JP7820179B2 - Fire-resistant cable and manufacturing method thereof - Google Patents

Description

The present invention relates to a fire-resistant cable and a method for manufacturing the same.

The fire resistance, electrical characteristics, structure, dimensions, etc. of fire-resistant cables used as electrical wiring for disaster prevention equipment in buildings, underground shopping malls, etc. are regulated by Fire and Disaster Management Agency notices.

Fire-resistant cables that meet these standards include cables in which a fire-resistant layer, an insulating layer, a sheath, etc. are arranged around the conductor (see, for example, Patent Document 1). In this document, a fire-resistant layer is formed by attaching mica tape (fire-resistant tape) vertically to the conductor and then wrapping glass mica tape on top of that. In recent years, fire-resistant layers in which glass yarn is wrapped around mica tape have also become known.

Japanese Utility Model Application Laid-Open Publication No. 7-41876

When winding glass yarn around mica tape to form a fire-resistant layer for a fire-resistant cable, a coarse winding device 100 such as that shown in Figure 1 may be used. In the coarse winding device 100 shown in Figure 1, the glass yarn 24 is wound on a bobbin (not shown) and housed in the coarse winding head 120 of the coarse winding device 100. To form the fire-resistant layer 20, first, a jig 110 is used to attach the mica tape 22 longitudinally to the conductor 10. Then, a fixed length of glass yarn 24 is unwound from the coarse winding head 120, and the coarse winding head 120 is rotated while feeding out the conductor 10 and mica tape 22 in a predetermined direction. This causes the glass yarn 24 to be wound spirally around the mica tape 22.

Here, conventional glass yarn 24 has a structure in which multiple strands of yarn are simply pulled together. Therefore, as shown in Figure 2, when the glass yarn 24 is unwound from a bobbin (not shown), some of the strands may become loose or fray. These strands may then become tangled in the winding head 120 or break when the winding head 120 rotates. Furthermore, the tangled portions may become knots, causing defects in the fire-resistant cable. When such defects occur, the affected areas must be repaired. Furthermore, the winding device 100 must be stopped, which makes it difficult to efficiently manufacture fire-resistant cables. Furthermore, to address such defects, the winding device 100 must be constantly monitored by an operator.

The main object of the present invention is to provide a method for efficiently manufacturing fire-resistant cables without the need for constant worker supervision, and to provide the fire-resistant cables obtained using this method.

After extensive technical research to solve the above problems, the inventors discovered that by using glass yarns made by twisting together multiple raw yarns, the glass yarns are almost never loosened or frayed, allowing for the efficient production of fire-resistant cables, leading to the completion of the present invention.

That is, according to one aspect of the present invention,
applying a fire-resistant tape longitudinally onto the conductor;
and winding a glass yarn around the outer periphery of the fire-resistant tape.
There is provided a method for producing a fire-resistant cable, characterized in that a glass yarn formed by twisting together a plurality of raw yarns is used as the glass yarn.

According to another aspect of the present invention,
The conductor is covered with a fire-resistant layer and an insulating layer.
The fire-resistant layer is composed of a fire-resistant tape longitudinally attached to the conductor and a glass yarn wound around the outer periphery of the fire-resistant tape,
The fire-resistant cable is characterized in that a plurality of strands of glass yarn are twisted together.

According to the present invention, fire-resistant cables can be manufactured efficiently with almost no loosening or fraying of glass yarns during production. Furthermore, fire-resistant cables manufactured using this method are less likely to experience a decline in insulation performance.

10A and 10B are diagrams illustrating a state in which a fire-resistant layer is formed around a conductor. FIG. 2 is a diagram showing the state when the glass yarn is unwound from the bobbin. 1 is a schematic cross-sectional view of a fire-resistant cable. FIG. 2 is a perspective view showing a schematic configuration of a fire-resistant layer. FIG. 2 is a perspective view showing the structure of a glass yarn. FIG. 1 is a diagram showing an outline of a fire resistance test (exposure test). FIG. 1 is a diagram showing an outline of a fire resistance test (electrical conduit test).

