Cathode assembly

Abstract

Provided is a cathode assembly that suppresses CVD and enables stable operation of an electrolytic furnace. A cathode assembly 100 comprises: a carbon cathode block 10 provided with a groove 11; a collector bar unit 20 inserted into the groove 11; and a filler 31. The collector bar unit 20 includes collector bars 21 and 22, an upper plate 23, and conductive members 24 and 25. Each of the collector bars 21 and 22 and the upper plate 23 is composed of iron or an iron alloy, and the conductive members 24 and 25 are composed of copper or a copper alloy. The collector bars 21 and 22 are in contact with the corresponding side surface 11b of the groove 11, and the upper plate 23 is in contact with the bottom surface 11a of the groove 11 and the collector bars 21 and 22. The filler 31 is disposed in a space surrounded by the collector bars 21 and 22 and the upper plate 23.

Description

Cathode Assembly

[0001] The present invention relates to a cathode assembly.

[0002] Carbon cathode blocks are used as cathodes in electrolytic furnaces for aluminum smelting. The cathode blocks are installed in an iron box called a shell, which forms the bottom of the electrolytic furnace. The cathode blocks also play a role in supplying electrons to the electrolytic bath.

[0003] Electrons are supplied to the cathode block via a metal collector bar. Hereinafter, in this specification, the assembly of the cathode block and the collector bar connected thereto will be referred to as a "cathode assembly."

[0004] WO 2018 / 134754 discloses a cathode assembly including a cathode body made of a carbonaceous material and at least one cathode collector bar made of a metallic material. The cathode collector bar includes two bar elements. Each of the two bar elements has a major side surface that contacts a side surface of a slot in the cathode body and a tapered surface. The two tapered surfaces form a contact line between the two bar elements.

[0005] JP 2017-534770 A discloses a cathode current collector assembly assembled within a carbon cathode. The cathode current collector assembly includes a highly conductive metal current collector bar disposed below the carbon cathode. The current collector bar has a conductive flexible foil or sheet at its interface with the carbon cathode.

[0006] WO 2021 / 240353 discloses a cathode assembly comprising a cathode body made of a carbonaceous material with at least one slot and a collector bar system partially housed in the slot, the collector bar system comprising two individual bars and retention means attached to the individual bars to ensure that the outer surfaces of the collector bar system are in firm contact with the inner walls of the slot.

[0007] Chinese Patent Publication No. 116397276 discloses a copper cathode conductive rod assembly for an aluminum electrolysis furnace, which includes a cathode carbon block having a surface with longitudinal grooves and a cathode conductive rod disposed in the groove. The publication also describes that the conductive rod includes a protective cover for housing the (copper) rod body, and that sealing paste is disposed on both ends of the protective cover to prevent corrosion of the copper conductive rod.

[0008] International Publication No. WO 2018 / 134754 Special Publication No. 2017-534770 International Publication No. WO 2021 / 240353 Chinese Patent Application Publication No. 116397276 Specification International Publication No. WO 2023 / 119802

[0009] The cathode block and collector bar are typically connected by casting iron. Specifically, a groove is formed in the bottom surface of the cathode block, the collector bar is fitted into the groove, and molten iron heated to approximately 1250°C is poured into the gap. This method not only requires a large workload, but also requires energy costs for heating to melt the iron and preheating the cathode block and collector bar. Furthermore, because the cathode block oxidizes if the preheating temperature is too high, the preheating temperature can only be raised to 300-400°C, which poses a risk of the cathode block cracking due to heat shock when the molten iron is poured in.

[0010] The present inventors previously developed a cathode assembly to solve this problem and filed a patent application under PCT / JP2022 / 038136 (International Publication No. WO 2023 / 119802). This cathode assembly includes a cathode block having a groove and a collector bar unit inserted into the groove. The collector bar unit includes two collector bars arranged side by side in the width direction of the groove and a spacing adjustment member for adjusting the spacing between the two collector bars. With this configuration, the contact pressure between the collector bars and the cathode block can be adjusted by adjusting the spacing between the two collector bars using the spacing adjustment member. This reduces variations in contact resistance between the collector bars and the cathode block without the need to pour molten iron into the gap between the collector bars and the cathode block. WO 2023 / 119802 also discloses that the collector bar unit includes a conductive member made of a metal with higher conductivity than the collector bars and that a filler such as alumina cement is disposed between the two collector bars.

