A method for preparing high-purity copper ingot

Abstract

The application discloses a preparation method of high-purity copper ingot, comprising the following steps: placing ultra-high-purity electrolytic copper in a graphite smelting crucible, and performing vacuum smelting in an electromagnetic rotary smelting furnace; first, starting a vacuum unit to vacuumize to below 0.1 Pa, performing first-stage heating to completely melt and degas the copper; closing the vacuum unit, injecting nitrogen, maintaining 2000 Pa low vacuum, performing second-stage heating, and starting electromagnetic stirring refining to remove high-melting-point metal impurities; vacuumizing again to below 0.1 Pa, performing third-stage heating, and taking out the crucible at a speed of 1-10 mm / min to perform directional solidification, and obtaining 6N copper ingot. The method adopts a three-stage heating program combined with multi-stage vacuum control, electromagnetic stirring refining and directional solidification technology, can effectively remove low-boiling-point components, high-melting-point metals and insoluble impurities in a single smelting process, and realizes stable preparation of 6N copper ingot. The method has the advantages of simple process flow, low equipment investment, high energy utilization efficiency, stable product quality and suitability for industrialized batch production.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy technology, specifically to a method for preparing high-purity copper ingots. Background Technology

[0002] 6N copper ingots (99.9999% purity) have a wide range of applications in modern industry and high-tech fields due to their ultra-low impurity content and excellent physical properties. For example, they are used in the physical vapor deposition (PVD) process of 7-nanometer and below advanced process chips to form highly conductive, low-defect integrated circuit interconnect layers; they are used to manufacture bonding wires with diameters as low as 18 micrometers (about 1 / 3 the thickness of a human hair) for chip packaging and high-frequency magnetic wires to improve signal transmission stability; and they are used as key components in nuclear medical equipment and high-energy physics experiments to build low-background radiation environments.

[0003] Existing processes for preparing 6N copper ingots mainly include electron beam refining and vacuum induction melting. However, high-purity copper ingots prepared using these methods suffer from high equipment investment, high energy consumption, and low efficiency, making them unsuitable for industrial production. Furthermore, the product yield is low due to process limitations. Therefore, developing a stable method for preparing 6N copper ingots is particularly necessary.

[0004] Patent CN121519159A discloses a process for preparing 6N high-purity single-crystal copper ingots. This method includes controlling the lifting and moving of a graphite ingot crucible and graphite plugging plate via a copper cooling base, combined with high-temperature smelting, heat preservation stirring, and unidirectional cooling steps to directly prepare 6N high-purity single-crystal copper ingots. However, this patent's technical solution mainly targets the preparation of single-crystal copper ingots. The process involves complex mechanical control and precise coordination of multiple temperature zones, resulting in a relatively complex equipment configuration and challenges to the stability and consistency of production operations.

[0005] Patent CN117265591A discloses a method for preparing 6N high-purity copper ingots. This method uses 2N copper as raw material and employs a two-step electrolysis and one-step smelting process. By adding hydrochloric acid to adjust the chloride ion concentration in the electrolyte and by pre-pressurizing and filtering the solution, the content of silver and other impurity ions in the ultra-high-purity copper is reduced, resulting in a total impurity element content of less than 1.517 ppm and a copper content of more than 99.999%. However, the technical solution of this patent has a relatively long process flow, requiring two electrolysis steps and one smelting step. The process involves many steps and requires high control over the electrolyte composition, making it difficult to maintain stable control of process parameters during large-scale industrial production.

[0006] Both of the above-mentioned existing technical solutions provide useful technical references for the preparation of 6N high-purity copper ingots, but there is still room for further improvement in terms of process simplification, equipment investment, production efficiency and product stability. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing high-purity copper ingots. The method aims to solve the problems of high equipment investment, high energy consumption, low efficiency, and low product qualification rate in existing technologies by using multi-stage vacuum and heating program control, combined with electromagnetic stirring purification and directional solidification technology, thereby achieving stable preparation of 6N copper ingots.

[0008] Includes the following steps:

[0009] S10: Place ultra-high purity electrolytic copper in a graphite melting crucible, cover it with a graphite cover plate, and place the graphite crucible in an electromagnetic rotary melting furnace for vacuum melting.

[0010] S20: First, start the vacuum unit. After the vacuum level inside the furnace is lower than 0.1 Pa, start a heating program.

