Stranded wires, insulated wires and cables

Abstract

This twisted wire is obtained by twisting a plurality of sub-twisted wires together. Each of the sub-twisted wires has the same structure in which a plurality of strands of which the cross-sectional shapes perpendicular to the longitudinal direction are circles of the same diameter, are twisted together. The strands include a steel core wire, and a copper or copper alloy cover layer covering the surface of the core wire. The twist pitch of the sub-twisted wires is at least 40 times the diameter of the circumscribed circle of the sub-twisted wires. The twist pitch of the twisted wires is 5-20 times the diameter of the circumscribed circle of the twisted wires.

Description

Technical Field

[0001] The present disclosure relates to twisted wires, insulated electric wires, and cables.

[0002] This application claims priority based on Japanese Application No. 2022-85853 filed on May 26, 2022, and incorporates by reference all the descriptions recited in the above Japanese application.

Background Art

[0003] In FA (Factory Automation) equipment, robots, automobiles, other industrial equipment, and consumer equipment, twisted wires, insulated electric wires, and cables used in movable parts that bend during operation are required not only to have strength such as tensile strength but also durability against repeated bending stress, that is, bending resistance. In contrast, it has been proposed to employ a clad wire including a steel core wire and a copper coating layer covering the drawn wire as a base wire (see, for example, Japanese Unexamined Patent Application Publication No. 2020-2162 (Patent Document 1)). The steel core wire contributes to the improvement of strength, and the copper coating layer is responsible for high conductivity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The twisted wire according to the present disclosure is a twisted wire in which a plurality of sub-twisted wires are twisted together. Each of the sub-twisted wires has the same structure in which a plurality of base wires having a circular cross-sectional shape with the same diameter perpendicular to the longitudinal direction are twisted together. The base wire includes a steel core wire and a coating layer made of copper or a copper alloy that covers the surface of the core wire. The twist pitch of the sub-twisted wire is 40 times or more the diameter of the circumscribed circle of the sub-twisted wire. The twist pitch of the twisted wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the twisted wire.

Brief Description of the Drawings

[0006] [Figure 1] Figure 1 is a schematic diagram showing the structure of stranded wire. [Figure 2] Figure 2 is a schematic diagram showing the structure of a stranded wire. [Figure 3] Figure 3 is a schematic cross-sectional view showing the structure of the wire strands. [Figure 4] Figure 4 is a schematic cross-sectional view showing the structure of stranded wire. [Figure 5] Figure 5 is a schematic diagram illustrating the twist pitch of stranded wire and sub-stranded wire. [Figure 6] Figure 6 is a flowchart illustrating the general method for manufacturing stranded wire. [Figure 7] Figure 7 is a schematic diagram showing the structure of the stranded wire in Embodiment 2. [Figure 8] Figure 8 is a schematic diagram showing the structure of an insulated wire in Embodiment 3. [Figure 9] Figure 9 is a schematic diagram showing the cable structure in Embodiment 4. [Figure 10] Figure 10 is a schematic diagram showing the cable structure in Embodiment 5. [Figure 11] Figure 11 is a schematic perspective view showing the connection between an insulated wire and a crimp terminal. [Figure 12] Figure 12 is a schematic diagram illustrating the method of tensile testing. [Figure 13] Figure 13 is a schematic perspective view showing the structure of the testing apparatus for the bending test. [Figure 14] Figure 14 is a schematic diagram illustrating the method of the bending test. [Figure 15] Figure 15 is a schematic diagram illustrating the method of the bending test. [Modes for carrying out the invention]

[0007] [Issues this disclosure aims to address] In the stranded wires, insulated wires, and cables described above, connection to crimp terminals is an important and simple connection method. However, when the clad wire material described above is used as the strand, the low toughness of the steel core wire may cause cracking in the core wire during connection to the crimp terminal. This cracking of the core wire can lead to a problem of reduced crimping strength.

[0008] Therefore, one of the objectives of this disclosure is to provide stranded wires, insulated wires, and cables that not only improve bending resistance but also achieve both strength and conductivity, and that can suppress cracking of the core wire when connected to crimp terminals.

[0009] [Effects of this disclosure] The above stranded wire not only improves bending resistance but also achieves a balance between strength and conductivity, while suppressing cracking of the core wire when connected to a crimp terminal.

[0010] [Description of Embodiments in this Disclosure] Embodiments of the present disclosure will be listed and described first. The stranded wire of the present disclosure is a stranded wire in which a plurality of sub-stranded wires are twisted together. Each sub-stranded wire has the same structure in which a plurality of strands, each having a circular cross-sectional shape perpendicular to the longitudinal direction and having the same diameter, are twisted together. The strands include a steel core wire and a coating layer made of copper or a copper alloy covering the surface of the core wire. The twist pitch of the sub-stranded wire is 40 times or more the diameter of the circumscribed circle of the sub-stranded wire. The twist pitch of the stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the stranded wire.

