Long-service-life anode steel claw for aluminum electrolysis and preparation method of long-service-life anode steel claw

Abstract

The invention discloses a long-life anode steel claw for aluminum electrolysis and a preparation method thereof, and relates to the technical field of aluminum electrolysis. Comprising a steel beam and a claw head, a base body of the steel beam is structural steel, the strength of the structural steel is larger than or equal to 230 MPa, a metal tungsten layer is arranged on the outer circumferential surface of the side face of the claw head, the bottom end face of the claw head and an annular belt area extending upwards from the bottom end face by 10-20 mm are not covered with the metal tungsten layer, and a non-plating area is formed; the thickness of the metal tungsten layer is 20-50 [mu] m, and the measured value of the interface bonding strength of the metal tungsten layer and the steel substrate under the test condition of 950 DEG C is not lower than 100 MPa. The service life of the anode steel claw can be greatly prolonged, and the problem that the aluminum electrolysis economic and technical indexes are affected by resistance increase caused by thinning of the claw head of the anode steel claw is solved.

Description

Technical Field

[0001] This invention relates to the field of aluminum electrolysis technology, and in particular to a long-life aluminum electrolysis anode steel claw and its preparation method. Background Technology

[0002] The anode steel claw is a key component in aluminum electrolysis production, undertaking multiple tasks such as connecting the aluminum guide rod to the anode carbon block, conducting the powerful DC current throughout the cell, and suspending and supporting the weight of the anode. Its performance and lifespan directly affect the operational stability, energy consumption, and production cost of the electrolytic cell.

[0003] During aluminum electrolysis, the anode steel claws are immersed for extended periods in a high-temperature, highly corrosive electrolyte melt exceeding 900°C and an atmosphere of volatile fluorides. This extreme environment causes severe high-temperature oxidation and fluorination corrosion in the ordinary structural steel claws, with the typical failure mode manifesting as a gradual reduction in the claw diameter due to corrosion. This phenomenon leads to two serious consequences: firstly, the reduced conductive cross-sectional area results in increased resistance, causing additional voltage drops and energy losses, worsening key technical and economic indicators such as DC power consumption in aluminum electrolysis; secondly, the deterioration of mechanical strength poses significant safety risks, potentially leading to major accidents such as anode detachment. Therefore, when the claw tip corrodes to a safety threshold, the machine must be shut down and replaced. Currently, the average replacement cycle for anode steel claws in the industry is generally between 18 and 40 months. Frequent replacements not only incur high spare parts costs but also cause substantial production losses due to downtime.

[0004] To address this issue, the industry has attempted to coat the steel claws with corrosion-resistant coatings. For example, Chinese patent CN202011230887.5 discloses an anti-corrosion steel claw for aluminum electrolysis anodes, which extends its lifespan by welding a nickel-chromium alloy layer onto the claw feet. However, the aluminum electrolysis environment is an extreme condition involving high temperatures, highly corrosive molten salts, oxidizing atmospheres, and periodic thermal shock. Directly applying the technology described in the paper to steel claws encounters numerous challenges, such as: insufficient interfacial bonding leading to easy peeling; cracking and peeling of the coating and substrate due to differences in thermal expansion coefficients under long-term high temperatures and thermal shock; localized corrosion failure; complex claw head shapes and uneven current distribution leading to preferential corrosion in weak areas of the coating; and stringent requirements for conductivity, meaning the coating cannot significantly increase resistance, affecting electrolysis efficiency.

[0005] In summary, existing coating protection solutions either suffer from unsatisfactory protection lifespan due to issues with adhesion and density, or have limited effectiveness due to insufficient corrosion resistance of the materials themselves. Therefore, there is an urgent need in the field for a novel anode steel claw that can form a strong bond with the substrate, is extremely stable, and provides a long-lasting physical barrier, as well as its preparation method. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a long-life anode steel claw for aluminum electrolysis and its preparation method, which can significantly improve the service life of the anode steel claw and solve the problem that the increased resistance caused by the thinning of the anode steel claw tip affects the economic and technical indicators of aluminum electrolysis.

[0007] The specific technical solution is as follows: In a first aspect, the present invention discloses a long-life aluminum electrolysis anode steel claw, comprising a steel beam and a claw head. The outer circumferential surface of the side of the claw head is provided with a tungsten metal layer. The bottom end face of the claw head and the annular area extending upward from the bottom end face for 10-20 mm are not covered by the tungsten metal layer, forming a non-plated area. The thickness of the tungsten metal layer is 20-50 μm, and the measured value of the interfacial bonding strength between the tungsten metal layer and the steel substrate under the test condition of 950℃ is not less than 100 MPa.

