CA3027826C

CA3027826C - Cathode

Info

Publication number: CA3027826C
Application number: CA3027826A
Authority: CA
Inventors: Tatsuya Okamoto; Yasuhiro Koyama
Original assignee: SEC Carbon Ltd
Current assignee: SEC Carbon Ltd
Priority date: 2016-06-16
Filing date: 2017-05-29
Publication date: 2023-06-27
Anticipated expiration: 2037-05-29
Also published as: JP6089137B1; WO2017217225A1; AU2017285539A1; JP2017222914A; AU2017285539B2; CA3027826A1

Abstract

Provided is a cathode that is easy to install while ensuring electric conductivity. The cathode 10 is a cathode for metal refinery and is provided with a carbon cathode block 11, and at least one carbon collector bar 12, each of which is disposed so as to contact the cathode block 11. The bottom surface of the cathode block 11 is a flat surface. The upper surface of each collector bar 12 is a flat surface. The cathode block 11 is disposed so that the bottom surface of the cathode block 11 contacts the upper surface of each of the collector bars 12.

Description

--Our Ref. 338W0006P1 CATHODE
TECHNICAL FIELD
[0001] The present invention relates to cathodes, and more particularly to cathodes for smelting metal.
BACKGROUND ART

[0002] Cathodes in electrolytic furnaces for smelting metal, such as aluminum, typically take the form of cathode blocks made of carbon.
Cathode blocks are positioned in a steel box called "shell" to form the bottom of the electrolytic furnace. The cathode blocks also function to supply the electrolytic bath with electrons (see, for example, JP 2012-529567 A and JP
2013-537940 A).

[0003] The cathode blocks are supplied with electric power via steel collector bars. The connection between the cathode blocks and the collector bars is established by pouring cast iron into the gaps between them. Specifically, the bottom surface of each cathode block is provided with a groove, into which collector bars are fitted, and cast iron that has been heated to about 1300 C to be melted is poured into the gaps between the groove and collector bars.

[0004] It has been reported that, even in cases where the cathode blocks are connected to the collector bars through cast iron, gaps may be produced between a cathode block and cast iron and/or between cast iron and a collector bar to increase the contact resistance. According to Richard Beeler, "Bar to Block Contact Resistance in Aluminum Reduction Cell Cathode Assemblies", Light Metals 2014, pp. 507-510, the proportion of the reduction in voltage in the cathode blocks and collector bars represented by the contact resistance is about 25 %, and is equivalent to at least 2 % of the electric power consumption in aluminum smelting.

[0005] The document cited above teaches that, inter alia, (1) the solidification behavior of cast iron adjacent to the top of a collector bar is different from that adjacent to the bottom of the bar; (2) the collector bars may experience creep deformation; and (3) phase change in steel may cause discontinuous thermal expansion, thus producing gaps between the cathode blocks and collector bars.

[0006] To reduce contact resistance, Canadian Patent No. 2846409 teaches AA A A. . A A ^ . = .= = =
-Our Ref. 338W0006P1 using a compression device to compress the collector bars to eliminate the gaps between the cathode blocks and collector bars. Further, Canadian Patent No. 2838113 discloses inserting metallic conductors between the cathode blocks and collector bars to establish electrical connection.
DISCLOSURE OF THE INVENTION

[0007] Approaches in which cast iron is poured in to connect the cathode blocks to the collector bars, as discussed above, require equipment and energy to melt cast iron and thus require considerable costs, and, if conducted manually, may present safety concerns. Further, the resulting quality is unstable, and variations in contact resistance may occur among individual blocks/bars.

[0008] An object of the present invention is to provide a cathode that provides a certain level of electric conductivity and that can be easily installed.

[0009] One cathode disclosed herein is a cathode for smelting metal, including: a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block. The cathode block has a flat bottom surface; each of the one or more collector bars has a flat top surface; and the cathode block is positioned such that the bottom surface of the cathode block is in contact with the top surface of each of the one or more collector bars.

[0010] Another cathode disclosed herein is a cathode for smelting metal, including: a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block. The cathode block has a bottom surface provided with a groove; each of the one or more collector bars has a top surface provided with a groove complementary to the groove of the cathode block; and the cathode block is positioned such that the bottom surface of the cathode block is in contact with the top surface of each of the one or more collector bars.

[0011] Yet another cathode disclosed herein is a cathode for smelting metal, including: a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block. The cathode further includes a screw adapted to fasten the cathode block and the one or more collector bars together.