[0011] In recent years, in electrolytic furnaces for aluminum smelting, it has become common to use copper in part of the collector bars in order to improve the power consumption rate and current efficiency.However, with the cathode assemblies related to the above-mentioned prior development, the following problems have newly become apparent, especially when copper is used in part of the collector bars.

[0012] The first problem is that the components of the electrolytic bath may penetrate the cathode block and reach the vicinity of the collector bars, where they may react with the filler material placed between the two collector bars, weakening the filler material's strength. If the filler material's strength is weakened, it may not be able to maintain sufficient contact pressure between the collector bars and the cathode block, resulting in high contact resistance. This increase in contact resistance causes an increase in cathode voltage drop (CVD).

[0013] The second problem is that a phenomenon called cathode heaving, in which the central part of the cathode bulges upward due to a distortion in the thermal balance of the electrolytic furnace, can cause stress on the collector bar, distorting it and posing a risk of shearing the collector bar. It has been found that distortion of the collector bar due to cathode heaving occurs at a position approximately 100 mm outside the end of the cathode block.

[0014] As mentioned above, in recent years, it has become common to use copper partially in collector bars. However, it is known that copper undergoes an embrittlement phenomenon called intermediate temperature embrittlement in the temperature range of approximately 300°C to approximately 800°C, causing grain boundary cracking. When the bath temperature during operation of an electrolytic furnace is approximately 960°C, the temperature of the end of the cathode block is approximately 850°C, and the temperature of the shell of the electrolytic furnace is approximately 250°C. The temperature range between the end of the cathode block (approximately 850°C) and the shell (approximately 250°C) is one in which copper becomes significantly embrittled, making it prone to cracking.

[0015] Therefore, copper collector bars are very vulnerable to cathode heaving. Furthermore, if copper is used for only a portion of a collector bar, the remaining portion (the iron portion) also has a smaller cross-sectional area, which reduces the strength of the iron portion. If both the copper and iron portions shear, the current path is lost, resulting in unstable operation.

[0016] An object of the present invention is to provide a cathode assembly that can suppress CVD and ensure stable operation of an electrolytic furnace even when copper or a copper alloy is used for a part of the collector bar.

[0017] a conductive member having a shape extending in the same direction as the groove and disposed on top of the two collector bars; and a conductive member having a shape extending in the same direction as the groove and disposed so as to contact at least one of the two collector bars and the upper plate, wherein each of the two collector bars and the upper plate is made of iron or an iron alloy, and the conductive member is made of copper or a copper alloy. The two collector bars are in contact with corresponding side surfaces of the groove, and the upper plate is in contact with the bottom surface of the groove and the two collector bars. The filler is disposed in a space surrounded by the two collector bars and the upper plate.

[0018] According to the present invention, a cathode assembly is obtained that can suppress CVD and ensure stable operation of an electrolytic furnace.

[0019] FIG. 1 is a cross-sectional view schematically illustrating the overall configuration of an example of an electrolytic furnace for aluminum smelting. FIG. 2 is a perspective view schematically illustrating the configuration of a cathode assembly according to an embodiment of the present invention. FIG. 3 is a cross-sectional view (yz cross-sectional view) of the cathode assembly of FIG. 2 taken along line III-III in FIG. 2. FIG. 4 is an enlarged cross-sectional view showing the vicinity of one collector bar unit (region A in FIG. 3). FIG. 5 is a cross-sectional view (xy cross-sectional view) of the cathode assembly of FIG. 2 taken along line V-V in FIG. 4. FIG. 6 is a diagram schematically illustrating one configuration of a specific example of a gap adjustment member. FIG. 7 is a diagram schematically illustrating another configuration of a specific example of a gap adjustment member. FIG. 8 is a schematic diagram for explaining cathode heaving. FIG. 9 is a cross-sectional view showing one configuration of a modified collector bar unit. FIG. 10 is a cross-sectional view showing another configuration of a modified collector bar unit. FIG. 11 is a cross-sectional view showing yet another configuration of a modified collector bar unit.

