EP3546620A1 - Cathode block having a slot with varying depth and a securing system - Google Patents

Abstract

A cathode block for an aluminum electrolysis cell based on carbon and / or graphite has at least one extending in the longitudinal direction of the cathode block groove for receiving at least one bus bar, wherein at least one of the at least one groove, seen over the length of the cathode block, varying Has depth, this groove is bounded by a wall, wherein on the wall at least one extending into the groove extending projection is provided.

Description

The present invention relates to a cathode block for an aluminum electrolysis cell, its use and a cathode comprising it.

Electrolysis cells are used, for example, for the electrolytic production of aluminum, which is usually carried out industrially by the Hall-Heroult process. In the Hall-Heroult process, a melt composed of alumina and cryolite is electrolyzed. The cryolite, Na ₃ [AlF ₆ ], serves to lower the melting point from 2045 ° C. for pure aluminum oxide to approximately 950 ° C. for a mixture containing cryolite, aluminum oxide and additives such as aluminum fluoride and calcium fluoride.

The electrolytic cell used in this method has a cathode bottom, which is composed of a plurality of, for example, up to 28 adjacent cathode blocks forming the cathode. The spaces between the cathode blocks are usually filled with a carbon-containing ramming mass to seal the cathode against molten components of the electrolytic cell, and to compensate for mechanical stresses that occur during commissioning of the electrolysis cell. In order to withstand the thermal and chemical conditions prevailing in the operation of the cell, the cathode blocks are usually composed of a carbonaceous material, such as graphite. On the undersides of the cathode blocks are usually provided in each case grooves, in each of which at least one or two bus bars are arranged, through which the current supplied via the anodes is dissipated. The gaps between the individual walls delimiting the grooves of the cathode blocks and the busbars are often poured with cast iron to to thereby electrically and mechanically connect the bus bars to the cathode blocks by the covering of the bus bars with cast iron produced thereby. About 3 to 5 cm above the located on the cathode top, usually 15 to 50 cm high, layer of liquid aluminum is formed, in particular of individual anode blocks, anode, between the and the surface of the aluminum, the electrolyte, ie the alumina and Cryolite-containing melt is located. During the electrolysis carried out at about 1000 ° C., the aluminum formed is deposited below the electrolyte layer due to its greater density compared to that of the electrolyte, ie as an intermediate layer between the upper side of the cathode and the electrolyte layer. In the electrolysis, the dissolved in the melt aluminum oxide is split by electric current flow to aluminum and oxygen. From an electrochemical point of view, the layer of liquid aluminum is the actual cathode because aluminum ions are reduced to elemental aluminum on its surface. Nevertheless, the term cathode will not be understood below to mean the cathode from an electrochemical point of view, ie the layer of liquid aluminum, but rather the component forming the base of the electrolytic cell, for example composed of one or more cathode blocks.

A major disadvantage of the cathode assemblies used in the Hall-Heroult method is their relatively low wear resistance, which manifests itself by a removal of the cathode block surfaces during the electrolysis. In this case, the removal of the cathode block surfaces due to an inhomogeneous current distribution within the cathode blocks is not uniform over the length of the cathode blocks, but to an increased extent at the cathode block ends, so that the surfaces of the cathode blocks change after a certain electrolysis time to a W-shaped profile. By the uneven removal of the cathode block surfaces, the useful life of the cathode blocks is limited by the locations with the largest removal. To counter this problem is in the WO 2007/118510 A2 a cathode block has been proposed, whose groove for receiving one or more busbars, relative to the cathode block length, has a greater depth in the middle than at the cathode block ends. Thereby, a substantially homogeneous vertical current distribution is achieved in the operation of the electrolysis cell over the cathode block length, whereby the increased wear on the cathode block ends is reduced and thus the life of the cathode is increased. The bus bar (s) is or are wrapped in a conventional manner with cast iron, said wrapping is done by pouring liquid cast iron in the space between the groove and the or the bus bar (s). However, such a cathode block is subject to disadvantages. During and after the pouring of the molten cast iron into the space between the groove and the busbar (s), during and after startup of the electrolysis cell comprising the cathode block, and during and after the switching off of the electrolysis cell and subsequent recommissioning, the cathode block is comparatively large Subjected to temperature changes, which lead to expansion or shrinkage of the cast iron and the bus bar (s) relative to the cathode block. This effect of expansion or shrinkage can be enhanced by occurring temperature gradients. Hereinafter, when referring to "large temperature change (s)", it is understood that one or both of said effects, ie, expansion / shrinkage or temperature gradient, is / are present. Because of the higher coefficients of thermal expansion of cast iron and the material of the bus bar (s) than the thermal expansion coefficient of the cathode block material, the cast iron and the bus bar (s) expand with a temperature increase relative to the cathode block, whereas they shrink with a temperature reduction relative to the cathode block. Thereby In particular, in conventional grooves having a rectangular cross-sectional shape, the electrical contact between the busbar, cast iron and cathode block deteriorates, which leads to an increased electrical resistance of the arrangement and thus to a poor energy efficiency of the electrolysis process. Apart from that, the bus bar (s) are movable in the space between the groove and the bus bar (s) both in the vertical and in the horizontal direction before pouring the molten cast iron so that they are poured of the molten cast iron and during the subsequent cooling and solidification of the cast iron can move uncontrollably in the groove, which can also lead to a non-uniform electrical contact between busbar, cast iron and cathode block. This also leads to an increased electrical resistance of the arrangement and thus to a poor energy efficiency of the electrolysis process. Instead of the cast iron ramming mass can also be used. As ramming mass ramming compounds based on anthracite, graphite and any mixtures thereof can be used. Preferably, a ramming mass based on graphite is used.