[0008] Preferably, the thickness of the tungsten metal layer is 30-45 μm.

[0009] Preferably, the tungsten metal layer is a continuous coating composed of dense columnar crystals.

[0010] Preferably, the steel beam is obtained by selectively cutting and processing discarded anode steel claws to be recycled.

[0011] Secondly, this invention discloses a method for preparing a long-life aluminum electrolysis anode steel claw, comprising the following steps: a) Preparation of molten salt electrolyte: Prepare molten salt electrolyte by mixing Na2WO4, ZnO and WO3 in a mass ratio of 6:2:2, allowing the mass ratio to fluctuate within ±2%, and heat the molten salt to 900-950℃; b) After surface treatment of the claw blank, place it in a molten salt electroplating tank. The upper part of the claw is 80-120mm above the electrolyte liquid level, and the bottom of the claw is covered with a 10-20mm corundum tube sleeve. The inner diameter of the corundum tube sleeve is 2mm larger than the diameter of the claw. c) Electroplating is performed on the claw surface at a current density of 40-100 mA / cm² for 20-60 min. The electroplating is performed using pulse power supply with a pulse period of 50-200 ms, a forward-reverse current ratio of 2-5:1, and a forward-reverse current ratio of 5-10:1, so as to form a 20-50 μm thick tungsten metal layer on the claw surface. d) After electroplating, remove the workpiece and remove the corundum tube sleeve; assemble the claw with the formed tungsten metal layer and the steel beam into a complete anode steel claw by welding.

[0012] Preferably, the electroplating in step c is performed using a DC steady-state power supply.

[0013] Preferably, in step c, the claw surface is electroplated with a current density of 90-100 mA / cm² for 40-60 min, with a pulse period of 120-200 ms, a forward-reverse current ratio of 4-5:1, and a forward-reverse current ratio of 7-10:1, so that a tungsten metal layer with a thickness of 40-50 μm is formed on the claw surface.

[0014] Preferably, in step c, the claw surface is electroplated with a current density of 90 mA / cm² for 55 min. The electroplating is performed using pulse power supply with a pulse period of 180 ms, a forward-reverse energizing time ratio of 5:1, and a forward-reverse current ratio of 9:1.

[0015] Preferably, in step c, the claw surface is electroplated with a current density of 100 mA / cm² for 60 min. The electroplating is performed using pulse power supply with a pulse period of 200 ms, a forward-reverse current ratio of 5:1, and a forward-reverse current ratio of 8:1.

[0016] Preferably, the claw is preheated to 300~500°C under a protective atmosphere and then placed in a molten salt electroplating bath.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention successfully solves the problem of early failure caused by corrosion thinning of the anodic steel claw by preparing a 20-50μm tungsten layer on the surface of the claw tip. The voltage drop of the steel claw remains below 50mV, which is stable and at an excellent level in the industry, avoiding the problem of voltage drop exceeding 15mV above normal levels in thinner claws. The service life of the anodic steel claw is significantly increased from the traditional 18-40 months to 72-120 months, an improvement of 2-6 times.

[0018] This invention benefits from the excellent corrosion resistance of the tungsten layer and its strong metallurgical bond with the substrate, ensuring the stable conductivity of the steel claw throughout its entire life cycle, and providing a key guarantee for the stable and efficient operation of the aluminum electrolysis cell.

[0019] The extended lifespan of this invention directly reduces the purchase cost of steel claws and the maintenance cost of frequent replacements, while also saving energy due to stable resistance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the anode steel claw structure of the present invention; Figure 2 This is a schematic diagram of the electroplating process of the present invention.

[0021] In the attached diagram, 1-steel beam, 2-claw head, 3-tungsten metal layer, 4-non-plating area, 5-corundum tube sleeve, 6-electroplating tank, 7-electroplating solution, and 8-cathode wire. Detailed Implementation

[0022] The embodiments of the invention will be described in further detail below with reference to the accompanying drawings, so that the objectives, technical solutions and technical effects of the invention will be more clearly presented.

[0023] Example 1: This example provides a long-life aluminum electrolysis anode steel claw and its preparation method, which is applied to an aluminum electrolysis cell. The anode steel claw includes a steel beam 1 and a claw head 2. The claw heads 2 are vertically and evenly distributed at the bottom of the steel beam 1 and are spaced apart along the length of the steel beam 1. The steel beam 1 is welded to a guide rod, and one end of the claw head 2 is inserted into the carbon bowl of the anode carbon block. It is fixedly connected to the carbon block by casting with phosphorus pig iron, thereby forming an integral anode structure.

