EP0099066B1 - Process for manufacturing a composite article from chromium and copper - Google Patents

Process for manufacturing a composite article from chromium and copper Download PDF

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Publication number
EP0099066B1
EP0099066B1 EP83106620A EP83106620A EP0099066B1 EP 0099066 B1 EP0099066 B1 EP 0099066B1 EP 83106620 A EP83106620 A EP 83106620A EP 83106620 A EP83106620 A EP 83106620A EP 0099066 B1 EP0099066 B1 EP 0099066B1
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Prior art keywords
powder
copper
temperature
furnace
chromium
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German (de)
French (fr)
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EP0099066A1 (en
EP0099066B2 (en
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Horst Dr. Kippenberg
Heinrich Dr. Hässler
Manfred Hühnlein
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Siemens AG
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Siemens AG
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Priority claimed from DE19823226604 external-priority patent/DE3226604A1/en
Priority claimed from DE19833322866 external-priority patent/DE3322866A1/en
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22FWORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24After-treatment of workpieces or articles
    • B22F3/26Impregnating
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00Contacts
    • H01H1/02Contacts characterised by the material thereof
    • H01H1/0203Contacts characterised by the material thereof specially adapted for vacuum switches
    • H01H1/0206Contacts characterised by the material thereof specially adapted for vacuum switches containing as major components Cu and Cr

Definitions

  • the invention relates to a method for producing a composite material from chrome and copper as a contact material for medium-voltage vacuum circuit breakers.
  • the composite material CrCu with about 40 to 60% Cr has already proven itself as a contact material for vacuum circuit breakers.
  • the component Cu ensures sufficient electrical and thermal conductivity, while the framework material Cr both reduces burn-off and, with its low melting point of about 2173 K compared to tungsten, eliminates the risk of harmful thermal electron emission.
  • the Cr greatly reduces the tendency of the contact pieces to weld and has good gettering properties.
  • porous blanks produced by pressing or pouring metal powder which either consist of pure Cr powder or in which one or more other powder additives are mixed with the Cr powder to achieve a liquid phase during sintering.
  • the subsequent sintering in a high vacuum or pure protective gas at temperatures from 1 573 K to 1 773 K leads to the desired formation of sinter bridges between the powder grains, so that the structural strength increases, which enables problem-free handling of the porous sintered blanks after the sintering process.
  • the blanks are then placed in impregnation molds or placed on impregnation pads, receive an amount of impregnation metal, in this case copper, corresponding to the pore volume, and are again heated in a high vacuum or pure protective gas above the melting temperature of the impregnation metal.
  • impregnation metal in this case copper
  • infiltration of the porous framework occurs due to capillary forces.
  • the invention is therefore based on the object to develop a new method with which it is possible to produce a high-quality contact material made of chrome and copper, which meets the requirements of vacuum medium-voltage circuit breakers up to 36 kV operating voltage and breaking currents above 30 kA, and in which the aforementioned sources of error as well as the use of Cu powder with a high oxygen content are avoided.
  • the object is achieved in that Cr powder is poured into a degassed mold, that a piece of low-oxygen copper is placed on the Cr powder, that the mold is then closed with a porous lid, that the mold is then in a high vacuum furnace is outgassed at room temperature, until a pressure of less than 10- 2 Pa achieved that after the furnace temperature is increased to the highest possible temperature below the melting temperature of copper, that this furnace temperature is kept constant until a constant internal furnace pressure of less than 10- 2 Pa is reached and that, subsequently, without intermediate cooling, the furnace temperature is further increased is maintained up to a final value of 100 K to 200 K above the melting temperature of the copper and this temperature as long porosity given to the Cr powder mixture in the completely filled with liquid copper.
  • the furnace temperature just below the melting point of copper can contribute to a technical implementation lie.
  • the furnace is kept constant at this temperature for about one hour, an internal furnace pressure in the range of 10 -3 Pa being preferably achieved.
  • the holding time at the temperature above the melting point of copper is preferably 20 to 30 minutes.
  • Chromium-produced or electrolytically produced chromium can be used for the process according to the invention.
  • the Cr powder should have a particle size distribution of 50 ⁇ m to 200 ⁇ m, but preferably with proportions of at least 150 ktm; in the second case the particle size can be below this, in the range from 25 ⁇ m.
  • the Cr powder produced therefrom is filled into a previously degassed graphite mold with a particle size in portions of at least 150 ⁇ m.
  • the crucible has e.g. B. a diameter of 85 mm and a length of 250 mm and is filled to a height of about 180 mm with Cr powder.
  • Oxygen-poor copper is placed on the Cr powder as a solid piece that fills the remaining crucible contents.
  • the crucible is closed with a porous graphite lid and degassed in a high vacuum oven at room temperature until. a pressure in the range of 10- 3 Pa, that is less than 10- 2 Pa is reached.
  • electrolytically produced chromium which also has a maximum oxygen content of 500 ppm.
  • the Cr powder produced from this can have a particle size distribution which is smaller than in the case of chromium produced thermally, for example with particle sizes from 25 ⁇ m. Otherwise, the individual sub-process steps are carried out according to the first example.
  • the blank produced according to the above examples is cooled under vacuum. After cooling, the Cr-Cu composite block can be broken down into contact pieces of the required geometry. Will Metallographic cuts of the material produced, it can be seen that the composite material produced with the inventive method has practically no strength-increasing sintered bridges and practically no pores. With the new process, contact pieces can be reproducibly produced on Cr-Cu basis, which have suitable properties for medium-voltage vacuum circuit breakers.
  • further elements can be used as additives in a manner known per se: for example, titanium and zircon as alloy components for copper can be used to improve the getter properties; on the other hand, iron, cobalt or nickel can be added to the Cr powder to thereby improve the wetting properties.

