EP1481115A2 - Graphitized cathode blocks - Google Patents

Graphitized cathode blocks

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Publication number
EP1481115A2
EP1481115A2 EP02796687A EP02796687A EP1481115A2 EP 1481115 A2 EP1481115 A2 EP 1481115A2 EP 02796687 A EP02796687 A EP 02796687A EP 02796687 A EP02796687 A EP 02796687A EP 1481115 A2 EP1481115 A2 EP 1481115A2
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EP
European Patent Office
Prior art keywords
cathode blocks
cathode
parts
blocks
graphitized
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP02796687A
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German (de)
French (fr)
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EP1481115B1 (en
Inventor
Johann Daimer
Frank Hiltmann
Jörg MITTAG
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SGL Carbon SE
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SGL Carbon SE
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Publication date
Application filed by SGL Carbon SE filed Critical SGL Carbon SE
Publication of EP1481115A2 publication Critical patent/EP1481115A2/en
Application granted granted Critical
Publication of EP1481115B1 publication Critical patent/EP1481115B1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

  • the invention relates to graphitized cathode blocks, a process for their production and their use in particular for the electrolytic production of aluminum.
  • electrolysis cells which comprise a base composed of a multiplicity of blocks, which acts as a cathode.
  • the electrolyte is a melt, essentially a solution of aluminum oxide in cryolite.
  • the working temperature is around 1000 ° C, for example.
  • the electrolytically deposited molten aluminum collects on the bottom of the cell under a layer of the electrolyte.
  • Around the cells is a metallic housing (preferably steel) with a lining made of high temperature resistant material.
  • the material of the cathode blocks is preferably carbon because of the required chemical and thermal resistance, which can be partially or completely graphitized by thermal treatment.
  • mixtures of pitches, cokes, anthracite and / or graphite in selected particle sizes or particle size distributions for the solids are mixed, shaped and fired and optionally (partially) graphitized.
  • the firing (carbonization) usually takes place at temperatures of approx. 1200 ° C, the graphitization usually at temperatures of over 2400 ° C.
  • While graphitized cathodes are preferred because of their higher electrical conductivity, they show greater wear during operation, corresponding to an average annual decrease in their thickness of up to 80 mm. This wear is not evenly distributed over the length of the cathode blocks (corresponding to the width of the cell), but changes the surface of the cathode blocks into a W-shaped profile. Due to the uneven removal, the service life of the cathode blocks is limited by the places with the greatest removal.
  • One way to equalize the removal over the length of the cathode block and thus to extend the service life is to design the cathode blocks so that their electrical resistance varies over the length such that the current density (and thus the Wear) is uniform over its length or at least exhibits the smallest possible deviation over the length from its mean value.
  • a solution is described in DE 20 61 263, in which composite cathodes are formed either from several carbon blocks with different electrical conductivity, which are arranged in such a way that a uniform or approximately uniform current distribution results, or from carbon blocks, the electrical resistances of which are in the direction of the cathodic Derivatives increase continuously.
  • the number of carbon blocks and their electrical resistance depend on the cell size and type, they must be recalculated for each case.
  • Cathode blocks made of a large number of individual carbon blocks require a great deal of effort in the construction; the joints must also be properly sealed to prevent the liquid aluminum from flowing out at the joints.
  • WO 00/46426 describes a graphite cathode which consists of a single block which has an electrical conductivity which is variable over its length, the conductivity at the ends of the block being lower than in the middle. This uneven distribution of electrical conductivity is achieved, while during the graphitization the end zones are brought to a temperature of 2200 to 2500 ° C, while the other zone is exposed to a temperature of 2700 to 3000 ° C.
  • This different heat treatment can be achieved according to this teaching in two ways: first, the heat dissipation in the graphitization furnace can be limited differently, or heat sinks can be introduced in the vicinity of the end zones, which increase the heat loss.
  • the density of the heat-insulating bed is changed so that the heat loss becomes uneven over the length of the cathodes and the desired temperatures are thus set.
  • the heat loss in the vicinity of the ends can be increased by different designs of the heat-insulating bed, or heat-dissipating bodies made of graphite, which cause a greater heat outflow to the furnace wall, are preferably introduced for this purpose.
  • the difference in the heat treatment can be done by locally changing the current density, with the result of different heat development.
  • the current density can be changed by different resistances of the conductive bed between two cathodes in an Acheson furnace (cross-graphing); no solution of this type is specified for a longitudinal graphitization process.
  • cathode blocks are graphitized using the longitudinal graphitization method, an electrical transition with an increased resistance compared to the resistance inside the individual cathode blocks or the connecting element results at the joints between the individual cathode blocks with one another or with electrically conductive connecting elements arranged between them.