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0021] [Overall Configuration] FIG. 1 is a cross-sectional view that schematically shows the overall configuration of an electrolytic furnace 1, which is an example of an electrolytic furnace for aluminum smelting.

[0022] The electrolytic furnace 1 includes a cathode assembly 100 according to one embodiment of the present invention. A plurality of cathode assemblies 100 are arranged side by side in the depth direction (y direction) of FIG. 1 . Each cathode assembly 100 includes a carbon cathode block 10 and a collector bar unit 20. The cathode block 10 forms the bottom of the electrolytic furnace 1. The collector bar unit 20, the detailed configuration of which will be described later, includes a metal collector bar that is electrically connected to the cathode block 10. An end of the collector bar unit 20 extends outside the electrolytic furnace 1.

[0023] The electrolytic furnace 1 includes an anode 91, a shell 92, a lining 93, etc. in addition to the cathode assembly 100. An electrolytic bath 94 containing aluminum oxide is contained inside the electrolytic furnace 1. The collector bar unit 20 and the anode 91 are electrically connected to a power supply (not shown). A voltage is applied between the cathode block 10 and the anode 91 by the power supply. This reduces the aluminum oxide in the electrolytic bath 94, producing aluminum 95.

[0024] [Configuration of Cathode Assembly 100] The configuration of the cathode assembly 100 will be described with reference to Figures 2 to 5. Figure 2 is a perspective view schematically illustrating the configuration of the cathode assembly 100. Figure 3 is a cross-sectional view (yz cross-sectional view) of the cathode assembly 100 taken along line III-III in Figure 2. Figure 4 is an enlarged cross-sectional view showing the vicinity of one collector bar unit 20 (region A in Figure 3). Figure 5 is a cross-sectional view (xy cross-sectional view) of the cathode assembly 100 taken along line V-V in Figure 4.

[0025] As described above, the cathode assembly 100 includes the cathode block 10 and the collector bar unit 20. The cathode assembly 100 further includes a filler 31 and a spacer 32 (FIGS. 4 and 5). The collector bar unit 20 is disposed in a groove 11 provided in the cathode block 10.

[0026] 2 and other figures show a so-called "double slot type" cathode assembly in which two grooves 11 are provided in the cathode block 10 and a collector bar unit 20 is disposed in each of the two grooves 11, but the cathode assembly 100 may also be a "single slot type" cathode assembly. The cathode assembly 100 may include the cathode block 10 and at least one collector bar unit 20.

[0027] The cathode block 10 is made of carbon. The "carbon cathode block" includes TiB ２The cathode block 10 may also be made of a composite material of carbon and TiC or the like. The cathode block 10 is preferably made of graphite. The cathode block 10 has a rectangular parallelepiped shape and has a groove 11 formed in the bottom. The groove 11 is open not only in the bottom of the cathode block 10 but also in the side surface (surface perpendicular to the x-direction) of the cathode block 10.

[0028] The groove 11 has a bottom surface 11a and two side surfaces 11b (see FIG. 4). The bottom surface 11a is a plane that is approximately parallel to the horizontal plane. On the other hand, the two side surfaces 11b are inclined relative to the vertical direction. More specifically, the two side surfaces 11b are inclined so that the distance between them decreases as they approach the bottom surface (the lower side in the z direction) of the cathode block 10. The inclination angle is, for example, 1 to 20°. As a result, the groove 11 has a shape that is close to a trapezoid in the yz cross section (a cross section perpendicular to the extension direction of the groove 11). This cross-sectional shape is preferable because it can prevent the collector bar unit 20 from falling off the groove 11. However, the cross-sectional shape of the groove 11 is arbitrary. The cross-sectional shape of the groove 11 may be, for example, rectangular. In other words, the two side surfaces 11b of the groove 11 may be perpendicular to the horizontal plane.

[0029] Collector bar unit 20 is disposed in groove 11 so that its end in the x direction protrudes outside groove 11 (see FIGS. 2 and 5). In this specification, when a certain member is said to be "disposed in groove 11," it means that at least a part of the member is disposed in groove 11, and includes the case where another part of the member protrudes outside groove 11.