Description

Die Erfindung bezieht sich auf ein Verfahren zum Herstellen eines Verbundwerkstoffes aus Chrom und Kupfer als Kontaktwerkstoff für Mittelspannungs-Vakuum-Leistungsschalter.The invention relates to a method for producing a composite material from chrome and copper as a contact material for medium-voltage vacuum circuit breakers.

Als Kontaktmaterial für Vakuum-Leistungsschalter hat sich bereits der Verbundwerkstoff CrCu mit etwa 40 bis 60 % Cr gut bewährt. Dabei gewährleistet die Komponente Cu eine hinreichende elektrische und thermische Leitfähigkeit, während das Gerüstmaterial Cr sowohl abbrandmindernd als auch mit seinem im Vergleich zu Wolfram niedrigen Schmelzpunkt von etwa 2173 K die Gefahr einer schädlichen thermischen Elektronenemission beseitigt. Außerdem setzt das Cr die Verschweißneigung der Kontaktstücke stark herab und besitzt gute Gettereigenschaften.The composite material CrCu with about 40 to 60% Cr has already proven itself as a contact material for vacuum circuit breakers. The component Cu ensures sufficient electrical and thermal conductivity, while the framework material Cr both reduces burn-off and, with its low melting point of about 2173 K compared to tungsten, eliminates the risk of harmful thermal electron emission. In addition, the Cr greatly reduces the tendency of the contact pieces to weld and has good gettering properties.

Für die Herstellung des Verbundwerkstoffes CrCu kommen aufgrund der Mischungslücke im System Cr-Cu für den gewünschten Konzentrationsbereich von etwa 40 bis 60 % Cr-Gehalt nur pulvermetallurgische Verfahren in Betracht. Am gebräuchlichsten ist das Herstellen von Preßkörpern aus Cr-Pulver oder CrCu-Pulvermischungen, deren Poren nach der Sinterung mit flüssigem Cu aufgefüllt werden. Derartige Sintertränkverfahren sowie auch die übrigen bekannten pulvermetallurgischen Verfahren sind wegen der Oxidationsneigung des Chroms schwierig zu beherrschen. Insbesondere besteht die Gefahr, durch schlechte Benetzbarkeit einzelner Kornflächen oder Passivschichtbildung Poren- oder Tränkfehler zu erhalten. Auch wenn diese nur in der Größenordnung von 5 bis 50 µm liegen, kann durch sie eine Beeinträchtigung des Schaltverhaltens bewirkt werden. In der Praxis ergibt sich daraus eine gewisse Streubreite im Ausschaltvermögen.For the production of the composite material CrCu, only powder metallurgical processes can be considered due to the mixture gap in the Cr-Cu system for the desired concentration range of approximately 40 to 60% Cr content. The most common is the production of compacts from Cr powder or CrCu powder mixtures, the pores of which are filled with liquid Cu after sintering. Such sintering impregnation processes as well as the other known powder metallurgy processes are difficult to master because of the tendency of chromium to oxidize. In particular, there is a risk of poor porosity or impregnation errors due to poor wettability of individual grain areas or the formation of a passive layer. Even if they are only in the order of 5 to 50 µm, they can impair the switching behavior. In practice, this results in a certain spread in the breaking capacity.

