EP0144371B1 - Cathode bar comprising a metal sole for hall-heroult electrolysis tanks - Google Patents

Cathode bar comprising a metal sole for hall-heroult electrolysis tanks Download PDF

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Publication number
EP0144371B1
EP0144371B1 EP84902015A EP84902015A EP0144371B1 EP 0144371 B1 EP0144371 B1 EP 0144371B1 EP 84902015 A EP84902015 A EP 84902015A EP 84902015 A EP84902015 A EP 84902015A EP 0144371 B1 EP0144371 B1 EP 0144371B1
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EP
European Patent Office
Prior art keywords
electrolytic cell
cell according
cathode
sole
metal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
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EP84902015A
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German (de)
French (fr)
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EP0144371A1 (en
Inventor
Michel Leroy
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Rio Tinto France SAS
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Aluminium Pechiney SA
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Priority claimed from FR8308334A external-priority patent/FR2546184B1/en
Application filed by Aluminium Pechiney SA filed Critical Aluminium Pechiney SA
Priority to AT84902015T priority Critical patent/ATE30053T1/en
Publication of EP0144371A1 publication Critical patent/EP0144371A1/en
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    • 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
    • C25C3/16—Electric current supply devices, e.g. bus bars

Definitions

  • the invention relates to the construction of electrolytic cells for the production of aluminum by the Hall-Héroult process. It relates more particularly to an electrolysis tank in which each cathode bar comprises a metal soleplate, intended to increase the passage section and to standardize the distribution of the cathode current.
  • the cathode of a Hall-Héroult electrolysis tank is formed by the juxtaposition of a set of carbonaceous blocks, provided, at their lower base, with one (or sometimes two) open groove (s) in which are sealed, generally by casting, steel bars of square, rectangular or circular section, on which are connected the connecting conductors between the successive tanks forming a series.
  • the steel bars used for the extraction of the cathode current therefore offer a limited contact surface with the carbon, which causes a significant voltage drop at the carbon / cast iron interface.
  • the object of the present invention is to increase substantially (more than 10%) the section of steel available for the evacuation of the cathode current, and the contact surface between the carbon and the cathode conductors. It consists, in an electrolytic cell of the type defined in the preamble of claim 1, to provide each cathode bar with a metal sole, constituted by a metal sheet, welded to the cathode bar before the establishment of the carbonaceous block in the tank, to ensure the passage of electric current and the electrical contact between said soleplate and the base of the carbonaceous block being ensured by at least one layer of elastic material conducting electricity.
  • the sole must have a thickness at least equal to 4 mm, and preferably at least equal to 10 mm.
  • a continuous steel screen can be placed under the soleplate, in electrical contact with the soleplate, which prevents infiltration of liquid aluminum and molten cryolite, which appreciably increases the service life of the electrolysis tank.
  • Figure 1 relates to the prior art.
  • FIG. 2 to 15 illustrate the implementation of the invention.
  • Figure 1 shows the classic arrangement of a carbonaceous cathode block (1) in which the bar (2A) is sealed by cast iron (3).
  • the bar is flush with the base of the carbon block.
  • the bar (2B) in an alternative embodiment can more or less exceed the base plane of the carbonaceous block (3).
  • the successive cathode blocks are most often assembled by a joint (4) made of carbonaceous paste.
  • FIG. 2 illustrates a first embodiment of the invention.
  • two thick sheets of mild steel (5) were welded connected to the base of the carbon block (1) by a layer of electrically conductive elastic material (6).
  • the steel soleplate (5) can consist of a steel-copper colamine, the copper-colored face (5A) being in contact with the carbonaceous block (1) via the elastic conductive layer ( 6).
  • the thickness of the copper layer (5A) must be greater than a minimum value, which can be estimated at around 5% of the steel layer, corresponding to the solubility of the copper. in steel at 900-950 ° C, so that the entire copper layer does not disappear by diffusion in the solid state in the steel.
  • the malleability of hot copper facilitates the establishment of good contact with the cathode block and can, if necessary, partially compensate for deformations of the steel soleplate.
  • Figure 3 shows the four stages 3a, 3b, 3c, 3d of the procedure used to carry out the assembly of Figure 2.
  • Figure 3a shows the first step
  • the carbon block (1) having been turned over so that the groove (7) faces upwards, the cathode bar (2) is sealed by casting iron (3).
  • Figure 3b shows the second step
  • an elastic, electrically conductive layer (6) is placed on the upper face of the inverted block: it is advantageous to use a carbon or graphite felt, or a laminated graphite sheet, or another complex formed by bonding a strip of carbon felt or graphite and a strip of laminated graphite.
  • RVG graphite felts or “Papyex” (R) (trademarks registered by the Company “Le Carbone-Lorraine”).
  • Figure 3c shows the third step
  • the sole (5) consists of two thick steel sheets, which are applied strongly, by pressing, to the elastic link layer (6) on the elastic connection layer (6).
  • a steel flange is thus produced electrically connected to the cathode bar.
  • the thickness of the sole is at least equal to 4 mm and, preferably, at least equal to 10 mm and generally of the order of 10 to 15 mm.
  • the cross-section of the cathode bar can be, for example, 160 x 120 mm.
  • Figure 3d shows the cathode carbon block returned to normal position by inversion.
  • Figure 4 shows a variant of the invention where the steel base is located astride two carbon cathode blocks, and in electrical contact with these two blocks.
  • Figure 5 shows that when performing the assembly, it is preferable to provide a slight clearance between the flanges (5) of two adjacent blocks (1) and (1 ') so that when the normal operating temperature is reached, and due to the greater expansion of the steel base compared to the carbonaceous block, the edges of the two adjacent flanges (5) and (5 '), are in contact with a pressure just sufficient to ensure a weld to hot of these edges between them, without this pressure being excessive to the point of causing deformation of the soles, detrimental to the electrical contact between carbonaceous blocks and steel soles.
  • the blanks of the bevels of (5) and (5 ') may be parallel to each other (5A) or not (5B).
  • the value of the clearance (9) necessary for mounting or installation depends on the exact nature of the carbonaceous block: based on anthracite, or semi-graphite or semi-graphitized or graphite, and on the exact dimension of the blocks and footings , as well as the nature and thickness of the joint between carbonaceous blocks: blocks glued together or separated by a small joint (4) of pot lining. Generally, this game will be defined by an e / L ratio of the order of 1 to 2%.
  • Figure 6 shows the mounting detail of the sealing strips (10).
  • the upper strip (10A) is welded for example on the sheet (5) and the lower strip (10B) is welded on the sheet (5 ') so that, during the first heating, they can slide freely and take their definitive place.
  • a lower porosity graphite piece (12) can be placed at the bottom of the joint (4) which improves the seal of the joint (4 ) and reduces the risk of infiltration of molten cryolite when the electrolysis tank is started.
  • Figure 7 shows another alternative embodiment of the joint between the flanges (5) and (5 ') of adjacent cathode blocks (1) and (1').
  • a flexible joint (14) preferably electrically conductive and compressible, such as graphite braid, or a tube thin-walled metal (thickness less than half the thickness of the sole, (5) or (5 '), resting freely between the strips 10A and 10B.
  • FIG. 8 represents another variant, in which the flexible carbon joint (14) is replaced by a deformable tube (15), welded beforehand to at least one of the flanges (5) or (5 '), which absorbs the expansion effects and which can be filled with an inert pulverulent material (19), to limit internal hot oxidation.
  • FIGS 9 and 10 illustrate the implementation of the invention in the case of carbon blocks (1) provided with two parallel cathode bars (2C and 2D), an arrangement which is sometimes encountered in order to increase the surface contact with the carbon block.
  • the two bars 2C, 2D were sealed simultaneously by casting iron (3), the thickness (e) of the iron plate between the two bars preferably being less than or equal to the difference in the ratings h o and h 1 (e ⁇ h o - h i ).
  • the soleplate (5) can be made of single or mixed steel-copper sheet steel as described above.
  • the two cathode bars 2C, 2D were individually sealed, then connected by welding with a sheet (21) preformed in a vault, so as to obtain, when hot, good electrical contact with the central part of the carbonaceous block. via the elastic conductive layer (6).
  • the metal soleplate is in contact with the base of the carbon blocks by means of the elastic material (6) over at least 20% of the surface of this base.
  • a screen (26) under the base of the carbon blocks constituting the cathode of the electrolytic cell and in which the cathode bars are sealed, this screen extending at least over the entire space located below the cathode (fig. 11). It consists of at least one continuous sheet of steel, at least half of the surface of which consists of a part having at least 5 mm, and preferably 8 to 12 mm thick, and which comprises at least one zone. deformable absorbing stresses due to temperature differences between the central part, located directly above the cathode, and the less hot peripheral part. To avoid any risk of electrochemical corrosion, it is then preferable to put the metal soleplate (5) in electrical contact with the screen (26).
  • the electrical connection between the sole (5) and the screen (26) can be ensured by welding, for example, by a continuous or discontinuous bead between at least one edge of the sole and the continuous screen. It can also be ensured by the fusion of a brazing alloy previously disposed between the sole and the continuous screen, the points of solidus and liquidus of this alloy being suitably chosen.
  • FIG. 12 shows an embodiment of this principle, according to which the sole (5) of each cathode bar (2) is placed directly on the continuous screen (26) of thick steel, to which it is connected by solder (16) or by welding (17).
  • the advantage of this arrangement is that the continuous thick steel screen (26) is, at all points, at the electrical potential of the cathode bars, which eliminates any effect of electrochemical cell generating rapid corrosion.
  • the thickness of the screen is at least 5 mm, and preferably between 8 and 12 mm.
  • the sole (5) has a thickness at least equal to 4 mm and, preferably, at least equal to 10 mm.
  • Figure 12 shows how this device can be implemented during the construction of the tank.
  • the cathode bar (2) was put in place and sealed with cast iron (3) in each cathode block (1).
  • a sole (5) whose length is at most equal and, in practice slightly less than the distance between two successive bars.
  • the block is then placed on the screen (26), resting on the insulating layer (20), and welded at (9), preferably by a continuous cord, so as to ensure good electrical contact.
  • the layers (24) and (25) are insulating and refractory bricks, arranged on the bottom (27) of the casing of the electrolysis tank.
  • the optimal brazing compositions for implementing the invention comprise at least 50% of a first metal chosen from aluminum, copper, zinc, the remainder being at least a second metal chosen from manganese, nickel, vanadium, beryllium, silicon, tin and titanium, as well as aluminum and copper if the first metal is not copper or aluminum.
  • compositions no. 1, 3, 6 and 7 are particularly suitable in industrial practice. Some are fragile and can be ground to the desired fineness, others must be treated in a known manner, by spraying in the liquid state.
  • the solder can be used in the form of a thin, laminated sheet, introduced during assembly between the sole and the screen.
  • a reducing metal with respect to iron oxide (scale) which most often covers the steel plates used to constitute the sole or the screen (metal such as AI and / or Si) dispenses with using any other stripper to promote spreading of the solder when it passes into the liquid state.
  • the sole (5) and the screen (26) in a single part, constituted by a thick steel sheet (22), as shown in the figures. 13 and 14, which may be provided with seals or deformable zones, capable of withstanding thermal expansions, for example the tube (15) of FIG. 2.
  • the thickness of the screen may be between 10 and 20 mm.
  • the bars (2) are positioned on the screen (22), then connected by a weld bead (23). After which, the cathode blocks (1) are put in place, the sealing being ensured by carbonaceous paste (13).
  • the connection can also be made by a solder (16).
  • Fig. 14 shows another method of assembly, according to which the cathode bars (2) are no longer arranged directly above the axis of the block (1), but straddling two blocks adjacent to the vertical line of the joint between these two blocks.
  • the advantage of this arrangement is that the carbonaceous paste (4) ensuring the sealing between the blocks (1) and the bars (2) can be injected, hot, in the space separating two adjacent blocks.
  • FIG. 15 very schematically shows the partial cross-section of an electrolytic cell according to the invention, with the external metal box (30), the side soldering (31) in carbonaceous paste, the cathode carbon block (1 ) surmounted by the sheet of liquid aluminum (32), the electrolyte (33) and the anode system (34), the cathode bar (2) made of steel, sealed with cast iron (3), and the soleplate (5) steel, object of the invention. It is noted that the cross section of the cathode bar (2) is reduced in the crossing of the external part of the lining (31) and of the box (30).

