JP3311430B2 - Electric cable manufacturing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for manufacturing an electric cable formed by extruding and coating a cross-linkable resin such as cross-linked polyethylene on the outer periphery of a conductor.

[0002]

2. Description of the Related Art A conventional electric cable manufacturing apparatus of this type includes:
As shown in FIG. 2, a conductor 2 is passed through a first nipple 1, and a semiconductive resin 5 is passed from a first resin passage 4 between the first nipple 1 and a second nipple 3 outside the first nipple 1. Is extruded from a second resin passage 7 between the second nipple 3 and a first die 6 outside the second nipple 3, and is extruded and coated with a crosslinkable resin 8 such as polyethylene containing a crosslinking agent. The semiconductive resin 12 was extruded and coated from the third resin passage 10 between the second die 6 and the second die 9 outside the die 6 to manufacture an electric cable. 6A is a die land portion of the first die 6. The manufactured electric cable is fed into a bridge tube 11 connected to the second die 9, and is heated and bridged. In this case, the semiconductive resin 5 extruded from the first resin passage 4 can be either crosslinkable or non-crosslinkable because migration of the crosslinking agent from the crosslinkable resin 8 can be expected.

However, in such a conventional electric cable manufacturing apparatus, when the cross-linkable resin 8 passes through the second resin passage 7, the seizure of the cross-linkable resin 8 near the tip of the second nipple 3 occurs. As a result, there is a problem that the semiconductive resin 12 grows and protrudes toward the semiconductive resin 5, and the semiconductive resin 5 is damaged. If the semiconductive resin 5 is scratched, the electrical characteristics of the electrical cable may be significantly reduced, leading to dielectric breakdown.

In order to solve such a problem, the present applicant has proposed a power cable manufacturing apparatus as shown in FIG. 3 (Japanese Patent Application No. 62-52172). In this electric cable manufacturing apparatus, a die land 6
A is formed by gradually reducing the inner diameter so that the inlet Di becomes smaller than the inner diameter Do of the outlet.

[0005] As a result of examining the seizure situation, the decomposition rate of the cross-linking agent contained in the cross-linkable resin 8 was about 16%.
From the above, it was found that the crosslinkable resin 8 seized near the tip of the nipple 3, and based on this fact, the structure described above was used as a structure for controlling the decomposition rate of the crosslinker so as not to be 16% or more. It is.

That is, in the invention of Japanese Patent Application No. 62-52172, the cross-linkability of the die land 6A passing through the second resin passage 7 by making the inner diameter Di of the inlet smaller than the inner diameter Do of the outlet is changed. The flow rate of the resin 8 is increased, the shearing stress of the crosslinkable resin 8 on the outer wall surface of the second nipple 3 is increased, and the crosslinkable resin 8 flowing on the outer wall surface of the second nipple 3 is increased.
Of the cross-linkable resin 8 is shortened so that the cross-linking agent does not decompose at a rate of 16% or more, thereby preventing the cross-linkable resin 8 from sticking to the nipple 3.

However, in the electric cable manufacturing apparatus shown in FIG. 3, the shear stress of the resin on the wall surface of the die land portion 6A is reduced, and the resin is baked on the wall surface of the die land portion 6A with a thickness of about several hundred microns. Sometimes. In particular, when the coating thickness of the crosslinkable resin 8 is large, the tendency is strong. When the resin is baked, the surface of the crosslinkable resin 8 is disturbed and the smoothness is lost. When the surface of the cross-linkable resin 8 in which the turbulence has occurred is coated with the semi-conductive resin 12, irregularities occur at the interface between the semi-conductive resin 12 and the cross-linkable resin 8, and a phenomenon that the electrical characteristics are deteriorated. appear. In particular, experiments have shown that when the entrance is smaller than the exit of the die land 6A, the shear stress on the wall surface of the die land 6A is smaller than the theoretical value.

In order to prevent the crosslinkable resin from burning on the wall surface of the die land, the applicant further proposed a power cable manufacturing apparatus as shown in FIG.
No. 3-22408). In this electric cable manufacturing apparatus, as shown in the figure, an outlet 10A of a resin passage 10 for extruding a semiconductive resin 12 into an inlet of a die land 6A of a die 6.
Is opened.

