Multi-core cable manufacturing method and multi-core cable

Abstract

To provide a multicore cable production method capable of improving uniformity of a sheath, and a multicore cable.SOLUTION: Provided is a method for producing a multicore cable 1, the multicore cable 1 comprising: an inclusion 10, a plurality of electric wires 20 twisted around the inclusion 10 while tension is applied to the inclusion 10; a shield part 30 disposed around the plurality of electric wires 20; and a sheath 40. The method for producing the multicore cable includes the following steps: preparing the inclusion 10 with a diameter exceeding a predetermined diameter, assuming that tension is applied to the inclusion 10 to reduce its diameter to the predetermined diameter; twisting the plurality of electric wires 20, while applying tension to the inclusion 10, using the inclusion 10 prepared in the preparation step as a center member; producing an inner conductor IC by having the shield part 30 provided around the plurality of electric wires 20 twisted in the twisting step; and extruding the sheath 40 with respect to the inner conductor IC produced in the inner conductor production step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a multi-core cable and a multi-core cable. [Background technology]

[0002] Conventionally, a multi-core cable has been proposed that includes a long inclusion placed in the center, multiple electric wires twisted around the inclusion, and a sheath that covers the entire inclusion (see, for example, Patent Document 1). This multi-core cable has a tension member in the center, which allows it to have high tensile strength (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-116254 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, multi-core cables such as those described in Patent Document 1 must be manufactured by applying tension to the inclusions to stabilize the twist pitch of the electric wires around the inclusions. As a result, the inclusions become slightly thinner than their original diameter. If the inclusions become thinner than their original diameter, the circular structure of the inclusions and the surrounding electric wires collapses when viewed in cross section. If the sheath is extruded in this state, the sheath thickness becomes less uniform. As a result of the reduced sheath thickness uniformity, the multi-core cable may develop wrinkles on its appearance and have reduced abrasion resistance in the thin sheath areas. Furthermore, the multi-core cable requires an increased amount of resin due to unnecessary thickness in the thick sheath areas, which increases the cost of the electric wire.

[0005] The present invention has been made to solve these conventional problems, and its object is to provide a method for manufacturing a multi-core cable that can improve the uniformity of the sheath, and a multi-core cable. [Means for solving the problem]

[0006] The method for manufacturing a multi-core cable according to the present invention is a method for manufacturing a multi-core cable by extruding a sheath around an inner wire portion having an inclusion with a circular cross section that serves as a long central member, a plurality of electric wires twisted around the inclusion while tension is applied to the inclusion, and an outer layer arranged around the plurality of electric wires, and is characterized by comprising: a preparation step of preparing the inclusion having a diameter exceeding a predetermined diameter on the assumption that tension will be applied to the inclusion to thin it to the predetermined diameter; a twisting step of twisting the plurality of electric wires while applying tension to the inclusion, using the inclusion prepared in the preparation step as a central member; an inner wire manufacturing step of manufacturing the inner wire portion by providing the outer layer around the plurality of electric wires twisted in the twisting step; and an extrusion step of extruding a sheath around the inner wire portion manufactured in the inner wire manufacturing step.

[0007] Furthermore, the multi-core cable of the present invention is a multi-core cable comprising an inclusion having a circular cross section that serves as a long central member, a plurality of electric wires that are arranged around the inclusion and are twisted together, an outer layer that is arranged around the plurality of electric wires, and a sheath that is formed in contact with the outer layer, wherein the inclusion contacts the plurality of electric wires on its outer side in a state where tension is applied to the inclusion and it is thinner than when it is in a free state, and the plurality of electric wires are arranged in a circular cross section. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for manufacturing a multi-core cable and a multi-core cable that can improve the uniformity of the sheath. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a cross-sectional view showing a multi-core cable according to an embodiment of the present invention. [Figure 2] FIG. 10 is a cross-sectional view showing a multi-core cable according to a comparative example. [Figure 3] 3A to 3C are process diagrams showing a method for manufacturing a multi-core cable according to the present embodiment. [Figure 4] 1 is a table showing manufacturing conditions for the multi-core cable according to the present embodiment. [Figure 5] FIG. 1 is a diagram showing the state of a scrape test. [Figure 6] 1 is a graph showing the results of a scrape test. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below and can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiments shown below, some components are omitted from illustration and description, but it goes without saying that publicly known or well-known technologies are applied as appropriate to the details of the omitted technologies within the scope of the content described below.

