Multicore cable production method and multicore 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 Art

[0002] Conventionally, a multi-core cable has been proposed that includes a long inclusion disposed in the center, a plurality of electric wires twisted around the inclusion, and a sheath covering the periphery thereof (see, for example, Patent Document 1). Since this multi-core cable includes a tension member in the center, the tensile strength can be increased (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in the multi-core cable as described in Patent Document 1, it is necessary to apply tension to the inclusion during manufacturing in order to stabilize the twist pitch of the electric wires around the inclusion. For this reason, the inclusion becomes slightly thinner than its original diameter. When the inclusion becomes thinner than its original diameter, the circular structure collapses when the inclusion and the surrounding electric wires are viewed in cross section, and in this state, when the sheath is extrusion-molded, the uniformity of the sheath thickness decreases. As a result of the decrease in the uniformity of the sheath thickness, the multi-core cable may develop wrinkles on the appearance or the wear resistance may decrease at the thin portion of the sheath thickness. Furthermore, in the thick portion of the sheath thickness of the multi-core cable, an increase in the amount of resin due to unnecessary thickness occurs, leading to an increase in the cost of the electric wire.

[0005] The present invention has been made to solve such conventional problems, and an object thereof is to provide a method for manufacturing a multi-core cable and a multi-core cable capable of improving the uniformity of a sheath.

Means for Solving the Problems

[0006] A method for manufacturing a multi-core cable according to the present invention includes an inclusion having a circular cross-section serving as a long central member, a plurality of electric wires twisted around the inclusion with tension applied to the inclusion, and an outer layer disposed around the plurality of electric wires. A method for manufacturing a multi-core cable, which manufactures a multi-core cable by extruding a sheath onto an inner wire portion, includes a preparation step of preparing the inclusion having a diameter exceeding a predetermined diameter assuming that the inclusion is stretched to become thinner to the predetermined diameter, a twisting step of twisting the plurality of electric wires with the inclusion prepared in the preparation step as a central member while applying tension to the inclusion, an inner wire manufacturing step of manufacturing the inner wire portion by providing the outer layer around the plurality of electric wires twisted by the twisting step, and an extrusion step of extruding a sheath onto the inner wire portion manufactured in the inner wire manufacturing step.

[0007] Further, a multi-core cable according to the present invention includes an inclusion having a circular cross-section serving as a long central member, a plurality of electric wires provided around the inclusion and twisted with each other, an outer layer disposed around the plurality of electric wires, and a sheath formed in contact with the outer layer. The inclusion is in a state of being thinner than when it is in a free state with tension applied, and contacts the plurality of electric wires on the outer peripheral side thereof, and the plurality of electric wires are arranged in a circular cross-sectional shape.

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 capable of improving the uniformity of a sheath.

Brief Description of the Drawings

[0009]

Figure 1

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MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, the present invention will be described along preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be appropriately changed without departing from the gist of the present invention. Also, in the embodiments shown below, there are some parts where the illustration and description of some configurations are omitted. However, it goes without saying that well-known or well-understood technologies are appropriately applied within the range not conflicting with the content described below regarding the details of the omitted technologies.

[0011] FIG. 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 part (outer layer) 30, and a sheath 40.

[0012] The inclusion 10 is what is called a so-called tension member, and is a central member having a circular cross-section and formed in a long shape similar to the multi-core cable 1. In the present embodiment, the inclusion 10 is in a state where tension is applied in its longitudinal direction, and its diameter is thinner than that in the free state (the state of 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 state where tension is applied. In the present embodiment, all of the plurality of electric wires 20 are of the same dimensions, shape, and material, but some of them may have one or more differences in dimensions, shape, and material. Also, the plurality of electric wires 20 are not limited to six.

[0014] The shield portion 30 protects the internal electric wires 20 from noise reaching from the outside, for example, and is disposed around the plurality of electric wires 20. This shield portion 30 is composed of a metal foil, or is composed of a braid in which metal wires or the like are braided. Also, the shield portion 30 may be one in which a fiber with metal plating is braided into a braid or the like, or one in which a non-woven fabric is metal-plated. Also, when the shield portion 30 is composed of a metal foil, the metal foil may be wound in a spiral or laid longitudinally.

[0015] The sheath 40 is an insulating member provided in contact with the shield portion 30. This sheath 40 is formed on the shield portion 30 by being extrusion-molded with respect to the inner wire portion IC having the inclusion 10, the plurality of electric wires 20, and the shield portion 30.