A fire-resistant cable according to a preferred embodiment of the present invention will be described below, followed by a description of a method for manufacturing the fire-resistant cable.
In this specification, the use of "to" indicating a range of values means that the range includes both the lower limit and the upper limit.

FIG. 3 is a cross-sectional view showing a schematic configuration of the fire-resistant cable 1 of this embodiment.
As shown in Figure 3, the fire-resistant cable 1 of this embodiment has a structure in which multiple (four in the example of Figure 3) fire-resistant insulated cores 40, each having a conductor 10 covered in turn with a fire-resistant layer 20 and an insulating layer 30, are twisted together and the outer periphery of the twisted cores is covered with a sheath 50.

The conductor 10 may be made of any electrically conductive material, such as a wire-shaped member made of copper. Its diameter is selected appropriately depending on the intended use of the fire-resistant cable.

The fire-resistant layer 20 is a layer that covers the outer periphery of the conductor 10 and is a layer that insulates the conductor 10 even in high-temperature environments. As shown in Figure 4, the fire-resistant layer 20 of this embodiment is composed of a mica tape 22 and a glass yarn 24. As shown in Figure 4, in this embodiment, the mica tape 22 is attached longitudinally to the conductor 10, and the glass yarn 24 is wrapped around the mica tape 22. In other words, the glass yarn 24 is loosely wound to provide a pressure winding.

The mica tape 22 that constitutes the fire-resistant layer 20 is a layer that exhibits insulating properties even at high temperatures. Mica is a natural mineral (also known as "mica") that is dark green and has excellent electrical insulating and heat-resistant properties. Although mica itself is a mineral, when processed into tape, it exhibits good flexibility, making it an ideal material for cables. The mica tape 22 may be a glass mica tape in which mica is bonded to glass cloth, or a plastic mica tape in which mica is bonded to a plastic film such as polyethylene.
The mica tape 22 is an example of a fire-resistant tape, and tapes made of other materials may also be used.

On the other hand, the glass yarn 24 that constitutes the fire-resistant layer 20 contains multiple yarns that are twisted together. In this embodiment, the number of yarns in the glass yarn 24 is three, but is not limited to this number. The number is selected appropriately depending on the strength required of the glass yarn 24 and the thickness of each yarn. The twist pitch of the glass yarn 24 is not particularly limited as long as some of the multiple yarns do not slacken or fray during the manufacture of the fire-resistant cable 1 (fire-resistant insulated wire core 40), but is typically between 5 mm and 10 mm. When the twist pitch of the glass yarn 24 is within this range, problems are less likely to occur when the glass yarn 24 is wound around the mica tape 22 using the coarse winding device 100.

Furthermore, it is preferable that the twisting direction of the raw yarns of the glass yarn 24 coincide with the winding direction of the glass yarn 24. In Fig. 4, the winding direction of the glass yarn 24 is indicated by A, and in Fig. 5, an enlarged view of the glass yarn 24, the twisting direction of the raw yarns of the glass yarn 24 is indicated by B. In this embodiment, the winding direction A of the glass yarn 24 and the twisting direction B of the raw yarns of the glass yarn 24 are both right-handed and twisted. When the winding direction A of the glass yarn 24 and the twisting direction B of the raw yarns of the glass yarn 24 are the same, the glass yarn 24 is tightly fastened, making it difficult for foreign matter to be mixed between the conductor 10 and the fire-resistant layer 20. As a result, even if char is generated due to incomplete combustion of organic matter during use of the fire-resistant cable 1, the char is unlikely to be mixed between the conductor 10 and the fire-resistant layer 20, and a decrease in the insulation performance of the fire-resistant cable 1 is suppressed.
The twisting direction B of the raw yarn of the glass yarn 24 may be left-handed, and in that case, the winding direction A of the glass yarn 24 is also preferably left-handed.

The winding pitch of the glass yarn 24 depends on the size of the conductor 10, but is usually preferably 4 mm to 15 mm. When the winding pitch of the glass yarn 24 is within this range, gaps are less likely to form between the mica tape 22 and the conductor 10.