In order to prevent or at least complicate a displacement of a busbar in the groove of a cathode block, it is in the WO 2012/107412 A2 has been proposed in which the graphite foil-lined groove of a cathode block bounding wall to provide at least one recess and after inserting the busbar (s) into the groove the forming space between the groove and the busbar (s) so with liquid Fill cast iron so that the solidified cast iron engages in the at least one depression. If the groove has a varying depth, as seen over the length of the cathode block, the at least one depression should run parallel to the groove bottom-that is, obliquely relative to the horizontal direction-that is to say have a constant distance from the bottom wall of the groove, in order to be displaceable the busbar (s) to ensure parallel to the groove bottom. However, this is disadvantageous because, due to the higher coefficients of thermal expansion of cast iron and the material of the busbar (s) compared to that of the cathode block during and after the pouring of the molten cast iron into the space between the groove and the busbar (s) of the Kathodenblocks occurring temperature changes as well as during start-up and shutdown, and possibly restarting, the cathode block comprehensive electrolysis cell occurring temperature changes between the cast iron and the or the busbar (s) on the one hand and the cathode block on the other hand shear stresses occur, which to a the function of Damaging the cathode block in the form of, for example, cracking in the cathode block or even a breakage of the cathode block. Such damage leads to a reduced electrical conductivity between the bus bar or the cast iron and the cathode block and to a lower stability of the arrangement or even leads to the failure of the entire assembly. Instead of the cast iron can also ramming - as described above - are used.

In the following, when talking about cast iron, it is to be understood that the cast iron can be replaced by ramming mass without being explicitly described each time.

It is therefore an object of the present invention to provide a cathode block which is suitable, in particular, for use with an aluminum electrolysis cell, with which a substantially homogeneous vertical current distribution is achieved over the cathode block length during operation of the electrolysis cell. n) even with large changes in temperature a low and especially over longer operating times permanently low electrical resistivity and low contact resistance between the cast iron sheathed busbar and the cathode block, and which is stable at high temperature changes, even with inserted and cast iron busbar (s) against mechanical damage, such as cracking. Instead of the cast iron ramming mass can be used.

According to the invention, this object is achieved by a cathode block for an aluminum electrolytic cell based on carbon and / or graphite, wherein the cathode block has at least one extending in the longitudinal direction of the cathode block groove for receiving at least one busbar, wherein at least one of the at least one groove , seen over the length of the cathode block, varying depth, said groove being bounded by a wall, wherein on the wall at least one projection extending into the groove is provided.