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Water Treatment By Electricity Or Magnetism (AREA)
  • Laminated Bodies (AREA)
  • Insulated Conductors (AREA)

Abstract

Cathode bar provided for the extraction of current from a tank intended to the electrolysis production of aluminium according to the Hall-Héroult method, sealed in at least one groove opened at the base of each carbonated blocks (1) forming the cathode of the electrolysis tank. According to the invention, the cathode bar (2) is extended by a metal sole (5) in electric contact with the base of the carbonated blocks (1) on at least 20% of the total surface of said base. The sole (5) is comprised of metal sheet having a thickness of at least 4 mm and preferably at least equal to 10 mm welded to the cathode bar (2) before setting in place the carbonated block (1) in the tank. To prevent electrolyte infiltrations in the under-cathode space, the lower face of the sole (5) is arranged in superposed relationship and in electric contact with a continuous thick metal screen (26) arranged to the upper part of the heat-insulating lining.

Description

L'invention se rapporte à la construction des cuves d'électrolyse pour la production d'aluminium par le procédé Hall-Héroult. Elle concerne plus particulièrement une cuve d'électrolyse dans laquelle chaque barre cathodique comporte une semelle métallique, destinée à augmenter la section de passage et à uniformiser la répartition du courant cathodique.The invention relates to the construction of electrolytic cells for the production of aluminum by the Hall-Héroult process. It relates more particularly to an electrolysis tank in which each cathode bar comprises a metal soleplate, intended to increase the passage section and to standardize the distribution of the cathode current.

Exposé de l'art antérieurPresentation of the prior art

La cathode d'une cuve d'électrolyse Hall-Héroult est constituée par la juxtaposition d'un ensemble de blocs carbonés, munis, à leur base inférieure, d'une (ou parfois deux) rainure(s) ouverte(s) dans lesquelles sont scellées, généralement par coulée de fonte, des barres d'acier de section carrée, rectangulaire ou circulaire, sur lesquelles sont raccordées les conducteurs de liaison entre les cuves successives formant une série.The cathode of a Hall-Héroult electrolysis tank is formed by the juxtaposition of a set of carbonaceous blocks, provided, at their lower base, with one (or sometimes two) open groove (s) in which are sealed, generally by casting, steel bars of square, rectangular or circular section, on which are connected the connecting conductors between the successive tanks forming a series.

Les barres d'acier servant à l'extraction du courant cathodique offrent donc une surface de contact limitée avec le carbone, ce qui provoque une chute de tension non négligeable à l'interface carbone/fonte.The steel bars used for the extraction of the cathode current therefore offer a limited contact surface with the carbon, which causes a significant voltage drop at the carbon / cast iron interface.

Pour réduire cette chute de tension; il est également connu d'augmenter la section de la barre d'acier, au moins dans la zone scellée dans le carbone, tout en gardant une section normale ou rétrécie à la traversée de la partie extérieure du calorifugeage de la cuve, de façon à éviter des fuites thermiques trop importantes.To reduce this voltage drop; it is also known to increase the section of the steel bar, at least in the area sealed in carbon, while keeping a normal or narrowed section at the crossing of the external part of the insulation of the tank, so as to avoid excessive thermal leakage.

