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EP1592284B1 - Workpiece support for inductive heating of workpieces - Google Patents

Workpiece support for inductive heating of workpieces Download PDF

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Publication number
EP1592284B1
EP1592284B1 EP04010372A EP04010372A EP1592284B1 EP 1592284 B1 EP1592284 B1 EP 1592284B1 EP 04010372 A EP04010372 A EP 04010372A EP 04010372 A EP04010372 A EP 04010372A EP 1592284 B1 EP1592284 B1 EP 1592284B1
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EP
European Patent Office
Prior art keywords
workpiece carrier
workpiece
carbon
process according
ceramic material
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EP04010372A
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German (de)
French (fr)
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EP1592284A1 (en
Inventor
Bodo Benitsch
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SGL Carbon SE
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SGL Carbon SE
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Application filed by SGL Carbon SE filed Critical SGL Carbon SE
Priority to AT04010372T priority Critical patent/ATE374514T1/en
Priority to EP04010372A priority patent/EP1592284B1/en
Priority to DE502004005078T priority patent/DE502004005078D1/en
Priority to US11/080,712 priority patent/US7323668B2/en
Publication of EP1592284A1 publication Critical patent/EP1592284A1/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
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
    • H05B6/101—Induction heating apparatus, other than furnaces, for specific applications for local heating of metal pieces

