EP2989235B1 - Cathode block having a slot with varying depth and a securing system - Google Patents

Description

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

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 decrease 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. DE 2 405 461 and EP 0 052 577 describe a cathode block based on carbon having a groove in whose side walls in each case a recess is present.

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 in the length of the cathode block, varying depth, wherein in the at least one groove of varying depth bounding wall of the cathode block at least one recess having a semicircular, triangular, rectangular or trapezoidal cross section is provided, which in the longitudinal direction of the cathode block at least extends horizontally over approximately the entire length of the at least one groove.

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 has an angle of less than 5 °, particularly preferably less than 2 °, very particularly preferably less than 1 °, most preferably less than 0.5 °, at each of its points. 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.

According to the invention it has been recognized that 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 created, which also has inserted into the groove and sheathed with cast iron power rail has 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 the cathode block has in its groove a horizontally extending in the longitudinal direction of the cathode block recess, a vertical fixation of the cast iron sheathed busbar is achieved in the groove of the cathode block, but which some movement in the horizontal direction of the Cathode blocks allowed. 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. As a result, damage to the cathode block, for example in the form of crack formation or even breakage of the cathode block, is reliably prevented even during a long service life of the electrolysis cell, while ensuring excellent electrical conductivity between the busbar or 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 even with large changes in temperature, which excellent electrical conductivity and excellent mechanical Stability of the cathode block also ensured with inserted into the groove and sheathed with cast iron busbar.

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 reduces the electrical resistance between the anode and the aluminum melt and increases the energy efficiency of the fused-salt electrolysis carried out. Another particular advantage of this embodiment is that in this embodiment of the groove provided in the recess of the groove possibly sheathed with cast iron busbar (s) during and after the occurring during commissioning of the electrolytic cell increasing the temperature in the horizontal direction expands As a result, the bus bar (s) are respectively pressed against the bottom wall of the cathode block delimiting the groove at this point, whereby the contact resistance between the busbar-covered bus bar and the cathode block is reduced.

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 another 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, each of the two side walls each having at least one recess extending horizontally in the longitudinal direction of the cathode block. In this way, a particularly good vertical fixation of the busbar is achieved in the groove, at the same time sufficiently high mobility of the busbar in the horizontal direction to reliably avoid the occurrence of shearing stresses due to the different thermal expansion coefficients of cast iron, busbar and cathode block, even with large temperature changes.

Preferably, the wall bounding the at least one groove of varying depth comprises a bottom wall and two side walls, each side wall each having exactly one recess extending horizontally in the longitudinal direction of the cathode block. In this way, a particularly good vertical fixation of the busbar in the groove is achieved at a comparatively low production cost, at the same time sufficiently high mobility in the horizontal direction to reliably avoid the occurrence of shear stresses due to the different thermal expansion coefficients of cast iron, busbar and cathode block at large temperature changes ,

Likewise, it is preferable that the wall bounding the at least one groove of varying depth comprises a bottom wall and two side walls, each side wall each having two recesses each extending horizontally in the longitudinal direction of the cathode block. In this way, a particularly good vertical fixation of the busbar in the groove at the same time sufficiently high mobility in the horizontal direction is also achieved when the depth of the individual wells is comparatively low.

In this case, the cathode block may have two grooves arranged on the same side of the cathode block, wherein both grooves have the same dimensions and the limiting walls each comprise a bottom wall and two side walls, each side wall each having a recess which extends horizontally in the longitudinal direction of the cathode block, or wherein each side wall each has two recesses extending horizontally in the longitudinal direction of the cathode block. Thus, for a two-slot cathode block with comparatively low production costs, a particularly good vertical fixation of the two busbars in the grooves achieved at the same time sufficiently high mobility in the horizontal direction to large temperature changes, the occurrence of shear stresses due to the different thermal expansion coefficients of cast iron, busbar and To reliably prevent cathode block.

As an alternative to the above embodiment, the cathode block may also comprise only one groove.