According to the invention, it has been recognized that by providing at least one protrusion extending into the groove, which serves as a bearing surface for busbar ends or their cast iron cladding, a cathode block is also provided in the cathode block in particular when the groove of varying depth is formed in which the Busbar inserted in the groove and - especially in the case of two mutually adjoining inserted into the groove busbars, each with respect to the length of the cathode block half length - the busbar (s) - depending on the configuration of the projection - in vertical and / or be fixed in the horizontal direction, so that an uncontrolled movement or displacement of the busbars in the case of the preparation of a cathode assembly with a cathode block and in its groove inserted cast-iron busbar (s) carried out pouring liquid cast iron into the space between the Nu t and the busbar (s) and in particular during the subsequent cooling and solidifying the cast iron despite the typically higher thermal expansion of cast iron and the material of the bus bar (s) as compared to the thermal expansion of the cathode block material, which movement may result in poor electrical contact between bus bar, cast iron and cathode block, reliably avoided. The at least one projection extending into the groove is therefore a support nose or a support journal on which an end piece of a busbar or two end pieces of two busbars rest. Because of this, the produced cathode assembly of cathode block with inserted and cast iron busbar (s) has a low electrical resistivity and low contact resistance between the cast iron sheathed busbar (s) and the cathode block, and in particular also a permanently low electrical resistivity and low contact resistance between the cast iron sheathed busbar (s) and the cathode block, even at high temperature changes. Thus, the cathode block according to the invention is particularly suitable for receiving two mutually adjacent in the groove busbars, each with respect to the length of the cathode block half length, in which case the projection is preferably provided in the middle of the cathode block, so that in each case one end both busbars can rest on the contact surface formed by the projection. Furthermore, the cathode block according to the invention is also particularly suitable for cross-sectionally rectangular busbars. In particular, in the case that in the groove wall of the cathode block is additionally provided in the longitudinal direction of the cathode block horizontally extending recess is in the groove bounding the cathode block wall, even with large changes in temperature mechanical damage to the cathode block with inserted into the groove and with Cast iron sheathed busbar, such as cracking of the cathode block, reliably avoided. It is by using a groove with variable depth in the longitudinal direction of the cathode block reaches such a uniform current density distribution on the cathode block surface, that in the operation of the electrolytic cell comprising the cathode block, an excessive removal of cathode block material in those areas is effectively avoided, where using a cathode block with the same depth depth in the longitudinal direction of the cathode block a high local Current density would be present. By appropriate adjustment of the groove depth, the current density distribution can be widely modified and evened out. Overall, a control of - due to the different coefficients of thermal expansion of cast iron, busbar and cathode block occurring - tensile stresses, shear stresses and compressive stresses is thus achieved even with large or strong temperature changes, which excellent electrical conductivity and excellent mechanical stability of the cathode block also in the groove used and cast iron sheathed busbar guaranteed.

In order to achieve a particularly uniform vertical current density distribution at the cathode block surface in the electrolysis operation, it is proposed in a development of the invention that at least one of the at least one groove and preferably all of the grooves with varying depth have or have a smaller depth at their longitudinal ends than in FIG their middle (s). In this way a uniform distribution of the electric current supplied in the electrolysis operation is achieved over the entire length of the cathode block, whereby an excessive electric current density at the longitudinal ends of the cathode block and thus premature wear at the ends of the cathode block is avoided. As a result of such a uniform current density distribution over the length of the cathode block, movements in the aluminum melt caused by the interaction of electromagnetic fields during electrolysis are also avoided, making it possible to arrange the anode at a lesser height above the surface of the aluminum melt. This will increase the electrical resistance between the anode and the Reduces aluminum melt and increases the energy efficiency of the carried out melt electrolysis. A further particular advantage of this embodiment is that, in this embodiment, the bus bar (s), which is fixed by the at least one projection and may be covered with cast iron, during and after the increase in temperature in the horizontal direction occurring during the startup of the electrolysis cell As a result, the bus bar (s) are respectively pressed against the bottom wall of the cathode block groove (s) delimiting the groove at that point, thereby reducing the contact resistance between the cast iron covered bus bar (s) and the cathode block ,

In the above embodiment, the depth of at least one of the at least one groove of varying depth, seen in the longitudinal direction of the cathode block, preferably at least substantially monotonically increases from one longitudinal end to the center of the cathode block and takes it from the center to the other longitudinal side End of the cathode block at least substantially monotonically, so that, as seen in the longitudinal section of the cathode block, results in an at least substantially triangular groove. As a result, the above advantages are achieved to an increased extent.

According to a further preferred embodiment of the present invention, the wall bounding the at least one groove of varying depth comprises a bottom wall and two side walls, wherein at least one projection extending into the groove is provided on the bottom wall, which preferably extends vertically into the at least one groove extends into it. In this way, a particularly good fixation of the busbar in the groove can be achieved, while at the same time sufficiently high mobility of the busbar in the horizontal direction to reliably occur even with large temperature changes, the occurrence of shear stresses due to the different thermal expansion coefficients of cast iron, busbar and cathode block avoid.

According to a further preferred embodiment of the present invention, the at least one projection in the embodiment described above on its side opposite the bottom wall at least one support surface for at least one bus bar, which at least partially at least substantially parallel, preferably parallel, to the surface of the groove opposite side of the cathode block, ie perpendicular to the lower end of the side walls of the wall of the groove bounding the cathode block. Such a bearing surface is particularly well suited to rest a busbar or to support two busbars.

Good results are obtained in this regard, in particular, if at least one of the at least one support surface of the at least one projection is designed to be planar, preferably at least substantially rectangular and parallel, particularly preferably rectangular and parallel to the surface of the opposite side of the cathode block.

In order to achieve a sufficiently large bearing surface, in particular for two adjoining end pieces of two busbars, it is proposed in development of the invention that the bottom wall opposite side of the at least one projection is bounded by a support surface, which is completely planar, preferably at least substantially rectangular and parallel, more preferably rectangular and parallel, to the surface of the opposite side of the groove of the cathode block is designed to extend. In this embodiment, therefore, all of the bottom wall of the cathode block opposite surface of the projection is formed as a support surface for one or two end pieces of one or two busbar (s).

