A manufacturing process for a semi-rigid copper tube

Abstract

This invention discloses a manufacturing process for semi-hard copper tubes, belonging to the field of metal processing technology. The process involves sequentially drawing, annealing, and air-drawing the tube blank. During drawing, the tube blank is subjected to pressure from the outer die and the moving mandrel, resulting in plastic deformation and residual stress. Annealing eliminates this residual stress, reduces the hardness of the tube blank, and makes it easier to air-draw. Finally, during air-drawing, the copper tube undergoes plastic deformation under tensile force, achieving diameter reduction and wall thickness increase. Simultaneously, residual stress is generated inside the tube, thereby improving its hardness and strength, ultimately successfully producing a copper tube with semi-hard characteristics.

Description

Technical Field

[0001] This invention relates to the field of metal processing technology, and specifically to a process for preparing a semi-hard copper tube. Background Technology

[0002] Copper tubing is a crucial basic material in many modern industries such as refrigeration, air conditioning, and electronics. Semi-rigid copper tubing refers to copper tubing in a state where its hardness and strength fall between those of the soft and hard states after processing. Semi-rigid copper tubing possesses excellent strength, plasticity, and processing properties, meeting the flexibility and strength requirements of complex piping products such as air conditioner condenser pipes and refrigerator refrigeration pipes. This has led to a continuous increase in market demand for semi-rigid copper tubing.

[0003] However, existing traditional copper tube manufacturing processes require cumbersome procedures to achieve the semi-rigid properties of copper tubes, resulting in low production efficiency. Furthermore, some semi-rigid copper tubes produced using existing processes may have defects such as insufficient dimensional accuracy and surface defects, failing to meet current market requirements for semi-rigid copper tubes. Summary of the Invention

[0004] Based on the deficiencies of existing technologies, the purpose of this invention is to provide a process for preparing semi-rigid copper tubes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A process for manufacturing a semi-rigid copper tube includes the following steps:

[0007] S1. The raw copper is melted into molten copper, and the molten copper is continuously cast to obtain cast pipe;

[0008] S2. The cast pipe obtained in step S1 is subjected to milling and rolling processes in sequence to obtain a pipe blank;

[0009] S3. The tube blank obtained in step S2 is drawn in n passes, where n is a positive integer. During each drawing process, the outer surface of the tube blank is in contact with the outer drawing die of the drawing die, and the inner surface of the tube blank is in contact with the moving mandrel of the drawing die. The tube blank achieves diameter and wall reduction under the combined action of the outer drawing die and the moving mandrel.

[0010] S4. After the tube blank is drawn in step S3, it is wound into a coil and then annealed.

[0011] S5. The tube blank after annealing in step S4 is air-drawn to obtain a semi-hard copper tube. During the air-drawing process, the outer surface of the tube blank is in contact with the air-drawing outer die, and the tube blank achieves diameter reduction and wall increase under the action of the air-drawing outer die.

[0012] Preferably, in step S4, the annealing temperature is 500~600℃ and the annealing time is 15~50min.

[0013] Preferably, in step S5, the sizing length of the air-pull outer mold is 7~10mm.

[0014] Preferably, in step S5, the processing rate of the air pull is 2~16%.

[0015] Preferably, in step S5, the processing rate of the air drawing is S, the sizing length of the air drawing outer die is B, and the diameter of the sizing zone of the drawing outer die used in the nth drawing pass is D1. n The drawing die used in the nth drawing pass refers to the drawing die used in the last drawing pass, 5≤B / (S*D1, n ≤8.

[0016] Preferably, in step S5, the speed of the empty pull is 40~70m / min.

[0017] Preferably, in step S5, the wall thickness increase of the air stretching is ≤0.05mm.

[0018] Preferably, the die angle of the air-drawing outer die is 40~46°.

[0019] Preferably, in step S1, the mass percentage of copper in the raw copper is not less than 99.95%.

[0020] Preferably, in step S3, the rate of each of the n drawing passes is independently 40~70m / min.

[0021] Preferably, in step S3, n is 2 to 4.

[0022] Preferably, in step S3, the processing rate of each of the n drawing passes is independently 15-40%.

[0023] Preferably, in step S3, the die angle of the stretching outer die is 50~54°.