[0011] S30: After a heating process is completed, turn off the vacuum unit and slowly inject nitrogen into the furnace;

[0012] S40: After the vacuum degree reaches 2000Pa, start the water ring vacuum pump to maintain the low vacuum in the furnace, and start the second stage heating program and electromagnetic stirrer to electromagnetically stir and refine the copper melt.

[0013] S50: After the second heating process is completed, turn off the electromagnetic stirrer and water ring vacuum pump, stop injecting nitrogen, and restart the vacuum unit.

[0014] S60: After the vacuum degree inside the furnace is lower than 0.1Pa, the three-stage heating program is started. At the same time, the graphite melting crucible containing copper melt is pulled out from the heating zone at a speed of 1-10mm / min for directional solidification to obtain 6N copper ingots.

[0015] This invention uses ultra-high purity electrolytic copper as raw material and employs vacuum melting in a graphite melting crucible. Combined with a three-stage heating process and multi-stage vacuum control, along with electromagnetic stirring refining and directional solidification technology, it can effectively remove low-boiling-point components, high-melting-point metals, and insoluble impurities from ultra-high purity electrolytic copper in a single melting process. This improves the purity of the copper ingot and enables the direct preparation of 6N copper ingots. The method has a relatively simple process flow and streamlined equipment configuration, making it suitable for industrial-scale mass production. It also ensures stable product quality and good batch consistency.

[0016] Furthermore, the ultra-high purity electrolytic copper used in step S10 is a 6N high-purity copper plate product electrolyzed using a nitric acid system. The nitric acid system electrolysis process effectively removes common impurity elements such as iron, zinc, lead, and nickel from copper, resulting in a 6N high-purity copper plate product with extremely low impurity content, making it suitable as the starting material for this method. By using the 6N high-purity copper plate product electrolyzed using a nitric acid system as raw material, the burden on subsequent refining processes can be reduced, which is beneficial for improving the final product's yield.

[0017] Furthermore, all graphite components used in the electromagnetic rotary melting furnace, including the graphite melting crucible and graphite cover plate, are purified twice, with a purity greater than 99.9999%. Graphite components may react with molten copper at high temperatures; insufficient purity in the graphite components can introduce additional impurities, affecting the purity of the final copper ingot. By using high-purity graphite components after double purification, impurities can be avoided from being introduced into the graphite material during the melting process, ensuring that the copper ingot purity meets the 6N requirement.

[0018] Furthermore, in step S20, the first heating stage is set at a temperature of 1250-1300℃ and a melting time of 1-2 hours. The main function of this first heating stage is to completely melt the ultra-high purity electrolytic copper to form a copper melt, while simultaneously degassing and removing impurities from the molten copper. Within the temperature range of 1250-1300℃, the molten copper exhibits good fluidity, allowing dissolved gaseous impurities such as hydrogen and oxygen to escape fully. Simultaneously, some low-boiling-point trace impurities can also be removed during this stage. Setting the temperature of this first heating stage below the boiling point of copper (approximately 2562℃) prevents violent evaporation of the molten copper, ensuring the stability of the melting process. Setting the melting time to 1-2 hours ensures complete melting of the molten copper and sufficient gas escape, while avoiding excessively long holding times that would increase energy consumption.

[0019] Furthermore, in step S30, nitrogen gas is slowly injected into the furnace at a uniform and controllable rate. The purpose of injecting nitrogen is to form an inert atmosphere protective layer on the surface of the molten copper, preventing oxidation in subsequent processes and creating suitable atmospheric conditions for the subsequent low-vacuum electromagnetic stirring refining. Nitrogen injection should be carried out slowly to avoid excessive gas flow causing fluctuations on the molten copper surface, which would affect the refining effect.

[0020] Furthermore, in step S40, the second-stage heating program is set at a temperature of 1100-1130℃, a melting time of 1-2 hours, and the electromagnetic stirring refining process involves 3-15 forward and reverse rotations at a speed of 5-25 r / min. The second-stage heating program's temperature is lower than the first-stage program's. Within the 1100-1130℃ temperature range, the copper liquid remains molten but has a relatively high surface tension, which is conducive to the formation of regular melt flow during electromagnetic stirring. In this temperature range, high-melting-point metal impurities (such as iron, nickel, and cobalt) and insoluble impurities have significant density differences. The circulating melt flow generated by electromagnetic stirring allows these impurity particles to float to the surface of the copper liquid, forming scum, which is easily removed later. The alternating forward and reverse rotation of the electromagnetic stirring enhances the mixing effect of the melt. Controlling the stirring speed within the range of 5-25 r / min ensures good stirring without causing violent splashing of the melt. The number of forward and reverse rotations should be controlled between 3 and 15 times. This ensures that impurities float to the surface while avoiding excessive stirring that could cause the melt to come into contact with the graphite crucible wall, thus increasing the risk of introducing impurities.

