EP2695482A1 - Method for producing a resistance heating element, and resistance heating element - Google Patents

Method for producing a resistance heating element, and resistance heating element

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Publication number
EP2695482A1
EP2695482A1 EP12713138.1A EP12713138A EP2695482A1 EP 2695482 A1 EP2695482 A1 EP 2695482A1 EP 12713138 A EP12713138 A EP 12713138A EP 2695482 A1 EP2695482 A1 EP 2695482A1
Authority
EP
European Patent Office
Prior art keywords
heating element
resistance heating
shaped body
powder
sintered material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP12713138.1A
Other languages
German (de)
French (fr)
Inventor
Gotthard Nauditt
Roland Weiss
Jeremias SCHÖNFELD
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Schunk Kohlenstofftechnik GmbH
Original Assignee
Schunk Kohlenstofftechnik GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Schunk Kohlenstofftechnik GmbH filed Critical Schunk Kohlenstofftechnik GmbH
Publication of EP2695482A1 publication Critical patent/EP2695482A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/30—Apparatus or processes specially adapted for manufacturing resistors adapted for baking
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
    • C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/62605—Treating the starting powders individually or as mixtures
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/52—Multiple coating or impregnating multiple coating or impregnating with the same composition or with compositions only differing in the concentration of the constituents, is classified as single coating or impregnation
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/89—Coating or impregnation for obtaining at least two superposed coatings having different compositions
    • C04B41/90—Coating or impregnation for obtaining at least two superposed coatings having different compositions at least one coating being a metal
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • 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
    • H05B3/40—Heating elements having the shape of rods or tubes
    • H05B3/42—Heating elements having the shape of rods or tubes non-flexible
    • 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
    • H05B3/62—Heating elements specially adapted for furnaces
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/604—Pressing at temperatures other than sintering temperatures
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/612—Machining
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/72—Products characterised by the absence or the low content of specific components, e.g. alkali metal free alumina ceramics
    • C04B2235/728—Silicon content
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/94—Products characterised by their shape
    • 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 method for producing a resistance heating element having the features of claim 1 and to a resistance heating element having the features of claim 16.
  • Resistance heating elements are regularly used as heating elements for thermal analysis in so-called D SC furnaces (differential scanning calorimetry furnaces).
  • the known resistance heating elements are therefore tubular and integrally formed and are contacted on their underside at an anode and a cathode or pads.
  • One wall of the resistance heating element is provided with two slots which are formed spirally and thus form heating coils of the resistance heating element.
  • a temperature of up to 1650 ° C is reached.
  • a glow pattern should be distributed as homogeneously as possible over the area of the heating coils.
  • a high purity of the material of the resistance heating element is of great importance, as for example in a determination of the purity of samples in the D SC furnace Unwanted unwanted additives out of the resistance heating element and could falsify a measurement.
  • the known resistance heating elements are essentially formed of silicon carbide.
  • a resistance heating element is manufactured by forming a material blank of a fiber material, such as carbon fibers, its shape stabilization by means of resin with final pyrolysis and infiltration of silicon in order to obtain a resistance heating element made of silicon carbide.
  • cracks can result in particular by an inhomogeneous distribution of silicon in the molded body.
  • a reduced stability in the operating state sSullivan of the resistance heating element is effected, since there is an uneven temperature distribution in the resistance heating by the inhomogeneous material concentrations.
  • Operating temperature is limited to about 1400 ° C.
  • the present invention is therefore based on the object to propose a method for producing a resistance heating element or a resistance heating element, which avoids the disadvantages known from the prior art.
  • This object is achieved by a method having the features of claim 1 and a resistance heating element having the features of claim 16.
  • the resistance heating element has a tubular shape, wherein the resistance heating element is formed integrally and wherein the resistance heating element is formed from silicon carbide, the method comprising the following steps:
  • the one-piece molded body is pressed from a sintered material formed from a powder, it is possible to form moldings almost j eder shape, which have a substantially uniform distribution of the sintered material within the molding. This can avoid that undesired material concentrations occur within the shaped body, which promotes crack formation during the production of the resistance heating element or during operation. It is also possible to produce the molded article comparatively inexpensively, since the formation of the shaped article of sintered material can be carried out relatively easily. Furthermore, a reduced rejection reduces possible rejects during production, which also contributes to a reduction in costs.
  • the resistance heating element thus produced contains substantially no free silicon, which makes it particularly suitable for use at over 1400 ° C.
  • the shaped body of sintered material can be formed by isostatic pressing of the powder.
  • isostatic pressing the powder is placed in a mold envelope, for example in a tubular shape, and subjected to pressure in a liquid medium. Due to the liquid medium, the pressure spreads evenly over the surface of the mold shell, resulting in a uniform compression of the powder.
  • a pressure in the mechanical pressing may be 2000 bar or more.
  • the molding can also be formed by semi-static pressing of the powder, that is to say parts of the molding or of the molding are then covered and are not subjected to pressure.
  • the mold envelope or the powder to be pressed may be arranged around a mandrel, wherein ends of the mandrel each have an annular web.
  • the powder can then be easily placed between the annular lands on the mandrel and covered with a flexible mold envelope. It is also conceivable to form the molded body so already in his from closing shape.
  • the shaped body of sintered material can also be formed by die pressing of the powder. Both tubular shaped bodies can be formed by axial die pressing of the sintered material as well as plate-shaped shaped bodies.
  • the annealing of the pressed shaped body made of sintered material can take place under a protective atmosphere.
  • the annealing at, for example, 50 to 600 ° C leads to a hardening of the molding.
  • the protective atmosphere may be formed by an inert gas or a vacuum.
  • the shaped body of sintered material can be formed plate-shaped in a particularly simple embodiment. This can then be made a flat, straight resistance heating.
  • the molded body of sintered material may have a round tube cross-section.
  • the shaped body, the desired shape of the Wider- Stand heating element have. It is also conceivable that it is then possible to dispense with mechanical processing of the shaped body in the further production process.
  • a circular pipe cross-section can be formed, since a seamless molded body can then be easily formed on a mandrel. In principle, however, the molded body can have any desired tubular shape.
  • the shaped body of sintered material has a homogeneous distribution of powder. That is, within the material of the molded body then exist no significant density differences. Thus, an undesirable material accumulation of, for example, silicon between particle structures consisting of silicon carbide can be avoided. Cracking due to inhomogeneities can thus be avoided. Furthermore, a homogeneous powder mixture can be formed. Then there are no significant differences in a distribution within the material of the molding or no areas with accumulations of certain materials. Good mixing of the powder can be achieved, for example, with an Eirich mixer. A homogeneous powder mixture causes the same strength properties at each point of the material of the shaped body and thus avoids the formation of cracks.