Cependant, une telle action est forcément limitée, car l'épaisseur de carbone des ailes de la rainure doit être suffisante pour résister mécaniquement aux contraintes dues à la dilatation thermique de la barre cathodique, et de son scellement, lors de la mise en régime de la cuve.However, such an action is necessarily limited, since the carbon thickness of the wings of the groove must be sufficient to mechanically resist the stresses due to the thermal expansion of the cathode bar, and of its sealing, when the system is brought into operation. tank.

Dans le brevet US-A-2 593 751 (Pechiney), on décrit une cuve d'électrolyse du type Hall-Héroult, dans laquelle chaque barre cathodique, scellée à la fonte dans le bloc carboné correspondant, a une dimension telle qu'elle fait saillie hors du bloc carboné, la partie en saillie ainsi que la base du bloc carboné sont recouvertes d'une plaque en fonte moulée qui assure un écoulement plus facile et plus homogène du courant électrique entre les blocs carbonés et la barre cathodique proprement dite.In patent US-A-2,593,751 (Pechiney), an electrolysis cell of the Hall-Héroult type is described, in which each cathode bar, sealed with cast iron in the corresponding carbon block, has a dimension such that it protrudes out of the carbon block, the projecting part as well as the base of the carbon block are covered with a molded cast iron plate which ensures an easier and more homogeneous flow of electric current between the carbon blocks and the cathode bar itself.

Dans la demande de brevet japonais JA-A-56/150195 (Sumitomo), il est prévu de disposer sous les blocs cathodiques un écran en acier, de préférence recouvert de pâte carbonée dont le but est de réduire les risques d'infiltration de l'électrolyte dans l'espace sous-cathodique constitué de briques.In Japanese patent application JA-A-56/150195 (Sumitomo), provision is made to place a steel screen under the cathode blocks, preferably covered with carbonaceous paste, the aim of which is to reduce the risks of infiltration of the electrolyte in the sub-cathodic space made up of bricks.

Objet de l'inventionSubject of the invention

La présente invention a pour objet d'augmenter de façon substantielle (plus de 10 %) la section d'acier disponible pour l'évacuation du courant cathodique, et la surface de contact entre le carbone et les conducteurs cathodiques. Elle consiste, dans une cuve d'électrolyse du type défini dans le préambule de la revendication 1, à munir chaque barre cathodique d'une semelle métallique, constituée par une tôle métallique, soudée à la barre cathodique avant la mise en place du bloc carboné dans la cuve, pour assurer le passage du courant électrique et le contact électrique entre ladite semelle et la base du bloc carboné étant assuré par au moins une couche de matériau élastique conducteur de l'électricité. La semelle doit avoir une épaisseur au moins égale à 4 mm, et de préférence au moins égale à 10 mm.The object of the present invention is to increase substantially (more than 10%) the section of steel available for the evacuation of the cathode current, and the contact surface between the carbon and the cathode conductors. It consists, in an electrolytic cell of the type defined in the preamble of claim 1, to provide each cathode bar with a metal sole, constituted by a metal sheet, welded to the cathode bar before the establishment of the carbonaceous block in the tank, to ensure the passage of electric current and the electrical contact between said soleplate and the base of the carbonaceous block being ensured by at least one layer of elastic material conducting electricity. The sole must have a thickness at least equal to 4 mm, and preferably at least equal to 10 mm.

En outre, on peut disposer sous la semelle, un écran continu en acier, en contact électrique avec la semelle, ce qui permet d'éviter les infiltrations d'aluminium liquide et de cryolithe fondue, ce qui augmente sensiblement la durée de vie de la cuve d'électrolyse.In addition, a continuous steel screen can be placed under the soleplate, in electrical contact with the soleplate, which prevents infiltration of liquid aluminum and molten cryolite, which appreciably increases the service life of the electrolysis tank.

La figure 1 se rapporte à l'art antérieur.Figure 1 relates to the prior art.

Les figures 2 à 15 illustrent la mise en oeuvre de l'invention.Figures 2 to 15 illustrate the implementation of the invention.

Toutes les figures sont des représentations en coupe verticale.All the figures are representations in vertical section.

Description des figuresDescription of the figures

La figure 1 montre la disposition classique d'un bloc cathodique carboné (1) dans lequel la barre (2A) est scellée par de la fonte (3).Figure 1 shows the classic arrangement of a carbonaceous cathode block (1) in which the bar (2A) is sealed by cast iron (3).

Dans ce cas, la barre affleure à la base du bloc carboné. Sur la partie droite de la figure 2, la barre (2B) dans une variante d'exécution, peut dépasser plus ou moins du plan de base du bloc carboné (3). Les blocs cathodiques successifs sont assemblés le plus souvent par un joint (4) en pâte carbonée.In this case, the bar is flush with the base of the carbon block. On the right part of Figure 2, the bar (2B) in an alternative embodiment, can more or less exceed the base plane of the carbonaceous block (3). The successive cathode blocks are most often assembled by a joint (4) made of carbonaceous paste.

La figure 2 illustre un premier mode de mise en oeuvre de l'invention. Sur la barre cathodique (2), on a soudé deux tôles épaisses en acier doux (5) reliées à la base du bloc carboné (1) par une couche de matériau élastique électriquement conducteur (6).FIG. 2 illustrates a first embodiment of the invention. On the cathode bar (2), two thick sheets of mild steel (5) were welded connected to the base of the carbon block (1) by a layer of electrically conductive elastic material (6).

En variante (figure 2A), la semelle en acier (5) peut être constituée par un colaminé acier-cuivre, la face cuivrée (5A) étant en contact avec le bloc carboné (1) par l'intermédiaire de la couche conductrice élastique (6). De préférence, l'épaisseur de la couche de cuivre (5A) doit être supérieure à une valeur minimale, que l'on peut estimer à environ 5 % de la couche d'acier, correspondant à la solubilité du cuivre dans l'acier à 900-950 °C, de façon que toute la couche de cuivre ne disparaisse pas par diffusion à l'état solide dans l'acier.As a variant (FIG. 2A), the steel soleplate (5) can consist of a steel-copper colamine, the copper-colored face (5A) being in contact with the carbonaceous block (1) via the elastic conductive layer ( 6). Preferably, the thickness of the copper layer (5A) must be greater than a minimum value, which can be estimated at around 5% of the steel layer, corresponding to the solubility of the copper. in steel at 900-950 ° C, so that the entire copper layer does not disappear by diffusion in the solid state in the steel.

La malléabilité du cuivre à chaud facilite l'établissement d'un bon contact avec le bloc cathodique et peut, le cas échéant, compenser en partie des déformations de la semelle en acier.The malleability of hot copper facilitates the establishment of good contact with the cathode block and can, if necessary, partially compensate for deformations of the steel soleplate.

En outre, la conductivité électrique du cuivre étant très supérieure à celle de l'acier, il s'ensuit un abaissement significatif de la chute de tension dans les collecteurs cathodiques.In addition, the electrical conductivity of copper being much higher than that of steel, it follows a significant lowering of the voltage drop in cathode collectors.

La figure 3 montre les quatre stades 3a, 3b, 3c, 3d de la procédure utilisée pour réaliser le montage de la figure 2.Figure 3 shows the four stages 3a, 3b, 3c, 3d of the procedure used to carry out the assembly of Figure 2.

La figure 3a montre la première étape :Figure 3a shows the first step:

Le bloc de carbone (1) ayant été retourné pour que la rainure (7) se présente vers le haut, on scelle la barre cathodique (2) par coulée de fonte (3).The carbon block (1) having been turned over so that the groove (7) faces upwards, the cathode bar (2) is sealed by casting iron (3).

La figure 3b montre la deuxième étape :Figure 3b shows the second step:

Après scellement de la barre cathodique (2), on pose sur la face supérieure du bloc retourné une couche élastique (6), conductrice électrique : on peut avantageusement utiliser un feutre de carbone ou de graphite, ou encore une feuille de graphite laminé, ou encore un complexe formé par collage d'une bande de feutre de carbone ou de graphite et d'une bande de graphite laminé.After sealing the cathode bar (2), an elastic, electrically conductive layer (6) is placed on the upper face of the inverted block: it is advantageous to use a carbon or graphite felt, or a laminated graphite sheet, or another complex formed by bonding a strip of carbon felt or graphite and a strip of laminated graphite.