[0021] Furthermore, in step S40, the water ring vacuum pump is activated to maintain a low vacuum state inside the furnace. The water ring vacuum pump can operate stably under a low vacuum condition of around 2000 Pa. Combined with a nitrogen atmosphere, it can create a slight negative pressure environment on the surface of the molten copper, which is beneficial for the evaporation and removal of low-boiling-point impurities, while preventing oxidation caused by direct contact between the melt and air. The low vacuum environment can also reduce the oxidation tendency of the melt during electromagnetic stirring, improving the refining effect.

[0022] Furthermore, in step S50, after shutting down the electromagnetic stirrer and the water ring vacuum pump, nitrogen injection is stopped, and the vacuum unit is restarted to evacuate the gas inside the furnace, bringing the vacuum level below 0.1 Pa. The purpose of this step is to remove slag and gaseous products generated during the second-stage refining process, while simultaneously creating a high-vacuum environment for subsequent directional solidification. Under high-vacuum conditions, residual gaseous impurities in the molten copper can further escape, improving the density and purity of the copper ingot.

[0023] Furthermore, the temperature set for the three-stage heating process in step S60 is 1150-1200℃. This temperature setting is slightly higher than the two-stage heating process but lower than the one-stage process. Within this 1150-1200℃ temperature range, the molten copper maintains good fluidity and moderate viscosity, which is beneficial for the orderly growth of crystals during directional solidification. Setting the temperature sufficiently above the melting point of copper (1084.62℃) ensures that the molten copper is completely molten, preventing the formation of semi-molten zones during solidification that could affect the crystal structure.

[0024] Further, in step S60, a graphite melting crucible containing molten copper is uniformly pulled out of the heating zone at a speed of 1-10 mm / min for directional solidification. The graphite melting crucible is pulled out vertically downwards. Directional solidification technology, by controlling the solidification direction, allows the molten copper to gradually solidify from the bottom of the crucible upwards, forming a directionally grown columnar crystal structure. During solidification, remaining trace impurities accumulate at the solidification front, with a relatively high impurity concentration at the last solidified area. By controlling the pull-out speed, the high-impurity enrichment zone can be controlled at the head of the copper ingot, facilitating subsequent removal and improving overall purity. The pull-out speed is controlled within the range of 1-10 mm / min; too high a speed leads to an unstable solidification interface and disordered crystal growth direction; too slow a speed affects production efficiency. By adjusting the pull-out speed, a good balance can be achieved between crystal quality and production efficiency.

[0025] This application effectively removes low-boiling-point components, high-melting-point metals, and insoluble impurities from ultra-high purity electrolytic copper, thereby improving the purity of copper ingots and enabling the direct preparation of 6N copper ingots. The method employs multi-stage vacuum and heating program control, combining electromagnetic stirring purification with directional solidification technology, enabling stable production of 6N copper ingots with consistent product quality. Compared to existing technologies, the method of this application has a simpler process flow, relatively lower equipment investment, and higher energy efficiency, making it suitable for large-scale industrial production.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] First, the process is relatively simple, requiring only one vacuum melting process to complete the preparation of 6N copper ingots, avoiding the process complexity caused by multiple electrolysis processes in existing technologies.

[0028] Secondly, the equipment investment is relatively low. The production needs can be met by using an electromagnetic rotary melting furnace, without the need to purchase expensive electron beam melting equipment.

[0029] Third, it has high energy efficiency and a reasonable three-stage heating program design, which makes full use of the heat energy demand at different temperature stages.

[0030] Fourth, the product quality is stable. Through the combination of electromagnetic stirring refining and directional solidification technology, impurity elements can be effectively removed, resulting in good batch consistency.

[0031] Fifth, it is suitable for industrialized mass production, has a wide process parameter window, and relatively low requirements for equipment precision, which helps to reduce production costs. Detailed Implementation

[0032] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0033] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] The technical solutions of this application are described in detail below with reference to specific embodiments. These embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application.

