A method for manufacturing a capillary tube of iron white copper

Abstract

The application relates to a preparation method of iron-white copper capillary tubes and belongs to the technical field of material processing. Firstly, a bar with a diameter of 50-70 mm is prepared by adopting a smelting and hot processing process; then a pipe material with an outer diameter of 35-50 mm and a wall thickness of 4.0-6.0 mm is prepared by adopting a piercing and hot rolling process; then a pipe material with an outer diameter of 4-6 mm and a wall thickness of 0.11 mm is prepared by adopting a cold rolling and intermediate annealing process; finally, a capillary tube with an outer diameter of 0.15-0.20 mm and a wall thickness of 0.05 mm is prepared by adopting a drawing process. The application solves the technical problem that the length and size of the iron-white copper capillary tube cannot be compatible, obtains relevant key preparation technologies, and realizes the stable preparation of the super-long-length iron-white copper capillary tube. The iron-white copper capillary tube has stable quality, excellent strength and toughness, is suitable for small condensers and heat exchangers, and has a wide application space.

Description

Technical Field

[0001] This invention relates to a method for preparing an iron-copper capillary tube, belonging to the field of materials processing technology. Background Technology

[0002] Iron-copper capillary tubes are highly favored in the marine industry due to their superior performance. Their resistance to seawater corrosion, resistance to marine organism adhesion, and excellent thermal conductivity make them an ideal choice for nuclear-powered submarines, missile ships, coastal power plants, and seawater desalination. With the rapid development of my country's marine industry, iron-copper capillary tubes, as an important material in the manufacture of precision instruments in marine engineering and shipbuilding, have enormous market potential and continuously rising demand, demonstrating a remarkable development prospect.

[0003] As a highly complex product in the copper processing industry, the challenges of producing iron-copper capillary tubes mainly lie in the difficulty of machining small diameters, the requirement that the inner and outer surfaces be kept clean and extremely smooth, the surface roughness not exceeding Ra≤3.2μm, the tensile strength need to reach ≥295MPa, and the continuous length exceeds 10,000 meters.

[0004] The specifications for iron-copper capillary tubes range from an outer diameter of Φ0.5 to 6.1 mm and a wall thickness of 0.2 to 2 mm. However, in the domestic capillary manufacturing field, especially for the manufacture of high-precision capillary tubes with dimensions of Φ0.15 to 0.20 mm and a wall thickness of 0.05 mm, there is a certain technological gap. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-precision, ultra-long iron-copper capillary tubes. It employs a complete material preparation process involving ultra-pure smelting, hot working, cold working, cold drawing, and annealing. This method overcomes key technological barriers in preparing small-diameter, multi-variety metal capillary tubes, achieving a complete process for thin-walled capillary tube preparation. Ultimately, it yields a stable process for preparing capillary tubes with an outer diameter of Φ0.15–0.20 mm and a wall thickness of 0.05 mm.

[0006] The technical solution of the present invention:

[0007] A method for preparing a copper-iron capillary tube involves first preparing Φ50-70mm rods using smelting and hot working processes, then preparing tubes with an outer diameter of Φ35-50mm and a wall thickness of 4.0-6.0mm using piercing and hot rolling processes, then preparing tubes with an outer diameter of Φ4-6mm and a wall thickness of 0.11mm using cold rolling and intermediate annealing processes, and finally preparing capillary tubes with an outer diameter of Φ0.15-0.20mm and a wall thickness of 0.05mm using a drawing process.

[0008] The preparation method of the iron-copper capillary, by weight percentage, the chemical composition of the iron-copper is: Ni: 27.0-35.0%, Fe: 0.40-1.5%, Zn: 0-0.5%, Mn: 0-1.5%, O<0.0020%, N<0.0020%, with the balance being copper.

[0009] The method for preparing the iron-white copper capillary tubes involves first mixing various chemical elements in proportion and then obtaining high-purity iron-white copper ingots with low oxygen and nitrogen content through vacuum smelting and casting; next, subjecting the iron-white copper ingots to high-temperature homogenization annealing treatment at 930–1050℃ for 10–12 hours, followed by forging to produce iron-white copper rods with a diameter of Φ50–70mm.

