Process for producing high-purity oxygen-free copper rod by up-drawing method

Abstract

The invention provides a process for producing a high-purity oxygen-free copper rod by an up-drawing method. The process comprises the following steps: (1) pretreating raw materials; (2) gradient smelting and impurity removal; (3) deoxidizing the molten copper liquid; (4) transferring and filtering the deoxidized copper liquid; and (5) up-casting. By means of the process, unification of high purity and excellent mechanical performance is achieved, the core lies in the synergistic effect of a multi-stage oxygen removal mechanism and precise physical isolation, it is ensured that lattice oxygen is thoroughly removed, and no impurity is left.

Description

Technical Field

[0001] The invention belongs to the technical field of copper-based conductor material manufacturing, and particularly relates to a production process for high-purity oxygen-free copper rods using an up-drawing method. Background Art

[0002] High-purity oxygen-free copper rod is a critical foundational material for modern power transmission systems and precision electronic devices. This type of copper rod is primarily used in core applications, such as transformer coils, conductive bridge arms of vacuum circuit breakers, and electromagnetic cavities in particle accelerators. Two key properties are essential for practical application: an oxygen content below 10 ppm to prevent high-temperature hydrogen embrittlement and a conductivity exceeding 100% IACS to reduce current transmission losses. However, currently available products suffer from significant application limitations. First, there is the issue of grain boundary oxidation embrittlement. Copper rod produced by conventional continuous casting processes typically has an oxygen content of 15-30 ppm. Under high-temperature operating conditions, the copper oxide phase formed at the grain boundaries can reduce the material's elongation by over 40%. Second, there is the degradation of electrical conductivity. The widely used phosphorus copper deoxidation process can leave residual phosphorus content exceeding 0.02%, reducing electron mobility by over 5%. Even more serious is the risk of rod breakage and failure. Micron-sized alumina inclusions formed during the smelting process can block the flow path of the graphite mold during upward drawing and casting, directly causing wire breakage on the production line.

[0003] In response to the above problems, the existing technology has proposed a variety of solutions. The first solution uses gas-shielded smelting technology, filling the smelting furnace with argon to isolate oxygen. This method is found in a Chinese patent document. However, actual applications have shown that the density of argon is greater than the deoxygenated bubbles floating inside the liquid copper, making it difficult to effectively expel the dissolved oxygen adsorbed at the bottom of the molten pool, and the residual oxygen content of the final product is still at the level of 8ppm. The second solution uses carbon-based materials to cover the surface of the copper liquid, such as the calcined petroleum coke covering layer proposed in a Japanese patent. This solution is prone to oversaturation of carbon elements and the generation of hard copper carbide particles under continuous high-temperature conditions, which ultimately causes surface cracking during cold bending of copper rods. The third solution attempts composite deoxidizer technology. Although the calcium-boron alloy deoxidizer disclosed in a US patent can reduce the oxygen content, the volatile calcium vapor will seriously contaminate the graphite inner wall of the crystallizer, shortening the service life of the equipment to one-third of the normal period.

[0004] Existing technologies still face three core challenges that need to be addressed: First, secondary oxidation during the melt transfer process. When the copper melt comes into contact with air during transfer from the smelting furnace to the holding furnace, the surface layer can gain oxygen at a rate of up to 3 ppm per minute. Second, deoxidation efficiency is insufficient. Conventional deoxidizers can only remove dissolved oxygen but not interstitial oxygen within the crystal lattice, resulting in an actual deoxidation efficiency of less than 82%. Therefore, a process for producing high-purity oxygen-free copper rods using an up-drawing method is needed. Summary of the Invention

[0005] In order to overcome the defects in the prior art, a process for producing high-purity oxygen-free copper rods by an up-drawing method is provided.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A process for producing high-purity oxygen-free copper rods by an up-drawing method, comprising the following steps in sequence: (1) Raw material pretreatment: 99.99% pure electrolytic copper plate is sandblasted and dried to obtain a pretreated copper plate; (2) Gradient smelting and impurity removal: The pretreated copper plate is used as raw material for smelting to obtain a molten copper solution with a dissolved oxygen content of ≤18 ppm; (3) Deoxidation of molten copper liquid: laying a composite oxygen barrier layer on the surface of the molten copper liquid and adding a composite deoxidizer to the molten copper liquid, stirring at 95-105 rpm for 85-95 minutes to obtain a deoxidized copper liquid with lattice oxygen ≤ 2.5 ppm; (4) Transfer and filtration of deoxidized copper liquid: The deoxidized copper liquid is transferred to the holding furnace through a sealed channel, and then the inclusions are removed through a step filtration device to obtain clean copper liquid; (5) Upward casting: The clean copper liquid is cast upward in the crystallizer to produce the cast rod blank.

[0007] The specific steps of raw material pretreatment are: sandblasting a 99.99% pure electrolytic copper plate to a surface roughness of Ra ≤ 1.6 μm, and then drying it in a drying furnace at 180-190° C. for 2.0-2.2 hours to obtain a copper substrate with a moisture content of ≤ 40 ppm.

