Preparation process of semi-hard copper pipe

Abstract

The invention discloses a preparation process of a semi-hard copper pipe, and belongs to the technical field of metal processing. According to the method, a pipe blank is sequentially subjected to drawing machining, annealing treatment and empty drawing machining; in the drawing machining process, a pipe blank is extruded by the stretching outer die and the moving core head, plastic deformation can occur, and residual stress is generated in the pipe blank; through annealing treatment, residual stress generated in the drawing process is eliminated, the hardness of the pipe blank is reduced, and the pipe blank is easily subjected to empty drawing machining; and finally, in the air drawing machining process, the copper pipe is subjected to plastic deformation under the action of drawing force, diameter reducing and wall increasing are achieved, meanwhile, residual stress is generated in the pipe, and therefore the hardness and strength of the pipe are improved, and the copper pipe with the semi-hard state characteristic is successfully prepared finally.

Description

Technical Field

[0001] The present invention relates to the technical field of metal processing, and particularly relates to a preparation process for semi-hard state copper tubes. Background Art

[0002] In many modern industries such as refrigeration, air conditioning, electronic appliances, etc., copper tubes are key basic materials. A semi-hard state copper tube refers to a state in which the hardness and strength of the copper tube are between the soft state and the hard state after processing. The semi-hard state copper tube has good strength, plasticity and processing performance, and can meet the requirements of complex pipeline products such as air-conditioning condenser tubes and refrigerator refrigeration pipelines for the flexibility and strength of copper tubes, making the current market demand for semi-hard state copper tubes continue to rise.

[0003] However, for the existing traditional production process of copper tubes, in order to achieve the semi-hard state characteristics of copper tubes, a cumbersome process flow is required, and the production efficiency is low. Moreover, some semi-hard state copper tubes made by existing processes may also have defects such as insufficient dimensional accuracy and surface defects, and cannot meet the requirements of the current market for semi-hard state copper tubes. Summary of the Invention

[0004] Based on the defects existing in the prior art, the purpose of the present invention is to provide a preparation process for semi-hard state copper tubes.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A preparation process for semi-hard state copper tubes includes the following steps:

[0007] S1. Melting the raw material copper into copper liquid, and subjecting the copper liquid to continuous casting to obtain a cast tube;

[0008] S2. Successively subjecting the cast tube obtained in step S1 to milling and rolling to obtain a tube blank;

[0009] S3. Subjecting the tube blank obtained in step S2 to n passes of drawing, where n is a positive integer; during each pass of drawing, the outer surface of the tube blank contacts the drawing outer die of the drawing die, the inner surface of the tube blank contacts the floating plug of the drawing die, and the tube blank realizes diameter reduction and wall thickness reduction under the combined action of the drawing outer die and the floating plug;

[0010] S4. After winding the tube blank drawn in step S3 into a coil, performing annealing treatment;

[0011] S5. Subjecting the tube blank annealed in step S4 to tube sinking to obtain a semi-hard state copper tube; during tube sinking, the outer surface of the tube blank contacts the tube sinking outer die, and the tube blank realizes diameter reduction and wall thickness increase under the action of the tube sinking outer die.

[0012] Preferably, in step S4, the temperature of the annealing treatment is 500 - 600 °C, and the time of the annealing treatment is 15 - 50 min.

[0013] Preferably, in step S5, the sizing length L of the tube sinking outer die is 7 - 10 mm.

[0014] Preferably, in step S5, the processing rate of the tube sinking is 2 - 16%.

[0015] Preferably, in step S5, the processing rate of the tube sinking is S, the sizing length of the tube sinking outer die is B, and the diameter of the sizing zone of the drawing outer die used in the nth pass of drawing is D 1,n , where the drawing outer die used in the nth pass of drawing refers to the drawing outer die used in the last pass of drawing, and 5 ≤ B / (S * D 1,n ) ≤ 8.

[0016] Preferably, in step S5, the speed of the tube sinking is 40 - 70 m / min.

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

[0018] Preferably, the die angle of the tube sinking outer die is 40 - 46°.

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

[0020] Preferably, in step S3, the speeds of the n passes of drawing are each independently 40 - 70 m / min.

