JP7637585B2 - Wire drawing method - Google Patents

Description

The present invention relates to a wire drawing method and a wire drawing device.

High-temperature superconducting wire is manufactured by filling a metal tube with the mixed powder, introducing multiple metal tubes filled with the mixed powder into a further tube, and processing the tube into a long, thin wire using a wiredrawing method. This method is a wiredrawing method generally used for metal tubes or metal rods. A drawing method, which is an example of a wiredrawing method, is described in, for example, Patent Document 1.

The drawing method is a processing method in which the material is passed through a die hole whose diameter is smaller than the maximum diameter of the material to be drawn, thereby reducing the cross-sectional diameter of the material in the same manner as the hole diameter. The process of passing the material through die holes with gradually smaller diameters is repeated multiple times until the desired cross-sectional diameter is reached.

JP 2013-252565 A

For example, high-temperature superconducting wire is made up of multiple metal tubes with different deformation resistances, such as copper tubes, aluminum tubes, or iron tubes, and the material made up of multiple metal tubes is drawn.

When using the drawing method, a long, thin wire is produced by repeatedly passing the material through a die hole. When drawing a tube made up of multiple tube materials, deformation begins from the metal tube located on the outermost side. For this reason, the closer the metal tube is positioned in the center of the cross-sectional direction, the slower it tends to start to deform.

As a result, the material located on the outermost periphery deforms first, resulting in a longer longitudinal length. On the other hand, the material located in the center of the cross section deforms later, resulting in a shorter longitudinal length.

For example, when a wire is made up of metal materials with different deformation resistances, such as a high-temperature superconducting wire, the amount of deformation varies for each metal material, and therefore the longitudinal length also varies for each metal material. In order to obtain the geometric characteristics required for a high-temperature superconducting wire, it is necessary to make the cross-sectional shape of the wire in the longitudinal direction uniform.

The object of the present invention is to make the cross-sectional shape of the wire in the longitudinal direction uniform in a wire drawing method.

A wire drawing method according to one aspect of the present invention is a wire drawing method for reducing the cross-sectional diameter of a wire having at least a first tube and a second tube arranged around the first tube by wire drawing, comprising the steps of: preparing a first wire having the first tube having a first longitudinal length and the second tube having a second longitudinal length different from the first longitudinal length; reducing the cross-sectional diameter of the first wire by wire drawing to produce a second wire having the first tube having a third longitudinal length and the second tube having a fourth longitudinal length different from the third longitudinal length; and making a first difference between the third longitudinal length and the fourth longitudinal length of the second wire smaller than a second difference between the first longitudinal length and the second longitudinal length of the first wire.

A wire drawing device according to one aspect of the present invention includes a die having a hole diameter smaller than the maximum diameter of a wire having at least a first tube material and a second tube material provided around the first tube material, and a gripping portion that grips one end of the wire material and pulls it in a predetermined direction with a predetermined tensile force. The wire material is passed through the hole of the die, and the gripping portion gripping the end of the wire material is pulled in the predetermined direction with the predetermined tensile force, thereby reducing the cross-sectional diameter of the wire material. The first wire material has a first longitudinal length and a second longitudinal length different from the first longitudinal length. A material is prepared, the first wire is passed through the hole of the die, and the gripping portion gripping the end of the first wire is pulled in the predetermined direction with the predetermined tensile force to reduce the cross-sectional diameter of the first wire, thereby producing a second wire having the first tube material having a third longitudinal length and the second tube material having a fourth longitudinal length different from the third longitudinal length, and the first difference between the third longitudinal length and the fourth longitudinal length of the second wire is made smaller than the second difference between the first longitudinal length and the second longitudinal length of the first wire.

According to one aspect of the present invention, the cross-sectional shape of the wire in the longitudinal direction can be made uniform in a wire drawing method.