[0010] The method for preparing the iron-white copper capillary tube involves using a skew rolling and piercing process. Iron-white copper bars with a diameter of 50-70mm are pierced to obtain iron-white copper blank tubes with an outer diameter of 35-50mm. The tube walls are then thinned using an elongation machine to obtain iron-white copper tubes with an outer diameter of 35-50mm and a wall thickness of 4.0-6.0mm.

[0011] The method for preparing the iron-copper capillary tube involves subjecting a tube with an outer diameter of Φ35-50mm and a wall thickness of 4.0-6.0mm to multiple cold rolling passes, with a diameter reduction rate of 7-15% per rolling pass, combined with an intermediate annealing process. During the intermediate annealing process, when the outer diameter of the iron-copper tube is greater than 8mm, annealing heat treatment is performed when the deformation reaches 50-90%; when the outer diameter of the iron-copper tube is less than 8mm, annealing heat treatment is performed when the deformation reaches 20-40%, ultimately obtaining an iron-copper capillary tube with an outer diameter of Φ4-6mm and a wall thickness of 0.11mm.

[0012] The method for preparing the iron-copper capillary tube involves a multi-layer stepped annealing heat treatment process during the intermediate annealing process. The cold-rolled and deformed iron-copper tube is annealed at 450-550℃ for 5-10 minutes, then raised to 650-730℃ for 5-10 minutes, and finally raised to 730-810℃ for 5-20 minutes. It is then rapidly cooled to below 60℃ at a cooling rate of 10-15℃ / s before being removed.

[0013] The method for preparing the iron-copper capillary involves drawing a tube with an outer diameter of Φ4-6mm and a wall thickness of 0.11mm in multiple passes using a mandrel-less drawing process to obtain an iron-copper capillary with an outer diameter of Φ0.15-0.20mm and a wall thickness of 0.05mm.

[0014] The design concept of this invention is as follows:

[0015] like Figure 1As shown, the process flow for preparing the iron-copper capillary tubes of this invention is as follows: raw material preparation → ultra-pure smelting → hot working (homogenization annealing, forging) → cold working (piercing, cold rolling + annealing heat treatment, cold drawing) → iron-copper capillary tubes with an outer diameter of Φ0.15~0.20mm and a wall thickness of 0.05mm. The capillary material used is iron-copper alloy. The oxygen and nitrogen content is controlled through ultra-pure smelting to ensure material purity and avoid cracks and defects caused by inclusions during capillary tube preparation. By rationally arranging intermediate annealing heat treatment, the iron-copper alloy tube can restore its original microstructure after cold working, eliminating stress concentration and internal stress, which helps improve the material's plasticity and toughness, and avoids cracking caused by excessive deformation during capillary rolling. Simultaneously, it improves the production efficiency of iron-copper alloy tubes, saves energy, and achieves green production. In addition, the multi-layer stepped annealing heat treatment process ensures that the capillary has a uniform and fine grain structure, avoiding crack defects caused by coarse grains during the capillary processing, and enabling the stable preparation of ultra-long iron-copper capillary tubes.

[0016] In this invention, the ultrapure smelting process is described as follows:

[0017] Ultra-pure smelting is a highly refined smelting process designed to reduce the content of elements such as oxygen and nitrogen in materials to achieve high purity. In the ultra-pure smelting of iron-copper alloys, vacuum smelting is employed to prevent contamination of raw materials by impurities such as oxygen and nitrogen from the external air. The oxygen and nitrogen content is controlled to be below 0.002 wt%, removing oxygen and nitrogen inclusions and avoiding cracks and defects caused by inclusions during capillary rolling.