Bei anderen bekannten Verfahren werden z. B. poröse Rohlinge durch Pressen oder Schütten von Metallpulver hergestellt, die entweder aus reinem Cr-Pulver bestehen oder bei denen zum Erzielen einer flüssigen Phase beim Sintern ein oder mehrere weitere Pulverzusätze dem Cr-Pulver zugemischt werden. Das anschließende Sintern im Hochvakuum oder reinem Schutzgas bei Temperaturen von 1 573 K bis 1 773 K führt zu einer gewünschten Ausbildung von Sinterbrücken zwischen den Pulverkörnern, so daß ein Anstieg der Gerüstfestigkeit erfolgt, der eine problemlose Handhabung der porösen Sinterrohlinge nach dem Sinterprozeß erlaubt. In einem weiteren Arbeitsgang werden die Rohlinge dann in Tränkformen eingelegt oder auf Tränkunterlagen aufgelegt, erhalten als Auf- oder Unterlage eine dem Porenvolumen entsprechende Menge an Tränkmetall, in diesem Fall Kupfer, und werden wiederum im Hochvakuum oder reinem Schutzgas über die Schmelztemperatur des Tränkmettals erhitzt. Hierbei tritt durch Kapillarkräfte eine Infiltration des porösen Gerüstes ein.In other known methods such. B. porous blanks produced by pressing or pouring metal powder, which either consist of pure Cr powder or in which one or more other powder additives are mixed with the Cr powder to achieve a liquid phase during sintering. The subsequent sintering in a high vacuum or pure protective gas at temperatures from 1 573 K to 1 773 K leads to the desired formation of sinter bridges between the powder grains, so that the structural strength increases, which enables problem-free handling of the porous sintered blanks after the sintering process. In a further operation, the blanks are then placed in impregnation molds or placed on impregnation pads, receive an amount of impregnation metal, in this case copper, corresponding to the pore volume, and are again heated in a high vacuum or pure protective gas above the melting temperature of the impregnation metal. In this case, infiltration of the porous framework occurs due to capillary forces.

Mit den vorstehend beschriebenen Tränkverfahren zur Herstellung der Cr-Cu-Verbundwerkstoffe lassen sich jedoch trotz sorgfältigster Arbeitsweise keine völlig fehlerfreien Tränkungen erzielen : Dafür sind im wesentlichen drei Gründe verantwortlich :

  • Beim Umchargieren der Öfen zwischen Sinter-und Tränkprozeß kommt es bei den stark getteraktiven Cr-Gerüsten zu einer Neubelegung der Gerüstoberfläche mit dünnen Oxid- bzw. chemiesorbierten Gashäuten, die die Benetzung mit dem flüssigen Tränkmetall erschweren. Aus thermodynamischen Gründen treten diese Oxidationsprozesse bereits unterhalb von etwa 1 000 K selbst im Hochvakuum und in reinem Schutzgas auf, da sich in wirtschaftlich anwendbaren Öfen keine Sauerstoffpartialdrücke unter 1" Pa erzielen lassen. Als Resultat dieser Erscheinung treten Tränkfehler auf, die sich in Form von Mikrolunkern und Poren äußern.
With the impregnation processes described above for the production of the Cr-Cu composite materials, however, despite the most careful working method, completely impeccable impregnations cannot be achieved: There are essentially three reasons for this:
  • When the furnaces are re-charged between the sintering and impregnation processes, the strongly getter-active Cr frameworks are re-coated with thin oxide or chemically sorbed gas skins, which make wetting with the liquid impregnation metal more difficult. For thermodynamic reasons, these oxidation processes already occur below around 1,000 K even in a high vacuum and in a pure protective gas, since no oxygen partial pressures below 1 "Pa can be achieved in economically applicable furnaces. As a result of this phenomenon, impregnation errors occur, which can be in the form of Express micro voids and pores.