The insulating layer 30 is a layer that covers the above-mentioned fire-resistant layer 20 .
The insulating layer 30 is formed by extruding vinyl chloride resin, polyolefin, etc. Examples of polyolefin include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), very low-density polyethylene (VLDPE), linear low-density polyethylene (LLDPE), polypropylene, polyisobutylene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, ethylene-butene copolymer, etc.
Examples of polyolefins also include copolymers obtained by copolymerizing ethylene with one or more α-olefins, such as propylene, butene, pentene, hexene, and octene, or cyclic olefins using a metallocene catalyst. These may be used alone or in combination.
From the viewpoints of fire resistance and environmental friendliness, the material of the insulating layer 30 preferably contains low-density polyethylene (LDPE), and more preferably is low-density polyethylene (LDPE) alone.

The insulating layer 30 may contain additives such as an antioxidant and an ultraviolet stabilizer as needed, in addition to the insulating resin such as the vinyl chloride resin or polyolefin.
However, if a flame retardant is contained, the electrical properties and water resistance of the insulating layer 30 may be reduced, so it is preferable that the insulating layer 30 does not contain a flame retardant.

Here, in the fire-resistant cable 1, multiple fire-resistant insulated wire cores 40 (four in the example shown in Figure 3) each having the above-mentioned conductor 10, fire-resistant layer 20, and insulator layer 30 are twisted together. The twist pitch of the fire-resistant insulated wire cores 40 is set to a value based on the Electrical Appliance and Material Safety Act. There are no particular restrictions on the twist direction of the fire-resistant insulated wire cores 40, but it is preferable that the twist direction be the same as the winding direction A of the above-mentioned glass yarn 24, as this makes it less likely that gaps will occur between the conductor 10 and the fire-resistant layer 20.

The sheath 50 is a layer that covers the twisted fire-resistant insulated wire cores 40, and is formed by extruding, for example, a vinyl chloride resin, a polyolefin, or a flame-retardant polymer obtained by compounding a flame retardant with one of these resins.
The type of polyolefin is the same as the polyolefin listed above for the insulating layer 30. The polyolefin may be used alone or in combination.
Among the above, vinyl chloride resin, flame-retardant polyethylene, and a composition obtained by blending a flame retardant into a mixed polymer of polyethylene and an ethylene-based copolymer such as ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), or ethylene-methyl acrylate copolymer (EMA) are preferred as materials for the sheath 50 from the viewpoints of flame retardancy, fire resistance, external damage resistance, weather resistance, etc. Furthermore, from the viewpoint of coating (sheath) removability during terminal processing, flame-retardant polyethylene is particularly preferred.

Examples of the flame retardant contained in the sheath 50 include metal oxides such as antimony oxide and molybdenum oxide; metal hydrates such as aluminum hydroxide and magnesium hydroxide; halogen-based flame retardants; and phosphorus-based flame retardants such as red phosphorus.
Among these, from the viewpoint of environmental conservation, non-halogen flame retardants are preferred, and for example, metal hydrates such as aluminum hydroxide and magnesium hydroxide are preferred.

The sheath 50 may further contain a cross-linking agent, a cross-linking aid, an antioxidant, a lubricant, etc., as needed. The sheath 50 may also be cross-linked using an electron beam, organic peroxides, etc.

Next, we will explain the manufacturing method of fire-resistant cable 1.

First, one piece of mica tape 22 is applied vertically onto the conductor 10. Two pieces of mica tape 22 may be applied vertically, in which case the second piece of mica tape 22 is applied vertically so that the overlapping portion of the second piece of mica tape 22 is reversed relative to the overlapping portion of the first piece of mica tape.
Thereafter, the glass yarn 24 is wound around the outer periphery of the mica tape 22 (press-wound with the glass yarn 24) to form the fire-resistant layer 20. In this process, the winding direction A of the glass yarn 24 is set to be clockwise, in accordance with the twisting direction B (right-handed in this embodiment) of the raw yarn of the glass yarn 24.