  • the powder can be sieved prior to pressing. Screening of the powder may, among other things, effect an improved mixing of the powder.
  • a binder can be used.
  • a binder or a so-called precursor can be a polymer which is crosslinked by applying a temperature and can thus fix the powder in the form of the shaped body.
  • a Silicon carbide precursor are used, of which remains after the implementation of the manufacturing process only silicon carbide in the material of the resistive sheizelements.
  • the sintered material may be formed of the materials phenol resin, furan resin, formadehyde resin, epoxies, silicon carbide, silicon, graphite, carbon black, polysilazanes, polycarbosilanes, polysiloxanes, polycarbosilazanes or molybdenum disilizate, or combinations of such powders.
  • the phenolic resin may also be in powder or liquid form.
  • stearic acid may be mixed as a lubricant and to prevent oxidation of the powder or sintered material.
  • a powder mixture of silicon carbide, silicon, carbon and polycarbosilanes can be used.
  • a mechanical processing of the shaped body can take place, wherein a closing shape of the resistance heating element can be formed by the mechanical processing.
  • an inner diameter of the shaped body further drilled or turned and a cylinder or outer diameter are ground on, for example, a lathe, so that a uniform wall thickness of the shaped body of example, up to 1 mm is formed.
  • the method can thus also allow the production of filigree heating coils.
  • helical slots can be milled in the shaped body thus processed, such that a later heating coil of the resistance heating element is formed.
  • the slots can be formed as bridges bridging, which ensure stability of the molded body during the manufacturing process. These webs can be easily severed after formation of the resistance heating and thus removed.
  • a high-temperature treatment of the resistance heating element can take place. Sintering may take place in a tempera- range of 13 50 to 1900 ° C and the high-temperature treatment in a temperature range of 1900 to 2400 ° C are performed.
  • the high-temperature treatment can serve, inter alia, for the decomposition of oxygen and nitrogen in the molding and be carried out under vacuum or inert gas. By means of the high-temperature treatment, dimensional deviations of the shaped body caused in particular by the process steps can be minimized.
  • a CVD coating (chemical vapor deposition) of the resistance heating element with silicon carbide can take place.
  • CVD coating is applied to the resistance heating element at, for example, 700 to 1500 C 0, a silicon carbide layer. Essentially, the silicon carbide layer completely surrounds the resistance heating element, so that any silicon that is included in the material of the resistance heating element can not escape from it.
  • a particularly good contacting of the resistance heating element with connection contacts can be achieved if, after the sintering or the CVD coating, coating surfaces of the resistance heating element are coated by means of flame spraying.
  • the pads can be so provided with an electrically good contactable aluminum layer.
  • Aluminum can be well processed by means of flame spraying and does not melt away from it during operation of the resistance heating element.
  • the resistance heating element according to the invention has a basically arbitrary shape, wherein the resistance heating element is integrally formed, wherein the resistance heating element is formed of silicon carbide, and wherein the resistance heating element has a homogeneous microstructure or a homogeneous distribution of silicon carbide.
  • the homogeneous microstructure of silicon carbide within the Material structure of the resistance heating element causes a probability of cracking during operation of the resistance heating element is minimized.
  • an operating safety of the resistance heating element can be substantially increased.
  • the resistance heating element has a tubular shape.
  • the silicon carbide in the material of the resistance heating element can be structured in accordance with a particle orientation of a powder.
  • Fig. 1 A perspective view of a resistance heating element
  • FIG. 2 shows a flow chart for an embodiment of the method.
  • Fig. 1 shows a resistance heating element 1 0, which is tubular, formed with a round, circular cross-section.
  • the resistance heating element 10 has a thin tube wall 1 1, which is broken through two slots 12 and 13.
  • the slits 12 and 13 are straight in the region of a lower end 14 of the resistance heating element 10 in the longitudinal direction thereof and thus form two connection surfaces 1 5 and 16 for connecting the resistance heating element 10 to connection contacts of a connection device of a D SC furnace not shown here.
  • the slots 12 and 13 extend in each case in a spiral shape Longitudinal along the circumference of the pipe wall 1 1 up to an upper end of the resistance heating element 10 10.
  • the slots 12 and 13 thus form two heating coil 19 and 20, the cut at the upper end 1 8 in a Ringab 21 are interconnected.
  • a heating of the resistance heating element 10 during operation s occurs essentially in the area of the heating coil 19 and 20.
  • the resistance heating element is integrally formed and consists essentially of silicon carbide, within the material of the resistance heating element 10 production-related residual amounts of silicon, carbon and other materials to be involved can .
  • a surface 22 of the resistance heating element 10 is almost completely coated with silicon carbide, wherein in the region of the connection surfaces 1 5 and 16 a layer of aluminum, not shown here, is applied.
  • Fig. 2 shows a possible flowchart of an embodiment of the method.
  • a mixing and sieving of various powdered sintered materials such as silicon carbide, silicon, carbon, polymers, such as polysilazanes, polycarbosilazanes, polycarbosilanes, polysiloxanes, or other prepolymers such as phenolic resin, polyinides, polyfurans, etc. and.
  • This powder mixture is arranged around a round mandrel, so that a tubular shaped body is formed.
  • the powder mixture is covered by a mold shell and pressed semiiso static, so that it comes to a compaction of the powder mixture.
  • the shaped body thus formed is annealed at about 400 ° C and cured so that a mechanical processing of the shaped article can be carried out by grinding on a lathe.
  • An inner and an outer diameter of the tubular, round shaped body is thereby processed so that the shaped body has a substantially uniform wall thickness of 3 mm. Further, slots for the formation of heating coils and pads in the pipe wall of the molded body are milled. Finally, a pyrolysis of the material of the molding at 850 to 1200 ° C, in which the material is partially converted to carbon, and sintering of the molded article at 1650 to 1900 ° C, wherein the shaped body is formed into the resistance heating element.
  • the resistance heating element essentially consists now of silicon carbide. After sintering, an optional high-temperature treatment and a coating of the connection surfaces with aluminum by flame spraying follow.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Structural Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electromagnetism (AREA)
  • Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Resistance Heating (AREA)
  • Ceramic Products (AREA)

Abstract

The invention relates to a method for producing a resistance heating element and to a resistance heating element (10), wherein the resistance heating element has a tubular shape, wherein the resistance heating element is formed in one piece, wherein the resistance heating element is made of silicon carbide, comprising at least the following steps: forming a one-piece molded body from a powder of a sintered material, wherein the powder is pressed; tempering the pressed molded body; pyrolyzing the material of the molded body; and sintering the molded body, wherein the molded body is formed into the resistance heating element.