Durch den Sinterprozeß und die damit verbundene Ausbildung von Sinterbrücken werden schlecht zugängliche Porenbereiche erhalten, die von flüssigem Tränkmetall gar nicht oder nur unvollkommen erreicht werden. Damit ist auch die Möglichkeit, reduzierende Substanzen wie z. B. Kohlenstoff über die flüssige Tränkmetallphase an das Gerüstmetall zu bringen, eingeschränkt, so daß in diesen Restporenbereichen, die von der Sinterbrückenbildung herrühren, Restoxide vorhanden sind, die das Schaltvermögen des Werkstoffes beeinträchtigen.Due to the sintering process and the associated formation of sintered bridges, poorly accessible pore areas are obtained which are not or only incompletely reached by liquid impregnation metal. This is also the possibility of reducing substances such. B. to bring carbon over the liquid impregnated metal phase to the framework metal, so that in these residual pore areas, which result from the formation of sintered bridges, residual oxides are present which impair the switching capacity of the material.

Durch die versteifende Wirkung fester Sinterbrücken wird die Möglichkeit des Gerüstmaterials zur Deformation beträchtlich verringert. Wird das mit Cu oder Legierungen davon imprägnierte Cr-Gerüst von der Infiltrationstemperatur des flüssigen Tränkmetalls abgekühlt, so tritt wegen der unterschiedlichen Wärmeausdehnungen zwischen Cr und Cu ein Volumendefizit auf, das durch einen gemeinsamen gleichmäßigen Schrumpf von Gerüst- und Tränkmetall nicht aufgefangen werden kann. Diese bekannte Erscheinung kann ebenfalls zu Fehlstellen und im Lichtmikroskop unsichtbaren Mikroporositäten führen, die die Qualität des Werkstoffes für Hochleistungsschaltaufgaben verschlechtern können.The stiffening effect of solid sintered bridges considerably reduces the possibility of the framework material for deformation. If the Cr framework impregnated with Cu or alloys thereof is cooled from the infiltration temperature of the liquid impregnation metal, a volume deficit arises due to the different thermal expansions between Cr and Cu, which cannot be compensated for by a uniform shrinkage of framework and impregnation metal. This known phenomenon can also lead to imperfections and microporosities which are invisible in the light microscope and which can deteriorate the quality of the material for high-performance switching tasks.

Es ist versucht worden, diese Störungen zu vermeiden. So kann z. B. Cr-Pulver und Cu-Pulver gemischt werden, dadurch unterbleibt eine direkte Berührung der Cr-Körner weitgehend und es bilden sich im anschließenden Sinterprozeß keine oder nur vereinzelte deformationsbehindernde Sinterbrücken aus. Obwohl dieser Fertigungsprozeß die sterische Behinderung der Cr-Partikel aufhebt, kann mit einem derartigen Werkstoff keine ausreichende Schaltleistung erzielt werden. Ursache dafür ist die Wechselwirkung zwischen dem üblicherweise mit etwa 500 ppm sauerstoffverunreinigtem Cu-Pulver und dem getteraktiven Cr-Pulver. Bereits unterhalb 1 273 K, d. h. also 1 000 °C, wird dabei bei einsetzender CU20-Dissoziation das oxidationsfreudige Cr-Pulver aufoxidiert. Wegen der hohen Oxidationswärme des Cr kommt es zur Ausbildung stabiler Oberflächenoxide, die durch eine normale Vakuumentgasung nicht mehr entfernt werden können.Attempts have been made to avoid these disturbances. So z. B. Cr powder and Cu powder are mixed, this largely prevents direct contact of the Cr grains and there are no or only occasional deformation-preventing sinter bridges in the subsequent sintering process. Although this manufacturing process removes the steric hindrance of the Cr particles, a sufficient switching capacity cannot be achieved with such a material. The reason for this is the interaction between the Cu powder, which is usually contaminated with about 500 ppm of oxygen, and the getter-active Cr powder. Even below 1 273 K, ie 1 000 ° C, a setting C U2 0 dissociation oxidized the oxidation-friendly Cr powder. Due to the high heat of oxidation of the Cr, stable surface oxides are formed which cannot be removed by normal vacuum degassing.