[0018] In this invention, the intermediate annealing heat treatment is arranged as follows:

[0019] During cold rolling, the increased deformation of the copper tube increases processing difficulty and the risk of cracking. To avoid cracking during cold rolling and improve processing efficiency, this invention designs a reasonable intermediate annealing heat treatment method. For copper-nickel tubes with an outer diameter of 8 mm or more and a wall thickness of 0.4 mm or more: annealing heat treatment is performed when the deformation is 55-85%. The purpose of this step is to eliminate internal stress caused by work hardening, ensure a uniform microstructure, avoid the risk of cracking due to work hardening, and simultaneously reduce the number of intermediate annealing heat treatments, thus improving the efficiency of capillary preparation. For copper-nickel capillary tubes with an outer diameter of less than 8 mm and a wall thickness of less than 0.4 mm: the grain size is greater than 9.0, and the wall thickness consists of 5-20 grains. Due to the reduction in wall thickness and grain number, processing difficulty increases. Therefore, intermediate annealing heat treatment is performed when the deformation reaches 20-55%. This helps to reduce internal stress generated during processing, obtain a more uniform and stable grain structure, and ensure the quality and stability of the copper-nickel capillary tube during processing.

[0020] In this invention, the multi-layer stepped annealing heat treatment process is as follows:

[0021] When cold-rolled copper tubes undergo conventional high-temperature annealing, they develop larger grain sizes, increasing their brittleness, making cold rolling more difficult, and increasing the risk of processing cracks. Therefore, multi-layer stepped annealing heat treatment is employed. Figure 2 As shown, the material is first held at 450–550°C (preferably 480–530°C) for 5–10 minutes to control the recrystallization process and obtain a more uniform and finer grain size. Then, the temperature is raised to 650–730°C (preferably 680–730°C) and held for 5–10 minutes to further eliminate residual internal stress, reduce stress accumulation, and promote complete grain recrystallization, further adjusting the grain size and uniformity. Finally, the temperature is raised to 730–810°C (preferably 750–810°C) for 5–20 minutes of annealing, which helps improve the material's plasticity and toughness, providing a superior material basis for subsequent processing. Finally, the material is rapidly cooled to below 60°C by gas injection at a cooling rate of 10–15°C / s and then removed.

[0022] The advantages and beneficial effects of this invention are:

[0023] 1. This invention employs ultra-pure smelting to strictly control oxygen and nitrogen content, avoiding oxygen and nitrogen inclusions and preventing cracking during rolling and cold drawing. Simultaneously, the use of cold rolling combined with a rational multi-layer stepped annealing heat treatment ensures that the capillary achieves a uniform and fine grain structure, improving the efficiency of the production process and achieving low-energy, green production. Finally, through cold drawing, capillary tubes with dimensions of Φ0.15–0.20 mm and a wall thickness of 0.05 mm are obtained, achieving stable preparation of ultra-long iron-copper capillary tubes and filling the gap in domestic high-precision capillary preparation technology.

[0024] 2. The yield strength of the annealed iron-copper capillary tube of the present invention is as high as ≥140MPa, the tensile strength is as high as ≥295MPa, and the continuous length exceeds 10,000 meters. Attached Figure Description

[0025] Figure 1 A process flow diagram for the preparation of iron-copper capillary tubes.

[0026] Figure 2 A schematic diagram of the multi-layer stepped annealing heat treatment process for preparing iron-copper capillary tubes.

[0027] Figure 3 This is a schematic diagram of the cross-section of the iron-copper capillary tube in Example 1.

[0028] Figure 4 This is a schematic diagram of the cross-section of the iron-copper capillary tube in Example 2.

[0029] Figure 5 Metallographic images of the cracked Φ5mm × 0.4mm wall thickness iron-copper pipe for Comparative Example 1.

[0030] Figure 6 Metallographic image of oxide inclusions for Comparative Example 2.

[0031] Figure 7 The image shows the grain structure after multi-layer stepped annealing heat treatment in Example 1.

[0032] Figure 8 Image showing the grain structure of Example 3 after conventional annealing heat treatment. Detailed Implementation

[0033] The present invention will now be further described in detail with reference to embodiments and accompanying drawings.

[0034] Example 1

[0035] In this embodiment, the chemical composition of the iron-copper alloy by weight percentage is: Ni: 30.6%, Fe: 0.6%, Zn: 0.3%, Mn: 0.9%, O: 0.0013%, N: 0.0015%, with the balance being copper.

[0036] Step 1: Mix the chemical components according to the specified ratio, and obtain iron-copper ingots through ultra-pure vacuum smelting and casting. Then, perform homogenization annealing at 970℃ and hold for 10 hours. After that, remove the ingots from the furnace and forge them to obtain iron-copper rods with a size of Φ55mm.

