JPH03194802A - Manufacture of bridged-polyethylene cable - Google Patents

Abstract

PURPOSE:To reduce moisture in an outer semiconductive layer and an insulating material layer by using the pressurized inert gas at high temperature as the heat-bridging medium, and using the pressurized silicone oil as the cooling medium. CONSTITUTION:A conductor is coated with polyethylene in which organic peroxide is compounded, and it is heated to chemical-bridge the polyethylene. Next, in manufacture of bridged polyethylene cable for cooling, the pressurized inert gas at high temperature is used as the heat-bridging medium, and the pressurized silicone oil is used as the cooling medium. Since the inert gas is used for heating to bridge and the silicone oil as the insoluble liquid against polyethylene is used for cooling, an intrusion of water or the like into an outside semiconductive layer and an insulating material layer is eliminated, and the cooling efficiency is not lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for manufacturing a crosslinked polyethylene cable with good manufacturing efficiency and with a small amount of water a in the coated insulator.

[Prior Art] Cross-linked polyethylene, which is made by cross-linking the molecules of linear polyethylene to form a network macromolecule, has greatly increased heat resistance and mechanical strength, and together with its excellent electrical insulation, Widely used as an insulator for power cables.

Crosslinking methods for this polyethylene include a method in which the molded product is irradiated with high-energy radiation such as an electron beam, and a chemical crosslinking method in which polyethylene is blended with an organic peroxide, coated on a conductor, and then heat treated. Chemical crosslinking is usually used to form thick cable insulation.

To make a crosslinked polyethylene cable by this chemical crosslinking method, a known catenary type continuous crosslinking device (hereinafter referred to as catenary type) or a vertical type continuous crosslinking device (hereinafter referred to as vertical type) is used, and the conductor is After forming the internal semiconductive layer, insulator, and external semiconductive layer simultaneously by extrusion molding, the material was introduced into the crosslinking cylinder of the continuous crosslinking device and crosslinked under a pressure of 5 to 1 kg/cta to prevent foaming. A wet crosslinking method is used in which coating is performed by heating using water vapor as a medium and then cooling using water as a cooling medium.

However, since this wet crosslinking method uses water, there is a problem in that water gets mixed into the external semiconductor layer and the insulator, and this water causes microvoids and water tree deterioration.

. For this reason, at present, a dry crosslinking method that does not use water vapor but uses an inert gas such as nitrogen gas as a heating medium is currently used.

[Problems to be Solved by the Invention] However, even in the dry crosslinking method described above, water is often used as a cooling medium, and since the crosslinked cable comes into contact with water, An increase in water content was inevitable.

In addition, to avoid the increase in water content, as a cooling medium,
Forced circulation of cooled inert gas, which is the same as the heating medium, is also used, but the heat transfer efficiency is lower than that of water cooling.
This had the disadvantage of reducing manufacturing efficiency.

The present invention has been made in view of the above circumstances, and provides a method for manufacturing a crosslinked polyethylene cable that prevents moisture increase in the cable coating and does not reduce manufacturing efficiency.
The purpose is to provide.

"Means for Solving the Problems" In order to achieve the above object, the method for manufacturing a cross-linked polyethylene cable according to the present invention is as follows. death,
In a method for manufacturing a crosslinked polyethylene cable, in which the polyethylene is chemically crosslinked by heating and then cooled, pressurized high temperature inert gas is used as the heating crosslinking medium, and pressurized silicone oil is used as the cooling medium.

"Function" Since the present invention has the above-mentioned structure, heating is performed using an inert gas for thermal crosslinking, and silicone oil, which is a liquid insoluble in polyethylene, is used for cooling. There is no impregnation of water or other substances into the semiconducting layer or the insulating layer, and there is no reduction in cooling efficiency.

"Example" The present invention will be explained in detail below.

First, the conductor is introduced into an extruder equipped with a crosshead, and the conductor is coated with an internal semiconductive layer, an insulating layer made of polyethylene and a crosslinking agent, and an external semiconductive layer at the same time, and then this coated conductor is transferred to a continuous catenary type. Continuously introduce it into the crosslinking tube of a crosslinking device or vertical continuous crosslinking device.