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

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

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

[0024] Preferably, in step S3, the cone angle of the floating plug is 20 - 24°.

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

[0026] In this application, the tube blank is successively subjected to drawing, annealing, and ironing. During the drawing process, the tube blank is extruded by the drawing outer die and the floating plug, resulting in plastic deformation and the generation of residual stress inside. Through annealing, the residual stress generated during drawing is eliminated, the hardness of the tube blank is reduced, and the tube blank is easily ironed. Finally, during the ironing process, the copper tube undergoes plastic deformation under the action of the tensile force, achieving diameter reduction and wall thickening. At the same time, residual stress is generated inside the tube material, thereby improving the hardness and strength of the tube material, and finally successfully preparing a copper tube with semi-hard state characteristics.

[0027] Compared with the prior art, the present invention simplifies the preparation process of the semi-hard state copper tube and improves the production efficiency of the semi-hard state copper tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the working principle diagram of the drawing die provided by the present invention;

[0029] Figure 2 is the working principle diagram of the ironing outer die provided by the present invention.

[0030] In the figure, 1 is the drawing outer die, 2 is the floating plug, 3 is the ironing outer die, 4 is the tube blank, 5 is the semi-hard state copper tube, α is the die angle of the drawing outer die, β is the taper angle of the floating plug, γ is the die angle of the ironing outer die, A is the sizing length of the drawing die, D max is the maximum diameter of the floating plug, D min is the minimum diameter of the floating plug, D1 is the sizing zone diameter of the drawing outer die, B is the sizing length of the ironing outer die, and D2 is the sizing zone diameter of the ironing outer die. DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to better illustrate the purpose, technical solutions, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples. The purpose is to understand the content of the present invention in detail, rather than limiting the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] Among the technical features described in the present invention in an open-ended manner, there are also closed technical solutions composed of the listed features, as well as the listed open technical solutions.

[0033] It should be understood that, unless otherwise specified, the numerical ranges involved in the present invention are considered continuous, including the minimum and maximum values of the numerical range, as well as each value between the minimum and maximum values. Further, when the range refers to integers, it includes each integer between the maximum and minimum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in the present invention should be understood to include any or all of the sub-ranges subsumed therein.

[0034] A preparation process for a semi-hard state copper tube provided by the present invention includes the following steps:

[0035] S1. Melting the raw materials into copper liquid, and subjecting the copper liquid to continuous casting to obtain a cast tube;

[0036] S2. Successively subjecting the cast tube obtained in step S1 to milling and rolling to obtain a tube blank;

[0037] S3. Subjecting the tube blank obtained in step S2 to n passes of drawing, where n is a positive integer;

[0038] As Figure 1 shown, during each pass of drawing in step S3, the outer surface of the tube blank 4 contacts the drawing outer die 1 of the drawing die, the inner surface of the tube blank 4 contacts the floating plug 2 of the drawing die, and the tube blank realizes diameter reduction and wall thickness reduction under the combined action of the drawing outer die 1 and the floating plug 2;

[0039] S4. Coiling the tube blank drawn in step S3 into a coil and then annealing it;

[0040] S5. Subjecting the tube blank annealed in step S4 to tube sinking to obtain a semi-hard state copper tube;

[0041] As Figure 2 shown, during the tube sinking process in step S5, the outer surface of the tube blank contacts the tube sinking outer die 3, and the tube blank realizes diameter reduction and wall thickness increase under the action of the tube sinking outer die 3 to obtain a semi-hard state copper tube 5.

[0042] In this application, the tube blank is successively subjected to drawing, annealing, and tube sinking. During the drawing process, the tube blank is extruded by the drawing outer die and the floating plug, and plastic deformation will occur, resulting in residual stress inside. Through annealing, the residual stress generated during the drawing process is eliminated, the hardness of the tube blank is reduced, and the tube blank is easy to be processed by tube sinking. Finally, during the tube sinking process, the copper tube undergoes plastic deformation under the action of the tensile force to realize diameter reduction and wall thickness increase, and at the same time, residual stress is generated inside the tube material, thereby improving the hardness and strength of the tube material, and finally successfully preparing a copper tube with semi-hard state characteristics.