[0011] The twisted wire of the present disclosure is formed by further twisting a plurality of sub-twisted wires formed by twisting individual strands together. As a result, high flexibility is obtained and a certain degree of bend resistance is ensured. The individual strands constituting the sub-twisted wires include a steel core wire and a coating layer made of copper or a copper alloy that covers the surface of the core wire. This makes it possible to achieve both high strength and conductivity. Since the cross-sectional shape perpendicular to the longitudinal direction of each individual strand is a circle with a constant diameter, local stress concentration during repeated bending is reduced, contributing to an improvement in bend resistance. Furthermore, by setting the twist pitch of the sub-twisted wire to be 40 times or more the diameter of the circumscribed circle of the sub-twisted wire, the individual strands are properly rearranged when connected to a crimp terminal, avoiding stress concentration on some of the individual strands. As a result, cracking of the core wire during connection to the crimp terminal is suppressed. Additionally, by setting the twist pitch of the twisted wire to be 5 times or more the diameter of the circumscribed circle of the twisted wire, unevenness on the surface of the twisted wire can be suppressed, improving bend resistance. Also, by setting the twist pitch of the twisted wire to be 20 times or less the diameter of the circumscribed circle of the twisted wire, stress concentration on some of the sub-twisted wires during bending can be avoided. In the present application, the state where the individual strands constituting the sub-twisted wire have the same diameter means that the difference between the average diameter of the plurality of individual strands constituting each sub-twisted wire and the diameter of each individual strand is 6.0% or less with respect to the average diameter.

[0012] As described above, according to the twisted wire of the present disclosure, not only can the bend resistance be improved, but it is also possible to achieve both high strength and conductivity, and suppress cracking of the core wire during connection to the crimp terminal.

[0013] In the above-mentioned twisted wire, the diameter of the individual strand may be 0.02 mm or more and 0.09 mm or less. By setting the diameter of the individual strand to be 0.02 mm or more, disconnection of the individual strand during the manufacturing process of the twisted wire can be suppressed, improving productivity. By setting the diameter of the individual strand to be 0.09 mm or less, the difference in strain between the outer and inner sides of the bend when the individual strand is bent is suppressed, further improving bend resistance.

[0014] In the above-mentioned stranded wire, the tensile strength of the core wire may be 1800 MPa or more and 4500 MPa or less. When the tensile strength of the core wire is 1800 MPa or more, it becomes easy to impart sufficient strength to the core wire. When the tensile strength of the core wire is 4500 MPa or less, it becomes easy to impart sufficient toughness to the core wire.

[0015] In the above-mentioned stranded wire, the carbon content of the steel constituting the core wire may be 0.70 mass% or more and 0.95 mass% or less. The carbon content of the steel has a great influence on the strength and toughness of the steel. By setting the carbon content of the steel constituting the core wire to 0.70 mass% or more, it becomes easy to impart sufficient strength to the core wire. By setting the carbon content of the steel constituting the core wire to 0.95 mass% or less, it becomes easy to impart sufficient toughness to the core wire.

[0016] In the above-mentioned stranded wire, in a cross-section perpendicular to the longitudinal direction of the strand, the area of the coating layer with respect to the area of the strand may be 20% or more and 80% or less. By setting the area of the coating layer with respect to the area of the strand to 20% or more, it becomes easy to obtain sufficient conductivity. By setting the area of the coating layer with respect to the area of the strand to 80% or less, it becomes easy to obtain sufficient strength and flexural resistance.

[0017] A stranded wire in one aspect of this disclosure is a stranded wire in which a plurality of sub-stranded wires are twisted together. Each sub-stranded wire has the same structure in which a plurality of strands, each having a circular cross-section perpendicular to the longitudinal direction and having the same diameter, are twisted together. The strands include a steel core wire and a coating layer made of copper or a copper alloy covering the surface of the core wire. The twist pitch of the sub-stranded wire is 40 times or more the diameter of the circumscribed circle of the sub-stranded wire. The twist pitch of the stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the stranded wire. The diameter of the core wire is 0.02 mm or more and 0.09 mm or less. The tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less. The carbon content of the steel constituting the core wire is 0.70 mass% or more and 0.95 mass% or less. In a cross-section perpendicular to the longitudinal direction of the strands, the area of ​​the coating layer relative to the area of ​​the strands is 20% or more and 80% or less. Each of the above-mentioned stranded wires includes, in a cross section perpendicular to the longitudinal direction of the stranded wire, a central stranded wire positioned in the center, and six first surrounding stranded wires positioned in contact with the central stranded wire so as to surround its outer circumference. Each stranded wire includes two to twenty individual wires.

[0018] A stranded wire in another aspect of this disclosure is a stranded wire in which a plurality of sub-stranded wires are twisted together. Each sub-stranded wire has the same structure in which a plurality of strands, each having a circular cross-section perpendicular to the longitudinal direction and having the same diameter, are twisted together. The strands include a steel core wire and a coating layer made of copper or a copper alloy covering the surface of the core wire. The twist pitch of the sub-stranded wire is 40 times or more the diameter of the circumscribed circle of the sub-stranded wire. The twist pitch of the stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the stranded wire. The diameter of the core wire is 0.02 mm or more and 0.09 mm or less. The tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less. The carbon content of the steel constituting the core wire is 0.70 mass% or more and 0.95 mass% or less. In a cross-section perpendicular to the longitudinal direction of the strands, the area of ​​the coating layer relative to the area of ​​the strands is 20% or more and 80% or less. Each of the above-mentioned stranded wires includes, in a cross section perpendicular to the longitudinal direction of the stranded wire, a central stranded wire positioned in the center, six first surrounding stranded wires positioned in contact with the central stranded wire so as to surround its outer circumference, and twelve second surrounding stranded wires positioned in contact with the first surrounding stranded wires on the outer circumference of the area where the first surrounding stranded wires are positioned. Each stranded wire includes two to twenty individual wires.