Definitions

  • the invention relates to a workpiece carrier for the inductive heating of workpieces, which contains ceramic materials at least at the areas of its surface, which are touched by the workpieces.
  • An important field of application of the heating by means of electromagnetic induction is the hardening of workpieces made of steel or cast iron. Surface hardening of steel or cast workpieces takes place at temperatures below the softening temperature. Typically, curing is carried out at temperatures of 850 to 1000 ° C.
  • inductive hardening a coil (inductor), through which high-frequency alternating current flows, encloses the workpiece to be hardened. According to the law of induction, an alternating magnetic field builds up around each conductor through which an alternating current flows. As a result, eddy currents are induced in a conductive workpiece located within this field.
  • the induced eddy currents which are forced by the skin effect into the outer workpiece layers, heat these areas very quickly because of the electrical resistance.
  • the hardness depth is largely determined by the frequency f of the alternating current.
  • the lowest hardness depth achievable at high frequencies is approx. 0.1 mm.
  • the current-carrying layer is thicker, that is, the workpiece is flowed through by the current deeper and warmed through. This effect is used to set the desired warming depth by selecting the frequency.
  • the particular advantage of inductive heating is that the heat is generated in the workpiece itself, without an external heat source is required. The heating by induction is very easy to control and therefore well reproducible.
  • inductive heating of workpieces made of metal are the melting of steels and non-ferrous metals with temperatures up to 1500 ° C; heating for forging to 1250 ° C, soft annealing and normalization after cold forming with temperatures of 750 to 950 ° C, soft and brazing with temperatures up to 1100 ° C, and tempering of steel at 200 to 300 ° C.
  • heating for bonding, for sintering or for other machining processes are special fields of application, for example in heating for bonding, for sintering or for other machining processes.
  • induction hardening compared to conventional hardening methods are the defined heat input and the uniform heating of the hardness ranges. It is possible to partially harden the workpiece. The heat is not transferred from the outside to the workpiece as in flame hardening, but is created inside. Therefore, high heating rates can be achieved. Thanks to the short heating times during inductive hardening, the cycle times are short, the scale formation is low, and the formation of coarse grain in the hardened material is largely avoided. The short heating time reduces the risk of distortion and cracking. The current induced in the workpiece depends very much on the position of the workpiece relative to the induction coil.
  • each workpiece for the curing process must be placed in the same position relative to the induction coil.
  • Different workpiece geometries require different inductors and workpiece carriers that are matched to the respective workpiece geometry.
  • the material of the workpiece carrier used for the inductive hardening should not or only very little be electrically conductive, so that as possible no current is induced in the workpiece carrier, because this energy is lost.
  • the workpiece carrier should heat itself as little as possible by the contact with the workpiece, so that the workpiece is extracted little heat.
  • the quenching process is completed with a quenching process to accelerate cooling and to optimize the specific properties of the workpiece to be cured.
  • the workpiece If the workpiece is still on the workpiece carrier at this point in time, then it must also have a thermal shock resistance of at least 1200 K / s. At the same time, a high resistance against chemical and / or oxidative attacks is required to be free in the choice of quenching medium. Furthermore, materials should be chosen which do not absorb and / or swell under the influence of liquids, such as the quenching emulsion.
  • the workpiece receiving areas of the workpiece carrier usually have individual, matched to the particular workpiece geometries and the necessary high investment only at a high number of hardened workpieces are profitable, a long life of the workpiece carrier is required. Prerequisites for this, in turn, are low wear and high dimensional stability (geometric accuracy) of the workpiece carrier.
  • a device for heating a workpiece comprises a chamber, a ceramic workpiece carrier (eg AlN, Si 3 N 4 , Al 2 O 3 ), a conductive layer embedded in the workpiece carrier and a coil which heats the conductive layer embedded in the workpiece carrier by electromagnetic induction.
  • a ceramic workpiece carrier eg AlN, Si 3 N 4 , Al 2 O 3
  • a conductive layer embedded in the workpiece carrier e.g AlN, Si 3 N 4 , Al 2 O 3
  • a coil which heats the conductive layer embedded in the workpiece carrier by electromagnetic induction.
  • the patent US Pat. No. 4,960,967 discloses a protection device for induction poles of an electromagnetic inductor as used in the heating of metal workpieces, prior to heat radiation of the hot workpiece and chemical and mechanical attacks.
  • the protection device consists of a heat exchanger comprising at least one non-magnetic metal tube for the passage of a coolant, each tube consisting of a plurality of tubular elements which are connected at their ends and arranged substantially parallel in a plane with the pole faces, wherein between each two tubular elements at most a single electrical contact exists.
  • the tubes are embedded in a refractory material, particularly in a refractory silicon carbide concrete. This concrete can be additionally covered with an insulating layer of glass ceramic, alumina or silica.
  • the patent US-A 2 482 364 discloses a device for heat treatment of magnetic materials.
  • ceramic supports are provided for the support of the workpieces to be treated.
  • the ceramic supports are made, for example, of clay or clay, brick or the like. formed electrically insulating materials.
  • Ceramic workpiece carriers for the heat treatment of workpieces are also made of Japanese Patent Application JP 57 057 049 A known.
  • the object of the present invention is to provide a workpiece carrier for inductive heating, in particular for the inductive hardening of workpieces, made of a material that meets the aforementioned requirements and allows the production of workpiece carriers with complex geometries.
  • the object is achieved in that at least the region of the workpiece carrier, which contacts the workpiece to be heated, contains ceramic material having an electrical resistance of at least 50 ⁇ , wherein the ceramic material in addition to carbide phases of elemental carbon or phases of elemental carbon and metallic phases from which the carbide-forming metal or the carbides forming metals.
  • a workpiece carrier according to the invention according to FIG. 1 can be produced by forming the surface of a workpiece carrier .beta. From a conventional material, for example from a high-temperature-resistant duroplastic reinforced with glass fibers, in the region a, which is intended for supporting the workpiece to be hardened Material is coated. The not touched by the workpiece ⁇ surface b of the workpiece carrier is uncoated. However, the entire surface of the workpiece can also be coated, for example, in those cases in which a complete coating is easier to produce in terms of process engineering than a specific coating which is limited to certain parts of the surface. Methods for producing ceramic coatings, for example plasma spraying or chemical vapor deposition (CVD), are known to the person skilled in the art.
  • CVD chemical vapor deposition
  • FIG. 1 An alternative variant of the workpiece carrier according to the invention is shown in FIG.
  • a workpiece carrier body ⁇ of a conventional high temperature resistant material for example glass fiber reinforced high temperature thermoset
  • at least one recess is provided, in which a precisely shaped insert (inlay) ⁇ used from a ceramic material becomes.
  • the outwardly facing surfaces of the inserts are designed according to the requirements of the geometries of the workpieces to be cured, for example, grooves, grooves or other shaped recesses for receiving the workpiece (not shown in Figure 2).
  • the inlay or inlays take over the support function for the workpiece, ie the workpiece is held by the inlay or inlays, so that only the surfaces of the inlay (s) are touched by the workpiece, but not the surface of the main body.
  • the inlays can be removable, so that the workpiece carrier can be adapted to different workpiece geometries, while in each case suitable for the workpiece to be hardened inlays are used.
  • the inlays can be glued, pressed or similar. firmly connected to the workpiece carrier.
  • the geometries of the workpiece carriers and workpieces illustrated in FIGS. 1 and 2 are only to be understood as examples, since the invention is not limited to specific geometries of workpiece carrier and workpiece. Of course, it is within the scope of the present invention also possible to form the entire workpiece carrier in one piece from a ceramic material.
  • the specific electrical resistance of the ceramic material used in the workpiece carriers according to the invention is at least 50 ⁇ * m, preferably more than 100 ⁇ * m and particularly preferably more than 150 ⁇ * m.
  • the compositions of suitable ceramic materials are given for the workpiece carriers according to the invention.
  • the compositions apply only to the inlays ⁇ .
  • the material does not have to be 100% ceramic, but its ceramic content must be at least 10% by mass.
  • the ceramic material contains not only carbide phases of elemental carbon or phases of elemental carbon and metallic phases of the carbide-forming metal or the carbides forming metals such as silicon, titanium, tungsten.
  • the mass-based proportion of the carbide in this material is at least 10%.
  • the residual content of the material, which adds up to 100%, contains a maximum of 50% of carbon and a maximum of 80% of fusible elements (the carbide-forming metal or the carbide-forming metals in elemental form).
  • a material that meets the above requirements in terms of dimensional stability, low electrical and thermal conductivity, chemical resistance and thermal shock resistance is a ceramic composite of at least 35 mass% silicon carbide with fractions of elemental carbon (1-35 mass%) and elemental silicon (1 - 60 mass%).
  • the starting point for the production of this high-ceramic material is a porous carbon skeleton. This is infiltrated with liquid silicon to form a predominantly silicon carbide, silicon and carbon containing composite. Alternatively, the siliconization can be done via the gas phase. Silicon carbide and carbon composites are also obtainable by addition of silicon-containing polymers which, upon pyrolysis, form silicon carbide, eg, silanes or siloxanes, to the porous carbon skeleton and subsequent pyrolysis.
  • Materials according to the last-described variant can be densified with silicon by means of a liquid-silica process immediately after the pyrolysis or in a separate step.
  • the porous carbon skeleton of the starting material is either already present in carbonized form, for example as a carbonized felt or nonwoven, or it is by pyrolysis (carbonization) of a preform made of a carbonizable solid material, ie a carbon source which can be converted into carbon with high yield, for example wood, wood-based materials , Wood shavings, wood flour, cellulose, pulp, or wool or textile structures made of cellulose or wool.
  • porous carbon skeleton or the pyrolyzable preform from which the porous carbon skeleton is made can be impregnated once or several times with a carbonizable binder for the purpose of densification, which is then carbonized.
  • carbonizable, ie, with a high carbon yield pyrolysable binders include phenolic resins, melamine resins, lignin and pitch.
  • binders which simultaneously act as a source of silicon carbide for example a silane or siloxane, the pyrolysis of which produces silicon carbide in addition to carbon, or mixtures of different binders or various binders in various impregnation steps.
  • the starting material for the porous carbon skeleton is a mixture of carbon, for example in the form of fibers or ground material, or one or more solid carbon sources which pyrolyze (carbonize) with high carbon yield, eg wood flour, wood shavings, pulp or cellulose fibers, and a carbonizable binder. From this mixture, for example, by pressing or another method of shaping a green body is produced, the pyrolysis, a porous carbon skeleton is obtained. Additives can be added to the mixture in order to better match the properties of the composite with the requirements to be met, for example to reduce the thermal and electrical conductivity and to increase the strength.
  • additives in the form of powders or fibers with a length of less than 10 mm of ceramic materials are suitable.
  • carbon By adding carbon to the mixture of solid pyrolyzable carbon sources (eg, wood chips, wood flour, cellulose fibers, pulp) and carbonizable binders from which the green body is made, shrinkage in pyrolysis can be significantly reduced.
  • This carbon content is obtained by adding carbon to the mixture in the form of carbon or graphite powder, carbon black, short carbon fibers (less than 10 mm in length) or carbon nanotubes.
  • the amount of carbon in the starting material can influence the degree of conversion to silicon carbide.
  • the composition of the ceramic composite is adjusted such that the non-silicon carbide converted carbon components are largely encapsulated by silicon and / or silicon carbide such that there are no contiguous conductive paths.
  • the content of the composite material to non-carbide converted carbon must be very low and preferably at zero, inter alia, to avoid carburizing of the workpiece. So it is a high degree of conversion of carbon to silicon carbide needed. This can be achieved, for example, by a relative long residence time of the siliconization temperature above the melting temperature of the silicon (typically more than 60 minutes).
  • the material Due to the encapsulation of the non-carbide converted residual carbon, the material has the requisite high electrical resistance. Specific resistances were determined around 170 ⁇ * m, ie within the particularly preferred range of more than 150 ⁇ * m. Surprisingly, this encapsulation of the carbon simultaneously has a positive effect on the thermal shock behavior of the materials described. This is greater than 1200 K / s and thus meets the requirements mentioned above. The resistance to oxidative effects is also positively influenced by the encapsulation of the carbon.
  • the workpiece carriers according to the invention were able to be exposed to up to 10,000 curing cycles at about 1,000 ° C. for 3 to 5 minutes in each case, without a noticeable decrease in mass or oxidative attack of the surface being observed.
  • the ceramic body of the silicon carbide, silicon and carbon-containing composite material either serves itself as a workpiece carrier, or as an insert for the workpiece holder in a workpiece carrier made of a conventional material according to FIG. 2.
  • an already near net shape green or preform is preferably prepared. This happens, depending on the nature of the starting material, for example by means of injection molding, pressing (eg in a suitably shaped die), stamping, cutting, turning or other common methods.
  • the green body it must be taken into account that some material shrinkage occurs, in particular during pyrolysis. Therefore, the green body may have to compensate for the shrinkage excess.
  • the shrinkage can be reduced by adding carbon to the starting material to be pyrolyzed. As far as a final contouring of the ceramic body according to the geometry of the male workpieces is necessary, this is done by conventional methods such as drilling, grinding, erosion, etc.
  • the ceramic body or the ceramic portions of the workpiece carrier with such a surface and Geoemtriegüte that it does not have to be machined or only slightly in the ceramic state, for example, the post-processing limited to the production of holes.
  • Measures for the production of ceramic bodies with high surface quality, which require no post-processing, are known in the art. In this context, for example, the use of very fine-grained starting materials is advantageous.
  • a plate-shaped porous carbon body having a density of 0.5 - 0.8 g / cm 3 is made of stacked and compacted carbonized felt mats. This preform was contacted with liquid silicon under vacuum. In the process, most of the carbon components were converted to silicon carbide. The residual porosity is largely filled by elemental silicon. After the siliconization, the final shaping took place to a workpiece carrier for the acceptance of crankshafts during the hardening process. For this purpose, elongated recesses having a U-shaped cross-section were produced from a surface of the plate-shaped body by means of electroerosion processes with a tolerance of less than + -0.1 mm. Through this machining process, the required surface quality was achieved without additional surface treatment.
  • Example 1 The carbonized felt used in Example 1 was ground.
  • the millbase was mixed with a pyrolyzable binder, pressed into a round disc-shaped blank, cured, pyrolyzed, shaping and siliconized.
  • a surface of the blank was machined to have a raised peripheral edge.
  • the resulting ceramic molded body serves as a workpiece carrier in the inductive surface hardening of running surfaces for ball bearings.
  • the raised peripheral edge acts as a fixing edge for the workpieces to be hardened.
  • a beechwood panel was pyrolyzed, placed in the form of a workpiece carrier for receiving gears, and then silicated over the liquid phase. Due to the expected shrinkage of about 40% of the initial volume in siliciding, the shaping of the pyrolyzed wood panel was carried out with a corresponding excess.
  • the silicided molded body was post-processed to precisely set the desired dimensions.
  • Ground, powdered wood flour was mixed with phenolic resin and cured under pressure (12 N / mm 2 ) and temperature (up to a maximum of 130 ° C) in a die-shape to a so-called wood material.
  • the die used formed the contour of a molded article having an elongated U-shaped cross-section on a surface.
  • the green body thus obtained was pyrolyzed and converted by siliconization into a ceramic body rich in silicon carbide. This serves to fix threaded rods during inductive hardening.
  • Carbon powder having a particle diameter of 5-30 ⁇ m was added as an additive to wood meal infiltrated with a pyrolyzable binder. From this, a green body in the form of a perforated plate was produced. This was pyrolyzed and silicided. The additive substantially reduces the shrinkage of the preforms during pyrolysis. As a result, the desired geometry could be implemented in sufficient dimensional accuracy without reworking.
  • the ceramic body thus obtained was used as a receptacle for metal bolts to be hardened.
  • a mixture of pulp and cellulose with lignin as binder was pressed into a near-net shape green body in the form of a plate with fixing edges for workpieces.
  • This body had a very fine-pored structure after pyrolysis.
  • a SiSiC material with a mass fraction of elemental, non-carbide bonded silicon of more than 30% was formed.
  • the mass fraction of elemental carbon was below 3%.
  • the moldings thus obtained serve as locking aids for workpieces in induction hardening plants.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Ceramic Products (AREA)
  • General Induction Heating (AREA)
  • Furnace Charging Or Discharging (AREA)
  • Porous Artificial Stone Or Porous Ceramic Products (AREA)

Abstract

A workpiece carrier comprises surface regions for contact with a workpiece, and ceramic material disposed at the surface regions. Independent claims are also included for: (A) production of ceramic material for a workpiece carrier, by producing a porous carbon skeleton, and infiltrating the porous skeleton with silicon; and (B) inductive heating of workpieces by inductively hardening workpieces with the above workpiece carrier by placing the workpiece carrier partially within an induced field during a hardening operation.