A titre d'exemple, on peut utiliser des feutres de graphite RVG, ou du « Papyex » (R) (marques déposées par la Société « Le Carbone-Lorraine »).By way of example, it is possible to use RVG graphite felts, or “Papyex” (R) (trademarks registered by the Company “Le Carbone-Lorraine”).

La figure 3c montre la troisième étape :Figure 3c shows the third step:

On pose sur la couche de liaison élastique (6), la semelle (5) constituée par deux tôles épaisses en acier que l'on applique fortement, par pressage, sur la couche de liaison élastique (6).The sole (5) consists of two thick steel sheets, which are applied strongly, by pressing, to the elastic link layer (6) on the elastic connection layer (6).

On peut alors réaliser des cordons de soudure (8), de préférence continus, pour relier ces tôles épaisses à la barre cathodique : on a ainsi réalisé une semelle d'acier reliée électriquement à la barre cathodique. L'épaisseur de la semelle est au moins égale à 4 mm et, de préférence, au moins égale à 10 mm et généralement de l'ordre de 10 à 15 mm. La section de la barre cathodique peut être par exemple, de 160 x 120 mm.It is then possible to produce weld seams (8), preferably continuous, to connect these thick sheets to the cathode bar: a steel flange is thus produced electrically connected to the cathode bar. The thickness of the sole is at least equal to 4 mm and, preferably, at least equal to 10 mm and generally of the order of 10 to 15 mm. The cross-section of the cathode bar can be, for example, 160 x 120 mm.

La figure 3d montre le bloc carboné cathodique remis en position normale par retournement.Figure 3d shows the cathode carbon block returned to normal position by inversion.

La figure 4 montre une variante de l'invention où la semelle d'acier est située à cheval entre deux blocs carbonés cathodiques, et en contact électrique avec ces deux blocs.Figure 4 shows a variant of the invention where the steel base is located astride two carbon cathode blocks, and in electrical contact with these two blocks.

La figure 5 montre qu'au moment de la réalisation du montage, il est préférable de prévoir un léger jeu entre les semelles (5) de deux blocs adjacents (1) et (1') de façon que lorsque la température de fonctionnement normal est atteinte, et du fait de la dilatation plus importante de la semelle d'acier comparativement au bloc carboné, les bords des deux semelles adjacentes (5) et (5'), se retrouvent en contact avec une pression juste suffisante pour assurer une soudure à chaud de ces bords entre eux, sans que cette pression ne soit excessive au point d'entraîner une déformation des semelles, préjudiciables au contact électrique entre blocs carbonés et semelles d'acier.Figure 5 shows that when performing the assembly, it is preferable to provide a slight clearance between the flanges (5) of two adjacent blocks (1) and (1 ') so that when the normal operating temperature is reached, and due to the greater expansion of the steel base compared to the carbonaceous block, the edges of the two adjacent flanges (5) and (5 '), are in contact with a pressure just sufficient to ensure a weld to hot of these edges between them, without this pressure being excessive to the point of causing deformation of the soles, detrimental to the electrical contact between carbonaceous blocks and steel soles.

Les extrémités en regard des deux semelles adjacentes (5) et (5') peuvent être perpendiculaires au plan de la semelle - et parallèles entre elles - comme représenté, sur la figure, ou taillées en biseau (figures 5a, 5b).The opposite ends of the two adjacent flanges (5) and (5 ') can be perpendicular to the plane of the flange - and parallel to each other - as shown in the figure, or cut in a bevel (Figures 5a, 5b).

Les flans des biseaux de (5) et (5') peuvent être parallèles entre eux (5A) ou non (5B).The blanks of the bevels of (5) and (5 ') may be parallel to each other (5A) or not (5B).

Pour empêcher la pénétration de produits pulvérulents provenant du lit de pose (11) dans le jeu (9) entre les deux tôles (5) et (5'), on peut prévoir l'interposition d'une bande de tôle mince (10) faisant office de joint. Cette tôle évite également que la pâte carbonée qui remplit le joint (4) ne s'écoule, lors de la première chauffe, dans l'espace (9).To prevent the penetration of powdery products from the laying bed (11) into the clearance (9) between the two sheets (5) and (5 '), provision may be made for the interposition of a strip of thin sheet (10) acting as a seal. This sheet also prevents the carbonaceous paste which fills the joint (4) from flowing, during the first heating, into the space (9).

La valeur du jeu (9) nécessaire au montage ou à la pose dépend de la nature exacte du bloc carboné : à base d'anthracite, ou semi-graphite ou semi-graphitisé ou graphite, et de la dimension exacte des blocs et des semelles, ainsi que de la nature et de l'épaisseur du joint entre blocs carbonés : blocs collés entre eux ou séparés par un petit joint (4) de pâte de brasque. Généralement, ce jeu sera défini par un rapport e/L de l'ordre de 1 à 2 %.The value of the clearance (9) necessary for mounting or installation depends on the exact nature of the carbonaceous block: based on anthracite, or semi-graphite or semi-graphitized or graphite, and on the exact dimension of the blocks and footings , as well as the nature and thickness of the joint between carbonaceous blocks: blocks glued together or separated by a small joint (4) of pot lining. Generally, this game will be defined by an e / L ratio of the order of 1 to 2%.

La figure 6 montre le détail de montage des bandes d'étanchéité (10). La bande supérieure (10A) est soudée par exemple sur la tôle (5) et la bande inférieure (10B) est soudée sur la tôle (5') de telle sorte que, lors de la première chauffe, elles peuvent coulisser librement et prendre leur place définitive.Figure 6 shows the mounting detail of the sealing strips (10). The upper strip (10A) is welded for example on the sheet (5) and the lower strip (10B) is welded on the sheet (5 ') so that, during the first heating, they can slide freely and take their definitive place.

Par ailleurs, et à condition de prévoir un rainurage adéquat dans les blocs cathodiques (1), on peut placer à la partie inférieure du joint (4) une pièce en graphite à faible porosité (12) qui améliore l'étanchéité du joint (4) et réduit les risques d'infiltration de cryolithe fondue lors du démarrage de la cuve d'électrolyse.Furthermore, and provided that adequate grooving is provided in the cathode blocks (1), a lower porosity graphite piece (12) can be placed at the bottom of the joint (4) which improves the seal of the joint (4 ) and reduces the risk of infiltration of molten cryolite when the electrolysis tank is started.

La figure 7 montre une autre variante de réalisation du joint entre les semelles (5) et (5') de blocs cathodiques adjacents (1) et (1'). On renonce à établir une soudure directe entre (5) et (5') et on dispose dans le jeu (9) un joint souple (14), de préférence conducteur électrique et compressible, tel que de la tresse de graphite, ou un tube métallique à paroi mince (épaisseur inférieure à la moitié de l'épaisseur de la semelle, (5) ou (5'), reposant librement entre les bandes 10A et 10B. On peut, en outre, au montage, prévoir un recouvrement et un collage des feuilles de matière carbonée élastique (13) qui améliore l'étanchéité du joint, dans le but précédemment indiqué.Figure 7 shows another alternative embodiment of the joint between the flanges (5) and (5 ') of adjacent cathode blocks (1) and (1'). We renounce to establish a direct weld between (5) and (5 ') and we have in the set (9) a flexible joint (14), preferably electrically conductive and compressible, such as graphite braid, or a tube thin-walled metal (thickness less than half the thickness of the sole, (5) or (5 '), resting freely between the strips 10A and 10B. It is also possible, during mounting, to provide a covering and a bonding of sheets of elastic carbonaceous material (13) which improves the seal of the joint, for the purpose previously indicated.

