JPH0212361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a watertight insulated electric wire in which the gaps between the strands of a stranded conductor are filled with a watertight mixture from the outer periphery, and a method for manufacturing the same.

<Prior art> Overhead distribution lines using conventional hard copper stranded wires as conductors have recently been made by filling the gaps between the strands of hard copper strands with a watertight mixture from the outer periphery in order to prevent disconnection due to stress corrosion cracking. Watertight insulated wire is used. The water-tight mixture mentioned above has a high viscosity.
This is preferable because it maintains sufficient watertightness even after filling and is easy to handle, but on the other hand, it has the disadvantage that it is not easy to fill from the outer periphery. In particular, in the concentrically twisted conductor with a single central strand, which is the most commonly used conductor structure, there is no gap between the strands of the first layer surrounding the central strand, so watertight mixtures are not allowed to flow from the outside to the center. Difficult to fill. As a countermeasure against this, attempts have been made to, for example, coat the central strand with a watertight mixture in advance, lay the first and second layers on top of it in sequence, and then fill the outer periphery with a watertight mixture. However, the problem is that the process becomes complicated. In addition, other countermeasures are taken from the structure of the stranded conductor, such as making the wire diameter of the inner layer thicker than that of the outer layer, or reducing the number of wires in the outer layer to create gaps between the outer layer wires. so that
Watertight admixtures with improved filling properties have also been proposed. However, even in these cases, since the outer layer wire and the inner layer wire are in point or line contact, it is extremely difficult to completely fill the minute gaps at or near the contact point when the watertight mixture has a high viscosity. This is difficult, and for this reason, the causes of stress corrosion cracking have not yet been completely eliminated. Furthermore, once conventional watertight insulated wires break due to stress corrosion cracking, there is a risk that the wires will dangle to the ground and cause secondary disasters, so even though they are not sufficient from a safety standpoint. Nakatsuta.

<Purpose> The present invention solves the conventional problems, improves the filling properties of watertight admixtures, prevents voids from remaining between the wires, prevents stress corrosion cracking, and prevents stress corrosion cracking in the unlikely event of wire breakage. The purpose is to ensure safety even when accidents occur.

<Structure> Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 is a sectional view of the watertight insulated wire of this embodiment. The watertight insulated electric wire 1 of this embodiment includes an inner layer 4 made of one annealed copper strand 2, and on the outer periphery of this inner layer 4, six hard copper strands 6 having a smaller diameter than the annealed copper strand 2 are arranged.
An outer layer 8 is provided which is actually twisted together, and the inner layer 4 and the outer layer 8 are formed by compression molding so that they are in surface contact with each other. Further, the gaps between the strands of the stranded wire conductor are filled with a watertight mixture 10 mainly composed of a thermoplastic substance, and an insulating coating layer 12 made of polyethylene or the like is provided around the outer periphery of the outer layer 8.

The watertight insulated electric wire 1 having the above structure is manufactured as follows.

First, as shown in FIG. 3, a wire twisting machine 20 is applied to twist hard copper wires 6 having a smaller diameter around the inner layer 4 made of soft copper wires 2. As a result, an outer layer 8 with gaps between the hard copper strands 6 as shown in FIG. 2 is formed through the die 22. The stranded wire conductor thus formed is preheated by the preheating device 24 and sent to the next stage watertight mixture filling device 26, where the watertight mixture 10 is applied from the outer periphery of the outer layer 8 to the gaps between the strands of the stranded wire conductor. Press-fit and fill. In this case, the gap between the hard copper wires 6 is set to a size that takes into consideration the viscosity of the watertight mixture 10, and the viscosity of the watertight mixture 10 is reduced by preheating each of the wires 2 and 6. However, at this stage, the outer layer strand and the inner layer strand are in point or line contact, and the minute voids near the point contact or contact line cannot be completely filled. For this reason, watertight admixture 1
After filling with zero, the entire stranded wire is further compressed through compression rollers 28. At that time, the inner layer 4 is easily deformed due to the annealed copper strands 2, and as a result, each hard copper strand 6 of the outer layer 8 and the annealed copper strand 2 of the inner layer 4 come into surface contact, the strand gap is reduced, and at the same time , the unfilled void portions of the watertight mixture 10 will disappear. Therefore, there is almost no risk of stress corrosion cracking occurring. Finally, the insulating coating layer 12 is formed by extrusion molding or the like. In the thus obtained watertight insulated wire 1, stress corrosion cracking does not occur in the annealed copper wire 2, so in the unlikely event that the hard copper wire 6 of the outer layer 8 breaks due to stress corrosion cracking. There is also no danger that the entire electric wire 1 will break immediately and fall to the ground instantly.

In the above embodiment, the inner layer 4 is composed of one annealed copper strand 2, but the invention is not limited to this. For example, as shown in FIG. The present invention can be widely applied to those having a structure in which the wire 2' is used, and furthermore, to those having a multilayer structure as an outer layer.

<Effects> As described above, according to the present invention, after filling with the watertight mixture, the entire inner and outer layers are compressed, so that the voids remaining during filling with the watertight mixture disappear as the inner layer deforms. This improves the filling properties of the watertight mixture and almost eliminates wire breakage due to stress corrosion cracking. Further, even if the hard copper wire is broken due to stress corrosion cracking, the annealed copper wire prevents the entire electric wire from breaking, thereby providing an excellent effect of providing a watertight insulated wire with high safety. Furthermore, the method for forming the outer layer with gaps between the strands is not limited to the method of forming the outer layer with hard copper strands having a wire diameter smaller than that of the annealed copper strands of the inner layer; This method also includes a method in which wires of the same diameter are used in both layers and the number of wires in the outer layer is smaller than the standard configuration to provide a gap between the outer layer wires.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is a cross-sectional view of a watertight insulated wire, FIG. 2 is a cross-sectional view of the inner and outer layers of the watertight insulated wire shown in FIG. 1 during manufacture, and FIG. 3 is a watertight insulated wire. FIG. 4 is a schematic cross-sectional view of the manufacturing apparatus of FIG. 1, 1'...Watertight insulated wire, 2, 2'...Annealed copper wire, 4,4'...Inner layer, 6,6'...Hard copper wire,
8, 8'... outer layer, 10, 10'... watertight mixture.

Claims (1)

[Scope of Claims] 1 The inner layer of the stranded wire conductor is made of annealed copper strands, and the outer layer is made of hard copper strands, and the strands of the inner layer and the strands of the outer layer are formed in surface contact by compression molding, and the strands are A watertight insulated wire characterized in that the gap is filled with a watertight mixture. 2 Hard copper wires having a predetermined number and wire diameter are twisted around an inner layer made of annealed copper wires to form an outer layer with gaps between the hard copper wires, and a watertight mixture is press-filled from the outer periphery. After that, the stranded conductor is compressed to bring the annealed copper strands and the hard copper strands into surface contact, thereby eliminating gaps between the strands.