The above embodiment can be realized, for example, by the at least one projection, in the longitudinal extension of the cathode block seen cut, over its entire height at least substantially rectangular or trapezoidal, preferably rectangular or trapezoidal, is configured, wherein the bottom wall opposite side of the at least one projection is bounded by a support surface which planar, at least substantially rectangular and parallel, preferably rectangular and parallel, to the surface of the groove opposite side of the cathode block is designed to extend.

Preferably, the extension of the rectangular support surface extending in the longitudinal extent of the cathode block is 20 to 600 mm, particularly preferably 50 to 400 mm, very particularly preferably 100 to 300 mm and most preferably 150 to 250 mm, such as 200 mm, whereas the extending in the width extension of the cathode block, expansion of the rectangular support surface is preferably at least 50%, more preferably at least 80%, more preferably at least 90% and most preferably 100% of the width of the groove measured in the plane of the rectangular support surface.

According to an alternative and particularly preferred embodiment of the present invention, the bottom wall opposite side of the at least one projection is delimited by a surface comprising two outer portions and a middle portion disposed therebetween in the longitudinal direction of the cathode block. wherein the two outer portions each form a support surface for a busbar and each planar, preferably at least substantially rectangular and parallel, more preferably rectangular and parallel, are designed to extend to the surface of the opposite side of the groove of the cathode block and, based on the depth the groove, are at the same height, whereas the middle portion opposite to the two outer portions, as seen from the bottom wall, is formed in the groove raised. This embodiment is particularly preferred for cathode blocks, which are designed to receive two each, based on the length of the cathode block, busbars, approximately half the length. This is because by the elevation provided in the central portion of the protrusion, the two adjacent outer portions of the protrusion forming the abutment surface for each one end of a bus bar are separated from each other by a partition wall extending in the depth direction of the groove, so that the end pieces of FIG two busbars bear against opposite sides of the partition wall, whereby the two busbars are fixed not only in the vertical direction, but also at these two end pieces in the horizontal direction. This ensures that the two busbars in the case of an expansion due to a temperature increase in a defined direction, namely in the direction of the cathode end block, expand. As a result, the two conductors possibly sheathed with cast iron during and after the increase in the temperature occurring in the horizontal direction due to the expansion in the direction of the cathode block end are pressed against the bottom wall of the cathode block delimiting the groove at this point Transition resistance between the cast iron sheathed busbar and the cathode block is reduced.

In order to achieve the above-described advantages to a particularly great extent, it is preferred that the central portion of the projection, as seen in the longitudinal direction of the cathode block cut, rectangular - ie in the form of a rectangular nose - is designed so that between the two outer Sections and the middle section in each case a step is formed. This step may be at right angles or rounded at the transition region from the support surface to the elevation.

Good results are obtained in particular if the height of the steps is 10 to 100 mm, preferably 40 to 80 mm and particularly preferably 50 to 70 mm, whereas the extent of the steps extending in the widthwise extent of the cathode block is preferably at least 50%, more preferably at least 80%, more preferably at least 90% and most preferably 100% of the width of the groove.

The above embodiment can for example be realized by the at least one projection, seen in the longitudinal extension of the cathode block cut, over 20% to 80% and preferably over 30 to 50% of its height at least substantially rectangular or trapezoidal, preferably rectangular or trapezoidal configured is, wherein on the bottom wall opposite side of this portion of the projection is provided in the longitudinal extent of the cathode block centrally arranged elevation or nose, which extends over the remaining height of the projection.

According to a further preferred embodiment of the present invention, it is provided that the at least one projection, with respect to the longitudinal extension of the cathode block, is arranged at the point at which the groove has the highest depth, wherein the projection itself is disregarded here. As particularly preferred as set forth above, the groove of varying depth has a smaller depth at its longitudinal ends than at its center, and more particularly the depth of the groove seen in the longitudinal direction of the cathode block from a longitudinal end to the center of the cathode block Cathode block at least substantially continuously increases and these at least substantially monotonically decreases from the center to the other longitudinal end of the cathode block, the at least one projection is therefore preferably, based on the longitudinal extent of the cathode block, arranged centrally.

Furthermore, it has proved to be advantageous that the at least one projection over at least 50%, preferably over at least 80%, more preferably over at least 90% and most preferably over the entire Width of the groove extends. This on the one hand achieves sufficient mechanical stability of the projection and, on the other hand, ensures that the busbar (s) with its end piece (s) rest over at least a major part or their entire width on the support surface (s) formed by the projection ,

In principle, the at least one projection may be composed of any material, such as metal. However, it is preferred that the at least one projection is composed of a material which has the same coefficient of thermal expansion as the material of the remaining cathode block. Particularly preferably, the at least one projection consists of the same material as the remaining part of the cathode block.