[0019] By having a stranded wire structure that includes a central stranded wire and a first surrounding stranded wire, or a central stranded wire, a first surrounding stranded wire, and a second surrounding stranded wire, the cross-section perpendicular to the longitudinal direction of the stranded wire becomes nearly circular. As a result, localized stress concentration during repeated bending is reduced, and bending resistance is improved. Furthermore, by having a stranded wire containing two or more strands, the flexibility of the stranded wire can be ensured, further improving bending resistance. By having a stranded wire containing 20 or fewer strands, a practical outer diameter for a stranded wire can be obtained when used as an electric wire.

[0020] In the stranded wire described above, the coating layer may be a plated layer. That is, the coating layer may be formed by plating. A plated layer is suitable as the coating layer in this disclosure because its thickness can be easily adjusted and it can be formed by a simple process.

[0021] An insulated wire in one aspect of the present disclosure comprises the stranded wire described above and an insulating layer covering the outer circumference of the stranded wire. According to the insulated wire in one aspect of the present disclosure, it is possible to provide an insulated wire that not only improves bending resistance but also achieves both strength and conductivity, and suppresses cracking of the core wire when connected to a crimp terminal, by including the stranded wire described above which is capable of improving bending resistance but also achieving both strength and conductivity, and suppressing cracking of the core wire when connected to a crimp terminal.

[0022] Insulated wires in other embodiments of the present disclosure include a core in which a plurality of insulated stranded wires are twisted together, and a protective layer made of an insulating material covering the outer circumference of the core. Each insulated stranded wire includes the stranded wire of the present disclosure and the insulating layer covering the outer circumference of the stranded wire. According to insulated wires in other embodiments of the present disclosure, it is possible to provide an insulated wire that not only improves bending resistance but also achieves both strength and conductivity, and suppresses cracking of the core wire when connected to a crimp terminal, by including the stranded wire of the present disclosure which is capable of improving bending resistance but also achieving both strength and conductivity, and suppressing cracking of the core wire when connected to a crimp terminal.

[0023] A cable according to one aspect of the present disclosure includes an insulated wire according to the present disclosure, a conductive shield portion arranged to surround the outer circumference of the insulated wire, and an insulating outer sheath layer arranged to surround the outer circumference of the shield portion. According to the cable according to one aspect of the present disclosure, it is possible to provide a cable that not only improves bending resistance but also achieves both strength and conductivity, and suppresses cracking of the core wire when connected to a crimp terminal, by including the stranded wire of the present disclosure which is capable of achieving both strength and conductivity, and suppressing cracking of the core wire when connected to a crimp terminal.

[0024] A cable in another aspect of the present disclosure includes an insulated wire in the other aspect of the present disclosure, a conductive shield portion arranged to surround the outer circumference of the insulated wire, and an insulating sheath layer arranged to surround the outer circumference of the shield portion. According to the cable in another aspect of the present disclosure, it is possible to provide a cable that not only improves bending resistance but also achieves both strength and conductivity, and suppresses cracking of the core wire when connected to a crimp terminal, by including the stranded wire of the present disclosure which is capable of improving bending resistance but also achieving both strength and conductivity, and suppressing cracking of the core wire when connected to a crimp terminal.

[0025] [Details of the embodiments of this disclosure] Next, embodiments of the stranded wires, insulated wires, and cables according to this disclosure will be described below with reference to the drawings. In the following drawings, identical or corresponding parts will be given the same reference numerals, and their descriptions will not be repeated.

[0026] (Embodiment 1) Figure 1 is a schematic diagram showing the structure of a stranded wire. Referring to Figure 1, the stranded wire 1 in this embodiment has a structure in which a plurality of sub-stranded wires 10 are twisted together. In this embodiment, the plurality of sub-stranded wires 10 include one central sub-stranded wire 10A and six first peripheral sub-stranded wires 10B. In a cross section perpendicular to the longitudinal direction of the stranded wire 1, the central sub-stranded wire 10A is positioned in the center. The six first peripheral sub-stranded wires 10B are positioned in contact with the central sub-stranded wire 10A so as to surround its outer circumference. The central sub-stranded wire 10A is in contact with all six first peripheral sub-stranded wires 10B on its outer surface. Each first peripheral sub-stranded wire 10B is in contact with two adjacent first peripheral sub-stranded wires 10B in the circumferential direction and with the central sub-stranded wire 10A on its outer surface.

[0027] Figure 2 is a schematic diagram showing the structure of a stranded wire. Referring to Figure 2, each stranded wire 10 has the same structure in which multiple strands 100, each having a circular cross-sectional shape of the same diameter perpendicular to the longitudinal direction, are twisted together. In this embodiment, the multiple strands 100 include one central strand 100A and six first surrounding strands 100B. The stranded wire 10 contains two to twenty strands (specifically seven) of strands 100. In a cross-section perpendicular to the longitudinal direction of the stranded wire 1, the central strand 100A is positioned in the center. The six first surrounding strands 100B are positioned in contact with the central strand 100A so as to surround its outer periphery. The central strand 100A is in contact with all six first surrounding strands 100B on its outer surface. Each first surrounding strand 100B is in contact with two adjacent first surrounding strands 100B in the circumferential direction and with the central strand 100A on its outer surface.