[0011] 1 is a cross-sectional view showing a multi-core cable according to an embodiment of the present invention. As shown in Fig. 1, the multi-core cable 1 includes an inclusion 10, a plurality of electric wires 20, a shield portion (outer layer) 30, and a sheath 40.

[0012] The inclusion 10 is what is called a tension member, a central member with a circular cross section, and formed in a long shape similar to the multi-core cable 1. In this embodiment, the inclusion 10 is in a state where tension is applied in the longitudinal direction, and the diameter is made smaller than in a free state (a state where the inclusion has a natural length).

[0013] The plurality of electric wires 20 are, for example, insulated electric wires having a conductor and an insulator. The plurality of electric wires 20 are twisted around the inclusion 10 in a tensioned state. In this embodiment, the plurality of electric wires 20 all have the same size, shape, and material, but some of the electric wires 20 may differ in one or more of size, shape, and material. Furthermore, the number of the plurality of electric wires 20 is not limited to six.

[0014] The shielding portion 30 protects the internal electric wires 20 from, for example, external noise and the like, and is disposed around the plurality of electric wires 20. The shielding portion 30 may be made of metal foil or a braid of woven metal wires or the like. The shielding portion 30 may also be made of metal-plated fibers woven into a braid or a metal-plated nonwoven fabric. When the shielding portion 30 is made of metal foil, the metal foil may be wound spirally or attached vertically.

[0015] The sheath 40 is an insulating member provided on and in contact with the shield portion 30. The sheath 40 is formed on the shield portion 30 by extrusion molding the inner wiring portion IC, which is configured to include the inclusion 10, the plurality of electric wires 20, and the shield portion 30.

[0016] In the multi-core cable 1 according to this embodiment, tension is applied to the inclusions 10, which are thinner than in a free state and have a predetermined diameter. The electric wires 20 are twisted around the inclusions 10, which have been given such tension and have a predetermined diameter, and thus have a circular cross section. In this state, each electric wire 20 is in contact with the inclusions 10 and also with the adjacent electric wires 20.

[0017] In this embodiment, the circular cross section refers to a case where, for example, the value obtained by dividing the circularity by the average value of the maximum and minimum circle diameters in a cross section perpendicular to the longitudinal direction (circularity ratio) is 0.05 or less. Specifically, the maximum circle refers to the circumscribing circle of the outermost of the multiple electric wires 20, with the center of the inclusion 10 defined as the center of the circle. The maximum circle diameter is the diameter of the maximum circle. The minimum circle refers to the circumscribing circle of the innermost of the multiple electric wires 20, with the center of the inclusion 10 defined as the center of the circle. The minimum circle diameter is the diameter of the minimum circle. Circularity generally refers to the difference between the maximum and minimum circle diameters divided by 2. The circularity ratio in this embodiment refers to the value obtained by further dividing the circularity by the average value of the maximum and minimum circle diameters. When this circularity ratio is 0.05 or less, it can be said that the multiple electric wires 20 are arranged in a circular cross section.

[0018] Fig. 2 is a cross-sectional view showing a multi-core cable according to a comparative example. As shown in Fig. 2, multi-core cable 101 according to the comparative example includes inclusion 110, a plurality of electric wires 120, a shielding portion 130, and a sheath 140. Note that the plurality of electric wires 120 and the shielding portion 130 according to the comparative example are the same as those described with reference to Fig. 1.