[0030] Collector bar unit 20 includes two collector bars (collector bar 21 and collector bar 22), an upper plate 23, conductive members 24 and 25 (FIGS. 3 to 5), and a spacing adjustment member 26 (FIG. 5).

[0031] Each of the collector bars 21 and 22 is made of metal, more specifically, iron or an iron alloy. Each of the collector bars 21 and 22 has a shape extending in the same direction (x direction) as the groove 11. The collector bars 21 and 22 are arranged side by side in the width direction of the groove 11 within the groove 11. More specifically, the width direction of the groove 11 is the direction (y direction) perpendicular to both the direction in which the groove 11 extends (x direction) and the vertical direction (z direction).

[0032] Each of the collector bars 21 and 22 is disposed so as to contact the corresponding side surface 11b of the groove 11. That is, the collector bars 21 and 22 have surfaces 21a and 22a, respectively, that contact the corresponding side surface 11b of the groove 11. The surfaces 21a and 22a are preferably shaped to closely fit the corresponding side surface 11b.

[0033] The upper plate 23 is made of metal, more specifically, iron or an iron alloy. Like the collector bars 21 and 22, the upper plate 23 has a shape that extends in the same direction as the grooves 11 (x direction).

[0034] Upper plate 23 is disposed above collector bars 21 and 22. More specifically, upper plate 23 is disposed so as to be in contact with bottom surface 11a of groove 11 and collector bars 21 and 22. That is, upper plate 23 has surface 23a in contact with bottom surface 11a of groove 11 and surface 23b in contact with the upper end surfaces of collector bars 21 and 22. Surface 23a preferably has a shape that closely conforms to bottom surface 11a of groove 11, and surface 23b preferably has a shape that closely conforms to the upper end surfaces of collector bars 21 and 22.

[0035] The metals constituting the collector bars 21, 22, and upper plate 23 may each be iron or an iron alloy, and do not necessarily have to be the same type of metal. Note that "iron alloy" refers to a metal with an iron content of 50% by mass or more. The iron content of the metals constituting the collector bars 21, 22, and upper plate 23 is preferably 70% by mass or more, and more preferably 90% by mass or more.

[0036] Each of the conductive members 24 and 25 is formed of a metal having higher conductivity than the collector bars 21 and 22, more specifically, copper or a copper alloy. The term "copper alloy" refers to a metal having a copper content of 50% by mass or more. The copper content of the metal constituting the conductive members 24 and 25 is preferably 70% by mass or more, and more preferably 90% by mass or more.

[0037] Like collector bars 21 and 22, conductive members 24 and 25 each have a shape extending in the same direction as grooves 11 (x direction).

[0038] In this embodiment, the conductive members 24 and 25 are arranged so as to be in contact with the collector bars 21 and 22, respectively. More specifically, the conductive members 24 and 25 are arranged inside the collector bars 21 and 22, respectively, in the y direction. The conductive members 24 and 25 are also arranged so as to be in contact with the upper plate 23 at their upper end surfaces. As will be described later, it is sufficient that the conductive members are arranged so as to be in contact with at least one of the collector bars 21, 22, and upper plate 23.

[0039] Each of the collector bars 21, 22, and upper plate 23 protrudes outward beyond the end of the cathode block 10 (see FIG. 5 ). In this embodiment, the conductive members 24 and 25 also protrude outward beyond the end of the cathode block 10. As will be described later, the ends of the conductive members may be located at the same position as the end of the cathode block 10, or may be located more inward than the end of the cathode block 10.

[0040] When the conductive members 24 and 25 protrude outward beyond the ends of the cathode block 10, the electrical resistance of the entire collector bar unit 20 can be reduced. In this case, the distance L ( FIG. 5 ) between the ends of the conductive members 24 and 25 and the end of the cathode block 10 is preferably 100 mm or more, more preferably 300 mm or more, and even more preferably 500 mm or more. The distance between the ends of the collector bars 21, 22, and upper plate 23 and the end of the cathode block 10 is equal to or greater than the distance L. That is, the ends of the collector bars 21, 22, and upper plate 23 are located at the same positions as the ends of the conductive members 24 and 25, or are located farther from the end of the cathode block 10 than the ends of the conductive members 24 and 25.