[0028] Figure 3 is a schematic cross-sectional view showing the structure of a wire strand. Figure 3 shows a cross-section perpendicular to the longitudinal direction of the wire strand. Referring to Figure 3, the wire strand 100 includes a core wire 101 and a coating layer 102. The core wire 101 is made of steel. The diameter of the wire strand 100 is, for example, 0.02 mm or more and 0.09 mm or less. The carbon content of the steel constituting the core wire 101 can be, for example, 0.70% by mass or more and 0.95% by mass or less. The carbon content of the steel constituting the core wire 101 may be 0.90% by mass or less. As the steel constituting the core wire 101, for example, steel corresponding to piano wire as specified in JIS standard (Japanese Industrial Standards) G3502 can be used. The tensile strength of the core wire 101 may be, for example, 1800 MPa or more and 4500 MPa or less. The tensile strength of the core wire 101 can be 2500 MPa or more. The tensile strength of the core wire 101 can be 3800 MPa or less.

[0029] The coating layer 102 is made of copper (Cu) or a copper alloy. The coating layer 102 covers the surface 101A (outer surface) of the core wire 101. The thickness of the coating layer 102 is constant in the circumferential direction. The coating layer 102 may be a plating layer. The coating layer 102 may be a layer formed by plating. In a cross section perpendicular to the longitudinal direction of the strand 100 (the cross section shown in Figure 3), the area of ​​the coating layer 102 relative to the area of ​​the strand 100 may be 20% or more and 80% or less. The state in which the thickness of the coating layer 102 is constant in the circumferential direction means that the difference between the maximum and minimum thickness of the coating layer 102 within each strand 100 is 7.0% or less of the average thickness of the coating layer 102.

[0030] Figure 4 is a schematic cross-sectional view showing the structure of a stranded wire. Figure 5 is a schematic diagram illustrating the twist pitch of the stranded wire and sub-stranded wires. Figure 4 shows a cross-section perpendicular to the longitudinal direction of the stranded wire 1. Referring to Figures 4 and 5, in this embodiment, the twist pitch P of the sub-stranded wire 10 is 40 times or more the diameter d2 of the circumscribed circle of the sub-stranded wire 10. Here, referring to the reference numbers in parentheses in Figure 5, the twist pitch P of the sub-stranded wire 10 is defined as the length measured parallel to the longitudinal direction of the sub-stranded wire 10, which is the length of one rotation of a single strand 100 constituting the sub-stranded wire 10 around the sub-stranded wire 10. Also in this embodiment, the twist pitch P of the stranded wire 1 is 5 times or more and 20 times or less the diameter d1 of the circumscribed circle of the stranded wire 1. Here, referring to the reference numbers in Figure 5 (excluding those indicated in parentheses), the twist pitch P of the stranded wire 1 is defined as the length measured parallel to the longitudinal direction of the stranded wire 1, which is the length over which one of the sub-stranded wires 10 constituting the stranded wire 1 makes one full rotation around the stranded wire 1.

[0031] In this embodiment, the stranded wire 1 is constructed by further twisting together multiple sub-stranded wires 10, each composed of strands 100 twisted together. This provides high flexibility and ensures a certain level of bending resistance. The strands 100 constituting the sub-stranded wires 10 include a steel core wire 101 and a copper or copper alloy coating layer 102 covering the surface 101A of the core wire 101. This achieves a balance between strength and conductivity. The shape of the cross-section perpendicular to the longitudinal direction of each strand 100 is a circle of the same diameter, which reduces localized stress concentration during repeated bending and contributes to improved bending resistance. Furthermore, by setting the twist pitch P of the sub-stranded wires 10 to 40 times or more the diameter d2 of the circumscribed circle of the sub-stranded wire 10, the strands 100 are appropriately rearranged when connected to a crimp terminal, avoiding stress concentration on some strands 100. As a result, cracking of the core wire 101 when connected to a crimp terminal is suppressed. Furthermore, by setting the twist pitch P of the stranded wire 1 to 5 times or more the diameter d1 of the circumscribed circle of the stranded wire 1, it is possible to suppress irregularities on the surface of the stranded wire 1 and improve its bending resistance. Also, by setting the twist pitch P of the stranded wire 1 to 20 times or less the diameter d1 of the circumscribed circle of the stranded wire 1, it is possible to avoid stress concentration on some of the sub-stranded wires 10 when bending. Thus, the stranded wire 1 of this embodiment is a stranded wire that not only improves bending resistance but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal.

[0032] Furthermore, in this embodiment, each of the multiple sub-twisted wires 10 constituting the stranded wire 1 includes a central sub-twisted wire 10A positioned in the center of a cross section perpendicular to the longitudinal direction of the stranded wire 1, and six first peripheral sub-twisted wires 10B positioned in contact with the central sub-twisted wire 10A so as to surround its outer circumference. Each sub-twisted wire 10 contains two to twenty strands 100. This makes the cross section perpendicular to the longitudinal direction of the stranded wire 1 nearly circular. As a result, localized stress concentration during repeated bending is reduced, and bending resistance is improved. Moreover, by including two or more strands 100 in each sub-twisted wire 10, it is possible to ensure the flexibility of the stranded wire 1 and improve bending resistance. By including 20 or fewer strands 100 in each sub-twisted wire 10, it is possible to obtain a practical outer diameter for the stranded wire 1 when used as an electric wire.