  • This increased resistance leads to increased heat development and thus to a higher temperature, that is to say an acceleration of the graphitization reaction. Therefore, the electrical resistance in longitudinal graphitization at the ends of the cathode blocks is usually lower than that in the center of the cathode blocks. This distribution of the resistance or the electrical conductivity over the length of the cathode block is precisely the opposite of the desired course.
  • cathode blocks with the desired course can be produced in a simple manner by placing the cathode blocks described above in the middle cut apart and reassembled in the opposite direction. This results in a profile of the electrical resistance in the form of an N. rounded on the legs.
  • the present invention therefore relates to graphitized cathode blocks for the production of aluminum by electrolytic reduction of aluminum oxide in a bath of molten cryolite, characterized in that the cathode blocks are composed of at least two parts and have a V-shaped profile of their electrical resistance over their length, wherein the resistance in the center of the cathode blocks has a discontinuity and increases steadily towards the ends, such that the resistance at the ends of the parts is at least 1.05: 1 to that in the center.
  • the cathode blocks are preferably composed of at least two parts, the electrical resistance of which increases continuously over their length, such that the resistance at the ends of the parts is at least 1.15: 1 in relation to that in the middle. This ratio is particularly preferably 1.3: 1.
  • FIG. 2 shows a side view of a cathode block which has been separated and reversed in the middle, a connecting layer of ramming mass being introduced in the middle,
  • Fig. 3 is a side view of a cathode block which has been separated in the middle and reversed '' ', with an adhesive joint connecting the two parts in the middle
  • Fig. 4 is a side view of a cathode block separated in the middle and assembled in reverse, the two parts being merely flush with one another.
  • FIG. 1 shows the course of the specific electrical resistance p shown in the interior of the side view of a cathode block 4, calculated as (R & /), where R is the electrical resistance of a cuboid test specimen, a its cross-sectional area, and 6 its length, along the length of the cathode block.
  • R is the electrical resistance of a cuboid test specimen, a its cross-sectional area, and 6 its length, along the length of the cathode block.
  • the ends of the block are marked with A.
  • the cathode block is cut apart along the line BB, the end faces at A being designated as 4-1, and the separating surface along the line BB in the side section is called 4-2.
  • the separated cathode block is now assembled as shown in FIGS. 2 to 4, that the ends A and the end faces 4-1 are in the middle of the assembled cathode block.
  • Fig. 2 shows an embodiment, wherein between the two ends A now located in the middle with the end surfaces 4-line position of the ramming mass 5, which is otherwise also used to seal the contact surfaces between the individual cathode blocks on the bottom of the tub of the electrolytic cell becomes.
  • Ramming compounds based on anthracite and graphite with a density of approx. 1700 kg / m 3 such as BST 17/1 from SGL Carbon AG, are suitable for this.
  • the areas 4-2 that were previously inside have now become outside areas.
  • the course of the specific electrical resistance p is now such that the lowest value lies in the center of the cathode block, and the specific electrical resistance now rises symmetrically towards the center towards the ends.
  • the course of the electrical conductivity is then reversed, namely descending from a peak in the middle of the cathode block to the ends.
  • FIG. 3 A further preferred embodiment is shown in which case the two half-blocks are each joined together with ends A by a layer of adhesive 6 with the required temperature resistance.
  • FIG. 4 shows an embodiment in which an adhesive or intermediate layer has been dispensed with and the two half blocks have only been joined together with their ends A.
  • the required surface pressure is applied due to the thermal expansion of the half-blocks, which after flush installation are pressed together during heating in the electrolysis cells. It has been shown that the pressing force is large enough to ensure a secure and tight connection of the two half blocks if the end faces were sufficiently flat before the division.
  • the graphitized cathode blocks according to the invention show in the production of aluminum by electrolytic reduction of aluminum oxide in a bath of molten cryolite a more uniform wear over the length of the cathode compared to the conventional ones with homogeneous distribution of the electrical conductivity and therefore a significantly increased service life.

Abstract

Disclosed are graphitized cathode blocks for producing aluminum by electrolytically reducing aluminum oxide in a molten cryolite bath. The electrical resistance of the inventive cathode blocks has a V-shaped profile across the length of the cathode blocks, increases towards the ends, and has a place of discontinuity in the middle thereof. Also disclosed are a method for the production of said cathode blocks and the use thereof for producing aluminum.

Description

Gtaphitierte KathodenblöckeGtaphitized cathode blocks
Die Erfindung betrifft graphitierte Kathodenblöcke, ein Verfahren zu ihrer Herstellung und ihre Verwendung insbesondere für die elektrolytische Herstellung von Aluminium.The invention relates to graphitized cathode blocks, a process for their production and their use in particular for the electrolytic production of aluminum.