Description

Verfahren zur Herstellung eines Widerstandsheizelements sowie  Method for producing a resistance heating element as well
Widerstandsheizelement  resistance
Die Erfindung betrifft ein Verfahren zur Herstellung eines Widerstandsheizelements mit den Merkmalen des Anspruchs 1 sowie ein Widerstandsheizelement mit den Merkmalen des Anspruchs 16. The invention relates to a method for producing a resistance heating element having the features of claim 1 and to a resistance heating element having the features of claim 16.
Widerstandsheizelemente werden regelmäßig als Heizelemente für eine thermische Analyse in sogenannten D SC-Öfen eingesetzt (Dynamische- Differenzkalorimetrie Öfen) . Die bekannten Widerstandsheizelemente sind daher rohrförmig und einstückig ausgebildet und werden an ihrer Unterseite an einer Anode und einer Kathode bzw. Anschlussflächen kontaktiert. Eine Wandung des Widerstandsheizelements ist mit zwei Schlitzen versehen, die spiralförmig ausgebildet sind und so Heizwendeln des Widerstandsheizelements ausbilden. Im Bereich der Heizwendeln des Widerstandsheizelements wird eine Temperatur von bis zu 1650°C erreicht. Dabei soll ein Glühbild möglichst homogen über den Bereich der Heizwendeln verteilt sein. Weiter ist eine hohe Reinheit des Materials des Widerstandsheizelements von großer Wichtigkeit, da beispielsweise bei einer Reinheitsbestimmung von Proben im D SC-Ofen unerwünschte Zusatzstoffe aus dem Widerstandsheizelement herausdiffundieren und eine Messung verfälschen könnten. Resistance heating elements are regularly used as heating elements for thermal analysis in so-called D SC furnaces (differential scanning calorimetry furnaces). The known resistance heating elements are therefore tubular and integrally formed and are contacted on their underside at an anode and a cathode or pads. One wall of the resistance heating element is provided with two slots which are formed spirally and thus form heating coils of the resistance heating element. In the area of the heating coils of the resistance heating element a temperature of up to 1650 ° C is reached. In this case, a glow pattern should be distributed as homogeneously as possible over the area of the heating coils. Furthermore, a high purity of the material of the resistance heating element is of great importance, as for example in a determination of the purity of samples in the D SC furnace Unwanted unwanted additives out of the resistance heating element and could falsify a measurement.
Die bekannten Widerstandsheizelemente sind im Wesentlichen aus Siliziumcarbid gebildet. Eine Herstellung eines Widerstandsheizelements erfolgt durch eine Ausbildung eines Materialrohlings aus einem Faserwerkstoff, wie zum B eispiel Kohlenstofffasern, dessen Formstabilisierung mittels Harz mit abschließender Pyrolyse sowie einen Infiltration von Silizium, um ein Widerstandsheizelement aus Siliziumcarbid zu erhalten. Auch können sich Risse durch insbesondere eine inhomogene Verteilung von Silizium im Formkörper ergeben . Dadurch wird auch eine verminderte Stabilität im Betrieb szustand des Widerstandsheizelements bewirkt, da es zu einer ungleichen Temperaturverteilung im Widerstandsheizelement durch die inhomogenen Materialkonzentrationen kommt. Weiter ist es bekannt, einen zylindrischen Formkörper zur Ausbildung eines Si SiC-Widerstandsheizelements durch ein Schlickerverfahren auszubilden. Dabei muss, um eine gewünschte Heizwendelstruktur auszubilden, ein im S chlickerverfahren ausgebildeter Grünkörper bearbeitet werden. Eine geringe Festigkeit des Grünkörpers schränkt dabei die B earbeitungsmöglichkeiten erheblich ein, so dass durch das Schlickerverfahren keine vergleichswei se filigranen Heizwendeln hergestellt werden können. Ein weiterer Nachteil des bekannten Verfahrens stellt das freie Silizium des mit diesem Verfahren hergestellten Widerstandsheizelements dar, da durch das freie Silizium, welches aus dem Widerstandsheizelement herausdiffundieren kann, eine maximale The known resistance heating elements are essentially formed of silicon carbide. A resistance heating element is manufactured by forming a material blank of a fiber material, such as carbon fibers, its shape stabilization by means of resin with final pyrolysis and infiltration of silicon in order to obtain a resistance heating element made of silicon carbide. Also, cracks can result in particular by an inhomogeneous distribution of silicon in the molded body. As a result, a reduced stability in the operating state szustand of the resistance heating element is effected, since there is an uneven temperature distribution in the resistance heating by the inhomogeneous material concentrations. Further, it is known to form a cylindrical shaped body for forming a Si SiC resistance heating element by a slurry method. In this case, in order to form a desired heating coil structure, a green body formed in the slickering process must be processed. A low strength of the green body thereby considerably restricts the processing possibilities, so that no comparatively filigree heating coils can be produced by the slip process. Another disadvantage of the known method is the free silicon of the resistance heating element produced by this method, since a maximum through the free silicon, which can diffuse out of the resistance heating
Einsatztemperatur auf ca. 1400°C beschränkt ist. Operating temperature is limited to about 1400 ° C.
Der vorliegenden Erfindung liegt daher die Aufgabe zu Grunde, ein Verfahren zur Herstellung eines Widerstandsheizelements bzw. ein Widerstandsheizelement vorzuschlagen, welches die aus dem Stand der Technik bekannten Nachteile vermeidet. Diese Aufgabe wird durch ein Verfahren mit den Merkmalen des Anspruchs 1 und ein Widerstandsheizelement mit den Merkmalen des Anspruchs 16 gelöst. The present invention is therefore based on the object to propose a method for producing a resistance heating element or a resistance heating element, which avoids the disadvantages known from the prior art. This object is achieved by a method having the features of claim 1 and a resistance heating element having the features of claim 16.