[0012] Still another cathode disclosed herein is a cathode for smelting metal, . , Our Ref. 338W0006P
including: a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block. The cathode block includes a male or female thread, or a protrusion or recess; and each of the one or more collector bars includes a female or male thread to be fastened to the male or female thread, or a recess into which the protrusion is to be fitted or a protrusion to be fitted into the recess.

[0013] Yet another cathode disclosed herein is a cathode for smelting metal, including: a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block. The cathode further includes a second cathode block; and at least one of the one or more collector bars is in contact with both the cathode block and the second cathode block.

[0014] In these arrangements, the difference in coefficient of thermal expansion between the cathode block(s) and collector bars is small, thereby keeping them in close contact even at high temperatures. This will simplify the working process for keeping them in close contact. This will provide a cathode that provides a certain level of electric conductivity and that can be easily installed.
BRIEF DESCRIPTION OF THE DRAWINGS

[0015] [FIG. 1] FIG. 1 is a schematic cross-sectional view of metal-smelting equipment.
[FIG. 2] FIG. 2 is a perspective view some components of the metal-smelting equipment.
[FIG. 31 FIG. 3 shows an example of a manner in which the collector bars are connected to the bus bars.
[FIG. 41 FIG. 4 is a perspective view of a cathode according to a first embodiment.
[FIG. 51 FIG. 5 is a perspective view of a conventional common cathode.
[FIG. 61 FIG. 6 is a cross-sectional view taken along line VI-VI of FIG.
5.
[FIG. 7A] FIG. 7A is a cross-sectional view of a model of a conventional cathode along a plane perpendicular to the longitudinal direction thereof.
[FIG. 7B] FIG. 7B is a cross-sectional view of the model of the Our Ref. 338W0006P1 conventional cathode along a plane perpendicular to the width direction thereof.
[FIG. 8A1 FIG. 8A is a cross-sectional view of a model of the cathode according to the present embodiment along a plane perpendicular to the longitudinal direction thereof.
[FIG. 8B] FIG. 8B is a cross-sectional view of the model of the cathode according to the present embodiment along a plane perpendicular to the width direction thereof.
[FIG. 91 FIG. 9 is a perspective view of a cathode according to a second embodiment.
[FIG. 10] FIG. 10 is a perspective view of a cathode according to a third embodiment.
[FIG. 11] FIG. 11 is a perspective view of a cathode according to a fourth embodiment.
[FIG. 12] FIG. 12 is a perspective view of a cathode according to a fifth embodiment.
[FIG. 13] FIG. 13 is a perspective view of a cathode according to a sixth embodiment.
[FIG. 14] FIG. 14 is a perspective view of a cathode according to a seventh embodiment.
[FIG. 151 FIG. 15 is a perspective view of a cathode according to an eighth embodiment.
EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0016] Embodiments of the present invention will now be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are labeled with the same characters and their description will not be repeated. For ease of understanding of the description, the drawings, which will be referred to below, show simplified or schematic constructions, or show only some of the components. Further, the size ratios between components shown in the drawings do not necessarily represent the actual size ratios.

[0017] [First Embodiment]
[Overall Construction]
FIG. 1 is a schematic cross-sectional view of metal-smelting equipment 1000 including cathodes 10 according to a first embodiment of the present invention. The metal-smelting equipment 1000 includes a plurality Our Ref. 338W0006P1 of cells 100. Each of the cells 100 includes a plurality of cathodes 10, a plurality of anodes 20 and a furnace body 30. The cell 100 is loaded with an electrolytic bath 33 and a pad 34 made of the metal to be smelted (for example, aluminum).

[0018] Each cell 100 further includes a raw-material supply device 35. The raw-material supply device 35 regularly supplies the electrolytic bath 33 with raw material (for example, alumina).

[0019] Each of the cathodes 10 includes a cathode block 11 and two collector bars 12 electrically connected to the cathode block 11. FIG. 2 is a perspective view of some components of the cell 100: the cathodes 10 (i.e.
cathode blocks 11 and collector bars 12) and the furnace body 30. As shown in FIG. 2, the cathodes blocks 11 are placed all over the bottom of the furnace body 30. The collector bars 12 are configured to extend to outside of the furnace body 30 via slots 31a defined in the furnace body 30.