Bei der elektrolytischen Herstellung von Aluminium nach dem HaU-Heroult-Verfahren werden Elektrolysezellen eingesetzt, die einen aus einer Vielzahl von Blöcken zusammengesetzten Boden umfassen, der als Kathode wirkt. Der Elektrolyt ist eine Schmelze, im wesentlichen eine Lösung von Aluminiumoxid in Kryolith. Die Arbeitstemperatur liegt beispielsweise bei ca. 1000 °C. Das elektrolytisch abgeschiedene geschmolzene Alurninium sammelt sich auf dem Boden der Zelle unter einer Schicht des Elektrolyten. Um die Zellen ist ein metallisches Gehäuse (bevorzugt Stahl) mit einer Auskleidung aus hochtemperaturbeständigem Material.In the electrolytic production of aluminum by the HaU-Heroult process, electrolysis cells are used which comprise a base composed of a multiplicity of blocks, which acts as a cathode. The electrolyte is a melt, essentially a solution of aluminum oxide in cryolite. The working temperature is around 1000 ° C, for example. The electrolytically deposited molten aluminum collects on the bottom of the cell under a layer of the electrolyte. Around the cells is a metallic housing (preferably steel) with a lining made of high temperature resistant material.
Das Material der Kathodenblöcke ist wegen der erforderlichen chemischen und thermischen Beständigkeit bevorzugt Kohlenstoff, der durch thermische Behandlung teilweise oder vollständig graphitiert sein kann. Zur Herstellung solcher Kathodenblöcke werden Mischungen von Pechen, Koksen, Anthrazit und/oder Graphit in ausgewählten Teilchengrößen bzw. Teilchengrößenverteilungen für die Feststoffe gemischt, geformt und gebrannt und gegebenenfalls (teilweise) graphitiert. Das Brennen (Carbonisierung) erfolgt üblicherweise bei Temperaturen von ca. 1200 °C, die Graphitierung üblicherweise bei Temperaturen von über 2400 °C.The material of the cathode blocks is preferably carbon because of the required chemical and thermal resistance, which can be partially or completely graphitized by thermal treatment. To produce such cathode blocks, mixtures of pitches, cokes, anthracite and / or graphite in selected particle sizes or particle size distributions for the solids are mixed, shaped and fired and optionally (partially) graphitized. The firing (carbonization) usually takes place at temperatures of approx. 1200 ° C, the graphitization usually at temperatures of over 2400 ° C.
Während graphitierte Kathoden wegen ihrer höheren elektrischen Leitfähigkeit bevorzugt werden, zeigen sie eine stärkere Abnutzung während des Betriebs, entsprechend einer mittleren jährlichen Abnahme ihrer Dicke von bis zu 80 mm. Diese Abnutzung ist nicht gleichmäßig über die Länge der Kathodenblöcke (entsprechend der Breite der Zelle) verteilt, sondern verändert die Oberfläche der Kathodenblöcke zu einem W-förmigen Profil. Durch den ungleichmäßigen Abtrag wird die Nutzungsdauer der Kathodenblöcke begrenzt durch die Stellen mit dem größten Abtrag.While graphitized cathodes are preferred because of their higher electrical conductivity, they show greater wear during operation, corresponding to an average annual decrease in their thickness of up to 80 mm. This wear is not evenly distributed over the length of the cathode blocks (corresponding to the width of the cell), but changes the surface of the cathode blocks into a W-shaped profile. Due to the uneven removal, the service life of the cathode blocks is limited by the places with the greatest removal.
Eine Möglichkeit, den Abtrag über die Länge des Kathodenblocks zu vergleichmäßigen und damit die Nutzungsdauer zu verlängern, besteht darin, die Kathodenblöcke so auszuführen, daß ihr elektrischer Widerstand über die Länge variiert, derart daß die Stromdichte (und damit die Abnutzung) über ihre Länge gleichmäßig ist oder zumindest eine möglichst geringe Abweichung über die Länge von ihrem Mittelwert aufweist.One way to equalize the removal over the length of the cathode block and thus to extend the service life is to design the cathode blocks so that their electrical resistance varies over the length such that the current density (and thus the Wear) is uniform over its length or at least exhibits the smallest possible deviation over the length from its mean value.