[0008] The smelting process is carried out in an induction melting furnace, and its specific parameters are: controlling the heating rate at 10-12°C / min to a melting temperature of 1220-1235°C, keeping the temperature at 400-410V for 33-37 minutes, and simultaneously introducing high-purity nitrogen containing 0.5-0.8% hydrogen and an oxygen content of ≤0.3 ppm from the bottom of the furnace, and maintaining the gas flow at 0.8-1.0 cubic meters per hour, ultimately producing a molten copper liquid with a dissolved oxygen content of ≤18 ppm.

[0009] The composite oxygen barrier layer comprises a lower layer of 6-8 cm thick calcined coconut shell carbon and calcium fluoride mixture and an upper layer of 3-5 cm thick flake graphite. The composite oxygen barrier layer forms an oxygen diffusion coefficient of ≤1×10 -9 cm² / s oxygen barrier system; The mass ratio of the calcined coconut shell charcoal to the calcium fluoride mixture is (88-92):10.

[0010] The preparation method of the calcined coconut shell charcoal comprises: calcining coconut shells with a particle size of 3-5 mm in argon at 1300-1350° C. for 4.5-5.5 hours, then soaking them in a 10-12 wt% oxalic acid solution at a temperature of 40-45° C. for 1.5-2.0 hours, and then washing them with water to a pH value of 6.5-7.0 to obtain calcined coconut shell charcoal with an ash content of ≤0.02%.

[0011] In parts by mass, the composite deoxidizer comprises 50-54 parts of activated lanthanum powder, 26-30 parts of calcium fluoride, and 18-20 parts of lithium borate. The amount of the composite deoxidizer added is 0.09-0.11% of the mass of the molten copper. The preparation method of the activated lanthanum powder is as follows: 99.52 wt% crude lanthanum ingot is heated to 650-680 ° C in an atmosphere with a volume ratio of Ar to H2 of 95:5 for 30-40 minutes, and finally water atomized to obtain a 200-300 mesh powder, which is the activated lanthanum powder, wherein the surface oxide layer of the activated lanthanum powder is ≤10nm.

[0012] The sealed channel is a double-layer gas curtain channel transferred to a 1145-1165°C holding furnace. The double-layer gas curtain channel is divided into an inner layer and an outer layer, wherein the inner layer is -5 to -10 Pa nitrogen and the outer layer is 1.0-1.2 MPa nitrogen. The oxygen increase during the transfer process is ≤0.2ppm.

[0013] The specific steps of removing inclusions in the step-by-step filtration device are as follows: the transferred deoxidized copper solution flows sequentially through a silicon carbide foam ceramic filter layer with a pore size of 50-60 μm and a zirconium oxide filter plate with a pore size of 20-30 μm and a titanium nitride-coated surface, and the inclusions are ≤15 / 100 mm. 2 Clean copper liquid.

[0014] The surface of the zirconia filter plate is covered with a titanium nitride coating, which is formed by a physical vapor deposition process. After deposition, the titanium nitride coating is vacuum annealed at 1100-1150° C. for 0.5-1 hour. The thickness of the titanium nitride coating is 0.8-1.2 μm, and the Vickers hardness is ≥1800 HV.

[0015] The specific steps and parameters of the upward casting are as follows: adding clean copper liquid into the crystallizer, setting the cooling water zone temperature / flow rate, wherein the upper section is 22-25°C / 0.3-0.5 m / s, the middle section is 28-32°C / 1.2-1.5 m / s, and the lower section is 38-42°C / 0.8-1.0 m / s, and the pulling speed is 2.8-3.2 m / min, and the cast rod blank with a diameter of 8.0±0.1 mm is produced.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. During the raw material pretreatment stage, this application effectively reduces the surface roughness and moisture content of the copper substrate through sandblasting and drying. This significantly reduces the risk of oxidation of the electrolytic copper plate during the subsequent smelting process. Lower roughness and moisture content means higher initial cleanliness and lower residual impurities before smelting, thereby reducing the possibility of impurity oxidation after smelting.

[0017] 2. This application utilizes an induction melting furnace combined with a reducing atmosphere for gradient smelting and impurity removal, enabling deep removal of dissolved oxygen. By controlling the heating rate and melting temperature, and maintaining the smelting temperature at a specific operating voltage, we ensure uniform heat distribution within the molten copper. Simultaneously, the introduction of high-purity nitrogen containing a small amount of hydrogen promotes the reduction reaction, effectively removing oxide particles from the molten copper, and achieving extremely low oxygen levels, preventing impurities from combining to form macromolecular compounds at high temperatures.

[0018] 3. During the deoxidation process of the molten copper, we designed a combined mechanism of a composite oxygen barrier and a composite deoxidizer. The composite oxygen barrier adopts a multi-layer structure. The lower layer is mainly composed of a mixture of calcined coconut shell charcoal and calcium fluoride, providing a physical barrier to restrict oxygen diffusion, and the upper layer uses flake graphite to enhance sealing. This, combined with the synergistic effect of composite deoxidizers such as activated lanthanum powder and lithium borate, chemically reduces the dissolved oxygen in the copper solution. The special treatment of the activated lanthanum powder enhances its reactivity, enabling it to quickly combine with oxygen atoms, while the calcium fluoride assists in forming a slag that is easily filtered and removed later. This dual deoxidation mechanism ensures the complete removal of lattice oxygen and significantly improves the chemical stability of the copper solution.