[0036] This application provides a method for preparing high-purity copper ingots. The method includes using ultra-high purity electrolytic copper as raw material, vacuum melting through a graphite melting crucible, combined with a three-stage heating program and multi-stage vacuum control, and combining electromagnetic stirring refining and directional solidification technology to achieve stable preparation of 6N copper ingots.

[0037] In the specific implementation process, the first step is to prepare ultra-high purity electrolytic copper raw materials. This ultra-high purity electrolytic copper is a 6N high-purity copper plate product obtained through electrolysis using a nitric acid system. The nitric acid system electrolysis process can effectively remove common impurity elements such as iron, zinc, lead, and nickel from copper. The resulting 6N high-purity copper plate product has extremely low impurity content, making it suitable as the starting material for the method of this invention. The specific process of nitric acid system electrolysis is well known to those skilled in the art and will not be described in detail here. By using the 6N high-purity copper plate product obtained through nitric acid system electrolysis as raw material, the burden on subsequent refining processes can be reduced, which is beneficial to improving the yield of the final product.

[0038] When preparing graphite smelting crucibles and graphite covers, high-purity graphite components with a purity greater than 99.9999% after secondary purification are required. Graphite components may react with molten copper at high temperatures; insufficient purity in the graphite components will introduce additional impurities, affecting the purity of the final copper ingot. By using high-purity graphite components after secondary purification, impurities can be avoided from being introduced into the graphite material during the smelting process, ensuring that the copper ingot purity meets the 6N requirement. Secondary purification processes are well-known to those skilled in the art and include, but are not limited to, high-temperature purification and chlorine purification methods, and will not be elaborated upon here.

[0039] Ultra-high purity electrolytic copper is placed in a graphite melting crucible, covered with a graphite lid, and then placed in an electromagnetic rotary melting furnace for vacuum melting. Electromagnetic rotary melting furnaces are commonly used equipment in this field, and their structure and working principle are well known to those skilled in the art. An electromagnetic rotary melting furnace typically includes a furnace body, a vacuum system, a heating system, an electromagnetic stirring system, and a cooling system. The furnace body is made of stainless steel, with a high-temperature resistant material lining the inner wall. The vacuum system includes components such as a mechanical pump and a diffusion pump, capable of achieving a vacuum level below 0.1 Pa within the furnace. The heating system uses graphite heating elements or resistance heating to achieve uniform heating of the graphite melting crucible. The electromagnetic stirring system includes an electromagnetic coil and a stirring controller, enabling the rotational stirring of the molten copper.

[0040] Before initiating the first heating cycle, the vacuum unit is first activated to evacuate the copper material to be melted. Once the vacuum level inside the furnace is below 0.1 Pa, the first heating cycle is started. The temperature for the first heating cycle is set at 1250-1300℃, and the melting time is 1-2 hours. The main function of the first heating cycle is to completely melt the ultra-high purity electrolytic copper to form a copper melt, while simultaneously degassing and removing impurities from the molten copper. Within the temperature range of 1250-1300℃, the molten copper exhibits good fluidity, allowing dissolved gaseous impurities such as hydrogen and oxygen to escape fully, while some low-boiling-point trace impurities can also be removed during this stage. The temperature of the first heating cycle is set below the boiling point of copper (approximately 2562℃) to prevent violent evaporation of the molten copper and ensure the stability of the melting process. The melting time is set to 1-2 hours to ensure complete melting of the molten copper and sufficient gas escape, while avoiding excessively long holding times that would increase energy consumption.

[0041] Regarding specific temperature control, a heating program can employ a multi-stage heating approach. First, the temperature is raised from room temperature to 800℃, with the heating rate controlled at 5-10℃ / min to avoid excessive thermal stress on the graphite crucible due to rapid heating. Then, the temperature is raised from 800℃ to 1250-1300℃, with the heating rate controlled at 3-5℃ / min. After reaching the target temperature, the temperature is maintained stable for 1-2 hours. During this holding period, the vacuum unit operates continuously, maintaining a vacuum level below 0.1 Pa within the furnace. The vacuum unit can employ a combination of a mechanical pump and a diffusion pump; the mechanical pump is used for rough vacuuming, while the diffusion pump is used to achieve a high vacuum.