Der Erfindung liegt daher die Aufgabe zugrunde, ein neues Verfahren zu entwickeln, mit dem es möglich ist, einen hochwertigen Kontaktwerkstoff aus Chrom und Kupfer herzustellen, der den Anforderungen von Vakuum-Mittelspannungs-Leistungsschaltern bis 36 kV Betriebsspannung und Ausschaltströmen oberhalb 30 kA genügt, und bei dem die vorerwähnten Fehlerquellen sowie zusätzlich die Verwendung von Cu-Pulver mit hohem Sauerstoffgehalt vermieden werden.The invention is therefore based on the object to develop a new method with which it is possible to produce a high-quality contact material made of chrome and copper, which meets the requirements of vacuum medium-voltage circuit breakers up to 36 kV operating voltage and breaking currents above 30 kA, and in which the aforementioned sources of error as well as the use of Cu powder with a high oxygen content are avoided.

Gemäß der Erfindung wird die Aufgabe dadurch gelöst, daß Cr-Pulver in eine entgaste Form geschüttet wird, daß auf das Cr-Pulver ein Stück aus sauerstoffarmen Kupfer gelegt wird, daß anschließend die Form mit einem porösen Deckel verschlossen wird, daß dann die Form in einem Hochvakuumofen bei Raumtemperatur entgast wird, bis ein Druck von weniger als 10-2 Pa erreicht ist, daß danach die Ofentemperatur auf eine möglichst hohe Temperatur unterhalb der Schmelztemperatur von Kupfer erhöht wird, daß diese Ofentemperatur solange konstant gehalten wird, bis ein konstanter Ofeninnendruck von weniger als 10-2 Pa erreicht ist, und daß anschließend ohne Zwischenabkühlen die Ofentemperatur weiter erhöht wird bis zu einem Endwert von 100 K bis 200 K oberhalb der Schmelztemperatur des Kupfers und diese Temperatur solange beibehalten wird, bis die in der Cr-Pulvermischung enthaltene Porosität vollständig vom flüssigen Kupfer ausgefüllt ist.According to the invention the object is achieved in that Cr powder is poured into a degassed mold, that a piece of low-oxygen copper is placed on the Cr powder, that the mold is then closed with a porous lid, that the mold is then in a high vacuum furnace is outgassed at room temperature, until a pressure of less than 10- 2 Pa achieved that after the furnace temperature is increased to the highest possible temperature below the melting temperature of copper, that this furnace temperature is kept constant until a constant internal furnace pressure of less than 10- 2 Pa is reached and that, subsequently, without intermediate cooling, the furnace temperature is further increased is maintained up to a final value of 100 K to 200 K above the melting temperature of the copper and this temperature as long porosity given to the Cr powder mixture in the completely filled with liquid copper.

Die Ofentemperatur dicht unterhalb des Schmelzpunktes von Kupfer kann bei einer technischen Durchführung bei

Figure imgb0001
liegen. Bei dieser Temperatur wird der Ofen etwa eine Stunde konstant gehalten, wobei vorzugsweise ein Ofeninnendruck im Bereich von 10-3 Pa erreicht wird. Die Haltezeit bei der Temperatur oberhalb des Schmelzpunktes von Kupfer liegt vorzugsweise bei 20 bis 30 Minuten.The furnace temperature just below the melting point of copper can contribute to a technical implementation
Figure imgb0001
lie. The furnace is kept constant at this temperature for about one hour, an internal furnace pressure in the range of 10 -3 Pa being preferably achieved. The holding time at the temperature above the melting point of copper is preferably 20 to 30 minutes.