Eine Lösung ist in DE 20 61 263 beschrieben, wobei zusammengesetzte Kathoden gebildet werden entweder aus mehreren Kohlenstoffblöcken mit unterschiedlicher elektrischer Leitfähigkeit, die so angeordnet werden, daß sich eine gleichmäßige oder annähernd gleichmäßige Stromverteilung ergibt, oder aus Kohlenstoffblöcken, deren elektrische Widerstände in Richtung der kathodischen Ableitungen kontinuierlich zunehmen. Die Anzahl der Kohlenstoffblöcke und deren elektrischer Widerstand richten sich jeweils nach Zellengröße und Zellentyp, sie müssen für jeden Fall neu errechnet werden. Kathodenblöcke aus einer Vielzahl von einzelnen Kohlenstoff-Blöcken erfordern einen hohen Aufwand bei der Konstruktion; auch müssen die Stoßstellen jeweils gut abgedichtet werden, um ein Ausfließen des flüssigen Aluminiums an den Stoßstellen zu vermeiden.A solution is described in DE 20 61 263, in which composite cathodes are formed either from several carbon blocks with different electrical conductivity, which are arranged in such a way that a uniform or approximately uniform current distribution results, or from carbon blocks, the electrical resistances of which are in the direction of the cathodic Derivatives increase continuously. The number of carbon blocks and their electrical resistance depend on the cell size and type, they must be recalculated for each case. Cathode blocks made of a large number of individual carbon blocks require a great deal of effort in the construction; the joints must also be properly sealed to prevent the liquid aluminum from flowing out at the joints.
In der WO 00/46426 ist eine Graphitkathode beschrieben worden, die aus einem einzelnen Block besteht, der eine über seine Länge veränderliche elektrische Leitfähigkeit aufweist, wobei die Leitfähigkeit an den Enden des Blocks niedriger ist als in der Mitte. Diese ungleichmäßige Verteilung der elektrischen Leitfähigkeit wird erreicht, inde während der Graphitierung die Endzonen auf eine Temperatur von 2200 bis 2500 °C gebracht werden, während die mitdere Zone einer Temperatur von 2700 bis 3000 °C ausgesetzt wird. Diese unterschiedliche Wärmebehandlung kann gemäß dieser Lehre durch zwei Weisen erreicht werden: einmal kann die Wärmeableitung im Graphitierungsofen unterschiedlich begrenzt werden, oder es können Wärmesenken in der Nachbarschaft der Endzonen eingebracht werden, die den Wärmeverlust erhöhen. Bei einer Quergraphitierung wird dabei die Dichte der wärmeisolierenden Schüttung so verändert, daß der Wärmeverlust über die Länge der Kathoden ungleichmäßig wird und damit die gewünschten Temperaturen eingestellt werden. Auch bei der Längsgraphitierung kann durch unterschiedliche Ausführung der wärmeisolierenden Schüttung der Wärmeverlust in der Nähe der Enden vergrößert werden, oder es werden zu diesem Zweck wärmeableitende Körper bevorzugt aus Graphit in deren Nähe eingebracht, die einen stärkeren Wärmeabfluß nach außen zur Ofenwand bin bewirken.WO 00/46426 describes a graphite cathode which consists of a single block which has an electrical conductivity which is variable over its length, the conductivity at the ends of the block being lower than in the middle. This uneven distribution of electrical conductivity is achieved, while during the graphitization the end zones are brought to a temperature of 2200 to 2500 ° C, while the other zone is exposed to a temperature of 2700 to 3000 ° C. This different heat treatment can be achieved according to this teaching in two ways: first, the heat dissipation in the graphitization furnace can be limited differently, or heat sinks can be introduced in the vicinity of the end zones, which increase the heat loss. In the case of cross-graphitization, the density of the heat-insulating bed is changed so that the heat loss becomes uneven over the length of the cathodes and the desired temperatures are thus set. Also in longitudinal graphitization, the heat loss in the vicinity of the ends can be increased by different designs of the heat-insulating bed, or heat-dissipating bodies made of graphite, which cause a greater heat outflow to the furnace wall, are preferably introduced for this purpose.
Gemäß einer anderen Methode kann der Unterschied der Wärmebehandlung durch lokale Veränderung der Stromdichte erfolgen, mit der Folge unterschiedlicher Wärmeentwicklung. Diese Veränderung der Stromdichte kann gemäß der Lehre durch unterschiedliche Widerstände der leitenden Schüttung zwischen zwei Kathoden in einem Acheson-Ofen (QuergrapHtierung) erfolgen, für ein Längsgraphitierungsverfahren ist kein derartige Lösung angegeben.According to another method, the difference in the heat treatment can be done by locally changing the current density, with the result of different heat development. This According to the teaching, the current density can be changed by different resistances of the conductive bed between two cathodes in an Acheson furnace (cross-graphing); no solution of this type is specified for a longitudinal graphitization process.