The crosslinking cylinder is filled with heating and pressurized inert gas such as nitrogen gas, argon gas, SF, etc. as a heating and pressurizing medium, and the polyethylene that forms the insulator is crosslinked by this heating and pressurizing medium. . At this time, if the resin compositions forming the inner semiconductive layer and the outer semiconductive layer are crosslinkable, crosslinking is performed. The temperature of the heating and pressurizing medium is 200 to 300°C, and the pressure is 5 to 10 kg/ell'.

The coated conductor with the insulator bridged through the bridge tube is led to the cooling tube, where its temperature is lowered slightly by air cooling, and then introduced into a cooling tank filled with a cooling medium.

The cooling tank has a pressure of 5 to 10 kg/cm'' as a cooling medium.
The conductor is filled with methylsilicone-based or phenylsilicone-based silicone oil, and the coated conductor is cooled by coming into contact with this silicone oil. Even when the core surface temperature of the ml conductor introduced into the cooling tank reaches a high temperature of 120 to 150° C., unlike water cooling, there is no water intrusion, so efficient cooling can be achieved. After the temperature of the coated conductor drops to 50°C or less in the cooling tank, the coated conductor is taken out from the cooling tank, the silicone oil adhering to the surface is removed, a shielding layer is applied, and the sheath is made of polyvinyl chloride or the like. Extrusion coating to make an electric cable.

This manufacturing method prevents silicone oil from penetrating into the external semiconducting layer or insulator, and since no water is used, moisture does not enter. Additionally, since it has better thermal conductivity than gas cooling, the cooling rate is faster. In addition, since the boiling point of silicone oil is high, even if a high-temperature coated conductor is introduced into a cooling tank, the cooling medium will not vaporize, and the coated conductor can be immediately introduced from the bridge pipe into the cooling tank. Manufacturing speed can be increased.

Furthermore, since the bridging tube and the cooling tank are maintained under pressure, the formation of bubbles in the conductor coating layer is prevented.

Example I M [: 3.2 g/l 0 min low density polyethylene 1
A conductor of 400+nm' Simultaneously extrude to be located between the inner conductive layer and the outer conductive layer on top, linear speed 1
A coated conductor was made with an inner semiconducting layer of 1.0 mff1 thickness, an insulating layer of 9 mm, and an outer semiconducting layer of 0.51 mm in . This was introduced into the cross-linked tube, and the weight was 10 kg/c.
m' After crosslinking in nitrogen gas at 300°C, when the cable core surface temperature reaches 150°C, l Ok
g/am”/licon oil and cooled.

Comparative Example 1 A crosslinked polyethylene cable was manufactured in the same manner as in Example I, except that the manufacturing line speed was 0.8 tn1 minute, and after crosslinking, the cable core was cooled by passing it in water when the temperature reached 90°C.

The manufacturing linear speed of Example 1 was 15 times the manufacturing linear speed of Comparative Example 1.
The gel fraction of the insulator was 80% or more in both cases.

In addition, the moisture content in the outer semiconducting layer and the outer layer, middle layer, and inner layer of the 9 mm-thick insulating layer of Example 1 and Comparative Example 1 was measured immediately after production. The results are shown in Table 1.

Table 1 "Effects of the Invention" As explained above, the method for manufacturing a crosslinked polyethylene cable of the present invention involves crosslinking in an inert gas and cooling in a liquid silicone oil. There is less moisture in the layer, and the production efficiency does not decrease compared to when water is used as a cooling medium.

Claims (1)

[Claims] A method for manufacturing a crosslinked polyethylene cable in which a conductor is coated with polyethylene blended with an organic peroxide, heated to chemically crosslink the polyethylene, and then cooled. A method for producing a cross-linked polyethylene cable, characterized in that a high-temperature inert gas is used and pressurized silicone oil is used as a cooling medium.