Bei dem erfindungsgemäßen Verfahren zur Herstellung eines Wider- Standsheizelements, weist das Widerstandsheizelement eine rohrförmige Gestalt auf, wobei das Widerstandsheizelement einstückig ausgebildet ist und wobei das Widerstandsheizelement aus Siliziumcarbid gebildet ist, wobei das Verfahren folgende Schritte umfasst : In the inventive method for producing a resistive heating element, the resistance heating element has a tubular shape, wherein the resistance heating element is formed integrally and wherein the resistance heating element is formed from silicon carbide, the method comprising the following steps:
Ausbildung eines einstückigen Formkörpers aus einem Pulver ei- nes Sinterwerkstoffes, wobei das Pulver gepresst wird, Forming a one-piece shaped body from a powder of a sintered material, wherein the powder is pressed,
Glühen des gepressten Formkörpers, Annealing the pressed molding,
- Pyrolyse der Werkstoffe des Formkörpers, Pyrolysis of the materials of the shaped body,
Sintern des Formkörpers, wobei der Formkörper zu dem Widerstandsheizelement ausgebildet wird. Insbesondere dadurch, dass der einstückige Formkörper aus einem aus einem Pulver gebildeten Sinterwerkstoff gepresst wird, wird es möglich Formkörper nahezu j eder Gestalt auszubilden, die eine im Wesentlichen gleichmäßige Verteilung des Sinterwerkstoffes innerhalb des Formkörpers aufweisen. Dadurch kann vermieden werden, dass es zu uner- wünschten Materialkonzentrationen innerhalb des Formkörpers kommt, welche eine Rissbildung bei der Herstellung des Widerstandsheizelements bzw. während des B etrieb s begünstigt. Auch wird es so möglich den Formkörper vergleichsweise kostengünstig herzustellen, da die Ausbildung des Formkörpers aus Sinterwerkstoff relativ einfach durch- geführt werden kann. Weiter wird durch eine verminderte Ri ssbildung ein möglicher Ausschuss bei der Herstellung verringert, was ebenfalls zu einer Kostensenkung beiträgt. Weiter enthält das so hergestellte Widerstandsheizelement im Wesentlichen kein freies Silizium, wodurch es sich für eine Verwendung bei über 1400°C besonders gut eignet. Der Formkörper aus Sinterwerkstoff kann durch isostatisches Pressen des Pulvers gebildet werden. Beim isostatischen Pressen, wird das Pulver in einer Formhülle, beispielsweise in einer rohrförmigen Gestalt, angeordnet und in einem flüssigen Medium einem Druck ausgesetzt. Bedingt durch das flüssige Medium verteilt sich der Druck gleichmäßig über die Oberfläche der Formhülle, wodurch es zu einer gleichmäßigen Verdichtung des Pulvers kommt. Ein Druck beim i sostatischen Pressen kann 2000 bar oder mehr betragen. Der Formkörper kann auch durch semii- sostatisches Pressen des Pulvers gebildet werden, das heißt Teile des Formkörpers bzw. der Formhülle sind dann abgedeckt und werden nicht mit Druck beaufschlagt. Beispielsweise kann die Formhülle bzw. das zu pressende Pulver um einen Dorn herum angeordnet sein, wobei Enden des Dorns j eweils einen ringförmigen Steg aufweisen. Das Pulver kann dann zwischen den ringförmigen Stegen an dem Dorn leicht angeordnet und mit einer flexiblen Formhülle abgedeckt werden. Auch ist es denkbar, den Formkörper so bereits in seiner ab schließenden Gestalt auszubilden. Sintering the shaped body, wherein the shaped body is formed to the resistance heating element. In particular, the fact that the one-piece molded body is pressed from a sintered material formed from a powder, it is possible to form moldings almost j eder shape, which have a substantially uniform distribution of the sintered material within the molding. This can avoid that undesired material concentrations occur within the shaped body, which promotes crack formation during the production of the resistance heating element or during operation. It is also possible to produce the molded article comparatively inexpensively, since the formation of the shaped article of sintered material can be carried out relatively easily. Furthermore, a reduced rejection reduces possible rejects during production, which also contributes to a reduction in costs. Furthermore, the resistance heating element thus produced contains substantially no free silicon, which makes it particularly suitable for use at over 1400 ° C. The shaped body of sintered material can be formed by isostatic pressing of the powder. In isostatic pressing, the powder is placed in a mold envelope, for example in a tubular shape, and subjected to pressure in a liquid medium. Due to the liquid medium, the pressure spreads evenly over the surface of the mold shell, resulting in a uniform compression of the powder. A pressure in the mechanical pressing may be 2000 bar or more. The molding can also be formed by semi-static pressing of the powder, that is to say parts of the molding or of the molding are then covered and are not subjected to pressure. For example, the mold envelope or the powder to be pressed may be arranged around a mandrel, wherein ends of the mandrel each have an annular web. The powder can then be easily placed between the annular lands on the mandrel and covered with a flexible mold envelope. It is also conceivable to form the molded body so already in his from closing shape.
Der Formkörper aus Sinterwerkstoff kann auch durch Gesenkpressen Pressen des Pulvers gebildet werden. Dabei können sowohl rohrförmige Formkörper durch axiales Gesenkpressen des Sinterwerkstoffs als auch plattenförmige Formkörper ausgebildet werden. The shaped body of sintered material can also be formed by die pressing of the powder. Both tubular shaped bodies can be formed by axial die pressing of the sintered material as well as plate-shaped shaped bodies.
Das Glühen des gepressten Formkörpers aus Sinterwerkstoff kann unter einer Schutzatmosphäre erfolgen. Das Glühen bei beispielsweise 50 bis 600C° führt zu einem Härten des Formkörpers. Die Schutzatmosphäre kann durch ein Schutzgas oder ein Vakuum ausgebildet werden. The annealing of the pressed shaped body made of sintered material can take place under a protective atmosphere. The annealing at, for example, 50 to 600 ° C leads to a hardening of the molding. The protective atmosphere may be formed by an inert gas or a vacuum.
Der Formkörper aus Sinterwerkstoff kann in einer besonders einfachen Ausführungsform plattenförmig ausgebildet werden. Damit kann dann ein flaches, gerades Widerstandsheizelement hergestellt werden. The shaped body of sintered material can be formed plate-shaped in a particularly simple embodiment. This can then be made a flat, straight resistance heating.
Der Formkörper aus Sinterwerkstoff kann einen runden Rohrquerschnitt aufweisen. So kann der Formkörper die gewünschte Form des Wider- Standsheizelements aufweisen. Auch ist es denkbar, dass dann auf eine mechanische B earbeitung des Formkörpers im weiteren Herstellungspro- zess verzichtet werden kann. Vorzugsweise kann ein kreisförmiger Rohrquerschnitt ausgebildet werden, da ein nahtloser Formkörper dann einfach auf einem Dorn ausgebildet werden kann. Grundsätzlich kann der Formkörper j edoch j ede gewünschte rohrförmige Gestalt aufweisen. The molded body of sintered material may have a round tube cross-section. Thus, the shaped body, the desired shape of the Wider- Stand heating element have. It is also conceivable that it is then possible to dispense with mechanical processing of the shaped body in the further production process. Preferably, a circular pipe cross-section can be formed, since a seamless molded body can then be easily formed on a mandrel. In principle, however, the molded body can have any desired tubular shape.