1 , the mica tape 22 is laid longitudinally, and then the glass yarn 24 is wound around the outer periphery of the mica tape 22 by rotating the coarse winding head 120. At this time, the glass yarn 24 can be wound spirally around the outer periphery of the mica tape 22 by rotating the coarse winding head 120 while moving the conductor 10 around which the mica tape 22 is wound in a predetermined direction at a constant speed.
The rotation speed of the coarse winding head 120 is adjusted appropriately depending on the desired winding pitch of the glass yarn 24 .

Subsequently, an insulating material is extruded to coat the outside of the fire-resistant layer 20, thereby forming the insulator layer 30 (fire-resistant insulated wire core 40). A plurality of the obtained fire-resistant insulated wire cores 40 are twisted together.
In this step, it is preferable to set the twisting direction of the fire-resistant insulated wire cores 40 to match the winding direction A of the glass yarn 24 of the fire-resistant layer 20. In this embodiment, since the winding direction A of the glass yarn 24 is right-handed, the twisting direction of the fire-resistant insulated wire cores 40 is also right-handed.

Then, the stranded assembly of fire-resistant insulated wire cores 40 is sent to an extruder, and sheath material is extruded around its outer circumference to form the sheath 50. By performing these steps, the fire-resistant cable 1 can be manufactured.

In this embodiment, the glass yarn 24 is made of multiple twisted strands of yarn. This means that when the glass yarn 24 is wound around the mica tape 22, some of the strands of the glass yarn 24 are less likely to loosen or fray. Therefore, there is no need to stop the machine or repair cut sections when winding the glass yarn 24. Furthermore, because the above-mentioned problems are less likely to occur when winding the glass yarn 24, the fire-resistant cable 1 can be manufactured efficiently. Furthermore, there is no need to constantly monitor the winding head 120 used to wind the glass yarn 24, and unmanned manufacturing is also possible (see Example 1 below).

In addition, by using glass yarn 24 made of twisted raw yarns, the glass yarn 24 is tightly fastened, making it difficult for foreign matter to get between the conductor 10 and the fire-resistant layer 20. As a result, foreign matter is less likely to get between the conductor 10 and the fire-resistant layer 20 of the fire-resistant cable 1, and the insulation performance of the fire-resistant cable 1 is less likely to deteriorate (see Example 2 below).

[Example 1]
(1) Preparation of Samples (1.1) Comparative Sample A copper conductor having a diameter of about 1.2 mm was prepared.
Meanwhile, a bobbin carrying a glass yarn made by drawing together three strands of yarn was placed in the winding head of the winding device shown in Figure 1. Using the winding device, two sheets of plastic mica tape, each about 0.13 mm thick, were attached vertically to the copper conductor. The glass yarn was then unwound from the bobbin, and while the copper conductor and mica tape were moving in a fixed direction, the winding head was rotated to wind the glass yarn around the mica tape.
The outer diameter after the fire-resistant layer (mica tape and glass yarn) was formed was about 2.3 mm.
The winding direction of the glass yarn was also "right-handed" and the winding pitch was about 4 mm.

Low-density polyethylene (LDPE) was extrusion coated on the outside of the fire-resistant layer to form an insulating layer with an outer diameter of approximately 3.9 mm, thereby obtaining a fire-resistant insulated wire core. Thirty fire-resistant insulated wire cores were then twisted together. The twisting direction of the fire-resistant insulated wire cores was "right twist." Numbers 1 to 30 were printed on the insulating layers to distinguish the 30 fire-resistant insulated wire cores from one another.
Thereafter, the stranded fire-resistant insulated wire core was sent to an extruder, and its outer periphery was extruded and covered with flame-retardant polyethylene (oxygen index (JIS K7201) 27) to form a sheath with an outer diameter of approximately 28 mm.

(1.2) Example Sample A fire-resistant cable was produced in the same manner as the comparative example sample, except that a glass yarn made by twisting three raw yarns was used. The twisting direction of the raw yarns of the glass yarn was "right twist" and the winding direction of the glass yarn was also "right winding."