[0020] The cathode blocks 11 and collector bars 12 are preferably made of materials that can resist high temperatures and have high electric conductivity. In the present embodiment, both the cathode blocks 11 and collector bars 12 are made of carbon. Details of the constructions of the cathode blocks 11 and collector bars 12 will be given further below.

[0021] Each of the anodes 20 (see FIG. 1) includes an anode block 21 and a connection member 22 electrically connected to the anode block 21. The anode blocks 21 and connection members 22 are preferably made of materials that can resist high temperatures and have high electric conductivity. The anode blocks 21 may be made of carbon, for example.
The connection members 22 may be made of metal, for example.

[0022] The furnace 30 includes a box-shaped shell 31 and a lining 32 positioned within the shell 31. The shell 31 is preferably made of a material with high toughness to resist thermal expansion of the lining 32. The shell 31 may be made of metal, for example. The lining 32 insulates various in-furnace components from each other and also prevents the electrolytic bath 33 from leakage. The lining 32 may be made of fire bricks, for example.

[0023] The collector bars 12 extending to outside of the furnace body 30 are electrically connected to the anodes 20 of an adjacent cell 100 via metallic bus bars 36. This construction results in a plurality of cells 100 being electrically connected in series.

Our Ref. 338W0006P1

[0024] The bus bars 36 are preferably made of a material with low electric resistivity. The bus bars 36 may be made of aluminum, for example. The collector bars 12 are connected to the bus bars 36 in areas outside of the furnace body 30 at relatively low temperatures. As such, the difference in coefficient of thermal expansion between the collector bars 12 and bus bars 36 poses no problem. The same applies to the connection between the bus bars 36 and connection members 22.

[0025] The connection between the collector bars 12 and bus bars 36 is not limited to any particular manner. However, since the collector bars 12 of the present embodiment are made of carbon, the collector bars 12 and bus bars 36 cannot be welded. FIG. 3 shows an example of a manner in which the collector bars 12 are connected to the bus bars 36. In this example, both sides of each collector bar 12 as determined along the height direction are sandwiched by a bus bar 36, and bolts 37 and nuts 38 are tightened together to connect the collector bar 12 to the bus bar 36.

[0026] The cathodes 10 at one end of the series of connected cells 100 (see FIG. 1) and the anodes 20 at the other end of the cell series are connected to a power source, not shown. Electric power from the power source applies a voltage between the cathodes 10 and anodes 20 of each cell 100. This causes raw material in the electrolytic bath 33 to be reduced and deposited on the pad 34.

[0027] Thus, the metal-smelting equipment 1000 is capable of manufacturing metal in a continuous manner. The metal-smelting equipment 1000 is particularly suitable for smelting aluminum.

[0028] [Construction of Cathodes]
FIG. 4 is a perspective view of a cathode 10 according to the first embodiment of the present invention. As discussed above, the cathode 10 includes a cathode block 11 and two collector bars 12. The cathode block 11 and two collector bars 12 have the shape of rectangular parallelepipeds.
The cathode block 11 is located on the top surfaces of the two collector bars 12. The bottom surface of the cathode block 11 is in contact with the top surfaces of the two collector bars 12 to establish electrical connection between the cathode block 11 and the two collector bars 12.

[0029] For ease of explanation, the longitudinal direction of the cathode 10 (i.e. x-direction) will be referred to as longitudinal direction, while the vertical direction (i.e. z-direction) will be referred to as height direction.

õ., = = = = ===.===el=
4.,Y0=.=,lnr.KW ¾=V= =y..0 =

Our Ref. 338W0006P1 The direction perpendicular to both the longitudinal direction and vertical direction (i.e. y-direction) will be referred to as width direction. The dimensions of a part as measured in the longitudinal direction, height direction and width direction will be referred to as length, height and width, respectively.

[0030] The larger the width w of the collector bar 12, the better. The larger the width w, the larger the contact area between the bar and the cathode block 11. Further, the larger the width w, the larger the cross-sectional area of the collector bar 12, which means lower electrical resistance of the collector bar 12. More preferably, the width w of the collector bar 12 is equal to the width W of the cathode block 11. Further, the larger the height h of the collector bar 12, the better.

[0031] The two collector bars 12 are arranged in the longitudinal direction of the cathode block 11. The two collector bars 12 are separated by a distance sp. The distance sp may be in the range of 15 to 50 cm, for example.