According to the invention, the cathode block is composed on the basis of carbon and / or graphite. Good results in terms of a sufficiently high electrical conductivity and a sufficiently high wear resistance are obtained in particular when the at least one projection and the remaining part of the cathode block are composed of amorphous, graphitic and / or graphitized carbon.

In a further development of the inventive concept, it is proposed that the at least one projection and the remainder of the cathode block are monolithic, i. in one piece, are. As a result, a particularly high mechanical stability of the connection of the projection to the remaining part of the cathode block is achieved.

Alternatively, the at least one projection on the bottom wall of the cathode block may also be connected to a connection means. This can for example be achieved by the at least one projection on an adhesive such as resin, cement, tar or similar substances or any mixture of the above substances, to the remaining part of the cathode block is glued or mechanically connected with a fastening means with the remaining part of the cathode block.

In addition, the present invention relates to a cathode assembly, which contains at least one cathode block described above, wherein at least one of the at least one groove with varying depth of the at least one cathode block is provided at least one bus bar, which preferably at least partially has a sheath made of cast iron, which if necessary ., Covered with cast iron busbar rests at least on a portion of the at least one projection.

Preferably, the cathode assembly comprises at least one cathode block, wherein in at least one of the at least one groove of varying depth of the at least one cathode block two preferably at least partially a sheath of cast iron having busbars are provided, each with one of its end pieces at least on a portion of the at least one projection rest.

According to a further preferred embodiment of the present invention, the at least one busbar is at least partially and particularly preferably completely encased in cast iron.

Furthermore, the present invention relates to the use of a previously described cathode block or a previously described cathode arrangement for carrying out a fused-salt electrolysis for the production of metal, preferably for the production of aluminum.

Hereinafter, the present invention will be described purely by way of example with reference to advantageous embodiments and with reference to the accompanying drawings.

Fig. 1

einen Querschnitt eines Ausschnitts einer Aluminium-Elektrolysezelle mit einer Kathodenanordnung gemäß eines ersten nicht erfindungsgemäßen Ausführungsbeispiels der vorliegenden Erfindung,

Fig. 2

einen Längsschnitt der Kathodenanordnung der in der Fig. 1 gezeigten Aluminium-Elektrolysezelle,

Fig. 3

einen Längsschnitt eines Ausschnitts einer Aluminium-Elektrolysezelle mit einer Kathodenanordnung gemäß eines zweiten nicht erfindungsgemäßen Ausführungsbeispiels der vorliegenden Erfindung,

Fig. 4

einen Querschnitt der Kathodenanordnung der in der Fig. 3 gezeigten Aluminium-Elektrolysezelle,

Fig. 5a-d

beispielhafte Querschnitte von Vertiefungen, die in einer Nut eines nicht erfindungsgemäßen Kathodenblocks vorgesehen sind,

Fig. 6

einen Längsschnitt eines Kathodenblocks gemäß eines ersten Ausführungsbeispiels der vorliegenden Erfindung und

Fig. 2

einen Längsschnitt eines Kathodenblocks gemäß eines zweiten Ausführungsbeispiels der vorliegenden Erfindung.

Showing:

Fig. 1

a cross section of a section of an aluminum electrolysis cell with a cathode assembly according to a first non-inventive embodiment of the present invention,

Fig. 2

a longitudinal section of the cathode assembly in the Fig. 1 shown aluminum electrolytic cell,

Fig. 3

a longitudinal section of a section of an aluminum electrolysis cell with a cathode assembly according to a second non-inventive embodiment of the present invention,

Fig. 4

a cross section of the cathode assembly of the in Fig. 3 shown aluminum electrolytic cell,

Fig. 5a-d

exemplary cross sections of depressions, which are provided in a groove of a non-inventive cathode block,

Fig. 6

a longitudinal section of a cathode block according to a first embodiment of the present invention and

Fig. 2

a longitudinal section of a cathode block according to a second embodiment of the present invention.

In the Fig. 1 a section of an aluminum electrolysis cell 10 with a cathode assembly 12 is shown in cross-section, which at the same time the bottom of a trough for an aluminum melt 14 produced during operation of the electrolytic cell 10 and for above the molten aluminum 14 located cryolite-alumina melt 16 forms. With the cryolite-alumina melt 16 is an anode 18 in contact. Laterally formed by the lower part of the aluminum electrolysis cell 10 trough by a in the Fig. 1 not shown lining of carbon and / or graphite limited.

The cathode arrangement 12 comprises a plurality of cathode blocks 20, which are each connected to one another via a ramming mass 24 inserted into a ramming mass gap 22 arranged between the cathode blocks 20. A cathode block 20 in this case comprises two grooves 26 arranged on its underside and having a rectangular, namely substantially rectangular cross section, wherein in each groove 26 in each case a bus bar 28 made of steel with likewise rectangular cross section is accommodated.

