Assembly process of composite cathode assembly

Abstract

The invention discloses an assembling process of a composite cathode group, which comprises the following steps: taking a graphitized carbon block subjected to primary impregnation and secondary roasting as a cathode carbon block body, performing material optimization and precision processing on the carbon block body to realize the balance of low resistance and high strength, improving the conductivity through a composite structure of steel and copper, and meanwhile, retaining the mechanical strength of the steel; and gapless assembly is realized through screw-thread fit and insulation filling. The invention relates to the technical field of electrolytic aluminum processing and manufacturing, in particular to an assembling process of a composite cathode assembly, which can remarkably reduce power consumption, prolong the service life of a tank body, reduce comprehensive cost and optimize a conductive structure.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytic aluminum processing and manufacturing, and in particular to an assembly process for a composite cathode group of an aluminum electrolytic cell. Background Art

[0002] In electrolytic aluminum production, the cathode group is the core component of the aluminum electrolytic cell. Its conductive performance, structural stability and service life directly affect the power consumption per ton of aluminum and the operating efficiency of the electrolytic cell.

[0003] Currently, the existing cathode assembly method has the following main problems:

[0004] Assembly material limitations: Cathode carbon blocks are often made of 50% high-graphite carbon blocks or single-baked graphitized carbon blocks; cathode steel rods are often made of steel materials such as Q195, SAE1006, or HYT2. 50% high-graphite carbon blocks offer greater compressive strength but higher resistivity, resulting in higher power consumption per ton of aluminum after operation. Single-baked graphitized carbon blocks have lower resistivity but lower compressive strength, and poor resistance to aluminum erosion, which is detrimental to extending the cell life. Steel, due to its inherent properties, is less conductive than metals like copper, aluminum, and silver, and has limited room for reducing its resistance, resulting in relatively limited conductivity.

[0005] Assembly process defects: When using paste for consolidation, the pressure drop between the steel rod and the carbon block is relatively high due to the influence of the paste material and manual skills; when using phosphorus pig iron for casting, gaps are easily generated due to the shrinkage of phosphorus pig iron, and the phosphorus pig iron itself has a high resistance due to the high content of carbon, silicon and phosphorus elements, and the effect of reducing the voltage drop is limited.

[0006] High overall energy consumption: The existing assembly method leads to large overall conductive loss in the cathode group, and the casting of phosphorus pig iron requires preheating, melting and other processes, which additionally increases energy consumption and costs.

[0007] Therefore, improvements need to be made to the existing problems. Summary of the Invention

[0008] In view of the above situation, in order to make up for the above existing defects, the present invention aims to solve the problems of "large conductive loss, short cell life and high assembly cost" in the existing cathode group assembly process, and provide a low-energy consumption, high-stability and easy-to-implement composite cathode group assembly process.

[0009] The present invention provides the following technical solution: an assembly process of a composite cathode group, comprising the following steps:

[0010] Step 1: Cathode carbon block pretreatment:

[0011] A single-impregnation and double-calcination graphitized carbon block is used as the cathode carbon block body. The carbon block body is optimized in material and precision processed to achieve a balance between low resistance and high strength. The specific process is as follows:

[0012] (1) Primary impregnation: Place the carbon blocks after primary calcination into the impregnation furnace, seal and evacuate, then inject low-quinoline medium-temperature asphalt. Maintain the pressure at 300-400℃ and 1.7-4MPa for 5-8 hours to allow the asphalt to fully penetrate the pores of the carbon blocks to increase the density of the carbon blocks.

[0013] (2) Secondary roasting: After the impregnation, the carbon blocks are cooled and then loaded into the roasting furnace and roasted for 8-25 days according to the preset process curve to remove volatiles and strengthen the bonding between the asphalt and the carbon blocks.