[0032] In the present embodiment, both the cathode block 11 and collector bars 12 are made of carbon. Preferably, the cathode block 11 and collector bars 12 are made of materials with low electrical resistivities. The cathode block 11 and collector bars 12 are preferably made of graphite. Further, the collector bars 12 are preferably made of a material with a lower electrical resistivity than the cathode block 11.

[0033] [Effects of Cathode 10]
To help demonstrate the effects of the cathode 10, the construction of a conventional common cathode 90 will be described. FIG. 5 is a perspective view of the cathode 90. FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 5.

[0034] The cathode 90 includes a cathode block 91 and four collector bars 92.
The cathode block 91 is made of carbon, typically graphite. The collector bars 92 are made of metal, typically steel.

[0035] Steel usually has a lower electrical resistivity (specific resistance) than carbon. Accordingly, with the collector bars 92 made of steel, it is easier to achieve low electrical resistance. On the other hand, the collector bars 92 made of steel have a coefficient of thermal expansion different from that of the cathode block 91, which is made of carbon, making it difficult to keep them in close contact with the cathode block 91 at high temperatures, and thus the contact resistance tends to be high. The contact resistance Our Ref. 338W0006P1 between the cathode block 91 and collector bars 92 must be reduced in one way or the other.

[0036] As shown in FIG. 6, the bottom surface of the cathode block 91 is provided with grooves, into which the collector bars 92 are fitted. Further, cast iron 93 is poured into the gaps between the cathode block 91 and collector bars 92.

[0037] Creating this construction requires working time and costs.
Particularly, the step of pouring cast iron 93 represents a heavy load and, if conducted manually, presents safety concerns. Further, the resulting quality is unstable, and variations in contact resistance may occur among individual blocks/bars.

[0038] The cross-sectional area of the collector bars 92 significantly affects the electrical resistance. To reduce the electrical resistance, it is preferable to increase the cross-sectional area of the collector bars 92. However, if the cross-sectional area of the collector bars 92 is to be increased, the grooves in the cathode block 91 must be increased accordingly. If the grooves are too large, the strength of the cathode block 91 may be insufficient and thermal stress caused by cast iron 93 being poured and other factors may produce a crack 91a, called wing crack.

[0039] Instead of cast iron 93, paste may be used that is mainly composed of coke and coal-tar pitch. However, such paste has a high electrical resistance, which means a high energy loss.

[0040] If cast iron 93 is used, as discussed in the background section, (1) the solidification behavior of cast iron adjacent to the top of a collector bar is different from that adjacent to the bottom of the bar; (2) the collector bars may experience creep deformation; and (3) phase transition in iron may cause discontinuous thermal expansion, thus producing gaps between the cathode block 91 and collector bars 92. This increases the contact resistance between the cathode block 91 and collector bars 92.

[0041] In the construction of the cathode 10 according to the present embodiment, both the cathode block 11 and collector bars 12 are made of carbon, which means that there is no difference in coefficient of thermal expansion between them. This makes it possible to keep the cathode block 11 and collector bars 12 in close contact even at high temperatures.

[0042] This eliminates the necessity to provide grooves on the bottom surface of the cathode block 11 or to pour cast iron into the gaps between the Our Ref. 338W0006P1 cathode block 11 and collector bars 12. This reduces working time and costs.

[0043] The collector bars 12 made of carbon have a lower thermal conductivity than the collector bars 92 made of steel. This prevents heat in the cell 100 from dissipation.

[0044] The cathode block 11 or 91 may wear down due to friction with the pad 34 (see FIG. 1) and other factors. In the case of the cathode 90, when the cathode block 91 has worn down to a level with the collector bars 92 that are fitted in, the collector bars 92 made of steel come in contact with the content of the electrolytic bath 33 (see FIG. 1), potentially contaminating the content of the electrolytic bath 33; to prevent this, the cathode block 91 is not used anymore. That is, the portions of the volume of the cathode block 91 that are at the same levels as the fit-in collector bars 92 do not contribute to the life of the cathode 90. In contrast, in the construction of the cathode 10, the entire volume of the cathode block 11 contributes to the life of the cathode 10. Thus, from a given volume of raw material, a cathode with a longer life can be produced.

[0045] In the construction of the cathode 10, the collector bars 12 do not need to be fixed to the cathode block 11, and the cathode block 11 may be simply put on the collector bars 12. The interface between the cathode block 11 and collector bars 12 receives a certain level of pressure from the weights of the cathode block 11, electrolytic bath 33 and pad 34. Further, the lining 32 and other elements can thermally expand, thus applying a compression stress on the cathode block 11 and collector bars 12. This further facilitates keeping the cathode block 11 and collector bars 12 in close contact even at high temperatures.