[0042] After a heating cycle is completed, the vacuum unit is shut down, and nitrogen is slowly injected into the furnace. The purpose of injecting nitrogen is to form an inert atmosphere protective layer on the surface of the molten copper, preventing oxidation in subsequent processes and creating suitable atmospheric conditions for the subsequent low-vacuum electromagnetic stirring refining. Nitrogen injection should be slow to avoid excessive airflow causing fluctuations in the copper surface, which would affect the refining effect. The purity of the nitrogen should be greater than 99.999% to avoid introducing new impurities. Nitrogen injection can be controlled using a mass flow controller, and the injection rate should be uniform and controllable. While injecting nitrogen, monitor the pressure changes inside the furnace. Once the vacuum level reaches 2000 Pa, proceed to the next process.

[0043] Once the vacuum level reaches 2000 Pa, the water ring vacuum pump is started to maintain the low vacuum inside the furnace. The second-stage heating program and electromagnetic stirrer are then activated to perform electromagnetic stirring and refining of the molten copper. The water ring vacuum pump can operate stably under a low vacuum of approximately 2000 Pa. Combined with a nitrogen atmosphere, this creates a slight negative pressure environment on the surface of the molten copper, which facilitates the evaporation and removal of low-boiling-point impurities while preventing oxidation from direct contact between the melt and air. The low vacuum environment also reduces the oxidation tendency of the melt during electromagnetic stirring, improving the refining effect.

[0044] The second-stage heating program is set at a temperature of 1100-1130℃, with a melting time of 1-2 hours. Within this temperature range, the molten copper remains in a molten state, but with high surface tension, which facilitates regular melt flow during electromagnetic stirring. In this temperature range, high-melting-point metal impurities (such as iron, nickel, and cobalt) and insoluble impurities have significant density differences. The molten fluid circulation generated by electromagnetic stirring allows these impurity particles to float to the surface of the molten copper, forming scum that is easily removed later. The second-stage heating program is set at a lower temperature than the first-stage program to prevent overheating of the molten copper and reduce energy consumption.

[0045] The electromagnetic stirring refining process involves 3-15 cycles of forward and reverse rotation, with a rotation speed of 5-25 r / min. Alternating forward and reverse rotation enhances the mixing of the melt. Maintaining a stirring speed of 5-25 r / min ensures good stirring without causing violent splashing of the melt. The 3-15 cycles of forward and reverse rotation ensure that impurities float to the surface while avoiding excessive stirring that could cause the melt to contact the graphite crucible wall, increasing the risk of impurity introduction. The specific parameters of the electromagnetic stirrer should be adjusted according to the furnace size and the volume of molten copper to achieve the optimal stirring effect.

[0046] During the two-stage heating and electromagnetic stirring refining process, the water ring vacuum pump operates continuously to maintain a low vacuum state inside the furnace. Nitrogen is continuously injected to maintain a nitrogen atmosphere inside the furnace. After slag forms, it can be skimmed off using specialized tools to remove it from the surface of the molten copper. The skimming operation should be performed gently to avoid agitating the molten copper and causing the slag to re-mix into the melt.

[0047] After the second-stage heating process is completed, turn off the electromagnetic stirrer and water ring vacuum pump, stop injecting nitrogen, and restart the vacuum unit. The purpose of this step is to remove slag and gaseous products generated during the second-stage refining process, and to create a high-vacuum environment for subsequent directional solidification. Under high-vacuum conditions, residual gaseous impurities in the molten copper can further escape, improving the density and purity of the copper ingots. After the vacuum unit is started, continue evacuation until the vacuum level inside the furnace drops below 0.1 Pa, then proceed to the next process.

[0048] Once the vacuum level inside the furnace drops below 0.1 Pa, the three-stage heating program is initiated. Simultaneously, the graphite melting crucible containing molten copper is uniformly pulled out of the heating zone at a speed of 1-10 mm / min for directional solidification. The temperature setting for the three-stage heating program is 1150-1200℃. This temperature setting is slightly higher than the two-stage heating program but lower than the first-stage program. Within this temperature range of 1150-1200℃, the molten copper maintains good fluidity and moderate viscosity, which is beneficial for the orderly growth of crystals during directional solidification. Setting the temperature sufficiently above the melting point of copper (1084.62℃) ensures that the molten copper is completely molten, avoiding the formation of semi-molten zones during solidification, which would affect the crystal structure.