La figure 8 représente une autre variante, dans laquelle le joint carboné souple (14) est remplacé par un tube (15) déformable, soudé préalablement à au moins une des semelles (5) ou (5'), qui absorbe les effets de dilatation et que l'on peut remplir d'un matériau pulvérulent inerte (19), pour limiter l'oxydation interne à chaud.FIG. 8 represents another variant, in which the flexible carbon joint (14) is replaced by a deformable tube (15), welded beforehand to at least one of the flanges (5) or (5 '), which absorbs the expansion effects and which can be filled with an inert pulverulent material (19), to limit internal hot oxidation.

Bien entendu, de telles liaisons souples ou déformables peuvent être utilisées pour la jonction entre les demi-écrans d'un même bloc lorsque celui-ci comporte un scellement avec les demi-barres d'acier, séparées au centre du bloc par un espace de dilatation.Of course, such flexible or deformable connections can be used for the junction between the half-screens of the same block when the latter comprises a seal with the steel half-bars, separated in the center of the block by a space of dilation.

les figures 9 et 10 illustrent la mise en oeuvre de l'invention dans le cas des blocs carbonés (1) munis de deux barres cathodiques parallèles (2C et 2D), disposition que l'on rencontre parfois dans le but d'augmenter la surface de contact avec le bloc carboné.Figures 9 and 10 illustrate the implementation of the invention in the case of carbon blocks (1) provided with two parallel cathode bars (2C and 2D), an arrangement which is sometimes encountered in order to increase the surface contact with the carbon block.

Sur la figure 9, il apparaît que l'on a procédé au scellement simultané des deux barres 2C, 2D par coulée de fonte (3), l'épaisseur (e) de la plaque de fonte entre les deux barres étant, de préférence, inférieure ou égale à la différence des cotes ho et h1 (e < ho - hi).In FIG. 9, it appears that the two bars 2C, 2D were sealed simultaneously by casting iron (3), the thickness (e) of the iron plate between the two bars preferably being less than or equal to the difference in the ratings h o and h 1 (e <h o - h i ).

La semelle (5) peut être en tôle d'acier simple ou mixte acier-cuivre comme on l'a décrit précédemment.The soleplate (5) can be made of single or mixed steel-copper sheet steel as described above.

Sur la figure 10, les deux barres cathodiques 2C, 2D ont été scellées individuellement, puis reliées par soudure avec une tôle (21) prédéformée en voûte, de façon à obtenir, à chaud, un bon contact électrique avec la partie centrale du bloc carboné par l'intermédiaire de la couche conductrice élastique (6).In FIG. 10, the two cathode bars 2C, 2D were individually sealed, then connected by welding with a sheet (21) preformed in a vault, so as to obtain, when hot, good electrical contact with the central part of the carbonaceous block. via the elastic conductive layer (6).

Dans tous les cas représentés (figures 2 à 10), la semelle métallique est en contact avec la base des blocs carbonés par l'intermédiaire du matériau élastique (6) sur au moins 20 % de la surface de cette base.In all the cases shown (FIGS. 2 to 10), the metal soleplate is in contact with the base of the carbon blocks by means of the elastic material (6) over at least 20% of the surface of this base.

Il est possible d'améliorer l'étanchéité de l'espace sous-cathodique et de supprimer à peu près totalement les infiltrations d'aluminium liquide et de cryolithe fondue en disposant un écran (26) sous la base des blocs carbonés constituant la cathode de la cuve d'électrolyse et dans lesquels sont scellées les barres cathodiques, cet écran s'étendant au moins sur tout l'espace situé à l'aplomb de la cathode (fig. 11). Il est constitué par au moins une tôle d'acier continue dont au moins la moitié de la surface est constituée par une partie ayant au moins 5 mm, et de préférence de 8 à 12 mm d'épaisseur, et qui comporte au moins une zone déformable absorbant les contraintes dues aux écarts de température entre la partie centrale, située à l'aplomb de la cathode, et la partie périphérique moins chaude. Pour éviter tout risque de corrosion électrochimique, il est alors préférable de mettre la semelle métallique (5) en contact électrique avec l'écran (26).It is possible to improve the tightness of the sub-cathode space and to almost completely eliminate the infiltration of liquid aluminum and molten cryolite by placing a screen (26) under the base of the carbon blocks constituting the cathode of the electrolytic cell and in which the cathode bars are sealed, this screen extending at least over the entire space located below the cathode (fig. 11). It consists of at least one continuous sheet of steel, at least half of the surface of which consists of a part having at least 5 mm, and preferably 8 to 12 mm thick, and which comprises at least one zone. deformable absorbing stresses due to temperature differences between the central part, located directly above the cathode, and the less hot peripheral part. To avoid any risk of electrochemical corrosion, it is then preferable to put the metal soleplate (5) in electrical contact with the screen (26).

La liaison électrique entre la semelle (5) et l'écran (26) peut être assurée par une soudure, par exemple, par un cordon continu ou discontinu entre au moins un rebord de la semelle et l'écran continu. Elle peut, également, être assurée par la fusion d'un alliage de brasure préalablement disposé entre la semelle et l'écran continu, les points de solidus et de liquidus de cet alliage étant convenablement choisis.The electrical connection between the sole (5) and the screen (26) can be ensured by welding, for example, by a continuous or discontinuous bead between at least one edge of the sole and the continuous screen. It can also be ensured by the fusion of a brazing alloy previously disposed between the sole and the continuous screen, the points of solidus and liquidus of this alloy being suitably chosen.

La figure 12 montre un mode de réalisation de ce principe, selon lequel la semelle (5) de chaque barre cathodique (2) est posée directement sur l'écran continu (26) en acier épais, auquel elle est reliée par brasure (16) ou par soudure (17).FIG. 12 shows an embodiment of this principle, according to which the sole (5) of each cathode bar (2) is placed directly on the continuous screen (26) of thick steel, to which it is connected by solder (16) or by welding (17).

L'avantage de cette disposition est que l'écran continu en acier épais (26) est, tous points, au potentiel électrique des barres cathodiques, ce qui élimine tout effet de pile électrochimique générateur de corrosion rapide. L'épaisseur de l'écran est d'au moins 5 mm, et, de préférence, comprise entre 8 et 12 mm. La semelle (5) a une épaisseur au moins égale à 4 mm et, de préférence, au moins égale à 10 mm.The advantage of this arrangement is that the continuous thick steel screen (26) is, at all points, at the electrical potential of the cathode bars, which eliminates any effect of electrochemical cell generating rapid corrosion. The thickness of the screen is at least 5 mm, and preferably between 8 and 12 mm. The sole (5) has a thickness at least equal to 4 mm and, preferably, at least equal to 10 mm.

La figure 12 montre comment ce dispositif peut être mis en place lors de la construction de la cuve. la barre cathodique (2) a été mise en place et scellée à la fonte (3) dans chaque bloc cathodique (1). Puis on soude en (18), une semelle (5) dont la longueur est au plus égale et, en pratique légèrement inférieure à l'entraxe de deux barres successives. Le bloc est alors posé sur l'écran (26), reposant sur la couche isolante (20), et soudé en (9), de préférence par un cordon continu, de façon à assurer un bon contact électrique. Les couches (24) et (25) sont des briques isolantes et réfractaires, disposées sur le fond (27) du caisson de la cuve d'électrolyse.Figure 12 shows how this device can be implemented during the construction of the tank. the cathode bar (2) was put in place and sealed with cast iron (3) in each cathode block (1). Then welded in (18), a sole (5) whose length is at most equal and, in practice slightly less than the distance between two successive bars. The block is then placed on the screen (26), resting on the insulating layer (20), and welded at (9), preferably by a continuous cord, so as to ensure good electrical contact. The layers (24) and (25) are insulating and refractory bricks, arranged on the bottom (27) of the casing of the electrolysis tank.