[0014] (3) Graphitization and processing: After the carbon block has been roasted twice and its end face is milled flat, it is placed in a graphitization furnace and energized with low voltage and high current for about 38 hours to complete graphitization to reduce the resistivity of the carbon block; after cooling to below 300°C, four through holes are processed on the carbon block body to replace the traditional slotted structure. The depth of the through holes matches the penetration length of the cathode steel rod; the hole is divided into a light hole section and a threaded section, wherein the threaded section is located in the middle of the hole and its length is about 1 / 3 of the hole depth to ensure its screwing stability.

[0015] Step 2: Preparation of copper-clad high-conductivity steel rod

[0016] The conductive properties are improved through the composite structure of steel and copper while retaining the mechanical strength of steel. The specific process is as follows:

[0017] (1) Steel rod base material processing: HYT2 high-conductivity pure iron is used to prepare round steel rods. The middle section of the steel rod is processed with a thread profile that matches the carbon block hole thread, and one end is rolled into a rectangular structure for welding with the busbar outside the slot.

[0018] (2) Copper embedding treatment: A through hole is opened in the axial direction of the steel rod, and a TU2 oxygen-free copper rod is selected to penetrate the through hole. The copper rod and the steel rod are required to be tightly combined without any gap; a space for the copper rod to expand at high temperature is reserved in the through hole, and finally an iron plug is used to weld and seal the steel rod hole to make a composite steel rod.

[0019] (3) Surface treatment: Shot blast the steel rod to remove the surface oxide layer and impurities to ensure good conductive contact.

[0020] Step 3: Assembly Preparation

[0021] (I) Pretreatment of auxiliary materials: prepare 4 groups of round aluminum silicate asbestos blocks for thermal insulation and buffering; use silicon carbide ramming material for insulation filling and silicon carbide fire clay for end sealing.

[0022] (2) Component inspection: Check the dimensional tolerance of the four holes of the cathode carbon block and the thread accuracy of the composite steel rod to ensure matching.

[0023] Step 4: Assembly and implementation

[0024] Gapless assembly is achieved through thread matching and insulation filling. The specific process is as follows:

[0025] (1) Bottom insulation padding: Place 4 groups of aluminum silicate asbestos blocks at the bottom of the 4 holes of the cathode carbon block respectively.

[0026] (2) Screw in and fix the steel rods: Insert the four copper-clad high-conductivity steel rods that have been shot blasted into the holes of the cathode carbon block according to the thread direction, and adjust the assembly shape, position and dimensional tolerance of the fixed steel rods and the carbon block.

[0027] (3) Gap filling: plug the gap between the carbon block hole and the steel rod with silicon carbide ramming material.

[0028] (4) End sealing: Apply 1mm thick silicon carbide fire clay to the 10cm area of ​​the steel rod at the end of the cathode carbon block.

[0029] As a preferred embodiment, the performance indicators of the carbon block are: compressive strength ≥ 26MPa, bulk density ≥ 1.68g / cm 3 , after graphitization, the resistivity is ≤10μΩ·m.

[0030] Preferably, the chemical composition and mass fraction of the round bar steel bar are: C≤0.1%, Si≤0.2%, Mn≤0.03%, P≤0.012%, S≤0.007%, Al≤0.05%, Cr≤0.02%, Ni≤0.02%, Cu≤0.05%, and Ti≤0.02%.

[0031] Preferably, the chemical composition of the copper rod and its mass fraction are: Cu+Ag≥99.95%, P≤0.002%, Bi≤0.001%, Sb≤0.002%, As≤0.002%, Fe≤0.004%, Ni≤0.002%, Pb≤0.004%, Sn≤0.002%, S≤0.004%, and Zn≤0.003%.

[0032] As a preferred performance index of the composite steel bar: resistivity ≤ 14×10 at 20°C -8 Ω·m, tensile strength ≥245MPa, lower yield strength ≥140MPa, elongation after fracture ≥25%, linear expansion coefficient α≤16×10 -6 .

