Continuous wire annealing apparatus

Abstract

The wire annealing device (1) for annealing and recrystallizing a wire (12) in a continuous process comprises two contact disks (2,3) for contacting a first wire portion extending therebetween, an annealing section (8) arranged between the disks (2,3) and annealing means for treating the first wire portion in the section (8), in particular conductive or inductive means, in which a first recrystallization partial process is carried out on the first wire portion in the section (8). Downstream of the second disk (3) is arranged a recrystallization section (11), through which the first wire portion passes downstream of the section (8) as a second wire portion, in which a second recrystallization partial process is carried out on the second wire portion. After leaving the section (8), the wire (12) is given a further opportunity for recrystallization without further heat supply. The recrystallization temperature is reduced by extending the recrystallization time. This results in an equivalent recrystallization with less energy than if the wire (12) were cooled immediately after leaving the section (8).

Description

Technical Field

[0001] The entire content of the priority application DE102021201104.7 is incorporated herein by reference.

Background Art

[0002] The present invention relates to a continuous wire annealing apparatus for annealing and recrystallizing a wire in a continuous process. The wire is particularly a metal wire, preferably made of copper or aluminum or an alloy of a plurality of metals.

[0003] When manufacturing a wire, generally, in order to reduce the cross-section, wire drawing of the wire is performed in multiple steps. That is, the wire is guided to pass through a wire drawing die having an opening with a diameter slightly smaller than the diameter of the passing wire. In this way, the wire material is deformed and the diameter of the wire decreases to the diameter of the opening of the wire drawing die. In such a wire drawing process, since the cross-section of the wire that can be reduced at one time is small, a wire drawing process of continuously reducing the diameter of the wire is continuously performed multiple times until the desired wire diameter is obtained.

[0004] However, due to the shaping of the wire material, in addition to the decrease in the diameter of the wire in the wire drawing process, strain hardening of the wire material also occurs simultaneously. This results in a decrease in the ductility of the wire and a decrease in the residual strain. That is, the wire after wire drawing breaks more quickly when strained or fractures more quickly when elongated than before wire drawing.

[0005] For this reason, the wire is recrystallized by heat supply after wire drawing. That is, the crystal lattice of the wire material having lattice defects in the form of dislocations in the lattice structure is regenerated by wire drawing and thereby "repaired".

[0006] Recrystallization is basically determined by three parameters: degree of deformation, temperature, and holding time. - The higher the degree of deformation, the more effectively recrystallization occurs. - Recrystallization is more effective at higher temperatures, but it cannot exceed certain material-dependent limits. - The longer the temperature is maintained, the more effectively recrystallization occurs.

[0007] In this case, the degree of deformation refers to the extent to which the crystal structure changes due to the wire drawing process, particularly to the extent to which the cross-section of the wire shrinks.

[0008] In addition to recrystallization, heat supply also regenerates the granular structure of the wire material. During this process, prolonged heat supply promotes grain growth. As the grains grow larger, the residual strain in the wire improves, increasing its ductility before breakage.

[0009] Recrystallization is carried out at high temperatures (e.g., 550°C), and the wire is annealed during this process, so the associated equipment is also called a "wire annealing apparatus."

[0010] The heat supply for recrystallization can, on the one hand, be performed "offline." That is, the drawn and hardened wire is heated in a stationary heat treatment device, particularly a recrystallization furnace, thereby inducing recrystallization. In this case, the recrystallization process is determined, in particular by the temperature curve over time, and by process parameters such as ramp-up time, holding time, holding temperature, and cooling time.

[0011] On the other hand, wire recrystallization can be performed in a continuous process, that is, while the wire is passing through the wire drawing machine without reducing its speed. Although technically difficult to achieve, this can improve efficiency and productivity because recrystallization is not performed in a separate process downstream of the wire drawing process, which would require removing the wire from the machine, winding it onto a reel, and possibly winding it back into the wire drawing machine for further processing.

[0012] In a continuous process, the wire feed rate can reach up to 50 meters per second, so recrystallization must be performed within a fraction of a second.

[0013] After recrystallization, the wire needs to be cooled again, but this too is carried out as a continuous process and integrated into a single piece of equipment called a continuous wire annealing apparatus. This, too, is done in a fraction of a second.

[0014] Cooling is typically performed immediately after recrystallization by immersing the wire in a coolant, particularly an emulsion or oil. Direct immersion of the wire in the coolant also prevents surface discoloration.

