating spiral, is impressed, preferably while still hot, into the still moist composition of the supporting layer.
  8. Process according to Claim 7, characterized in that the supporting layer is subsequently dried or hardened and after removal of its base is made available as a prefabricated component with a heating spiral anchored to it.
  9. Process according to Claim 7, characterized in that the compacted insulating layer is used as the base, and to the still moist composition of the supporting layer there are attached by adhesion other attachments such as a circumferential supporting ring.
EP86100466A 1985-01-25 1986-01-15 Heating device, especially for a cooking plate heated by radiation, and its manufacturing process Revoked EP0189108B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86100466T ATE65150T1 (en) 1985-01-25 1986-01-15 HEATING DEVICE, IN PARTICULAR FOR A RADIANT-HEATED COOKING PLATE, AND PROCESS FOR THEIR MANUFACTURE.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3502497 1985-01-25
DE19853502497 DE3502497A1 (en) 1985-01-25 1985-01-25 HEATING DEVICE, ESPECIALLY FOR A RADIATED HEATING COOKING PLATE, AND METHOD FOR THE PRODUCTION THEREOF

Publications (2)

Publication Number Publication Date
EP0189108A1 EP0189108A1 (en) 1986-07-30
EP0189108B1 true EP0189108B1 (en) 1991-07-10

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP86100466A Revoked EP0189108B1 (en) 1985-01-25 1986-01-15 Heating device, especially for a cooking plate heated by radiation, and its manufacturing process

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EP (1) EP0189108B1 (en)
AT (1) ATE65150T1 (en)
DE (2) DE3502497A1 (en)

Families Citing this family (3)

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Publication number Priority date Publication date Assignee Title
DE4028743A1 (en) * 1990-09-11 1992-03-12 Miele & Cie OVEN WITH A MUFFLE
DE4331702A1 (en) * 1993-09-17 1995-03-23 Wacker Chemie Gmbh Radiant heater, in particular for heating a glass ceramic hotplate
GB2324693A (en) * 1997-04-12 1998-10-28 Ceramaspeed Ltd Vapour barrier in a radiant electric heater

Citations (4)

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DE2729930A1 (en) * 1977-07-02 1979-01-11 Karl Fischer Radiation heater for glass ceramic cooker hob - has insulating ring with rebate and base plate holding support plate for heating element
EP0031514A1 (en) * 1979-12-14 1981-07-08 E.G.O. Elektro-Geräte Blanc u. Fischer Electric heating radiator, and process and apparatus for its manufacture
EP0041203A1 (en) * 1980-05-29 1981-12-09 Grünzweig + Hartmann und Glasfaser AG Arrangement for the thermally insulated accommodation of an electrical helical heating element, in particular for a cooking plate heated by radiation and method for its manufacture
EP0071048A1 (en) * 1981-07-24 1983-02-09 E.G.O. Elektro-Geräte Blanc u. Fischer Radiant electric heating element and method of manufacturing the same

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GB1433478A (en) * 1972-08-05 1976-04-28 Mcwilliams J A Electrical heating apparatus
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DE3102935A1 (en) * 1981-01-29 1982-09-02 Grünzweig + Hartmann und Glasfaser AG, 6700 Ludwigshafen DEVICE FOR THE HEAT-INSULATING STORAGE OF AN ELECTRIC HEATER, IN PARTICULAR FOR A RADIATION-HEATED COOKING PLATE, AND A HEAT-INSULATING PLATE THEREFOR AND METHOD FOR THE PRODUCTION THEREOF
DE3144661A1 (en) * 1981-11-10 1983-05-19 Wacker-Chemie GmbH, 8000 München HEATING PLATE
EP0105968B1 (en) * 1982-10-20 1987-03-18 Elpag Ag Chur Electric heating device for ranges or cooking plates
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Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2729930A1 (en) * 1977-07-02 1979-01-11 Karl Fischer Radiation heater for glass ceramic cooker hob - has insulating ring with rebate and base plate holding support plate for heating element
EP0031514A1 (en) * 1979-12-14 1981-07-08 E.G.O. Elektro-Geräte Blanc u. Fischer Electric heating radiator, and process and apparatus for its manufacture
EP0041203A1 (en) * 1980-05-29 1981-12-09 Grünzweig + Hartmann und Glasfaser AG Arrangement for the thermally insulated accommodation of an electrical helical heating element, in particular for a cooking plate heated by radiation and method for its manufacture
EP0071048A1 (en) * 1981-07-24 1983-02-09 E.G.O. Elektro-Geräte Blanc u. Fischer Radiant electric heating element and method of manufacturing the same

Also Published As

Publication number Publication date
DE3680120D1 (en) 1991-08-14
DE3502497A1 (en) 1986-07-31
EP0189108A1 (en) 1986-07-30
ATE65150T1 (en) 1991-07-15

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