[0033] Next, the method for manufacturing the stranded wire 1 in this embodiment will be described. Figure 6 is a flowchart illustrating the method for manufacturing the stranded wire. Referring to Figure 6, in the method for manufacturing the stranded wire 1 in this embodiment, first, a raw material steel wire preparation step is carried out as step S10. In this step S10, the raw material steel wire is prepared. Specifically, a steel wire made of steel with a carbon content of 0.70% by mass or more and 0.95% by mass or less is prepared. The steel constituting the raw material steel wire may contain silicon (Si) in an amount of 0.4% by mass or more and 2.5% by mass or less, manganese (Mn) in an amount of 0.6% by mass or more and 0.9% by mass or less, and chromium (Cr) in an amount of 0.1% by mass or more and 1.8% by mass or less. As the steel constituting the raw material steel wire, piano wire material (for example, SWRS82A) as specified in G3502 can be used.

[0034] Next, a patenting process is carried out as step S20. In this step S20, patenting is performed on the raw steel wire prepared in step S10. Specifically, the raw steel wire is heated to a temperature range above the austenitization temperature (point A1), then rapidly cooled to a temperature range higher than the martensitization initiation temperature (MS point), and then heat-treated by holding it at that temperature range. As a result, the metal structure of the raw steel wire becomes a fine pearlite structure with small lamellar spacing. Here, in the above patenting process, it is preferable that the process of heating the raw steel wire to a temperature range above point A1 be carried out in an inert gas atmosphere from the viewpoint of suppressing the occurrence of decarburization.

[0035] Next, a surface roughening process is carried out as step S30. In this step S30, a surface roughening treatment is performed on the raw steel wire that has been patented in step S20. Specifically, the surface roughness of the raw steel wire is increased by bringing it into contact with an acid such as hydrochloric acid or sulfuric acid. The concentration of hydrochloric acid can be, for example, 35% by mass, and the concentration of sulfuric acid can be, for example, 65% by mass.

[0036] Next, a coating layer formation process is carried out as step S40. In this step S40, a coating layer is formed on the first intermediate steel wire obtained up to step S30. Specifically, for example, a coating layer made of copper (pure copper) is formed on the first intermediate steel wire by plating. In addition to copper, metal layers such as tin (Sn) and zinc (Zn) may be formed by plating, and these may be alloyed to form a coating layer made of a copper alloy.

[0037] Next, the wire drawing process is carried out as step S50. In this step S50, the second intermediate steel wire obtained up to step S40 is drawn (drawn). The true strain in the wire drawing process of step S50 can be, for example, 2.3 or more and 4.9 or less, and preferably 3.0 or more and 4.0 or less. This yields the wire strand 100 in this embodiment.

[0038] Next, the first stranding process is carried out as process S60. In this process S60, the strands 100 obtained up to process S50 are twisted together to produce a sub-stranded wire 10. Specifically, referring to Figure 2, seven strands 100 produced in processes S10 to S50 are prepared, and one is used as the central strand 100A and six as the first surrounding strands 100B, and they are twisted together. This gives rise to the sub-stranded wire 10. At this time, referring to Figures 4 and 5, the twist pitch P of the sub-stranded wire 10 is set to be 40 times or more the diameter d2 of the circumscribed circle of the sub-stranded wire 10.

[0039] Next, the second stranding process is carried out as process S70. In this process S70, the sub-stranded wires 10 obtained in process S60 are twisted together to produce the stranded wire 1. Specifically, referring to Figure 1, seven sub-stranded wires 10 produced in process S60 are prepared, one is made into the central sub-stranded wire 10A, and six are made into the first surrounding sub-stranded wires 10B, and twisted together. This gives rise to the stranded wire 1. At this time, referring to Figures 4 and 5, the twist pitch P of the stranded wire 1 is set to be at least 5 times and at least 20 times the diameter d1 of the circumscribed circle of the stranded wire 1. By following the above procedure, the stranded wire 1 of this embodiment can be easily manufactured.

[0040] (Embodiment 2) Next, another embodiment of the present disclosure, Embodiment 2, will be described. Figure 7 is a schematic diagram showing the structure of the stranded wire in Embodiment 2. Referring to Figures 7 and 1, the stranded wire 1 in Embodiment 2 has basically the same structure as the stranded wire 1 in Embodiment 1 and produces the same effects. However, the stranded wire 1 in Embodiment 2 differs from that in Embodiment 1 in the number of sub-stranded wires 10 that constitute the stranded wire 1.

[0041] Referring to Figure 7, the plurality of sub-twisted wires 10 constituting the stranded wire 1 of this embodiment include, in a cross section perpendicular to the longitudinal direction of the stranded wire 1, a central sub-twisted wire 10A positioned in the center, six first peripheral sub-twisted wires 10B positioned in contact with the central sub-twisted wire 10A so as to surround its outer periphery, and twelve second peripheral sub-twisted wires 10C positioned in contact with the first peripheral sub-twisted wires 10B on the outer periphery of the area where the first peripheral sub-twisted wires 10B are positioned. In this embodiment, the stranded wire 1 includes 19 sub-twisted wires 10.

[0042] The central stranded wire 10A is in contact with all six first periphery stranded wires 10B on its outer surface. Each first periphery stranded wire 10B is in contact with two adjacent first periphery stranded wires 10B in the circumferential direction and with the central stranded wire 10A on its outer surface. Each second periphery stranded wire 10C is in contact with two adjacent second periphery stranded wires 10C in the circumferential direction and with the first periphery stranded wire 10B located radially inward on its outer surface. The stranded wire 1 of this embodiment, in which the number and arrangement of stranded wires 10 included in the stranded wire 1 are changed in this way, is a stranded wire that, like the stranded wire 1 of Embodiment 1 above, not only improves bending resistance but also achieves both strength and conductivity, and suppresses cracking of the core wire when connected to a crimp terminal.