Description

Die Erfindung betrifft einen Werkstückträger für die induktive Erwärmung von Werkstücken, der zumindest an den Bereichen seiner Oberfläche, die von den Werkstücken berührt werden, keramische Materialien enthält.The invention relates to a workpiece carrier for the inductive heating of workpieces, which contains ceramic materials at least at the areas of its surface, which are touched by the workpieces.

Ein wichtiges Anwendungsgebiet der Erwärmung mittels elektromagnetischer Induktion ist die Härtung von Werkstücken aus Stahl oder Guss. Das Oberflächenhärten von Werkstücken aus Stahl oder Guss erfolgt bei Temperaturen unterhalb der Erweichungstemperatur. Typischerweise werden Härtungen bei Temperaturen von 850 bis 1000 °C ausgeführt.
Beim induktiven Härten umschließt eine i.a. von hochfrequentem Wechselstrom durchflossene Spule (Induktor) das zu härtende Werkstück. Nach dem Induktionsgesetz baut sich um jeden von einem Wechselstrom durchflossenen Leiter ein magnetisches Wechselfeld auf. Dadurch werden in einem leitfähigen Werkstück, das sich innerhalb dieses Feldes befindet, Wirbelströme induziert. Die induzierten Wirbelströme, die durch den Skineffekt in die äußeren Werkstückschichten gedrängt werden, erwärmen diese Bereiche wegen des elektrischen Widerstands sehr schnell. Die Härtetiefe wird maßgeblich von der Frequenz f des Wechselstroms bestimmt. Die Dicke δ der Schicht, in der etwa 85% der erzeugten Wärme wirksam ist, beträgt: δ = ρ fμ

Figure imgb0001

(ρ = spezifischer elektrischer Widerstand, µ = magnetische Permeabilität (µr* µ0)
Die geringste - bei hohen Frequenzen - erreichbare Härtetiefe beträgt ca. 0,1 mm. Bei kleineren Frequenzen ist die stromdurchflossene Schicht dicker, das heißt, das Werkstück wird tiefer vom Strom durchflossen und durchgewärmt. Dieser Effekt wird ausgenutzt, um durch Auswahl der Frequenz die gewünschte Einwärmtiefe einstellen.
Der besondere Vorteil der induktiven Erwärmung besteht darin, dass die Wärme im Werkstück selbst erzeugt wird, ohne dass eine äußere Wärmequelle erforderlich ist. Die Erwärmung mittels Induktion ist sehr gut regelbar und daher gut reproduzierbar.An important field of application of the heating by means of electromagnetic induction is the hardening of workpieces made of steel or cast iron. Surface hardening of steel or cast workpieces takes place at temperatures below the softening temperature. Typically, curing is carried out at temperatures of 850 to 1000 ° C.
In inductive hardening, a coil (inductor), through which high-frequency alternating current flows, encloses the workpiece to be hardened. According to the law of induction, an alternating magnetic field builds up around each conductor through which an alternating current flows. As a result, eddy currents are induced in a conductive workpiece located within this field. The induced eddy currents, which are forced by the skin effect into the outer workpiece layers, heat these areas very quickly because of the electrical resistance. The hardness depth is largely determined by the frequency f of the alternating current. The thickness δ of the layer in which about 85% of the heat generated is effective is: δ = ρ fμ
Figure imgb0001
(ρ = specific electrical resistance, μ = magnetic permeability (μ r * μ 0 )
The lowest hardness depth achievable at high frequencies is approx. 0.1 mm. At lower frequencies, the current-carrying layer is thicker, that is, the workpiece is flowed through by the current deeper and warmed through. This effect is used to set the desired warming depth by selecting the frequency.
The particular advantage of inductive heating is that the heat is generated in the workpiece itself, without an external heat source is required. The heating by induction is very easy to control and therefore well reproducible.

Weitere verbreitete Anwendungsgebiete der induktiven Erwärmung von Werkstücken aus Metall sind das Schmelzen von Stählen und Buntmetallen mit Temperaturen bis zu 1500 °C; die Erwärmung für das Schmieden auf 1250 °C, das Weichglühen und Normalisieren nach dem Kaltverformen mit Temperaturen von 750 bis 950 °C, Weich- und Hartlöten mit Temperaturen bis 1100 °C, sowie das Anlassen von Stahl bei 200 bis 300 °C. Daneben bestehen Sonderanwendungsgebiete beispielsweise im Erwärmen zum Verkleben, zum Sintern oder für andere Bearbeitungsprozesse.Other common applications of inductive heating of workpieces made of metal are the melting of steels and non-ferrous metals with temperatures up to 1500 ° C; heating for forging to 1250 ° C, soft annealing and normalization after cold forming with temperatures of 750 to 950 ° C, soft and brazing with temperatures up to 1100 ° C, and tempering of steel at 200 to 300 ° C. In addition, there are special fields of application, for example in heating for bonding, for sintering or for other machining processes.

Vorteile des Induktionshärtens gegenüber konventionellen Härtungsverfahren sind die definierte Wärmezufuhr und die gleichmäßige Aufheizung der Härtebereiche. Es ist möglich, dass Werkstück partiell zu härten.
Die Wärme wird nicht wie beim Flammhärten von außen auf das Werkstück übertragen, sondern entsteht in seinem Inneren. Daher lassen sich hohe Aufheizgeschwindigkeiten erreichen. Dank der kurzen Erwärmzeiten beim induktiven Härten sind die Taktzeiten kurz, die Zunderbildung ist gering, und die Bildung von Grobkorn im Härtegut wird weitgehend vermieden. Die kurze Erwärmzeit verringert die Verzugs- und Rissgefahr.
Der im Werkstück induzierte Strom hängt sehr stark von der Position des Werkstücks relativ zur Induktionsspule ab. Um reproduzierbare Härtungsergebnisse bei der Serienfertigung von Werkstücken zu erreichen, muss jedes Werkstück für den Härtungsprozess in der gleichen Position relativ zur Induktionsspule platziert werden. Unterschiedliche Werkstückgeometrien bedingen unterschiedliche, auf die jeweilige Werkstückgeometrie abgestimmte Induktoren und Werkstückträger.
Das Material des für die induktive Härtung verwendeten Werkstückträgers sollte nicht oder nur sehr wenig elektrisch leitend sein, damit möglichst kein Strom im Werkstückträger induziert wird, denn dadurch geht Energie verloren.
Der Werkstückträger sollte sich durch den Kontakt mit dem Werkstück möglichst wenig selbst erwärmen, so dass dem Werkstück wenig Wärme entzogen wird. Üblicherweise wird der Härteprozess mit einem Abschreckvorgang abgeschlossen, um die Abkühlung zu beschleunigen und die spezifischen Eigenschaften des zu härtenden Werkstücks zu optimieren. Befindet sich das Werkstück zu diesem Zeitpunkt noch auf dem Werkstückträger, so muss auch dieser eine Thermoschockbeständigkeit von mindestens 1200 K/s aufweisen. Gleichzeitig ist eine hohe Resistenz gegen chemische und/oder oxidative Angriffe gefordert, um in der Wahl des Abschreckmediums frei zu sein. Weiterhin sind Materialien zu wählen, die unter dem Einfluss von Flüssigkeiten wie etwa der Abschreckemulsion nicht absorbierend wirken und/oder quellen.Advantages of induction hardening compared to conventional hardening methods are the defined heat input and the uniform heating of the hardness ranges. It is possible to partially harden the workpiece.
The heat is not transferred from the outside to the workpiece as in flame hardening, but is created inside. Therefore, high heating rates can be achieved. Thanks to the short heating times during inductive hardening, the cycle times are short, the scale formation is low, and the formation of coarse grain in the hardened material is largely avoided. The short heating time reduces the risk of distortion and cracking.
The current induced in the workpiece depends very much on the position of the workpiece relative to the induction coil. In order to achieve reproducible curing results in the series production of workpieces, each workpiece for the curing process must be placed in the same position relative to the induction coil. Different workpiece geometries require different inductors and workpiece carriers that are matched to the respective workpiece geometry.
The material of the workpiece carrier used for the inductive hardening should not or only very little be electrically conductive, so that as possible no current is induced in the workpiece carrier, because this energy is lost.
The workpiece carrier should heat itself as little as possible by the contact with the workpiece, so that the workpiece is extracted little heat. Typically, the quenching process is completed with a quenching process to accelerate cooling and to optimize the specific properties of the workpiece to be cured. If the workpiece is still on the workpiece carrier at this point in time, then it must also have a thermal shock resistance of at least 1200 K / s. At the same time, a high resistance against chemical and / or oxidative attacks is required to be free in the choice of quenching medium. Furthermore, materials should be chosen which do not absorb and / or swell under the influence of liquids, such as the quenching emulsion.