[0041] The spacing adjustment member 26 ( FIG. 5 ) is a member for adjusting the spacing between the collector bars 21 and 22 when assembling the cathode assembly 100. Adjusting the spacing between the collector bars 21 and 22 makes it possible to adjust the contact pressure between the surface 21 a of the collector bar 21 and the side surface 11 b of the groove 11, and the contact pressure between the surface 22 a of the collector bar 22 and the side surface 11 b of the groove 11. This makes it possible to adjust the contact resistance between the collector bars 21 and 22 and the cathode block 10.

[0042] The gap adjusting member 26 is disposed between the collector bar 21 and the collector bar 22. It is preferable that a plurality of the gap adjusting members 26 are disposed along the direction in which the grooves 11 extend (x direction).

[0043] 6 and 7, a more specific example of the configuration of the gap adjusting member 26 will be described. Fig. 6 is a diagram schematically illustrating the configuration of a gap adjusting member 26A, which is one specific example of the gap adjusting member 26. The gap adjusting member 26A has a threaded portion 26a at one end and a threaded portion 26b at the other end. A threaded hole 24a is formed in the conductive member 24 to be fastened to the threaded portion 26a, and a threaded hole 25a is formed in the conductive member 25 to be fastened to the threaded portion 26b.

[0044] According to this configuration, by changing the degree of fastening between threaded portion 26a and threaded hole 24a and the degree of fastening between threaded portion 26b and threaded hole 25a, it is possible to adjust the distance between conductive member 24 and conductive member 25. By adjusting the distance between conductive member 24 and conductive member 25, it is possible to adjust the distance between collector bar 21 and collector bar 22.

[0045] In the gap adjustment member 26A, the threaded portions 26a and 26b are formed with threads in opposite directions. That is, when the threaded portion 26a is a right-handed thread, the threaded portion 26b is a left-handed thread. When the threaded portion 26a is a left-handed thread, the threaded portion 26b is a right-handed thread. With this configuration, when the gap adjustment member 26 is rotated in one direction, the threaded portions 26a and 26b can both be moved in a direction to tighten (or loosen). This allows the conductive members 24 and 25 to be moved evenly, and the collector bars 21 and 22 to be moved evenly.

[0046] 7 is a diagram schematically illustrating the configuration of a gap adjusting member 26B, which is another specific example of the gap adjusting member 26. The gap adjusting member 26B has a threaded portion 26a at one end. The conductive member 24 has a screw hole 24a formed therein to be fastened to the threaded portion 26a.

[0047] While the gap adjusting member 26A (FIG. 6) has threaded portions formed on both ends, the gap adjusting member 26B (FIG. 7) has a threaded portion 26a formed on only one end. In the gap adjusting member 26B, the threaded portion 26a is fastened to the threaded hole 24a of the conductive member 24, and the end of the gap adjusting member 26B on the side where the threaded portion 26a is not formed is brought into contact with the conductive member 25, thereby adjusting the gap between the conductive member 24 and the conductive member 25.

[0048] The configurations of the gap adjusting members 26A and 26B described above are merely examples, and the configuration of the gap adjusting member 26 is not limited to these. The gap adjusting member 26 may be any member that can adjust the gap between the two collector bars (collector bar 21 and collector bar 22). Note that the gap adjusting members 26A and 26B described above directly adjust the gap between the conductive member 24 and the conductive member 25, but can also indirectly adjust the gap between the collector bar 21 and the collector bar 22. In this specification, the phrase "adjusting the gap between two collector bars" includes the above-mentioned mode of indirectly adjusting the gap between the two collector bars.

[0049] It is preferable that the spacing adjustment member 26 includes a mechanism for adjusting the spacing between the two collector bars using a screw, such as spacing adjustment member 26A or spacing adjustment member 26B. By including a screw mechanism, the spacing between collector bar 21 and collector bar 22 can be adjusted more precisely, thereby enabling more precise control of the contact pressure between surface 21a of collector bar 21 and side surface 11b of groove 11, and the contact pressure between surface 22a of collector bar 22 and side surface 11b of groove 11. However, spacing adjustment member 26 may also adjust the spacing between collector bar 21 and collector bar 22 using a mechanism other than a screw. For example, spacing adjustment member 26 may be a wedge.