[0016] Here, in the multi-core cable 1 according to the present embodiment, tension is applied to the inclusion 10, and the inclusion 10 is thinner than in the free state and has a predetermined diameter. The plurality of electric wires 20 are twisted around the inclusion 10 having such a tension and having a predetermined diameter, so as to have a circular cross-sectional shape. In this state, each electric wire 20 contacts the inclusion 10 and also contacts the adjacent electric wire 20.

[0017] In this embodiment, the cross-sectional circular shape means, for example, a case where the roundness value (roundness ratio) obtained by dividing the roundness by the average value of the maximum diameter and the minimum diameter in a cross-section orthogonal to the longitudinal direction is 0.05 or less. To explain in detail, the maximum circle is defined with the center of the inclusion 10 as the center of the circle, and is the circumscribed circle of the outermost one among the plurality of electric wires 20. The maximum circle diameter is the diameter of the maximum circle. The minimum circle is defined with the center of the inclusion 10 as the center of the circle, and is the circumscribed circle of the innermost one among the plurality of electric wires 20. The minimum circle diameter is the diameter of the minimum circle. The roundness generally refers to the value obtained by dividing the difference between the maximum circle diameter and the minimum circle diameter by 2. The roundness ratio in this embodiment refers to the value obtained by further dividing the roundness by the average value of the maximum circle diameter and the minimum circle diameter. When this roundness ratio is 0.05 or less, it can be said that the plurality of electric wires 20 are arranged in a cross-sectional circular shape.

[0018] FIG. 2 is a cross-sectional view showing a multi-core cable according to a comparative example. As shown in FIG. 2, the multi-core cable 101 according to the comparative example includes an inclusion 110, a plurality of electric wires 120, a shield portion 130, and a sheath 140. Note that the plurality of electric wires 120 and the shield 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, an inclusion 110 having a predetermined diameter is prepared, and a tension is applied to the inclusion 110 having the predetermined diameter so that the plurality of electric wires 120 are twisted. That is, in the multi-core cable 101 according to the comparative example, an inclusion 110 having a predetermined diameter in a free state is used. For this reason, in a state where tension is applied, the inclusion 110 is thinner than the predetermined diameter. Therefore, when the plurality of electric wires 120 are twisted around such an inclusion 110, it is difficult to say that any of the plurality of electric wires 120 is separated from the inclusion 110 as shown by reference numeral 101a and has a roundness ratio exceeding 0.05 and is arranged in a cross-sectional circular shape. In particular, when the roundness ratio deteriorates, there may also be a portion S where adjacent electric wires 120 are in a separated state.

[0020] Then, the shield portion 130 is formed in a state where the roundness exceeds 0.05, and further, when the sheath 140 is extrusion-molded, the uniformity of the thickness of the sheath 140 will decrease. For example, in the multi-core cable 101 according to the comparative example, the sheath thickness is ensured at the location indicated by reference numeral 101b, but the sheath is thin at the location indicated by reference numeral 101c and the thickness cannot be ensured.

[0021] Thus, in the multi-core cable 101 according to the comparative example, the uniformity of the sheath thickness is reduced, resulting in the occurrence of wrinkles on the appearance and a reduction in abrasion resistance at the thin portion of the sheath thickness (the portion of reference numeral 101c). Furthermore, in the multi-core cable 101 according to the comparative example, an increase in the resin amount due to unnecessary thickness occurs at the thick portion of the sheath thickness (the portion of reference numeral 101b), leading to an increase in the cable cost.

[0022] On the other hand, in the multi-core cable 1 according to the present embodiment, an inclusion 10 having a diameter larger than a predetermined diameter is prepared in advance so as to have a predetermined diameter in a state where tension is applied to the inclusion 10, and the multi-core cable 1 is manufactured using such an inclusion 10. As a result, as shown in FIG. 1, the plurality of electric wires 20 are each in contact with the inclusion 10 and are arranged in a circular cross-sectional shape with a roundness of 0.05 or less. Furthermore, the plurality of electric wires 20 are in contact with each other adjacent to each other.

[0023] In this way, the multi-core cable 1 according to the present embodiment has a high degree of circularity of the plurality of electric wires 20, and when the shield portion 30 is provided and the sheath 40 is extrusion-molded, the uniformity of the sheath thickness is enhanced.

[0024] FIG. 3 is a process diagram showing a manufacturing method of the multi-core cable 1 according to the present embodiment. First, as shown in FIG. 3, first, a step of calculating the diameter of the twisted inclusion 10 is executed. In this step, based on the diameter of the multi-core cable 1 to be manufactured and the respective diameters of the plurality of electric wires 20, the diameter of the twisted inclusion 10 is calculated by calculation so that the inner wire portion IC becomes more circular.