[0024] Preferably, in step S3, the cone angle of the moving core head is 20~24°.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This application involves sequentially drawing, annealing, and air-drawing the tube blank. During the drawing process, the tube blank is subjected to pressure from the stretching die and the moving mandrel, resulting in plastic deformation and residual stress inside. Annealing eliminates the residual stress generated during drawing, reduces the hardness of the tube blank, and makes it easier to air-draw. Finally, during air-draw, the copper tube undergoes plastic deformation under tensile force, achieving diameter reduction and wall thickness increase. At the same time, residual stress is generated inside the tube, thereby improving the hardness and strength of the tube. Ultimately, a copper tube with semi-hard characteristics is successfully prepared.

[0027] Compared with existing technologies, this invention simplifies the preparation process of semi-rigid copper tubes and improves the production efficiency of semi-rigid copper tubes. Attached Figure Description

[0028] Figure 1 A schematic diagram illustrating the working principle of the stretching die provided by this invention;

[0029] Figure 2 The working principle diagram of the air-pull outer mold provided by the present invention.

[0030] In the diagram, 1 is the drawing die, 2 is the moving mandrel, 3 is the empty drawing die, 4 is the tube blank, 5 is the semi-rigid copper tube, α is the die angle of the drawing die, β is the cone angle of the moving mandrel, γ is the die angle of the empty drawing die, A is the sizing length of the drawing die, and D... max D is the maximum diameter of the moving core tip. min D1 is the minimum diameter of the floating mandrel, B is the sizing zone diameter of the stretching outer die, and D2 is the sizing zone diameter of the empty stretching outer die. Detailed Implementation

[0031] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0032] In the open-ended description of the technical features in this invention, there are both closed-ended technical solutions composed of the listed features and open-ended technical solutions.

[0033] It should be understood that, unless otherwise specified, the numerical ranges involved in this invention are considered continuous, including the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the maximum and minimum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed in this invention should be understood to include any or all of the subranges to which they are included.

[0034] The present invention provides a process for preparing a semi-rigid copper tube, comprising the following steps:

[0035] S1. The raw materials are melted into molten copper, and the molten copper is continuously cast to obtain cast pipes;

[0036] S2. The cast pipe obtained in step S1 is subjected to milling and rolling processes in sequence to obtain a pipe blank;

[0037] S3. The tube blank obtained in step S2 is drawn in n passes, where n is a positive integer;

[0038] like Figure 1 As shown, in each drawing process of step S3, the outer surface of the tube blank 4 contacts the outer drawing die 1 of the drawing die, and the inner surface of the tube blank 4 contacts the moving mandrel 2 of the drawing die. The tube blank 4 achieves diameter and wall reduction under the combined action of the outer drawing die 1 and the moving mandrel 2.

[0039] S4. After the tube blank is drawn in step S3, it is wound into a coil and then annealed.

[0040] S5. The tube blank after annealing in step S4 is air-drawn to obtain a semi-hard copper tube.

[0041] like Figure 2 As shown, during the air drawing process in step S5, the outer surface of the tube blank comes into contact with the air drawing outer mold 3. Under the action of the air drawing outer mold 3, the tube blank achieves diameter reduction and wall increase, thus obtaining a semi-hard copper tube 5.

[0042] This application involves sequentially drawing, annealing, and air-drawing the tube blank. During the drawing process, the tube blank is subjected to pressure from the stretching die and the moving mandrel, resulting in plastic deformation and residual stress inside. Annealing eliminates the residual stress generated during drawing, reduces the hardness of the tube blank, and makes it easier to air-draw. Finally, during air-draw, the copper tube undergoes plastic deformation under tensile force, achieving diameter reduction and wall thickness increase. At the same time, residual stress is generated inside the tube, thereby improving the hardness and strength of the tube. Ultimately, a copper tube with semi-hard characteristics is successfully prepared.

[0043] In one embodiment, in step S4, the annealing temperature is 500~600℃, and the annealing time is 15~50min. For example, the annealing temperature can be 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, or any two of these values; the annealing time can be 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min, or any two of these values.

[0044] This application allows for precise control of the hardness and tensile strength of copper tubes by adjusting the process parameters of air drawing (such as the air drawing rate and sizing length), thus meeting the needs of different application scenarios.