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

[0044] In the present application, by regulating the process parameters of the sinking drawing process (such as the processing rate of sinking drawing, the sizing length, etc.), the hardness and tensile strength of the copper tube can be precisely controlled to meet the requirements of different application scenarios.

[0045] In one embodiment, in step S5, the sizing length B of the sinking drawing outer die is 7 - 10 mm. The sizing length B of the sinking drawing outer die can be 7 mm, 8 mm, 9 mm, 10 mm or a range composed of any two sets of these values. The sizing area of the sinking drawing outer die is the part of the sinking drawing outer die used to finally determine the outer diameter of the copper tube. The sizing length B of the sinking drawing outer die refers to the dimension of the sizing area of the sinking drawing outer die in its axial direction. The size of the sizing length determines the contact time and force distribution between the copper tube and the sinking drawing outer die during the sinking drawing process. The inventors have found through research that controlling the sizing length of the sinking drawing outer die within an appropriate range can reduce the residual stress during the metal deformation process, make the metal flow more smoothly, and improve the wall thickness yield of the semi-hard copper tube. If the sizing length of the sinking drawing outer die is too short, it will cause unstable metal flow and affect the dimensional accuracy of the semi-hard copper tube finished product.

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

[0047] The inventors have found through research that if the processing rate of the sinking drawing is too large, it will cause excessive residual stress during the copper tube drawing process, resulting in too high hardness of the copper tube, which does not meet the requirements of the semi-hard tube. On the other hand, if the processing rate of the sinking drawing is too large, it may also cause uneven metal flow during the sinking drawing process, resulting in uneven wall thickness distribution.

[0048] In one embodiment, in step S5, the processing rate of the sinking drawing is S, the sizing length of the sinking drawing outer die is B, and the diameter of the sizing area of the drawing outer die used in the nth pass of drawing is D 1,n , the drawing outer die used in the nth pass of drawing refers to the drawing outer die used in the last pass of drawing, 5 ≤ B / (S * D1,n ) ≤ 8. For example, B / (S * D 1,n ) can be 5, 5.4, 5.5, 6, 6.2, 6.9, 7, 7.2, 7.5, 7.7, 8 or a range composed of any two sets of these values.

[0049] The inventor has found through research that the diameter D of the sizing zone of the drawing external die used in the nth pass drawing 1,n , the processing rate S of the tube sinking, and the sizing length B of the tube sinking external die jointly affect the dimensional accuracy and surface quality of the semi - hard copper tube. On the premise that B and S are each within a suitable range, controlling B / (S * D 1,n ) within the range of 5 - 8 can ensure that the metal flow is more stable during the tube sinking process, improve the dimensional accuracy of the semi - hard copper tube, reduce the phenomenon of uneven wall thickness and surface defects, and improve the wall thickness yield rate of the semi - hard copper tube.

[0050] In one embodiment, in step S5, the wall - thickening amount of the tube sinking ≤ 0.05 mm. For example, the wall - thickening amount of the tube sinking can be 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm or a range composed of any two sets of these values. In the present invention, the wall - thickening amount of the tube sinking refers to the increase in the wall thickness of the copper tube during the tube sinking process.

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

[0052] In one embodiment, in step S5, the rate of the tube sinking is 40 - 70 m / min. For example, the rate of the tube sinking 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 composed of any two sets of these values.

[0053] The present invention has no particular limitation on the source of the raw copper. For example, the raw copper can be at least one of oxygen - free copper of grade TU0, oxygen - free copper of grade TU1, oxygen - free copper of grade TU2, pure copper of grade T2, and phosphor - deoxidized copper of grade TP2.

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

[0055] The impurity components in the raw copper are not more than 0.05%. Specifically, the impurity components in the raw copper and their mass percentages 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 have found through research that the preparation process of the present invention uses raw copper with a mass percentage of copper element not less than 99.95% as raw material, and processes it into semi-hard state copper tubes, which can avoid the problem that the hardness of the copper tubes does not meet the requirements of semi-hard state tubes due to excessive impurity components.