Um eine gleichmäßige Verteilung von Siliziumcarbid und Silizium im Widerstandsheizelement zu erhalten, ist es vorteilhaft, wenn der Formkörper aus Sinterwerkstoff eine homogene Verteilung von Pulver auf- weist. Das heißt innerhalb des Materials des Formkörpers bestehen dann keine wesentlichen Dichteunterschiede. S o kann eine unerwünschte Materialanhäufung von beispielsweise Silizium zwischen aus Siliziumcarbid bestehenden Partikelstrukturen vermieden werden. Eine Rissbildung in Folge von Inhomogenitäten kann so vermieden werden. Weiter kann eine homogene Pulvermischung ausgebildet werden. Dann liegen keine wesentlichen Unterschiede bei einer Verteilung innerhalb des Materials des Formkörpers bzw. keine Bereiche mit Anhäufungen bestimmter Materialien vor. Eine gute Durchmischung des Pulvers kann beispielsweise mit einem Eirich Mischer erzielt werden. Eine homogene Pulvermischung bewirkt gleiche Festigkeitseigenschaften an j edem Punkt des Materials des Formkörpers und vermeidet somit eine Bildung von Rissen. In order to obtain a uniform distribution of silicon carbide and silicon in the resistance heating element, it is advantageous if the shaped body of sintered material has a homogeneous distribution of powder. That is, within the material of the molded body then exist no significant density differences. Thus, an undesirable material accumulation of, for example, silicon between particle structures consisting of silicon carbide can be avoided. Cracking due to inhomogeneities can thus be avoided. Furthermore, a homogeneous powder mixture can be formed. Then there are no significant differences in a distribution within the material of the molding or no areas with accumulations of certain materials. Good mixing of the powder can be achieved, for example, with an Eirich mixer. A homogeneous powder mixture causes the same strength properties at each point of the material of the shaped body and thus avoids the formation of cracks.
Um eine Bildung von Materialeinschlüssen oder Lunkern innerhalb des Formkörpers zu vermeiden, kann das Pulver vor einem Pressen gesiebt werden. Ein Sieben des Pulvers kann unter anderem auch eine verbesserte Mischung des Pulvers bewirken. In order to avoid formation of material inclusions or voids within the molding, the powder can be sieved prior to pressing. Screening of the powder may, among other things, effect an improved mixing of the powder.
Vorteilhaft kann ein Bindemittel verwendet werden. Ein Bindemittel oder ein sogenannter Precursor kann ein Polymer sein, welches durch eine Temperaturbeaufschlagung vernetzt wird und damit das Pulver in der Gestalt des Formkörpers fixieren kann. Vorzugsweise kann ein Siliziumkarbid-Precursor verwendet werden, von dem nach Durchführung des Herstellungsprozesses lediglich Siliziumcarbid im Material des Widerstand sheizelements zurückbleibt. Advantageously, a binder can be used. A binder or a so-called precursor can be a polymer which is crosslinked by applying a temperature and can thus fix the powder in the form of the shaped body. Preferably, a Silicon carbide precursor are used, of which remains after the implementation of the manufacturing process only silicon carbide in the material of the resistive sheizelements.
Der Sinterwerkstoff kann aus den Materialien Phenolharz, Furanharz, Formadehydharz, Epoxiden, Siliziumcarbid, Silizium, Graphit, Ruß, Polysilazane, Polycarbosilane, Polysiloxane, Polycarbosilazane oder Molybdän-Disilizit oder Kombinationen derartiger Pulver ausgebildet werden. Das Phenolharz kann ebenfalls in Pulverform oder in flüssiger Form vorliegen. Weiter kann als ein S chmiermittel und zur Vermeidung einer Oxidation des Pulvers bzw. Sinterwerkstoffes Stearinsäure beigemischt werden. Bevorzugt kann eine Pulvermischung aus Siliziumcarbid, Silizium, Kohlenstoff und Polycarbosilanen verwendet werden. The sintered material may be formed of the materials phenol resin, furan resin, formadehyde resin, epoxies, silicon carbide, silicon, graphite, carbon black, polysilazanes, polycarbosilanes, polysiloxanes, polycarbosilazanes or molybdenum disilizate, or combinations of such powders. The phenolic resin may also be in powder or liquid form. Further, stearic acid may be mixed as a lubricant and to prevent oxidation of the powder or sintered material. Preferably, a powder mixture of silicon carbide, silicon, carbon and polycarbosilanes can be used.
Nach dem Glühen kann eine mechanische Bearbeitung des Formkörpers erfolgen, wobei eine ab schließende Gestalt des Widerstandsheizelements durch die mechanische Bearbeitung ausgebildet werden kann. So kann ein Innendurchmesser des Formkörpers weiter aufgebohrt oder ausgedreht sowie ein Zylinder bzw. Außendurchmesser auf beispielsweise einer Drehmaschine geschliffen werden, so dass eine gleichmäßige Wandstärke des Formkörpers von beispiel sweise bis zu 1 mm ausgebildet wird. Insbesondere durch eine hohe mechani sche Stabilität des Formkörpers kann das Verfahren so auch eine Herstellung filigraner Heizwendeln ermöglichen. Weiter können in den so bearbeiteten Formkörper spiralförmige Schlitze gefräst werden, derart, dass eine spätere Heizwendel des Widerstandsheizelements ausgebildet wird. In einem Fußbereich bzw. zwischen Anschlussflächen des Formkörpers bzw. Widerstandsheizelements können die Schlitze als überbrückende Stege ausgebildet sein, die eine Stabilität des Formkörpers während des Herstellungsprozesses sicherstellen. Diese Stege können nach Ausbildung des Widerstandsheizelements einfach durchtrennt und somit entfernt werden. Vorteilhaft kann nach dem Sintern eine Hochtemperaturb ehandlung des Widerstandsheizelements erfolgen. Das Sintern kann in einem Tempera- turbereich von 13 50 bis 1900°C und die Hochtemperaturbehandlung in einem Temperaturbereich von 1900 bis 2400°C durchgeführt werden. Die Hochtemperaturbehandlung kann unter anderem zum Abbau von Sauerstoff und Stickstoff im Formkörper dienen und unter Vakuum oder Schutzgas durchgeführt werden. Mittels der Hochtemperaturbehandlung können insbesondere durch die Prozessschritte bedingte Maßabweichungen des Formkörpers minimiert werden. After annealing, a mechanical processing of the shaped body can take place, wherein a closing shape of the resistance heating element can be formed by the mechanical processing. Thus, an inner diameter of the shaped body further drilled or turned and a cylinder or outer diameter are ground on, for example, a lathe, so that a uniform wall thickness of the shaped body of example, up to 1 mm is formed. In particular, by a high mechanical cal stability of the molded body, the method can thus also allow the production of filigree heating coils. Further, helical slots can be milled in the shaped body thus processed, such that a later heating coil of the resistance heating element is formed. In a foot region or between connection surfaces of the shaped body or resistance heating element, the slots can be formed as bridges bridging, which ensure stability of the molded body during the manufacturing process. These webs can be easily severed after formation of the resistance heating and thus removed. Advantageously, after the sintering, a high-temperature treatment of the resistance heating element can take place. Sintering may take place in a tempera- range of 13 50 to 1900 ° C and the high-temperature treatment in a temperature range of 1900 to 2400 ° C are performed. The high-temperature treatment can serve, inter alia, for the decomposition of oxygen and nitrogen in the molding and be carried out under vacuum or inert gas. By means of the high-temperature treatment, dimensional deviations of the shaped body caused in particular by the process steps can be minimized.