[0015] The drawback of this method is that the thermal energy introduced into the wire is removed again by immersing the wire in the coolant immediately after recrystallization. This shortens the temperature retention time, which must be compensated for by a higher heat input. This increases the energy consumption of the continuous wire annealing apparatus. [Overview of the project] [Problems that the invention aims to solve]

[0016] Therefore, the object of the present invention is to reduce the energy consumption of a continuous wire annealing apparatus. [Means for solving the problem]

[0017] This problem is solved by the continuous wire annealing apparatus described in claim 1, or by the method for annealing and recrystallizing wires described in claim 11. Further advantageous configurations of the present invention are included in the dependent claims.

[0018] The present invention is based on a continuous wire annealing apparatus for annealing and recrystallizing wires, particularly metal wires, in a continuous process, and the apparatus is -At least two contact disks, wherein the first contact disk is set to contact the rear end of a first wire portion extending between the first contact disk and the second contact disk, as viewed in the direction of wire travel, and the second contact disk is set to contact the front end as viewed in the direction of wire travel, - An annealing section is positioned between the first contact disk and the second contact disk, and is configured such that the first wire portion passes through the annealing section. - An annealing means for annealing a first wire portion in an annealing section, wherein a first recrystallization process is performed on the first wire portion in the annealing section.

[0019] In this configuration, the first and / or second contact disks are preferably configured as rotatably mounted pulleys for the wires. Preferably, such pulleys have a concave raceway for the wires on their outer circumference, within which the wires partially rotate or fully rotate one or more turns around the pulley.

[0020] The present invention is based on the idea of ​​extending the recrystallization time (corresponding to the holding time in the "offline process") by not immediately cooling the wire after it leaves the annealing section and giving it an opportunity to continue recrystallizing without further heat supply. In some cases, the cooling section may be moved further back in the direction of wire travel.

[0021] Accordingly, according to the present invention, a recrystallization section is located downstream of the second contact disk when viewed in the direction of wire travel, and the recrystallization section is configured such that the second wire portion, which previously passed through the annealing section as the first wire portion, passes through the recrystallization section and a second recrystallization process is performed in the second wire portion.

[0022] In this case, the concepts of "the first recrystallization partial process" and "the second recrystallization partial process" should not be understood as that recrystallization stops after the first recrystallization partial process and the second recrystallization partial process newly starts. Rather, from a physical perspective, both the first and second recrystallization partial processes together form a continuous and uninterrupted recrystallization process, and the recrystallization process is merely conceptually divided into two partial processes. In other words, the entire recrystallization process is initiated by the first recrystallization partial process and extended by the second recrystallization partial process.

[0023] By the method according to the present invention, in particular, the entire section where recrystallization occurs is extended, and thus the recrystallization time is also extended. At the same time, in some cases, the subsequent cooling section is shifted further backward in the advancing direction of the wire.

[0024] By extending the recrystallization time, it is possible to lower the recrystallization temperature when obtaining the same residual strain, thereby bringing about a direct energy saving.

[0025] Since the second recrystallization partial process is carried out without further heat supply, the same degree of recrystallization can be obtained with an overall clearly reduced energy supply. Realistically, according to the applicant's understanding, energy savings of up to 20% can be expected.

[0026] Conversely, it is also possible not to reduce the energy input. According to the present invention, since the recrystallization section is extended and thus the recrystallization time becomes longer, the residual strain of the wire is improved in this way. In this case, with the method according to the present invention, a strain value approximately the same as the strain value in the furnace can be obtained.

[0027] When applying the present invention, the operator of the continuous wire annealing device can choose to save energy or to improve the residual strain of the wire.

[0028] In a preferred embodiment of the present invention, the annealing means is a means for conductively heating the first wire portion, and the first contact disk and the second contact disk are configured to supply current to the first wire portion or to discharge current from the first wire portion, respectively.

[0029] High efficiency is achieved through conductive heating of the first wire section. This is because, as a result of the electrical (ohmic) resistance of the first wire section, electrical energy is directly converted into thermal energy.

[0030] In another preferred embodiment of the present invention, which is an alternative to the embodiment described most recently, the annealing means is a means for inductively heating the first wire portion.

