JPH07105176B2 - Electric wire / cable manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a crosslinked rubber / plastic insulated wire / cable, and particularly to a method for producing a wire / cable in which shrinkage of an insulator is minimized. It is about.

<Prior art> As a method for manufacturing crosslinked rubber / plastic insulated electric wires / cables, first, an insulating material such as rubber / plastic is extruded and coated on a conductor by an extruder, and then the core wire is vertical or horizontal, and further catenary. A general method is to introduce it into a continuous cross-linking device such as a mold, cross-link the insulator with steam, gas, infrared rays, or other heat medium, and then introduce this into a cooling tank to cool it.

As described above, in the currently used manufacturing method, the extruded insulator is generally subjected to the heat treatment in the crosslinking device and the cooling treatment in the cooling tank generally once.

<Problems to be Solved by the Invention> However, in the case of the rubber / plastic insulator of the electric wire / cable obtained by the above-described manufacturing method, the insulator shrinks during use and a void is formed in the connecting portion or the terminal portion. There was inconvenience such as occurrence. This is a so-called shrinkback phenomenon, which may lead to conductor jump-out or, in extreme cases, to dielectric breakdown of the insulator.

Therefore, conventionally, in order to eliminate the contraction of the insulator, a method of heating or heating the connection portion or the terminal portion has been performed, but such heating / heating treatment is performed on site. In this case, there are problems in that there are restrictions on location, the processing itself is troublesome, and extra time is required.

Therefore, it has been desired to provide an electric wire / cable in which the amount of shrinkage of the insulator is small.

Therefore, the present inventor diligently studied the shrinkage phenomenon of this insulator, and reached the following conclusion. In other words, it is considered that the shrinkage of the insulator is due to the residual stress remaining in the insulator, and this residual stress is generated between the heating process in the continuous cross-linking device and the cooling process in the cooling unit during the wire / cable manufacturing. It is thought to be due to the "cooling distortion" that occurs in.

This means that when the cooling is conducted by introducing the cooling from the bridge portion of the continuous crosslinking device to the cooling portion, the insulator is generally gradually cooled from the outer peripheral side. This is because the temperature distribution with the insulator becomes non-uniform.

From this, it is understood that the residual stress can be removed by basically cooling the insulator uniformly.

However, it is almost impossible and extremely difficult to uniformly cool the inside and outside of the insulator on an actual industrial scale.

Therefore, the present inventor considers that the temperature distribution inside and outside the insulator is approximately equalized, and when the insulator that has started cooling is not yet cooled to the inside, the insulator is heated again from the outside. A method has been found in which the temperature distribution inside and outside the insulator is gradually made uniform by repeating reheating and recooling at least once, such as (reheating) and further cooling (recooling).

The present invention has been completed from this point of view.

<Means for Solving Problems and Actions Thereof> The feature of the present invention is that at least a rubber / plastic insulator is extrusion-coated on a conductor, and then the insulator is crosslinked in a crosslinking device. In the method for manufacturing an electric wire / cable that is further introduced into pressurized cooling water at room temperature or lower for cooling treatment, while the insulator is not completely cooled by the cooling treatment, continuously and again at a temperature equal to the crosslinking temperature. It is a method for manufacturing an electric wire / cable that leads to a heating zone, performs at least one reheat treatment, and again leads to pressurized cooling water at room temperature or lower, and performs recooling treatment at least once at room temperature or lower. .

In the present invention, it is preferable that all heating steps and cooling steps in the crosslinking device are performed under pressure. The pressure applied is preferably at least about 3 Kg / cm ² . Further, in these heating and cooling steps, a heating medium such as gas, liquid, water vapor, infrared ray, etc. can be used. However, considering the electrical characteristics of the wire / cable and the pressure treatment, it can be used as a pressure medium. It is preferable to use gas, liquid, or the like.

As described above, according to the present invention, since reheating and recooling are repeated at least once, the temperature distribution of the insulator is approximately uniformized, and the residual stress is satisfactorily removed. As a result, the shrinkage of the insulator can be made extremely small.

Incidentally, in the case of gas crosslinking or heat crosslinking by infrared rays, an annealing zone is often provided between the normal heating step and the cooling step, but in the present invention as well, heating during crosslinking and subsequent reheating are performed. There is no problem in providing this slow cooling zone to each of the above.

<Example> Next, the effect of the method of the present invention was confirmed by the following experiments.

A 250 mm ² , 66 KV cross-linked polyethylene insulated cable was created. At this time, the insulator thickness is 9 mm, and the inner and outer semi-conductive layers are coated on the conductor by the co-extrusion machine, and then the cross-linking temperature is set.
The polyethylene insulator was cross-linked by a N ₂ gas (pressure 9 Kg / cm ² ) filling type cross-linking device at 250 ° C., then introduced into pressurized cooling water at 15 ° C. and heated again at 10 m after starting cooling. After passing through the zone (250 ° C.) for 10 m through this heating zone, it was introduced again into pressurized cooling water to obtain the above polyethylene insulated cable. The production linear velocity was 2 m / min.

When the amount of shrinkage of this cable insulator was examined by a dimensional stability test specified by AEIC, it was about 0.2 mm.

<Comparative Example> For comparison, a polyethylene insulated cable was obtained by the same method as described above, except that the polyethylene insulator was cross-linked by a cross-linking device and then cooled in a normal cooling step.

The amount of contraction of this insulator is 3.2 mm, which is
It turns out that it is about 10 times.

<Effects of the Invention> As described above, according to the present invention, as compared with the conventional method for manufacturing an electric wire / cable, the insulator is continuously reheated at least once before being completely cooled by cooling. Since the cooling process is performed again, the shrinkage amount of the insulator is significantly reduced.

Further, since the transition from the crosslinking / cooling process to the reheating / recooling process is continuously performed, good workability (productivity) can be obtained. Furthermore, the reheating / recooling process at this time is
Since it is performed before the insulator is completely cooled, thermal efficiency is good and good productivity can be obtained as compared with the case where the electric wire / cable once brought to the normal temperature state is heated / cooled again.

Therefore, in the processing work of the connection part and the terminal part of the electric wire / cable obtained in this way, there is no need for locational restrictions and heating / heating treatment as in the conventional case, and no extra labor is required. It is possible to provide an excellent electric wire / cable that can be easily and quickly handled.

Claims (1)

[Claims] 1. A method of manufacturing an electric wire / cable in which at least a rubber / plastic insulator is extrusion-coated on a conductor, then the insulator is subjected to a crosslinking treatment in a crosslinking device, and then the conductor is cooled in pressurized cooling water at room temperature or lower. In the method, while the insulator is not completely cooled by the cooling treatment, continuously, again led to a heating zone of the same temperature as the crosslinking temperature, and at least one reheating treatment,
A method for producing an electric wire / cable, which is characterized in that it is again introduced into pressurized cooling water at room temperature or lower and recooled at least once at room temperature.