[0057] In one embodiment, in step S3, the rates of the n-pass drawing are each independently 40 - 70 m / min. For example, the rates of the n-pass drawing are each independently 40 m / min, 45 m / min, 50 m / min, 55 m / min, 60 m / min, 65 m / min, 70 m / min or the range composed of any two sets of these values.

[0058] In one embodiment, in step S3, the reduction ratios of the n-pass drawing are each independently 15 - 40%. For example, the reduction ratios of the n-pass drawing can be each independently 15%, 17.5%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 30%, 31%, 32%, 35%, 37%, 38%, 40% or the range composed of any two sets of these values.

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

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

[0061] In one embodiment, in step S3, the taper angle β of the floating plug is 20 - 24°. In the present invention, the taper angle β of the floating plug refers to twice the angle between the outer wall surface of the floating plug corresponding to the die cavity deformation area and its central axis.

[0062] In one embodiment, in step S3, the sizing lengths A of the drawing outer dies used in the n-pass drawing are each independently 4 - 6 mm. For example, the sizing lengths A of the drawing outer dies used in the n-pass drawing can be each independently 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm or the range composed of any two sets of these values. The sizing area of the drawing outer die is the part of the drawing outer die used to finally determine the outer diameter of the tube blank, and the sizing length A of the drawing outer die refers to the dimension of the sizing area of the drawing outer die in its axial direction.

[0063] In order to enable those skilled in the art to better understand the solution of 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 a part of the embodiments of the present invention, rather than all the embodiments.

[0064] The following is the test method for tensile strength: The test is carried out according to GB / T 228.1:2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The qualified range of the tensile strength of the semi-hard copper tube is: 245 - 325 MPa.

[0065] The following is the test method for hardness: The hardness of the finished copper tube is tested by using a Vickers hardness tester. The qualified range of the hardness of the semi-hard copper tube is 70 - 120 HV.

[0066] The following is the test method for the wall thickness defect rate: A copper tube with a certain length (100 m) 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 the measurement points are measured. The average wall thickness and average outer diameter of the copper tube are calculated, and 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, and the following formula is used to calculate the defect rate: Defect rate = (Number of measurement points with a relative deviation ≥ 5%) / Total number of measurement points * 100%.

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

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

[0069] Embodiments and comparative examples of the preparation process of the semi-hard copper tube according to the present invention. The preparation process of the semi-hard copper tube includes the following steps:

[0070] S1. Add raw copper into a melting furnace and heat it to melt into copper liquid. Carry out horizontal continuous casting treatment on the copper liquid to obtain a cast tube; the raw copper is oxygen-free copper with a grade of TU0, and the mass percentage of copper is not less than 99.95%.

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

[0072] S3. Subject the tube blank obtained in step S2 to three passes of drawing. During each pass of drawing, the outer surface of the tube blank contacts the drawing outer die of the drawing die, and the inner surface of the tube blank contacts the floating plug of the drawing die. The tube blank is reduced in diameter and wall thickness under the combined action of the drawing outer die and the floating plug. The outer diameter and wall thickness of the tube blank after each pass of drawing are shown in Table 1. The die angle α of the drawing outer die for each pass is 52°, and the taper angle β of the floating plug is 24°;

[0073] The dimensional parameters of the drawing die used for each pass of drawing (the sizing zone diameter of the drawing outer die, the maximum diameter D max of the floating plug, the minimum diameter D min of the floating plug, and the sizing length A), and the drawing reduction rate are shown in Table 1.

[0074] S4. Wind the tube blank drawn in step S3 into a coil and then perform annealing treatment in a nitrogen atmosphere. The temperature of the annealing treatment is 560 °C, and the time of the annealing treatment is 23 min;

[0075] S5. Subject the tube blank annealed in step S4 to tube sinking to obtain a semi-hard state copper tube product. During tube sinking, the outer surface of the tube blank contacts the tube sinking outer die, and the tube blank is reduced in diameter and increased in wall thickness under the action of the tube sinking outer die. The die angle γ of the tube sinking outer die is 44°, the sizing length of the tube sinking outer die is B, the sizing zone diameter D2 of the tube sinking outer die is 15.88 mm, the reduction rate of the tube sinking is S, and the sizing zone diameter of the drawing outer die used for the last pass of drawing is D 1,n , S, B, and B / (S * D 1,n ) are shown in Table 2.