[0009]

In this case, since the semiconductive resin 12 has a slower cross-linking reaction rate than the cross-linkable resin 8, it is possible to prevent the semiconductive resin 12 from burning on the wall surface of the die land portion 6A. . However, in the structure shown in FIG. 4, since the diameter of the portion where the outlet 10A of the resin passage 10 for extruding the semiconductive resin 12 is open gradually increases toward the die land portion 6A, Resin 12
The pressure at the tip of the resin passage 10 that extrudes the resin tends to fluctuate slightly, and this causes a phenomenon that the coating thickness of the semiconductive resin 12 fluctuates.

As means for preventing the thickness variation, an entrance portion of the tapered portion 6B of the die 6 or the tapered portion 6B is formed.
It is also conceivable to open an outlet of the resin passage 10 for extruding the semiconductive resin 12 on the further front side of B, and to inject the semiconductive resin 12 into the second resin passage 7 from there. In this case, two kinds of resins having different flow characteristics such as viscosity such as a semiconductive resin 12 and a crosslinkable resin 8 are extruded and injected into a place where the diameter is gradually reduced. The possibility that the conductive resin 12 buckled was high.

[0011]

SUMMARY OF THE INVENTION The present invention eliminates pressure fluctuation at the tip of a resin passage for extruding a semiconductive resin, and
An object of the present invention is to provide an electric cable manufacturing apparatus which eliminates fluctuations in the coating thickness of a semiconductive resin, further prevents buckling of the semiconductive resin, and enables stable extrusion coating of the semiconductive resin. A die is provided on the outer periphery of the nipple through which a resin passage is provided, and a die land portion of the die is formed by gradually decreasing the inner diameter so that the inner diameter of the inlet is smaller than the inner diameter of the outlet, and the die land is formed from the resin passage. In an electric cable manufacturing apparatus for manufacturing an electric cable by extruding and coating a cross-linkable resin on the outer periphery of the conductor, an outlet of a resin passage for extruding a semiconductive resin is opened in the middle of a tapered portion of the die. It is a feature.

[0012]

Since the exit of the resin passage for extruding the semiconductive resin is opened in the middle of the tapered portion of the die, the semiconductive resin at the time when the semiconductive resin is extruded into the second resin passage is injected. There is no very large difference between the coating thickness of the conductive resin and the coating thickness at the time of reaching the entrance portion of the die land portion, and the possibility of buckling of the resin is eliminated. Further, the injected semi-conductive resin flows through the tapered portion of the die, the diameter of which gradually decreases, so that the pressure only gradually increases,
Unlike the case shown in FIG. 4, the pressure does not decrease. Therefore, even if a slight pressure fluctuation occurs, the flow of the resin is not largely affected, and the coating thickness of the semiconductive resin does not change.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIG. Parts corresponding to those in FIG. 4 described above are denoted by the same reference numerals. In the electric cable manufacturing apparatus according to the present embodiment, the outlet 10 of the third resin passage 10 for extruding the semiconductive resin 12 in the middle of the tapered portion 6B of the die 6
A is provided.

In this case, since the crosslinkable resin 8 does not flow on the wall surface of the die land portion 6A as described above, the crosslinkable resin 8 does not seize on the wall surface of the die land portion 6A. In this case, the semiconductive resin 12 always flows on the wall surface of the die land portion 6A, but the semiconductive resin 12 does not seize on the wall surface of the die land portion 6A because the crosslinking reaction speed is lower than that of the crosslinkable resin.

Further, an outlet 10A of a resin passage 10 for extruding a semiconductive resin 12 in the middle of the tapered portion 6B of the die 6.
Are opened, the semiconductive resin 12 at the time when the semiconductive resin 12 is extruded and injected into the second resin passage 7 is
And the coating thickness at the time of reaching the entrance of the die land portion 6A does not have a very large difference, and the possibility of buckling of the resin is eliminated. Further, the injected semiconductive resin 12
Tapered portion 6B of die 6 whose diameter gradually decreases
, The pressure only increases gradually and does not decrease. Therefore, even if a slight pressure fluctuation occurs, the flow of the resin is not largely affected, and the coating thickness of the semiconductive resin 12 does not fluctuate.