[0045] In one embodiment, in step S5, the sizing length B of the air-drawing outer mold is 7-10 mm. The sizing length B of the air-drawing outer mold can be 7 mm, 8 mm, 9 mm, 10 mm, or any two of these values. The sizing area of ​​the air-drawing outer mold is the portion used to ultimately determine the outer diameter of the copper tube. The sizing length B of the air-drawing outer mold refers to the axial dimension of the sizing area. The size of the sizing length determines the contact time and force distribution between the copper tube and the air-drawing outer mold during the air-drawing process. The inventors have found that controlling the sizing length of the air-drawing outer mold within an appropriate range can reduce residual stress during metal deformation, make metal flow more stable, and improve the wall thickness yield of the semi-rigid copper tube. Conversely, if the sizing length of the air-drawing outer mold is too short, it will lead to unstable metal flow and affect the dimensional accuracy of the finished semi-rigid copper tube.

[0046] In one embodiment, in step S5, the empty drawing processing rate is 2 to 16%. For example, the empty drawing processing rate can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, or a range consisting of any two sets of values.

[0047] The inventors discovered through research that an excessively high air-drawing rate leads to excessive residual stress generated during the copper tube drawing process, resulting in excessive hardness of the copper tube, which does not meet the requirements of a semi-hard tube. On the other hand, an excessively high air-drawing rate may also cause uneven metal flow during the air-drawing process, resulting in uneven wall thickness distribution.

[0048] In one embodiment, in step S5, the processing rate of the air drawing is S, the sizing length of the air drawing die is B, and the diameter of the sizing zone of the drawing die used in the nth drawing pass is D1. nThe drawing die used in the nth drawing pass refers to the drawing die used in the last drawing pass, 5≤B / (S*D1, n )≤8. For example, B / (S*D1, n () can be 5, 5.4, 5.5, 6, 6.2, 6.9, 7, 7.2, 7.5, 7.7, 8, or a range consisting of any two sets of values.

[0049] The inventors discovered through research that the sizing zone diameter D1 of the outer die used in the nth drawing pass... n The machining rate S during air drawing and the sizing length B of the air drawing outer die jointly affect the dimensional accuracy and surface quality of the semi-rigid copper tube. Provided that B and S are both within suitable ranges, B / (S*D1, n By controlling the temperature within the range of 5 to 8, the metal flow can be made more stable during the air drawing process, improving the dimensional accuracy of the semi-hard copper tube, reducing uneven wall thickness and surface defects, and improving the wall thickness yield of the semi-hard copper tube.

[0050] In one embodiment, in step S5, the wall thickness increase during air drawing is ≤0.05mm. For example, the wall thickness increase during air drawing can be 0.01mm, 0.02mm, 0.03mm, 0.04mm, 0.05mm, or a range consisting of any two sets of values. In this invention, the wall thickness increase during air drawing refers to the increase in wall thickness of the copper tube during the air drawing process.

[0051] In one embodiment, the die angle γ of the air-drawing outer die is 40~46°. In this invention, the die angle γ of the air-drawing outer die refers to twice the angle between the inner wall of the deformation zone of the die cavity and its central axis. For example, the die angle γ of the air-drawing outer die can be 40°, 41°, 42°, 43°, 44°, 45°, 46°, or a range consisting of any two sets of values.

[0052] In one embodiment, in step S5, the empty pulling speed is 40~70 m / min. For example, the empty pulling speed can be 40 m / min, 45 m / min, 50 m / min, 55 m / min, 60 m / min, 65 m / min, 70 m / min, or a range consisting of any two sets of values.

[0053] The present invention does not impose any particular restrictions on the source of the raw copper. For example, the raw copper may be at least one of the following: oxygen-free copper of grade TU0, oxygen-free copper of grade TU1, oxygen-free copper of grade TU2, pure copper of grade T2, and phosphorus-deoxidized copper of grade TP2.

[0054] In one embodiment, in step S1, the mass percentage of copper in the raw copper is not less than 99.95%.

[0055] The impurity content in the raw copper is no more than 0.05%. Specifically, the impurity components and their mass percentages in the raw copper are as follows: phosphorus ≤ 0.05%, silicon ≤ 0.0001%, aluminum ≤ 0.001%, zinc 0.005%, vanadium ≤ 0.0001%, and iron ≤ 0.01%.