The grooves 26 are each bounded by two side walls 32 and a bottom wall 34 of the cathode block 20, wherein in each of the side walls 32 is provided a substantially perpendicular in the side wall 32 extending recess 36 having an approximately semicircular cross-section. Each recess 36 is bounded by an upper and a lower transition region 37 of the cathode block 20, respectively. The transition regions 37 are formed in the present non-inventive embodiment angularly at an angle α between the adjacent portion of the groove wall and the wall of the recess of 90 degrees. The space between the busbar 28 and the groove 26 is in each case cast with cast iron 38. In this case, the cast iron 38 forms an enclosure 39 for the busbar 28 and is connected to the busbar 28 in a material-locking connection.

In addition, the received in the wells 36 cast iron 38 forms with the recess 36 delimiting material of the cathode block 20 each have a positive connection, which prevents movement of the connected to the cast iron 38 busbar 28 in the direction of the arrow 40.

In the Fig. 1 In particular, the cross section of the cathode assembly 12 is shown at a longitudinal end of the cathode block 20. The depth of the groove 26 of the cathode block 20 varies over the length of the groove 26. The groove cross-section in the region of - relative to the longitudinal direction of the cathode block - the middle of the groove 26 is in the Fig. 1 indicated by a dashed line 42. The difference between the groove depth at the longitudinal ends of the groove 26 and in the - with respect to the longitudinal direction of the cathode block - the middle of the groove 26 in the present embodiment is about 5 cm. The depth of the groove 26 at the two longitudinal ends of the groove 26 is about 16 cm, whereas the depth of the groove 26 in the - relative to the longitudinal direction of the cathode block - center of the groove 26 is about 21 cm. The width 44 of each groove 26 is substantially constant over the entire groove length and is about 15 cm, whereas the width 46 of the cathode blocks 20 is about 42 cm each.

In the present non-inventive embodiment, a plurality of anodes 18 and a plurality of cathode blocks 20 are arranged one above the other so that each anode 18 in width covers two juxtaposed cathode blocks 20 and covers in length half of a cathode block 20, wherein each two juxtaposed anodes 18 the Cover length of a cathode block 20.

The Fig. 2 shows the in the Fig. 1 shown cathode block 20 in longitudinal section. Like from the Fig. 2 As can be seen, the groove 26 viewed in its longitudinal section extends toward the center of the cathode block 20 in the shape of a triangle, thereby ensuring a substantially uniform electrical vertical current density over the entire cathode length. The recess 36 extends as in the Fig. 2 indicated by the corresponding marked line parallel to the horizontal direction, ie parallel to the surface of the groove 26 opposite side of the cathode block 20. The in the Fig. 2 the sake of clarity, not shown bus bar 28 is in the present Embodiment bar-shaped and has a rectangular longitudinal section, so that between the busbar and the groove bottom 34 to the middle of the groove 26 toward becoming larger gap which can be filled either by cast iron 38 or by additional connected to the busbar 28 metal plates.

The in the Fig. 3 and 4 in longitudinal section and cross-section shown cathode assembly and cathode block according to a second non-inventive embodiment of the present invention differs from that in the Fig. 1 and 2 shown in that in the cathode block 20, only one groove 26 is provided, which has two recesses 36,36 '.

Furthermore, the show Fig. 5a to d exemplary depressions 36 which are provided in a groove 26 of a cathode block 20 according to the invention, in cross section. The recesses 36 each have a substantially semicircular cross-section ( Fig. 5a ), a substantially trapezoidal cross section ( Fig. 5b ) or a substantially triangular cross section ( Fig. 5c ) on. The angle α of the transition regions 37 between the wall of the recess 36 and the adjacent portion of the groove wall 32, viewed from the inside of the cathode block 20, is in Fig. 5a about 90 degrees, in the Fig. 5b about 120 degrees and in the Fig. 5c about 125 degrees. The Fig. 5d shows an embodiment in which several as in the Fig. 5c shown depressions 36 are arranged with triangular cross-section in the depth direction of the groove 26 consecutively to effect a particularly reliable support of a bus bar 28 used. The transition regions 48 between two adjoining depressions 36 have an angle β of approximately 70 degrees between the walls of two adjoining depressions 36, viewed from the inside of the cathode block 20. The in the Fig. 5a to d Wells 36 shown in each case extend perpendicularly into the groove 26 delimiting side wall 32 of the cathode block 20 so that they are received in the wells 36 a cast iron Forming fix, which is effective in the depth direction of the groove 26 and prevents unwanted movement of the bus bar 28 parallel to the depth direction of the groove 26 after the pouring of the bus bar 28 with cast iron 38, but a horizontal movement of the cast iron sheathed busbar - for example, due to an expansion the busbar encased in cast iron due to a large temperature change - allows.