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

[0077] The differences between Examples 5 - 7 and Comparative Examples 4 - 5 and Example 1 are that in Examples 5 - 7 and Comparative Examples 4 - 5, by changing the sizing length B of the tube sinking outer die, B / (S * D 1,n ) is changed, as specifically 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]

[0084] As can be seen from Tables 1 to 2, in the embodiments of the present invention, by controlling the sizing length B of the sinking die and the processing rate of sinking in appropriate ranges respectively, the copper tubes prepared can have semi-hard state characteristics and at the same time have a low wall thickness defect rate. When the sizing length B and the processing rate of sinking are within their respective suitable ranges, controlling B / (S*D 1,n ) within an appropriate range can further improve the wall thickness uniformity and increase the wall thickness yield of the semi-hard state copper tubes.

[0085] Compared with Embodiments 1 to 4, the processing rate of sinking in Comparative Examples 1 to 3 is too large, which will generate a large amount of residual stress inside, and the metal flows unevenly during the sinking process, resulting in uneven wall thickness distribution, and thus the tensile strength of the finished copper tubes is too large and the wall thickness defect rate increases.

[0086] Compared with Embodiment 1 and Embodiments 5 to 7, the sizing length B of the sinking die in Comparative Examples 4 to 5 is too small, resulting in unstable metal flow during the sinking process, uneven wall thickness distribution of the copper tubes, and a significant increase in the wall thickness defect rate.

[0087] Embodiments 8 to 14 and Comparative Example 6

[0088] The differences between Embodiments 8 to 14 and Comparative Example 6 and Embodiment 1 are as follows:

[0089] In Embodiments 8 to 14 and Comparative Example 6, the die angle of the drawing die used in each drawing pass, the taper angle of the floating plug, the drawing rate, the sinking rate, the die angle of the sinking die, the annealing temperature, and the annealing time are shown in Table 3.

[0090] 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 Embodiments 8 to 14 and Comparative Example 6 are shown in Table 3.

[0091] Table 3

[0092]

[0093] As can be seen from Table 3, compared with Embodiment 1, the taper angle of the sinking die in Comparative Example 6 is too large, which makes the metal flow unstable during the sinking process, thus affecting the dimensional accuracy of the copper tubes and resulting in uneven wall thickness distribution of the copper tubes.

[0094] Comparative Example 7

[0095] The present embodiment provides a preparation process for copper tubes, including the following steps:

[0096] S1. Adding raw copper into a melting furnace to heat and melt it into copper liquid, and performing horizontal continuous casting on the copper liquid to obtain a cast tube; the raw copper is oxygen-free copper with a grade of TU0, wherein the mass percentage of copper is not less than 99.95%;

[0097] S2. The cast pipes obtained in step S1 are successively subjected to milling and rolling to obtain billets. The outer diameter of the billets is 30 mm and the wall thickness is 1.4 mm.

[0098] S3. The billets obtained in step S2 are drawn in 3 passes; during each pass of drawing, the outer surface of the billet contacts the drawing outer die of the drawing die, the inner surface of the billet contacts the floating plug of the drawing die, and the billet realizes diameter and wall thickness reduction under the combined action of the drawing outer die and the floating plug; the die angle α of the drawing outer die for each pass is 52°, and the taper angle β of the floating plug is 24°.

[0099] The dimensional parameters of the drawing die used for each pass of drawing (the diameter of the sizing zone of the drawing outer die, the maximum diameter D max of the floating plug, the minimum diameter D min of the floating plug, and the sizing length A), the drawing reduction rate are the same as those in Example 1.