1A and 1B are cross-sectional and side views of a material that is constructed into multiple metal tubes and metal bars. FIG. 1 is a simplified diagram of a drawing device. FIG. 2A is a side view of a material composed of a plurality of metal tubes and metal bars before drawing, and FIGS. 2B and 2C are side views of the material after drawing. FIG. 2A is a side view of a material composed of a plurality of metal tubes and metal bars before drawing, and FIG. 2B is a side view of the material after drawing. FIG. 1A is a side view of a material composed of a plurality of metal tubes and metal bars having the same deformation resistance before drawing, and FIG. 1B is a side view of the material after drawing. FIG. 1A is a side view of a material composed of multiple metal tubes and metal bars with different deformation resistances, in which the metal tubes located at the outermost periphery have low deformation resistance, before drawing, and FIG. 1B is a side view of the material after drawing. FIG. 1A is a simplified diagram of a drawing device, and FIG. FIG. 1A is a side view of a material composed of multiple metal tubes and metal bars with different deformation resistances, in which the metal tubes located at the outermost periphery have the greatest deformation resistance, before drawing, and FIG. 1B is a side view of the material after drawing.

The present invention will be described in detail below with reference to the embodiments.

The embodiment relates to the wire drawing process of a material composed of high-temperature superconducting wire or multiple metal tube materials. For example, in the drawing process, the longitudinal length of the metal tube materials differs, so cutting work must be performed on both ends that have different cross-sectional shapes.

As a result, when multiple drawing processes are performed, multiple cutting operations are also required. In order to obtain the performance of high-temperature superconducting wire, it is necessary to make the cross-sectional shape in the longitudinal direction uniform and reduce the number of steps in the drawing process.

For this reason, in the embodiment, for a material composed of multiple metal tubes or rods, the length of each metal tube or rod before processing is not made uniform, but is made to have different lengths and thicknesses due to the deformation resistance and arrangement of the material.

For example, the deformation resistance of the metal tube and the length before processing depending on the arrangement are calculated using CAE (Computer Aided Engineering). In the CAE study, the wire drawing process that reduces the maximum cross-sectional diameter of the material before wire drawing by 10% or more is considered.

The longitudinal length of each metal tube is measured when the cross-sectional diameter of the metal tube becomes 10% or more smaller than the initial cross-sectional diameter, and the difference between the longitudinal length of each metal tube material and the minimum longitudinal length of the metal tube is calculated, and the length of the metal tube before wire drawing is shortened by that difference.

In the above embodiment, the cut portions at the ends of the material are reduced by making the cross-sectional deformation in the longitudinal direction uniform during the wire drawing process. This reduces the loss of material. Furthermore, the reduction in the number of cutting steps makes it possible to reduce the number of steps in the wire drawing process, thereby reducing manufacturing costs.

The following describes the examples using the drawings.

With reference to FIG. 1, an example of a wire material that is composed of a plurality of metal tubes and one metal rod will be described.
1, a metal tube 120 is disposed on the inner diameter side of a metal tube 110, and a metal rod 130 is disposed on the inner diameter side of the metal tube 120 to form a wire. The metal tube 110, the metal tube 120, and the metal rod 130 have the same length, different inner and outer diameters, and a cross-sectional shape of a circular arc. The length of the wire in the longitudinal direction is H1.

The methods for drawing wire include drawing, cassette roll processing, and groove roll processing. Of these methods, drawing will be used as an example in Example 1.

The configuration of a drawing apparatus, which is an example of a wire drawing apparatus, will be described with reference to FIG.
As shown in Fig. 2, the drawing device has a die 210 having a hole 230 and a gripping portion (chuck portion) 220. The wire 100 having an initial diameter D1 at end B5 is advanced by pulling the gripping portion 220 in the B4 direction with a predetermined tensile force while the end B6 of the wire 100 is gripped by the gripping portion 220. As a result, the cross-sectional diameter D1 at end B5 is reduced to the cross-sectional diameter D2 at end B6.

Specifically, the wire 100 is pulled in the B4 direction by the gripping portion 220, so that the wire 100 passes through the hole 230 of the die 210. The wire 100 that passes through the hole 230 of the die 210 has an initial diameter D1 that is smaller than the die diameter B7, and is reduced to a cross-sectional diameter D2. As a result, the cross-sectional diameter of the wire 100 that passes through the hole 230 is reduced, while the length in the longitudinal direction is increased.

During the drawing process in which the cross-sectional diameter is reduced, deformation occurs from the outer diameter side of the wire 100, and as the cross-sectional reduction rate increases, i.e., as the cross-sectional diameter becomes smaller, the deformation moves toward the center of the cross section.

In addition, the deformation speed of the metal tubes 110, 120 or metal rods 130, which have low deformation resistance, is fast. Therefore, the longitudinal length after drawing is longer than that of the metal tubes 110, 120 or metal rods 130, which have low deformation resistance before drawing.