[0049] The graphite melting crucible is pulled out of the heating zone vertically downwards. Directional solidification technology, by controlling the solidification direction, allows the molten copper to gradually solidify upwards from the bottom of the crucible, forming a directionally grown columnar crystal structure. During solidification, remaining trace impurities accumulate at the solidification front, with a relatively high impurity concentration at the last solidified area. By controlling the pull-out speed, the high-impurity enrichment zone can be controlled at the head of the copper ingot, facilitating subsequent removal and improving overall purity. The pull-out speed is controlled within the range of 1-10 mm / min. Too high a speed leads to an unstable solidification interface and disordered crystal growth direction; too slow a speed affects production efficiency. By adjusting the pull-out speed, a good balance can be achieved between crystal quality and production efficiency.

[0050] During directional solidification, a high vacuum is maintained inside the furnace, with a vacuum level below 0.1 Pa. This high vacuum environment facilitates the escape of residual gases from the molten copper, reducing porosity and defects within the copper ingot. Simultaneously, the cooling rate needs to be controlled during directional solidification to prevent excessively rapid cooling that could lead to excessive thermal stress and defects such as cracks. The cooling rate can be controlled by adjusting the pull-out speed and the furnace cooling system.

[0051] After directional solidification is completed, 6N copper ingots are obtained. After the copper ingots are removed from the graphite crucible, they can be further processed by cutting, grinding, etc., to remove the high impurity enrichment area at the head, thus obtaining the final 6N copper ingot product.

[0052] The technical solutions of this application are described in detail below through specific embodiments. However, these embodiments are only used to illustrate the technical solutions of this application and do not constitute a limitation on the scope of protection of this application.

[0053] Example 1

[0054] Ultra-high purity electrolytic copper was placed in a graphite melting crucible, covered with a graphite lid, and then placed in an electromagnetic rotary melting furnace for vacuum melting. First, the vacuum unit was started. Once the vacuum level inside the furnace was below 0.1 Pa, a heating program was initiated. The first heating program was set to a temperature of 1260℃ and a melting time of 1.5 hours. The specific operation process was as follows: First, the temperature was increased from room temperature to 800℃ at a rate of 8℃ / min, then increased to 1260℃ at a rate of 4℃ / min, and held at that temperature for 1.5 hours. During the holding period, the vacuum unit continued to operate, maintaining the vacuum level inside the furnace below 0.1 Pa.

[0055] After the first heating cycle is complete, the vacuum unit is shut down, and nitrogen is slowly injected into the furnace. The nitrogen injection rate is controlled between 5-10 L / min. Once the vacuum reaches 2000 Pa, the water ring vacuum pump is started to maintain a low vacuum inside the furnace, and the second heating cycle and electromagnetic stirrer are initiated. The second heating cycle is set at 1120℃, with a melting time of 1 hour. The electromagnetic stirring refining process involves 10 forward and reverse rotations at a speed of 10 r / min to refine the copper melt. During the second refining process, nitrogen is continuously injected to maintain the furnace pressure at approximately 2000 Pa. The water ring vacuum pump continues to run, maintaining a low vacuum. The electromagnetic stirrer operates according to the set number of forward and reverse rotations and speed, causing the copper melt to flow in a regular pattern and promoting the floating of impurities.

[0056] After the second heating stage is completed, the electromagnetic stirrer and water ring vacuum pump are turned off, nitrogen injection is stopped, and the vacuum unit is restarted. The vacuum unit continues to evacuate the furnace until the vacuum level inside the furnace is lower than 0.1 Pa, then the third heating stage is started. The temperature of the third heating stage is set at 1160℃. Simultaneously, the graphite melting crucible containing molten copper is pulled out of the heating zone at a uniform speed of 2 mm / min for directional solidification. During directional solidification, the vacuum level inside the furnace is maintained below 0.1 Pa, and the crucible is pulled out at a uniform and stable speed. After directional solidification, 6N copper ingots are obtained. The composition of the 6N copper ingots prepared in Example 1 is analyzed. The content of each impurity element is below the detection limit, and the copper content is greater than 99.9999%, meeting the purity requirements for 6N copper ingots.