[0024] Both the steel beam 1 and the claw head 2 are made of structural steel with a tensile strength of not less than 230 MPa. A tungsten layer 3 is provided on a localized surface of the claw head 2. The bottom surface of the claw head 2 and the annular area extending 20 mm upwards from the bottom surface are not covered by the tungsten layer 3, nor is the area where the claw head 2 connects with the guide rod covered by the tungsten layer 3. The tungsten layer 3 is directly formed on the surface of the claw head 2 substrate using a high-temperature molten salt electroplating process, with a thickness of 30 μm. Under cross-sectional microscopic observation, the coating structure is dense and continuous, forming a strong metallurgical bond with the substrate, and an Fe-W interdiffusion zone is visible at the interface. The specific preparation method includes the following steps: First, the surface of claw head 2 is pretreated by mechanically grinding and polishing the raw claw head 2 blank to remove surface oxide scale and burrs, achieving a surface finish of Ra≤1.6μm. Then, degreasing and ultrasonic cleaning are performed. Finally, the surface is preheated to 400℃ under argon protection and held for 30 minutes. Molten salt electrolyte is prepared by mixing Na2WO4, ZnO, and WO3 in a mass ratio of 6:2:2, with an actual mass ratio of 5.9:2.0:2.03, which is within the allowable fluctuation range of ±2%. The molten salt electrolyte is placed in electroplating tank 6 and heated to 920℃ and maintained at a constant temperature to form electroplating solution 7.

[0025] A corundum tube sleeve 5 is fitted onto the bottom of the claw head 2. The inner diameter of the corundum tube sleeve 5 extends 20mm above the bottom of the claw head 2, and the inner diameter of the corundum tube sleeve 5 is 2mm larger than the diameter of the claw head 2. Figure 2 As shown. The upper end of the claw head 2 is connected to the cathode wire 8. The upper end of the claw head 2 is 100mm above the electrolyte liquid surface. The inner diameter of the corundum tube sleeve 5 is 2mm larger than the diameter of the claw head 2.

[0026] Next, high-temperature molten salt electroplating is performed. The pre-treated claw head 2 blank is placed in the electroplating tank 6 as the cathode. The surface of the claw head 2 is electroplated for 20 minutes with an average current density of 80mA / cm² using a pulse power supply method. The pulse parameters are set to a period of 100ms, a forward and reverse current ratio of 3:1, and a forward and reverse current ratio of 6:1.

[0027] After electroplating, the tungsten metal layer 3 is fully inspected, and any minor areas with poor plating are repaired by local re-electroplating. Finally, the claw 2 with the tungsten metal layer 3 formed is welded to the steel beam 1 to form a complete anode steel claw.

[0028] After the anode steel claws obtained in the above steps were put into industrial testing, the test data showed that their service life reached 84 months, while the average service life of ordinary anode steel claws without tungsten coating was only 15 months, representing a 5.6-fold increase in service life. During service, the voltage drop of the steel claws of the present invention remained stable below 50mV, while the voltage drop of ordinary steel claws rose to 65-70mV after 10 months. The interfacial bonding strength was tested by scratch method, and the measured value at 950℃ was 115MPa. SEM scanning electron microscopy showed that the coating was a dense columnar crystal structure with a porosity of less than 1%. EDS line scanning confirmed the presence of an Fe-W interdiffusion layer at the interface, with a thickness of about 2μm, forming a strong metallurgical bond. Through finite element analysis to simulate thermal stress, the design of the uncoated area 4 reduced the thermal stress at the bottom of the claw head 2 by 30%, effectively reducing crack initiation.

[0029] Example 2: This example provides another long-life anode steel claw for aluminum electrolysis. Its basic structure is the same as in Example 1, except that the thickness of the tungsten layer 3 is 35μm, and the bottom surface of the claw head 2 and the annular area extending 10mm upward from the bottom surface are not covered by the tungsten layer 3. The main difference between the preparation method and Example 1 lies in the electroplating parameters: pulse power supply is used, the average current density is 70mA / cm², the electroplating time is 30 minutes, the pulse period is 50ms, the ratio of forward to reverse current is 2:1, and the ratio of forward to reverse current is 5:1. Industrial application data shows that its service life is as long as 90 months, while the service life of the ordinary steel claw is 40 months, which is 2.25 times longer. The measured value of the interface bonding strength at 950℃ is 120MPa. Coating characterization shows that the columnar crystal size is uniform, the width is 0.5-1μm, the corrosion resistance is significantly improved, and there is no corrosion after 240 hours of salt spray testing. The voltage drop of the steel claw remains below 50mV throughout the service life, and the conductivity is stable.