Für das erfindungsgemäße Verfahren kann aluminotermisch oder elektrolytisch hergestelltes Chrom verwendet werden. Im ersten Fall sollte das Cr-Pulver eine Teilchengrößenverteilung von 50 µm bis 200 µm haben, vorzugsweise aber mit Anteilen von mindestens 150 ktm ; im zweiten Fall kann die Teilchengröße darunter und zwar im Bereich ab 25 µm liegen.Chromium-produced or electrolytically produced chromium can be used for the process according to the invention. In the first case, the Cr powder should have a particle size distribution of 50 μm to 200 μm, but preferably with proportions of at least 150 ktm; in the second case the particle size can be below this, in the range from 25 µm.

Weiterhin hat es sich als zweckmäßig erwiesen, eine Arbeitsform aus Graphit zu verwenden, weil Kohlenstoff im flüssigen Kupfer in geringer Menge löslich ist und daher über einen Transport in der flüssigen Phase als Reduktionsmittel für Cr-Oxidverunreinigungen Anwendung findet.Furthermore, it has proven to be expedient to use a working form made of graphite, because carbon is soluble in the liquid copper in a small amount and is therefore used as a reducing agent for Cr oxide impurities via transport in the liquid phase.

Besonders vorteilhaft bei der Erfindung ist, daß kein festigkeitssteigernder Sinterprozeß mit Ausbildung von stabilen Sinterbrücken durchgeführt, sondern daß unmittelbar von der in einer Form befindlichen Cr-Pulverschüttung ausgegangen wird. Ohne Umschargieren des Ofens und zusätzliche Handhabung von Sinterrohlingen kann das Porenvolumen der Pulverschüttung vollständig mit flüssigem Kupfer aufgefüllt werden, so daß sich ein praktisch porenfreier Verbundwerkstoff ergibt.It is particularly advantageous in the invention that no strength-increasing sintering process with the formation of stable sintering bridges is carried out, but that the Cr powder fill located in a mold is used directly. The pore volume of the powder filling can be completely filled with liquid copper without re-loading the furnace and additional handling of sintered blanks, so that a practically non-porous composite material results.

Anhand nachfolgender Ausführungsbeispiele wird die Erfindung im einzelnen beschrieben :The invention is described in detail using the following exemplary embodiments:

Bei Verwendung von aluminothermisch hergestelltem Chrom mit einem maximalen Sauerstoffgehalt von 500 ppm wird das daraus erzeugte Cr-Pulver mit einer Teilchengröße mit Anteilen von mindestens 150 µm in eine vorher entgaste Graphitform eingefüllt. Der Tiegel besitzt z. B. einen Durchmesser von 85 mm und eine Länge von 250 mm und wird bis zu einer Höhe von etwa 180 mm mit Cr-Pulver gefüllt. Auf das Cr-Pulver wird sauerstoffarmes Kupfer als massives Stück aufgelegt, das den restlichen Tiegelinhalt füllt. Der Tiegel wird mit einem porösen Graphitdeckel verschlossen und im Hochvakuumofen zunächst solange bei Raumtemperatur entgast, bis. ein Druck im Bereich von 10-3 Pa, also weniger als 10-2 Pa erreicht ist. Anschließend wird mit dem Aufheizen begonnen, das immer dann unterbrochen wird, wenn der Druck auf über 10-4 Pa ansteigt. Bei einer Temperatur von etwa