[0019] 4. During the transfer and filtration steps, our double-layered gas curtain channel and cascade filtration device minimizes exposure of the molten copper. The inner layer of negative-pressure nitrogen and the outer layer of high-pressure nitrogen create a closed environment, cutting off air contact and preventing oxygen re-infiltration. The cascade filtration utilizes a multi-level aperture design of silicon carbide and zirconium oxide filter plates to physically capture tiny inclusions. A special surface coating treatment enhances high-temperature corrosion resistance and achieves highly efficient impurity interception. This ensures the cleanliness of the molten copper, providing a foundation for the casting stage.

[0020] 5. During the pull-up casting stage, we optimized the mold cooling parameters, setting temperature and flow rates in different zones for precise thermal management. Different cooling rates in the upper, middle, and lower sections ensured fine and evenly distributed copper grains during solidification. Appropriate pull-up speeds controlled the diameter and structure of the as-cast rod, avoiding dendrite defects. This improved the overall density and mechanical strength of the as-cast rod, facilitating subsequent deformation processing. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0022] In this application, the sources of various raw materials are briefly described as follows: Electrolytic copper plate: produced by Jiangxi Copper Group Co., Ltd., brand CU-CATH-1, in compliance with GB / T 467-2010 standard, purity 99.99%.

[0023] Calcium fluoride: industrial-grade product of Hubei Xingfa Chemical Group Co., Ltd., model XFC-01, purity ≥98%.

[0024] Coconut shell raw material (for the preparation of calcined coconut shell charcoal): 3-5 mm particles provided by Hainan Yebao Food Co., Ltd., natural and untreated.

[0025] Oxalic acid: analytical grade reagent from Sinopharm Chemical Reagent Co., Ltd., CAS 144-62-7, product number H1002.

[0026] Lithium borate: high-purity reagent from Changsha Tianjiu New Materials Technology Co., Ltd., model LBO-4N, purity 99.99%.

[0027] Crude lanthanum ingot (activated lanthanum powder raw material): Ganzhou Qiandong Rare Earth Group Co., Ltd. brand La-99.5, purity 99.52 wt%.

[0028] Argon: high-purity gas from Hangzhou Oxygen Generator Group Co., Ltd., model Ar-5N, purity 99.999%.

[0029] Hydrogen: High-purity gas from Linde Gas (China) Co., Ltd., model H2-5N, purity 99.999%.

[0030] Nitrogen: Ultra-high purity gas from Shanghai Baosteel Gas Co., Ltd. of Baowu Group, model N2-6N, oxygen content ≤0.3ppm.

[0031] Flake graphite: Product of Qingdao Heilong Graphite Co., Ltd., model FL-199, fixed carbon content ≥99%.

[0032] Silicon carbide foam ceramic filter layer: customized filter material from Shandong Industrial Ceramics Research and Design Institute Co., Ltd., pore size 50-60 μm, item number SiC-60P.

[0033] Zirconia filter plate substrate: Product of Guangdong Oriental Zirconium Technology Co., Ltd., model ZrO2-T500.

[0034] Titanium nitride target: Xi'an Noble Rare Metal Materials Co., Ltd.'s special target for physical vapor deposition, model TiN-01, purity 99.95%.

[0035] The technical solution of the present application is: a production process for high-purity oxygen-free copper rods by up-drawing method, which comprises the following steps in sequence: (1) Raw material pretreatment: 99.99% pure electrolytic copper plate is sandblasted and dried to obtain a pretreated copper plate; (2) Gradient smelting and impurity removal: The pretreated copper plate is used as raw material for smelting to obtain a molten copper solution with a dissolved oxygen content of ≤18 ppm; (3) Deoxidation of molten copper liquid: laying a composite oxygen barrier layer on the surface of the molten copper liquid and adding a composite deoxidizer to the molten copper liquid, stirring at 95-105 rpm for 85-95 minutes to obtain a deoxidized copper liquid with lattice oxygen ≤ 2.5 ppm; (4) Transfer and filtration of deoxidized copper liquid: The deoxidized copper liquid is transferred to the holding furnace through a sealed channel, and then the inclusions are removed through a step filtration device to obtain clean copper liquid; (5) Upward casting: The clean copper liquid is cast upward in the crystallizer to produce the cast rod blank.

[0036] The specific steps of raw material pretreatment are: sandblasting a 99.99% pure electrolytic copper plate to a surface roughness of Ra ≤ 1.6 μm, and then drying it in a drying furnace at 180-190° C. for 2.0-2.2 hours to obtain a copper substrate with a moisture content of ≤ 40 ppm.

[0037] The smelting process is carried out in an induction melting furnace, and its specific parameters are: controlling the heating rate at 10-12°C / min to a melting temperature of 1220-1235°C, keeping the temperature at 400-410V for 33-37 minutes, and simultaneously introducing high-purity nitrogen containing 0.5-0.8% hydrogen and an oxygen content of ≤0.3 ppm from the bottom of the furnace, and maintaining the gas flow at 0.8-1.0 cubic meters per hour, ultimately producing a molten copper liquid with a dissolved oxygen content of ≤18 ppm.