Pour la pose du premier et du dernier bloc, on peut être amené à modifier la longueur et la disposition des semelles pour faciliter l'assemblage.For the installation of the first and last block, it may be necessary to modify the length and the arrangement of the soles to facilitate assembly.

Il est possible de réaliser la liaison électrique entre la semelle (5) et l'écran (26) par brasage (16) au moyen d'un alliage, ayant un point de solidus et un point de liquidus convenablement choisi, interposé entre la semelle et l'écran.It is possible to make the electrical connection between the sole (5) and the screen (26) by brazing (16) by means of an alloy, having a point of solidus and a point of liquidus suitably chosen, interposed between the sole and the screen.

Cet alliage de brasure doit remplir les conditions suivantes :

  • 1. Sa température de solidus (= température de solidification finissante) doit être supérieure à environ 600 °C et de préférence 650 °C, de façon qu'à la première mise en service de la cuve, il autorise les déplacements relatifs entre les semelles (5) et l'écran (26), provoqués par les dilatations différentielles entre les blocs et barres cathodiques munis de leurs semelles, et l'écran continu. Si la brasure est introduite sous forme d'un lit pulvérulent, ou en grains très fins, d'alliage restant solide jusque vers 650 °C, cette condition sera remplie.
  • 2. Cette même température de solidus ne doit pas, de préférence, excéder la température atteinte par les semelles en régime de marche continue; c'est-à-dire environ 850 à 920 °C, afin que l'alliage de brasure se liquéfie au moins partiellement pendant la mise en température, lors du démarrage de la cuve. Il se produit alors une soudure par interdiffusion métallique entre les tôles d'acier des semelles (5) et de l'écran (26) lors de cette fusion au moins partielle de l'alliage intermédiaire. Ceci implique que :
    • l'un au moins des éléments d'alliage soit suffisamment soluble dans le fer, à l'état solide, dans un domaine de température correspondant aux températures de fonctionnement des semelles et de l'écran ;
    • le fer soit au moins partiellement soluble dans l'alliage intermédiaire liquide, pour que la soudure soit effective après que les éléments d'alliage de la brasure aient été absorbés par une diffusion dans l'acier solide : on réalise de fait une fusion superficielle de l'acier par l'alliage, cet alliage disparaissant ensuite par diffusion dans l'acier, et laissant en place une soudure solide.
  • 3. L'alliage, ou l'un de ses constituants, ne doit pas favoriser l'oxydation de l'acier.
  • 4. L'alliage, ou l'un de ses constituants, ne doit pas favoriser une fragilisation mécanique ou chimique de l'acier.
  • 5. Enfin, pour la pratique industrielle, le coût de cet alliage doit être modéré.
This brazing alloy must meet the following conditions:
  • 1. Its solidus temperature (= finishing solidification temperature) must be greater than approximately 600 ° C and preferably 650 ° C, so that when the tank is put into service for the first time, it allows relative movements between the soles (5) and the screen (26), caused by the differential expansions between the blocks and cathode bars provided with their soles, and the continuous screen. If the solder is introduced in the form of a pulverulent bed, or in very fine grains, of alloy remaining solid up to around 650 ° C., this condition will be fulfilled.
  • 2. This same solidus temperature should preferably not exceed the temperature reached by the soles in continuous running conditions; that is to say approximately 850 to 920 ° C., so that the brazing alloy at least partially liquefies during the setting in temperature, during the starting of the tank. There is then produced a weld by metallic interdiffusion between the steel sheets of the flanges (5) and of the screen (26) during this at least partial melting of the intermediate alloy. This implies that:
    • at least one of the alloying elements is sufficiently soluble in iron, in the solid state, in a temperature range corresponding to the operating temperatures of the soles and of the screen;
    • the iron is at least partially soluble in the liquid intermediate alloy, so that the soldering is effective after the alloying elements of the solder have been absorbed by a diffusion in the solid steel: a surface fusion of steel by the alloy, this alloy then disappearing by diffusion in the steel, and leaving in place a solid weld.
  • 3. The alloy, or one of its constituents, must not favor the oxidation of steel.
  • 4. The alloy, or one of its constituents, must not promote mechanical or chemical embrittlement of the steel.
  • 5. Finally, for industrial practice, the cost of this alloy must be moderate.

Les compositions optimales de la brasure pour la mise en oeuvre de l'invention comportent au moins 50 % d'un premier métal choisi parmi l'aluminium, le cuivre, le zinc, le reste étant au moins un second métal choisi parmi le manganèse, le nickel, le vanadium, le beryllium, le silicium, l'étain et le titane, ainsi que l'aluminium et le cuivre si le premier métal n'est pas le cuivre ou l'aluminium.

Figure imgb0001
The optimal brazing compositions for implementing the invention comprise at least 50% of a first metal chosen from aluminum, copper, zinc, the remainder being at least a second metal chosen from manganese, nickel, vanadium, beryllium, silicon, tin and titanium, as well as aluminum and copper if the first metal is not copper or aluminum.
Figure imgb0001

Parmi ces alliages, les compositions n° 1, 3, 6 et 7 conviennent particulièrement bien, dans la pratique industrielle. Certains sont fragiles et peuvent être broyés jusqu'à la finesse désirée, d'autres doivent être traités de façon connue, par pulvérisation à l'état liquide.Among these alloys, compositions no. 1, 3, 6 and 7 are particularly suitable in industrial practice. Some are fragile and can be ground to the desired fineness, others must be treated in a known manner, by spraying in the liquid state.

Si la composition de l'alliage le permet, la brasure peut être utilisée sous forme d'une feuille mince, laminée, introduite au montage entre la semelle et l'écran. La présence, parmi les constituants principaux ou secondaires de l'alliage, d'un métal réducteur vis-à-vis d'oxyde de fer (calamine) qui recouvre le plus souvent les plaques d'acier utilisées pour constituer la semelle ou l'écran (métal tel que AI et/ou Si) dispense d'utiliser tout autre décapant pour favoriser l'étalement de la brasure lorsqu'elle passe à l'état liquide.If the composition of the alloy allows, the solder can be used in the form of a thin, laminated sheet, introduced during assembly between the sole and the screen. The presence, among the main or secondary constituents of the alloy, of a reducing metal with respect to iron oxide (scale) which most often covers the steel plates used to constitute the sole or the screen (metal such as AI and / or Si) dispenses with using any other stripper to promote spreading of the solder when it passes into the liquid state.

Il est également possible en variante de l'invention de confondre la semelle (5) et l'écran (26) en une seule partie, constituée par une tôle d'acier épaisse (22), comme on l'a représenté sur les figures 13 et 14, qui peut être munie de joints ou de zones déformables, capables de supporter les dilatations thermiques, par exemple le tube (15) de la figure 2. Dans un tel cas, l'épaisseur de l'écran peut se situer entre 10 et 20 mm.It is also possible, as a variant of the invention, to confuse the sole (5) and the screen (26) in a single part, constituted by a thick steel sheet (22), as shown in the figures. 13 and 14, which may be provided with seals or deformable zones, capable of withstanding thermal expansions, for example the tube (15) of FIG. 2. In such a case, the thickness of the screen may be between 10 and 20 mm.

Pour le montage, les barres (2) sont positionnées sur l'écran (22), puis raccordées par un cordon de soudure (23). Après quoi, les blocs cathodiques (1) sont mis en place, le scellement étant assuré par de la pâte carbonée (13). Le raccordement peut aussi être effectué par une brasure (16).For mounting, the bars (2) are positioned on the screen (22), then connected by a weld bead (23). After which, the cathode blocks (1) are put in place, the sealing being ensured by carbonaceous paste (13). The connection can also be made by a solder (16).