Weil die das Werkstück aufnehmenden Bereiche des Werkstückträgers in der Regel individuelle, auf das jeweilige Werkstück abgestimmte Geometrien aufweisen und die dafür nötigen hohen Investitionen nur bei einer hohe Stückzahl an gehärteten Werkstücken rentabel sind, ist eine lange Standzeit des Werkstückträgers erforderlich. Voraussetzungen dafür sind wiederum geringer Verschleiß und eine hohe Formstabilität (Geometrietreue) des Werkstückträgers.Because the workpiece receiving areas of the workpiece carrier usually have individual, matched to the particular workpiece geometries and the necessary high investment only at a high number of hardened workpieces are profitable, a long life of the workpiece carrier is required. Prerequisites for this, in turn, are low wear and high dimensional stability (geometric accuracy) of the workpiece carrier.

In der englischen Zusammenfassung zur japanischen Patentanmeldung JP 2003-124085 wird eine Vorrichtung zum Erwärmen eines Werkstücks offenbart. Diese Vorrichtung umfasst eine Kammer, einen Werkstückträger aus Keramik (z.B. AlN, Si3N4, Al2O3), eine in den Werkstückträger eingelassene leitfähige Schicht sowie eine Spule, welche die im Werkstückträger eingelassene leitfähige Schicht durch elektromagnetische Induktion erwärmt. Somit wird indirekt das Werkstück erwärmt.In the English summary to Japanese Patent Application JP 2003-124085 a device for heating a workpiece is disclosed. This device comprises a chamber, a ceramic workpiece carrier (eg AlN, Si 3 N 4 , Al 2 O 3 ), a conductive layer embedded in the workpiece carrier and a coil which heats the conductive layer embedded in the workpiece carrier by electromagnetic induction. Thus, indirectly, the workpiece is heated.

Die Patentschrift US-A 4 960 967 offenbart eine Schutzvorrichtung für Induktionspole eines elektromagnetischen Induktors, wie er bei der Erwärmung von Metallwerkstücken verwendet wird, vor der Wärmeabstrahlung des heißen Werkstücks sowie chemischen und mechanischen Angriffen. Die Schutzvorrichtung besteht aus einem Wärmetauscher umfassend mindestens ein nichtmagnetisches Metallrohr für den Durchfluss eines Kühlmittels, wobei jedes Rohr aus mehreren Rohrelementen besteht, die an ihren Enden miteinander verbunden sind und im wesentlichen parallel in einer Ebene mit den Polflächen angeordnet sind, wobei zwischen jeweils zwei Rohrelementen höchstens ein einziger elektrischer Kontakt besteht. Die Rohre sind in einem feuerfesten Material eingebettet, insbesondere in einem feuerfesten Siliciumcarbid-Beton. Dieser Beton kann zusätzlich mit einer Isolierschicht aus Glaskeramik, Aluminiumoxid oder Siliciumoxid bedeckt werden.The patent US Pat. No. 4,960,967 discloses a protection device for induction poles of an electromagnetic inductor as used in the heating of metal workpieces, prior to heat radiation of the hot workpiece and chemical and mechanical attacks. The protection device consists of a heat exchanger comprising at least one non-magnetic metal tube for the passage of a coolant, each tube consisting of a plurality of tubular elements which are connected at their ends and arranged substantially parallel in a plane with the pole faces, wherein between each two tubular elements at most a single electrical contact exists. The tubes are embedded in a refractory material, particularly in a refractory silicon carbide concrete. This concrete can be additionally covered with an insulating layer of glass ceramic, alumina or silica.

Die Patentschrift US-A 2 482 364 offenbart eine Vorrichtung zur Wärmebehandlung magnetischer Materialien. In dieser Vorrichtung sind keramischen Träger für die Auflage der zu behandelnden Werkstücke vorgesehen. Die keramischen Träger sind beispielsweise aus nur Lehm bzw. Ton, Ziegel o .ä. elektrisch isolierenden Materialien ausgebildet.The patent US-A 2 482 364 discloses a device for heat treatment of magnetic materials. In this device ceramic supports are provided for the support of the workpieces to be treated. The ceramic supports are made, for example, of clay or clay, brick or the like. formed electrically insulating materials.

Werkstückträger aus Keramik für die Wärmebehandlung von Werkstücken sind außerdem aus der japanischen Patentanmeldung JP 57 057 049 A bekannt.Ceramic workpiece carriers for the heat treatment of workpieces are also made of Japanese Patent Application JP 57 057 049 A known.

Die Aufgabe der vorliegenden Erfindung besteht darin, einen Werkstückträger für die induktive Erwärmung, insbesondere für die induktive Härtung von Werkstücken, aus einem Material bereit zu stellen, das die vorgenannten Anforderungen erfüllt und die Herstellung von Werkstückträgern mit komplexen Geometrien erlaubt.
Die Aufgabe wird dadurch gelöst, dass zumindest der Bereich des Werkstückträgers, den das zu erwärmende Werkstück berührt, keramisches Material mit einem elektrischen Widerstand mindestens von 50 µΩ enthält, wobei das keramische Material neben Carbidphasen Phasen aus elementaren Kohlenstoff oder Phasen aus elementaren Kohlenstoff sowie metallische Phasen aus dem das Carbid bildenden Metall bzw. den die Carbide bildenden Metallen enthält.The object of the present invention is to provide a workpiece carrier for inductive heating, in particular for the inductive hardening of workpieces, made of a material that meets the aforementioned requirements and allows the production of workpiece carriers with complex geometries.
The object is achieved in that at least the region of the workpiece carrier, which contacts the workpiece to be heated, contains ceramic material having an electrical resistance of at least 50 μΩ, wherein the ceramic material in addition to carbide phases of elemental carbon or phases of elemental carbon and metallic phases from which the carbide-forming metal or the carbides forming metals.

Weitere Details, Vorteile und Ausführungsvarianten der Erfindung sind aus der folgenden ausführlichen Beschreibung und den Figuren ersichtlich.Further details, advantages and embodiments of the invention will become apparent from the following detailed description and the figures.

Die Figuren zeigen

Figur 1
einen erfindungsgemäßen Werkstückträger, dessen Oberfläche in den für die Auflage des Werkstücks vorgesehenen Bereichen eine Beschichtung aus einem keramischen Werkstoff aufweist
Figur 2
einen erfindungsgemäßen Werkstückträger, in dessen Oberfläche Einlagen aus einem keramischen Werkstoff eingesetzt sind, welche eine Auflage für das zu härtende Werkstück bilden
The figures show
FIG. 1
a workpiece carrier according to the invention, the surface of which has a coating of a ceramic material in the areas provided for the support of the workpiece
FIG. 2
a workpiece carrier according to the invention, in the surface deposits of a ceramic material are used, which form a support for the workpiece to be hardened

Ein erfindungsgemäßer Werkstückträger entsprechend Figur 1 lässt sich herstellen, indem die Oberfläche eines Werkstückträgers β aus einem herkömmlichen Material, beispielsweise aus einem mit Glasfasern verstärkten hochtemperaturbeständigen Duroplast, in dem Bereich a, der für die Auflage des zu härtenden Werkstücks α vorgesehen ist, mit einem keramischen Material beschichtet wird. Die nicht vom Werkstück α berührte Oberfläche b des Werkstückträgers ist unbeschichtet. Jedoch kann auch die gesamte Oberfläche des Werkstücks beschichtet werden, z.B. in solchen Fällen, in denen eine komplette Beschichtung verfahrenstechnisch einfacher herzustellen ist als eine gezielte, auf bestimmte Teile der Oberfläche beschränkte Beschichtung. Verfahren zur Herstellung keramischer Beschichtungen, beispielsweise Plasmaspritzen oder chemische Dampfphasenabscheidung (CVD) sind dem Fachmann bekannt.A workpiece carrier according to the invention according to FIG. 1 can be produced by forming the surface of a workpiece carrier .beta. From a conventional material, for example from a high-temperature-resistant duroplastic reinforced with glass fibers, in the region a, which is intended for supporting the workpiece to be hardened Material is coated. The not touched by the workpiece α surface b of the workpiece carrier is uncoated. However, the entire surface of the workpiece can also be coated, for example, in those cases in which a complete coating is easier to produce in terms of process engineering than a specific coating which is limited to certain parts of the surface. Methods for producing ceramic coatings, for example plasma spraying or chemical vapor deposition (CVD), are known to the person skilled in the art.