[0043] (Embodiment 3) Next, as Embodiment 3 of the present disclosure, an example of an insulated wire of the present disclosure will be described. Figure 8 is a schematic diagram showing the structure of an insulated wire in Embodiment 3. Referring to Figure 8, the insulated wire 3 of this embodiment comprises a core 9 and an insulating layer 12. The core 9 has a structure in which a plurality of (in this case, two) insulated stranded wires 2 are twisted together. The insulating layer 12 is made of an insulator such as resin. The insulating layer 12 is a protective layer arranged to cover the outer circumference of the core 9. The insulated stranded wire 2 includes the stranded wire 1 of Embodiment 1 or Embodiment 2 and an insulating layer 11 that covers the outer circumference of the stranded wire 1. The insulating layer 11 is made of an insulator such as resin.

[0044] The insulated wire 3 of this embodiment not only improves bending resistance but also achieves a balance of strength and conductivity, and suppresses cracking of the core wire 101 when connected to a crimp terminal, by including the stranded wire 1 of Embodiment 1 or 2 described above. In addition, the insulated stranded wire 2 that constitutes the core 9 can also be used as an insulated wire. That is, the insulated stranded wire 2 as an insulated wire in another embodiment comprises the stranded wire 1 of Embodiment 1 or Embodiment 2 described above and an insulating layer 11 that covers the outer circumference of the stranded wire 1. The insulated stranded wire 2 not only improves bending resistance but also achieves a balance of strength and conductivity, and suppresses cracking of the core wire 101 when connected to a crimp terminal, by including the stranded wire 1 of Embodiment 1 or 2 described above.

[0045] (Embodiment 4) Next, an example of a cable according to the present disclosure will be described as Embodiment 4 of the present disclosure. Figure 9 is a schematic diagram showing the structure of the cable in Embodiment 4. Referring to Figure 9, the cable 300 includes a stranded wire 1 according to Embodiment 1 or Embodiment 2, an insulating layer 4 disposed to cover the outer circumference 1A of the stranded wire 1, a shield portion 5 disposed to surround the outer surface 4A of the insulating layer 4, and an outer sheath layer 6 disposed to cover the outer circumference 5A of the shield portion 5. From another point of view, the cable 300 includes an insulated stranded wire 2 as an insulated electric wire as described in Embodiment 3 above, a conductive shield portion 5 disposed to surround the outer circumference of the insulated stranded wire 2, and an insulating outer sheath layer 6 disposed to surround the outer circumference of the shield portion 5. The shield portion 5 may have a structure in which metal wires are braided. The stranded wires 100 in the above embodiment may be used as the metal wires constituting the shield portion 5.

[0046] The cable 300 of this embodiment not only improves bending resistance but also achieves a balance of strength and conductivity, and suppresses cracking of the core wire 101 when connected to a crimp terminal, by including the stranded wire 1 of this embodiment 1 or 2.

[0047] (Embodiment 5) Next, as Embodiment 5 of the present disclosure, another example of the cable of the present disclosure will be described. Figure 10 is a schematic diagram showing the structure of the cable in Embodiment 5. Referring to Figure 10, the cable 400 of this embodiment includes an insulated wire 3 (see Figure 8) as described in Embodiment 3 above, a conductive shield portion 5 arranged to surround the outer circumference of the insulated wire 3, and an insulating outer sheath layer 6 arranged to surround the outer circumference 5A of the shield portion 5. The shield portion 5 may have a structure in which metal wires are braided. The strands 100 in the above embodiment may be used as the metal wires constituting the shield portion 5.

[0048] The cable 400 of this embodiment not only improves bending resistance but also achieves a balance of strength and conductivity, and suppresses cracking of the core wire 101 when connected to a crimp terminal, by including the stranded wire 1 of this embodiment 1 or 2. [Examples]

[0049] Experiments were conducted to confirm the bending resistance of the stranded wires, insulated wires, and cables described herein, and to verify the suppression of core wire cracking when connected to crimp terminals. The experimental procedure was as follows.

[0050] A stranded wire 1 was prepared according to the manufacturing method described in Embodiment 1 above. The outer surface of this stranded wire 1 was covered with an insulating layer 11 to produce an insulated electric wire (insulated stranded wire 2). SWRS82A, a piano wire material specified in JIS G3502, was used as the raw material steel wire prepared in step S10. In step S40, a coating layer 102 made of pure copper was formed by plating. By adjusting the thickness of the coating layer 102, the area ratio of the coating layer 102 in a cross section perpendicular to the longitudinal direction of the strand 100 was changed. In step S50, drawing was performed so that the outer diameter (diameter) of the strand 100 was 0.05 mm. Furthermore, in step S60, the twist pitch of the sub-stranded wire 10 was changed to 60, and the number of strands 100 contained in the sub-stranded wire 10 was changed in the range of 7 to 16. Also, in step S70, the twist pitch of the stranded wire 1 was changed. Samples A to S were obtained in this way. Furthermore, in process S10, raw steel wires with different outer diameters and carbon content were prepared, and by changing the outer diameter of the individual wires 100 during the drawing process in process S50, samples T to W were produced.

[0051] Then, the obtained samples were measured as follows: (1) the strength of the crimped portion when connected to the crimp terminal and (2) the bending resistance.