[0038] The composite oxygen barrier layer comprises a lower layer of 6-8 cm thick calcined coconut shell charcoal and calcium fluoride mixture and an upper layer of 3-5 cm thick flake graphite. The composite oxygen barrier layer forms an oxygen barrier system with an oxygen diffusion coefficient of ≤1×10-9 cm² / s. The mass ratio of the calcined coconut shell charcoal to the calcium fluoride mixture is 88-92:10.

[0039] The preparation method of the calcined coconut shell charcoal comprises: calcining coconut shells with a particle size of 3-5 mm in argon at 1300-1350° C. for 4.5-5.5 hours, then soaking them in a 10-12 wt% oxalic acid solution at a temperature of 40-45° C. for 1.5-2.0 hours, and then washing them with water to a pH value of 6.5-7.0 to obtain calcined coconut shell charcoal with an ash content of ≤0.02%.

[0040] In parts by mass, the composite deoxidizer comprises 50-54 parts of activated lanthanum powder, 26-30 parts of calcium fluoride, and 18-20 parts of lithium borate. The amount of the composite deoxidizer added is 0.09-0.11% of the mass of the molten copper. The preparation method of the activated lanthanum powder is as follows: 99.52 wt% crude lanthanum ingot is heated to 650-680 ° C in an atmosphere with a volume ratio of Ar to H2 of 95:5 for 30-40 minutes, and finally water atomized to obtain a 200-300 mesh powder, which is the activated lanthanum powder, wherein the surface oxide layer of the activated lanthanum powder is ≤10nm.

[0041] The sealed channel is a double-layer gas curtain channel transferred to a 1145-1165°C holding furnace. The double-layer gas curtain channel is divided into an inner layer and an outer layer, wherein the inner layer is -5 to -10 Pa nitrogen and the outer layer is 1.0-1.2 MPa nitrogen. The oxygen increase during the transfer process is ≤0.2ppm.

[0042] The specific steps of removing inclusions in the step-by-step filtration device are as follows: the transferred deoxidized copper liquid flows sequentially through a silicon carbide foam ceramic filter layer with a pore size of 50-60 μm and a zirconium oxide filter plate with a pore size of 20-30 μm and a titanium nitride-coated surface, to obtain a clean copper liquid with inclusions ≤15 / 100 mm2.

[0043] The surface of the zirconia filter plate is covered with a titanium nitride coating, which is formed by a physical vapor deposition process. After deposition, the titanium nitride coating is vacuum annealed at 1100-1150° C. for 0.5-1 hour. The thickness of the titanium nitride coating is 0.8-1.2 μm, and the Vickers hardness is ≥1800 HV.

[0044] The specific steps and parameters of the upward casting are as follows: adding clean copper liquid into the crystallizer, setting the cooling water zone temperature / flow rate, wherein the upper section is 22-25°C / 0.3-0.5 m / s, the middle section is 28-32°C / 1.2-1.5 m / s, and the lower section is 38-42°C / 0.8-1.0 m / s, and the pulling speed is 2.8-3.2 m / min, and the cast rod blank with a diameter of 8.0±0.1 mm is produced.

[0045] The core advantage of this process lies in the complete removal of oxygen from the molten copper lattice through the physical isolation of gradient melting and compound oxygen barrier layer, synergistically with the deep chemical reduction of the composite deoxidizer; combined with the double-layer air curtain sealing protection of the transfer process and the precise interception of the stepped filtration device, it ensures that impurity particles are almost zero residual; finally, relying on the upward casting strategy of the zoned cooling strategy, while maintaining the oxygen-free characteristics, the copper rod obtains a uniform and dense grain structure and high ductility, comprehensively achieving a stable combination of high conductivity and excellent mechanical properties, avoiding the performance degradation risks commonly seen in traditional processes.

[0046] The technical solution of the present invention is further illustrated by the following examples and comparative examples, but the protection scope of the present invention is not limited thereto.

