Classifications

• • 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
• • 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
  • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
  • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
  • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
  • H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds
• • 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
• • 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

Definitions

• the invention relates to a ceramic hob with a hotplate made of glass ceramic or glass, with an electrical heating conductor layer, with an insulating layer between the hotplate and the heating conductor layer, and with an electrically conductive intermediate layer between the hotplate and the insulating layer.
• Such a ceramic hob is known from DE 31 05 065 C2 and from US 6 037 572.
• the hotplate according to DE 31 05 065 C2 consists of glass ceramic, on the underside of which a metallic layer is applied, for example by a spraying process, on which in turn a ceramic insulating layer is also applied by a spraying process, on which a heating conductor element is finally vapor-deposited or in a spraying process is applied.
• glass ceramics used for hobs have an NTC characteristic, i.e. the electrical conductivity increases noticeably as the temperature rises.
• NTC characteristic i.e. the electrical conductivity increases noticeably as the temperature rises.
• an electrical insulation layer is therefore a prerequisite for operating such a cooking system.
• the system must have a dielectric strength of 3,750 volts at operating temperatures.
• dielectric strength can be reduced if, according to DE 31 05 065 C2 or according to US 6 037 572, an electrically conductive layer is applied between the insulating layer and the hotplate, which is earthed. In such a case, a dielectric strength of around 1500 volts is sufficient for the ceramic insulation layer to ensure the necessary operational safety in accordance with VDE.
• the layer thickness of the ceramic insulating layer can be significantly reduced, which causes problems. be reduced due to the different thermal expansions.
• the invention is therefore based on the object of improving a ceramic cooktop in accordance with the type mentioned at the outset in such a way that the operational safety of the ceramic cooktop is improved and good long-term stability in rough everyday operation is ensured.
• the intermediate layer is a thermally sprayed layer made of an electrically conductive ceramic or of a cermet.
• the intermediate layer By forming the intermediate layer in the form of an electrically conductive ceramic, a considerably better adaptation of the coefficient of expansion of the intermediate layer to the coefficient of expansion of the hotplate is achieved, which is almost zero, since the coefficient of expansion of suitable ceramic materials is significantly lower than the coefficient of expansion of metals. Even when using a As a result of the ceramic particles embedded in a metallic matrix, the cermet layer has a reduced thermal expansion, as a result of which the thermal stresses are reduced.
• an electrically conductive ceramic as an intermediate layer has the further advantage that the ceramic can be better matched to the glass ceramic of the hotplate in terms of the choice of material, with particularly good adhesion and low thermal stresses in use being able to be achieved through a targeted choice of material.
• the intermediate layer is an oxide layer which is electrically conductive due to the loss of oxygen during thermal spraying.
• the intermediate layer can in particular be made of Ti0 2 , from a mixture of Al 2 0 3 with a Ti0 2 content of at least 50% by weight, preferably at least 90% by weight, of Zr0 2 , from a mixture of Al 2 0 3 with Zr0 2 with a proportion of Zr0 2 of at least 50% by weight, preferably of at least 90% by weight, from a mixture of Ti0 2 and Zr0 2 , or from a mixture of Al 2 0 3 with Ti0 2 and Zr0 2 with a proportion of at least 50% by weight, preferably at least 90% by weight, of Ti0 2 and Zr0 2 (be prepared.
• These intermediate layers made of Ti0 2 from a mixture of Al 2 0 3 with a Ti0 2 content of at least 50% by weight, preferably at least 90% by weight, of Zr0 2 , from a mixture of Al 2 0 3 with Zr0 2 with a proportion of Zr0 2 of at least 50% by weight, preferably of at least 90% by weight, of Ti0 2 and
• Ti0 2 _ x For example, for Ti0 2 _ x with x - 0.1, a volume conductivity of about 10 3 ohm x cm to about 5 x 10 2 ohm x cm (at room temperature) results. As a result of the relatively low thermal expansion of Ti0 2 _ x and the particularly good affinity of Ti0 2 _ x for glass ceramics, Ti0 2 _ x appears to be particularly suitable for use as a conductive intermediate layer.
• the intermediate layer can also be produced from a cermet with a metal matrix.
• the metal matrix preferably has at least one of the constituents nickel, cobalt and chromium.
• the intermediate layer is made of a cermet with a metal matrix, which is an alloy of the main components nickel, cobalt and chromium.
• a metal matrix which is an alloy of the main components nickel, cobalt and chromium.
• particles of carbide such as tungsten carbide, chromium carbide or the like, can also be embedded in the metal matrix.
• the intermediate layer there is good electrical conductivity of the intermediate layer, and at the same time the thermal expansion coefficient is considerably reduced compared to a pure metal matrix due to the ceramic inclusions.
• the metal matrix in question also has good adhesion to a glass ceramic surface and, owing to the increased ductility, is suitable for absorbing or reducing certain thermal stresses which occur during operation.
• a ceramic adhesion promoter layer is provided between the electrically conductive intermediate layer and the hotplate.
• This adhesion promoter layer preferably consists of aluminum oxide, titanium oxide or mixtures thereof and is preferably applied by thermal spraying.