[0052] (1) Strength of the connection when connected to a crimp terminal Figure 11 is a schematic perspective view showing the connection between an insulated wire and a crimp terminal. Figure 12 is a schematic diagram illustrating the method of tensile testing. Referring to Figure 11, the crimp terminal 80 includes a main body 83, a conductor barrel 81 connected to the main body 83, and an insulation barrel 82 connected to the opposite side of the conductor barrel 81 from the side connected to the main body 83. When connecting an insulated stranded wire 2, which is an insulated wire, to the crimp terminal 80, first the insulating layer 11 at the end of the insulated stranded wire 2 is removed to expose the stranded wire 1. Then, by crimping the conductor barrel 81, the exposed stranded wire 1 is held by the conductor barrel 81, and the insulating layer 11 is held by the insulation barrel 82. At this time, if a crack occurs in the core wire 101 of the strands 100 that make up the stranded wire 1 held by the conductor barrel 81, the strength of the connection between the conductor barrel 81 and the stranded wire 1 will decrease.

[0053] In this experiment, for each sample, the stranded wire 1 was held by the conductor barrel 81 as described above, while the insulating layer 11 was not held by the insulation barrel 82, and the insulated stranded wire 2 and the crimp terminal 80 were connected. Then, as shown in Figure 12, the main body 83 of the crimp terminal 80 was held by the first chuck 91 of the tensile testing machine, and the insulated stranded wire 2 was held by the second chuck 92 of the tensile testing machine, and a tensile test was performed, and the strength of the connection was evaluated by the load at which it broke.

[0054] (2) Flexibility Figure 13 is a schematic perspective view showing the structure of the bending test apparatus. Figures 14 and 15 are schematic diagrams illustrating the bending test method. Referring to Figure 13, the bending test apparatus 70 includes mandrels 71 and 72, a pair of jigs 73a and 73b, and a weight 74. The weight 74 is attached to one end of the insulated stranded wire 2 in the longitudinal direction. In this test, the mass of the weight 74 was set to 100 g. The pair of jigs 73a and 73b sandwich the insulated stranded wire 2. Cylindrical mandrels 71 and 72 are positioned between the weight 74 and the jigs 73a and 73b. The outer circumferential surface 711 of mandrel 71 and the outer circumferential surface 721 of mandrel 72 are in contact with the outer circumferential surface of the insulated stranded wire 2. The longitudinal directions of the mandrels 71 and 72 are perpendicular to the longitudinal direction of the insulated stranded wire 2. The diameter Q of mandrels 71 and 72 is 20 mm (see Figures 14 and 15). The initial state is as shown in Figure 13. The test is then carried out as follows.

[0055] Referring to Figures 13 to 15, first the insulated stranded wire 2 is bent in the direction of arrow R1 in Figure 13. At this time, the insulated stranded wire 2 bends along the outer surface 711 of the mandrel 71, as shown in Figure 14. The maximum bending angle θ1 of the insulated stranded wire 2 is 90°. Next, after being returned to the initial state shown in Figure 13, the insulated stranded wire 2 is bent in the direction of arrow R2 in Figure 13. At this time, the insulated stranded wire 2 bends along the outer surface 721 of the mandrel 72, as shown in Figure 15. The maximum bending angle θ2 of the insulated stranded wire 2 is 90°. The above operations were repeated, and the number of bends until the stranded wire 1 inside the insulated stranded wire 2 broke was investigated for each sample.

[0056] Table 1 shows the experimental results for (1) and (2) above.

[0057] [Table 1]

[0058] In Table 1, a value of ∞ (infinity) in the "Twist Pitch / d2" column for the sub-stranded wire means that the individual wires constituting the sub-stranded wire are not twisted, i.e., the individual wires are arranged parallel to the longitudinal direction of the sub-stranded wire. Furthermore, the indication "No breakage" in the "Number of bends until breakage" column in Table 1 means that no breakage occurred after 10 million bends, and the test was stopped.

[0059] Referring to Table 1, the strength of the connection points of samples A to C, where the twist pitch / d2 (diameter of the circumscribed circle of the twisted wire) is 40 or less, which is within the range of this disclosure, clearly exceeds the strength of the connection points of samples D, E, H, K, N, and Q, where the twist pitch / d2 is outside the range of this disclosure. This is thought to be because cracking of the core wire 101 during connection with the crimp terminal 80 was suppressed. Furthermore, samples F and G, where the twist pitch / d1 (diameter of the circumscribed circle of the twisted wire) is outside the range of 5 to 20, which is within the range of this disclosure, broke earlier than the other samples, which did not break even after 10 million bending cycles. In addition, for sample G, insulation failure was confirmed due to the large surface irregularities of the twisted wire 1. From the above experimental results, it was confirmed that the twisted wire, insulated wire, and cable of this disclosure can not only improve bending resistance but also suppress cracking of the core wire during connection with the crimp terminal.

[0060] The embodiments and examples disclosed herein are illustrative in all respects and should be understood not to be restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0061] 1 Stranded wire, 1A Outer circumference, 2 Insulated stranded wire, 3 Insulated wire, 4 Insulation layer, 4A Outer surface, 5 Shield section, 5A Outer circumference, 6 Outer sheath layer, 9 Core, 10 Sub-stranded wire, 10A Central sub-stranded wire, 10B First surrounding sub-stranded wire, 10C Second surrounding sub-stranded wire, 11 Insulation layer, 12 Insulation layer, 70 Bending test device, 71 Mandrel, 72 Mandrel, 73a Jig, 73b Jig, 80 Crimp terminal, 81 Conductor barrel, 82 Insulation barrel, 83 Main body, 91 First chuck, 92 Second chuck, 100 Stranded wire, 100A Central stranded wire, 100B First surrounding stranded wire, 101 Core wire, 101A Surface, 102 Coating layer, 300 Cable, 400 Cable, 711 Outer surface, 721 outer surface, P twist pitch, R1 arrow, R2 arrow, θ1 maximum bending angle, θ2 maximum bending angle.