Um einen Austritt freien Siliziums während eines Betriebes des Widerstandsheizelements zu verhindern, kann zusätzlich nach dem Sintern eine CVD-B eschichtung (chemische Gasphasenabscheidung) des Widerstandsheizelements mit Siliziumcarbid erfolgen. Bei der In order to prevent leakage of free silicon during operation of the resistance heating element, in addition to the sintering, a CVD coating (chemical vapor deposition) of the resistance heating element with silicon carbide can take place. In the
CVD-B eschichtung wird bei beispielsweise 700 bis 1 500C0 eine Silizi- umcarbidschicht auf das Widerstandsheizelement aufgebracht. Die Siliziumcarbidschicht umgibt das Widerstandsheizelement im Wesentli- chen voll ständig, so dass eventuell im Material des Widerstandsheizelements eingeschlo ssenes, Silizium nicht aus diesem austreten kann. CVD coating is applied to the resistance heating element at, for example, 700 to 1500 C 0, a silicon carbide layer. Essentially, the silicon carbide layer completely surrounds the resistance heating element, so that any silicon that is included in the material of the resistance heating element can not escape from it.
Eine besonders gute Kontaktierung des Widerstandsheizelements mit Anschlusskontakten kann erzielt werden, wenn nach dem Sintern oder der CVD-B eschichtung Anschlussflächen des Widerstandsheizelements mittels Flammspritzen beschichtet werden. Durch thermisches Spritzen von pulverförmigem Aluminium können die Anschlussflächen so mit einer elektrisch gut kontaktierbaren Aluminiumschicht versehen werden. Aluminium kann mittels Flammspritzen gut verarbeitet werden und schmilzt während des Betriebes des Widerstandsheizelements von diesem nicht ab . A particularly good contacting of the resistance heating element with connection contacts can be achieved if, after the sintering or the CVD coating, coating surfaces of the resistance heating element are coated by means of flame spraying. By thermal spraying of powdered aluminum, the pads can be so provided with an electrically good contactable aluminum layer. Aluminum can be well processed by means of flame spraying and does not melt away from it during operation of the resistance heating element.
Das erfindungsgemäße Widerstandsheizelement weist eine grundsätzlich beliebige Gestalt auf, wobei das Widerstandsheizelement einstückig ausgebildet ist, wobei das Widerstandsheizelement aus Siliziumcarbid gebildet ist, und wobei das Widerstandsheizelement ein homogenes Gefüge bzw. eine homogene Verteilung von Siliziumcarbid aufweist. Insbesondere das homogene Gefüge von Siliziumcarbid innerhalb der Materialstruktur des Widerstandsheizelements bewirkt, dass eine Wahrscheinlichkeit von Rissbildung während des B etrieb s des Widerstandsheizelements minimiert wird. Somit kann eine Betrieb ssicherheit des Widerstandsheizelements wesentlich erhöht werden. Vorzugsweise weist das Widerstandsheizelement eine rohrförmige Gestalt auf. The resistance heating element according to the invention has a basically arbitrary shape, wherein the resistance heating element is integrally formed, wherein the resistance heating element is formed of silicon carbide, and wherein the resistance heating element has a homogeneous microstructure or a homogeneous distribution of silicon carbide. In particular, the homogeneous microstructure of silicon carbide within the Material structure of the resistance heating element causes a probability of cracking during operation of the resistance heating element is minimized. Thus, an operating safety of the resistance heating element can be substantially increased. Preferably, the resistance heating element has a tubular shape.
Vorteilhaft kann das Siliziumcarbid im Werkstoff des Widerstandsheizelements entsprechend einer Partikelorientierung eines Pulvers strukturiert sein. Advantageously, the silicon carbide in the material of the resistance heating element can be structured in accordance with a particle orientation of a powder.
Weitere vorteilhafte Ausführungsformen eines Widerstandsheizelements ergeben sich aus den Merkmalsbeschreibungen der auf den Verfahrensanspruch 1 rückbezogenen Unteransprüche. Further advantageous embodiments of a resistance heater resulting from the feature descriptions of the back to the method claim 1 dependent claims.
Im Folgenden wird die Erfindung unter Bezugnahme auf die beigefügte Zeichnung näher erläutert. In the following the invention will be explained in more detail with reference to the accompanying drawings.
Es zeigen: Show it:
Fig. 1 : Eine perspektivische Ansicht eines Widerstandsheizelements; Fig. 1: A perspective view of a resistance heating element;
Fig. 2 : ein Ablaufdiagramm für eine Ausführungsform des Verfahrens. 2 shows a flow chart for an embodiment of the method.