Diese bekannten Methoden weisen für die Praxis erhebliche Nachteile auf. Ein Unterschied von 500 °C für die gewünschten Graphitierungstemperaturen in der Mitte und an den Enden der Kathoden ist durch Wärmesenken allein nicht erreichbar. Unterschiedliche Wärmeableitung nach außen in dem erforderlichen Maße bringt einen erheblichen Energieverlust, der die Fertigung wesentlich verteuert. Der höhere Wärmeverlust nach der Seite des Ofens bedeutet auch eine höhere thermische Beanspruchung, die die Konstruktion des Ofens verteuert oder seine Lebensdauer vei rtindert. Schließlich ist eine Inhomogenität der wärmeisolierenden bzw. der leitenden Schüttung wenig praktikabel, da das Schüttungsmaterial zur Befüllung in mehreren Schritten eingebracht werden müßte und nach dem Abschluß des Ofenzyklus und dem Entfernen der Kathoden wieder entsprechend seiner Wärmeleitung bzw. elektrischen Leitfähigkeit klassiert werden müßte.These known methods have considerable disadvantages in practice. A difference of 500 ° C for the desired graphitization temperatures in the middle and at the ends of the cathodes cannot be achieved by heat sinks alone. Different heat dissipation to the outside to the required extent results in a considerable loss of energy, which makes production much more expensive. The higher heat loss to the side of the furnace also means higher thermal stress, which makes the construction of the furnace more expensive or reduces its service life. Finally, an inhomogeneity of the heat-insulating or the conductive bed is not practicable, since the bed material would have to be introduced in several steps for filling and after the end of the furnace cycle and the removal of the cathodes would have to be classified again according to its heat conduction or electrical conductivity.
Es ist daher die Aufgabe der vorliegenden Erfindung, graphitierte Kathodenblöcke bereitzustellen, die über ihre Länge eine unterschiedliche elektrische Leitfähigkeit aufweisen.It is therefore the object of the present invention to provide graphitized cathode blocks which have a different electrical conductivity over their length.
Werden Kathodenblöcke nach dem Verfahren der Längsgraphitierung graphitiert, so ergibt sich an den Stoßstellen der einzelnen Kathodenblöcke untereinander oder mit zwischen diesen angeordneten elektrisch leitenden Verbindungselementen ein elektrischer Übergang mit einem gegenüber dem Widerstand im Inneren der einzelnen Kathodenblöcke oder des Verbindungselements erhöhtem Widerstand. Dieser erhöhte Widerstand führt zu erhöhter Wärmeentwicklung und damit zu höherer Temperatur, also einer Beschleunigung der Graphitierungsreaktion. Daher ist der elektrische Widerstand bei Längsgraphitierung an den Enden der Kathodenblöcke üblicherweise geringer als der in der Mitte der Kathodenblöcke. Diese Verteilung des Widerstandes bzw. der elektrischen Leitfähigkeit über die Länge des Kathodenblocks ist gerade das Gegenteil des gewünschten Verlaufs.If cathode blocks are graphitized using the longitudinal graphitization method, an electrical transition with an increased resistance compared to the resistance inside the individual cathode blocks or the connecting element results at the joints between the individual cathode blocks with one another or with electrically conductive connecting elements arranged between them. This increased resistance leads to increased heat development and thus to a higher temperature, that is to say an acceleration of the graphitization reaction. Therefore, the electrical resistance in longitudinal graphitization at the ends of the cathode blocks is usually lower than that in the center of the cathode blocks. This distribution of the resistance or the electrical conductivity over the length of the cathode block is precisely the opposite of the desired course.
Es wurde nun gefunden, daß sich Kathodenblöcke mit dem gewünschten Verlauf auf einfache Weise herstellen lassen, indem man die oben beschriebenen Kathodenblöcke in der Mitte auseinanderschneidet und in umgekehrter Richtung wieder zusammenfügt. Dabei ergibt sich ein Profil des elektrischen Widerstandes in Form eines an den Schenkeln gerundeten N.It has now been found that cathode blocks with the desired course can be produced in a simple manner by placing the cathode blocks described above in the middle cut apart and reassembled in the opposite direction. This results in a profile of the electrical resistance in the form of an N. rounded on the legs.
Gegenstand der vorliegenden Erfindung sind daher graphitierte Kathodenblöcke zur Herstellung von Aluminium durch elektrolytische Reduktion von Aluminiumoxid in einem Bad von geschmolzenem Kryolith, dadurch gekennzeichnet, daß die Kathodenblöcke aus mindestens zwei Teilen zusammengesetzt sind und über ihre Länge ein V-förmiges Profil ihres elektrischen Widerstandes aufweisen, wobei der Widerstand in der Mitte der Kathodenblöcke eine Unstetigkeitsstelle aufweist und zu den Enden hin stetig zunimmt, derart daß der Widerstand an den Enden der Teile zu dem in der Mitte im Verhältnis von mindestens 1,05 : 1 steht.The present invention therefore relates to graphitized cathode blocks for the production of aluminum by electrolytic reduction of aluminum oxide in a bath of molten cryolite, characterized in that the cathode blocks are composed of at least two parts and have a V-shaped profile of their electrical resistance over their length, wherein the resistance in the center of the cathode blocks has a discontinuity and increases steadily towards the ends, such that the resistance at the ends of the parts is at least 1.05: 1 to that in the center.