[0025] Next, a step of calculating the diameter of the inclusion 10 before applying tension (before twisting) is executed. Here, at the time of manufacturing, it is known in advance how much tension will be applied. Therefore, based on the tension applied to the inclusion 10 and the diameter of the inclusion 10 after twisting, the diameter of the inclusion 10 before applying tension (before twisting) is calculated by calculation.

[0026] Next, the inclusion 10 having the calculated diameter before applying tension is prepared (preparation step). Note that when using the inclusion 10 with a cross-sectional area of 1.77 mm 2 assume that when using the inclusion 10, the tension applied to this inclusion 10 is about 20 MPa (35.4 N). In this case, of course, for the inclusion 10, a material with a tensile yield stress exceeding 20 MPa, that is, a material that becomes the target diameter even when the above tension is applied (for example, PP (Polypropylene) or PA (Polyamide)) is selected.

[0027] Thereafter, a twisting step of twisting a plurality of electric wires 20 around the inclusion 10 is executed (twisting step). At this time, tension is applied to the inclusion 10. Also, due to the twisting, the plurality of electric wires 20 will be twisted while tension is applied to them. In this twisting step, the inclusion 10 is made to have a predetermined diameter by the tension applied to the inclusion 10, and the plurality of electric wires 20 are twisted into a cross-sectional circular shape with a circularity of 0.05 or less, for example.

[0028] Next, a shield portion 30 is formed on the plurality of electric wires 20 twisted in the twisting step (inner wire manufacturing step). Thereby, the inner wire portion IC before extrusion molding is manufactured. Thereafter, a sheath 40 is extruded onto the inner wire portion IC manufactured in the inner wire manufacturing step (extrusion step).

[0029] As described above, the multi-core cable 1 is manufactured. In particular, since the plurality of electric wires 20 are arranged in a cross-sectional circular shape, the inner wire portion IC provided with the shield portion 30 is also likely to have a cross-sectional circular shape. Therefore, the subsequent sheath 40 will cover the inner wire portion IC with high uniformity.

[0030] Next, an example of the multi-core cable 1 manufactured by the manufacturing method according to the present embodiment will be described, and the scrape test results for the multi-core cable 1 manufactured by the example will be described.

[0031] FIG. 4 is a chart showing the manufacturing conditions of the multi-core cable 1 according to the present embodiment. In the example shown in FIG. 4, the shield portion 30 is composed of a metal foil, and PVC (Polyvinyl Chloride) is used as the material of the inclusion 10. Also, the number of wires 20 is six.

[0032] As shown in FIG. 4, when the sheath 40 is extruded, the set temperature in the screw (not shown) of the extruder (not shown) varies depending on the location, but is 170°C or higher and 175°C or lower. The measured temperature is 171°C or higher and 175°C or lower. Also, the set temperature of the head (not shown) of the extruder is 175°C, and the measured temperature is 174°C or higher and 177°C or lower.

[0033] The core wire diameter is 4.9 mm, and the die exit diameter is 7.3 mm. The cap diameter for evacuating the periphery of the inner wire part IC and making the sheath 40 adhere is 5.3 mm, the foil width is 16.0 mm, and the diameter of the inclusion 10 (after tension application) is 1.5 mm.

[0034] The width of the guide for winding the foil is 5.3 mm, the foil temperature is 125°C, and the pressure around the inner wire part IC (in the evacuated state) is 12.6 kPa. The tension applied to the foil is 55%, and the wire speed is 40 m / min.

[0035] A scrape test was conducted between 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 state of the scrape test.

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

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

[0038] Also, after one measurement is performed, the sample Sa is moved about 100 mm in the longitudinal direction and rotated 90 degrees clockwise and fixed by the support SU. Then, the number of reciprocations is measured in the same manner as above. And a total of 4 measurements are performed, and the minimum value is adopted as the result.

[0039] FIG. 6 is a graph showing the results of the scrape test. In FIG. 6, the number of samples is 5, and the maximum value, average value, and minimum value are shown.