[0033] The beneficial effects achieved by the present invention using the above structure are as follows:

[0034] 1. Significantly reduce power consumption: the resistivity of the graphitized carbon block after one-time impregnation and two-time roasting is ≤10μΩ·m (33%-50% lower than that of 50% high-graphite carbon block); the resistivity of the copper-clad steel rod is ≤14×10 -8Ω·m (11%-22% lower than traditional steel bars); the direct thread combination eliminates the ferrophosphorus / paste intermediate layer, effectively reducing the contact voltage drop; the three work together to save 300-500KWh of electricity per ton of aluminum, which can meet the 2025 policy requirement of 13,300KWh / tAl.

[0035] 2. Extend the life of the tank: the volume density of the graphitized carbon block after one-time impregnation and double calcination is ≥1.68g / cm 3 , compressive strength ≥ 26MPa (increased by 18%-44% compared with single-baked graphitized carbon blocks), and the resistance to aluminum water erosion is significantly enhanced; thread matching and silicon carbide material filling avoid the generation of gaps, improve structural stability, and help extend the life of the slot.

[0036] 3. Reduce overall costs: Eliminate the preheating and melting processes of phosphorus pig iron casting, saving energy per ton of cathode group; use a steel and copper composite structure instead of all-copper rods, reducing material costs and eliminating the material costs of paste and phosphorus pig iron; mechanized processing and standardized assembly reduce manual operations and improve the assembly qualification rate.

[0037] 4. Optimize the conductive structure: The conductive path is simplified from the traditional components of steel rods, ferrophosphorus, paste and carbon blocks to a combination of steel rods and carbon blocks, reducing one conductive interface. The threaded fit increases the contact area, reduces the current density per unit area, and significantly improves the conductive stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0039] Figure 1 Schematic diagram of the cathode group structure of the composite cathode group assembly process of the present invention (AA cross-sectional view);

[0040] Figure 2 Schematic diagram of the cathode carbon block structure (BB cross-sectional view) of the assembly process of the composite cathode group of the present invention;

[0041] Figure 3 Schematic diagram of the composite steel rod structure (CC cross-sectional view) of the assembly process of the composite cathode group of the present invention.

[0042] Among them, A1 is the cathode carbon block, A2 is the silicon carbide fireclay insulation layer, A3 is the composite steel rod group, A4 is the aluminum silicate asbestos block, A5 is the silicon carbide ramming material insulation layer; B1 is the cathode carbon block body, B2 is the hole 1, B3 is the threaded part of the hole, B4 is the hole 2;

[0043] C1, steel rod, C2, round copper rod, C3, expansion space, C4, iron plug, C11, square part of steel rod, C12, round part of steel rod, C13, threaded part. DETAILED DESCRIPTION

[0044] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] The implementation process of the present invention is described below with reference to specific parameters:

[0046] The cathode carbon block adopts a one-time impregnation and two-time roasting graphitized carbon block, and its indicators are as follows:

[0047] Compressive strength: after impregnation, compressive strength ≥ 26MPa; Bulk density: after impregnation, bulk density ≥ 1.68g / cm3; Resistivity: after graphitization, resistivity ≤ 10μΩ·m;

[0048] Single impregnation and double calcination graphitized carbon blocks: The carbon blocks that have been roasted once are placed in an impregnation furnace, sealed and vacuumed, injected with low-quinoline medium-temperature asphalt, and heated to 300℃-400℃. The pressure in the furnace reaches 1.7-4MPa and is maintained at pressure for 5-8 hours to fully penetrate the asphalt into the carbon blocks; after being taken out of the furnace and cooled, they are placed in a roasting furnace and roasted twice according to the roasting process curve. The roasting cycle is generally about 8 to 25 days; after the second roasting is completed, the two end faces of the long side of the roasted carbon blocks are milled flat using a machine tool, and then loaded into a graphitization furnace in batches. Low voltage and high current are energized to perform electric shock graphitization on the carbon blocks. The power-on time is about 38 hours. Subsequently, the power is turned off and cooled to below 300℃ before being taken out of the furnace. After cleaning, the carbon block products are obtained by machining.