Bevorzugt sind die Kathodenblöcke aus rnindestens zwei Teilen zusammengesetzt, deren elektrischer Widerstand über ihre Länge stetig ansteigt, derart daß der Widerstand an den Enden der Teile zu dem in der Mitte im Verhältnis von mindestens 1,15 : 1 steht. Besonders bevorzugt beträgt dies Verhältnis 1,3 : 1.The cathode blocks are preferably composed of at least two parts, the electrical resistance of which increases continuously over their length, such that the resistance at the ends of the parts is at least 1.15: 1 in relation to that in the middle. This ratio is particularly preferably 1.3: 1.
Die Erfindung wird durch die Zeichnungen näher erläutert. Dabei zeigenThe invention is explained in more detail by the drawings. Show
Fig. 1 den Verlauf des spezifischen elektrischen Widerstandes p über die Länge des Kathodenblocks, wie er sich bei der Längsgraphitierung mit hohem Übergangswiderstand zwischen den einzelnen Kathodenblöcken ergibt, in die Seitenansicht eines Kathodenblocks eingezeichnet,1 shows the course of the specific electrical resistance p over the length of the cathode block, as is the case in longitudinal graphitization with high contact resistance between the individual cathode blocks, drawn in the side view of a cathode block,
Fig. 2 eine Seitenansicht eines in der Mitte auseinandergetrennten und umgekehrt zusammengesetzten Kathodenblocks, wobei in der Mitte eine Verbindungsschicht aus Stampfmasse eingebracht ist,2 shows a side view of a cathode block which has been separated and reversed in the middle, a connecting layer of ramming mass being introduced in the middle,
Fig. 3 eine Seitenansicht eines in der Mitte auseinandergetrennten und umgekehrt '"'zusammengesetzten Kathodenblocks, wobei in der Mitte eine Klebefuge die beiden Teile verbindet, und Fig. 4 eine Seitenansicht eines in der Mitte auseinandergetrennten und umgekehrt zusammengesetzten Kathodenblocks, wobei die beiden Teile lediglich bündig aneinandergesetzt sind.Fig. 3 is a side view of a cathode block which has been separated in the middle and reversed '' ', with an adhesive joint connecting the two parts in the middle, and Fig. 4 is a side view of a cathode block separated in the middle and assembled in reverse, the two parts being merely flush with one another.
Im einzelnen zeigt die Fig. 1 den im Inneren der Seitenansicht eines Kathodenblocks 4 dargestellten Verlauf des spezifischen elektrischen Widerstandes p, berechnet als (R &/ ), wobei R der elektrische Widerstand eines quaderförmigen Probekörpers ist, a dessen Querschnittsfläche, und 6 seine Länge, über die Länge des Kathodenblocks. Die Enden des Blocks, wie er bei der Längsgraphitierung anfällt, sind mit A bezeichnet. Der Kathodenblock wird längs der Linie BB auseinandergeschnitten, dabei sind die Endflächen bei A als 4-1 bezeichnet, und die Trennfläche längs der Linie BB im Seitenschnitt heißt 4-2. Der getrennte Kathodenblock wird nun so zusammengefügt wie in den Fig. 2 bis 4 dargestellt, daß die Enden A bzw. die Endflächen 4-1 sich in der Mitte des zusammengesetzten Kathodenblocks befinden.1 shows the course of the specific electrical resistance p shown in the interior of the side view of a cathode block 4, calculated as (R & /), where R is the electrical resistance of a cuboid test specimen, a its cross-sectional area, and 6 its length, along the length of the cathode block. The ends of the block, as is the case with longitudinal graphitization, are marked with A. The cathode block is cut apart along the line BB, the end faces at A being designated as 4-1, and the separating surface along the line BB in the side section is called 4-2. The separated cathode block is now assembled as shown in FIGS. 2 to 4, that the ends A and the end faces 4-1 are in the middle of the assembled cathode block.
Die Fig. 2 zeigt eine Ausführungsform, wobei sich zwischen den beiden nunmehr in der Mitte befindlichen Enden A mit den Endflächen 4-leine Lage der Stampfmasse 5 befindet, die ansonsten auch zur Abdichtung der Kontaktflächen zwischen den einzelnen Kathodenblöcken am Boden der Wanne der Elektrolysezelle verwendet wird. Geeignet sind hierzu Stampfmassen auf Basis von Anthrazit und Graphit mit einer Dichte von ca. 1700 kg/m3, wie BST 17/1 der SGL Carbon AG.Fig. 2 shows an embodiment, wherein between the two ends A now located in the middle with the end surfaces 4-line position of the ramming mass 5, which is otherwise also used to seal the contact surfaces between the individual cathode blocks on the bottom of the tub of the electrolytic cell becomes. Ramming compounds based on anthracite and graphite with a density of approx. 1700 kg / m 3 , such as BST 17/1 from SGL Carbon AG, are suitable for this.