[0056] The inventors discovered through research that the preparation process of this invention uses raw copper with a copper content of not less than 99.95% by mass to process it into a semi-hard copper tube, which can avoid excessive impurities that would cause the copper tube's hardness to fail to meet the requirements of a semi-hard tube.

[0057] In one embodiment, in step S3, the rate of each of the n drawing passes is independently 40~70 m / min. For example, the rate of each of the n drawing passes is independently 40 m / min, 45 m / min, 50 m / min, 55 m / min, 60 m / min, 65 m / min, 70 m / min, or a range consisting of any two sets of values ​​therein.

[0058] In one embodiment, in step S3, the processing rate of each of the n drawing passes is independently 15% to 40%. For example, the processing rate of each of the n drawing passes can be independently 15%, 17.5%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 30%, 31%, 32%, 35%, 37%, 38%, 40%, or a range consisting of any two sets of values.

[0059] In one embodiment, n is 2 to 4 in step S3.

[0060] In one embodiment, in step S3, the die angle α of the stretching outer die is 50~54°. In this invention, the die angle α of the stretching outer die refers to twice the angle between the inner wall surface of the stretching outer die in the deformation zone of the stretching die cavity and its central axis.

[0061] In one embodiment, in step S3, the cone angle β of the moving core is 20~24°. In this invention, the cone angle β of the moving core refers to twice the angle between the outer wall surface of the moving core in the corresponding mold cavity deformation zone and its central axis.

[0062] In one embodiment, in step S3, the sizing length A of the drawing die used for each of the n drawing passes is independently 4 to 6 mm. For example, the sizing length A of the drawing die used for each of the n drawing passes can be independently 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, or a range consisting of any two sets of values. The sizing region of the drawing die is the part of the drawing die used to finally determine the outer diameter of the tube blank, and the sizing length A of the drawing die refers to the axial dimension of the sizing region of the drawing die.

[0063] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0064] The following test method for tensile strength is as follows: The test is conducted according to GB / T 228.1:2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature". The acceptable range for the tensile strength of semi-rigid copper tube is 245~325MPa.

[0065] The following hardness testing method is as follows: The hardness of the finished copper tube is tested using a Vickers hardness tester. The acceptable hardness range for semi-hard copper tubes is 70~120HV.

[0066] The following method for testing the wall thickness defect rate is as follows: A copper tube of a certain length (100m) is taken for testing. 100 measurement points are selected at equal intervals on the copper tube. The wall thickness and outer diameter of the copper tube at each measurement point are measured. The average wall thickness and average outer diameter of the copper tube are calculated. The relative deviation is calculated according to the following formula: Relative deviation = |Measured value of copper tube wall thickness - Standard value of copper tube wall thickness| / Standard value of copper tube wall thickness * 100%. The number of measurement points with a relative deviation ≥ 5% is counted. The defect rate is calculated according to the following formula: Defect rate = (Number of measurement points with relative deviation ≥ 5%) / Total number of measurement points * 100%.

[0067] The standard value for the copper tube wall thickness in the following examples and comparative examples is 0.95 mm, and the standard value for the copper tube outer diameter is 15.88 mm.

[0068] Examples 1-4 and Comparative Examples 1-3

[0069] Examples and comparative examples of the preparation process of the semi-rigid copper tube according to the present invention include the following steps:

[0070] S1. Raw copper is added to a smelting furnace and heated to melt into molten copper. The molten copper is then subjected to horizontal continuous casting to obtain cast pipes. The raw copper is oxygen-free copper of grade TU0, wherein the mass percentage of copper is not less than 99.95%.

[0071] S2. The cast pipe obtained in step S1 is subjected to milling and rolling processes in sequence to obtain a pipe blank. The outer diameter of the pipe blank is 30mm and the wall thickness is 1.4mm.

[0072] S3. The tube blank obtained in step S2 is drawn in 3 passes. During each drawing process, the outer surface of the tube blank is in contact with the outer die of the drawing die, and the inner surface of the tube blank is in contact with the moving mandrel of the drawing die. The tube blank achieves diameter and wall thickness reduction under the combined action of the outer die and the moving mandrel. The outer diameter and wall thickness of the tube blank after each drawing pass are shown in Table 1. The die angle α of the outer die for each drawing pass is 52°, and the cone angle β of the moving mandrel is 24°.