[0031] In this configuration, the first wire section is arranged in the form of a short-circuited loop or coil, with both ends electrically connected. This wire loop or coil functions as a secondary coil for inductive energy transfer and is located near the primary coil through which the alternating current flows. As a result, an alternating voltage is induced in the wire loop or coil by electromagnetic induction, generating eddy currents. These overcurrents heat the first wire section through its electrical (ohmic) resistance.

[0032] Thus, heating of the first wire portion is performed non-contact, and therefore no wear occurs, but the energy transfer efficiency is lower than that of conductive heating of the wire.

[0033] In another preferred embodiment of the present invention, the recrystallization section is configured to place the second wire portion under a protective gas.

[0034] Preferred protective gases are water vapor, nitrogen, hydrogen, or a mixture of nitrogen and hydrogen. The protective gas replaces oxygen in the atmosphere, thus preventing oxidation of the wire surface and, consequently, discoloration.

[0035] In another preferred embodiment of the present invention, the continuous wire annealing apparatus does not have a wire cooling device between the annealing section and the recrystallization section.

[0036] By eliminating the need for a cooling system between the annealing and recrystallization sections, further energy savings can be achieved. This is because almost all of the residual heat present in the first wire section upon leaving the annealing section can be used in the second recrystallization process in the recrystallization section.

[0037] In another preferred embodiment of the present invention, which is an alternative to the most recently described embodiment, the continuous wire annealing apparatus has a cooling device for cooling the second contact disk.

[0038] A cooling device may be required for the second contact disk. This is because the second contact disk is continuously exposed to heat from the first wire portion flowing out of the annealing section, causing it to heat up considerably. Given that the temperature of the first wire portion in the annealing section is relatively high (e.g., 550°C), the absence of such a cooling device could lead to thermal overload of the second contact disk.

[0039] In the most recently described modified embodiment of the present invention, the cooling device for cooling the second contact disk includes means for spraying a coolant, particularly an emulsion or oil, onto the second contact disk.

[0040] In known cooling devices, for example, the second contact disk, along with the wire portion that contacts the second contact disk, is completely immersed in a cooling tank filled with a coolant, thereby strongly cooling not only the second contact disk but also the wire portion.

[0041] In contrast, when the second contact disk is cooled by spraying a coolant, the second contact disk is effectively cooled, but the wire portion in contact with the second contact disk is only slightly cooled. Furthermore, this method allows for the supply and discharge of the coolant without any problems. It is also possible to easily control the amount of coolant supplied per unit of time and adapt it to the amount of heat released.

[0042] By directing the coolant jet spray towards the second contact disk, particularly the contact strip portion on its outer circumference where the wire is not wound, it is possible to avoid excessive cooling of the wire portion wound around the outer circumference of the second contact disk.

[0043] In another preferred embodiment of the present invention, a cooling section and / or cooling tank is located downstream of the recrystallization section in the direction of wire travel, and the cooling section and / or cooling tank is configured such that a third wire section, which previously passed through the recrystallization section as a second wire section, passes through the cooling section and / or cooling tank and is cooled by a coolant in the cooling section and / or cooling tank.

[0044] Such a cooling section or cooling tank may be necessary if the wire is still too warm to undergo further processing, particularly winding onto a reel, after it has left the recrystallization section. Preferably, the cooling section is formed as a housing filled with a coolant, and the third wire portion is immersed in and passes through the cooling tank. In contrast, preferably, the third wire portion within the cooling tank is simply sprayed with a coolant, similar to the cooling device for the second contact disk described above.

[0045] In the most recently described modified embodiment of the present invention, the continuous wire annealing apparatus has a cooling section, the cooling section having means for spraying a coolant, particularly an emulsion or oil, onto the third wire portion.

[0046] In this case, it is particularly preferable that the cooling section has at least one device for adjusting the volumetric flow rate of the coolant in the cooling section. In particular, the device has at least one valve for introducing the coolant into the cooling section, and at least one valve is adjustable and is configured in particular as a proportional valve.

[0047] The use of a proportional valve makes it possible to precisely control the amount of coolant introduced into the cooling section through the valve per unit of time. In this way, the cooling action in the cooling section can be matched to the amount of heat to be released. This amount of heat depends in particular on the volume of wire material in the third wire section, and therefore on the diameter of the wire in the third wire section.