Die vorher innen liegenden Flächen 4-2 sind nun zu Außenflächen geworden. Der Verlauf des spezifischen elektrischen Widerstandes p ist nun derart, daß in der Mitte des Kathodenblocks der niedrigste Wert liegt, und der spezifische elektrische Widerstand nun symmetrisch zum Mittelpunkt zu den Enden hin ansteigt. In umgekehrter Weise ist dann der Verlauf der elektrischen Leitfähigkeit, nämlich von einem Gipfel in der Mitte des Kathodenblocks aus zu den Enden hin absteigend.The areas 4-2 that were previously inside have now become outside areas. The course of the specific electrical resistance p is now such that the lowest value lies in the center of the cathode block, and the specific electrical resistance now rises symmetrically towards the center towards the ends. The course of the electrical conductivity is then reversed, namely descending from a peak in the middle of the cathode block to the ends.
In der Fig. 3 ist eine weitere bevorzugte Ausfuhrungsform dargestellt, wobei in diesem Fall die beiden Halbblöcke jeweils mit den Enden A durch eine Schicht eines Klebstoffs 6 mit der erforderlichen Temperaturbeständigkeit zusamm.engefu.gt sind.A further preferred embodiment is shown in FIG. 3, in which case the two half-blocks are each joined together with ends A by a layer of adhesive 6 with the required temperature resistance.
Geeignete Klebstoffe sind kalthärtende Harze wie beispielsweise BVK6 der SGL Carbon AG. Die Fig. 4 schließlich zeigt eine Ausfuhrungsform., bei der auf eine Klebung oder Zwischenschicht verzichtet wurde, und die beiden Halbblöcke lediglich mit ihren Enden A aneinandergefügt wurden. Die erforderliche Flächenpressung wird in diesem Fall durch die thermische Ausdehnung der Halbblöcke aufgebracht, die nach bündigem Einbau in die Elektrolysezellen beim Aufheizen aufeinandergepreßt werden. Es hat sich gezeigt, daß die Preßkraft groß genug ist, um eine sichere und dichte Verbindung beider Halbblöcke sicherzustellen, wenn die Endflächen vor der Teilung ausreichend eben waren.Suitable adhesives are cold-curing resins such as BVK6 from SGL Carbon AG. Finally, FIG. 4 shows an embodiment in which an adhesive or intermediate layer has been dispensed with and the two half blocks have only been joined together with their ends A. In this case, the required surface pressure is applied due to the thermal expansion of the half-blocks, which after flush installation are pressed together during heating in the electrolysis cells. It has been shown that the pressing force is large enough to ensure a secure and tight connection of the two half blocks if the end faces were sufficiently flat before the division.
Die erfindungsgemäßen graphitierten Kathodenblöcke zeigen bei der Herstellung von Aluminium durch elektrolytische Reduktion von Aluminiumoxid in einem Bad von geschmolzenem Kryolith gegenüber den herkömmlichen mit homogener Verteilung der elektrischen Leitfähigkeit eine gleichmäßigere Abnutzung über die Länge der Kathode und daher eine deutlich erhöhte Standzeit. The graphitized cathode blocks according to the invention show in the production of aluminum by electrolytic reduction of aluminum oxide in a bath of molten cryolite a more uniform wear over the length of the cathode compared to the conventional ones with homogeneous distribution of the electrical conductivity and therefore a significantly increased service life.

Claims

Patentansprüche claims
1. Graphitierte Kathodenblöcke zur Herstellung von Aluminium durch elektrolytische Reduktion von Alurniniumoxid in einem Bad von geschmolzenem Kryolith, dadurch gekennzeichnet, daß die Kathodenblöcke aus mindestens zwei Teilen zusammengesetzt sind und über ihre Länge ein V-förmiges Profil ihres elektrischen Widerstandes aufweisen, wobei der Widerstand in der Mitte der KaÜiodenblöcke eine Unstetigkeitsstelle aufweist und zu den Enden hin stetig zunitnmt, derart daß der Widerstand an den Enden der Teile zu dem in der Mitte im Verhältnis von mindestens 1,05 : 1 steht.1. Graphitized cathode blocks for the production of aluminum by electrolytic reduction of aluminum oxide in a bath of molten cryolite, characterized in that the cathode blocks are composed of at least two parts and have a V-shaped profile of their electrical resistance over their length, the resistance in the center of the KaÜiodenblock has a discontinuity and increases steadily towards the ends, so that the resistance at the ends of the parts to that in the middle is at least 1.05: 1.