[0049] The traditional slotting structure is eliminated in carbon block processing. Hole 1 B2 and hole 2 B4 are drilled from the end face of the cathode carbon block body B1. The hole depth is equal to the penetration length of the steel rod. A threaded hole B3 is opened in the middle part of the hole. The length of the threaded hole is about one-third of the hole depth.

[0050] The cathode steel rod is made of copper-clad high-conductivity steel rod, which can effectively reduce the resistance of the steel rod and the horizontal current. The cathode steel rod is made of HYT2 high-conductivity steel rod, and the copper-embedded copper rod is made of Tu2 oxygen-free copper. This ensures that the resistance of the steel rod and the horizontal current are reduced while reducing the material cost of the full copper part, thereby reducing costs.

[0051] The cathode steel rod and copper rod indicators are: steel rod resistivity: at 20℃, δ≤14×10-8Ω·m;

[0052] Mechanical properties are:

[0053]

[0054] The linear expansion coefficient of the steel bar is: 20℃~700℃, α≤16×10-6;

[0055] The chemical composition requirements of steel bars are:

[0056]

[0057] The chemical composition requirements of steel bars are:

[0058]

[0059] Among them, the steel rod adopts a round rod structure C12 throughout its length, and a tooth-shaped thread C13 is processed in the middle part. The thread length is similar to that of the carbon block thread. After being assembled with the carbon block, the end of the steel rod near the end of the carbon block is rolled into a rectangular structure C11, which is connected to the busbar at the outer end of the connecting groove.

[0060] Assembly of copper-clad high-conductivity steel rod: Insert the round copper rod C2 into the high-conductivity steel rod C1 with a hole. The copper and steel must be tightly combined without any gaps. A space C3 for the copper rod to expand at high temperature is left in the perforated section of the steel rod. Finally, the steel rod hole is welded and sealed with an iron plug C4.

[0061] Assembly process: Install four circular aluminum silicate asbestos blocks A4 into the bottom of the four holes of the cathode carbon block A1 respectively, and then insert the four copper-clad high-conductivity steel rods A3 that have been shot blasted into the respective holes of the cathode carbon block A1 according to the thread direction, and adjust the assembly shape and dimensional tolerances of the steel rods and the carbon block; then plug the gap between the carbon block hole B2 and the steel rod with silicon carbide ramming material A5, and finally apply a 1mm thick silicon carbide fireclay insulation layer A2 on the 10cm area of ​​the steel rod at the end of the cathode carbon block.

[0062] After actual testing, it was found that when the cathode group assembled by this process was operated in a 150KA electrolytic cell, the power consumption per ton of aluminum was reduced by about 420KWh, there was no obvious corrosion or loosening of the cell body, and the operating stability was excellent.

[0063] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, material, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, material, or apparatus.

