JPH031467A - Forming method for extrusion mold connecting part of crosslinked polyolefin insulated cable - Google Patents

Abstract

PURPOSE:To raise the dielectric breakdown voltage by forming an insulation reinforcing member in the form of a spindle consisting of polyolefin by means of extrusion process, and machining the taper surface of this insulation reinforcing member so that the outside semiconductive layer of a cable is exposed to the foremost part. CONSTITUTION:An insulating member 11 at the end of a CV cable 10 and an outer semiconductive layer 12 are stripped steppedly, and a conductor connecting sleeve 14 is put in pressure contact on the exposed conductor 13 so as to form a conductor connecting part. Then a die 15 having a cavity in the form of a spindle is fitted in such a way as striding over the layer 12, and the die 15 is filled with polyethylene compound by means of extrusion. Then the die 15 is heated, and the compound 16 is bridged perfectly. After removing the die, the periphery of the obtained insulation reinforcing member 17 in the form of a spindle is machined so that its cylindrical drum part is cut in uniform depth while the tapered surfaces on both sides are cut deeper toward the ends. In particular, the two ends of tapered surface of the reinforcing member 17 are cut off entirely so as to expose the layer 12 perfectly to the foremost part. This prevents generation of recess in the insulating member 11.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention provides an insulator with high breakdown voltage and good insulation performance.
The present invention relates to a method of forming extrusion mold connections for crosslinked polyolefin insulated cables.

(Prior Art) Conventionally, a molding method called the extrusion mold joint method (EMJ method) has been used as one of the methods for forming the connecting part insulator of cross-linked polyolefin insulated cables such as CV cables (cross-linked polyethylene insulated cables). is being carried out.

This method is usually performed in the following steps.

That is, as shown in FIG. 2(A), first, the ends of a crosslinked polyolefin insulated cable such as a pair of Cv cables 1 are stripped in stages, and the exposed conductors 2 are connected via a conductor connection sleeve 3 or the like. A mold 5 is fitted onto the conductor connection portion of this cable, spanning over the insulator 4 of the Cv cable 1 on both sides. Next, into the cavity of this mold 5, a polyethylene composition 6 which is configured to be crosslinkable by blending a crosslinking peroxide, for example, is extruded and filled, and then heated to crosslink the polyethylene composition 6, as shown in FIG. As shown in B), a method is adopted in which the entire outer circumferential surface of the extruded spindle-shaped insulating reinforcement body 7 is cut to a certain depth to make it smooth.

In addition, in the same figure, the broken line shows the shape of the insulation reinforcement body 7 before cutting, and the solid line shows the shape of the insulation reinforcement body 7 after cutting.

(Problem to be Solved by the Invention) However, in such a method, when stripping the outer semiconducting layer 8 of the cable in the step stripping process of the end of the CV cable 1, the outer semiconducting layer 8 is attached to the cable conductor 2. Since the cutting blade is moved in this direction, the surface of the cable insulator 4 that is connected to the tip of the outer semiconducting layer 8 may be scraped off.

A polyethylene composition 6 is then extruded onto the cable insulator 4 whose surface has been partially shaved off.
Next, the outer circumferential surface of the molded insulation reinforcement 7 is cut, but since the insulation reinforcement 7 covers only the front end of the cable external semiconductive layer 8, the insulation reinforcement 7 is cut during the cutting process. The cable insulator 4 located below the edge of the tapered surface 7 is scraped, and the part that was scraped in the previous stage stripping process is scraped even more deeply.

Therefore, the cable insulator 4 often breaks from the cutting recess 9.

The present invention has been made to solve these problems, and is a cross-linking method that prevents the surface of the cable insulator from being scraped off during cutting of the insulation reinforcing body and prevents dielectric breakdown from occurring in the cable insulator. It is an object of the present invention to provide a method of forming extrusion mold connections for polyolefin insulated cables.

[Structure of the Invention] (Means for Solving the Problems) The method for forming an extrusion mold connection part of a crosslinked polyolefin insulated cable of the present invention includes:
After extruding a spindle-shaped insulating reinforcement made of polyolefin so as to span over the outer semiconductive layer of the cable on both sides, the insulating reinforcement is extruded so that the outer semiconductive layer of the cable is exposed up to the tip. It is characterized by cutting a tapered surface.

In the present invention, polyolefins include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), and ethylene-vinyl acetate copolymer (EVA).
Ethyl acrylate copolymer (EEA) or the like can be used.

In the present invention, extrusion molding of the spindle-shaped insulation reinforcement made of such polyolefin is usually carried out by the following method.