Fig. 1 zeigt ein Widerstandsheizelement 1 0, welches rohrförmig, mit einem runden, kreisförmigen Querschnitt ausgebildet ist. Das Widerstandsheizelement 10 weist eine dünne Rohrwandung 1 1 auf, die durch zwei Schlitze 12 und 13 durchbrochen ist. Die Schlitze 12 und 13 sind im B ereich eines unteren Endes 14 des Widerstandsheizelements 10 in Längsrichtung des selben gerade ausgebildet und bilden so zwei Anschlussflächen 1 5 und 16 zum Anschluss des Widerstandsheizelements 10 an Anschlusskontakte einer hier nicht dargestellten Anschlussvorrichtung eines D SC-Ofens aus. In einem Mittelbereich 17 des Widerstandsheizelements 10 verlaufen die Schlitze 12 und 13 j eweils spiralförmig in Längsrichtung entlang des Umfangs der Rohrwandung 1 1 bis hin zu einem oberen Ende 1 8 des Widerstandsheizelements 10. Die Schlitze 12 und 13 bilden so zwei Heizwendel 19 und 20 aus, die an dem oberen Ende 1 8 in einem Ringab schnitt 21 miteinander verbunden sind. Eine Erwärmung des Widerstandsheizelements 10 während eines Betrieb s erfolgt im Wesentlichen im Bereich der Heizwendel 19 und 20. Das Widerstandsheizelement ist einstückig ausgebildet und besteht im Wesentlichen aus Siliziumcarbid, wobei innerhalb des Materials des Widerstandsheizelements 10 herstellungsbedingte Restmengen von Silizium, Kohlenstoff und anderen Materialien eingebunden sein können . Weiter ist eine Oberfläche 22 des Widerstandsheizelements 10 nahezu vollständig mit Siliziumcarbid beschichtet, wobei im B ereich der Anschlussflächen 1 5 und 16 eine hier nicht näher dargestellte Schicht aus Aluminium aufgebracht ist. Fig. 2 zeigt ein mögliches Ablaufdiagramm einer Ausführungsform des Verfahrens. Zunächst erfolgt ein Mischen und ein Sieben verschiedener, pulverförmiger Sinterwerkstoffe, wie Siliziumcarbid, Silizium, Kohlenstoff, Polymere, wie zum Beispiel Polysil azane, Polycarbosilazane, Polycarbosilane, Polysiloxane, oder anderen Prepolymeren wie Phenol- harz, Polyinide, Polyfurane usw. und. Diese Pulvermischung wird um einen runden Dorn herum angeordnet, so dass ein rohrförmiger Formkörper entsteht. Die Pulvermischung wird von einer Formhülle abgedeckt und semiiso statisch gepresst, so dass es zu einer Verdichtung der Pulvermischung kommt. Der so gebildete Formkörper wird bei circa 400°C geglüht und damit gehärtet, so dass eine mechanische B earbeitung des Formkörpers durch Schleifen auf einer Drehmaschine erfolgen kann. Ein Innen- und ein Außendurchmesser des rohrförmigen, runden Formkörpers wird dabei so bearbeitet, dass der Formkörper eine im Wesentlichen gleichmäßige Wandstärke von 3 mm aufweist. Weiter werden Schlitze zur Ausbildung von Heizwendeln und Anschlussflächen in die Rohrwandung des Formkörpers gefräst. Abschließend erfolgen eine Pyrolyse des Werkstoffs des Formkörpers bei 850 bis 1200°C, bei der der Werkstoff teilweise in Kohlenstoff umgewandelt wird, sowie ein Sintern des Formkörpers bei 1650 bis 1900°C, bei dem der Formkörper zu dem Widerstandsheizelement ausgebildet wird. Das Widerstandsheizelement besteht im Wesentlichen nunmehr aus Siliziumcarbid. Nach dem Sintern folgen eine optionale Hochtemperaturbehandlung sowie eine Beschichtung der Anschlussflächen mit Aluminium durch Flammspritzen. Fig. 1 shows a resistance heating element 1 0, which is tubular, formed with a round, circular cross-section. The resistance heating element 10 has a thin tube wall 1 1, which is broken through two slots 12 and 13. The slits 12 and 13 are straight in the region of a lower end 14 of the resistance heating element 10 in the longitudinal direction thereof and thus form two connection surfaces 1 5 and 16 for connecting the resistance heating element 10 to connection contacts of a connection device of a D SC furnace not shown here. In a central region 17 of the resistance heating element 10, the slots 12 and 13 extend in each case in a spiral shape Longitudinal along the circumference of the pipe wall 1 1 up to an upper end of the resistance heating element 10 10. The slots 12 and 13 thus form two heating coil 19 and 20, the cut at the upper end 1 8 in a Ringab 21 are interconnected. A heating of the resistance heating element 10 during operation s occurs essentially in the area of the heating coil 19 and 20. The resistance heating element is integrally formed and consists essentially of silicon carbide, within the material of the resistance heating element 10 production-related residual amounts of silicon, carbon and other materials to be involved can . Furthermore, a surface 22 of the resistance heating element 10 is almost completely coated with silicon carbide, wherein in the region of the connection surfaces 1 5 and 16 a layer of aluminum, not shown here, is applied. Fig. 2 shows a possible flowchart of an embodiment of the method. First, a mixing and sieving of various powdered sintered materials, such as silicon carbide, silicon, carbon, polymers, such as polysilazanes, polycarbosilazanes, polycarbosilanes, polysiloxanes, or other prepolymers such as phenolic resin, polyinides, polyfurans, etc. and. This powder mixture is arranged around a round mandrel, so that a tubular shaped body is formed. The powder mixture is covered by a mold shell and pressed semiiso static, so that it comes to a compaction of the powder mixture. The shaped body thus formed is annealed at about 400 ° C and cured so that a mechanical processing of the shaped article can be carried out by grinding on a lathe. An inner and an outer diameter of the tubular, round shaped body is thereby processed so that the shaped body has a substantially uniform wall thickness of 3 mm. Further, slots for the formation of heating coils and pads in the pipe wall of the molded body are milled. Finally, a pyrolysis of the material of the molding at 850 to 1200 ° C, in which the material is partially converted to carbon, and sintering of the molded article at 1650 to 1900 ° C, wherein the shaped body is formed into the resistance heating element. The resistance heating element essentially consists now of silicon carbide. After sintering, an optional high-temperature treatment and a coating of the connection surfaces with aluminum by flame spraying follow.