For the wire 100 consisting of the metal tubes 110, 120 and metal rod 130 shown in Figure 1, if the metal tubes 110, 120 and metal rod 130 are made of materials with the same deformation resistance or materials with different deformation resistances, the length of each metal tube passing through the hole 230 of the die 210 of the drawing processing device shown in Figure 2 will be different.

Figure 3 shows the longitudinal lengths H1 and H2 of the wire 100 before and after drawing.

As shown in FIG. 3A, the metal tubes 110, 120 and the metal rod 130 have the same length H1 and an initial diameter D1.
After the cross-sectional diameter of the wire 100 shown in FIG. 3(a) is reduced from D1 to D2 by the drawing apparatus shown in FIG. 2, the wire 100 has a cross-sectional shape shown in FIG. 3(b) or FIG. 3(c).

As shown in FIG. 3(b), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal length of the metal tube 110 is the longest length. The longitudinal length of the metal tube 110 is longer than H2 by H11. The longitudinal length of the metal tube 120 is longer than H2 by H12.

As shown in FIG. 3(c), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal length of the metal tube 120 is the longest length. The longitudinal length of the metal tube 110 is longer than H2 by H12. The longitudinal length of the metal tube 120 is longer than H2 by H11.

As shown in FIG. 3(b), in a wire 100 in which the deformation resistances of the metal tubes 110, 120 and the metal rod 130 are the same, when the wire 100 is drawn, with a longitudinal length of H1 and a diameter of D1 before the drawing process, the longitudinal length after the drawing process will be different.

Specifically, in FIG. 3(b), the length of the metal rod 130 located at the center of the cross section after drawing is H2, and the length of the metal tube 110 located on the outermost side is longer than H2 by H11. The length of the metal tube 120 located on the inner diameter side of the metal tube 110 is longer than the length H2 of the metal rod 130 by H12.

On the other hand, as shown in FIG. 3(c), in the wire 100 in which the deformation resistances of the metal tubes 110, 120 and the metal rod 130 are different, the length of the metal tube 110 located on the outermost side is longer than the length H2 of the metal rod 130 located at the center of the cross section after drawing by H12. The length of the metal tube 120 located on the inner diameter side of the metal tube 110 is longer than the length H2 of the metal rod 130 by H11.

Referring to FIG. 5, in order to make the cross-sectional shape of the wire 100 in the longitudinal direction consistent after drawing, conditions for making the length of the wire 100 uniform after drawing using materials with the same deformation resistance will be considered. This consideration may be performed, for example, using CAE (Computer Aided Engineering).

5A, in the material 100 composed of the metal tube 110, the metal tube 120, and the metal rod 130, the length of the metal rod 130 is the longest at H1. The length of the metal tube 120 is H1-H11. The length of the metal tube 110 is H1-H12.
After the cross-sectional diameter of the wire 100 shown in FIG. 5(a) is reduced from D1 to D2 by the drawing apparatus shown in FIG. 2, the wire 100 has a cross-sectional shape shown in FIG. 5(b).

As shown in FIG. 5(b), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal lengths of the metal tubes 110 and 120 are the longest lengths, which are longer than H2 by H16.

For example, wire 100 having length H1 and made of metal tube 110, metal tube 120, and metal bar 130 made of low carbon steel with the same deformation resistance was measured for lengths H11 and H12 (see FIG. 3(b)) after drawing, in which the initial cross-sectional diameter D1 was reduced by 10-15% to a cross-sectional diameter D2. As a result, it was confirmed that the length of metal tube 110 was longer by H11, which corresponds to 20%, and the length of metal tube 120 was longer by H12, which corresponds to 10%, of the shortest length H2 of metal bar 130 after drawing.

The wire 100 is composed of a metal tube 120 having a difference of H11 from the length H1 of the metal rod 130, and a metal tube 110 having a difference of H12 from the length H1 of the metal rod 130. The wire 100 (see FIG. 5(b)) was examined after the cross-sectional diameter was reduced from D1 to D2 by the drawing device of FIG. 2. As a result, it was confirmed that the difference in length H16 after drawing shown in FIG. 5(b) is sufficiently smaller than the difference in length H11, H12 after drawing shown in FIG. 3(b).

For the wire 100 consisting of the metal tubes 110, 120 and metal rod 130 shown in Figure 1, if the metal tubes 110, 120 and metal rod 130 have different deformation resistances and the metal tube 110 is made of a material with low deformation resistance, the length of each metal tube passing through the hole 230 of the die 210 of the drawing processing device shown in Figure 2 will be different.