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A composite cathode assembly process, characterized in that: The following steps are included: Step 1: Cathode carbon block pretreatment: A single-impregnation and double-calcination graphitized carbon block is used as the cathode carbon block body. The carbon block body is optimized in material and precision processed to achieve a balance between low resistance and high strength. The specific process is as follows: (1) Primary impregnation: Place the carbon blocks after primary calcination into the impregnation furnace, seal and evacuate, then inject low-quinoline medium-temperature asphalt. Maintain the pressure at 300-400℃ and 1.7-4MPa for 5-8 hours to allow the asphalt to fully penetrate the pores of the carbon blocks to increase the density of the carbon blocks. (2) Secondary roasting: After the impregnation, the carbon blocks are cooled and then loaded into the roasting furnace and roasted for 8-25 days according to the preset process curve to remove volatiles and strengthen the bonding between the asphalt and the carbon blocks. (3) Graphitization and processing: After the carbon block has been roasted twice and its end face is milled flat, it is placed in a graphitization furnace and energized with low voltage and high current for about 38 hours to complete graphitization to reduce the resistivity of the carbon block; after cooling to below 300°C, four through holes are processed on the carbon block body to replace the traditional slotted structure. The depth of the through holes matches the penetration length of the cathode steel rod; the hole is divided into a light hole section and a threaded section, wherein the threaded section is located in the middle of the hole and its length is about 1 / 3 of the hole depth to ensure its screwing stability. Step 2: Preparation of copper-clad high-conductivity steel rod The conductive properties are improved through the composite structure of steel and copper while retaining the mechanical strength of steel. The specific process is as follows: (1) Steel rod base material processing: HYT2 high-conductivity pure iron is used to prepare round steel rods. The middle section of the steel rod is processed with a thread profile that matches the carbon block hole thread, and one end is rolled into a rectangular structure for welding with the busbar outside the slot. (2) Copper embedding treatment: A through hole is opened in the axial direction of the steel rod, and a TU2 oxygen-free copper rod is selected to penetrate the through hole. The copper rod and the steel rod are required to be tightly combined without any gap; a space for the copper rod to expand at high temperature is reserved in the through hole, and finally an iron plug is used to weld and seal the steel rod hole to make a composite steel rod. (3) Surface treatment: Shot blast the steel rod to remove the surface oxide layer and impurities to ensure good conductive contact. Step 3: Assembly Preparation (I) Pretreatment of auxiliary materials: prepare 4 groups of round aluminum silicate asbestos blocks for thermal insulation and buffering; use silicon carbide ramming material for insulation filling and silicon carbide fire clay for end sealing. (2) Component inspection: Check the dimensional tolerance of the four holes of the cathode carbon block and the thread accuracy of the composite steel rod to ensure matching. Step 4: Assembly and implementation Gapless assembly is achieved through thread matching and insulation filling. The specific process is as follows: (1) Bottom insulation padding: Place 4 groups of aluminum silicate asbestos blocks at the bottom of the 4 holes of the cathode carbon block respectively. (2) Screw in and fix the steel rods: Insert the four copper-clad high-conductivity steel rods that have been shot blasted into the holes of the cathode carbon block according to the thread direction, and adjust the assembly shape, position and dimensional tolerance of the fixed steel rods and the carbon block. (3) Gap filling: plug the gap between the carbon block hole and the steel rod with silicon carbide ramming material. (4) End sealing: Apply 1mm thick silicon carbide fire clay to the 10cm area of ​​the steel rod at the end of the cathode carbon block.

2. The process for assembling a composite cathode assembly according to claim 1, wherein: The performance indicators of the carbon block are compressive strength ≥ 26MPa and bulk density ≥ 1.68g / cm 3 , after graphitization, the resistivity is ≤10μΩ·m.

3. The process for assembling a composite cathode assembly according to claim 1, wherein: The chemical composition and mass fraction of the round bar steel bar are: C≤0.1%, Si≤0.2%, Mn≤0.03%, P≤0.012%, S≤0.007%, Al≤0.05%, Cr≤0.02%, Ni≤0.02%, Cu≤0.05%, Ti≤0.02%.

4. The process for assembling a composite cathode assembly according to claim 1, wherein: The chemical composition and mass fraction of the copper rod are: Cu+Ag≥99.95%, P≤0.002%, Bi≤0.001%, Sb≤0.002%, As≤0.002%, Fe≤0.004%, Ni≤0.002%, Pb≤0.004%, Sn≤0.002%, S≤0.004%, and Zn≤0.003%.

5. The process for assembling a composite cathode assembly according to claim 1, wherein: The performance index of composite steel bar is: resistivity ≤14×10 at 20℃ -8 Ω·m, tensile strength ≥245MPa, lower yield strength ≥140MPa, elongation after fracture ≥25%, linear expansion coefficient α≤16×10 -6 .

Images