JPS593086B2 - Method of forming rubber or plastic cable connections - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a cable connection part in which the coating at the end of a rubber or plastic cable shrinks in the longitudinal direction of the cable and prevents the conductor end from protruding from the coating.

A rubber or plastic cable is provided with a rubber or plastic insulation coating, a protective coating, or the like on the outside of the conductor.

When such cable connections are made, these sheaths shrink in the longitudinal direction of the cable, and the reason for this is thought to be as follows.

Usually, when extrusion coating an insulating coating onto a conductor, the insulating compound is extruded into a hollow cylindrical shape at the outside diameter at a die of an extruder.

Since the linear velocity of the conductor passing through the die is faster than the extrusion velocity of the compound, the compound is stretched out from the die and coated on the conductor.

Therefore, strain occurs in the insulation coating on the conductor in the longitudinal direction of the cable, and when the cable is cut, the coating contracts and the strain is released. Since it stops when the frictional forces are balanced, residual strain still exists.

In this state, when the temperature of the coating rises due to electricity being applied to the cable, etc., the above-mentioned frictional force decreases due to the softening of the coating, and the coating contracts again.

This phenomenon is called shrinkback, and due to this phenomenon, the conductor of the cable becomes stretched out at the terminal or connection part of the cable, which may lead to electrical breakdown.

This will be explained with reference to FIG.

The figure shows a part of a straight connection part as an example, and the end of the rubber or plastic cable is stripped, and the conductor 1 is partially exposed from the insulation coating 2 and connected to the conductor connection fitting 3. .

This connecting fitting 3 is firmly held on the conductor 1 by a wedge 4 and a wedge fastening fitting 5.

Further, the strene cone 7 is fitted onto the end of the insulating coating of the cable.

Note that 6 indicates a contracted portion of the covering 2.

In this case, when the insulation coating 2 is first connected, it is full to the left line of the contracted part 6, but when it is used, it contracts and retreats to the right line of the contracted part 6, unlike the conventional method. This can be seen through observation.

Therefore, the contracted portion 6 creates a void without insulation coating at the connection portion, and there is a risk that discharge will occur there and cause an electrical breakdown accident.

The present invention is aimed at eliminating such drawbacks, and is designed to remove residual strain in the longitudinal direction of the rubber or plastic cable sheath before performing cable terminal processing and connection processing. This is what I did.

That is, in the present invention, the cable sheath is heated at a predetermined temperature for a predetermined time and then cooled to cause the sheath to shrink back in the longitudinal direction of the cable.

This method will be described with reference to FIG. 2.A tape heater or band heater 8 is wrapped around the end of a cable in which a conductor 1 is coated with an insulating coating 2, and a heat insulating material 9 is wrapped thereon.

The end of the cable is heated by the heater 8 and maintained at a temperature at which strain in the longitudinal direction of the cable sheathing is removed for a certain period of time, and then cooled at a predetermined cooling rate.

For example, do as shown in the table below.

As a result, the temperature of the cable coating increases,
The frictional force at the interface between the conductor and the sheathing decreases, causing thermal contraction of the sheath, and by cooling it, the shrinkage is fixed, allowing the cable sheath to shrink in a way that alleviates strain in the longitudinal direction. .

In this way, if the cable end coating is shrink-backed in advance and the cable connection process is performed in substantially the same manner as shown in Fig. 1, a gap as shown in Fig. 16 will be created after the cable connection part is formed. This does not occur and a connection with high electrical breakdown strength can be obtained.

In addition, although the above explanation mentioned the insulating coating, the same applies to the case where there is an extruded protective coating.

As described above, according to the present invention, the strain in the longitudinal direction of the cable coating is reduced by heating the cable coating at the cable connection end prior to cable connection processing, so that the temperature rise of the cable due to current and the ambient temperature are reduced. Even if the temperature of the cable increases due to
There is a point.

[Brief explanation of the drawing]

FIG. 1 is a partially longitudinal side view showing an example of a cable terminal connection section, and FIG. 2 is a partially longitudinal side view showing an embodiment of a heating device used in the present invention. Explanation of main symbols: 1: conductor, 2: insulation coating, 8: heater, 9: heat insulating material.

Claims (1)

[Claims] 1. A method for forming a rubber or plastic cable connection part, which comprises heating the coating at the end of the cable in advance to cause shrink-back when forming the connection part of the rubber or plastic cable.