[0057] Example 2

[0058] Ultra-high purity electrolytic copper was placed in a graphite melting crucible, covered with a graphite lid, and then placed in an electromagnetic rotary melting furnace for vacuum melting. First, the vacuum unit was started. Once the vacuum level inside the furnace was below 0.1 Pa, a heating program was initiated. The first heating program was set to a temperature of 1280℃ and a melting time of 1.2 hours. The specific operation process was as follows: First, the temperature was increased from room temperature to 800℃ at a rate of 8℃ / min, then increased to 1280℃ at a rate of 4℃ / min, and held at that temperature for 1.2 hours. During the holding period, the vacuum unit continued to operate, maintaining the vacuum level inside the furnace below 0.1 Pa.

[0059] After the first heating cycle is complete, the vacuum unit is shut down, and nitrogen is slowly injected into the furnace. The nitrogen injection rate is controlled between 5-10 L / min. Once the vacuum reaches 2000 Pa, the water ring vacuum pump is started to maintain a low vacuum inside the furnace, and the second heating cycle and electromagnetic stirrer are initiated. The second heating cycle is set at 1120℃, with a melting time of 1.1 hours. The electromagnetic stirring refining process involves 12 forward and reverse rotations at a speed of 10 r / min to refine the copper melt. During the second refining process, nitrogen is continuously injected to maintain the furnace pressure at approximately 2000 Pa. The water ring vacuum pump continues to run, maintaining a low vacuum. The electromagnetic stirrer operates according to the set forward and reverse rotation cycles and speed.

[0060] After the second heating stage is completed, the electromagnetic stirrer and water ring vacuum pump are turned off, nitrogen injection is stopped, and the vacuum unit is restarted. The vacuum unit continues to evacuate the furnace until the vacuum level inside the furnace is lower than 0.1 Pa, then the third heating stage is started. The temperature of the third heating stage is set at 1170℃. Simultaneously, the graphite melting crucible containing molten copper is pulled out of the heating zone at a uniform speed of 5 mm / min for directional solidification. During directional solidification, the vacuum level inside the furnace is maintained below 0.1 Pa, and the crucible is pulled out at a uniform and stable speed. After directional solidification, 6N copper ingots are obtained. The composition of the 6N copper ingots prepared in Example 2 is analyzed. The content of each impurity element is below the detection limit, and the copper content is greater than 99.9999%, meeting the purity requirements for 6N copper ingots.

[0061] Example 3

[0062] Ultra-high purity electrolytic copper was placed in a graphite melting crucible, covered with a graphite lid, and then placed in an electromagnetic rotary melting furnace for vacuum melting. First, the vacuum unit was started. Once the vacuum level inside the furnace was below 0.1 Pa, a heating program was initiated. The first heating program was set to a temperature of 1250℃ and a melting time of 2 hours. The specific operation process was as follows: First, the temperature was increased from room temperature to 800℃ at a rate of 8℃ / min, then increased to 1250℃ at a rate of 4℃ / min, and held at that temperature for 2 hours. During the holding period, the vacuum unit continued to operate, maintaining the vacuum level inside the furnace below 0.1 Pa.

[0063] After the first heating cycle is complete, the vacuum unit is shut down, and nitrogen is slowly injected into the furnace. The nitrogen injection rate is controlled between 5-10 L / min. Once the vacuum reaches 2000 Pa, the water ring vacuum pump is started to maintain a low vacuum inside the furnace, and the second heating cycle and electromagnetic stirrer are initiated. The second heating cycle is set to a temperature of 1100℃, a melting time of 2 hours, and the electromagnetic stirring refining process is controlled to 15 forward and reverse rotations at a speed of 5 r / min, refining the copper melt using electromagnetic stirring. During the second refining process, nitrogen is continuously injected to maintain the furnace pressure at approximately 2000 Pa. The water ring vacuum pump continues to run, maintaining a low vacuum. The electromagnetic stirrer stirs according to the set number of forward and reverse rotations and speed.

[0064] After the second heating stage is completed, the electromagnetic stirrer and water ring vacuum pump are turned off, nitrogen injection is stopped, and the vacuum unit is restarted. The vacuum unit continues to evacuate the furnace until the vacuum level inside the furnace is lower than 0.1 Pa, then the third heating stage is started. The temperature of the third heating stage is set at 1150℃. Simultaneously, the graphite melting crucible containing molten copper is pulled out of the heating zone at a uniform speed of 1 mm / min for directional solidification. During directional solidification, the vacuum level inside the furnace is maintained below 0.1 Pa, and the crucible is pulled out at a uniform and stable speed. After directional solidification, 6N copper ingots are obtained. The composition of the 6N copper ingots prepared in Example 5 is analyzed. The content of each impurity element is below the detection limit, and the copper content is greater than 99.9999%, meeting the purity requirements for 6N copper ingots.

