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
  • C25C3/16—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 a cathode bar comprising a metal sole, 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 carbon 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, to which the connecting conductors between the successive tanks forming a series are connected.
• the steel bars used for the extraction of the cathode current offer a limited contact surface with 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 discharge of current cathodic, and the contact surface between carbon and cathodic conductors. It consists in providing each cathode bar with a metal sole, in electrical contact with the horizontal base of each carbon block, the sole being welded to the cathode bar to ensure the passage of electric current.
• 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 significantly increases the 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 carbon 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 carbonaceous block (1) by a layer of electrically conductive elastic material (6).
• the steel soleplate (5) can be constituted by a steel-copper laminate, the copper-colored face (5A) being in contact either directly with the carbonaceous block (1), or by means of the elastic conductive layer (6).
• the thickness of the copper layer (5A) must be greater than a minimum value, which can be estimated at approximately 5% of the steel layer, corresponding to the solubility of copper in the steel to be 900-950 ° C, so that the entire copper layer does not not disappear by diffusion in the solid state in 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) is 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). It is then possible to produce weld beads (8), preferably continuous, to connect these thick sheets to the cathode bar: a steel soleplate is thus electrically connected to the cathode bar.
• the thickness of the sole is at least equal to 4 mm and, preferably, at less 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.
• FIG. 4 shows a variant of the invention in which the steel base is located astride two carbonaceous cathode blocks, and in electrical contact with these two blocks.
• Figure 5 shows that when mounting is carried out, 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 carbon 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 size of the blocks and footings , as well as the nature and thickness of the joint between blocks carbonaceous: 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 lower part of the joint (4) which improves the sealing 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 metallic with thin wall (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 effects of expansion 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 carbonaceous 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 have been 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 dimensions h 0 and h 1 (e ⁇ h 0 - h 1 ).
• the sole (6) can be made of simple steel sheet or mixed steel-copper as described above.
• the two cathode bars 2C, 2D have been 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 carbonaceous blocks - directly or through 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 contact electric 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 solidus and liquidus points 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 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). 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.
• This brazing alloy must meet the following conditions:
• This same solidus temperature should preferably not exceed the temperature reached by the soles in continuous running mode, that is to say about 850 to 920 ° C, so that the brazing alloy liquefies at least partially during the warm-up, when starting the tank. There then occurs 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.
• the alloy, or one of its constituents, must not favor the oxidation of steel.
• the alloy, or one of its constituents, must not favor a fra mechanical or chemical stabilization of steel.
• the optimal compositions of the solder for the implementation of the invention comprise at least 50% of a first metal chosen from aluminum, copper, zinc, the rest 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 screen.
• a reducing metal with respect to iron oxide (calamine) which most often covers the steel plates used to constitute the sole or the screen ( metal such as Al 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 can 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 can 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 bases (2) are no longer placed directly above the axis of the block (1), but straddling two blocks adjacent to the base 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.
• Figure 15 shows very schematically, 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) in steel, sealed with cast iron (3), and the sole (5) in 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).
• 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.
• the metal sole associated with the screen ensures a very good distribution of the current over the entire surface of the cathode, hence the reduction of horizontal currents in the liquid aluminum, which have a harmful influence on the stability and the yield of the tank, due to the swirling effects in the resulting sheet of liquid aluminum.
• 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. .
• 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.
• 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.

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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)
• Laminated Bodies (AREA)
• Insulated Conductors (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)

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Publications (1)

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Citations (4)

Family Cites Families (5)

• 1984
  • 1984-03-02 FR FR8403864A patent/FR2560613B2/fr not_active Expired
  • 1984-05-14 AU AU29638/84A patent/AU569524B2/en not_active Expired - Fee Related
  • 1984-05-14 US US06/694,381 patent/US4647356A/en not_active Expired - Fee Related
  • 1984-05-14 DE DE8484902015T patent/DE3466561D1/de not_active Expired
  • 1984-05-14 ES ES1984288259U patent/ES288259Y/es not_active Expired
  • 1984-05-14 WO PCT/FR1984/000129 patent/WO1984004547A1/fr active IP Right Grant
  • 1984-05-14 EP EP84902015A patent/EP0144371B1/fr not_active Expired
  • 1984-05-14 IS IS2911A patent/IS1305B6/is unknown
  • 1984-05-15 IT IT20920/84A patent/IT1173645B/it active
  • 1984-05-15 NZ NZ208161A patent/NZ208161A/en unknown
  • 1984-05-15 CA CA000454375A patent/CA1214752A/fr not_active Expired
  • 1984-05-15 GR GR74721A patent/GR81586B/el unknown
  • 1984-05-15 YU YU00842/84A patent/YU84284A/xx unknown
• 1985
  • 1985-01-09 NO NO850095A patent/NO850095L/no unknown
  • 1985-01-15 SU SU853836862A patent/SU1349702A3/ru active

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Non-Patent Citations (1)

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