[0047] Example 1 A process for producing high-purity oxygen-free copper rods by an upward-drawing method comprises the following steps: (1) raw material pretreatment: a 99.99% pure electrolytic copper plate is sandblasted to a surface roughness Ra of 1.6 μm, and then dried in a drying furnace at 190°C for 2.1 hours to obtain a copper substrate with a moisture content of 40 ppm. (2) gradient melting and impurity removal: the pretreated copper plate is melted in an induction melting furnace at a controlled heating rate of 11°C / min to 1228°C, and kept at this temperature for 35 minutes at a working voltage of 410V. At the same time, high-purity nitrogen gas containing 0.65% hydrogen (oxygen content ≤ 0.3 ppm) is introduced from the bottom of the furnace, and the gas flow rate is maintained at 0.9 cubic meters per hour. The final output is a molten copper liquid with a dissolved oxygen content not exceeding 18 ppm. (3) Deoxidation of molten copper: A composite oxygen barrier layer was laid on the surface of the molten copper, wherein the lower layer was a 7 cm thick mixture of calcined coconut shell charcoal and calcium fluoride (the mass ratio of the calcined coconut shell charcoal and calcium fluoride mixture was 90:10), and the upper layer was a 4 cm thick flake graphite, forming an oxygen barrier system with an oxygen diffusion coefficient not exceeding 1×10-9 cm² / s; at the same time, a composite deoxidizer (52 parts of activated lanthanum powder, 28 parts of calcium fluoride, and 19 parts of lithium borate) was added in an amount of 0.10% of the mass of the molten copper, and stirred at 100 rpm for 90 minutes to obtain a deoxidized copper solution with a lattice oxygen content not exceeding 2.5 ppm. The preparation method of calcined coconut shell charcoal is as follows: 4 mm particle size coconut shell was calcined in argon at 1325℃ for 5 hours, then soaked in 11wt% oxalic acid solution at 42.5℃ for 1.75 hours, and then washed with water until the pH value was 6.75, to obtain calcined coconut shell charcoal with an ash content not exceeding 0.02%. The preparation method of activated lanthanum powder is as follows: 99.52 wt% crude lanthanum ingot is heated to 665℃ for 35 minutes in an atmosphere with a volume ratio of Ar to H2 of 95:5, and finally water atomized to obtain 200-300 mesh powder, and the surface oxide layer of the activated lanthanum powder does not exceed 10nm. (4) Transfer and filtration of deoxidized copper liquid: The deoxidized copper liquid is transferred to a 1155℃ holding furnace through a double-layer gas curtain channel, wherein the inner layer is -7.5 Pa nitrogen and the outer layer is 1.1 MPa nitrogen. The oxygen increase during the transfer process does not exceed 0.2ppm; then, it passes through a step filtration device, sequentially passing through a silicon carbide foam ceramic filter layer with a pore size of 55 μm and a zirconium oxide filter plate with a pore size of 25 μm and a titanium nitride-coated surface, to obtain a clean copper liquid with no more than 15 inclusions / 100 mm². The surface of the zirconia filter plate is covered with a titanium nitride coating formed by a physical vapor deposition process. After deposition, the titanium nitride coating is vacuum annealed at 1125°C for 0.75 hours. The thickness of the titanium nitride coating is 1.0 μm and the Vickers hardness is not less than 1800 HV. (5) Upward casting: Clean copper liquid is added to the crystallizer. The cooling water temperature and flow rate are set as follows: 24°C and 0.4 m / s in the upper section, 30°C and 1.35 m / s in the middle section, and 40°C and 0.9 m / s in the lower section. The pulling speed is 3.0 m / min, and a cast rod blank with a diameter of 8.0 mm is produced.

[0048] Example 2 In this embodiment, the same points as in Example 1 are not described in detail, and the differences are as follows: A process for producing high-purity oxygen-free copper rods by an upward-drawing method comprises the following steps: (1) raw material pretreatment: a 99.99% pure electrolytic copper plate is sandblasted to a surface roughness Ra of 1.6 μm, and then dried in a drying furnace at 180°C for 2.2 hours to obtain a copper substrate with a moisture content of 40 ppm. (2) gradient melting and impurity removal: the pretreated copper plate is melted in an induction melting furnace, the heating rate is controlled at 10°C / min to 1235°C, and the temperature is maintained at 400V for 37 minutes. At the same time, high-purity nitrogen gas containing 0.5% hydrogen (oxygen content ≤ 0.3 ppm) is introduced from the bottom of the furnace, and the gas flow rate is maintained at 1.0 cubic meters per hour. The final output is a molten copper liquid with a dissolved oxygen content not exceeding 18 ppm. (3) Deoxidation of molten copper: A composite oxygen barrier layer was laid on the surface of the molten copper, wherein the lower layer was a 6 cm thick mixture of calcined coconut shell charcoal and calcium fluoride (the mass ratio of the calcined coconut shell charcoal and calcium fluoride mixture was 92:10), and the upper layer was a 5 cm thick flake graphite, forming an oxygen barrier system with an oxygen diffusion coefficient not exceeding 1×10-9 cm² / s; at the same time, a composite deoxidizer (54 parts of activated lanthanum powder, 26 parts of calcium fluoride, and 20 parts of lithium borate) was added in an amount of 0.09% of the mass of the molten copper, and stirred at 105 rpm for 85 minutes to obtain a deoxidized copper solution with a lattice oxygen content not exceeding 2.5 ppm. The preparation method of calcined coconut shell charcoal is as follows: 3 mm particle size coconut shell was calcined in argon at 1350℃ for 4.5 hours, then soaked in 10wt% oxalic acid solution at 45℃ for 2.0 hours, and then washed with water to a pH value of 7.0 to obtain calcined coconut shell charcoal with an ash content not exceeding 0.02%. The preparation method of activated lanthanum powder is as follows: 99.52 wt% crude lanthanum ingot is heated to 680℃ for 30 minutes in an atmosphere with a volume ratio of Ar to H2 of 95:5, and finally water atomized to obtain 200-300 mesh powder, and the surface oxide layer of the activated lanthanum powder does not exceed 10nm. (4) Transfer and filtration of deoxidized copper liquid: The deoxidized copper liquid is transferred to a 1145℃ holding furnace through a double-layer gas curtain channel, wherein the inner layer is -10 Pa nitrogen and the outer layer is 1.2 MPa nitrogen. The oxygen increase during the transfer process does not exceed 0.2ppm; then, it passes through a step filtration device, sequentially passing through a silicon carbide foam ceramic filter layer with a pore size of 60 μm and a zirconium oxide filter plate with a pore size of 20 μm and a titanium nitride-coated surface, to obtain a clean copper liquid with no more than 15 inclusions / 100 mm². The surface of the zirconia filter plate is covered with a titanium nitride coating formed by a physical vapor deposition process. After deposition, the titanium nitride coating is vacuum annealed at 1150°C for 0.5 hours. The thickness of the titanium nitride coating is 1.2 μm and the Vickers hardness is not less than 1800 HV. (5) Upward casting: Clean copper liquid is added to the crystallizer. The cooling water temperature and flow rate are set as follows: 25°C and 0.3 m / s in the upper section, 32°C and 1.2 m / s in the middle section, and 42°C and 0.8 m / s in the lower section. The pulling speed is 2.8 m / min, and the cast rod blank with a diameter of 8.0 mm is produced.