Claims

1. A stranded wire in which multiple stranded wires are twisted together, Each of the aforementioned stranded wires has the same structure, in which multiple strands, each having a circular cross-section perpendicular to the longitudinal direction and of the same diameter, are twisted together. The aforementioned wire is Steel core wire, The core wire includes a coating layer made of copper or a copper alloy that covers the surface of the core wire, The twist pitch of the aforementioned stranded wire is 40 times or more the diameter of the circumscribed circle of the aforementioned stranded wire. The twist pitch of the aforementioned stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the aforementioned stranded wire. The steel constituting the core wire is a stranded wire, which corresponds to piano wire with a carbon content of 0.70% by mass or more and 0.95% by mass or less as specified in JIS standard G3502.

2. The stranded wire according to claim 1, wherein the diameter of the strand is 0.02 mm or more and 0.09 mm or less.

3. The stranded wire according to claim 1, wherein the tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less.

4. The stranded wire according to claim 1, wherein in a cross section perpendicular to the longitudinal direction of the strand, the area of ​​the coating layer relative to the area of ​​the strand is 20% or more and 80% or less.

5. A stranded wire in which multiple stranded wires are twisted together, Each of the aforementioned stranded wires has the same structure, in which multiple strands, each having a circular cross-section perpendicular to the longitudinal direction and of the same diameter, are twisted together. The aforementioned wire is Steel core wire, The core wire includes a coating layer made of copper or a copper alloy that covers the surface of the core wire, The twist pitch of the aforementioned stranded wire is 40 times or more the diameter of the circumscribed circle of the aforementioned stranded wire. The twist pitch of the aforementioned stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the aforementioned stranded wire. The diameter of the aforementioned core wire is 0.02 mm or more and 0.09 mm or less. The tensile strength of the aforementioned core wire is 1800 MPa or more and 4500 MPa or less. The steel constituting the core wire is a steel corresponding to piano wire material with a carbon content of 0.70% by mass or more and 0.95% by mass or less as specified in JIS standard G3502. In a cross-section perpendicular to the longitudinal direction of the wire, the area of ​​the coating layer relative to the area of ​​the wire is 20% or more and 80% or less. The plurality of the aforementioned stranded wires, in a cross-section perpendicular to the longitudinal direction of the stranded wire, The central stranded wire is positioned in the center, It includes six first peripheral strands arranged in contact with the central strand so as to surround the outer circumference of the central strand, The aforementioned stranded wire is a stranded wire that includes two to twenty of the aforementioned strands.

6. A stranded wire in which multiple stranded wires are twisted together, Each of the aforementioned stranded wires has the same structure, in which multiple strands, each having a circular cross-section perpendicular to the longitudinal direction and of the same diameter, are twisted together. The aforementioned wire is Steel core wire, The core wire includes a coating layer made of copper or a copper alloy that covers the surface of the core wire, The twist pitch of the aforementioned stranded wire is 40 times or more the diameter of the circumscribed circle of the aforementioned stranded wire. The twist pitch of the aforementioned stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the aforementioned stranded wire. The diameter of the aforementioned core wire is 0.02 mm or more and 0.09 mm or less. The tensile strength of the aforementioned core wire is 1800 MPa or more and 4500 MPa or less. The steel constituting the core wire is a steel corresponding to piano wire material with a carbon content of 0.70% by mass or more and 0.95% by mass or less as specified in JIS standard G3502. In a cross-section perpendicular to the longitudinal direction of the wire, the area of ​​the coating layer relative to the area of ​​the wire is 20% or more and 80% or less. The plurality of the aforementioned stranded wires, in a cross-section perpendicular to the longitudinal direction of the stranded wire, The central stranded wire is positioned in the center, Six first peripheral strands are arranged in contact with the central strand so as to surround the outer circumference of the central strand, It includes twelve second periphery strands arranged in contact with the first periphery strand on the outer circumference of the region where the first periphery strand is arranged, The aforementioned stranded wire is a stranded wire that includes two to twenty of the aforementioned strands.

7. The stranded wire according to claim 1, wherein the coating layer is a plating layer.

8. A stranded wire according to any one of claims 1 to 7, An insulated wire comprising an insulating layer covering the outer circumference of the stranded wire.

9. A core in which multiple insulated stranded wires are twisted together, The core comprises a protective layer made of an insulating material covering the outer circumference of the core, Each of the aforementioned insulated stranded wires is A stranded wire according to any one of claims 1 to 7, An insulated wire, comprising an insulating layer covering the outer circumference of the stranded wire.

10. The insulated wire according to claim 8, A conductive shield portion is arranged to surround the outer circumference of the insulated wire, A cable comprising an insulating outer sheath layer arranged to surround the outer periphery of the shield portion.

11. The insulated wire according to claim 9, A conductive shield portion is arranged to surround the outer circumference of the insulated wire, A cable comprising an insulating outer sheath layer arranged to surround the outer periphery of the shield portion.

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