[0100] S4. The billets drawn in step S3 are drawn without mandrel; during the drawing without mandrel, the outer surface of the billet contacts the drawing outer die without mandrel. The inner diameter of the drawing outer die without mandrel in the sizing section is, the die angle of the drawing outer die without mandrel is 44°, the sizing length of the drawing outer die without mandrel is B, the diameter D2 of the sizing zone of the drawing outer die without mandrel is 15.88 mm, the drawing reduction rate of the drawing without mandrel is S, and the diameter of the sizing zone of the drawing outer die used for the last pass of drawing is denoted as D 1,n , S, B, B / (S*D 1,n ) are the same as those in Example 1;

[0101] S5. The billets drawn without mandrel in step S4 are wound into coils and then annealed in a nitrogen atmosphere. The temperature of the annealing treatment is 560 °C, and the time of the annealing treatment is 23 min to obtain finished copper tubes.

[0102] It is found through detection that the hardness of the finished copper tubes is only 48.2 HV and the tensile strength is only 242 MPa, which are not within the qualified standards of semi-hard copper tubes.

[0103] Example 15

[0104] The difference between this example and Example 1 is that: in step S1 of this example, the raw copper is oxygen-free copper of grade TU2, and the mass percentage of copper is not less than 99.95%.

[0105] Example 16

[0106] The difference between this example and Example 1 is that: in step S1 of this example, the raw copper is phosphor-deoxidized copper of grade TP2, and the mass percentage of copper is not less than 99.95%.

[0107] 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 to 16 are shown in Table 4 below.

[0108] Table 4

[0109]

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation process of a semi-hard copper tube, characterized in that, It includes the following steps: S1. Melting the raw copper into copper liquid, and subjecting the copper liquid to continuous casting to obtain a cast pipe; S2. Successively subjecting the cast pipe obtained in step S1 to milling and rolling to obtain a tube blank; S3. Subjecting the tube blank obtained in step S2 to n passes of drawing, where n is a positive integer; During each pass of drawing, the outer surface of the tube blank contacts the drawing outer die of the drawing die, the inner surface of the tube blank contacts the floating plug of the drawing die, and the tube blank realizes diameter reduction and wall thickness reduction under the combined action of the drawing outer die and the floating plug; S4. Coiling the tube blank drawn in step S3 into a coil and then performing annealing treatment; S5. Subjecting the tube blank annealed in step S4 to ironing to obtain a semi-hard copper tube; During ironing, the outer surface of the tube blank contacts the ironing outer die, and the tube blank realizes diameter reduction and wall thickness increase under the action of the ironing outer die.

2. The preparation process of the semi-hard copper tube according to claim 1, characterized in that, In step S4, the temperature of the annealing treatment is 500 - 600 °C, and the time of the annealing treatment is 15 - 50 min.

3. The preparation process of the semi-hard copper tube according to claim 1, characterized in that, In step S5, the ironing rate is 2 - 16%; And / or, in step S5, the ironing speed is 40 - 70 m / min.

4. The preparation process of the semi-hard copper tube as described in claim 1, characterized in that, In step S5, the sizing length L of the ironing outer die is 7 - 10 mm.

5. The preparation process of the semi-hard copper tube as described in claim 1, characterized in that, In step S5, the processing rate of the tube sinking is S, the sizing length of the tube sinking external die is B, and the diameter of the sizing zone of the drawing external die used in the n-th pass drawing is D 1,n , and the drawing external die used in the n-th pass drawing refers to the drawing external die used in the last pass drawing, where 5 ≤ B / (S * D 1,n ) ≤ 8.

6. The preparation process of the semi-hard copper tube as described in claim 5, characterized in that, In step S5, the wall thickness increase amount of ironing ≤ 0.05 mm.

7. The preparation process of the semi-hard copper tube according to claim 1, characterized in that, In step S5, the die angle α of the ironing outer die is 40 - 46°.

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

9. The preparation process of the semi-hard copper tube according to claim 1, characterized in that, In step S3, the speeds of the n passes of drawing are independently 40 - 70 m / min.

10. The preparation process of the semi-hard copper tube as described in claim 1, characterized in that, In step S3, the drawing rates of the n passes of drawing are independently 15 - 40%; And / or, in step S3, n is 2 - 4; And / or, in step S3, the die angle of the outer die is 50 - 54°; And / or, in step S3, the taper angle of the floating plug is 20 - 24°.

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