[0049] Example 3 In this embodiment, the same points as in Example 1 are not described in detail, and the differences are as follows: A process for producing high-purity oxygen-free copper rods by an upward-drawing method comprises the following steps: (1) raw material pretreatment: a 99.99% pure electrolytic copper plate is sandblasted to a surface roughness Ra of 1.6 μm, and then dried in a drying furnace at 185°C for 2.0 hours to obtain a copper substrate with a moisture content of 40 ppm. (2) gradient melting and impurity removal: the pretreated copper plate is melted in an induction melting furnace, the heating rate is controlled at 12°C / min to 1220°C, and the temperature is maintained at 405V for 33 minutes. At the same time, high-purity nitrogen gas containing 0.8% hydrogen (oxygen content ≤ 0.3 ppm) is introduced from the bottom of the furnace, and the gas flow rate is maintained at 0.8 cubic meters per hour. The final output is a molten copper liquid with a dissolved oxygen content not exceeding 18 ppm. (3) Deoxidation of molten copper: A composite oxygen barrier layer was laid on the surface of the molten copper, wherein the lower layer was an 8 cm thick mixture of calcined coconut shell charcoal and calcium fluoride (the mass ratio of the calcined coconut shell charcoal and calcium fluoride mixture was 88:10), and the upper layer was a 3 cm thick flake graphite, forming an oxygen barrier system with an oxygen diffusion coefficient not exceeding 1×10-9 cm² / s; at the same time, a composite deoxidizer (50 parts of activated lanthanum powder, 30 parts of calcium fluoride, and 18 parts of lithium borate) was added in an amount of 0.11% of the mass of the molten copper, and stirred at 95 rpm for 95 minutes to obtain a deoxidized copper solution with a lattice oxygen content not exceeding 2.5 ppm. The preparation method of calcined coconut shell charcoal is as follows: 5 mm particle size coconut shell was calcined in argon at 1300°C for 5.5 hours, then soaked in 12 wt% oxalic acid solution at 40°C for 1.5 hours, and then washed with water to a pH of 6.5 to obtain a calcined coconut shell charcoal with an ash content not exceeding 0.02%. The preparation method of activated lanthanum powder is as follows: 99.52 wt% crude lanthanum ingot is heated to 650℃ for 40 minutes in an atmosphere with a volume ratio of Ar to H2 of 95:5, and finally water atomized to obtain 200-300 mesh powder, and the surface oxide layer of the activated lanthanum powder does not exceed 10nm. (4) Transfer and filtration of deoxidized copper liquid: The deoxidized copper liquid is transferred to a 1165℃ holding furnace through a double-layer gas curtain channel, wherein the inner layer is -5 Pa nitrogen and the outer layer is 1.0 MPa nitrogen. The oxygen increase during the transfer process does not exceed 0.2ppm; then, it passes through a step filtration device, sequentially passing through a silicon carbide foam ceramic filter layer with a pore size of 50 μm and a zirconium oxide filter plate with a pore size of 30 μm and a titanium nitride-coated surface, to obtain a clean copper liquid with no more than 15 inclusions / 100 mm². The surface of the zirconia filter plate is covered with a titanium nitride coating formed by a physical vapor deposition process. After deposition, the titanium nitride coating is vacuum annealed at 1100°C for 1.0 hour. The thickness of the titanium nitride coating is 0.8 μm and the Vickers hardness is not less than 1800 HV. (5) Upward casting: Clean copper liquid is added to the crystallizer. The cooling water temperature and flow rate are set as follows: 22°C and 0.5 m / s in the upper section, 28°C and 1.5 m / s in the middle section, and 38°C and 1.0 m / s in the lower section. The pulling speed is 3.2 m / min, and the cast rod blank with a diameter of 8.0 mm is produced.

[0050] Comparative Example 1 In this comparative example, the same points as in Example 1 are not repeated here, and the differences are as follows: The ratio of activated lanthanum powder in the composite deoxidizer is 48 parts, lithium borate is 15 parts, calcium fluoride is 25 parts, and the amount of deoxidizer added is 0.07%.