Figure 4 shows the longitudinal lengths H1 and H2 of the wire 100 before and after drawing.

4A show different deformation resistances among the metal tube 110, the metal tube 120, and the metal rod 130. For example, in the case of the wire 100 in which the deformation resistances are greatest for the metal tube 130, the metal rod 110, and the metal tube 120 in that order, the metal tube 120 has the smallest deformation resistance and therefore undergoes deformation quickly.
As shown in FIG. 4A, the metal tubes 110, 120 and the metal rod 130 have the same length H1 and an initial diameter D1.
After the cross-sectional diameter of the wire 100 shown in FIG. 4(a) is reduced from D1 to D2 by the drawing apparatus shown in FIG. 2, the wire 100 has a cross-sectional shape shown in FIG. 4(b).

As shown in FIG. 4(b), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal lengths of the metal tubes 110 and 120 are the longest lengths. The longitudinal lengths of the metal tubes 110 and 120 are longer than H2 by H15.

As shown in Example 2, the metal tube 110 located at the outermost periphery deforms faster, and when processing is performed under the same conditions, the smaller the deformation resistance, the faster the deformation. Therefore, the metal tube 120 with the smallest deformation resistance and the metal tube 110 located at the outermost periphery have a faster deformation speed. However, since the metal tube 110 located at the outermost periphery has a large deformation resistance, the deformation speed is suppressed and the lengths of the metal tubes 110 and 120 after drawing processing are approximately the same.

In this way, when the wire 100 has the same deformation resistance of the metal tubes 110, 120 and the metal rod 130, and has a longitudinal length of H1 and a diameter of D1 before drawing, the longitudinal length after drawing will be different.

Specifically, the length of the metal tube 110 located on the outermost side and the length of the metal tube 120 located on the inner diameter side of the metal tube 110 are longer than the length H2 of the metal rod 130 after drawing, which is H15, compared to the length H2 of the metal rod 130 located at the center of the cross section.

Referring to FIG. 6, in order to make the cross-sectional shape of the wire 100 in the longitudinal direction consistent after drawing, we will consider the conditions for making the length of the wire 100 uniform after drawing using materials with different deformation resistances. This consideration may be performed, for example, using CAE.

6A, in the material 100 composed of the metal tube 110, the metal tube 120, and the metal rod 130, the length of the metal rod 130 is the longest at H1. The lengths of the metal tubes 110, 120 are H1-H15.
After the cross-sectional diameter of the wire 100 shown in FIG. 6(a) is reduced from D1 to D2 by the drawing apparatus shown in FIG. 2, the wire 100 has a cross-sectional shape shown in FIG. 6(b).

As shown in FIG. 6(b), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal lengths of the metal tubes 110 and 120 are the longest lengths, which are longer than H2 by H19.

For example, metal materials with different deformation resistances are shown in FIG. 6(a), where the metal tube 110 is a low carbon steel tube, the metal tube 120 is a pure aluminum tube, and the metal bar 130 is a pure iron bar. Of the three metal materials, the metal tube 110 has the highest deformation resistance, and the metal tube 120 has the lowest deformation resistance.

The wire 100, which is made up of the metal tubes 110, 120, and metal rod 130 and has a length H1, was measured for its length H15 (see FIG. 4(b)) after drawing, in which the initial cross-sectional diameter D1 was reduced by 10-15% to a cross-sectional diameter D2. As a result, it was confirmed that the lengths of the metal tubes 110, 120 were longer by H15, which corresponds to 16%, than the shortest length H2 of the metal rod 130 after drawing.

The wire 100, which is composed of the metal tubes 110, 120 and the metal rod 130 and has a difference of H15 from the length H1 of the metal rod 130, was examined for the difference H19 of the wire 100 (see FIG. 6(b)) after the cross-sectional diameter was reduced from D1 to D2 by the drawing device of FIG. 2. As a result, it was confirmed that the difference in length H19 after drawing shown in FIG. 6(b) is sufficiently smaller than the difference in length H15 after drawing shown in FIG. 4(b).

The configuration of a drawing device for making the length in the longitudinal direction uniform in the first and second embodiments will be described with reference to FIG.
The drawing apparatus shown in FIG. 7 differs from the drawing apparatus shown in FIG. 2 in that a new die 240 is additionally disposed.