Eine alternative Variante des erfindungsgemäßen Werkstückträgers ist in Figur 2 dargestellt. In dem für die Auflage der zu härtenden Werkstücke vorgesehenen Oberflächenbereich eines Werkstückträger-Grundkörpers δ aus einem herkömmlichen hochtemperaturbeständigen Material, beispielsweise mit Glasfasern verstärkten hochtemperaturbeständigen Duroplast, ist mindestens eine Aussparung vorgesehen, in welche eine passgenau geformte Einlage (Inlay) γ aus einem keramischen Material eingesetzt wird. Die nach außen weisenden Oberflächen der Einlagen sind entsprechend den Erfordernissen der Geometrien der zu härtenden Werkstücke gestaltet, weisen beispielsweise Rillen, Nute oder anders geformte Vertiefungen zur Aufnahme des Werkstücks auf (in Figur 2 nicht dargestellt). Das Inlay oder die Inlays übernehmen die Trägerfunktion für das Werkstück, d.h. das Werkstück wird von dem Inlay oder den Inlays gehalten, so dass nur die Oberflächen des oder der Inlays vom Werkstück berührt werden, aber nicht die Oberfläche des Grundkörpers.
Die Inlays können herausnehmbar sein, so dass der Werkstückträger auf verschiedene Werkstückgeometrien angepasst werden kann, indern jeweils für das zu härtende Werkstück passenden Inlays eingesetzt werden. Alternativ können die Inlays durch Verkleben, Einpressen o.ä. fest mit dem Werkstückträger verbunden werden.
Die in Figur 1 und 2 dargestellten Geometrien der Werkstückträger und Werkstücke sind nur beispielhaft zu verstehen, denn die Erfindung ist nicht auf bestimmte Geometrien von Werkstückträger und Werkstück begrenzt.
Selbstverständlich ist es im Rahmen der vorliegenden Erfindung auch möglich, den gesamten Werkstückträger einstückig aus einem keramischen Werkstoff zu bilden.An alternative variant of the workpiece carrier according to the invention is shown in FIG. In the intended for the support of the workpieces to be hardened surface area of a workpiece carrier body δ of a conventional high temperature resistant material, for example glass fiber reinforced high temperature thermoset, at least one recess is provided, in which a precisely shaped insert (inlay) γ used from a ceramic material becomes. The outwardly facing surfaces of the inserts are designed according to the requirements of the geometries of the workpieces to be cured, for example, grooves, grooves or other shaped recesses for receiving the workpiece (not shown in Figure 2). The inlay or inlays take over the support function for the workpiece, ie the workpiece is held by the inlay or inlays, so that only the surfaces of the inlay (s) are touched by the workpiece, but not the surface of the main body.
The inlays can be removable, so that the workpiece carrier can be adapted to different workpiece geometries, while in each case suitable for the workpiece to be hardened inlays are used. Alternatively, the inlays can be glued, pressed or similar. firmly connected to the workpiece carrier.
The geometries of the workpiece carriers and workpieces illustrated in FIGS. 1 and 2 are only to be understood as examples, since the invention is not limited to specific geometries of workpiece carrier and workpiece.
Of course, it is within the scope of the present invention also possible to form the entire workpiece carrier in one piece from a ceramic material.

Der spezifische elektrische Widerstand des in den erfindungsgemäßen Werkstückträgern eingesetzten keramischen Materials beträgt mindestens 50 µΩ * m, bevorzugt mehr als 100 µΩ * m und besonders bevorzugt mehr als 150 µΩ * m.
Im folgenden werden die Zusammensetzungen geeigneter keramischer Materialien für die erfindungsgemäßen Werkstückträger angegeben. Im Fall von beschichteten Werkstückträgern (Figur 1) betreffen die folgenden Angaben nur die Zusammensetzung der Beschichtung in den vom Werkstück berührten Oberflächenbereichen a. Im Fall von Werkstückträgern mit Inlays (Figur 2) gelten die Zusammensetzungen nur für die Inlays γ.
Der Werkstoff muss nicht zu 100 % keramisch sein, sein keramischer Anteil muss aber mindestens 10 Massen-% betragen.The specific electrical resistance of the ceramic material used in the workpiece carriers according to the invention is at least 50 μΩ * m, preferably more than 100 μΩ * m and particularly preferably more than 150 μΩ * m.
In the following, the compositions of suitable ceramic materials are given for the workpiece carriers according to the invention. In the case of coated workpiece carriers (FIG. 1), the following information relates only to the composition of the coating in the surface areas a touched by the workpiece. In the case of workpiece carriers with inlays (Figure 2), the compositions apply only to the inlays γ.
The material does not have to be 100% ceramic, but its ceramic content must be at least 10% by mass.

Der keramische Werkstoff enthält neben Carbid Phasen aus elementaren Kohlenstoff oder Phasen aus elementarem Kohlenstoff und metallische Phasen aus dem das Carbid bildenden Metall oder den die Carbide bildenden Metallen wie Silicium, Titan, Wolfram. Der massebezogene Anteil des Carbids in diesem Werkstoff beträgt mindestens 10 %. Der sich auf 100 % ergänzende Restgehalt des Materials enthält maximal 50 % Kohlenstoff sowie maximal 80 % an schmelzbaren Elementen (dem carbidbildenden Metall oder den carbidbildenden Metallen in elementarer Form).The ceramic material contains not only carbide phases of elemental carbon or phases of elemental carbon and metallic phases of the carbide-forming metal or the carbides forming metals such as silicon, titanium, tungsten. The mass-based proportion of the carbide in this material is at least 10%. The residual content of the material, which adds up to 100%, contains a maximum of 50% of carbon and a maximum of 80% of fusible elements (the carbide-forming metal or the carbide-forming metals in elemental form).