[0046] [Example Calculations]
Model calculations were conducted to verify that collector bars made of carbon can provide electric conductivity levels substantially equal to those of collector bars made of steel. The model calculations were conducted in accordance with the method described in Richard Beeler, "An Analytical Model for Cathode Voltage Drop in Aluminum Reduction Cells", Light Metals 2003, pp. 241-245.

[0047] Table 1 shows the parameters used for the calculations and the calculation results.

[0048]

_ Our Ref. 338W0006P1 [Table 1]

Comp. Ex. Inv. Ex.
0.505 m 0.505 m 0.480 m 0.480 m 1.750 m 1.750 m 0.210 m 0.505 m 0.130 m 0.150 m L' 0.500 m 0.500 m pn 1.2 pgrn 4.0 pgm p's 0.6 pm 4.0 pQm pc 9.1 pm 9.1 pm 10.0 pQm2 1.0 pQm2 H* 0.39 m 0.36 m R'B 10.99 pg2 26.40 pg RB 76.92 pg 92.41 pg RC 3.97 pg 3.69 pg Rj 12.16 lig 1.13 pg a 2.18 4.38 Rcen 1.473 pg 1.484 pg

[0049] FIGS. 7A to 8B illustrate the models used for the calculations. FIG.
7A is a cross-sectional view of a model of a conventional cathode 95 (comparative example) along a plane perpendicular to the longitudinal direction thereof. FIG. 7B is a cross-sectional view of the same model along a plane perpendicular to the width direction thereof. FIG. 8A is a cross-sectional view of a model of the cathode 10 according to the present embodiment (inventive example) along a plane perpendicular to the longitudinal direction thereof. FIG. 8B is a cross-sectional view of the same model along a plane perpendicular to the width direction thereof.

[0050] As shown in FIGS. 7A to 8B, W, H and L indicate the width, height and length, respectively, of the cathode block 96 or 11. w and h indicate the width and height, respectively, of the collector bars 97 or 12. L' indicates the length of the portions of a collector bar 12 or 97 that protrude from the cathode block 96 or 11. As shown in Table 1, the cross-sectional area of the collector bars 96 was 21 cm x 13 cm, and the cross-sectional area of the collector bars 12 was 50.5 cm x 15 cm.

Our Ref. 338W0006P1

[0051] N is the number of cathode blocks in a cell multiplied by 2. This parameter is used to calculate the resistance Rcell per cell.

[0052] ps and p's indicate the electric resistivities (volume resistivities) of the collector bars at 1000 C and 500 C, respectively. The electric resistivity of the collector bars of the comparative example is represented by the value for steel. The electric resistivity of the collector bars of the inventive example is represented by the value for a nipple material for artificial graphite electrodes, which is a carbon material with a particularly low electric resistivity.

[0053] pc indicates the electric resistivity of the cathode block at 1000 C.
It is represented by the same value for graphite for the inventive and comparative examples.

[0054] a indicates the contact resistance per unit contact area at the interfaces between the cathode block and collector bars. The larger the contact area, the smaller the contact resistance becomes. a in the comparative example was calculated backward from a measured value of Rcell. It is assumed that a in the inventive example can be reduced to 1.0 ilS2m2, since no problem arises due to the difference in coefficient of thermal expansion, which would be the case in collector bars made of steel.

[0055] H* indicates the effective height and expressed by the following equation:
H*=H¨h(h+w)/(2h+w)

[0056] R's indicates the resistance of the portions of a collector bar that protrude from the cathode block as measured along the longitudinal direction thereof. R's is expressed by the equation provided below. In reality, a temperature distribution exists in the collector bar and electric resistivity may vary depending on location; however, for the sake of simplicity, the electric resistivity at the median temperature, i.e. 500 C, was used for calculation.
R's=p'sL7wh [0051 RB indicates the resistance of the portions of a collector bar that overlap the cathode block as seen in plan view, as measured along the longitudinal direction of the collector bar. Rs is expressed by the equation provided below. For the purpose of calculation, the temperature of these portions was 1000 C.
Rs=psL/wh Our Ref. 338W0006P1 [0058] Rc indicates the resistance of the cathode block as measured along the height direction. Rc is expressed by the equation provided below. For the purpose of calculation, the temperature of these portions was 1000 C.
Rc=pcH*/WL
[0059] RJ indicates the resistance of the connection between the cathode block and a collector bar, and is expressed by the following equations:
RJ=o/(2h+w)L (for FIGS. 7A and 7B) RJ=a/wL (for FIGS. 8A and 8B) [0060] a indicates the ratio of the resistance as measured along the longitudinal direction to the resistance as measured along the height direction, and is expressed by the following equation:
a2=RB/(Rc+RJ) [0061] The resistance Rcell of a cell can be calculated by the following equation:
[Math 1]