[0019] In the multi-core cable 101 according to the comparative example, inclusions 110 having a predetermined diameter are prepared, and tension is applied to the inclusions 110 of the predetermined diameter to twist multiple electric wires 120. That is, in the multi-core cable 101 according to the comparative example, the inclusions 110 have a predetermined diameter in a free state. Therefore, when tension is applied, the inclusions 110 are thinner than the predetermined diameter. Therefore, when multiple electric wires 120 are twisted around such inclusions 110, it is difficult to say that any of the multiple electric wires 120 is spaced from the inclusions 110, as shown by reference numeral 101a, and is arranged in a circular cross section with a circularity exceeding 0.05. In particular, if the circularity deteriorates, there may be a point S where adjacent electric wires 120 are spaced from each other.

[0020] Then, when shield portion 130 is formed with a circularity ratio exceeding 0.05, and sheath 140 is further extrusion-molded, the uniformity of the thickness of sheath 140 decreases. For example, in multi-core cable 101 according to the comparative example, the sheath thickness is ensured at the portion indicated by reference numeral 101b, but the sheath is thin at the portion indicated by reference numeral 101c, making it impossible to ensure the thickness.

[0021] As described above, the multi-core cable 101 according to the comparative example has a reduced uniformity in the sheath thickness, which results in wrinkles on the exterior and reduced abrasion resistance in the thin sheath portion (portion 101c).Furthermore, the multi-core cable 101 according to the comparative example has an increased amount of resin due to unnecessary thickness in the thick sheath portion (portion 101b), which leads to an increase in the cost of the electric wire.

[0022] In contrast, in the multi-core cable 1 according to this embodiment, inclusions 10 having a diameter larger than a predetermined diameter are prepared in advance so that the inclusions 10 have a predetermined diameter when tension is applied, and the multi-core cable 1 is manufactured using such inclusions 10. As a result, as shown in Fig. 1, the multiple electric wires 20 are arranged in a circular cross section such that each electric wire 20 contacts an inclusion 10 and has a circularity of 0.05 or less. Furthermore, adjacent ones of the multiple electric wires 20 are in contact with each other.

[0023] As described above, in the multi-core cable 1 according to the present embodiment, the plurality of electric wires 20 have a high degree of circularity, and when the shield portion 30 is provided and the sheath 40 is extrusion-molded, the uniformity of the sheath thickness is improved.

[0024] Fig. 3 is a process diagram showing the method for manufacturing the multi-core cable 1 according to this embodiment. First, as shown in Fig. 3, a process for calculating the diameter of the inclusions 10 after twisting is performed. In this process, the diameter of the inclusions 10 after twisting is calculated based on the diameter of the multi-core cable 1 to be manufactured and the diameters of each of the multiple electric wires 20, so that the inner wire portion IC becomes a more perfect circle.

[0025] Next, a step of calculating the diameter of the inclusions 10 before tension is applied (before twisting) is performed. Here, the amount of tension applied is known in advance during manufacturing. Therefore, the diameter of the inclusions 10 before tension is applied (before twisting) is calculated based on the tension applied to the inclusions 10 and the diameter of the inclusions 10 after twisting.

[0026] Next, an inclusion 10 having the calculated diameter before tension application is prepared (preparation step). 2 When using the inclusion 10, it is assumed that the tension applied to this inclusion 10 is about 20 MPa (35.4 N). In this case, it goes without saying that a material with a tensile yield stress exceeding 20 MPa, that is, a material (e.g., PP (Polypropylene) or PA (Polyamide)) that will maintain the target diameter even when the above tension is applied, is selected for the inclusion 10.

[0027] Thereafter, a twisting process is carried out in which the plurality of electric wires 20 are twisted around the inclusion 10 (twisting process). At this time, tension is applied to the inclusion 10. Furthermore, in order to perform twisting, tension is also applied to the plurality of electric wires 20 while twisting is being carried out. In this twisting process, the tension on the inclusion 10 makes the inclusion 10 have a predetermined diameter, and the plurality of electric wires 20 are twisted into a circular cross-sectional shape with a circularity of, for example, 0.05 or less.

[0028] Next, the shield portion 30 is formed on the multiple electric wires 20 twisted in the twisting process (inner wire manufacturing process). This produces an inner wire portion IC before extrusion molding. After that, a sheath 40 is extruded onto the inner wire portion IC manufactured in the inner wire manufacturing process (extrusion process).