Ein Material, das die vorgenannten Anforderungen hinsichtlich Formstabilität, geringer elektrischer und thermischer Leitfähigkeit, chemischer Resistenz und Thermoschockbeständigkeit besonders gut erfüllt, ist ein keramischer Verbundwerkstoff aus mindestens 35 Massen-% Siliciumcarbid mit Anteilen elementaren Kohlenstoffs (1 - 35 Massen-%) und elementaren Siliciums (1 - 60 Massen-%). Ausgangsbasis für die Herstellung dieses hochkeramisierten Materials ist ein poröses Kohlenstoffgerüst. Dieses wird mit flüssigem Silicium infiltriert, so dass ein vornehmlich Siliciumcarbid, Silicium und Kohlenstoff enthaltender Verbundwerkstoff entsteht. Alternativ kann die Silicierung über die Gasphase erfolgen.
Siliciumcarbid und Kohlenstoff enthaltende Verbundwerkstoffe sind auch erhältlich durch Zugabe von Silicium enthaltenden Polymeren, bei deren Pyrolyse Siliciumcarbid gebildet wird, z.B. Silanen oder Siloxanen, zu dem porösen Kohlenstoffgerüst, und anschließende Pyrolyse. Werkstoffe nach der zuletzt beschriebenen Variante können durch einen Flüssigsiliciervorgang unmittelbar im Anschluss an die Pyrolyse oder in einem separaten Schritt mit Silicium nachverdichtet werden.
Das poröse Kohlenstoffgerüst des Ausgangsmaterials liegt entweder bereits in carbonisierter Form vor, beispielsweise als carbonisiertes Filz oder Vlies, oder es wird durch Pyrolyse (Carbonisierung) eines Vorkörpers aus einem carbonisierbaren festen Material, d.h. einer mit hoher Ausbeute in Kohlenstoff umwandelbaren Kohlenstoffquelle, beispielsweise Holz, Holzwerkstoffe, Holzspäne, Holzmehle, Zellulose, Zellstoff, oder Wolle oder textile Strukturen aus Zellulose oder Wolle, hergestellt.
Das poröse Kohlenstoffgerüst bzw. der pyrolysierbare Vorkörper, aus dem das poröse Kohlenstoffgerüst hergestellt wird, kann zwecks Verdichtung einmal oder mehrfach mit ein carbonisierbaren Bindern imprägniert werden, der anschließend carbonisiert wird. Carbonisierbare, d.h. mit einer hohen Kohlenstoffausbeute pyrolysierbare Binder sind u.a. Phenolharze, Melaminharze, Lignin und Pech. Darüber hinaus können Binder verwendet werden, die gleichzeitig als Siliciumcarbidquelle wirken, beispielsweise ein Silan oder Siloxan, bei dessen Pyrolyse neben Kohlenstoff Siliciumcarbid entsteht, oder Mischungen verschiedener Binder oder verschiedene Binder in verschiedenen Imprägnationsschritten .
Alternativ ist das Ausgangsmaterial für das poröse Kohlenstoffgerüst ein Gemisch aus Kohlenstoff, beispielsweise in Form von Fasern oder gemahlenem Material, oder einer oder mehreren festen Kohlenstoffquellen, die sich mit hoher Kohlenstoffausbeute pyrolysieren (carbonisieren) lässt, z.B. Holzmehl, Holzspäne, Zellstoff oder Zellulosefasern, und einem carbonisierbaren Binder. Aus diesem Gemisch wird beispielsweise durch Verpressen oder eine andere Methode der Formgebung ein Grünkörper hergestellt, bei dessen Pyrolyse ein poröses Kohlenstoffgerüst erhalten wird.
Dem Gemisch können Additive zugesetzt werden, um die Eigenschaften des Verbundwerkstoffs noch besser an die zu erfüllenden Anforderungen anzupassen, z.B. die thermische und elektrische Leitfähigkeit zu vermindern und die Festigkeit zu erhöhen. Dazu sind beispielsweise Additive in Form von Pulvern oder Fasern mit einer Länge kleiner 10 mm aus keramischen Materalien, z.B. Siliciumcarbid- oder Aluminiumoxid-Fasern geeignet.
Durch einen Zusatz von Kohlenstoffanteil zu dem Gemisch aus festen pyrolysierbaren Kohlenstoffquellen (z.B. Holzspänen, Holzmehl, Zellulosefasern, Zellstoff) und carbonisierbaren Bindern, aus dem der Grünkörper hergestellt wird, lässt sich der Schrumpf bei der Pyrolyse merklich vermindern. Dieser Kohlenstoffanteil wird erhalten, indem dem Gemisch Kohlenstoff zugesetzt wird in Form von Kohlenstoff- oder Graphitpulver, Ruß, Kohlenstoff-Kurzfasem (mit einer Länge unter 10 mm) oder Kohlenstoff-Nanotubes.
Über die Kohlenstoffmenge des Ausgangsmaterials lässt sich der Grad der Konvertierung zu Siliciumcarbid beeinflussen. Für die erfindungsgemäße Verwendung wird die Zusammensetzung des keramischen Verbundwerkstoffs derart eingestellt, dass die nicht zu Siliciumcarbid umgewandelten Kohlenstoffbestandteile weitestgehend durch Silicium und/oder Siliciumcarbid gekapselt sind, so dass keine zusammenhängenden Leitungspfade existieren. Insbesondere in den Bereichen des Werkstückträgers, welche direkt von dem zu härtenden Werkstück berührt werden, muss der Gehalt des Vebundwerkstoffs an nicht zu Carbid umgewandelten Kohlenstoff sehr gering sein und vorzugsweise bei Null liegen, um u.a. ein Aufkohlen des Werkstücks zu vermeiden. Es wird also ein hoher Konvertierungsgrad des Kohlenstoffs zu Siliciumcarbid benötigt. Dies ist erreichbar beispielsweise durch eine relativ lange Verweildauer der Silicierungstemperatur über der Schmelztemperatur des Siliciums (typischerweise mehr als 60 Minuten).
Infolge der Kapselung des nicht zu Carbid umgewandelten Restkohlenstoffs weist das Material den anforderungsgemäßen hohen elektrischen Widerstand auf. Es wurden spezifische Widerstände um 170 µΩ * m ermittelt, also innerhalb des besonders bevorzugten Bereichs von mehr als 150 µΩ * m.
Überraschenderweise wirkt sich diese Kapselung des Kohlenstoffs gleichzeitig positiv auf das Thermoschockverhalten der beschriebenen Werkstoffe aus. Diese ist größer als 1200 K/s und erfüllt damit die eingangs genannten Anforderungen. Die Resistenz gegen oxidative Einwirkungen wird durch die Kapselung des Kohlenstoffs ebenfalls positiv beeinflußt. Die erfindungsgemäßen Werkstückträger konnten bis zu 10.000 Härtungszyklen bei ca. 1.000 °C von jeweils 3 bis 5 Minuten Dauer ausgesetzt werden, ohne dass eine merkliche Massenabnahme bzw. oxidativer Angriff der Oberfläche festzustellen war.
Der keramische Körper aus dem Siliciumcarbid, Silicium und Kohlenstoff enthaltenden Verbundwerkstoff dient entweder selbst als Werkstückträger, oder als Einsatz für die Werkstückaufnahme in einem Werkstückträger aus einem herkömmlichen Material entsprechend Figur 2.A material that meets the above requirements in terms of dimensional stability, low electrical and thermal conductivity, chemical resistance and thermal shock resistance is a ceramic composite of at least 35 mass% silicon carbide with fractions of elemental carbon (1-35 mass%) and elemental silicon (1 - 60 mass%). The starting point for the production of this high-ceramic material is a porous carbon skeleton. This is infiltrated with liquid silicon to form a predominantly silicon carbide, silicon and carbon containing composite. Alternatively, the siliconization can be done via the gas phase.
Silicon carbide and carbon composites are also obtainable by addition of silicon-containing polymers which, upon pyrolysis, form silicon carbide, eg, silanes or siloxanes, to the porous carbon skeleton and subsequent pyrolysis. Materials according to the last-described variant can be densified with silicon by means of a liquid-silica process immediately after the pyrolysis or in a separate step.
The porous carbon skeleton of the starting material is either already present in carbonized form, for example as a carbonized felt or nonwoven, or it is by pyrolysis (carbonization) of a preform made of a carbonizable solid material, ie a carbon source which can be converted into carbon with high yield, for example wood, wood-based materials , Wood shavings, wood flour, cellulose, pulp, or wool or textile structures made of cellulose or wool.
The porous carbon skeleton or the pyrolyzable preform from which the porous carbon skeleton is made can be impregnated once or several times with a carbonizable binder for the purpose of densification, which is then carbonized. carbonizable, ie, with a high carbon yield pyrolysable binders include phenolic resins, melamine resins, lignin and pitch. In addition, it is possible to use binders which simultaneously act as a source of silicon carbide, for example a silane or siloxane, the pyrolysis of which produces silicon carbide in addition to carbon, or mixtures of different binders or various binders in various impregnation steps.
Alternatively, the starting material for the porous carbon skeleton is a mixture of carbon, for example in the form of fibers or ground material, or one or more solid carbon sources which pyrolyze (carbonize) with high carbon yield, eg wood flour, wood shavings, pulp or cellulose fibers, and a carbonizable binder. From this mixture, for example, by pressing or another method of shaping a green body is produced, the pyrolysis, a porous carbon skeleton is obtained.
Additives can be added to the mixture in order to better match the properties of the composite with the requirements to be met, for example to reduce the thermal and electrical conductivity and to increase the strength. For this example, additives in the form of powders or fibers with a length of less than 10 mm of ceramic materials, such as silicon carbide or alumina fibers are suitable.
By adding carbon to the mixture of solid pyrolyzable carbon sources (eg, wood chips, wood flour, cellulose fibers, pulp) and carbonizable binders from which the green body is made, shrinkage in pyrolysis can be significantly reduced. This carbon content is obtained by adding carbon to the mixture in the form of carbon or graphite powder, carbon black, short carbon fibers (less than 10 mm in length) or carbon nanotubes.
The amount of carbon in the starting material can influence the degree of conversion to silicon carbide. For the inventive use, the composition of the ceramic composite is adjusted such that the non-silicon carbide converted carbon components are largely encapsulated by silicon and / or silicon carbide such that there are no contiguous conductive paths. In particular in the areas of the workpiece carrier which are directly contacted by the workpiece to be hardened, the content of the composite material to non-carbide converted carbon must be very low and preferably at zero, inter alia, to avoid carburizing of the workpiece. So it is a high degree of conversion of carbon to silicon carbide needed. This can be achieved, for example, by a relative long residence time of the siliconization temperature above the melting temperature of the silicon (typically more than 60 minutes).
Due to the encapsulation of the non-carbide converted residual carbon, the material has the requisite high electrical resistance. Specific resistances were determined around 170 μΩ * m, ie within the particularly preferred range of more than 150 μΩ * m.
Surprisingly, this encapsulation of the carbon simultaneously has a positive effect on the thermal shock behavior of the materials described. This is greater than 1200 K / s and thus meets the requirements mentioned above. The resistance to oxidative effects is also positively influenced by the encapsulation of the carbon. The workpiece carriers according to the invention were able to be exposed to up to 10,000 curing cycles at about 1,000 ° C. for 3 to 5 minutes in each case, without a noticeable decrease in mass or oxidative attack of the surface being observed.
The ceramic body of the silicon carbide, silicon and carbon-containing composite material either serves itself as a workpiece carrier, or as an insert for the workpiece holder in a workpiece carrier made of a conventional material according to FIG. 2.

Um den Bearbeitungsaufwand bei der Formgebung des keramischen Materials zu verringern, wird vorzugsweise ein bereits endkonturnaher Grün- oder Vorkörper hergestellt. Dies geschieht, je nach Beschaffenheit des Ausgangsmaterials, beispielsweise mittels Spritzgießen, Pressen (z.B. in einem passend geformten Gesenk), Stanzen, Schneiden, Drehen oder anderer geläufiger Verfahren. Bei der Auslegung des Grünkörpers ist zu berücksichtigen, dass es insbesondere bei der Pyrolyse zu einem gewissen Materialschwund kommt. Daher müssen die Grünkörper ggf. ein den Schwund kompensierendes Übermaß aufweisen. Jedoch lässt sich, wie bereits erwähnt, der Schwund vermindern, indem dem zu pyrolysierenden Ausgangsmaterial Kohlenstoff zugesetzt wird.
Soweit noch eine Endkonturierung des keramischen Körpers entsprechend der Geometrie der aufzunehmenden Werkstücke nötig ist, erfolgt diese mittels üblicher Verfahren wie Bohren, Schleifen, Erodieren u.ä. Es wird jedoch aus wirtschaftlichen Gründen angestrebt, den keramischen Körper oder die keramischen Teilbereiche des Werkstückträgers mit einer solchen Oberflächen- und Geoemtriegüte herzustellen, dass er im keramischen Zustand nicht oder nur wenig bearbeitet werden muss, beispielsweise sich die Nachbearbeitung auf das Herstellen von Bohrungen beschränkt. Maßnahmen zur Herstellung von keramischen Körpern mit hoher Oberflächengüte, die keine Nachbearbeitung verlangen, sind dem Fachmann bekannt. In diesem Zusammenhang ist beispielsweise die Verwendung sehr feinkörniger Ausgangsmaterialien vorteilhaft.In order to reduce the processing effort in the shaping of the ceramic material, an already near net shape green or preform is preferably prepared. This happens, depending on the nature of the starting material, for example by means of injection molding, pressing (eg in a suitably shaped die), stamping, cutting, turning or other common methods. When designing the green body, it must be taken into account that some material shrinkage occurs, in particular during pyrolysis. Therefore, the green body may have to compensate for the shrinkage excess. However, as already mentioned, the shrinkage can be reduced by adding carbon to the starting material to be pyrolyzed.
As far as a final contouring of the ceramic body according to the geometry of the male workpieces is necessary, this is done by conventional methods such as drilling, grinding, erosion, etc. However, it is desirable for economic reasons to produce the ceramic body or the ceramic portions of the workpiece carrier with such a surface and Geoemtriegüte that it does not have to be machined or only slightly in the ceramic state, for example, the post-processing limited to the production of holes. Measures for the production of ceramic bodies with high surface quality, which require no post-processing, are known in the art. In this context, for example, the use of very fine-grained starting materials is advantageous.