a tanh (ct )) [0062] Table 2 demonstrates that the use of collector bars made of carbon also provides a level of electrical conductivity that is substantially equal to those of collector bars made of metal.
[0063] The construction and effects of the cathode 10 according to the first embodiment of the present invention have been described. According to the present embodiment, both the cathode block 11 and collector bars 12 are made of carbon. In this construction, the difference in coefficient of thermal expansion between the cathode block 11 and collector bars 12 is small, making it possible to keep them in close contact even at high temperatures.
This simplifies the work for keeping them in close contact. This provides a cathode that provides a certain electrical conductivity and can be easily installed.
[0064] According to the present embodiment, the bottom surface of the cathode block 11 is flat, and the top surfaces of the collector bars 12 are flat.
The cathode block 11 is positioned such that the bottom surface of the cathode block 11 is in contact with the top surfaces of the collector bars 12.

This construction makes it particularly easy to machine the cathodes.
[0065] In FIG. 4, both the cathode block 11 and collector bars 12 have the Our Ref. 338W0006P I
shape of rectangular parallelepipeds. Alternatively, in the cathode block 11, only the bottom surface is required to be flat and the other surfaces may take any shapes. Similarly, in each of the collector bars 12, only the top surface is required to be flat and the other surfaces may take any shapes. The bottom surface of the cathode block 11 and the top surfaces of the collector bars 12 preferably have high smoothness. The higher the smoothness of these surfaces, the larger the contact area between them becomes, which means smaller contact resistance.
[0066] The present embodiment illustrates an implementation where two collector bars 12 are provided for each cathode block 11. Alternatively, only one collector bar may be provided or more than two collector bars may be provided for each cathode block 11.
[0067] Preferably, in the cathode 10, two or more collector bars 12 are provided for each cathode block 11. With this construction, even when one collector bar 12 is physically broken, the other collector bar(s) 12 will provide electrical connection.
[0068] According to the present embodiment, for each cathode block 11, two collector bars 12 are arranged in the longitudinal direction of the block, the two collector bars 12 being separated by the distance sp. In this construction, when a collector bar 12 thermally expands, stresses in the collector bar 12 in the longitudinal direction is allowed to escape. This prevents the collector bar 12 from deforming.
[0069] Preferably, the collector bars 12 are made of a carbon material with a lower electrical resistivity than the cathode block 11. For the cathode block 11, other properties than electric resistivity are required, such as reactivity with the content of the electrolytic bath 33 (see FIG. 1); accordingly, the selection of materials is limited to some degree. The collector bars 12 have no such limits and, as such, can be made of carbon materials with lower electric resistivities. This improves the electric conductivity of the cathode 10.
[0070] According to the present embodiment, the bus bars 36 (see FIG. 1) made of metal may be connected to the collector bars 12. The collector bars 12 and bus bars 36 need not be connected within the furnace at high temperatures. Thus, the difference in coefficient of thermal expansion between them does not pose a problem. Using bus bars 36 made of metal for connection reduces the overall electric resistance of the equipment.

-.