[0050] 2 to 5, the description of the configuration of the cathode assembly 100 will continue. The filler material 31 is disposed in the space surrounded by the collector bars 21, 22, and the upper plate 23 (see FIGS. 3 and 4). The filler material 31 may be, for example, cement such as alumina cement, ramming paste, ceramics, steel shot, coke granules, or the like. The filler material 31 may or may not be electrically conductive.

[0051] In this embodiment, conductive members 24 and 25 are disposed between collector bar 21 and collector bar 22. As will be described later, spacers 32 are disposed between conductive member 24 and filler 31. Therefore, filler 31 is disposed directly in the space surrounded by spacer 32, conductive member 25, and upper plate 23. In this specification, the phrase "disposed in the space surrounded by collector bar 21, collector bar 22, and upper plate 23" includes the above-described embodiment in which filler 31 is disposed in the space indirectly surrounded by collector bar 21, collector bar 22, and upper plate 23.

[0052] The filler 31 can be formed, for example, by adjusting the gap between the conductive members 24 and 25 using the gap adjustment member 26, and then pouring the material that makes up the filler 31 (cement, ramming paste, ceramics, steel shot, coke granules, etc.) between the conductive members 24 and 25.

[0053] Spacers 32 (FIGS. 4 and 5) are disposed between the conductive member 24 and the filler 31. Alternatively, spacers 32 may be disposed between the conductive member 25 and the filler 31, or may be disposed both between the conductive member 24 and the filler 31 and between the conductive member 25 and the filler 31. Furthermore, when the filler 31 and the collector bar (collector bar 21 or collector bar 22) are adjacent to each other (see, for example, FIG. 10), spacers 32 may be disposed between the filler 31 and the collector bar.

[0054] The spacer 32 is, for example, a thermoplastic resin or a metal or alloy having a melting point of 700°C or less. An example of a metal having a melting point of 700°C or less is aluminum. The spacer 32 is preferably in a sheet shape. The spacer 32 may or may not be electrically conductive. The spacer 32 is preferably a thermoplastic resin.

[0055] The cathode assembly 100 is heated to a high temperature (e.g., 960°C) during operation. Thermal expansion of the collector bars 21 and 22 may cause deformation of the gap adjustment member 26. By disposing the filler 31, the gap between the collector bars 21 and 22 can be maintained, thereby maintaining the contact pressure at high temperatures. Furthermore, by disposing the spacer 32, excessive stress due to thermal expansion of the collector bars 21 and 22 can be alleviated, thereby preventing damage to the cathode block 10. Furthermore, the spacer 32 softens as the temperature rises, thereby easing changes in the contact pressure during the temperature rise.

[0056] [Effects of the Cathode Assembly 100] In an aluminum smelting electrolytic furnace 1 ( FIG. 1 ), the electrolytic bath 94 may permeate the cathode block 10 and reach the vicinity of the collector bar unit 20. If the filler 31 ( FIG. 3 , etc.) is exposed at this time, the filler 31 may react with the electrolytic bath 94, resulting in a decrease in the strength of the filler 31. As described above, the filler 31 contributes to maintaining the gap between the collector bars 21 and 22. If the strength of the filler 31 decreases, the gap between the collector bars 21 and 22 may no longer be maintained, which may result in an insufficient contact pressure between the collector bars 21 and 22 and the cathode block 10. This may result in increased CVD.

[0057] According to the configuration of the cathode assembly 100 of this embodiment, the filler 31 is disposed in a space surrounded by the collector bars 21, 22, and upper plate 23. Therefore, even if the electrolytic bath 94 permeates the cathode block 10, the collector bars 21, 22, and upper plate 23 can prevent the electrolytic bath 94 from permeating into the filler 31, thereby suppressing a reaction between the filler 31 and the electrolytic bath 94.