On peut en outre interposer, entre les blocs carbonés (1) et l'écran épais (22) une couche de matériau souple et bon conducteur électrique, par exemple le « Papyex » (marque déposée par la Société « Le Carbone-Lorraine ») qui est une feuille de graphite souple ou le feutre de graphite RVG, de la même société.It is also possible to interpose, between the carbon blocks (1) and the thick screen (22) a layer of flexible material and good electrical conductor, for example “Papyex” (trademark registered by the Company “Le Carbone-Lorraine”) which is a flexible graphite sheet or RVG graphite felt, from the same company.

La figue 14 représente un autre mode d'assemblage, selon lequel les barres cathodiques (2) sont disposées non plus à l'aplomb de l'axe du bloc (1), mais à cheval sur deux blocs adjacents à l'aplomb du joint entre ces deux blocs. L'avantage de cette disposition est que la pâte carbonée (4) assurant le scellement entre les blocs (1) et les barres (2) peut être injectée, à chaud, dans l'espace séparant deux blocs adjacents.Fig. 14 shows another method of assembly, according to which the cathode bars (2) are no longer arranged directly above the axis of the block (1), but straddling two blocks adjacent to the vertical line of the joint between these two blocks. The advantage of this arrangement is that the carbonaceous paste (4) ensuring the sealing between the blocks (1) and the bars (2) can be injected, hot, in the space separating two adjacent blocks.

La figure 15 montre de façon très schématique, la coupe transversale partielle d'une cuve d'électrolyse selon l'invention, avec le caisson métallique externe (30), le brasquage latéral (31) en pâte carbonée, le bloc carboné cathodique (1) surmonté par la nappe d'aluminium liquide (32), l'électrolyte (33) et le système anodique (34), la barre cathodique (2) en acier, scellée à la fonte (3), et la semelle (5) en acier, objet de l'invention. On note que la section de la barre cathodique (2) est réduite dans la traversée de la partie externe du garnissage (31) et du caisson (30).FIG. 15 very schematically shows the partial cross-section of an electrolytic cell according to the invention, with the external metal box (30), the side soldering (31) in carbonaceous paste, the cathode carbon block (1 ) surmounted by the sheet of liquid aluminum (32), the electrolyte (33) and the anode system (34), the cathode bar (2) made of steel, sealed with cast iron (3), and the soleplate (5) steel, object of the invention. It is noted that the cross section of the cathode bar (2) is reduced in the crossing of the external part of the lining (31) and of the box (30).

Avantages procurés par l'inventionBenefits of the invention

La mise en oeuvre de l'invention procure les avantages suivants :

  • 1. La semelle métallique, sur chaque barre cathodique (une cuve peut en comporter plusieurs dizaines) augmente d'au moins 10 % et jusqu'à 20 à 50 % la section de passage du courant cathodique et la surface de contact acier-carbone avec réduction corrélative de la chute de tension au contact acier-carbone.
  • 2. La semelle métallique associée à l'écran assure une très bonne répartition du courant sur toute la surface de la cathode d'où réduction des courants horizontaux dans l'aluminium liquide, qui ont une influence néfaste sur la stabilité et le rendement de la cuve, en raison des effets tourbillonnaires dans la nappe d'aluminium liquide qui en résultent.
  • 3. La semelle métallique associée à l'écran assure également une excellente homogénéité de la température de l'ensemble de la cathode, ce qui réduit d'autant les risques d'infiltration dans les zones chaudes et de condensation dans les zones relativement plus froides.
  • 4. En cas de rupture d'une barre cathodique (par corrosion sous l'effet des infiltrations de cryolithe et d'aluminium liquide dans les joints), la semelle fonctionne pour le bloc considéré comme collecteur de secours, ce qui retarde d'autant le moment où il faudra arrêter et démonter la cuve pour refaire la cathode. En outre, le déséquilibre électrique de la cuve est limité, ce qui est favorable pour le rendement Faraday pendant la période séparant la rupture d'une barre et l'arrêt de la cuve.
The implementation of the invention provides the following advantages:
  • 1. The metal soleplate, on each cathode bar (a tank can have several tens) increases by at least 10% and up to 20 to 50% the cross-section of the cathode current and the steel-carbon contact surface with correlative reduction of the voltage drop on steel-carbon contact.
  • 2. The metallic sole associated with the screen ensures a very good distribution of current over the entire surface of the cathode, hence the reduction of horizontal currents in liquid aluminum, which have a harmful influence on the stability and the yield of tank, due to the swirling effects in the resulting sheet of liquid aluminum.
  • 3. The metal sole associated with the screen also ensures excellent temperature uniformity of the entire cathode, which reduces the risk of infiltration in hot areas and condensation in relatively cooler areas .
  • 4. In the event of a cathode rod breaking (by corrosion under the effect of infiltration of cryolite and liquid aluminum in the joints), the soleplate functions for the block considered as an emergency collector, which delays as much when to stop and disassemble the tank to redo the cathode. In addition, the electrical imbalance of the tank is limited, which is favorable for Faraday performance during the period between the breaking of a bar and the stopping of the tank.

La présence de l'écran (26) apporte les avantages supplémentaires suivants :

  • 5. Blocage de toutes les infiltrations des produits sodo-fluorés et de la cryolithe en direction de l'isolant thermique placé sur le fond du caisson, qui sont la principale cause de mise hors-service des cuves d'électrolyse.
  • 6. Plus grande facilité de construction de la cathode qui, dans le cas de la figure 3 par exemple, ne nécessite, par rapport aux solutions antérieures, qu'un simple cordon de soudure supplémentaire, qui est réalisé à plat et dans un espace accessible, ou qu'une application de brasure en poudre.
  • 7. Suppression du risque de corrosion électrochimique de l'écran du fait qu'il se trouve, en tous points, au potentiel des barres cathodiques. La mise en oeuvre de l'invention contribue à augmenter la durée de vie utile des cuves d'électrolyse et à maintenir la bonne isolation thermique du fond pendant la durée de vie.
The presence of the screen (26) provides the following additional advantages:
  • 5. Blockage of all infiltration of sodo-fluorinated products and cryolite in the direction of the thermal insulation placed on the bottom of the box, which are the main cause of decommissioning of the electrolytic cells.
  • 6. Greater ease of construction of the cathode which, in the case of FIG. 3 for example, requires, compared to the previous solutions, only a simple additional weld bead, which is made flat and in an accessible space , or an application of solder powder.
  • 7. Elimination of the risk of electrochemical corrosion of the screen because it is, at all points, at the potential of the cathode bars. The implementation of the invention contributes to increasing the useful life of the electrolytic cells and to maintaining good thermal insulation of the bottom during the service life.

Tous ces avantages concourent à augmenter de façon très importante la durée de vie d'une cuve d'électrolyse.All these advantages combine to significantly increase the life of an electrolytic cell.

Claims (20)