[0048] Instead of a proportional valve, a device for adjusting the volumetric flow rate may be, for example, a hand-lever valve. To improve the cooling effect using a larger volumetric flow rate, a frequency-controlled pump may also be considered.

[0049] In a continuous process using a continuous wire annealing apparatus according to the present invention, the method according to the present invention for annealing and recrystallizing a wire, particularly a metal wire, involves a first wire portion passing through an annealing section, being annealed in the annealing section, and undergoing a first recrystallization partial process in the first wire portion. Furthermore, a second wire portion, which previously passed through the annealing section as the first wire portion, passes through a recrystallization section, and undergoes a second recrystallization partial process in the second wire portion.

[0050] Further advantages, features, and applicability of the present invention are evident from the following description, which is related to the figures. The following figures are shown. [Brief explanation of the drawing]

[0051] [Figure 1] This figure shows a prior art continuous wire annealing apparatus that does not have a recrystallization section. [Figure 2] This figure shows a continuous wire annealing apparatus according to the present invention, which has a recrystallization section. [Modes for carrying out the invention]

[0052] Figure 1 shows a continuous wire annealing apparatus 1 according to prior art. The continuous wire annealing apparatus 1 has an annealing section 8 and a cooling section 4, but does not have a recrystallization section.

[0053] The wire 12, which has been drawn to a specific diameter in a wire drawing machine (not shown) and hardened, is heated in a continuous wire annealing apparatus 1 to largely stop the hardening and thus increase the residual strain, i.e., the maximum ductility before the wire breaks, thereby recrystallizing.

[0054] The wire 12 is inserted into the continuous wire annealing apparatus 1 from its left end and first passes around the pulley 10. All contact disks of the continuous wire annealing apparatus 1 shown in Figures 1 and 2 are similarly configured as pulleys. Furthermore, the wire 12 passes through several additional pulleys. The speed at which the wire 12 passes through the continuous wire annealing apparatus 1 is, for example, 30 m / s.

[0055] Subsequently, the wire 12 reaches the first contact disk 2, passes around the first contact disk 2, and flows into the annealing section 8, where it is heated. The annealing section 8 is configured as a closed housing (except for the inlet and outlet of the wire 12), thereby minimizing the amount of thermal energy that can leak from the heated wire into the surroundings. The length of the annealing section 8 in the continuous wire annealing apparatus 1 shown in Figure 1 is, for example, 2000 mm. The portion of the wire 12 that passes through the annealing section 8 is called the first wire portion. The direction of wire travel in the annealing section 8 is indicated by an arrow above the annealing section 8.

[0056] The first wire portion is heated by applying a voltage, preferably a DC voltage, and more preferably an AC voltage, to the first contact disk 2 and the second contact disk 3, thereby causing a DC or AC current to flow through the first wire portion, which heats the first wire portion based on its ohm resistance. In this case, the wire 12 reaches a temperature of, for example, 550°C when it enters the cooling nozzle 7 at the inlet of the cooling tank 9.

[0057] In the annealing section 8, the heating of the first wire portion causes a first recrystallization process to occur within the first wire portion, thereby virtually stopping the hardening of the first wire portion that occurred in the preceding wire drawing process.

[0058] The wire 12 leaves the annealing section 8 at the inlet of the cooling tank 9 and enters the inlet cooling nozzle 7. At the inlet cooling nozzle 7 of the cooling tank 9, a coolant, preferably an emulsion or oil, is sprayed or injected onto the wire 12, thereby releasing some of the thermal energy from the wire 12 at that location. Next, the wire 12 is routed around the second contact disk 3 within the cooling tank 9. The cooling tank 9 is filled with further coolant so that the second contact roller 3 and the portion of the wire 12 surrounding the second contact roller 3 are completely immersed in the coolant. The coolant in the cooling tank 9 releases heat from the portion of the wire. The heated coolant is discharged continuously or at regular time intervals and replaced with cooler coolant. Finally, the wire 12 leaves the cooling tank 9 again through the outlet cooling nozzle 6, where the wire 12 is again sprayed or injected with coolant.

[0059] Subsequently, the wire 12 passes through the cooling section 4. The cooling section 4 also has a closed housing (except for the inlet and outlet of the wire 12), into which further coolant flows, and the wire 12 is completely immersed within the housing. The direction of the wire's movement in the cooling section 4 is indicated by an arrow above the cooling section 4.