Figure imgb0002
also unterhalb der Schmelztemperatur von Kupfer (Tsm 1 1356 K), ist die eigentliche Entgasungstemperatur erreicht, die für eine Stunde, mindestens jedoch aber bis wieder ein Ofeninnendruck weniger als 10-2 Pa erreicht ist, beibehalten wird. Anschließend wird ohne Zwischenabkühlen die Temperatur weiter erhöht, bis zu einem Endwert, der 100 K bis 200 K oberhalb des Schmelzpunktes von Kupfer liegt. Die Temperatur kann z. B. 1 473 K sein, wobei bei dieser Temperatur nach etwa 30 Minuten ein praktisch vollständiges Ausfüllen der Poren in der Cr-Schüttung mit flüssigem Kupfer erreicht ist.When using aluminothermally produced chromium with a maximum oxygen content of 500 ppm, the Cr powder produced therefrom is filled into a previously degassed graphite mold with a particle size in portions of at least 150 µm. The crucible has e.g. B. a diameter of 85 mm and a length of 250 mm and is filled to a height of about 180 mm with Cr powder. Oxygen-poor copper is placed on the Cr powder as a solid piece that fills the remaining crucible contents. The crucible is closed with a porous graphite lid and degassed in a high vacuum oven at room temperature until. a pressure in the range of 10- 3 Pa, that is less than 10- 2 Pa is reached. Then starting the heating, which is always interrupted when the pressure to over 10 -4 Pa increases. At a temperature of about
Figure imgb0002
ie below the melting temperature of copper (T sm 1 1356 K), the actual degassing temperature is reached, which is for one hour, however, but to a furnace internal pressure is reached less than 10- 2 Pa again at least maintained. The temperature is then increased further without intermediate cooling to a final value which is 100 K to 200 K above the melting point of copper. The temperature can e.g. B. 1 473 K, at this temperature after about 30 minutes a practically complete filling of the pores in the Cr bed is achieved with liquid copper.

Bei einem anderen Ausführungsbeispiel wird elektrolytisch hergestelltes Chrom verwendet, das einen maximalen Sauerstoffgehalt von ebenfalls 500 ppm hat. Das daraus erzeugte Cr-Pulver kann aber in diesem Fall eine Teilchengrößenverteilung haben, die kleiner als bei aluminothermisch hergestelltem Chrom ist, beispielsweise mit Teilchengrößen ab 25 µm. Ansonsten werden die einzelnen Verfahrensteilschritte entsprechend dem ersten Beispiel durchgeführt.In another embodiment, electrolytically produced chromium is used, which also has a maximum oxygen content of 500 ppm. In this case, however, the Cr powder produced from this can have a particle size distribution which is smaller than in the case of chromium produced thermally, for example with particle sizes from 25 μm. Otherwise, the individual sub-process steps are carried out according to the first example.

Nach vollständiger Porenfüllung wird der gemäß obigen Beispielen hergestellte Rohling unter Vakuum abgekühlt. Nach dem Erkalten kann der Cr-Cu-Verbundblock in Kontaktstücke der erforderlichen Geometrie zerlegt werden. Werden metallographische Anschliffe des Werkstoffes hergestellt, so ist erkennbar, daß der mit dem erfindungsgemäßen Verfahren hergestellte Verbundwerkstoff praktisch keine festigkeitssteigernden Sinterbrücken und praktisch keine Poren aufweist. Mit dem neuen Verfahren können somit reproduzierbar auf Cr-Cu-Basis Kontaktstücke erzeugt werden, welche geeignete Eigenschaften für Mittelspannungs-Vakuum-Leistungsschalter haben.After complete pore filling, the blank produced according to the above examples is cooled under vacuum. After cooling, the Cr-Cu composite block can be broken down into contact pieces of the required geometry. Will Metallographic cuts of the material produced, it can be seen that the composite material produced with the inventive method has practically no strength-increasing sintered bridges and practically no pores. With the new process, contact pieces can be reproducibly produced on Cr-Cu basis, which have suitable properties for medium-voltage vacuum circuit breakers.

Bei dem auf Cr-Cu-Basis beschriebenen Ausführungsbeispielen sind in an sich bekannter Weise weitere Elemente als Zusätze verwendbar: Beispielsweise können einerseits durch Titan und Zirkon als Legierungsbestandteile zum Kupfer die Gettereigenschaften verbessert werden ; andererseits können Eisen, Kobalt oder Nickel dem Cr-Pulver zugesetzt werden, um dadurch die Benetzungseigenschaften zu verbessern.In the exemplary embodiments described on the basis of Cr-Cu, further elements can be used as additives in a manner known per se: for example, titanium and zircon as alloy components for copper can be used to improve the getter properties; on the other hand, iron, cobalt or nickel can be added to the Cr powder to thereby improve the wetting properties.