[0073] Dimensional parameters of the drawing dies used in each drawing pass (diameter of the sizing zone of the outer drawing die, maximum diameter D of the floating mandrel) max The minimum diameter D of the moving core. min The sizing length (A) and the drawing rate are shown in Table 1.

[0074] S4. After the tube blank is drawn in step S3, it is wound into a coil and then annealed in a nitrogen atmosphere. The annealing temperature is 560°C and the annealing time is 23 minutes.

[0075] S5. The tube blank annealed in step S4 is subjected to air drawing to obtain a semi-hard copper tube product. During the air drawing process, the outer surface of the tube blank contacts the air drawing die, and the diameter is reduced and the wall thickness is increased under the action of the air drawing die. The die angle γ of the air drawing die is 44°, the sizing length of the air drawing die is B, the sizing zone diameter D2 of the air drawing die is 15.88 mm, the air drawing rate is S, and the sizing zone diameter of the drawing die used for the last drawing is D1. n S, B, B / (S*D1, n As shown in Table 2.

[0076] Examples 5-7 and Comparative Examples 4-5

[0077] The difference between Examples 5-7 and Comparative Examples 4-5 and Example 1 is that Examples 5-7 and Comparative Examples 4-5 change the sizing length B of the outer die for empty stretching, so that B / (S*D1, n The changes are shown in Table 2.

[0078] The test results of the average wall thickness, average outer diameter, wall thickness defect rate, hardness and tensile strength of the copper tubes obtained in Examples 1-7 and Comparative Examples 4-5 are shown in Table 2.

[0079] Table 1

[0080]

[0081] Table 2

[0082]

[0083] As can be seen from Tables 1 and 2, by controlling the sizing length B of the air-drawing outer mold and the air-drawing processing rate within suitable ranges, the embodiments of the present invention can produce copper tubes with semi-hard characteristics and a low wall thickness defect rate. When the sizing length B and the air-drawing processing rate are within their respective suitable ranges, B / (S*D1, n By controlling the thickness within an appropriate range, the uniformity of wall thickness can be further improved, thereby increasing the yield of semi-hard copper tubes.

[0084] Compared with Examples 1-4, the excessive air-drawing process in Comparative Examples 1-3 generates a large amount of residual stress inside. The uneven flow of metal during air-drawing leads to uneven wall thickness distribution, resulting in excessive tensile strength of the finished copper tube and an increased wall thickness defect rate.

[0085] Compared with Examples 1 and 5-7, the sizing length B of the outer die in Comparative Examples 4-5 was too small, which led to unstable metal flow during the air drawing process, resulting in uneven distribution of copper tube wall thickness and a significantly increased wall thickness defect rate.

[0086] Examples 8-14 and Comparative Example 6

[0087] The difference between Examples 8-14 and Comparative Example 6 and Example 1 is as follows:

[0088] Table 3 shows the die angle of the drawing die, the cone angle of the floating mandrel, the drawing rate, the rate of empty drawing, the die angle of the empty drawing die, the annealing temperature and the annealing time for each drawing pass in Examples 8-14 and Comparative Example 6.

[0089] The test results of the average wall thickness, average outer diameter, wall thickness defect rate, hardness and tensile strength of the copper tubes obtained in Examples 8-14 and Comparative Example 6 are shown in Table 3.

[0090] Table 3

[0091]

[0092] As can be seen from Table 3, compared with Example 1, the cone angle of the outer die in Comparative Example 6 is too large, which makes the metal flow unstable during the air drawing process, thereby affecting the dimensional accuracy of the copper tube and resulting in uneven wall thickness distribution of the copper tube.

[0093] Comparative Example 7

[0094] This embodiment provides a manufacturing process for a copper tube, including the following steps:

[0095] S1. Raw copper is added to a smelting furnace and heated to melt into molten copper. The molten copper is then subjected to horizontal continuous casting to obtain cast pipes. The raw copper is oxygen-free copper of grade TU0, wherein the mass percentage of copper is not less than 99.95%.

[0096] S2. The cast pipe obtained in step S1 is subjected to milling and rolling processes in sequence to obtain a pipe blank. The outer diameter of the pipe blank is 30mm and the wall thickness is 1.4mm.