In the drawing device, when the wire 100 has both ends B5 and B9, a gripping part 220 is placed on end B9 and pulled in the B4 direction. In addition, a die 240 is placed on end B5 to limit deformation of end B5 of the wire 100.

The die 240 is a die for restricting or adjusting the longitudinal deformation of the end B5 of the wire 100, and applies a pressing force in a direction B8 similar to the tensile direction B4 using a force different from the tensile force of the wire 100.

As shown in FIG. 7(b), the die 240 is provided with a groove 250 larger than the maximum diameter of the wire 100, and the end B5 of the wire 100 is placed in the groove 250. The pressing force in the direction B8 is 100% to 300% of the pulling force in the direction B4. The other configurations are the same as those of the drawing device shown in FIG. 2, so the description thereof will be omitted.

According to the above embodiment, the cut portions at the ends of the material are reduced by making the cross-sectional deformation in the longitudinal direction uniform during the wire drawing process. This makes it possible to reduce material loss. Furthermore, the reduction in the number of cutting steps makes it possible to reduce the number of steps in the wire drawing process, thereby reducing manufacturing costs.

For the wire 100 consisting of the metal tubes 110, 120 and metal rod 130 shown in Figure 1, if the metal tubes 110, 120 and metal rod 130 have different deformation resistances and the metal tube 110 is made of a material with a high deformation resistance, the length of each metal tube passing through the hole 230 of the die 210 of the drawing processing device shown in Figure 2 will be different.

Figures 3(a) and 3(c) show the longitudinal lengths H1 and H2 of the wire 100 before and after drawing.

3A, the metal tube 110, the metal tube 120, and the metal rod 130 have different deformation resistances. For example, in the case of the wire 100, the deformation resistances of the metal tube 110 are greatest, followed by the metal rod 130 and the metal tube 120, in that order. Since the deformation resistance of the metal tube 110 is greatest, deformation occurs slowly.
As shown in FIG. 3A, the metal tubes 110, 120 and the metal rod 130 have the same length H1 and an initial diameter D1.
After the cross-sectional diameter of the wire 100 shown in FIG. 3(a) is reduced from D1 to D2 by the drawing apparatus shown in FIG. 2, the wire 100 has a cross-sectional shape shown in FIG. 3(c).

As shown in FIG. 3(c), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal length of the metal tube 120 is the longest length. The longitudinal length of the metal tube 110 is longer than H2 by H12. The longitudinal length of the metal tube 120 is longer than H2 by H11.

As shown in Example 2, the metal tube 110 located at the outermost periphery deforms faster, and when processing is performed under the same conditions, the smaller the deformation resistance, the faster the deformation. Therefore, the metal tube 120 with the smallest deformation resistance and the metal tube 110 located at the outermost periphery have a faster deformation speed. However, since the metal tube 110 located at the outermost periphery has a large deformation resistance, the deformation speed is suppressed and the length of the metal tube 110 after drawing processing is shorter than the length of the metal tube 120 after drawing processing.

In this way, in the wire 100 in which the deformation resistances of the metal tubes 110, 120 and the metal rod 130 are different, when the wire 100 having a longitudinal length H1 and a diameter D1 before drawing is subjected to drawing, the longitudinal length after drawing will be different.

Specifically, in FIG. 3(c), the length of the metal rod 130 located at the center of the cross section after drawing is H2, and the length of the metal tube 110 located on the outermost side is longer than H2 by H12. The length of the metal tube 120 located on the inner diameter side of the metal tube 110 is longer than the length H2 of the metal rod 130 by H11.

Referring to FIG. 8, in order to make the cross-sectional shape of the wire 100 in the longitudinal direction consistent after drawing, we will consider the conditions for making the length of the wire 100 uniform after drawing using materials with different deformation resistances. This consideration may be performed, for example, using CAE.

As shown in FIG. 8(a), in the material 100 composed of the metal tube 110, the metal tube 120, and the metal rod 130, the length of the metal rod 130 is the longest at H1. The length of the metal tube 110 is H1-H12. The length of the metal tube 120 is H1-H11.

The thickness of the metal tubes is also T1 for metal tube 110, which has a high resistance to deformation, and T2 for metal tube 120, which has a low resistance to deformation. In this way, the thickness T1 of metal tube 110 is always made thicker than the thickness T2 of metal tube 120.