In order to ensure a particularly good fixation of possibly cast iron sheathed busbar in the groove in the vertical direction while sufficient mobility in the horizontal direction, it may be that at least one of the at least one recess and more preferably each of the at least one recess continuously over at least 60%, preferably over at least 80%, more preferably over at least 90%, most preferably over at least 95% of the length of the at least one groove, which is not part of the invention. According to the invention, the at least one recess extends at least approximately over the entire length of the at least one groove.

For the same reason, it is preferable that at least one of the at least one recess and more preferably each of the at least one recess has a depth of 0.5 mm to 40 mm, preferably 2 mm to 30 mm, and more preferably 5 mm to 20 mm having.

For the same reason, it is also preferred that at least one of the at least one depression, and more preferably each of the at least one depression, has an opening width of 2 mm to 40 mm, preferably 5 mm to 30 mm and more preferably of the cathode block 10 mm to 20 mm.

In principle, the at least one recess can have any polygonal or curved cross section. Good results with regard to a good engagement of the cast iron casing in the at least one depression and at the same time with regard to a reliable and unproblematic fillability of the recess with cast iron during casting are achieved in particular if at least one of the at least one depression and particularly preferably each of the at least one depression an at least substantially semicircular, triangular, has rectangular or trapezoidal, preferably semi-circular, triangular, rectangular or trapezoidal, cross-section.

According to a further preferred embodiment of the present invention, the at least one recess extends at least substantially perpendicularly, preferably perpendicularly, into the wall of the cathode block bounding the at least one groove.

According to the present invention, the at least one depression, viewed in the depth direction of the groove, is delimited at each of its ends by a transitional area between the depression and an adjoining portion of the groove wall. When this transition region is angled, the angle between the adjacent portion of the groove wall and the wall of the depression, viewed from the cathode block inner side, is preferably 90 degrees to 160 degrees, more preferably 90 degrees to 135 degrees, and most preferably 100 degrees to 120 Degree.

In the event that this transition region is curved, possibly but not necessarily ideally circularly curved, the radius of curvature of the transition region is preferably at most 50 mm, more preferably at most 20 mm and most preferably at most 5 mm.

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 at least one bus bar is provided which at least partially has a cladding made of cast iron, which at least partially in which engages at least one depression.

According to a preferred embodiment of the present invention, the portion of the cast-iron casing engaging in the at least one recess is designed to be complementary to the recess. In this way, a particularly good positive engagement of the casing of cast iron in the recess and thus a particularly effective mechanical attachment of the cast iron casing and the associated bus bar to the cathode block can be achieved, which nevertheless due to avoid shear stress between cast iron, busbar and cathode block of large temperature changes sufficient mobility of the busbar in the horizontal direction allows.

Preferably, the cast iron shell engages over at least 50%, more preferably at least 80%, more preferably at least 90%, most preferably at least 95%, and most preferably at least substantially all of its length into the at least one recess. As a result, the advantages described above are achieved to a particularly high degree.

For the same reason, according to a further preferred embodiment of the present invention, it is provided that the portion of the envelope engaging in the at least one recess and possibly the conductor rail covered therewith at least 70%, preferably at least 80%, particularly preferably at least 90%, completely more preferably at least 95% and most preferably 100% of the well fills. Thereby, an unwanted displacement of the busbar in the vertical direction of the cathode block and in particular falling out of the busbar from the groove can be particularly reliably avoided.

In a further development of the inventive concept, it is proposed that the cathode block of the cathode arrangement has a groove with an at least substantially rectangular, preferably a rectangular, cross-section and in the groove one or two adjacent busbar (s) are used, wherein the gap between the groove and the busbar (s) is filled with cast iron so that the cast iron on at least substantially the same entire length engages the at least one recess.

A further subject of the present invention is a cathode, which comprises at least one previously described cathode block or at least one previously described cathode arrangement.

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

Another object of the present invention is a cathode assembly comprising at least one previously described cathode block.

Furthermore, the present invention relates to the use of a previously described cathode block, a previously described cathode assembly 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 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 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 erfindungsgemäßen Kathodenblocks vorgesehen sind,

Showing:

Fig. 1

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

Fig. 2

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

Fig. 3

1 is a longitudinal section of a section of an aluminum electrolysis cell with a cathode arrangement according to a second 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 recesses provided in a groove of a cathode block according to the invention,

In the Fig. 1 is a cross section of a section of an aluminum electrolytic cell 10 is shown with a cathode assembly 12, which simultaneously forms 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. 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 case Groove 26 each a bus bar 28 made of steel is also included with rectangular cross-section.