Ausführungsbeispieleembodiments Beispiel 1:Example 1:

Ein plattenförmiger poröser Kohlenstoffkörper mit einer Dichte von 0,5 - 0,8 g/cm3 wird hergestellt aus übereinander gestapelten und verdichteten carbonisierten Filzmatten. Dieser Vorkörper wurde mit flüssigem Silicium unter Vakuum in Berührung gebracht. Dabei wandelten sich die Kohlenstoffbestandteile zum überwiegenden Teil in Siliciumcarbid um. Die Restporosität wird weitestgehend durch elementares Silicium gefüllt.
Nach der Silicierung erfolgte die Endformgebung zu einem Werkstückträger für die Aufnahme von Kurbelwellen während des Härteprozesses. Dazu wurden aus einer Oberfläche des plattenförmigen Körpers langgestreckte Vertiefungen mit u-förmigem Querschnitt mittels Elektroerosionsverfahren mit einer Toleranz von weniger als +-0,1 mm herausgearbeitet. Durch diesen Bearbeitungsvorgang wurde die geforderte Oberflächengüte ohne zusätzliche Oberflächenbehandlung erreicht.A plate-shaped porous carbon body having a density of 0.5 - 0.8 g / cm 3 is made of stacked and compacted carbonized felt mats. This preform was contacted with liquid silicon under vacuum. In the process, most of the carbon components were converted to silicon carbide. The residual porosity is largely filled by elemental silicon.
After the siliconization, the final shaping took place to a workpiece carrier for the acceptance of crankshafts during the hardening process. For this purpose, elongated recesses having a U-shaped cross-section were produced from a surface of the plate-shaped body by means of electroerosion processes with a tolerance of less than + -0.1 mm. Through this machining process, the required surface quality was achieved without additional surface treatment.

Beispiel 2:Example 2:

Der in Beispiel 1 verwendete carbonisierte Filz wurde gemahlen. Das Mahlgut wurde mit einem pyrolysierbaren Bindemittel versetzt, zu einem runden scheibenförmigen Rohling verpresst, ausgehärtet, pyrolysiert, formgebend bearbeitet und siliciert. Bei der Formgebung wurde eine Oberfläche des Rohlings so ausgearbeitet, dass sie einen erhöhten umlaufenden Rand aufweist. Der so erhaltene keramische Formkörper dient als Werkstückträger bei der induktiven Oberflächenhärtung von Laufflächen für Kugellager. Der erhöhte umlaufende Rand wirkt als Fixierungskante für die zu härtenden Werkstücke.The carbonized felt used in Example 1 was ground. The millbase was mixed with a pyrolyzable binder, pressed into a round disc-shaped blank, cured, pyrolyzed, shaping and siliconized. During molding, a surface of the blank was machined to have a raised peripheral edge. The resulting ceramic molded body serves as a workpiece carrier in the inductive surface hardening of running surfaces for ball bearings. The raised peripheral edge acts as a fixing edge for the workpieces to be hardened.

Beispiel 3:Example 3:

Eine Platte aus Buchenholz wurde pyrolysiert, in die Form eines Werkstückträgers für die Aufnahme von Zahnrädern gebracht und anschließend über die Flüssigphase siliciert. Wegen der zu erwartenden Schrumpfung von ungefähr 40 % des Ausgangsvolumens beim Silicieren erfolgte die Formgebung der pyrolysierten Holzplatte mit einem entsprechenden Übermaß. Der silicierte Formkörper wurde zur genauen Einstellung der gewünschten Maße nachbearbeitet.A beechwood panel was pyrolyzed, placed in the form of a workpiece carrier for receiving gears, and then silicated over the liquid phase. Due to the expected shrinkage of about 40% of the initial volume in siliciding, the shaping of the pyrolyzed wood panel was carried out with a corresponding excess. The silicided molded body was post-processed to precisely set the desired dimensions.

Beispiel 4:Example 4:

Gemahlenes, pulverförmiges Holzmehl wurde mit Phenolharz versetzt und unter Einwirkung von Druck (12 N/mm2) und Temperatur (bis maximal 130 °C) in einer Gesenk-Form zu einem sogenannten Holzwerkstoff ausgehärtet. Das verwendete Gesenk bildete die Kontur eines Formteils mit einer langgestreckten Vertiefung mit U-förmigem Querschnitt auf einer Oberfläche.
Der so erhaltene Grünkörper wurde pyrolysiert und durch Silicierung zu einem an Siliciumcarbid reichen keramischen Körper umgewandelt. Dieser dient zur Fixierung von Gewindestangen bei der induktiven Härtung.Ground, powdered wood flour was mixed with phenolic resin and cured under pressure (12 N / mm 2 ) and temperature (up to a maximum of 130 ° C) in a die-shape to a so-called wood material. The die used formed the contour of a molded article having an elongated U-shaped cross-section on a surface.
The green body thus obtained was pyrolyzed and converted by siliconization into a ceramic body rich in silicon carbide. This serves to fix threaded rods during inductive hardening.

Beispiel 5:Example 5:

Aus einem durch Infiltration von Holzmehlen mit einem bei der Pyrolyse Siliciumcarbid bildenden Polymer erhaltenen Rohmaterial wurden durch Formpressen offenporige Grünkörper erzeugt, die bei der anschließenden Pyrolyse und Silicierung in hochkeramisierte SiSiC-Körper (Dichte 2,0 - 3,15 g/cm3, spezifischer Widerstand 172 µΩ * m) umgewandelt wurden.
Die Grünkörper hatten die Gestalt von Werkstückträgern mit Fixierungskanten für aufzunehmende Werkstücke. Die so erhaltenen Keramikkörper dienen als Werkstückträger bei der induktiven Härtung von Getriebekomponenten.From a raw material obtained by infiltrating wood flours with a pyrolysis silicon carbide-forming polymer raw material, open-pore green bodies were produced by molding, which in subsequent pyrolysis and siliconization into highly ceramized SiSiC bodies (density 2.0-3.15 g / cm 3 , more specific Resistance 172 μΩ * m) were converted.
The green bodies took the form of workpiece carriers with fixing edges for workpieces to be picked up. The ceramic bodies thus obtained serve as workpiece carriers in the inductive hardening of transmission components.

Beispiel 6:Example 6:

Zu mit einem pyroliserbaren Bindemittel infiltriertem Holzmehl wurde als Additiv Kohlenstoffpulver mit einem Teilchendurchmesser von 5-30 µm beigemischt. Daraus wurde ein Grünkörper in Form einer Lochplatte hergestellt. Dieser wurde pyrolysiert und siliciert.
Durch das Additiv wird der Schrumpf der Vorkörper während der Pyrolyse wesentlich verringert. Dadurch konnte die gewünschte Geometrie ohne Nachbearbeitung in ausreichender Formtreue umgesetzt werden.
Der so erhaltene Keramikkörper wurde als Aufnahmevorrichtung für zu härtende Metallbolzen verwendet.Carbon powder having a particle diameter of 5-30 μm was added as an additive to wood meal infiltrated with a pyrolyzable binder. From this, a green body in the form of a perforated plate was produced. This was pyrolyzed and silicided.
The additive substantially reduces the shrinkage of the preforms during pyrolysis. As a result, the desired geometry could be implemented in sufficient dimensional accuracy without reworking.
The ceramic body thus obtained was used as a receptacle for metal bolts to be hardened.