2. Graphitierte Kathodenblöcke nach Anspruch 1, dadurch gekennzeichnet, daß die Kathodenblöcke aus mindestens zwei Teilen zusammengesetzt sind, wobei die Kontaktflächen der Teile durch mechanische Pressung verbunden sind.2. Graphitized cathode blocks according to claim 1, characterized in that the cathode blocks are composed of at least two parts, the contact surfaces of the parts being connected by mechanical pressure.
3. Graphitierte Kathodenblöcke nach Anspruch 1, dadurch gekennzeichnet, daß die Kathodenblöcke aus mindestens zwei Teilen zusammengesetzt sind, wobei die Kontaktflächen der.Teile durch eine Stampfmasse verbunden sind.3. Graphitized cathode blocks according to claim 1, characterized in that the cathode blocks are composed of at least two parts, the contact surfaces of the parts being connected by a ramming compound.
4. Graphitierte Kathodenblöcke nach Anspruch 1, dadurch gekennzeichnet, daß die Kathodenblöcke aus mindestens zwei Teilen zusammengesetzt sind, wobei die Kontaktflächen der Teile verklebt sind.4. Graphitized cathode blocks according to claim 1, characterized in that the cathode blocks are composed of at least two parts, the contact surfaces of the parts being glued.
5. Verfahren zur Herstellung von graphitierten Kathodenblöcke gemäß Anspruch 1, dadurch gekennzeichnet, daß ein graphitierter Kathodenblock, dessen elektrische Leitfähigkeit über die Länge dem Profil eines flachen U entspricht, mittig . getrennt und mit den ursprünglichen Außenseiten nach innen gerichtet wieder zusammengesetzt wird.5. A method for producing graphitized cathode blocks according to claim 1, characterized in that a graphitized cathode block, the electrical conductivity of which corresponds over the length to the profile of a flat U, in the center. separated and reassembled with the original outsides facing inwards.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der zusammengesetzte Kathodenblock durch mechanische Pressung in der Elektrolysezelle verbunden wird.6. The method according to claim 5, characterized in that the assembled cathode block is connected by mechanical pressing in the electrolytic cell.
7. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der zusammengesetzte Kathodenblock durch die thermische Ausdehnung in der Elektrolysezelle verbunden wird. 7. The method according to claim 5, characterized in that the assembled cathode block is connected by the thermal expansion in the electrolytic cell.
8. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der zusammengesetzte Kathodenblock durch Stampfmasse in der Mitte verbunden wird.8. The method according to claim 5, characterized in that the assembled cathode block is connected by ramming mass in the middle.
9. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der zusammengesetzte Kathodenblock in der Mitte verklebt wird. 9. The method according to claim 5, characterized in that the assembled cathode block is glued in the middle.
EP02796687A 2001-12-28 2002-12-19 Graphitized cathode blocks Expired - Fee Related EP1481115B1 (en)

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DE2001164008 DE10164008C1 (en) 2001-12-28 2001-12-28 Graphitized cathode block, used for producing aluminum by electrolytically reducing aluminum oxide in a bath of molten cryolite, is composed of two parts and has a V-shaped profile of its electrical resistance over its length
DE10164008 2001-12-28
PCT/EP2002/014548 WO2003056068A2 (en) 2001-12-28 2002-12-19 Graphitized cathode blocks

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AU (1) AU2002361174A1 (en)
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US2728109A (en) * 1952-06-06 1955-12-27 Savoie Electrodes Refract Method of making cathodic electrodes for electrolysis furnaces
US4194959A (en) * 1977-11-23 1980-03-25 Alcan Research And Development Limited Electrolytic reduction cells
NO157462C (en) * 1985-10-24 1988-03-23 Hydro Aluminium As LAMINATED CARBON CATHOD FOR CELLS-MELT-ELECTROLYTIC ALUMINUM PREPARATION.
US4795540A (en) * 1987-05-19 1989-01-03 Comalco Aluminum, Ltd. Slotted cathode collector bar for electrolyte reduction cell
FR2789091B1 (en) * 1999-02-02 2001-03-09 Carbone Savoie GRAPHITE CATHODE FOR ALUMINUM ELECTROLYSIS
EP1233083A1 (en) * 2001-02-14 2002-08-21 Alcan Technology & Management AG Carbon bottom of electrolysis cell used in the production of aluminum

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CA2470753A1 (en) 2003-07-10
AU2002361174A1 (en) 2003-07-15
DE50205232D1 (en) 2006-01-12
AR037912A1 (en) 2004-12-22
EP1481115B1 (en) 2005-12-07
WO2003056068A2 (en) 2003-07-10
WO2003056068A3 (en) 2004-09-30
PL201672B1 (en) 2009-04-30

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