Under a horizontally extending in the longitudinal direction of the cathode block recess is understood in the present invention that the recess extends parallel to the longitudinal plane of the cathode block. A parallel extension is understood to mean that the depression at each of its points has an angle of less than 8 °, preferably less than 5 °, particularly preferably less than 2 °, very particularly preferably less than 1 °, most preferably of less than 0.5 °, and most preferably less than 0.1 ° to the longitudinal plane of the cathode block. In this context, the longitudinal plane is understood to mean the plane which extends in the direction of the longitudinal axis of the cathode block and runs parallel to the surface of the side of the cathode block opposite the groove.

In addition, in the context of the present invention, a depression, in contrast to a mere surface roughness, is understood to be a recess which has a depth of at least 0.5 mm, and preferably of at least 2 mm, relative to the surface of the wall delimiting the groove.

By providing at least one recess extending horizontally in the longitudinal direction of the cathode block in the wall delimiting the groove of the cathode block, preferably in both of the side walls, in particular also in forming the groove of varying depth in the cathode block, a cathode block is also provided with inserted into the groove and cast iron busbar a low electrical resistance and low contact resistance. Apart from this, due to the provision of the longitudinally extending in the longitudinal direction of the cathode block recess in the groove bounding the cathode block wall even with large temperature changes, mechanical damage to the cathode block with inserted into the groove and cast iron busbar, such as cracking of the cathode block , reliably avoided. Firstly, the use of a variable depth groove in the longitudinal direction of the cathode block achieves such a uniform current density distribution on the cathode block surface that the operation of the electrolysis cell comprising the cathode block effectively avoids excessive erosion of cathode block material in those areas where, in use Cathode blocks with in the longitudinal direction of the cathode block groove depth same high local current density would be present. By appropriate adjustment of the groove depth, the current density distribution can be widely modified and evened out. By having in its groove a recess extending horizontally in the longitudinal direction of the cathode block, the cathode block achieves a vertical fixation of the cast iron covered bus bar in the groove of the cathode block, but allowing some movement in the horizontal direction of the cathode block. Because of this horizontal mobility of the busbar sheathed busbar, the occurrence of shear stresses between the busbar sheathed busbar and the cathode block is reliably avoided, especially in the rapid and temperature changes occurring during and after startup of a cathode cell comprising the electrolysis cell at an obliquely located depression due to the higher expansion or shrinkage of the cast iron and the bus bar relative to the cathode block, due to the higher coefficients of thermal expansion of cast iron and the material of the bus bars as compared to the coefficient of thermal expansion of the material of the cathode block. This will damage the cathode block For example, in the form of cracking or even a breakage of the cathode block reliably prevented even during long periods of operation of the electrolysis cell, while ensuring excellent electrical conductivity between the busbar and the cast iron and the cathode block. Due to the vertical fixation of the cast iron sheathed busbar in the groove of the cathode block, there is an advantageous contact pressure of the cathode bar / cast iron assembly against the groove bottom by the thermal expansion of the ingot / cast iron assembly relative to the cathode block during commissioning. Thus, an improved electrical contact is achieved, which leads to a lower electrical resistance and thus to a higher energy efficiency. In addition to the advantage of the WO 2012/107412 A2 known cathode block, these excellent properties are achieved in particular even if the groove of the cathode block is not lined with an expensive and costly to be introduced graphite foil. Overall, a control of - due to the different thermal expansion coefficients of cast iron, busbar and cathode block occurring - tensile stresses, shear stresses and compressive stresses is thus achieved, which excellent electrical conductivity and excellent mechanical stability of the cathode block also inserted into the groove and with Cast iron sheathed busbar guaranteed.

In the Fig. 6 is a cathode block 20 according to a first embodiment of the present invention shown in longitudinal section, in contrast to those in the Fig. 1 to 4 shown upside down, based on the later installation in the electrolysis cell to illustrate the arrangement during the pouring with liquid cast iron. This cathode block 20 differs from that in the Fig. 1 to 4 illustrated in that it has no recess in the groove 26 delimiting wall. Instead, this cathode block 20 has in its groove 26 a projection 50, which is arranged centrally with respect to the longitudinal direction of the cathode block 20 and, in the Seen longitudinally of the cathode block cut, designed trapezoidal. Here, the bottom wall 34 of the cathode block 20 opposite side of the protrusion 50 limiting surface is planar, rectangular and parallel to the surface of the groove opposite side of the cathode block designed to extend and thereby forms a support surface for the end pieces of two bus bars 28. Of course, or can also at least one or both of the groove 26 delimiting side walls of the cathode block 20 each have a recess, as in the Fig. 1 and 2 represented, or two depressions, as in the Fig. 3 and 4 represented, be provided.