[0040] As shown in FIG. 6, as a result of the scrape test, for the multi-core cable 101 according to the comparative example, the number of reciprocations was from about 2,100 times to about 5,800 times, resulting in a wide range of results. Also, the average number of times was about 3,600 times. On the other hand, for an example of the multi-core cable 1 according to the present embodiment, the number of reciprocations was from about 3,500 times to about 4,800 times, which was narrower than that of the comparative example. That is, it was found that the uniformity of the sheath thickness was improved. Also, the average number of times was about 4,100 times, and an improvement was also confirmed in terms of the average number of times.

[0041] In addition, as a result of measuring the sheath thickness at various locations, the multi-core cable 101 according to the comparative example had a sheath thickness of 0.38 mm or more and 0.61 mm or less. In contrast, an example of the multi-core cable 1 according to the present embodiment had a sheath thickness of 0.37 mm or more and 0.54 mm or less. Therefore, it was found that the uniformity of the sheath thickness was improved also from the measured values of the sheath thickness.

[0042] Furthermore, as a result of visually checking the appearance of the multi-core cables 1 and 101, wrinkles were confirmed at various locations on the multi-core cable 101 according to the comparative example. In contrast, no wrinkles were confirmed on the multi-core cable 1 according to the present embodiment.

[0043] In this way, in the manufacturing method of the multi-core cable 1 according to the present embodiment, the inclusion 10 exceeding the predetermined diameter is prepared assuming that the tension is applied and the cable becomes thinner to the predetermined diameter. For this reason, the plurality of electric wires 20 are twisted around the inclusion 10 in a state where the inclusion 10 is near the assumed predetermined diameter. As a result, compared with the case where the inclusion 110 is not assumed to become thinner and the inclusion 110 having a predetermined diameter is prepared in advance, the inner wire part IC becomes more circular in cross section. Thereby, when the sheath 40 is subsequently extrusion-molded, the uniformity of the sheath thickness is enhanced. Therefore, it is possible to provide a manufacturing method of the multi-core cable 1 capable of improving the uniformity of the sheath 40.

[0044] Moreover, in the multi-core cable 1 according to the present embodiment, when the inclusion 10 is under tension and in a free state, it contacts the plurality of electric wires 20 on its outer peripheral side in a state where it has become thinner than when no tension is applied, and the plurality of electric wires 20 are arranged in a circular cross-sectional shape. Therefore, even though the inclusion 10 has become thinner due to the 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 tension is applied to the inclusion 10 and it becomes thinner, none of the plurality of electric wires 20 is arranged in a state of being separated from the inclusion 10 and collapsing from the circular cross-sectional shape. And since the plurality of electric wires 20 are arranged in a circular cross-sectional shape, the shield portion 30 also approximates a circular cross-sectional shape, and the sheath 40 formed by extrusion on this shield portion 30 will have a uniform thickness. Therefore, it is possible to provide a multi-core cable 1 capable of improving the uniformity of the sheath 40.

[0045] As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above embodiments, and modifications may be made without departing from the spirit of the present invention, and known or well-known techniques may be combined if possible.

[0046] For example, in the above embodiment, a shield portion 30 is provided outside the plurality of electric wires 20, but it is not particularly limited to the shield portion 30, and for example, a resin tape or the like may be wound around. Further, it is not limited to the case where a shield portion 30, a tape, or the like is provided in one layer outside the plurality of electric wires 20, and these may be provided in two or more layers.

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

Explanation of Reference Numerals

[0048] 1: Multi-core cable 10: Inclusion 20: Plurality of electric wires 30: Shield portion (outer layer) 40: Sheath IC: Inner wire part

Claims

1. A method for manufacturing a multi-core cable, which comprises extruding a sheath onto an inner wire portion having a long, circular cross-section intervening member serving as a central member, a plurality of electric wires twisted around the intervening member with tension applied thereto, and an outer layer disposed around the plurality of electric wires, a preparation step of preparing the intervening member having a diameter exceeding a predetermined diameter on the assumption that the intervening member is to be tensioned and thinned to the predetermined diameter; a twisting step of twisting the plurality of electric wires while applying tension to the intervening member with the intervening member 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; an extrusion step of extruding a sheath onto the inner wire portion manufactured in the inner wire manufacturing step; and characterized by comprising the above steps.

2. A multi-core cable comprising a long, circular cross-section intervening member serving as a central member, a plurality of electric wires provided around the intervening member and twisted together, an outer layer disposed around the plurality of electric wires, and a sheath formed in contact with the outer layer, wherein the intervening member is in a state of being thinner than when it is in a free state with tension applied thereto and contacts the plurality of electric wires on its outer peripheral side; and the plurality of electric wires are arranged in a circular cross-sectional shape. A multi-core cable characterized by the above.

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