Claims

Patentansprüche claims
1. Verfahren zur Herstellung eines Widerstandsheizelements, wobei das Widerstandsheizelement (10) eine rohrförmige Gestalt aufweist, wobei das Widerstandsheizelement einstückig ausgebildet ist, wobei das Widerstandsheizelement aus Siliziumcarbid gebildet ist, A method of manufacturing a resistance heating element, wherein the resistance heating element (10) has a tubular shape, wherein the resistance heating element is formed integrally, wherein the resistance heating element is formed from silicon carbide,
zumindest umfassend die Verfahrensschritte:  at least comprising the method steps:
- Ausbildung eines einstückigen Formkörpers aus einem Pulver eines Sinterwerkstoffs, wobei das Pulver gepresst wird,  Formation of a one-piece molded article from a powder of a sintered material, wherein the powder is pressed,
- Glühen des gepressten Formkörpers,  Annealing the pressed molding,
- Pyrolyse des Werkstoffs des Formkörpers,  Pyrolysis of the material of the shaped body,
- Sintern des Formkörpers, wobei der Formkörper zu dem Widerstandsheizelement ausgebildet wird.  - Sintering of the shaped body, wherein the shaped body is formed to the resistance heating element.
2. Verfahren nach Anspruch 1, 2. The method according to claim 1,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass der Formkörper aus Sinterwerkstoff durch isostatisches Pressen des Pulvers gebildet wird. that the shaped body of sintered material is formed by isostatic pressing of the powder.
3. Verfahren nach Anspruch 1, 3. The method according to claim 1,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass der Formkörper aus Sinterwerkstoff durch Gesenkpressen des Pulvers gebildet wird.  that the shaped body of sintered material is formed by die pressing of the powder.
4. Verfahren nach einem der Ansprüche 1 bis 3, 4. The method according to any one of claims 1 to 3,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass das Glühen des Formkörpers aus Sinterwerkstoff unter einer Schutzatmosphäre erfolgt.  that the annealing of the shaped body made of sintered material takes place under a protective atmosphere.
5. Verfahren nach einem der vorangehenden Ansprüche, 5. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass der Formkörper aus Sinterwerkstoff plattenförmig ausgebildet wird.  that the shaped body made of sintered material is plate-shaped.
6. Verfahren nach einem der Ansprüche 1 bis 4, 6. The method according to any one of claims 1 to 4,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass der Formkörper aus Sinterwerkstoff einen runden Rohrquerschnitt aufweist.  the shaped body of sintered material has a round tube cross section.
7. Verfahren nach einem der vorangehenden Ansprüche, 7. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass der Formkörper aus Sinterwerkstoff eine homogene Verteilung von Pulver aufweist.  the shaped body of sintered material has a homogeneous distribution of powder.
8. Verfahren nach einem der vorangehenden Ansprüche, 8. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass eine homogene Pulvermischung ausgebildet wird. that a homogeneous powder mixture is formed.
9. Verfahren nach einem der vorangehenden Ansprüche, dadurch g e k e n n z e i c h n e t , 9. The method according to any one of the preceding claims, characterized g e k e n e c e e n e,
dass das Pulver gesiebt wird.  that the powder is sieved.
10. Verfahren nach einem der vorangehenden Ansprüche, 10. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass ein Bindemittel verwendet wird.  that a binder is used.
11. Verfahren nach einem der vorangehenden Ansprüche, 11. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass der Sinterwerkstoff aus den Materialien Phenolharz, Furanharz, Formaldehydharz, Epoxiden, Siliziumcarbid, Silizium, Graphit, Ruß, Polysilazane, Polycarbosilane, Polysiloxane, Polycarbosilazane oder Molybdän-Disilizit oder Kombinationen derartiger Pulver ausgebildet wird.  the sintered material is formed from the materials phenolic resin, furan resin, formaldehyde resin, epoxides, silicon carbide, silicon, graphite, carbon black, polysilazanes, polycarbosilanes, polysiloxanes, polycarbosilazanes or molybdenum disilicite or combinations of such powders.
12. Verfahren nach einem der vorangehenden Ansprüche, 12. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass nach dem Glühen eine mechanische Bearbeitung des Formkörpers erfolgt, wobei eine abschließende Gestalt des Widerstandsheizelements (10) ausgebildet wird.  that after annealing, a mechanical processing of the shaped body takes place, wherein a final shape of the resistance heating element (10) is formed.
13. Verfahren nach einem der vorangehenden Ansprüche, 13. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass nach dem Sintern eine Hochtemperaturbehandlung des Widerstandsheizelements erfolgt.  that after sintering, a high-temperature treatment of the resistance heating element takes place.
14. Verfahren nach einem der vorangehenden Ansprüche, 14. The method according to any one of the preceding claims,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass nach dem Sintern eine CVD-Beschichtung des Widerstandsheizelements mit Siliziumcarbid erfolgt. that after sintering, a CVD coating of the resistance heating element with silicon carbide takes place.
15. Verfahren nach einem der vorangehenden Ansprüche, dadurch g e k e n n z e i c h n e t , 15. The method according to any one of the preceding claims, characterized g e c e n e c e s e,
dass nach dem Sintern Anschlussflächen des Widerstandsheizelements (10) mittels Flammspritzen beschichtet werden.  that after sintering pads of the resistance heating element (10) are coated by means of flame spraying.
16. Widerstandsheizelement (10), wobei das Widerstandsheizelement einstückig ausgebildet ist, wobei das Widerstandsheizelement aus Si- liziumcarbid gebildet ist, 16. Resistance heating element (10), wherein the resistance heating element is formed in one piece, wherein the resistance heating element is formed from silicon carbide,
dadurch g e k e n n z e i c h n e t ,  characterized ,
dass das Widerstandsheizelement eine homogene Verteilung von Sili- ziumcarbid aufweist.  the resistance heating element has a homogeneous distribution of silicon carbide.
EP12713138.1A 2011-04-06 2012-04-04 Method for producing a resistance heating element, and resistance heating element Withdrawn EP2695482A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102011006847A DE102011006847A1 (en) 2011-04-06 2011-04-06 Method for producing a resistance heating element and resistance heating element
PCT/EP2012/056133 WO2012136690A1 (en) 2011-04-06 2012-04-04 Method for producing a resistance heating element, and resistance heating element

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US (1) US20140091080A1 (en)
EP (1) EP2695482A1 (en)
JP (1) JP5756225B2 (en)
DE (1) DE102011006847A1 (en)
WO (1) WO2012136690A1 (en)

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DE102018121902A1 (en) * 2018-09-07 2020-03-12 Isabellenhütte Heusler Gmbh & Co. Kg Manufacturing method for an electrical resistance element and corresponding resistance element
CN114851352B (en) * 2022-05-23 2023-11-28 松山湖材料实验室 Resistance heating element and method for manufacturing same

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US20140091080A1 (en) 2014-04-03
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WO2012136690A1 (en) 2012-10-11
JP5756225B2 (en) 2015-07-29

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