JP2001268770A - Metal mold for molding internal semiconductive layer of rubber unit for power cable connection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal mold for molding the internal semiconductive layer of a rubber unit for power cable connection, in which the layer is capable of preventing dielectric breakdown in actual use at end portions subjected to severe field conditions. SOLUTION: The metal mold 21 is for molding the internal semiconductive layer of the rubber unit for power cable connection, comprising the internal semiconductive layer, an insulating layer formed on the periphery thereof, and an external semiconductive layer formed on the periphery thereof. The metal mold comprises a core 26 having circular cross sections for forming the center of the internal semiconductive layer, two-split dies 22 and 23 which form an air gap coaxial with the core bar 26 around the core 26 and the middle portion of the internal semiconductive layer, and slide cores 24 and 25 which are attached to both ends of the two-split dies 22 and 23, form an air gap identical in diameter to the coaxial air gap, an air gap narrowed in arc shape and connecting to the air gap, and the end portions of the internal semiconductive layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a mold for forming a semiconductive layer inside a rubber unit for connecting a power cable used in a connection portion of a rubber / plastic insulated power cable (hereinafter referred to as a power cable).

[0002]

2. Description of the Related Art In recent years, in order to simplify and shorten the connection work of power cables and to improve workability, the connection sections of the power cables are made of rubber at the outer periphery of the conductor connection section and the end of the cable insulator. The unit is configured to cover as a reinforcing insulating member. As shown in FIG. 2, the rubber unit 1
The insulating layer 2 has a one-piece cylindrical shape in which an inner semiconductive layer 3 mainly composed of a silicone rubber material and an outer semiconductive layer 4 are integrally formed. And this rubber unit 1
The inner diameter of the portion that comes into contact with the cable insulator is formed smaller than the outer diameter of the cable insulator, and when it is attached to the cable insulator, its surface contracts at the interface with the cable insulator due to its own contraction force. Apply pressure. Therefore, good electrical insulation characteristics can be obtained between the rubber unit 1 and the cable insulator.

The inner semiconductive layer 3 of the rubber unit 1 is composed of a body 3b having a uniform outer diameter and having a through hole in the center in the axial direction, and an end 3a having a thickness R. The internal semiconductive layer 3 was molded by injecting rubber into the molding die 11 by transfer or injection using a molding die 11 as shown in FIG. 3A, for example. The molding die 11 is divided into two dies 12, 1
3 and attached to both ends of the split molds 12 and 13,
It is composed of spinnerets 14 and 15 having a through hole at the center and a core 16 having a circular cross section. Split mold 12,
13 shapes the outer shape of the body 3b of the inner semiconductive layer 3.
The top dies 14 and 15 are connected to the end portions 3a of the inner semiconductive
Is molded. Further, the core 16 forms the hollow portion 3c of the inner semiconductive layer 3.

At the time of forming the inner semiconductive layer 3, FIG.
As shown in FIG. 7, after the measured rubber material is put into the pot portion 18, the molding die 11 is set in a press, and the pressing metal 19 is pressed by the pressure of the press, so that the rubber material is split into two dies 12, 13. Injection holes 12a, 1
Molding is performed by injecting into the molding die 11 from 3a and heating at a predetermined temperature and time. In addition,
Excess rubber material is split molds 12 and 13 and top mold 1
It flows out from the ring-shaped joints 4 and 15 (shown in FIG. 3A). As described above, since the mold for forming the inner semiconductive layer 3 has a split mold structure, a protrusion is formed at the joint of the mold over the entire length of the completed molded body. Therefore, the protruding portion is removed by polishing to form the internal semiconductive layer 3.

[0005]

However, if protrusions remain on the polished surface, the protrusions may be used as starting points when the molded body is actually used as an internal semiconductive layer, and dielectric breakdown may occur. is there. In particular, if the protrusions are present near the ends of the molded body (where the electric field is concentrated as the internal semiconductive layer and the electric field conditions are severe), the height of the protrusions may be several if the operating voltage is high. Even about 10 microns may cause dielectric breakdown. In the conventional molding die 11, FIG.
As shown in (a) and (b), the joint 17 between the split mold 12 or 13 and the top mold 14 or 15
However, since the end 3a of the inner semiconductive layer 3 where the electric field condition is severe is located at the rounded portion at the tip, the end 3a causes a dielectric breakdown even if the polishing is sufficiently performed. .

[0006] In view of the above problems, an object of the present invention is to provide a molding die capable of preventing dielectric breakdown at an end of an internal semiconductive layer.