• an adhesion promoter layer leads to a further improvement in adhesion to the glass ceramic surface, resulting overall in an extremely stable layer composite which has very good temperature resistance and resistance to temperature changes.
• the insulating layer which is applied to the intermediate layer preferably consists of cordierite or mullite and is preferably applied by thermal spraying.
• the use of these ceramics to produce the insulating layer has the advantage of a relatively low coefficient of thermal expansion which is between approximately 4.3 and 5.0 ⁇ 10 " 6 K -1 for mullite and between approximately 2.2 and 2.4 x 10 " 6 K _1 for cordierite. As a result of the low coefficient of thermal expansion, there are lower stresses in connection with the hotplate made of glass ceramic.
• Fig. 1 shows a cross section through an inventive ceramic hob in a first embodiment
• Fig. 2 shows a cross section through an inventive ceramic hob in a modified version compared to FIG. 1.
• a ceramic hob according to the invention is shown in cross section and generally designated by the number 10.
• the ceramic cooktop comprises a cooking plate 12 of glass ceramics, for example, from ceramic ®.
• This hotplate 12 is used to hold cooking vessels.
• a hotplate is generated at different locations. For household purposes, typically four or possibly five hotplates are provided on a ceramic hob. Only one hotplate is shown in FIGS. 1 and 2.
• An intermediate layer of TiO 2 was applied to the underside of the hotplate 12 by thermal spraying. This can be done, for example, by atmospheric plasma spraying (APS) with a layer thickness of approximately 50-250 ⁇ m.
• APS atmospheric plasma spraying
• the respective layers are preferably applied only in the area of the respective hotplates in order to keep the total voltages as low as possible.
• the glass ceramic is cleaned, e.g. degreased with acetone.
• the pretreatment by sandblasting, which is otherwise customary in thermal spraying, is dispensed with, since this would damage the glass ceramic.
• an insulating layer 16 which preferably consists of cordierite (2MgO »2Al 2 0 3 « 5Si0 2 ) or mullite (3Al 2 0 3 «2Si0 2 ), is sprayed onto it again by atmospheric plasma spraying.
• the layer thickness of the insulating layer 16 depends on the desired dielectric strength and the material used and is between approximately 100 and 500 ⁇ m, preferably between approximately 150 and 300 ⁇ m.
• the heating conductor 20 can be applied, for example, in a known manner by a screen printing process, the flow temperatures during the baking of the layers being able to be reduced by a glassy fraction of usually more than 5% in such a way that baking temperatures between about 500 and 850 ° C. result, a dense, closed conductor layer is created.
• the heating conductor layer 18 can also be produced by thermal spraying.
• the part not to be coated is first masked using a customary masking method and then the exposed parts are coated with the heating conductor material by thermal spraying.
• the part previously covered can then be removed, so that a winding heating conductor 20 is formed, the individual heating conductor tracks of which are insulated from one another.
• FIG. 2 A modification of the ceramic cooktop is shown in FIG. 2 and generally designated by the number 10 '.
• this intermediate layer 14 ′ which is a cermet layer, is separated by an adhesion promoter layer 24 sprayed onto the hotplate 12.
• the adhesion promoter layer 24 preferably consists of Al 2 0 3 or a mixture of Al 2 0 3 and Ti0 2 , for example 97% by weight Al 2 0 3 and 3% by weight Ti0 2 .
• the adhesion promoter layer 24 is thermally sprayed with a layer thickness of approximately 10 to 150 ⁇ m, preferably by APS. The preferred layer thickness is on the order of approximately 30 to 100 ⁇ m.
• a cermet layer consisting of a nickel / cobalt / chromium alloy with embedded carbide particles (tungsten carbide, chromium carbide etc.) is then sprayed onto the adhesion promoter layer 24.
• the intermediate layer 14 ' is produced with a layer thickness of approximately 50 to 250 ⁇ m, preferably approximately 50 to 100 ⁇ m.
• the insulating layer 16 and the heat conductor layer 18 are then applied in the manner already described with reference to FIG. 1.
• the individual layers lying one above the other gradually run out at the edge region and thus continuously pass to the layer below them.
• the total area of the individual layers decreases toward the heating conductor layer. This results in favorable stress conditions in the edge regions of the respective layers in order to counteract delamination of the layers.
• annular depression 26 which surrounds the intermediate layer 14 in an annular manner at the edge region thereof.
• This slight depression allows stresses that arise between the hotplate 12 and the intermediate layer 14 to be absorbed and partially reduced.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Coating By Spraying Or Casting (AREA)
• Cookers (AREA)
• Baking, Grill, Roasting (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)
• Inorganic Insulating Materials (AREA)
• Devices For Post-Treatments, Processing, Supply, Discharge, And Other Processes (AREA)

Priority Applications (1)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

Country Status (8)

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• 2001
  • 2001-03-06 DE DE10112235A patent/DE10112235C2/de not_active Expired - Fee Related
• 2002
  • 2002-02-20 AT AT02702359T patent/ATE284123T1/de not_active IP Right Cessation
  • 2002-02-20 CN CNA028059999A patent/CN1494816A/zh active Pending
  • 2002-02-20 CA CA002439177A patent/CA2439177A1/fr not_active Abandoned
  • 2002-02-20 ES ES02702359T patent/ES2232733T3/es not_active Expired - Lifetime
  • 2002-02-20 EP EP02702359A patent/EP1366641B1/fr not_active Expired - Lifetime
  • 2002-02-20 WO PCT/EP2002/001751 patent/WO2002078397A1/fr not_active Application Discontinuation
  • 2002-02-20 DE DE50201676T patent/DE50201676D1/de not_active Expired - Fee Related
• 2003
  • 2003-08-25 US US10/647,806 patent/US20040104212A1/en not_active Abandoned

Non-Patent Citations (1)

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