[0029] In this manner, the multi-core cable 1 is manufactured. In particular, since the multiple electric wires 20 are arranged to have a circular cross section, the internal wiring portion IC provided with the shield portion 30 is also likely to have a circular cross section. Therefore, the sheath 40 thereafter covers the internal wiring portion IC with high uniformity.

[0030] Next, an example of a multi-core cable 1 manufactured by the manufacturing method according to the present embodiment will be described, along with the results of a scrape test performed on the multi-core cable 1 manufactured by this example.

[0031] Fig. 4 is a table showing the manufacturing conditions of the multi-core cable 1 according to this embodiment. In the example shown in Fig. 4, the shield portion 30 is made of metal foil, and PVC (Polyvinyl Chloride) is used as the material for the inclusions 10. The number of electric wires 20 is six.

[0032] As shown in Figure 4, when extruding sheath 40, the set temperature inside the screw (not shown) of the extruder (not shown) varies depending on the location, but is between 170°C and 175°C. The actually measured temperature is between 171°C and 175°C. The set temperature of the extruder head (not shown) is 175°C, and the actually measured temperature is between 174°C and 177°C.

[0033] The core diameter is 4.9 mm, the die outlet diameter is 7.3 mm, the cap diameter for vacuuming the area around the internal wiring IC and tightly sealing the sheath 40 is 5.3 mm, the foil width is 16.0 mm, and the diameter of the inclusion 10 (after tensioning) is 1.5 mm.

[0034] The width of the guide around which the foil is wound is 5.3 mm, the foil temperature is 125°C, the pressure around the internal wiring part IC (vacuum state) is 12.6 kPa, the tension applied to the foil is 55%, and the line speed is 40 m / min.

[0035] A scrape test was carried out on the multi-core cable 1 manufactured under the above manufacturing conditions and the multi-core cable 101 according to the comparative example. Fig. 5 is a diagram showing the scrape test.

[0036] In the scrape test, a sample Sa, a multi-core cable 1,101 approximately 750 mm long, is fixed to a sample holder SH by a support SU. A metal plunger M, which has a conductive tip CT such as a spring wire or hard steel wire at its tip, is brought into contact with the sample Sa with a load of 7±0.05 N applied by a weight SI. The spring wire is specified in ISO 8458-2, and the hard steel wire is hard steel wire type C (SW-C) specified in JIS G 3521.

[0037] Next, the metal plunger M is reciprocated 15.5±1 mm at a speed of 50 to 60 times / min at room temperature of 23±1° C. The number of reciprocations until the shield portion 30, 130 and the conductive tip portion CT come into contact is measured.

[0038] After one measurement, the sample Sa is moved approximately 100 mm in the longitudinal direction, rotated 90 degrees clockwise, and fixed by the support SU. The number of reciprocating movements is then measured in the same manner as above. A total of four measurements are taken, and the minimum value is used as the result.

[0039] Figure 6 is a graph showing the results of the scrape test. Note that Figure 6 shows five samples, with the highest, average, and lowest values.

[0040] As shown in FIG. 6, the scrape test results for the multi-core cable 101 according to the comparative example showed a wide range of reciprocation times, from approximately 2,100 to approximately 5,800. The average number of reciprocation times was approximately 3,600. On the other hand, the example of the multi-core cable 1 according to the present embodiment showed a narrower range of reciprocation times, from approximately 3,500 to approximately 4,800, compared to the comparative example. This indicates that the sheath thickness uniformity was improved. The average number of reciprocation times was approximately 4,100, confirming an improvement in the average number of reciprocation times.

[0041] Additionally, the sheath thickness was measured at various locations, and the sheath thickness of the multi-core cable 101 according to the comparative example was 0.38 mm or more and 0.61 mm or less. In contrast, the sheath thickness of the example multi-core cable 1 according to the present embodiment was 0.37 mm or more and 0.54 mm or less. Therefore, the measured sheath thickness values ​​also showed that the uniformity of the sheath thickness was improved.