[0007]

According to the present invention, there is provided an inner semiconductive layer of a power cable connecting rubber unit comprising an inner semiconductive layer, an insulating layer provided on the outer periphery thereof, and an outer semiconductive layer provided on the outer periphery thereof. A core having a circular cross section for forming the center of the inner semiconductive layer, and a coaxial space formed with the core on the outer periphery of the core to form a body of the inner semiconductive layer. A halved mold and attached to both ends of the halved mold to form a gap having the same diameter as the coaxial gap and a gap narrowed in an arc shape continuous with the gap, and an end of the internal semiconductive layer. And a top mold.

[0008] As described above, according to the present invention, the top die attached to both ends of the split die has a coaxial space formed by the split die and a gap having the same diameter as the coaxial gap and an arc shape continuous with the gap. In order to form a narrowed gap, the joint between the top mold and the split mold is located on the outer peripheral surface of the body of the molded body. As described above, in the inner semiconductive layer formed by the forming die of the present invention, the projections formed by the joints of the split mold and the top die are not formed on the end face where the electric field condition is severe, but the body portion where the electric field condition is relatively loose On the outer peripheral surface of the inner semiconductive layer, it is possible to prevent dielectric breakdown from occurring at the end of the internal semiconductive layer during actual use.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional explanatory view in a longitudinal direction of a mold for forming an internal semiconductive layer of a rubber unit for connecting a power cable according to the present invention. As shown in FIG. 1, a molding die 21 of the present embodiment includes
23, and a top mold 2 attached to both ends of the split molds 22 and 23 and having through holes 24b and 25b at the center.
4 and 25 and a metal core 26 having a circular cross section. The split molds 22 and 23 form the outer shape of the body 3b of the inner semiconductive layer 3 shown in FIG. In addition, top die 2
4 and 25 form the end 3 a of the internal semiconductive layer 3. Further, the core metal 26 is formed with through holes 24b, 2
5b, and the hollow portion 3c of the inner semiconductive layer 3 is formed.

The present embodiment is different from the conventional example in that the top dies 24, 25 have circular openings 24a, 25a having the same inner diameter as the inner diameter D of the split dies 22, 23. It is. Then, the top molds 24 and 25
Forms a gap having the same diameter as the coaxial gap formed by the split molds 22 and 23 and the cored bar 26, and a gap narrowed in an arc shape continuous with the gap.

Therefore, in the molding die 21, the ring-shaped joint 27 between the split dies 22, 23 and the top dies 24, 25 is separated from the end of the gap by the depth H of the opening 24a. are doing.

Therefore, in the inner semiconductive layer formed by the molding die 21, the projections formed by the joints 27 are formed on the outer peripheral surface of the body away from the end, so that the dielectric breakdown occurs at the end where the electric field condition is severe. Can be prevented.

In the present embodiment, the openings 24a, 2a
By changing the depth H of 5a, the protrusion by the joint 27 can be separated from the end of the inner semiconductive layer by a desired distance. Further, the shapes of the openings 24a and 25a are not limited to the above embodiment.

As an example, an internal semiconductive layer was formed using the mold shown in FIG. 1 and a rubber unit shown in FIG. 2 was manufactured and subjected to a dielectric breakdown test.
The breakdown voltage has increased.

[0015]

As described above, according to the present invention, no projection due to the joint of the molding die is formed on the end surface of the internal semiconductive layer, and therefore, the actual condition is not obtained at the end of the internal semiconductive layer where the electric field condition is severe. There is an excellent effect that dielectric breakdown can be prevented from occurring during use.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional explanatory view of one embodiment of a mold for forming an internal semiconductive layer of a rubber unit for connecting a power cable according to the present invention.

FIG. 2 is a cross-sectional view of a power cable connecting rubber unit.

FIGS. 3A and 3B are a schematic cross-sectional view in a longitudinal direction and a schematic cross-sectional view in a direction orthogonal to the longitudinal direction of a mold for forming an internal semiconductive layer of a conventional rubber unit for power cable connection. is there.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rubber unit 2 Insulating layer 3 Inner semiconductive layer 3a End 3b Trunk part 3c Hollow part 4 Outer semiconductive layer 21 Mold 22 and 23 Split mold 24, 25 Top mold 24a, 25a Opening 24b, 25b Penetration Hole 26 Metal core 27 Seam

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B29L 31:36 B29L 31:36

Claims (1)

[Claims] 1. A mold for molding an internal semiconductive layer of a power cable connecting rubber unit comprising an internal semiconductive layer, an insulating layer provided on an outer periphery thereof, and an external semiconductive layer provided on the outer periphery thereof. A metal core having a circular cross section for forming the center of the internal semiconductive layer, a split mold for forming a coaxial space with the metal core on the outer periphery of the core, and forming a body of the internal semiconductive layer; Attached to both ends of the mold, forming a gap of the same diameter as the coaxial gap and a gap squeezed into an arc continuous with the gap, and forming the end of the internal semiconductive layer from a top mold. A mold for forming an internal semiconductive layer of a rubber unit for connecting a power cable.