(2) Evaluation of Samples Each sample was evaluated for workability during fire-resistant cable production, the number of machine stoppages, working speed, working time, and the feasibility of unmanned operation. The evaluation results are shown in Table 1.

(3) Summary As shown in Table 1, in the example samples, by using glass yarns made by twisting raw yarns together, machine stoppages caused by the glass yarns were almost completely suppressed. Furthermore, in the example samples, the average working line speed was improved by about 1.8 times, and the time required to manufacture fire-resistant cables of the same length was reduced by 44%. Furthermore, in the example samples, unmanned operation of the manufacturing equipment was possible.

[Example 2]
(1) Evaluation of Insulation Performance of Samples Each sample according to Example 1 was subjected to a fire resistance test in accordance with Notification No. 10 of the Fire and Disaster Management Agency.
In this test, two types of tests were conducted: an exposure test and a conduit test, as shown in Figures 6 and 7. In the exposure test (Figure 6), a 1.3 m cable was used as the test specimen, and a fire resistance test was conducted while applying a load twice the cable's own weight. In the conduit test (Figure 7), a 1.3 m cable was used as the test specimen, and this was inserted into a 400 mm long metal conduit, and rock wool was filled at both ends of the conduit, and a fire resistance test was conducted.
During the fire resistance test, the dielectric strength and insulation resistance were observed and measured before, during, and after the fire resistance test. The observation and measurement results are shown in Table 2. The dielectric strength was evaluated by applying a constant voltage shown in Table 2 for a certain period of time and determining whether or not dielectric breakdown occurred. The insulation resistance is calculated by multiplying the value read from the measuring device by the number of cores (30 cores).
In addition, after the fire resistance test, a voltage was applied to each sample and the voltage value at which the sample caused dielectric breakdown (breakdown voltage) was measured. The measurement results are shown in Table 2.

(2) Summary As shown in Table 2, in both the exposure test and the conduit test of the fire resistance test, each sample had good dielectric strength and did not experience dielectric breakdown, but the example samples maintained higher insulation resistance and breakdown voltage than the comparative example samples. This is because the infiltration of charcoal between the cable conductor and the fire-resistant layer was prevented, and it was found that using a glass yarn in which multiple original yarns are twisted together, and further, matching the winding direction of the glass yarn with the twisting direction of the original yarns of the glass yarn, are also useful in suppressing a decrease in insulation performance during the fire resistance test.

This invention relates to a method for manufacturing fire-resistant cables, which allows for efficient manufacturing of fire-resistant cables without the need for constant worker supervision. Furthermore, the fire-resistant cables obtained using this manufacturing method have excellent insulation performance.

A: Winding direction B: Twisting direction 1: Fire-resistant cable 10: Conductor 20: Fire-resistant layer 22: Mica tape 24: Glass yarn 30: Insulation layer 40: Fire-resistant insulated wire core 50: Sheath 100: Coarse winding device 110: Jig 120: Coarse winding head

Claims (4)

applying a fire-resistant tape longitudinally onto the conductor;
and winding a glass yarn around the outer periphery of the fire-resistant tape.
A method for producing a fire-resistant cable, characterized in that a glass yarn formed by twisting together a plurality of raw yarns is used as the glass yarn. 2. The method for producing a fire-resistant cable according to claim 1,
A method for manufacturing a fire-resistant cable, characterized in that the winding direction of the glass yarn and the twisting direction of the raw glass yarn are the same. The conductor is covered with a fire-resistant layer and an insulating layer.
The fire-resistant layer is composed of a fire-resistant tape longitudinally attached to the conductor and a glass yarn wound around the outer periphery of the fire-resistant tape,
A fire-resistant cable characterized in that the glass yarn is made of a plurality of twisted raw yarns. The fire-resistant cable of claim 3,
A fire-resistant cable characterized in that the winding direction of the glass yarn and the twisting direction of the raw yarn of the glass yarn are the same.