Moreover, in the Fig. 7 a cathode block 20 according to a second embodiment of the present invention shown in longitudinal section, again in contrast to that in the Fig. 1 to 4 shown upside down. This cathode block 20 differs from that in the Fig. 6 represented by the fact that the hatched here shown projection 50 is not cut in the longitudinal direction of the cathode block, designed trapezoidal, but is rectangular in its lower part, wherein on the bottom wall 34 of the cathode block 20 opposite side of this part of the projection 50 a seen in the longitudinal extent of the cathode block 20 centrally arranged nose 54 is provided, which extends over the remaining height of the projection 50. In other words, the side of the at least one protrusion 50 opposite the bottom wall 34 is delimited by a surface which comprises two outer sections 52, 52 ', viewed in the longitudinal direction of the cathode block, and an intermediate section 54 arranged therebetween, the two outer sections 52, 52 'each form a support surface for a busbar 28 and are planar, rectangular and parallel to the surface of the groove 26 opposite side of the cathode block 20 designed to extend and, based on the depth of the groove 26, are at the same height, whereas, the middle portion 54 faces the groove 26 opposite the two outer portions 52, 52 'as seen from the bottom wall 34 is formed sublime in it. In this case, the central portion 54, as seen in the longitudinal direction of the cathode block 20 cut, is designed rectangular, so that between the two outer portions 52,52 'and the central portion 54 each have a step is formed. Of course, at least one or both of the groove 26 delimiting side walls of the cathode block 20 may each have a recess, as in the Fig. 1 and 2 represented, or two depressions, as in the Fig. 3 and 4 represented, be provided.

LIST OF REFERENCE NUMBERS

10

Aluminum electrolysis cell

12, 12 '

cathode assembly

14

aluminum smelter

16

Cryolite-alumina melt

18

anode

20

cathode block

22

Stampfmassenfuge

24

ramming mix

26

groove

28

conductor rail

32

Side wall

34

bottom wall

36, 36 '

deepening

37

Transition region between the wall of the recess and the adjacent portion of the groove wall

38

cast iron

39

wrapping

40

arrow

42

dashed line

44

Width of the groove 26

46

Width of the cathode block 20

48

Transition area between two adjoining depressions

50

head Start

52, 52 '

outer portion of the projection

54

middle section of the protrusion / nose

Claims (9)

Cathode block (20) for an aluminum electrolytic cell based on carbon and / or graphite, the at least one in the longitudinal direction of the cathode block (20) extending groove (26) for receiving at least one bus bar (28), wherein at least one of at least a groove (26) having a varying depth across the length of the cathode block (20), said groove (26) being bounded by a wall (32, 34), at least one of which being in the wall (32, 34) Groove (26) extending into projection (50) is provided. Cathode block (20) according to claim 1,
characterized in that
the wall (32, 34) comprises a bottom wall (34) and two side walls (32), at least one projection (50) extending into the groove (26) being provided on the bottom wall (34) and preferably extending vertically inwards the at least one groove (26) extends into it. Cathode block (20) according to claim 1 or 2,
characterized in that
the at least one projection (50) has on its side opposite the bottom wall (34) at least one bearing surface for at least one bus bar (28) which is at least partially substantially parallel to the surface of the side opposite the groove (26) of the cathode block (20). runs. Cathode block (20) according to claim 3,
characterized in that
the side of the at least one projection (50) opposite the bottom wall (34) is delimited by a surface which comprises two outer sections (52, 52 ') viewed in the longitudinal direction of the cathode block and a central section (54) arranged therebetween, wherein the two outer portions (52, 52 ') each form a bearing surface for a busbar (28) and each planar, at least substantially rectangular and parallel to the surface of the groove (26) opposite side of the cathode block (20) are designed to extend and, based on the depth of the groove (26), are at the same height, whereas the central portion (54) opposite the two outer portions (52, 52 '), as viewed from the bottom wall (34), is in the groove (Fig. 26) is formed raised in it. Cathode block (20) according to claim 4,
characterized in that
the central portion (54), as seen in the longitudinal direction of the cathode block (20) cut, is rectangular, so that between the two outer portions (52, 52 ') and the central portion (54) each formed a step. Cathode block (20) according to claim 4,
characterized in that
the at least one projection (50), with respect to the longitudinal extent of the cathode block (20), is arranged at the point at which the groove (26) has the highest depth. Cathode block (20) according to claim 6,
characterized in that
the at least one projection (50) is composed of the same material as the remaining part of the cathode block (20). A cathode assembly (12) comprising at least one cathode block (20) according to at least one of claims 1 to 7, wherein at least one of said at least one groove (26) of varying depth of said at least one cathode block (20) comprises at least one bus bar (28). wherein the bus bar (28) rests on at least a portion of the at least one projection (50). Use of a cathode block (20) according to at least one of claims 1 to 7 or a cathode arrangement (12) according to claim 8 for carrying out a fused-salt electrolysis for the production of metal, preferably for the production of aluminum.

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