In the vicinity of the die land 6A, a plurality of hollow annular grooves 14 through which the heat medium 13 can flow are provided, and the temperature of the wall surface of the die land 6A is always maintained at a constant temperature. For this reason, the temperature of the resin 12 flowing on the wall surface is always maintained.

EXPERIMENTAL EXAMPLE 1 An inner diameter of the first nipple 1 was 56 mm, an inner diameter of the second nipple 3 was 58 mm, an inner diameter Di of the first die 6 was 95 mm, and an inner diameter Do of the first die 6 was 120 mm. 500 using
When an electric cable having a kV of 2000 SQ was manufactured and the interface between the semiconductive resin 5 and the crosslinkable resin 8 of the electric cable was examined, no damage was found on the semiconductive resin 5 at all. When the interface between the crosslinkable resin 8 and the semiconductive resin 12 was examined, no irregularities were found. At this time, the decomposition rate of the crosslinking agent near the tip of the second nipple 3 is 1
1.6%. The manufacturing conditions at this time were as follows. Production linear speed: 0.55 m / min. Extrusion time: 82 hours. Crosslinkable resin 8: 0.1 to 0.5 part of antioxidant in low density polyethylene, and 1.5 to 3 parts of dicumyl peroxide as a crosslinking agent. A mixture of 0 parts Resin temperature of the crosslinkable resin 8: 138 ° C. Semiconductive resin 12: Ethylene ethyl acrylate (EEA), ethylene vinyl acetate copolymer (EV
A), polyethylene alone or a copolymer thereof mixed with carbon or the like, and the crosslinking agent is 0.1 to 1.0.
Mix about parts. The crosslinking agent used is not dicumyl peroxide but a crosslinking agent having a low crosslinking reaction rate such as Parkadox 14 or Kayabutyl-C (both are trade names of Kayaku Nuuri).

[0018]

As described above, in the electric cable manufacturing apparatus according to the present invention, the outlet of the resin passage for extruding the semiconductive resin is opened in the middle of the tapered portion of the die.
There is no significant difference between the coating thickness of the semiconductive resin when the semiconductive resin is extruded and injected into the second resin passage and the coating thickness when the semiconductive resin reaches the entrance of the die land portion. The risk of buckling of the resin is eliminated. Further, the injected semiconductive resin flows through the tapered portion of the die whose diameter gradually decreases, so that the pressure only increases gradually, and the pressure does not decrease. Therefore, even if a slight pressure fluctuation occurs, the flow of the resin does not have a significant effect, and the coating thickness of the semiconductive resin does not fluctuate. This makes it possible to manufacture an electric cable having excellent electric performance.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a main part of an embodiment of an electric cable manufacturing apparatus according to the present invention.

FIG. 2 is a longitudinal sectional view of a conventional electric cable manufacturing device.

FIG. 3 is a longitudinal sectional view of another conventional electric cable manufacturing apparatus.

FIG. 4 is a longitudinal sectional view of still another conventional electric cable manufacturing apparatus.

[Explanation of symbols]

 1, 3 nipple 2 conductor 4, 7 resin passage 5 semiconductive resin 6 die 6A die land 6B taper 8 crosslinkable resin 10 resin passage 10A outlet 12 semiconductive resin

Claims (1)

(57) [Claims] 1. A die is provided on the outer periphery of a nipple through which a conductor passes through a resin passage, and a die land portion of the die is formed by gradually decreasing the inner diameter so that the inner diameter of the inlet is smaller than the inner diameter of the outlet. In an electric cable manufacturing apparatus for manufacturing an electric cable by extruding and coating a crosslinkable resin on the outer periphery of the conductor from the resin passage, an outlet of the resin passage for extruding a semiconductive resin in the middle of the tapered portion of the die is provided. An electric cable manufacturing apparatus characterized by being open.