[0065] The above embodiments demonstrate that the 6N copper ingot preparation method provided in this application can stably produce copper ingot products that meet the 6N purity requirements under different process parameter conditions. The process parameter window is wide, making it suitable for industrial-scale mass production. By adjusting the first-stage heating temperature, the second-stage heating temperature, the electromagnetic stirring parameters, and the pulling speed, the process conditions can be optimized within a certain range to adapt to different production needs.

[0066] The table below shows the results of compositional analysis of the 6N copper ingots prepared in Examples 1-3.

[0067]

[0068] This application uses ultra-high purity electrolytic copper as raw material, and employs vacuum melting in a graphite melting crucible. Combined with a three-stage heating process and multi-stage vacuum control, along with electromagnetic stirring refining and directional solidification technology, it can effectively remove low-boiling-point components, high-melting-point metals, and insoluble impurities from ultra-high purity electrolytic copper in a single melting process. This improves the purity of the copper ingot and enables the direct preparation of 6N copper ingots. The method has a relatively simple process flow and streamlined equipment configuration, making it suitable for industrial-scale mass production. The product quality is stable, and batch consistency is good.

[0069] Compared with existing technologies, this application has the following advantages: First, the process flow is relatively simple, requiring only one vacuum melting process to complete the preparation of 6N copper ingots, avoiding the process complexity caused by multiple electrolysis processes in existing technologies; Second, the equipment investment is relatively low, as an electromagnetic rotary melting furnace can meet production needs without the need to purchase expensive electron beam melting equipment; Third, the energy utilization efficiency is high, with a reasonable three-stage heating program design that fully utilizes the heat energy requirements at different temperature stages; Fourth, the product quality is stable, as the combination of electromagnetic stirring refining and directional solidification technology can effectively remove impurity elements, resulting in good batch consistency; Fifth, it is suitable for industrial mass production, with a wide process parameter window and relatively low requirements for equipment precision, which helps to reduce production costs.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing high-purity copper ingots, characterized in that, Includes the following steps: S10: Place ultra-high purity electrolytic copper in a graphite melting crucible, cover it with a graphite cover plate, and place the graphite crucible in an electromagnetic rotary melting furnace for vacuum melting. S20: First, start the vacuum unit. After the vacuum level inside the furnace is lower than 0.1 Pa, start a heating program. S30: After a heating process is completed, turn off the vacuum unit and slowly inject nitrogen into the furnace; S40: After the vacuum degree reaches 2000Pa, start the water ring vacuum pump to maintain the low vacuum in the furnace, and start the second stage heating program and electromagnetic stirrer to electromagnetically stir and refine the copper melt. S50: After the second heating process is completed, turn off the electromagnetic stirrer and water ring vacuum pump, stop injecting nitrogen, and restart the vacuum unit. S60: After the vacuum degree inside the furnace is lower than 0.1Pa, the three-stage heating program is started. At the same time, the graphite melting crucible containing copper melt is pulled out from the heating zone at a speed of 1-10mm / min for directional solidification to obtain 6N copper ingots.

2. The preparation method according to claim 1, characterized in that, The ultra-high purity electrolytic copper used in step S10 is a 6N high-purity copper plate product electrolyzed using a nitric acid system.

3. The preparation method according to claim 1, characterized in that, The graphite smelting crucible and graphite cover plate used in step S10 are both purified twice, with a purity greater than 99.9999%.

4. The preparation method according to claim 1, characterized in that, In step S20, the temperature of a heating program is set to 1250-1300℃, and the melting time is 1-2 hours.

5. The preparation method according to claim 1, characterized in that, In step S40, the temperature of the two-stage heating process is set to 1100-1130℃, and the melting time is 1-2 hours.

6. The preparation method according to claim 1, characterized in that, In step S40, the electromagnetic stirring refining process involves 3-15 reversals, with a rotation speed of 5-25 r / min.

7. The preparation method according to claim 1, characterized in that, The temperature set in the three-stage heating program of step S60 is 1150-1200℃.

8. The preparation method according to claim 1, characterized in that, In step S60, the graphite melting crucible is pulled out in a vertically downward direction.

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