[0058] In this embodiment, the collector bars 21, 22, and upper plate 23 are each made of iron or an iron alloy. In recent years, it has become common for aluminum smelting electrolytic furnaces to partially use copper in the collector bars in order to improve power consumption and current efficiency. However, copper is known to undergo an embrittlement phenomenon known as intermediate-temperature embrittlement in the temperature range of approximately 300°C to approximately 800°C, resulting in grain boundary cracking. The operating temperature of an aluminum smelting electrolytic furnace is typically around 960°C. However, a temporary temperature drop during furnace startup (when the temperature rises to 960°C) or during a power outage can cause the temperature to pass through a temperature range below 800°C, potentially resulting in cracks in the copper portion due to intermediate-temperature embrittlement.

[0059] Therefore, if there is a region between the filler 31 and the cathode block 10 where only copper members exist, the electrolytic bath 94 may seep in through cracks formed in that region, potentially causing a reaction between the filler 31 and the electrolytic bath 94. In this embodiment, the filler 31 is disposed in a space surrounded by the collector bars 21, 22, and the top plate 23, and each of the collector bars 21, 22, and the top plate 23 is made of iron or an iron alloy. In other words, there is no region between the filler 31 and the cathode block 10 where only copper members exist. This configuration more reliably prevents the filler 31 from reacting with the electrolytic bath 94.

[0060] Furthermore, in electrolytic furnaces for aluminum smelting, a phenomenon known as cathode heaving occurs, in which the central portion of the cathode bulges upward due to a distortion in the thermal balance of the electrolytic furnace. This can cause stress to distort the collector bar, posing a risk of shearing the collector bar (see FIG. 8). It is known that distortion of the collector bar due to cathode heaving occurs at a position approximately 100 mm outside the end of the cathode block (area B surrounded by a two-dot chain line in FIG. 8).

[0061] When the bath temperature during operation of an electrolytic furnace is approximately 960°C, the temperature of the end of the cathode block is approximately 850°C, and the temperature of the shell of the electrolytic furnace is approximately 250°C. The temperature range between the end of the cathode block (approximately 850°C) and the shell (approximately 250°C) is one in which copper becomes significantly embrittled, and cracks are likely to occur in the copper. Therefore, collector bars made of copper are very vulnerable to cathode heaving. Furthermore, if copper is used in part of a collector bar, the cross-sectional area of ​​the remaining part (the iron part) also becomes smaller, thereby reducing the strength of the iron part. If both the copper part and the iron part are sheared, the conductive path is lost, resulting in unstable operation.

[0062] In this embodiment, collector bar unit 20 includes two collector bars (collector bars 21 and 22) arranged side by side in the width direction of groove 11, and an upper plate 23 arranged thereon. Collector bar 21, collector bar 22, and upper plate 23 are each made of iron or an iron alloy.

[0063] According to this configuration, the collector bars 21, 22, and upper plate 23 form a cross-sectionally concave structure (channel structure), which increases the moment of inertia and increases the strength of the iron or iron alloy portions, thereby increasing the likelihood that the iron or iron alloy portions (collector bars 21, 22, and upper plate 23) will maintain a conductive path even if the copper or copper alloy portions (conductive members 24 and 25) are sheared.

[0064] The configuration of the cathode assembly 100 according to one embodiment of the present invention has been described above. According to this embodiment, CVD can be suppressed and the electrolytic furnace can be operated stably.

[0065] [Modification of Collector Bar Unit 20] In the above embodiment, the case where two conductive members (conductive member 24 and conductive member 25) are arranged inside two collector bars (collector bar 21 and collector bar 22) in the y direction has been described (see FIG. 4, etc.). This configuration is one example, and the locations where the conductive members are arranged are not limited to this. It is sufficient that the conductive members are arranged so as to be in contact with at least one of collector bar 21, collector bar 22, and upper plate 23.

[0066] 9 is a cross-sectional view showing the configuration of collector bar unit 20A, which is one of the modified examples of collector bar unit 20. Collector bar unit 20A includes conductive member 24A instead of conductive member 24 and conductive member 25 of collector bar unit 20 (FIG. 4). In collector bar unit 20 (FIG. 4), conductive members are arranged on the inner sides of the two collector bars in the y direction, but in collector bar unit 20A, a conductive member (conductive member 24A) is arranged on only one side of the two collector bars (collector bar 21 side).