After the cross-sectional diameter of the wire 100 shown in FIG. 8(a) is reduced from D1 to D2 by the drawing device shown in FIG. 2, the wire 100 has the cross-sectional shape shown in FIG. 8(b).

As shown in FIG. 8(b), the longitudinal length of the metal rod 130 is the shortest length H2. The longitudinal lengths of the metal tubes 110 and 120 are the longest lengths, which are longer than H2 by H19.

For example, in FIG. 8(a), the metal tube 110 is a nickel alloy tube, the metal tube 120 is a pure aluminum tube, and the metal rod 130 is a pure aluminum rod, and of the three metal materials, the metal tube 110 has the greatest deformation resistance, while the metal tube 120 and the metal rod 130 have the smallest deformation resistance.

The wire 100 having a length H1 and composed of the metal tube 110, metal tube 120, and metal rod 130 was measured for its length after drawing (see FIG. 3(c)), in which the initial cross-sectional diameter D1 was reduced by 10-15% to a cross-sectional diameter D2. As a result, it was confirmed that the length of the metal tube 110 was longer by H12, which corresponds to 10%, and the length of the metal tube 120 was longer by H11, which corresponds to 16%, of the shortest length H2 of the metal rod 130 after drawing.

The wire 100 (see FIG. 8(a)) is composed of a metal tube 110 with a thickness T1 having a difference of H12 with respect to the length H1 of the metal rod 130, a metal tube 120 with a thickness T2 having a difference of H11, and a metal rod 130. The wire 100 (see FIG. 8(b)) after the cross-sectional diameter is reduced from D1 to D2 by the drawing device of FIG. 2 was examined for the difference H19. As a result, it was confirmed that the difference H19 in length after drawing shown in FIG. 8(b) is sufficiently smaller than the difference H11, H12 in length after drawing shown in FIG. 3(c).

Reference Signs List 100 Wire rod 110 Metal tube 120 Metal tube 130 Metal rod 210 Die 220 Grip portion 230 Hole 240 Metal mold

Claims (7)

A wire drawing method for reducing a cross-sectional diameter of a wire having at least a metal rod and a first metal tube provided on an outer periphery of the metal rod by wire drawing, comprising:
A first wire is provided, the first wire including the metal rod having a first longitudinal length and the first metal tube having a second longitudinal length different from the first longitudinal length;
a second wire is produced by reducing the cross-sectional diameter of the first wire through the wiredrawing process to produce the second wire, the second wire including the metal bar having a third longitudinal length and the first metal tube having a fourth longitudinal length different from the third longitudinal length;
A wire drawing method, characterized in that a first difference between the third longitudinal length and the fourth longitudinal length of the second wire rod is made smaller than a second difference between the first longitudinal length and the second longitudinal length of the first wire rod. preparing a third wire having the metal rod and the first metal tube, the lengths of which are equal to each other in a longitudinal direction;
By the wire drawing process, the cross-sectional diameter of the third wire is reduced to produce a fourth wire having the metal bar having a fifth longitudinal length and the first metal tube having a sixth longitudinal length different from the fifth longitudinal length;
The wiredrawing method according to claim 1, characterized in that a third difference between the fifth longitudinal length and the sixth longitudinal length of the fourth wire rod is set as the second difference of the first wire rod, and the second wire rod is created from the first wire rod by the wiredrawing. the first longitudinal length of the metal rod in the first wire is longer than the second longitudinal length of the first metal tube by the second difference;
The wire drawing method according to claim 1, characterized in that the third longitudinal length of the metal rod in the second wire is shorter than the fourth longitudinal length of the first metal tube by the first difference. The wire drawing method according to claim 2, characterized in that the fifth longitudinal length of the metal rod in the fourth wire is shorter than the sixth longitudinal length of the first metal tube by the third difference. The wire drawing method according to claim 1, characterized in that the first difference is made smaller than the second difference so that the cross-sectional shape in the longitudinal direction of the second wire is made uniform at the end and the central portion. The wire drawing method according to claim 1, characterized in that the wire is made of a superconducting wire having a cylindrical cross section. the first wire rod has a second metal tube around the outer periphery of the first metal tube, the second metal tube having a length shorter than the second longitudinal direction;
2. The wire drawing method according to claim 1, wherein the first wall thickness of the first metal tube is thinner than the second wall thickness of the second metal tube.

Images