[0060] The cooling tank 9 and cooling section 4, which have cooling nozzles 6 and 7, cool the wire 12 to a temperature at which further processing, particularly winding onto a reel, is possible. However, in order to ensure the final temperature required for winding (approximately 50°C), as little thermal energy as possible is extracted from the wire 12.

[0061] Finally, the wire 12, which is still moistened by the coolant, passes through the drying section 5, where it is preferably dried by air blown into the drying section 5.

[0062] Subsequently, the wire 12 is guided out of the continuous wire annealing apparatus 1 through several additional pulleys at the right end of the continuous wire annealing apparatus 1, where it is further processed outside the continuous wire annealing apparatus 1, and in particular, wound onto a reel (not shown).

[0063] Figure 2 shows a continuous wire annealing apparatus 1 according to the present invention having a recrystallization section 11.

[0064] The continuous wire annealing apparatus 1 according to the present invention, shown in Figure 2, is based on the prior art continuous wire annealing apparatus 1 shown in Figure 1, and several modifications have been made to the prior art continuous wire annealing apparatus 1. Therefore, the corresponding elements of the two continuous wire annealing apparatuses 1 will not be explained again.

[0065] Similar to Figure 1, the wire 12 is guided into the annealing section 8, where it is heated, which causes a first recrystallization process in the first portion of the wire, after which it similarly enters the cooling tank 9.

[0066] If an inlet cooling nozzle is present at the inlet of the cooling tank 9, it is preferable not to use the inlet cooling nozzle. The same applies if an outlet cooling nozzle is present at the outlet of the cooling tank 9. Inside the cooling tank 9, the wire 12 is again routed around the second contact disk 3 (not shown in Figure 2).

[0067] In the cooling tank 9, the wire 12 is either slightly cooled or not cooled at all. Preferably, only the second contact disk 3 is sprayed with additional coolant to cool it, and the wire 12 remains largely uncooled. Preferably, the cooling tank 9 can also be filled with coolant, but since the cooling tank 9 is preferably only slightly circulated and replaced, or not circulated and replaced at all, the amount of thermal energy released by the coolant is small. The amount of coolant that must be present in the cooling tank 9, i.e., the filling level of the cooling tank 9, can be determined experimentally and may vary depending on the environment.

[0068] The wire 12 then passes through the recrystallization section 11, which, like the cooling section 4 located in the corresponding position in Figure 1, has a mostly closed housing. However, the wire 12 is not cooled in the recrystallization section 11. Therefore, even after leaving the cooling tank 9, the wire 12 retains a temperature sufficient for a second recrystallization partial process to be carried out in the recrystallization section 11.

[0069] In this way, the annealing section (meaning the section in which recrystallization takes place on wire 12) is extended, so to speak, even doubling in length, but the energy input is performed only in the first part of the original annealing section 8.

[0070] Therefore, when the degree of recrystallization achieved is the same, it is possible to reduce the thermal energy input to the annealing section 8, and as a result, energy savings of up to 20% can be achieved as described above.

[0071] Within the housing of the recrystallization section 11, a protective gas atmosphere, preferably consisting of nitrogen or water vapor, is present to prevent oxidation of the wire surface 12 and the resulting discoloration.

[0072] Finally, to lower the temperature of the wire 12 to a temperature suitable for further processing, the wire 12 passes through the cooling section 4 and the cooling tank 13. In the embodiment shown in Figure 2, for space reasons, the cooling section 4 and the cooling tank 13 are located at least partially within an additional housing 15, which is flange-mounted to the housing 14 of the continuous wire annealing apparatus 1. However, the cooling section 4 and the cooling tank 13 may be integrally configured with the housing 14 of the continuous wire annealing apparatus 1. It is also possible to provide only the cooling section 4 or only the cooling tank 13.

[0073] In cooling section 4, the wire 12 is immersed in a coolant, as in the continuous wire annealing apparatus 1 of Figure 1. The volumetric flow rate of the coolant can be adjusted in cooling section 4, thereby allowing the cooling effect on the wire 12 to be adjusted depending on the diameter and feed rate of the wire 12. This is preferably done through at least one proportional valve (not shown).