[0042] Furthermore, when the appearance of the multicore cables 1, 101 was visually inspected, wrinkles were found in various places in the multicore cable 101 according to the comparative example. In contrast, no wrinkles were found in the example of the multicore cable 1 according to the present embodiment.

[0043] In this way, in the manufacturing method of the multi-core cable 1 according to this embodiment, the inclusions 10 exceeding a predetermined diameter are prepared, assuming that the inclusions 10 will be thinned to the predetermined diameter when tension is applied. Therefore, the multiple electric wires 20 are twisted around the inclusions 10 with the inclusions 10 near the predetermined diameter. As a result, the inner wire portion IC has a more circular cross section than when the inclusions 110 are prepared with a predetermined diameter without assuming that the inclusions 110 will thin. This improves the uniformity of the sheath thickness when the sheath 40 is subsequently extruded. Therefore, a manufacturing method of the multi-core cable 1 capable of improving the uniformity of the sheath 40 can be provided.

[0044] Furthermore, in the multi-core cable 1 according to this embodiment, the inclusion 10 is in contact with the plurality of electric wires 20 at its outer periphery in a state where it is thinner than when it is in a free state due to tension, and the plurality of electric wires 20 are arranged in a circular cross-sectional shape. Therefore, even though the inclusion 10 is thinned due to tension, each of the plurality of electric wires 20 is in contact with the inclusion 10 and has a circular cross-sectional shape. In this way, when the inclusion 10 is thinned due to tension, the multi-core cable 1 is arranged in a state where none of the plurality of electric wires 20 separates from the inclusion 10 and loses its circular cross-sectional shape. Furthermore, because the plurality of electric wires 20 are arranged in a circular cross-sectional shape, the shield portion 30 also has a nearly circular cross-sectional shape, and the sheath 40 formed by extrusion on the shield portion 30 has a uniform thickness. Therefore, a multi-core cable 1 capable of improving the uniformity of the sheath 40 can be provided.

[0045] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and modifications may be made within the scope of the spirit of the present invention, and if possible, publicly known or well-known technologies may be combined.

[0046] For example, in the above embodiment, the shielding portion 30 is provided on the outside of the plurality of electric wires 20, but it is not limited to the shielding portion 30, and for example, a resin tape or the like may be wound around the outside of the plurality of electric wires 20. Furthermore, the shielding portion 30, tape, or the like may not be provided in a single layer on the outside of the plurality of electric wires 20, but may be provided in two or more layers.

[0047] In addition, when the multi-core cable 1 has the shield portion 30 as an outer layer, it may further have a separate drain wire, or may have the drain wire as one of the plurality of electric wires 20. [Explanation of symbols]

[0048] 1: Multi-core cable 10:Inclusions 20: Multiple wires 30: Shield part (outer layer) 40: Sheath IC: Internal line

Claims

1. A method for manufacturing a multi-core cable, comprising extruding a sheath around an inner wire section having an inclusion having a circular cross section that serves as a long central member, a plurality of electric wires twisted around the inclusion while tension is applied to the inclusion, and an outer layer disposed around the plurality of electric wires, the method comprising: a preparation step of preparing the inclusions having a diameter exceeding the predetermined diameter, assuming that tension is applied to the inclusions to thin them to the predetermined diameter; a twisting step of twisting the plurality of electric wires while applying tension to the inclusions prepared in the preparing step, using the inclusions as central members; an inner wire manufacturing process in which the outer layer is provided around the plurality of electric wires twisted in the twisting process to manufacture the inner wire portion; an extrusion step of extruding a sheath onto the inner wire portion manufactured in the inner wire manufacturing step; A method for manufacturing a multi-core cable, comprising:

2. A multi-core cable comprising: an inclusion having a circular cross section that serves as a long central member; a plurality of electric wires arranged around the inclusion and twisted together; an outer layer arranged around the plurality of electric wires; and a sheath formed on and in contact with the outer layer, the inclusion contacts the plurality of electric wires at its outer periphery in a state where the inclusion is subjected to tension and is thinner than when it is in a free state, The plurality of electric wires are arranged in a circular cross section. A multi-core cable characterized by:

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