Our Ref. 338W0006P1 [0071] [Second Embodiment]
FIG. 9 is a perspective view of a cathode 15 according to a second embodiment of the present invention. The cathode 15 includes a cathode block 16 and two collector bars 17. According to the present embodiment, too, both the cathode block 16 and collector bars 17 are made of carbon.
[0072] The cathode block 16 is positioned on the top surface of the two collector bars 17. The bottom surface of the cathode block 16 is in contact with the top surfaces of the two collector bars 17 to establish electrical connection between the cathode block 16 and two collector bars 17.
[0073] In the cathode 10 (see FIG. 4) according to the first embodiment, the bottom surface of the cathode block 11 and the top surfaces of the collector bars 12 are flat. In contrast, in the cathode 15 according to the present embodiment, the bottom surface of the cathode block 16 is provided with grooves 16a, while the top surfaces of the collector bars 17 are provided with grooves 17a complementary to the grooves 16a.
[0074] According to the present embodiment, the contact area between the cathode block 16 and collector bars 17 is increased. Further, when the cathode block 16 is placed on the collector bars 17, the block can easily be aligned with the bars. Furthermore, during operation, the cathode block 16 and collector bars are prevented from being displaced.
[0075] Since the cathode 15 requires formation of the grooves 16a and grooves 17a, it requires more work steps than the cathode 10 (see FIG. 4).
Still, compared with the cathode 90 (see FIG. 5), the process is simplified since cast iron need not be poured in, for example.
[0076] In FIG. 9, the cathode block 16 and collector bars 17 include V-shaped grooves. Alternatively, any number of grooves may be provided and the groove(s) may take any shape. The groove(s) may be saw-shaped or curved.
[0077] [Third Embodiment]
FIG. 10 is a perspective view of a cathode 40 according to a third embodiment of the present invention. In the cathode 40, the collector bars 12 of the cathode 10 (see FIG. 4) are replaced by collector bars 42.
[0078] As with the collector bars 12, the collector bars 42 are made of carbon.
The collector bars 42 have a planar shape different from that of the collector bars 12. The width of some of the portions of the collector bars 42 that do not overlap the cathode block 11 as seen in plan view is smaller than the width of the bar portions that overlap the cathode block 11. Specifically, the , Our Ref. 338W0006P1 portions of the collector bars 42 that do not overlap the cathode block 11 as seen in plan view include terminal portions 42a that have smaller widths than the bar portions that overlap the cathode block 11.
[0079] According to the present embodiment, the collector bars 42 can be configured to extend to outside of the furnace body 30 (see FIG. 2) even in implementations where the slots 31a of the furnace body 30 have small openings. Specifically, a furnace body 30 that has been constructed presupposing the shape of the collector bars 92 of the cathode 90 (see FIG. 5) can be used without a design modification.
[0080] On the other hand, maintaining a large width of the bar portions that overlap the cathode block 11 maintains a large contact area between the bars and the cathode block 11, thereby providing a low contact resistance.
Further, a large cross-sectional area as measured in a plane perpendicular to the longitudinal direction provides a low resistance along the longitudinal direction.
[0081] [Fourth Embodiment]
FIG. 11 is a perspective view of a cathode 45 according to a fourth embodiment of the present invention. The cathode 45 includes a cathode block 46 and two collector bars 47. According to the present embodiment, too, both the cathode block 46 and collector bars 47 are made of carbon.
[0082] According to the present embodiment, the cathode block 46 and collector bars 47 are fastened together by screws 48. Female threads 46a are formed in the cathode block 46 to be used to fasten the screws 48, while through-holes 47a are formed in the collector bars 47 through which the screws 48 can be inserted.
[0083] As discussed above, even with the cathode block 46 simply put on the collector bars 47, thermal expansion of the lining 32 (see FIG. 1) and other factors cause pressure on the interface between the cathode block 46 and collector bars 47. However, for some constructions of the furnace, sufficient pressure may not be applied. Further, in some cases, greater pressure may be desired. Fastening the block and bars using screws 48, as in the present embodiment, enables adjusting the contact area pressure between the cathode block 46 and collector bars 47.
[0084] [Fifth Embodiment]
FIG. 12 is a perspective view of a cathode 50 according to a fifth embodiment of the present invention. The cathode 50 includes a cathode Our Ref. 338W0006P1 block 51 and two collector bars 52. According to the present embodiment, too, both the cathode block 51 and collector bars 52 are made of carbon.
[0085] Female threads 51a are formed on sides of the cathode block 51. A
male thread 52a is formed on one end of each collector bar 52 as determined along the longitudinal direction to be used to fasten the male thread to the female threads 51a. According to the present embodiment, fastening the male threads 52a and female threads 51a connects the cathode block 51 to the collector bars 52.
[0086] This embodiment, too, simplifies the process compared with implementations using the cathode 90 (see FIG. 5).
[0087] In FIG. 12, female threads 51a are formed in the cathode block 51, while male threads 52a are formed on the collector bars 52. Alternatively, male threads may be formed on the cathode block 51 and female threads may be formed on the collector bars 52.
[0088] [Sixth Embodiment]
FIG. 13 is a perspective view of a cathode 55 according to a sixth embodiment of the present invention. The cathode 55 includes a cathode block 56 and two collector bars 57. According to the present embodiment, too, both the cathode block 56 and collector bars 57 are made of carbon.
[0089] Recesses 56a are formed on sides of the cathode block 56. A
protrusion 57a is formed on one end of each collector bar 57 as determined along the longitudinal direction to be fitted into the associated recess 56a.
According to the present embodiment, fitting the protrusions 57a into the recesses 56a connects the cathode block 56 and collector bars 57.
[0090] This embodiment, too, simplifies the process compared with implementations using the cathode 90 (see FIG. 5).
[0091] In FIG. 13, recesses 56a are formed in the cathode block 56, while protrusions 57a are formed on the collector bars 57. Alternatively, protrusions may be formed on the cathode block 56 and recesses may be formed in the collector bars 57.
[0092] [Seventh Embodiment]
FIG. 14 is a perspective view of a cathode 60 according to a seventh embodiment of the present invention. According to the present embodiment, a cathode block 61 and collector bars 62 are integrally formed. That is, the cathode block 61 and collector bars 62 are fabricated by machining a single raw material. The cathode 60, composed of a cathode block 61 and collector Our Ref. 338W0006P1 bars 62 that are integrally formed, is made of carbon.
[0093] According to the present embodiment, the cathode block 61 and collector bar 62 are integrally formed, which means that there is no interface.
As such, contact resistance is zero.
[0094] [Eighth Embodiment]
FIG. 15 is a perspective view of a cathode 65 according to an eighth embodiment of the present invention. The cathode 65 includes a plurality of cathode blocks 11 and two collector bars 67. According to the present embodiment, too, the cathode blocks 11 and collector bars 67 are made of carbon.
[0095] According to the present embodiment, each of the two collector bars 67 is in contact with the plurality of cathode blocks 11. This construction achieves a large cross-sectional area of the collector bars 67, thereby reducing electrical resistance.
[0096] In FIG. 15, two collector bars 67 are both in contact with seven cathode blocks. Meanwhile, the above-described effects can be obtained if at least one collector bar 67 is in contact with a plurality of cathode blocks.
The number of cathode blocks is only required to be not smaller than 2.
That is, the cathode 65 is only required to include at least two cathode blocks (cathode block and second cathode block) and one or more collector bars, where at least one of the collector bars is in contact with at least two cathode blocks.
[0097] Although embodiments of the present invention have been described, the present invention is not limited to the above-illustrated embodiments and various modifications are possible within the scope of the invention.

