JP2879779B2 - Manufacturing method of stranded conductor for coated electric wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of assembling a plurality of conductor strands into a stranded wire,
The present invention relates to a method for producing a stranded wire conductor for a covered electric wire in which an insulation coating is applied to the stranded wire with polyethylene or the like, and particularly to a method for producing a stranded wire conductor for a covered electric wire which is laid between utility poles.

[Conventional technology] As conductors for overhead distribution lines that are wired between telephone poles and the like,
Conventionally, hard copper wires have been used. The assembled plurality of hard copper wires are twisted, and an insulation coating of polyethylene, polyvinyl chloride, or the like is applied on the twisted wires.

[Problem to be Solved by the Invention] On the surface of each twisted hard copper wire, a twisted wire repulsive force for canceling the twist is inevitably generated. This stranded wire repulsion appears as a tensile residual stress on the surface of each hard copper wire. Further, each hard copper wire may have a residual stress due to a curl generated when the hard copper wire is wound on the drum.

In a conventional coated electric wire, the above-described residual stress may be one factor to cause disconnection. That is, when rainwater enters the covered electric wire, the inside of the covering layer becomes an easily corrosive environment, and an oxide film is formed on the surface of the hard copper wire. When such a corrosive environment and the above-mentioned residual stress interact with each other, stress corrosion cracking occurs in the hard copper wire, and as a result, the wire breaks.

If a soft copper wire is used as the conductor for the covered electric wire, the possibility of occurrence of the stress corrosion cracking phenomenon is reduced because the above-mentioned residual stress is small. However, on the other hand, a decrease in tensile strength is unavoidable, and therefore, in practice, a soft copper wire cannot be used as a stranded conductor for a covered wire.

Therefore, an object of the present invention is to provide a method for producing a stranded conductor for a covered electric wire which maintains tensile strength and does not cause a stress corrosion cracking phenomenon.

[Means for Solving the Problems] The method for producing a stranded conductor for a covered electric wire according to the present invention comprises:
Ag, Sn, Mg, Cr, In, Ni, Al, Fe, Si, Sb, Zr, Te, Se
A conductor in which the concentration of one or more elements selected from the group including is higher in the center than in the outer layer is reduced to 60 to 9
Wire drawing at 9.9%, the concentration of the element in the center and the concentration of the element in the outer layer are distributed with a step, and the ratio of the cross-sectional area of the center to the cross-sectional area is 70% or more. The method is characterized in that after a certain conductor strand is formed, a plurality of the conductor strands are assembled and twisted, and then only the outer layer portion of each conductor strand is recrystallized by heating.

The insulated wire obtained by the above method, a plurality of conductor strands are gathered into a stranded wire, and an insulation coating is applied on the stranded wire, and the conductor strands are Ag, Sn, Mg , Cr,
The concentration of one or more elements selected from the group including In, Ni, Al, Fe, Si, Sb, Zr, Te, and Se is higher in the central part than in the outer layer part, and Only the outer layer has a recrystallized structure.

[Operation and Effect of the Invention] As shown in FIG. 1, the inner crystal structure of the conductor strand obtained by the above method has an outer layer portion 1 having a recrystallized structure and a central portion 2 having a longer length in the longitudinal direction. It has an extended drawing structure. As described above, since only the outer layer portion 1 of each conductor strand constituting the stranded wire is recrystallized, the residual stress generated at the time of wire drawing or stranded wire processing is released, and the possibility of the occurrence of stress corrosion cracking is reduced. Become. On the other hand, since the central portion 2 of each conductor strand has a drawn structure, the tensile strength is relatively large. Therefore, each conductor strand can maintain a tensile strength enough to withstand use as a stranded conductor for a covered electric wire.

Note that the recrystallized structure used in this specification is not limited to the case where the structure of the outer layer part completely shows the recrystallized structure, and also that the dislocation density of the outer layer part is smaller than that of the central part. It must be understood as including.

The conductor is Ag, Sn, Mg, Cr, In, Ni, Al, Fe, Si, Sb,
When one or more elements selected from the group including Zr, Te, and Se are contained, the recrystallization temperature of the conductor increases.
For example, if copper contains 0.1% by weight of Ag, its recrystallization temperature will increase by about 100 ° C. Therefore, if a conductor is used in which the concentration of these elements is higher in the center than in the outer layer,
The recrystallization temperature of the conductor is higher at the center than at the outer layer. That is, if a conductor having such a concentration distribution is used, a conductor strand having a crystal structure as shown in FIG. 1 can be easily obtained by appropriate heating. For example, if the conductor strand is heated to a temperature intermediate between the relatively low recrystallization temperature of the outer layer portion and the relatively high recrystallization temperature of the central portion, only the outer layer portion is recrystallized.

The concentration of the element is preferably 0.03 at the center.
To 0.2% by weight, and 0.01% by weight or less in the outer layer portion. The reason why the concentration at the center is 0.03 to 0.2% by weight is as follows.
If it is less than 0.03% by weight, the degree of increase in the recrystallization temperature is small, so that the difference between the recrystallization temperature in the central part and the recrystallization temperature in the outer layer part does not become so large. on the other hand,
If the concentration exceeds 0.2% by weight, the electrical conductivity will decrease.