[0051] Comparative Example 2 In this comparative example, the same points as Example 2 are not repeated here, and the differences are as follows: The composite oxygen barrier layer does not have a lower layer of calcined coconut shell carbon and calcium fluoride mixture, and only uses flake graphite as a single material (the thickness is maintained at 4 cm), and the oxalic acid soaking concentration is reduced to 8wt%.

[0052] Comparative Example 3 In this comparative example, the same points as in Example 3 are not repeated here, and the differences are as follows: During the gradient melting and impurity removal process, no hydrogen was introduced, only high-purity nitrogen (without hydrogen content) with an oxygen content of ≤0.3 ppm was introduced, and the drying time was increased to 3.0 hours.

[0053] Comparative Example 4 In this comparative example, the same points as in Example 1 are not repeated here, and the differences are as follows: Only a single layer of nitrogen curtain (pressure maintained at −7.5 Pa) was used in the sealed channel, and no gradient filtration device was used.

[0054] Comparative Example 5 In this comparative example, the same points as in Example 1 are not repeated here, and the differences are as follows: The upward casting cooling parameters were changed to uniform values ​​(28°C / 1.0 m / s throughout the entire section), and the pulling speed was increased to 4.0 m / min.

[0055] Performance test results and analysis The products of Examples 1-3 and Comparative Examples 1-5 were tested using general testing methods. Each test parameter included oxygen content (ASTM E112 method), electrical conductivity (ASTM E140 method), tensile strength (ASTM E8 method), elongation (ASTM E8 method), number of inclusions (microscope counting method), and production interruption rate (statistics from 100 consecutive production batches). The test results are shown in Table 1. All values ​​are the average of three repeated tests.

[0056] Table 1 Analysis and test results Group Oxygen content (ppm) Electrical conductivity (%IACS) Tensile strength (MPa) Elongation (%) Number of inclusions (pieces / 100 mm²) Belt breakage rate (%) Example 1 5.0 101.8 238 48 13 0.2 Example 2 5.3 101.5 241 46 14 0.3 Example 3 4.8 102.1 235 50 12 0.1 Comparative Example 1 12.7 98.2 225 32 28 5.8 Comparative Example 2 15.3 96.5 218 25 35 8.3 Comparative Example 3 14.8 97.1 220 29 30 7.2 Comparative Example 4 9.5 99.3 230 40 22 3.1 Comparative Example 5 8.1 100.0 228 42 20 4.5 As can be seen from Table 1, the oxygen content of all embodiments is stable at 4.8-5.3 ppm, far below the 10 ppm threshold, effectively avoiding the high-temperature hydrogen embrittlement fracture problem mentioned in the background technology. This is due to the precise reduction atmosphere control in gradient smelting and impurity removal and the synergistic effect of the compound oxygen barrier layer and the composite deoxidizer in the deoxidation of molten copper liquid. In Comparative Example 1, the oxygen residue is significantly increased to 12.7 ppm due to insufficient deoxidizer, while the oxygen content in Comparative Example 2 increases to 15.3 ppm when there is no compound oxygen barrier layer, verifying the necessity of the combination mechanism. In contrast, in the examples, the reactivity of the activated lanthanum powder ensures the thorough removal of lattice oxygen, and the slag formed by calcium fluoride is efficiently removed in the gradient filtration, reducing the lattice oxygen content to no more than 2.5 ppm. In addition, the double-layer nitrogen curtain design of the sealed channel controls the transfer oxygenation to within 0.2 ppm, such as -7.5 Pa and 1.1 MPa nitrogen in Example 1, which solves the key defect of secondary oxidation of the melt in the background technology. Lithium borate in the deoxidizer removes impurity phosphorus, and the conductivity of the embodiment is improved by more than the expected 5%.

[0057] The tensile strength and elongation of the examples demonstrate excellent overall mechanical properties. The ribbon breakage rate is only 0.1-0.3%, significantly lower than the comparative examples (3.1-8.3%), demonstrating that gradient filtration and optimized cooling mitigate the risks of inclusion blockage and ribbon breakage. In comparative example 2, due to a single oxygen barrier layer, the number of inclusions increased to 35 per 100 mm², resulting in an 8.3% ribbon breakage rate, highlighting the importance of a composite oxygen barrier layer. Furthermore, the zoning of the casting cooling in the examples ensures grain refinement and avoids dendritic defects.

[0058] All examples exhibit low inclusion counts, a result of the combined oxygen barrier layer and cascade filtration. Furthermore, oxygen content, conductivity, and strength are well matched. For example, the 50% elongation of Example 3 far exceeds the 25% of Comparative Example 2 and the 29% of Comparative Example 3. This excellent performance addresses the energy consumption-performance trade-off described in the beneficial effects section—eliminating the need for an annealing step reduces costs while achieving efficient deoxidation through precise process parameter settings.

[0059] Test results confirm the present invention's breakthroughs in addressing the shortcomings of prior art, achieving oxygen content below 10 ppm and conductivity above 100% IACS. The diverse parameter settings in Examples 1-3 ensure the robustness of the solution. Appropriate variations in process details avoid the carbon contamination issues inherent in existing technologies, providing a reliable solution for the large-scale production of high-purity oxygen-free copper rods.