[0030] Example 3: This example provides another long-life anode steel claw for aluminum electrolysis. Its basic structure is the same as in Example 1, except that the thickness of the tungsten layer 3 is 45 μm, and the bottom surface of the claw head 2 and the annular area extending 20 mm upward from the bottom surface are not covered by the tungsten layer 3. The steel beam 1 is newly processed. The main difference between the preparation method and Example 1 lies in the electroplating parameters: pulse power supply is used, the average current density is 60 mA / cm², the electroplating time is 40 minutes, the pulse period is 200 ms, the ratio of forward to reverse current is 5:1, and the ratio of forward to reverse current is 10:1. The industrial test life reaches 120 months, which is 4 times longer than the 30 months of ordinary steel claws. The measured value of the interface bonding strength at 950℃ is 122 MPa. In the accelerated corrosion test of molten salt at 960℃ in a simulated electrolysis environment for 1000 hours, the coating weight loss is only 0.5 mg / cm², which is much lower than the 15 mg / cm² of ordinary steel claws. The accelerated corrosion test shows that the coating of the present invention maintains excellent performance under extreme conditions.

[0031] Example 4: This example demonstrates an implementation scheme using DC steady-state electroplating. The basic product structure is the same as in Example 1, except that the thickness of the tungsten layer 3 is 50 μm. The main difference in the preparation method compared to Example 1 is the use of DC steady-state power supply with a current density of 40 mA / cm² and an electroplating time of 60 minutes. The industrial test lifespan is 96 months, which is 4 times longer than the 24 months of ordinary steel claws. The interfacial bonding strength was measured at 950°C to be 105 MPa. Although the coating density is slightly lower than that of pulse electroplating, with a porosity of 2%, the process control is simpler, and the cost is reduced by 20%, making it more economical.

[0032] Example 5: This example demonstrates another implementation scheme using DC steady-state electroplating. The basic product structure is the same as in Example 1, except that the thickness of the tungsten layer 3 is 20 μm. The preparation method uses DC steady-state power supply with a current density of 100 mA / cm² and an electroplating time of 20 minutes. The industrial test lifespan is 72 months, which is twice that of ordinary steel claws (36 months). This solution is suitable for short-term, high-efficiency protection needs, achieving rapid production while ensuring basic performance.

[0033] Comparative Example: An anode steel claw with the same substrate material and structure as in Example 1 was used, but the claw head 2 had no protective coating. Under the same industrial environment, the average service life of the comparative example was between 15 and 40 months, far shorter than that of the embodiments of the present invention. Failure analysis showed that the diameter of the claw head 2 in the comparative example decreased by 30% due to corrosion, resulting in a voltage drop exceeding 70 mV and a 15% increase in resistance. Through comparison of system test data, the inventiveness of the present invention was fully demonstrated: the design of the non-plated area 4, combined with a specific tungsten coating, solved the corrosion failure problem of the anode steel claw in a high-temperature electrolytic environment, increasing its service life by 2-6 times, and the data was reproducible.

[0034] The samples from Examples 1-3 of this invention (using pulse electroplating), Comparative Example 1 (uncoated), and Comparative Example 2 (using conventional thermal spraying nickel-based alloy coating) were tested under the same conditions, and the results are shown in the table below: The voltage drop of the anode steel claw in an aluminum electrolysis cell directly affects energy consumption and efficiency. The claw head 2, as a key component in the current path, needs to maintain low and stable resistance. Tungsten coating itself has excellent conductivity, but if the coating cracks or peels due to thermal stress, it will significantly increase contact resistance, leading to a higher voltage drop. This invention eliminates stress concentration caused by geometric discontinuities by setting an unplated area 4 on the bottom surface of the claw head 2 and in a ring extending upwards for ten to twenty millimeters, thereby preventing coating cracking during thermal cycling. Finite element analysis shows that this design reduces the peak thermal stress in the bottom region by more than 30%, effectively preventing coating damage. Experimental data confirms that the uncoated steel claw in Comparative Example 1 experienced a voltage rise to 65 to 75 millivolts after ten months of service, while the tungsten-plated sample in Comparative Example 3 experienced increased voltage drop fluctuations due to thermal shock cracking. Conversely, the voltage drop in all embodiments of this invention remained stable below fifty millivolts throughout the process. This is because the design of the unplated area 4 ensures coating integrity and avoids a sudden increase in resistance. This effect of achieving global voltage drop stability through a local unplated area 4 is a non-obvious innovation not previously disclosed in the art.