[0037] Step 2: Pierce the Φ55mm iron-copper rod to obtain an iron-copper tube with an outer diameter of Φ39mm and a wall thickness of 4.5mm.

[0038] Step 3: The iron-copper tube with an outer diameter of Φ39mm and a wall thickness of 4.5mm is rolled in multiple passes, with a diameter reduction rate of 7.9% to 11.9% per pass and a total deformation of 84.7%, to obtain an iron-copper tube with an outer diameter of Φ21mm and a wall thickness of 1.2mm. Then, it undergoes multi-layer stepped annealing heat treatment.

[0039] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 730°C and held for 20 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0040] Step 4: The annealed 21mm outer diameter × 1.2mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 9.7-13.8% per pass and a total deformation of 59.64%, to obtain an 14.4mm outer diameter × 0.7mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0041] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 730°C and held for 20 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0042] Step 5: The annealed 14.4mm outer diameter and 0.7mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 10.2-11.3% per pass and a total deformation of 58.71%, to obtain an 10.3mm outer diameter and 0.4mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0043] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 730°C and held for 20 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0044] Step 6: The annealed 10.3mm outer diameter and 0.4mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 11.1-11.8% per pass and a total deformation of 51.07%, to obtain an 8mm outer diameter and 0.25mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0045] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 730°C and held for 20 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0046] Step 7: The annealed 8mm outer diameter × 0.25mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 7-11.8% per pass and a total deformation of 50.06%, to obtain an 8.6mm outer diameter × 0.15mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0047] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 730°C and held for 20 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0048] Step 8: The annealed 6.6mm outer diameter × 0.15mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 7.2-9.3% and a deformation of 28.93% per pass, to obtain an 5.85mm outer diameter × 0.12mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0049] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 800°C and held for 8 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0050] Step 9: The annealed 5.85mm outer diameter × 0.12mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 7-9.1% per rolling pass and a total deformation of 21.77%, to obtain an 5mm outer diameter × 0.11mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0051] The cold-rolled and deformed iron-copper tube is heated at 500°C for 10 minutes, then raised to 700°C and held for 10 minutes, and finally raised to 800°C and held for 8 minutes. It is then rapidly cooled to 50°C at a cooling rate of 10°C / s and removed.

[0052] Step 10: Cold draw the annealed iron-copper tube with an outer diameter of Φ5.00mm and a wall thickness of 0.11mm to obtain an iron-copper capillary tube with an outer diameter of Φ0.20mm and a wall thickness of 0.05mm and a length of more than 10,000 meters.

[0053] In this embodiment, the technical specifications of the annealed iron-copper capillary are as follows: yield strength of 142 MPa and tensile strength of 345 MPa.

[0054] Example 2

[0055] In this embodiment, the chemical composition of the iron-copper alloy by weight percentage is as follows: Ni: 32.1%, Fe: 0.5%, Zn: 0.35%, Mn: 0.8%, O: 0.0010%, N: 0.0008%, with the balance being copper.

[0056] Step 1: Mix the chemical components according to the specified ratio, and obtain iron-copper ingots through ultra-pure vacuum smelting and casting. Then, perform homogenization annealing at 970℃ and hold for 12 hours. After that, remove the ingots from the furnace and forge them to obtain iron-copper rods with a size of Φ52mm.

[0057] Step 2: Pierce the Φ52mm iron-copper rod to obtain an iron-copper tube with an outer diameter of Φ38mm and a wall thickness of 4.3mm.

[0058] Step 3: The iron-copper tube with an outer diameter of Φ38mm and a wall thickness of 4.3mm is rolled in multiple passes, with a diameter reduction rate of 8.0% to 12.1% per rolling pass and a total deformation of 81.43%, to obtain an iron-copper tube with an outer diameter of Φ22mm and a wall thickness of 1.3mm. This tube is then subjected to multi-stage stepped annealing heat treatment.