Die Handhabung der genannten Zusätze bei Cr-Cu-Verbundwerkstoffen ist im Zusammenhang mit der Erfindung beherrschbar und ändert nichts Grundsätzliches am beschriebenen Herstellungsverfahren.The handling of the additives mentioned for Cr-Cu composites is manageable in connection with the invention and does not change anything fundamentally in the production process described.

Claims (9)

1. A process for the production of a composite material consisting of chromium and copper as contact material for medium voltage-vacuum- power switches, comprising the following process steps :
a) Cr-powder is poured into a degassed working mould,
b) a piece of oxygen-poor copper is placed on the Cr-powder,
c) the working mould is then closed with a porous cover,
d) the working mould is then degassed in a high-vacuum furnace at room temperature until a pressure of less than 10-2 Pa is reached,
e) the furnace temperature is thereafter increased to the highest possible temperature below the melting temperature of copper,
f) this furnace temperature is held constant until a constant internal furnace pressure of less than 10-2 Pa is reached,
g) then, without intermediate cooling, the furnace temperature is again increased to a final value of 100 K to 200 K above the melting point of the copper and this temperature is maintained until the porosity contained in the Cr-powder mass is completely filled with the liquid copper.
2. A process as claimed in Claim 1, characterised in that the furnace temperature in process step e) is
Figure imgb0004
3. A process as claimed in Claim 1, characterised in that the pressure in process steps d) and f) is in the region of 10-3 Pa.
4. A process as claimed in Claim 1, characterised in that the holding time in process step f) is approximately 1 hour.
5. A process as claimed in Claim 1, characterised in that the holding time in process step g) is 20 to 30 minutes.
6. A process as claimed in Claim 1, characterised in that when aluminothermally-produced chromium is used, the Cr-powder produced therefrom has a particle size distribution of between 50 µm and 200 µm.
7. A process as claimed in Claim 6, characterised in that Cr-powder having a particle size with components of at least 150 µm is used.
8. A process as claimed in Claim 1, characterised in that when electrolytically-produced chromium is used, the Cr-powder produced therefrom has a particle size distribution of between 25 µm and 200 µm.
9. A process as claimed in one of Claims 1 to 8, characterised in that a working mould made of graphite is used.
EP83106620A 1982-07-16 1983-07-06 Process for manufacturing a composite article from chromium and copper Expired - Lifetime EP0099066B2 (en)

Applications Claiming Priority (4)

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DE19823226604 DE3226604A1 (en) 1982-07-16 1982-07-16 Process for the preparation of a composite material based on Cr/Cu for medium-voltage vacuum power switches
DE3226604 1982-07-16
DE19833322866 DE3322866A1 (en) 1983-06-24 1983-06-24 Process for the production of a composite material of chromium and copper
DE3322866 1983-06-24

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EP0099066B1 true EP0099066B1 (en) 1986-05-07
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JPH0760623B2 (en) * 1986-01-21 1995-06-28 株式会社東芝 Contact alloy for vacuum valve
JP2640142B2 (en) * 1989-06-05 1997-08-13 三菱電機株式会社 Contact material for vacuum switch tube and its manufacturing method
US5024899A (en) * 1990-10-22 1991-06-18 Lang Richard D Resilient metallic friction facing material
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US5701993A (en) * 1994-06-10 1997-12-30 Eaton Corporation Porosity-free electrical contact material, pressure cast method and apparatus
DE19537657A1 (en) * 1995-10-10 1997-04-17 Abb Patent Gmbh Method and device for producing a contact piece
JP3663038B2 (en) * 1997-09-01 2005-06-22 芝府エンジニアリング株式会社 Vacuum valve
US7832857B2 (en) * 2008-08-18 2010-11-16 Levinson Dennis J Microbial cellulose contact lens
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RU2751865C1 (en) * 2020-12-22 2021-07-19 Федеральное государственное бюджетное образовательное учреждение высшего образования "Волгоградский государственный технический университет" (ВолгГТУ) Method for obtaining carbon-graphite composite material

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DE3363383D1 (en) 1986-06-12
EP0099066A1 (en) 1984-01-25
EP0099066B2 (en) 1992-07-22
US4503010A (en) 1985-03-05

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