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 areas 37 are formed in the present embodiment 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 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 embodiment, a plurality of anodes 18 and a plurality of cathode blocks 20 are arranged one above the other so that each anode 18 covers two juxtaposed cathode blocks 20 and covers in length half of a cathode block 20, wherein each two juxtaposed anodes 18 the length of a Cover 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 busbar 28 is bar-shaped in the present embodiment and has a rectangular longitudinal section, so that between the busbar and the groove bottom 34 to the middle of the groove 26 toward increasing interspace consists of either by cast iron 38 or through additional metal plates connected to the busbar 28 may be filled.

The in the Fig. 3 and 4 in longitudinal section and cross section shown cathode assembly and cathode block according to a second embodiment of the present invention differs from that in the Fig. 1 and 2 shown thereby, 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 recesses 36 have between the walls of two adjacent recesses 36, seen from the inside of the cathode block 20, an angle ß of about 70 degrees. The in the Fig. 5a to d shown depressions 36 each extend perpendicularly into the groove 26 delimiting side wall 32 of the cathode block 20 so that they form a recorded in the recesses 36 cast iron, which is effective in the depth direction of the groove 26 and an unwanted movement of the bus bar 28 parallel to prevents the depth direction of the groove 26 after pouring the bus bar 28 with cast iron 38, but a horizontal movement of the cast iron sheathed busbar - for example, due to an expansion of the cast iron sheathed busbar due to a large change in temperature - allows.

LIST OF REFERENCE NUMBERS

10

Aluminum electrolysis cell

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

α

Angle between the wall of the recess and the adjacent portion of the groove wall

ß

Angle between the walls of two adjoining depressions

Claims (7)

1. Cathode block (20) for an aluminium electrolytic cell based on carbon and/or graphite, wherein the cathode block (20) has at least one slot (26) extending in the longitudinal direction of the cathode block (20) for accommodating at least one busbar (28), wherein at least one of the at least one slot (26) has a varying depth when viewed along the length of the cathode block (20), wherein the at least one slot (26) of varying depth comprises a delimiting wall (32, 34) of the cathode block (20), wherein at least one recess (36, 36') having a semicircular, triangular, rectangular or trapezoidal cross section is provided in at least one side wall (32) and extends horizontally in the longitudinal direction of the cathode block (20), wherein horizontally means that the at least one recess (36, 36') has, at each of its points, an angle of less than 5° with respect to the plane of the cathode block (20) which extends in the direction of the longitudinal axis of the cathode block (20) at least approximately along the entire length of the at least one slot and is parallel to the surface of the side of the cathode block (20) opposite the slot.
2. Cathode block (20) according to claim 1, characterised in that at least one of the at least one slot (26) of varying depth has a shallower depth at its longitudinal ends than in its centre.
3. Cathode block (20) according to either claim 1 or claim 2, characterised in that the wall (32, 34) delimiting the at least one slot (26) of varying depth comprises a bottom wall (34) and two side walls (32), each side wall (32) having at least one recess (36, 36') which extends horizontally in the longitudinal direction of the cathode block (20).
4. Cathode block (20) according to claim 3, characterised in that at least one of the at least one recess (36, 36') has a depth of from 0.5 mm to 40 mm.
5. Cathode block (20) according to claim 4, characterised in that at least one of the at least one recess (36, 36') has an opening width of from 2 mm to 40 mm based on the height of the cathode block (20).
6. Cathode assembly (12) which contains at least one cathode block (20) according to at least one of claims 1 to 5, wherein at least one busbar (28) is provided in at least one of the at least one slot (26) of varying depth in the at least one cathode block (20), which busbar has, at least in regions, a coating (39) of cast iron (38) or ramming mix which engages, at least in portions, in the at least one recess (36, 36').
7. Use of a cathode block (20) according to at least one of claims 1 to 5 or of a cathode assembly (12) according to claim 6 for carrying out fused-salt electrolysis to produce metal, preferably to produce aluminium.

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