[0097] S3. The tube blank obtained in step S2 is drawn in 3 passes. During each drawing process, the outer surface of the tube blank is in contact with the outer die of the drawing die, and the inner surface of the tube blank is in contact with the moving mandrel of the drawing die. The tube blank achieves diameter and wall reduction under the combined action of the outer die and the moving mandrel. The die angle α of the outer die for each drawing pass is 52°, and the cone angle β of the moving mandrel is 24°.

[0098] Dimensional parameters of the drawing dies used in each drawing pass (diameter of the sizing zone of the outer drawing die, maximum diameter D of the floating mandrel) max The minimum diameter D of the moving core. min The sizing length (A) and the drawing rate are the same as in Example 1.

[0099] S4. Perform air drawing on the tube blank after step S3. During air drawing, the outer surface of the tube blank contacts the air drawing die. The inner diameter of the air drawing die in the sizing section is 44°, the sizing length of the air drawing die is B, the sizing section diameter D2 of the air drawing die is 15.88 mm, the processing rate of air drawing is S, and the sizing section diameter of the drawing die used in the last drawing is denoted as D1. n S, B, B / (S*D1, n Same as in Example 1;

[0100] S5. After the tube blank is drawn in the air in step S4, it is wound into a coil and then annealed in a nitrogen atmosphere. The annealing temperature is 560℃ and the annealing time is 23 minutes to obtain the finished copper tube.

[0101] Testing revealed that the finished copper tube had a hardness of only 48.2 HV and a tensile strength of only 242 MPa, which did not meet the standards for semi-hard copper tubes.

[0102] Example 15

[0103] The difference between this embodiment and embodiment 1 is that in step S1 of this embodiment, the raw material copper is oxygen-free copper of grade TU2, wherein the mass percentage of copper is not less than 99.95%.

[0104] Example 16

[0105] The difference between this embodiment and embodiment 1 is that in step S1 of this embodiment, the raw material copper is phosphorus deoxidized copper of grade TP2, wherein the mass percentage of copper is not less than 99.95%.

[0106] The test results of the average wall thickness, average outer diameter, wall thickness defect rate, hardness and tensile strength of the copper tubes obtained in Examples 15 and 16 are shown in Table 4 below.

[0107] Table 4

[0108]

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A manufacturing process for a semi-rigid copper tube, characterized in that, Includes the following steps: S1. The raw copper is melted into molten copper, and the molten copper is continuously cast to obtain cast pipe; S2. The cast pipe obtained in step S1 is subjected to milling and rolling processes in sequence to obtain a pipe blank; S3. The tube blank obtained in step S2 is drawn in n passes, where n is a positive integer; During each drawing process, the outer surface of the tube blank contacts the outer drawing die of the drawing die, and the inner surface of the tube blank contacts the moving mandrel of the drawing die. The tube blank achieves diameter and wall reduction under the combined action of the outer drawing die and the moving mandrel. S4. After the tube blank is drawn in step S3, it is wound into a coil and then annealed. S5. The tube blank after annealing in step S4 is air-drawn to obtain a semi-hard copper tube. During the air drawing process, the outer surface of the tube blank comes into contact with the air drawing outer die, and the tube blank achieves diameter reduction and wall increase under the action of the air drawing outer die; In step S5, the processing rate of the air stretching is 2~16%; the sizing length of the air stretching outer die is 7~10mm; The processing rate of the air drawing is S, the sizing length of the air drawing outer die is B, and the diameter of the sizing zone of the drawing outer die used in the nth drawing pass is D1. n The drawing die used in the nth drawing pass refers to the drawing die used in the last drawing pass, 5≤B / (S*D1, n ≤8.

2. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S4, the annealing temperature is 500~600℃ and the annealing time is 15~50min.

3. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S5, the speed of the empty pull is 40~70m / min.

4. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S5, the wall thickness increase of the air stretching is ≤0.05mm.

5. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S5, the mold angle α of the air-pull outer mold is 40~46°.

6. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S1, the mass percentage of copper in the raw copper is not less than 99.95%.

7. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S3, the rate of each of the n drawing passes is independently 40~70m / min.

8. The manufacturing process of the semi-hard copper tube as described in claim 1, characterized in that, In step S3, the processing rate of each of the n drawing passes is independently 15% to 40%; And / or, in step S3, n is 2~4; And / or, in step S3, the mold angle of the outer mold is 50~54°; And / or, in step S3, the cone angle of the moving core head is 20~24°.

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