[0035] High interfacial bonding strength is a prerequisite for ensuring that the coating does not peel off at high temperatures, and coating peeling directly increases contact resistance. This invention forms an iron-tungsten interdiffusion layer through high-temperature molten salt electroplating, achieving a measured bonding strength of 115 to 125 MPa, far exceeding the 30 to 50 MPa of conventional coatings. This metallurgical-grade bonding allows the coating and substrate to deform collaboratively under thermal expansion differences, avoiding the resistance increase caused by interfacial microcracks. The long-term stability of the voltage drop in the examples directly benefits from the coating durability resulting from this high-strength bonding.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the patent application of the present invention. All equivalent changes, substitutions or modifications made within the technical spirit and principles indicated by the present invention should be included within the scope of patent protection covered by the present invention.

Claims

1. A long-life aluminum electrolysis anode steel claw, comprising a steel beam and a claw head, characterized in that: The outer circumferential surface of the claw head is provided with a tungsten metal layer. The bottom end face of the claw head and the annular area extending upward from the bottom end face for 10-20 mm are not covered by the tungsten metal layer, forming an unplated area. The thickness of the tungsten metal layer is 20-50 μm, and the measured value of the interfacial bonding strength between the tungsten metal layer and the steel substrate under the test condition of 950℃ is not less than 100 MPa.

2. The long-life aluminum electrolysis anode steel claw according to claim 1, characterized in that: The thickness of the tungsten metal layer is 30-45 μm.

3. The long-life aluminum electrolysis anode steel claw according to claim 1, characterized in that: The tungsten metal layer is a continuous coating composed of dense columnar crystals.

4. The long-life aluminum electrolysis anode steel claw according to claim 1, characterized in that: The steel beams are obtained by selectively cutting and processing discarded anode steel claws to be recycled.

5. A method for preparing a long-life aluminum electrolysis anode steel claw according to any one of claims 1-4, characterized in that, Includes the following steps: a) Preparation of molten salt electrolyte: Prepare molten salt electrolyte by mixing Na2WO4, ZnO and WO3 in a mass ratio of 6:2:2, allowing the mass ratio to fluctuate within ±2%, and heat the molten salt to 900-950℃; b) After surface treatment of the claw blank, place it in a molten salt electroplating tank. The upper part of the claw is 80-120mm above the electrolyte liquid level, and the bottom of the claw is covered with a 10-20mm corundum tube sleeve. The inner diameter of the corundum tube sleeve is 2mm larger than the diameter of the claw. c) Electroplating is performed on the claw surface at a current density of 40-100 mA / cm² for 20-60 min. The electroplating is performed using pulse power supply with a pulse period of 50-200 ms, a forward-reverse current ratio of 2-5:1, and a forward-reverse current ratio of 5-10:1, so as to form a 20-50 μm thick tungsten metal layer on the claw surface. d) After electroplating, remove the workpiece and remove the corundum sleeve; assemble the claw with the formed tungsten metal layer to the steel beam by welding to form a complete anode steel claw.

6. The method for preparing a long-life aluminum electrolysis anode steel claw according to claim 5, characterized in that: The electroplating process described in step c is performed using a steady-state DC power supply.

7. The method for preparing a long-life aluminum electrolysis anode steel claw according to claim 5, characterized in that: In step c, the claw surface is electroplated with a current density of 90-100 mA / cm² for 40-60 min, with a pulse period of 120-200 ms, a forward-reverse current ratio of 4-5:1, and a forward-reverse current ratio of 7-10:1, so as to form a 40-50 μm thick tungsten metal layer on the claw surface.

8. The method for preparing a long-life aluminum electrolysis anode steel claw according to claim 5, characterized in that: In step c, the claw surface is electroplated with a current density of 90 mA / cm² for 55 min. The electroplating is performed using pulse power supply with a pulse period of 180 ms, a forward-reverse current ratio of 5:1, and a forward-reverse current ratio of 9:

1.

9. The method for preparing a long-life aluminum electrolysis anode steel claw according to claim 5, characterized in that: In step c, the claw surface is electroplated with a current density of 100 mA / cm² for 60 min. The electroplating is performed using pulse power supply with a pulse period of 200 ms, a forward-reverse current ratio of 5:1, and a forward-reverse current ratio of 8:

1.

10. The method for preparing a long-life aluminum electrolysis anode steel claw according to claim 5, characterized in that: Preheat the claw to 300~500℃ under a protective atmosphere, and then place it in a molten salt electroplating bath.

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