[0060] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A process for producing high-purity oxygen-free copper rods by updrawing method, characterized in that: The production process includes the following sequential steps: (1) Raw material pretreatment: 99.99% pure electrolytic copper plate is sandblasted and dried to obtain a pretreated copper plate; (2) Gradient smelting and impurity removal: The pretreated copper plate is used as raw material for smelting to obtain a molten copper solution with a dissolved oxygen content of ≤18 ppm; (3) Deoxidation of molten copper liquid: laying a composite oxygen barrier layer on the surface of the molten copper liquid and adding a composite deoxidizer to the molten copper liquid, stirring at 95-105 rpm for 85-95 minutes to obtain a deoxidized copper liquid with lattice oxygen ≤ 2.5 ppm; (4) Transfer and filtration of deoxidized copper liquid: The deoxidized copper liquid is transferred to the holding furnace through a sealed channel, and then the inclusions are removed through a step filtration device to obtain clean copper liquid; (5) Upward casting: The clean copper liquid is cast upward in the crystallizer to produce the cast rod blank.

2. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, characterized in that: The specific steps of raw material pretreatment are: sandblasting a 99.99% pure electrolytic copper plate to a surface roughness of Ra ≤ 1.6 μm, and then drying it in a drying furnace at 180-190° C. for 2.0-2.2 hours to obtain a copper substrate with a moisture content of ≤ 40 ppm.

3. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, wherein: The smelting process is carried out in an induction melting furnace, and its specific parameters are: controlling the heating rate at 10-12°C / min to a melting temperature of 1220-1235°C, keeping the temperature at 400-410V for 33-37 minutes, and simultaneously introducing high-purity nitrogen containing 0.5-0.8% hydrogen and an oxygen content of ≤0.3 ppm from the bottom of the furnace, and maintaining the gas flow at 0.8-1.0 cubic meters per hour, ultimately producing a molten copper liquid with a dissolved oxygen content of ≤18 ppm.

4. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, wherein: The composite oxygen barrier layer comprises a lower layer of 6-8 cm thick calcined coconut shell carbon and calcium fluoride mixture and an upper layer of 3-5 cm thick flake graphite. The composite oxygen barrier layer forms an oxygen diffusion coefficient of ≤1×10 -9 cm² / s oxygen barrier system; The mass ratio of the calcined coconut shell charcoal to the calcium fluoride mixture is (88-92):10; The preparation method of the calcined coconut shell charcoal comprises: calcining coconut shells with a particle size of 3-5 mm in argon at 1300-1350° C. for 4.5-5.5 hours, then soaking them in a 10-12 wt% oxalic acid solution at a temperature of 40-45° C. for 1.5-2.0 hours, and then washing them with water to a pH value of 6.5-7.0 to obtain calcined coconut shell charcoal with an ash content of ≤0.02%.

5. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, characterized in that: In parts by mass, the composite deoxidizer comprises 50-54 parts of activated lanthanum powder, 26-30 parts of calcium fluoride, and 18-20 parts of lithium borate. The amount of the composite deoxidizer added is 0.09-0.11% of the mass of the molten copper. The preparation method of the activated lanthanum powder is as follows: 99.52 wt% crude lanthanum ingot is heated to 650-680 ° C in an atmosphere with a volume ratio of Ar to H2 of 95:5 for 30-40 minutes, and finally water atomized to obtain a 200-300 mesh powder, which is the activated lanthanum powder, wherein the surface oxide layer of the activated lanthanum powder is ≤10nm.

6. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, characterized in that: The sealed channel is a double-layer gas curtain channel transferred to a 1145-1165°C holding furnace. The double-layer gas curtain channel is divided into an inner layer and an outer layer, wherein the inner layer is -5 to -10 Pa nitrogen and the outer layer is 1.0-1.2 MPa nitrogen. The oxygen increase during the transfer process is ≤0.2ppm.

7. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, characterized in that: The specific steps of removing inclusions in the step-by-step filtration device are as follows: the transferred deoxidized copper solution flows sequentially through a silicon carbide foam ceramic filter layer with a pore size of 50-60 μm and a zirconium oxide filter plate with a pore size of 20-30 μm and a titanium nitride-coated surface, and the inclusions are ≤15 / 100 mm. 2 Clean copper liquid.

8. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 7, characterized in that: The surface of the zirconia filter plate is covered with a titanium nitride coating, which is formed by a physical vapor deposition process. After deposition, the titanium nitride coating is vacuum annealed at 1100-1150° C. for 0.5-1 hour. The thickness of the titanium nitride coating is 0.8-1.2 μm, and the Vickers hardness is ≥1800 HV.

9. The process for producing high-purity oxygen-free copper rod by updrawing method according to claim 1, characterized in that: The specific steps and parameters of the upward casting are as follows: adding clean copper liquid into the crystallizer, setting the cooling water zone temperature / flow rate, wherein the upper section is 22-25°C / 0.3-0.5 m / s, the middle section is 28-32°C / 1.2-1.5 m / s, and the lower section is 38-42°C / 0.8-1.0 m / s, and the pulling speed is 2.8-3.2 m / min, and the cast rod blank with a diameter of 8.0±0.1 mm is produced.