JPS6057657B2 - Method of forming insulated cable connections - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming connections in rubber or plastic insulated cables.

Rubber or plastic insulated cables are often used in combination, but deterioration of the electrical properties due to the connection is a serious problem, especially when used for very high voltages.

To solve this problem, the connection is conventionally made by exposing the conductor at the end of the cable, and then applying an internal semiconductor layer and a reinforcing insulating layer over the conductor connection after the conductor has been properly connected. The reinforcing insulating layer is integrated with the insulating layer of the cable by heating it under pressure. This reinforcing insulation layer should be made of a material that is the same as or at least similar to the insulation material of the cable, so as not to impair the electrical properties of the cable and to allow the dimensions of the connection itself to be as small as possible. It is generally formed by using a mold. Molds using such insulating materials generally include an internal semiconductor layer provided on the conductor connection by, for example, winding a semiconductive tape or heat-shrinking a semiconductive heat-shrinkable tube. The insulating material is placed in a mold, the mold is preheated to a predetermined temperature, and then an insulating material heated to an appropriate temperature is injection molded using an extrusion machine, for example. The mold used has a plurality of overflow holes, and the complete filling of the mold space with insulating material to be extruded and injected is detected by the flow of material from the overflow holes.

Therefore, when the mold is removed after molding is completed, a protrusion is generated at a location corresponding to the overflow hole, and a deburring process is essential to remove this protrusion. This step is relatively tedious and represents a significant drawback in connection formation. SUMMARY OF THE INVENTION It is an object of the present invention to provide a new method for forming connections in rubber or plastic insulated cables that does not substantially require a deburring step.

According to the invention, a conductor connection of a rubber or plastic insulated cable is provided as before, and an inner semiconducting layer is provided, and an elastic tube made of an insulating or semiconducting material is thus formed. cover the conductor connections.

In this state, the whole is placed in a mold in the conventional manner, and an insulating material that is the same as or similar to the insulator of the insulated cable is injected into the elastic tube using an extrusion processing machine until the tube contacts the inner wall of the mold. By doing so, a deburring process due to the presence of overflow holes becomes unnecessary. An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a schematic cross-sectional view of an apparatus for carrying out the method of the invention.

In the same figure, an insulated cable 1 to be connected is taken as an example of a cross-linked polyethylene insulated vinyl sheathed cable (hereinafter referred to as a CV cable), and this cable has a conductor 2.
, an inner semiconducting layer 3, an insulating layer 4 surrounding them made of crosslinked polyethylene, and a sheath made of vinyl (not particularly shown). The internal semiconducting layer 3 and the insulating layer 4 of this cable are suitably processed to expose the ends of the conductor 2, and these ends are appropriately connected using a connecting tube 5 or the like. The internal semiconductor layer 6 is provided in a conventional manner by heat shrinking a polyethylene heat shrink tube. According to the invention, the conductor connections prepared in this way are placed in molds 8, 9 after being covered with an elastic tube 7 made of a material such as semiconducting or insulating polyethylene resin.

The upper mold 9 has an appropriate number of gas vent holes 10 and a heating circulation device 12 that heats and supplies gas and liquid such as nitrogen gas, SFO gas, air, or silicone oil.
It has a gas hole 11 connected to. The heating circulation device 12 is
It is used for heating the molds 8, 9 and the elastic tube 7, but in some cases a heating device (not shown) already provided in the mold may be sufficient. Along the outer circumference of the CV cable 1, a plurality of injection nozzles 13 are inserted between the outer circumference of the cable 1 and the elastic tube 7 from one side of the mold. These nozzles are connected through suitable conduits 14 to a suitable extruder 15 of screw or ram type. An overflow nozzle 16 is similarly provided on the other side of the mold.

These nozzles 16 act as overflow holes for the insulating material injected by the extruder. In this state, the molds 8 and 9 and the elastic tube 7 are heated by the mold heating device and/or heated gas from the heating circulation device 12.
Preheat to desired temperature. After the preheating is completed, polyolefin insulating material is injected from the extruder 15 through the injection nozzle 13 between the elastic tube 7 and the conductor connection portion of the CV cable 1. As a result, the elastic tube 7 expands until it comes into contact with the inner wall of the mold as shown by the chain line 18. This abutment can be detected by the flow of insulating material from the overflow nozzle 16. This completes the extrusion injection of the insulating material, after which the connection part is obtained in the mold after cooling in the conventional manner.
The connections obtained in this way are covered with a jacket made of semiconducting or insulating polyolefin and are essentially free of flash on the external surface and therefore do not require a step for its removal. This makes it easier to form the connection.
The elastic tube 7 used as the outer jacket has been described using semiconductive or insulating polyolefin inch tube.
It may be made of a material with good heat resistance, such as an elastic tube such as silicone rubber or a plastic tube such as Teflon.

Furthermore, if an elastic tube made of a semiconductive material is used, it can also be used immediately as the outer semiconductive layer. In addition to the advantages described above, according to the present invention, since the extrusion injection is carried out while expanding the elastic tube, the flow of the insulating material becomes uniform and a uniform insulating layer can be formed, which improves the electrical properties. Excellent connections can be formed. Although the above description has been made using a CV cable as an example, it is clear that the present invention can be used to connect other insulated cables with similar effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an apparatus for carrying out the method of the invention. DESCRIPTION OF SYMBOLS 1... Insulated cable, 2... Conductor, 3... Internal semiconducting layer, 4... Insulating layer, 5... Connecting pipe, 6... Internal semiconducting layer, 7... Elastic tube, 8, 9... Mold, 10... Gas vent hole, 12... Heating circulation device,
13... Injection nozzle, 15... Extruder, 16...
overflow nozzle.

Claims (1)

[Claims] 1 After exposing the ends of a rubber or plastic insulated cable and connecting the conductors at these ends with a connecting tube, an internal semiconducting layer is provided around the outer periphery of this connecting tube, and the connection thus prepared is made of an insulating or The connection part thus prepared is placed in an elastic tube made of a semiconductive material, placed in a mold, and the mold is preheated to a predetermined temperature. A method of forming a connection part of a rubber or plastic insulated cable, which comprises extruding and injecting a similar material into the elastic tube, extruding it into a predetermined shape, and then cooling it.