[0059] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 730℃ and held for 20 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0060] Step 4: The annealed 22mm outer diameter × 1.3mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 9.4-13.4% per pass and a total deformation of 62.84%, to obtain an 13.3mm outer diameter × 0.8mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0061] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 730℃ and held for 20 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0062] Step 5: The annealed 13.3mm outer diameter × 0.8mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 10.1-11.7% per pass and a total deformation of 60.57%, to obtain an 10.5mm outer diameter × 0.39mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0063] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 730℃ and held for 20 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0064] Step 6: The annealed 10.5mm outer diameter × 0.39mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 7.6-11.4% per pass and a deformation of 65.51%, to obtain an 7mm outer diameter × 0.2mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0065] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 730℃ and held for 20 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0066] Step 7: The annealed Φ7mm outer diameter × 0.2mm wall thickness iron-copper tube is subjected to multi-pass rolling, with a diameter reduction rate of 10.1-12.3% per rolling pass and a total deformation of 40.07%, to obtain an Φ6.4mm outer diameter × 0.13mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0067] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 800℃ and held for 8 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0068] Step 8: The annealed 6.4mm outer diameter × 0.13mm wall thickness iron-copper tube is rolled in one pass, with a diameter reduction rate of 12.8% per rolling pass and a total deformation of 17.85%, to obtain an 5.7mm outer diameter × 0.12mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0069] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 800℃ and held for 8 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0070] Step 9: The annealed 5.7mm outer diameter × 0.12mm wall thickness iron-copper tube is rolled in two passes, with a diameter reduction rate of 8.9-11.1% per pass and a total deformation of 26.82%, to obtain an 5mm outer diameter × 0.10mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0071] The cold-rolled and deformed iron-copper tube is heated at 510℃ for 10 minutes, then raised to 710℃ and held for 10 minutes, and finally raised to 800℃ and held for 8 minutes. It is then rapidly cooled to 50℃ at a cooling rate of 15℃ / s and removed.

[0072] Step 10: The annealed 5.00mm outer diameter and 0.10mm wall thickness iron-copper tube is drawn to obtain an iron-copper capillary tube with an outer diameter of 0.19mm and a wall thickness of 0.05mm with a length of more than 10,000 meters.

[0073] In this embodiment, the technical specifications of the annealed iron-copper capillary are as follows: yield strength of 147 MPa and tensile strength of 358 MPa.

[0074] Comparative Example 1

[0075] The specific implementation process of this comparative example is the same as steps 1 to 7 of Example 1.

[0076] Step 8: The annealed iron-copper tube with an outer diameter of Φ6.6mm and a wall thickness of 0.15mm is rolled in multiple passes. The diameter reduction rate for each rolling pass is 10.6-12.1%, and the deformation is 44.40%, to obtain an iron-copper tube with an outer diameter of Φ5mm and a wall thickness of 0.11mm.

[0077] In this comparative example, the iron-copper pipe cracked during the rolling process due to excessive total deformation.

[0078] Comparative Example 2

[0079] In this comparative example, the chemical composition of the iron-copper alloy, by weight percentage, is: Ni: 31.2%, Fe: 0.5%, Zn: 0.3%, Mn: 0.8%, with the balance being copper.

[0080] Step 1: Mix the chemical components according to the specified ratio, and obtain iron-copper ingots through smelting and casting. Then, perform homogenization annealing at 970℃ and hold for 10 hours. After that, remove the ingots from the furnace and forge them to obtain bars with a size of Φ53mm.

[0081] Step 2: Pierce a Φ53mm rod to obtain a white copper iron tube with an outer diameter of Φ40mm and a wall thickness of 4.3mm.

[0082] Step 3: The iron-copper tube with an outer diameter of Φ40mm and a wall thickness of 4.3mm is rolled in multiple passes, with a diameter reduction rate of 9.8% to 12.1% per pass and a total deformation of 85.3%, to obtain an iron-copper tube with an outer diameter of Φ20mm and a wall thickness of 1.2mm. This tube is then subjected to multi-stage stepped annealing heat treatment.

[0083] The cold-rolled and deformed iron-copper tube is heated at 500℃ for 8 minutes, then raised to 700℃ and held for 8 minutes, and finally raised to 750℃ and held for 15 minutes. It is then rapidly cooled to 40℃ at a cooling rate of 10℃ / s and removed.