Claims

1. A cathode for smelting metal, comprising:
a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block, wherein the cathode block has a flat bottom surface;
each of the one or more collector bars has a flat top surface; and the cathode block is positioned such that the bottom surface of the cathode block is in contact with the top surface of each of the one or more collector bars.

2. A cathode for smelting metal, comprising:
a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block, wherein the cathode block has a bottom surface provided with a groove;
each of the one or more collector bars has a top surface provided with a groove complementary to the groove of the cathode block; and the cathode block is positioned such that the bottom surface of the cathode block is in contact with the top surface of each of the one or more collector bars.

3. The cathode according to claim 1 or 2, wherein the one or more collector bars are two collector bars arranged in a longitudinal direction of the cathode block; and the two collector bars are spaced apart from each other.

4. The cathode according to any one of claims 1 to 3, wherein a width of at least part of a portion of the one or more collector bars that does not overlap the cathode block as seen in plan view is smaller than a width of a portion that overlaps the cathode block.

5. A cathode for smelting metal, comprising:
a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block, wherein the cathode further comprises a screw adapted to fasten the cathode block and the one or more collector bars together.

6. A cathode for smelting metal, comprising:
a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block, wherein the cathode block includes a male or female thread, or a protrusion or recess; and each of the one or more collector bars includes a female or male thread to be fastened to the male or female thread, or a recess into which the protrusion is to be fitted or a protrusion to be fitted into the recess.

7. The cathode according to any one of claims 1 to 6, wherein the one or more collector bars are made of a carbon material with a lower electrical resistivity than the cathode block.

8. A cathode for smelting metal, comprising:
a cathode block made of carbon; and one or more collector bars made of carbon, each positioned to be in contact with the cathode block, wherein the cathode further comprises a second cathode block; and at least one of the one or more collector bars is in contact with both the cathode block and the second cathode block.