[0067] 10 is a cross-sectional view showing the configuration of collector bar unit 20B, which is another modified example of collector bar unit 20. Collector bar unit 20B includes conductive members 24B and 25B instead of conductive members 24 and 25 of collector bar unit 20 (FIG. 4). Conductive members 24B and 25B are embedded inside collector bar 21 and collector bar 22, respectively.

[0068] In these modified examples, the filler 31 is disposed in the space surrounded by the collector bar 21, the collector bar 22, and the upper plate 23, and the collector bar 21, the collector bar 22, and the upper plate 23 are each made of iron or an iron alloy. In addition, the collector bar 21, the collector bar 22, and the upper plate 23 form a concave cross-sectional structure (channel structure). Therefore, in these modified examples, the same effects as those of the collector bar unit 20 can be obtained.

[0069] In the above embodiment (collector bar unit 20), the conductive members 24 and 25 protrude outward beyond the ends of the cathode block 10 (see FIG. 5). This configuration is just one example, and the ends of the conductive members may be located at the same position as the ends of the cathode block 10, or may be located more inward than the ends of the cathode block 10.

[0070] FIG. 11 is a cross-sectional view showing the configuration of collector bar unit 20C, which is yet another modified example of collector bar unit 20. Collector bar unit 20C includes conductive members 24C and 25C instead of conductive members 24 and 25 of collector bar unit 20 ( FIG. 5 ). Collector bar unit 20C also includes members 27 and 28 made of iron or an iron alloy. Members 27 and 28 each have a shape extending in the same direction as groove 11 (x direction). Members 27 and 28 are disposed in contact with the ends of conductive members 24C and 25C, respectively. In other words, collector bar unit 20C has a configuration in which part of conductive members 24 and 25 of collector bar unit 20 ( FIG. 5 ) are replaced with iron or an iron alloy.

[0071] In the collector bar unit 20 (FIG. 5), the conductive members 24 and 25 protrude outward beyond the ends of the cathode block 10, whereas in the collector bar unit 20C, the ends of the conductive members 24C and 25C are located more inward than the ends of the cathode block 10. When the ends of the conductive members 24C and 25C are located more inward than the ends of the cathode block 10, the effects of reducing heat radiation from the conductive members 24C and 25C and preventing the conductive members 24C and 25C from being placed in an intermediate temperature range can be obtained. In this case, the lower limit of the distance D (FIG. 11) between the ends of the conductive members 24C and 25C and the end of the cathode block 10 is preferably 0 mm, and more preferably 200 mm. In this case, the upper limit of the distance D between the end of the conductive member 24C and the end of the conductive member 25C and the end of the cathode block 10 is preferably 600 mm, and more preferably 400 mm.

[0072] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0073] REFERENCE SIGNS LIST 1 Electrolytic furnace 100 Cathode assembly 10 Cathode block 11 Groove 20, 20A, 20B, 20C Collector bar unit 21, 22 Collector bar 23 Upper plate 24, 25, 24A, 24B, 25B, 24C, 25C Conductive member 26, 26A, 26B Spacing adjustment member 27, 28 Member 31 Filler 32 Spacer 91 Anode 92 Shell 93 Lining 94 Electrolytic bath 95 Aluminum

Claims

1. A cathode assembly for use in an electrolytic furnace for smelting aluminum, comprising: a carbon cathode block having grooves; a collector bar unit inserted into the grooves; and a filler material, wherein the collector bar unit includes: two collector bars, each having a shape extending in the same direction as the groove and arranged side by side in the width direction of the groove; an upper plate having a shape extending in the same direction as the groove and arranged on top of the two collector bars; and a conductive member having a shape extending in the same direction as the groove and arranged so as to contact at least one of the two collector bars and the upper plate, wherein each of the two collector bars and the upper plate are made of iron or an iron alloy, and the conductive member is made of copper or a copper alloy, the two collector bars are in contact with corresponding side surfaces of the groove, the upper plate is in contact with the bottom surface of the groove and the two collector bars, and the filler material is disposed in a space surrounded by the two collector bars and the upper plate.

2. A cathode assembly according to claim 1, wherein said collector bar unit further includes a spacing adjustment member for adjusting the spacing between said two collector bars.

3. A cathode assembly according to claim 1 or 2, further comprising a spacer disposed between said filler and said conductive member or between said filler and said collector bar.

Images