[0084] Step 4: The annealed 20mm outer diameter and 1.2mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 9.5-14.1% per pass and a total deformation of 64.36%, to obtain an 14.0mm outer diameter and 0.6mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0085] The cold-rolled and deformed iron-copper tube is heated at 500℃ for 8 minutes, then raised to 700℃ and held for 8 minutes, and finally raised to 750℃ and held for 15 minutes. It is then rapidly cooled to 40℃ at a cooling rate of 10℃ / s and removed.

[0086] Step 5: The annealed 14.0mm outer diameter × 0.6mm wall thickness iron-copper tube is rolled in multiple passes, with a diameter reduction rate of 10.3-11.8% and a deformation of 52.24% per pass, to obtain an 10.0mm outer diameter × 0.4mm wall thickness iron-copper tube, which is then subjected to multi-layer stepped annealing heat treatment.

[0087] The cold-rolled and deformed iron-copper tube is heated at 500℃ for 8 minutes, then raised to 700℃ and held for 8 minutes, and finally raised to 750℃ and held for 15 minutes. It is then rapidly cooled to 40℃ at a cooling rate of 10℃ / s and removed.

[0088] Step 6: The annealed iron-copper tube with an outer diameter of Φ10.0mm and a wall thickness of 0.4mm is rolled in multiple passes. The diameter reduction rate of each rolling pass is 10.9-11.5%, and the deformation is 47.59%, to obtain an iron-copper tube with an outer diameter of Φ8mm and a wall thickness of 0.26mm.

[0089] In this comparative example, the iron-copper pipe cracked during the rolling process due to oxygen and nitrogen inclusions.

[0090] Comparative Example 3

[0091] The specific implementation process of this comparative example is the same as steps 1 to 4 of Example 1.

[0092] Step 5: The annealed 14.4mm outer diameter and 0.7mm wall thickness iron-copper tube is rolled in multiple passes. The diameter reduction rate of each rolling pass is 10.2-11.3%, and the deformation is 58.71%, to obtain an 10.3mm outer diameter and 0.4mm wall thickness iron-copper tube. The tube is then subjected to annealing heat treatment at 780℃ for 25 minutes and rapidly cooled to 50℃ at a cooling rate of 10℃ / s before being removed.

[0093] In this comparative example, the grains of the iron-copper tube are coarse, which is not conducive to the processing of the iron-copper capillary.

[0094] Depend on Figure 3 and Figure 4 The images shown are cross-sectional images of the iron-copper capillary tubes from Examples 1 and 2. This invention utilizes ultra-pure smelting to control oxygen and nitrogen content, avoiding the harmful effects of inclusions on rolling. Simultaneously, cold working combined with a reasonable multi-layer stepped annealing heat treatment yields iron-copper capillary tubes with a length greater than 3m, a dimension of Φ0.20mm, and a wall thickness of 0.05mm.

[0095] Depend on Figure 5 As shown, the copper-iron tube in Comparative Example 1 cracked after cold rolling. A comparison between Example 1 and Comparative Example 1 illustrates that for thin-walled copper-iron tubes with an outer diameter less than 10 mm and a wall thickness less than 0.4 mm, excessive cold rolling deformation leads to cracks or deformation during processing. The present invention's reasonable arrangement of deformation control and intermediate annealing heat treatment for thin-walled copper tubes facilitates the processing of high-precision, small-sized copper-iron capillary tubes.

[0096] Depend on Figure 6As shown, in Comparative Example 2, for a copper-nickel alloy with an outer diameter of Φ8mm and a wall thickness of 0.26mm, an intermittent linear distribution of oxide inclusions was observed in the rolling direction, and cracking occurred during continued cold rolling. Compared to Example 1, this invention employs ultra-pure smelting technology and strictly controls the oxygen and nitrogen content, successfully avoiding the cracking risk that oxygen and nitrogen inclusions may cause when preparing high-precision, small-sized capillary tubes. This control is particularly crucial for preventing cold-rolling cracking of capillary tubes, especially for small-sized, high-precision tubes.