[0074] In the cooling tank 13, the wire 12 is similarly immersed in the coolant or simply sprayed with the coolant. [Explanation of symbols]

[0075] 1. Continuous wire annealing machine 2. First contact disk 3. Second contact disk 4 Cooling section 5. Dry section 6. Outlet cooling nozzle 7. Inlet cooling nozzle 8. Annealing section 9 Cooling tank 10 Pulley 11 Recrystallization interval 12 wires 13 Cooling tank 14. Housing of a continuous wire annealing machine 15. Housing of cooling section and cooling tank

Claims

1. A continuous wire annealing apparatus (1) for annealing and recrystallizing a metal wire (12) in a continuous process, - At least two contact disks (2, 3), wherein the first contact disk (2) is set to contact the rear end of a first wire portion extending between the first contact disk (2) and the second contact disk (3) in the direction of travel of the metal wire, and the second contact disk (3) is set to contact the front end in the direction of travel of the metal wire, - An annealing section (8) is positioned between the first contact disk (2) and the second contact disk (3), and is configured such that the first wire portion passes through the annealing section (8), - An annealing means for annealing the first wire portion in the annealing section (8), wherein the annealing means thereby performs a first recrystallization partial process on the first wire portion in the annealing section (8), A continuous wire annealing apparatus (1) is characterized in that, when viewed in the direction of travel of the metal wire, a recrystallization section (11) is located downstream of the second contact disk (3), and the recrystallization section is configured such that the second wire portion, which previously passed through the annealing section (8) as the first wire portion, passes through the recrystallization section (11), and a second recrystallization process is carried out in the second wire portion without further heat supply.

2. The continuous wire annealing apparatus (1) according to claim 1, characterized in that the annealing means is a means for resistively heating the first wire portion, and the first contact disk (2) and the second contact disk (3) are each set to supply current to the first wire portion or to discharge current from the first wire portion.

3. The continuous wire annealing apparatus (1) according to claim 1, characterized in that the annealing means is a means for inductively heating the first wire portion.

4. The continuous wire annealing apparatus (1) according to any one of claims 1 to 3, characterized in that the recrystallization section (11) is set to place the second wire portion under a protective gas.

5. A continuous wire annealing apparatus (1) according to any one of claims 1 to 4, characterized in that there is no cooling section for the metal wire (12) between the annealing section (8) and the recrystallization section (11).

6. A continuous wire annealing apparatus (1) according to any one of claims 1 to 4, characterized in that it has a cooling device (9) for cooling the second contact disk (3).

7. The continuous wire annealing apparatus (1) according to claim 6, characterized in that the cooling device (9) has means for spraying a coolant onto the second contact disk (3) in order to cool the second contact disk (3).

8. The continuous wire annealing apparatus (1) according to claim 7, characterized in that the means for spraying a coolant onto the second contact disk (3) is for spraying an emulsion or oil.

9. A continuous wire annealing apparatus (1) according to any one of claims 1 to 8, wherein a cooling section (4) and / or a cooling tank (13) are arranged downstream of the recrystallization section (11) when viewed in the direction of travel of the metal wire, and the cooling section and / or cooling tank are configured such that a third wire portion that previously passed through the recrystallization section (11) as a second wire portion passes through the cooling section (4) and / or the cooling tank (13) and is cooled by a coolant in the cooling section and / or the cooling tank.

10. The continuous wire annealing apparatus (1) according to claim 9, wherein the cooling section (4) has means for spraying a coolant onto the third wire portion.

11. The continuous wire annealing apparatus (1) according to claim 10, characterized in that the means for spraying a coolant onto the third wire portion is for spraying an emulsion or oil.

12. The continuous wire annealing apparatus (1) according to claim 10 or 11, characterized in that the cooling section (4) has at least one device for adjusting the volumetric flow rate of the coolant in the cooling section (4).

13. The continuous wire annealing apparatus (1) according to claim 12, wherein the apparatus has at least one valve for introducing a coolant into the cooling section (4), and at least one of the valves is adjustable.

14. The continuous wire annealing apparatus (1) according to claim 13, characterized in that at least one of the valves is configured as a proportional valve.

15. A method for annealing and recrystallizing a metal wire (12) in a continuous process using a continuous wire annealing apparatus (1) according to any one of claims 1 to 14, characterized in that a first wire portion passes through an annealing section (8), is annealed in the annealing section, and a first partial recrystallization process is performed on the first wire portion, and a second wire portion that previously passed through the annealing section (8) as the first wire portion passes through a recrystallization section (11), and a second partial recrystallization process is performed on the second wire portion without further heat supply.

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