Beispiel 7:Example 7:

Ein Gemisch aus Zellstoff und Zellulose mit Lignin als Bindemittel wurde zu einem endkonturnahen Grünkörper in Form einer Platte mit Fixierungskanten für Werkstücke verpresst. Dieser Körper wies nach der Pyrolyse ein sehr feinporiges Gefüge auf. Nach der Infiltration von flüssigem Silicium entstand ein SiSiC-Werkstoff mit einem massebezogenen Anteil an elementarem, nicht im Carbid gebundenem Silicium von über 30 %. Der massebezogene Anteil an elementarem Kohlenstoff lag unter 3%.
Die so erhaltenen Formteile dienen als Arretierhilfen für Werkstücke in Induktionshärteanlagen. A mixture of pulp and cellulose with lignin as binder was pressed into a near-net shape green body in the form of a plate with fixing edges for workpieces. This body had a very fine-pored structure after pyrolysis. After infiltration of liquid silicon, a SiSiC material with a mass fraction of elemental, non-carbide bonded silicon of more than 30% was formed. The mass fraction of elemental carbon was below 3%.
The moldings thus obtained serve as locking aids for workpieces in induction hardening plants.

Claims (24)

  1. A workpiece carrier for the inductive heating of workpieces, the workpiece carrier containing ceramic material with an electrical resistance of at least 50 µΩ at least on the surface regions contacted by the workpiece, characterised in that
    the ceramic material contains, apart from carbide phases, phases of elementary carbon or phases of elementary carbon as well as metallic phases of the metal forming the carbide or of the metals forming the carbides.
  2. A workpiece carrier according to claim 1, characterised in that the resistance of the ceramic material is at least 100 µΩ x m.
  3. A workpiece carrier according to claim 1, characterised in that the resistance of the ceramic material is at least 150 µΩ x m.
  4. A workpiece carrier according to claim 1, characterised in that the surface regions contacted by the workpiece are coated with the ceramic material.
  5. A workpiece carrier according to claim 1, characterised in that it consists of a body of a high-temperature-resistant material, in the surface of which is incorporated at least one inlay of the ceramic material, which takes over the carrier function of the workpiece.
  6. A workpiece carrier according to claim 1, characterised in that the whole workpiece carrier consists of the ceramic material.
  7. A workpiece carrier according to claim 1, characterised in that the mass fraction of the carbide in this material is at least 10% and the remaining content of the material making up the mass to 100% consists in an amount of at most 50% of elementary carbon as well as in an amount of at most 80% of the carbide-forming metal or metals in elementary form.
  8. A workpiece carrier according to claim 1, characterised in that the ceramic material is a composite of silicon carbide, elementary silicon and elementary carbon.
  9. A workpiece carrier according to claim 8, characterised in that the ceramic composite comprises mass fractions of at least 35% of silicon carbide, 1 to 60% of silicon and 1 to 35% of carbon.
  10. A workpiece carrier according to one of claims 1 to 9, characterised in that at least a part of the carbon present in elementary form and/or forming carbides is the product of the pyrolysis of wood, wood materials, wood chips, wood flour, cellulose, pulp or wool.
  11. A process for the production of the ceramic material for a workpiece carrier according to one of claims 8 to 10, comprising the steps:
    - production of a porous carbon framework,
    - infiltration of this porous framework with silicon.
  12. A process according to claim 11, characterised in that the porous carbon framework is a carbonised felt or nonwoven.
  13. A process according to claim 11, characterised in that the porous carbon framework is produced by pyrolysis of a precursor of a carbonisable material.
  14. A process according to claim 13, characterised in that the porous carbon framework is produced by pyrolysis of a precursor of wood, wood materials, wood chips, wood flour, cellulose, pulp or wool.
  15. A process according to one of claims 11 to 14, characterised in that the porous carbon framework or the pyrolysable precursor is impregnated with at least one carbonisable binder, which is then carbonised.
  16. A process according to claim 11, characterised in that the porous carbon framework is produced by pyrolysis of a green product comprising a mixture of at least one solid carbonisable material and at least one carbonisable binder.
  17. A process according to claim 16, characterised in that the porous carbon framework is produced by pyrolysis of a green product comprising a mixture of wood chips, wood flour, pulp and/or cellulose fibres and at least one carbonisable binder.
  18. A process according to claim 11, characterised in that the porous carbon framework is produced by pyrolysis of a green product comprising a mixture of carbon and a carbonisable binder.
  19. A process according to one of claims 15 to 18, characterised in that the carbonised binder is a phenol resin, a melamine resin, lignin, pitch, polymers that can be pyrolysed to SiC, or a mixture of several of these substances.
  20. A process according to one of claims 13 to 18, characterised in that the green product or precursor is produced with a contour close to the final contour by injection moulding, pressing, cutting, turning or punching.
  21. A process according to one of claims 18 to 20, characterised in that at least one of the following additives is added to the mixture from which the green product is formed: ceramic powder, ceramic fibres, carbon powder, short carbon fibres, carbon nanotubes, graphite powder, carbon black.
  22. A process according to claim 11, characterised in that the conversion to silicon carbide takes place by infiltration with silicon from the liquid phase or from the gaseous phase or by polymers forming SiC in the pyrolysis, or from a combination of these.
  23. Use of a workpiece carrier according to one of claims 1 to 10 for the inductive heating of workpieces.
  24. Use of a workpiece carrier according to one of claims 1 to 10 for the inductive hardening of workpieces, in which the workpiece carrier is arranged at least partly within the induced field during the hardening procedure.
EP04010372A 2004-04-30 2004-04-30 Workpiece support for inductive heating of workpieces Expired - Lifetime EP1592284B1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AT04010372T ATE374514T1 (en) 2004-04-30 2004-04-30 WORKPIECE CARRIER FOR INDUCTIVE HEATING OF WORKPIECES
EP04010372A EP1592284B1 (en) 2004-04-30 2004-04-30 Workpiece support for inductive heating of workpieces
DE502004005078T DE502004005078D1 (en) 2004-04-30 2004-04-30 Workpiece carrier for inductive heating of workpieces
US11/080,712 US7323668B2 (en) 2004-04-30 2005-03-15 Workpiece carrier for the inductive heating of workpieces, process for producing a ceramic material for the workpiece carrier and process for the inductive heating or hardening of workpieces

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP04010372A EP1592284B1 (en) 2004-04-30 2004-04-30 Workpiece support for inductive heating of workpieces

Publications (2)

Publication Number Publication Date
EP1592284A1 EP1592284A1 (en) 2005-11-02
EP1592284B1 true EP1592284B1 (en) 2007-09-26

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Application Number Title Priority Date Filing Date
EP04010372A Expired - Lifetime EP1592284B1 (en) 2004-04-30 2004-04-30 Workpiece support for inductive heating of workpieces

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US (1) US7323668B2 (en)
EP (1) EP1592284B1 (en)
AT (1) ATE374514T1 (en)
DE (1) DE502004005078D1 (en)

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Publication number Priority date Publication date Assignee Title
DE102009000889A1 (en) * 2009-02-16 2010-08-19 Henkel Ag & Co. Kgaa Process for carrying out oxidation reactions by means of an inductively heated heating medium
US8814557B2 (en) * 2010-03-24 2014-08-26 United Technologies Corporation Die inserts for die casting
JP6219229B2 (en) * 2014-05-19 2017-10-25 東京エレクトロン株式会社 Heater feeding mechanism
DE102015108624A1 (en) * 2015-06-01 2016-12-01 Hoerbiger Antriebstechnik Holding Gmbh Method of hardening metal components
US11665790B2 (en) * 2016-12-22 2023-05-30 Whirlpool Corporation Induction burner element having a plurality of single piece frames

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US2482364A (en) * 1941-10-22 1949-09-20 Bell Telephone Labor Inc Device for heat-treating magnetic materials
US3182168A (en) * 1962-08-15 1965-05-04 Ohio Crankshaft Co High frequency inductor arrangement for heating a number of bar ends in a solenoidal coil
US3383840A (en) * 1966-05-10 1968-05-21 Cottrell Res Inc Dust collecting system
JPS57168489A (en) * 1981-04-07 1982-10-16 Mitsubishi Electric Corp Stationary induction heater
JPS5757490A (en) * 1981-07-16 1982-04-06 Kyoto Ceramic Heated member supporting device in heating furnace
FR2630612B1 (en) * 1988-04-26 1996-05-24 Siderurgie Fse Inst Rech DEVICE FOR PROTECTING INDUCER POLES AND INDUCER PROVIDED WITH SUCH DEVICE
DE3904607A1 (en) * 1989-02-16 1990-08-23 Leybold Ag DIRECTLY HEATABLE MELT CONTAINER FOR INDUCTION MELTING OVENS
NZ282347A (en) * 1994-03-16 1999-01-28 Larkden Pty Ltd Converting rotational energy of shaft into heat, inducing eddy currents in graphite block
US5817406A (en) * 1995-07-14 1998-10-06 Applied Materials, Inc. Ceramic susceptor with embedded metal electrode and brazing material connection
FR2748885B1 (en) * 1996-05-14 1998-08-14 Europ Equip Menager HIGH EFFICIENCY INDUCTION COOKING FIREPLACE
JP3794309B2 (en) * 2001-10-18 2006-07-05 住友電気工業株式会社 Substrate heating structure and substrate processing apparatus

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Publication number Publication date
DE502004005078D1 (en) 2007-11-08
ATE374514T1 (en) 2007-10-15
US20050242089A1 (en) 2005-11-03
US7323668B2 (en) 2008-01-29
EP1592284A1 (en) 2005-11-02

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