The concentration of the element in the center of each conductor strand and the concentration of the element in the outer layer may be distributed with a smooth concentration gradient, or both may be distributed with a step. However, in this case, the ratio of the cross-sectional area of the central portion to the cross-sectional area of the conductor strand is preferably 70% or more from the viewpoint of maintaining the tensile strength.

As a method of changing the concentration of the element in the central portion of the conductor strand and the concentration of the element in the outer layer portion, for example, a method of fitting a material constituting the central portion into a pipe constituting the outer layer portion, hot-dip plating, There are a plating method such as electroplating, and a method of changing the concentration distribution of elements during casting, and any method may be employed.

If the reduction in area of the wire drawing is set to 60 to 99.9%, if it is less than 60%, the tensile strength cannot be maintained as specified. On the other hand, the higher the area reduction rate in wire drawing, the lower the recrystallization temperature. Therefore, in order to keep the recrystallization temperature in the center relatively high, it is desirable to limit the upper limit of the area reduction to 99.9%.

Since each conductor strand is heated after the stranded wire processing, the residual stress generated during the stranded wire processing by this heating can be effectively removed.

As a method for heating the stranded wire, for example, electric heating and the like can be mentioned. If the stranded wire is continuously heated by electric heating or the like while selecting appropriate conditions, only the outer layer portion of each conductor strand constituting the stranded wire can be recrystallized.

Example 1 A copper wire having a diameter of 8 mm and containing 0.05% by weight of Sn, 0.03% by weight of Te and 0.01% by weight of Ag was prepared. After electroplating pure copper with a thickness of 0.2 mm on the surface of the copper wire, wire drawing was performed until the diameter became 2 mmφ. After assembling 19 conductor strands obtained in this way into a stranded wire, this stranded wire was passed through a tunnel furnace, and only the outer layer (about 50 μm thick) of each conductor strand was recrystallized. Was presented. After cold working (area reduction ratio), the ratio of the cross-sectional area of the portion having a high concentration of the contained element, which was not recrystallized, to the entire cross-sectional area was 90%.

A crosslinked polyethylene coating was applied to the stranded wire obtained as described above to obtain a coated electric wire. Ammonia water was injected between the covering layer of the covered electric wire and the stranded conductor to conduct a stress corrosion cracking test. As a result, no stress corrosion cracking occurred even after 3 months.

For comparison, a similar test was performed on a conventional insulated wire using a hard copper wire as a conductor strand, and stress corrosion cracking occurred and broke in about one month.

Example 2 A copper wire having a diameter of 11 mm and containing 0.05% by weight of Ag was prepared. This Ag-containing copper wire was passed through a tank storing pure copper in a molten state, and the copper wire surface was coated with pure copper. The wire thus obtained had a diameter of 12 mmφ, an Ag concentration in the center of 0.08% by weight and an Ag concentration in the outer layer of 0.005% by weight.
% By weight or less. The ratio of the cross-sectional area at the center to the total cross-sectional area was 84%. The diameter of the wire was reduced to 2 mmφ by cold drawing. The degree of cold work (area reduction rate) is 97.2%.

After assembling the above 19 wires and twisting, this twisted wire is
Heated at 0 ° C for 2 hours. Each conductor strand of this stranded wire is
The outer layer had a recrystallized structure, and the center had a drawn structure elongated in the longitudinal direction. The tensile strength of each conductor strand was 45.7 kg / mm ² , and the conductivity was about 98%.

A polyethylene wire was applied to the stranded conductor obtained as described above to obtain a covered electric wire. Then, a stress corrosion cracking test was conducted by injecting aqueous ammonia between the coating layer of the coated electric wire and the stranded conductor, and no disconnection was observed even after 3 months.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing the internal crystal structure of a conductor strand obtained by carrying out the method of the present invention. In the drawing, 1 indicates an outer layer portion, and 2 indicates a center portion.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisashibu Torii 2-4-1, Nishi-Atsujigaoka, Chofu-shi, Tokyo Inside the Tokyo Electric Power Company R & D Laboratory (72) Inventor Yoshihiro Nakai 1-1-1, Shimaya, Konohana-ku, Osaka-shi, Osaka No. 3 Sumitomo Electric Industries, Ltd. Osaka Works (56) References JP-A-62-160611 (JP, A) JP-A-62-160610 (JP, A) JP-B-51-4258 (JP, B2) (58) ) Field surveyed (Int. Cl. ⁶ , DB name) H01B 1/00 H01B 5/08 H01B 13/00

Claims (1)

(57) [Claims] 1. Ag, Sn, Mg, Cr, In, Ni, Al, Fe, Si, S
Conductors with a concentration of one or more elements selected from the group containing b, Zr, Te, and Se in the center portion higher than the outer layer portion are drawn at a surface reduction rate of 60 to 99.9%. A conductor element wire in which the concentration of the element in the central portion and the concentration of the element in the outer layer portion are distributed with a step, and the ratio of the cross-sectional area of the central portion to the cross-sectional area is 70% or more; A method for producing a stranded conductor for a covered electric wire, comprising a step of, after assembling a plurality of conductor strands, performing stranded processing, and then recrystallizing only an outer layer portion of each conductor strand by heating.