1. An electrolytic cell for the production of aluminium by electrolysis, in which each cathode rod allowing extraction of the current is sealed in at least one open groove (7) at the base of each of the carbonated blocks (1) forming the cathode of the electrolysis cell, said cathoderod (2) being elongated by a metal portion in electrical contact with the base of the carbonated blocks (1) over at least 20 % of the total surface of said base, characterised in that this metal portion is a sole (5) constituted by a metal sheet having a thickness of a least 4 mm which is soldered to the cathode rod (2) before the carbonated block (1) is positioned in the cell, electrical contact between the sole (5) and the base of the carbonated block (1) being provided by at least one layer of electrically conductive elastic material (6).
2. An electrolytic cell according to claim 1, characterised in that the metal sole is composed of metal sheet.
3. An electrolytic cell according to claim 1, characterised in that the metal sole is an iron-copper composite of which the copper portion is turned upwards facing the base of the carbonated block.
4. An electrolytic cell according to claim 3, characterised in that the thickness of the copper portion is equal to at least 5 % of the thickness of the steel portion.
5. An electrolytic cell according to claim 1, characterised in that the elastic material (6) is a carbonated product selected from carbon felt, graphite felt, laminated graphite sheet and complexes of laminated graphite sheets stuck on a graphite or carbon felt.
6. An electrolytic cell according to any one of claims 1 to 5, characterised in that the soles (5) and (5') of two adjacent cathode blocks (1) and (1') are separated by a space (9) such that they come into contact when they have reached their equilibrium temperature of between about 800 and 900 °C during operation.
7. An electrolytic cell according to any one of claims 1 to 5, characterised in that the soles (5) and (5') of two adjacent cathode blocks (1) and (1') are separated by a space (9) provided with a flexible gasket (14).
8. An electrolytic cell according to claim 6 or 7, characterised in that the space (9) is provided with blocking means (10A) and (10B).
9. An electrolytic cell according to claim 1, characterised in that the lower face of the sole (5) is placed in superposed relation and in electrical contact with a thick continuous metal screen (26) which is positioned at the upper portion of the heat-insulating lining (10).
10. An electrolytic cell according to claim 9, characterised in that the electrical connection between the sole (5) and the screen (26) is provided by soldering.
11. An electrolytic cell according to claim 10, characterised in that the soldered joint is obtained by a wire of continuous or discontinuous solder between at least one edge of the sole (5) and the screen (26).
12. An electrolytic cell according to claim 10, characterised in that the solder is provided by melting a brazing alloy previously placed between. the sole and the continuous screen.
13. An electrolytic cell according to claim 12, characterised in that the brazing alloy has a point of solidus of from 600 to 900 °C and preferably from 650 to 850 °C.
14. An electrolytic cell according to claim 12, characterised in that the brazing alloy contains at least 50 % of a first metal selected from aluminium, copper and zinc, the remainder being at least one secondmetal selected from manganese, nickel, vanadium, beryllium, silicon, tin and titanium, as well as aluminium and copper if the first metal is not copper or aluminium.
15. An electrolytic cell according to claims 9 or 10, characterised in that the screen (26) comprises means such as (7) for absorbing thermal expansion and thermal stresses.
16. An electrolytic cell according to claim 9, characterised in that the sole (5) and the screen (26) are combined in a single plate (22) in direct contact with each cathode rod to which it is connected by welding or brazing and is provided with means (15) for absorbing thermal expansion and stresses.
17. An electrolytic cell according to claim 16, characterised in that the cathode rod is arranged directly below the axis of each cathode block (1).
18. An electrolytic cell according to claim 16, characterised in that the cathode rod is arranged directly below the gasket separating two adjacent cathode blocks.
19. An electrolytic cell according to claim 16, characterised in that the cathode rod is sealed to the cathode block (1) by a carbonated paste (4) which is subsequently baked in position.
20. An electrolytic cell according to any one of the preceding claims, characterised in that the metal sheet (5) is at least 10 mm thick.
EP84902015A 1983-05-16 1984-05-14 Cathode bar comprising a metal sole for hall-heroult electrolysis tanks Expired EP0144371B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT84902015T ATE30053T1 (en) 1983-05-16 1984-05-14 CATHODE BAR WITH A METAL BASE FOR HALLHEROULT ELECTROLYTIC FURNACES.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
FR8308334A FR2546184B1 (en) 1983-05-16 1983-05-16 CATHODE ROD WITH A METAL SOLE FOR HALL-HEROULT ELECTROLYSIS TANKS
FR8403864A FR2560613B2 (en) 1983-05-16 1984-03-02 IMPROVEMENT ON CATHODE RATES WITH A METAL SOLE, FOR HALL-HEROULT ELECTROLYSIS TANKS
FR8403864 1984-03-02
FR8308334 1984-03-02

Publications (2)

Publication Number Publication Date
EP0144371A1 EP0144371A1 (en) 1985-06-19
EP0144371B1 true EP0144371B1 (en) 1987-09-30

Family

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EP84902015A Expired EP0144371B1 (en) 1983-05-16 1984-05-14 Cathode bar comprising a metal sole for hall-heroult electrolysis tanks

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US (1) US4647356A (en)
EP (1) EP0144371B1 (en)
AU (1) AU569524B2 (en)
CA (1) CA1214752A (en)
DE (1) DE3466561D1 (en)
ES (1) ES288259Y (en)
FR (1) FR2560613B2 (en)
GR (1) GR81586B (en)
IS (1) IS1305B6 (en)
IT (1) IT1173645B (en)
NO (1) NO850095L (en)
NZ (1) NZ208161A (en)
SU (1) SU1349702A3 (en)
WO (1) WO1984004547A1 (en)
YU (1) YU84284A (en)

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US4912302A (en) * 1987-05-30 1990-03-27 Ngk Insulators, Ltd. Furnace for sintering ceramics, carbon heater used therefor and process for sintering ceramics
US5976333A (en) * 1998-01-06 1999-11-02 Pate; Ray H. Collector bar
NO315090B1 (en) * 2000-11-27 2003-07-07 Servico As Devices for conveying current to or from the electrodes in electrolytic cells, methods of making them, and electrolytic cell preparation of aluminum by electrolysis of alumina dissolved in a molten electrolyte
DK1502589T3 (en) * 2003-07-31 2006-09-25 Emdoka Bvba Drug Registration Veterinary aqueous injectable suspensions containing florfenicol
EP1927679B1 (en) * 2006-11-22 2017-01-11 Rio Tinto Alcan International Limited Electrolysis cell for the production of aluminium comprising means to reduce the voltage drop
CN104651882A (en) * 2014-09-29 2015-05-27 贵州航天乌江机电设备有限责任公司 Process for assembling cathodes in aluminium electrolysis cell
DE102016210693A1 (en) * 2016-06-15 2017-12-21 Sgl Cfl Ce Gmbh Cathode block having a novel groove geometry

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NL142156B (en) * 1947-09-05 Sandoz Ag PROCEDURE FOR PREPARING SUBSTITUTED DIARYLOXALAMIDES AND THEIR USE AS STABILIZERS AGAINST HEAT AND ADSORATING AGENTS FOR ULTRAVIOLET LIGHT IN PLASTICS.
NL69585C (en) * 1947-09-08
FR1125949A (en) * 1955-04-30 1956-11-12 Pechiney Improvements in the construction of the lower part of the crucible of igneous electrolysis cells
FR1161632A (en) * 1956-11-16 1958-09-02 Pechiney Improvements to igneous electrolysis cells
US3551319A (en) * 1968-09-06 1970-12-29 Kaiser Aluminium Chem Corp Current collector
CH527909A (en) * 1970-05-01 1972-09-15 Alusuisse Aluminum electrolytic cell
JPS56150190A (en) * 1980-01-16 1981-11-20 Agency Of Ind Science & Technol Preparation of composite material by thermite reaction
JPS56150195A (en) * 1980-04-23 1981-11-20 Sumitomo Alum Smelt Co Ltd Cathode furnace bottom for aluminum electrolytic furnace
FR2546183B1 (en) * 1983-05-16 1985-07-05 Pechiney Aluminium SUB-CATHODIC SCREEN COMPRISING DEFORMABLE AREAS, FOR HALL-HEROULT ELECTROLYSIS TANKS

Also Published As

Publication number Publication date
IT1173645B (en) 1987-06-24
YU84284A (en) 1987-12-31
FR2560613A2 (en) 1985-09-06
US4647356A (en) 1987-03-03
EP0144371A1 (en) 1985-06-19
AU2963884A (en) 1984-12-04
ES288259Y (en) 1986-07-16
IT8420920A1 (en) 1985-11-15
AU569524B2 (en) 1988-02-04
IS2911A7 (en) 1984-07-12
IS1305B6 (en) 1987-11-25
ES288259U (en) 1985-12-16
IT8420920A0 (en) 1984-05-15
CA1214752A (en) 1986-12-02
NO850095L (en) 1985-01-09
DE3466561D1 (en) 1987-11-05
GR81586B (en) 1984-12-11
FR2560613B2 (en) 1987-03-27
NZ208161A (en) 1988-03-30
SU1349702A3 (en) 1987-10-30
WO1984004547A1 (en) 1984-11-22

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