[0097] Depend on Figures 7-8 As shown, the grain structure of a 10.3mm outer diameter and 0.4mm wall thickness iron-copper tube after multi-layer stepped annealing heat treatment (Example 1) and conventional heat treatment (Comparative Example 3) is as follows. Compared with Example 1, the coarse grains in Comparative Example 3 increased the processing difficulty and the risk of cold rolling cracking during the ultra-thin wall capillary rolling process. The present invention designs a multi-layer stepped annealing heat treatment to ensure that the capillary obtains a uniform and fine grain structure, avoiding crack defects caused by coarse grains during the capillary preparation process.

[0098] The results demonstrate that, to fill the technological gap in the domestic manufacturing of high-precision capillaries, this invention has developed a novel end-to-end manufacturing process for high-strength iron-copper alloy capillaries. This process solves the technical challenge of simultaneously achieving the desired length and dimensions of iron-copper capillaries, acquires relevant key manufacturing technologies, and enables the stable fabrication of ultra-long iron-copper capillaries. The resulting iron-copper capillaries exhibit stable quality, excellent strength and toughness, and are suitable for small condensers and heat exchangers, offering a wide range of applications. This innovative manufacturing process aims to overcome challenges in the manufacturing process, meet the requirements of high-precision capillaries, fill the technological gap in this field in China, and promote the development and application of iron-copper capillary manufacturing technology.

[0099] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-copper capillary, characterized in that, First, Φ50~70mm bars are prepared using smelting and hot working processes. Then, tubes with an outer diameter of Φ35~50mm and a wall thickness of 4.0~6.0mm are prepared using piercing and hot rolling processes. Next, tubes with an outer diameter of Φ4~6mm and a wall thickness of 0.11mm are prepared using cold rolling and intermediate annealing processes. Finally, capillary tubes with an outer diameter of Φ0.15~0.20mm and a wall thickness of 0.05mm are prepared using drawing processes. Iron-copper tubes with outer diameters of Φ35~50mm and wall thicknesses of 4.0~6.0mm are produced by multi-pass cold rolling, with a diameter reduction rate of 7~15% per rolling pass, combined with intermediate annealing. During the intermediate annealing process, when the outer diameter of the iron-copper tube is greater than 8mm, annealing heat treatment is performed when the deformation reaches 50~90%; when the outer diameter of the iron-copper tube is less than 8mm, annealing heat treatment is performed when the deformation reaches 20~40%. During the intermediate annealing process, a multi-layer stepped annealing heat treatment process is adopted. The cold-rolled and deformed iron-copper tube is heated at 450~550℃ for 5~10 minutes, then raised to 650~730℃ for 5~10 minutes, and finally raised to 730~810℃ for 5~20 minutes. It is then rapidly cooled to below 60℃ at a cooling rate of 10~15℃ / s before being removed.

2. The method for preparing the iron-copper capillary according to claim 1, characterized in that, The chemical composition of iron-copper alloy by weight percentage is as follows: Ni: 27.0~35.0%, Fe: 0.40~1.5%, Zn: 0~0.5%, Mn: 0~1.5%, O<0.0020%, N<0.0020%, with the balance being copper.

3. The method for preparing the iron-copper capillary according to claim 2, characterized in that, First, various chemical elements are mixed in proportion, and high-purity iron-copper ingots with low oxygen and nitrogen content are obtained through vacuum smelting and casting. Then, the iron-copper ingots are subjected to high-temperature homogenization annealing treatment at 930~1050℃ for 10~12 hours, and then taken out of the furnace for forging to prepare iron-copper rods with Φ50~70mm.

4. The method for preparing the iron-copper capillary according to claim 1 or 3, characterized in that, The process of skew rolling and piercing is used to pierce iron-copper bars with a diameter of 50~70mm to obtain iron-copper blank tubes with an outer diameter of 35~50mm. The wall of the iron-copper tube is then rolled thin using an elongation machine to obtain iron-copper tubes with an outer diameter of 35~50mm and a wall thickness of 4.0~6.0mm.

5. The method for preparing the iron-copper capillary according to claim 1, characterized in that, The drawing process employs a mandrel-less drawing technique to draw tubes with an outer diameter of Φ4~6mm and a wall thickness of 0.11mm in multiple passes, resulting in iron-copper capillary tubes with an outer diameter of Φ0.15~0.20mm and a wall thickness of 0.05mm.

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