That is, after fitting a mold having a spindle-shaped cavity onto the conductor connection portion of the cable so that both ends reach above the outer semiconducting layer of the cable on both sides, di-α-cumyl peroxide is applied to the polyolefin. Oxide (DCP)
A polyolefin composition containing a crosslinking peroxide such as t-butyl oxide is extruded and filled into this mold, and then heated to a temperature higher than the decomposition temperature of the peroxide to form a polyolefin. crosslink.

In addition, the cutting of the insulating reinforcement body extruded in this way is
This is done by cutting the surface of the cylindrical body to approximately the same depth, and cutting the tapered surfaces on both sides deeper toward the end.

Through this cutting process, the surface of the insulation reinforcement is smoothed, and the edge of the tapered surface of the insulation reinforcement placed on the outer semiconducting layer is cut away, exposing the tip of the outer semiconducting layer. be done.

(Function) In the method for forming an extrusion mold connection part of a crosslinked polyolefin insulated cable of the present invention, an insulation reinforcing body made of polyolefin is formed on the cable conductor connection part so that both ends thereof straddle the cable external semiconductive layer. is extruded, so even if the cutting blade scrapes off the lower side of the tapered end of the insulation reinforcement during subsequent cutting, it only scrapes the cable's outer semiconductive layer, and the cable insulation The body will not be scraped off.

Also, when stripping off the external semiconducting layer for cable terminal processing,
Even if the insulator is scraped off, that part is filled with extruded polyolefin in a subsequent process, so no cut recesses will ultimately be formed on the surface of the cable insulator.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In the embodiment, as shown in FIG. 1(A), first, the insulator 11 and external semiconducting layer 12, etc. at the ends of a pair of Cv cables 10 arranged oppositely are stripped off, and then the exposed conductor 13 is The conductor connection sleeve 14 is crimped to form a conductor connection portion.

Then, on the conductor connections thus formed, Cv
After a mold 15 having a spindle-shaped cavity is fitted over the outer semiconductive layer 12 of the cable 10, a polyethylene composition 16 containing a crosslinking peroxide is placed in the mold 15. Extrusion filling using an extruder.

Next, the entire mold 15 is heated to a temperature higher than the decomposition temperature of the crosslinking peroxide for a suitable period of time, so that the polyethylene composition 16 within the mold 15 is completely crosslinked.

Next, after removing the mold 15, as shown in FIG. Scrape the surface deeper toward the edges.

During this cutting, both edges of the tapered surface of the insulating reinforcing body 17 are particularly scraped off without leaving any residue, so that the cable outer semiconductive layer 12 is completely exposed up to the tip.

In FIG. 1(B), the shape of the insulation reinforcement 17 before cutting is shown by a broken line, and the shape of the insulation reinforcement 17 after cutting is shown by a solid line.

In the method for forming the molded connection portion of the embodiment configured as described above, the insulation reinforcing body 17 is extruded so that both ends cover the ends of the cable external semiconductive layer 12, so cutting work is not required. Even if the lower side of the tapered end of the insulation reinforcing body 17 is scraped off during this process, only the surface of the cable outer semiconductive layer 12 is scraped off, and the cable insulator 11 is not scraped off.

Also, when stripping off the outer semiconductive layer 12 at the end of the cable,
Even if a part of the surface of the cable insulator 11 is scraped off, that part is completely buried by the polyethylene resin constituting the insulation reinforcing body 17, so that the cable insulator 11 does not have four parts in the end.

Therefore, no electrical weakness occurs in the cable insulator 11, and a high dielectric breakdown voltage is exhibited.

[Effects of the Invention] As explained above, according to the forming method of the present invention, there is no possibility that the cable insulator is shaved off and a recessed portion is formed during the cutting process of the extruded insulation reinforcing body. Therefore, an extrusion molded connection part with a high dielectric breakdown voltage of the cable insulator and excellent insulation performance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining a method of forming an extrusion mold connection part of a CV cable according to an embodiment of the present invention, and FIG.
The figure is a sectional view for explaining a conventional method of forming an extrusion mold connection part of a Cv cable. DESCRIPTION OF SYMBOLS 10... Cv cable 11... Cable insulator 12... Cable external semiconducting layer 13... Cable conductor 15... Mold 16... Polyethylene composition 17... Insulating reinforcement body. (A) Figure 1 (A) Figure 2

Claims (1)

[Claims] (1) After extruding and molding a spindle-shaped insulation reinforcement made of polyolefin on the conductor connection portion of the cross-linked polyolefin insulated cable, spanning over the outer semiconducting layers of the cable on both sides, the cable outer semiconducting layer is A method for forming an extrusion mold connection part of a crosslinked polyolefin insulated cable, characterized in that the tapered surface of the insulating reinforcing body is cut so that the tip part thereof is exposed.