JP3946280B2 - Coaxial cable insulator molding method and molding apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for forming an insulator of a coaxial cable, and in particular, in the manufacture of a coaxial cable, a method of extruding a tubular insulator on a spirally wound string-like insulator, and Relates to the device.
[0002]
[Prior art]
Recently, car phones, mobile phones, pagers, etc. have become extremely popular, and there is an urgent need to ensure communication with these mobile radios in places where radio waves are difficult to propagate, such as in tunnels, underground malls, and reinforced concrete buildings. ing.
[0003]
2. Description of the Related Art Conventionally, radio wave transmission / reception systems using leaky coaxial cables (LCX cables) have been widely used as communication systems aimed at providing services to moving bodies in such radio wave insensitive (non-propagating) zones.
[0004]
As shown in FIG. 2, the leaky coaxial cable (LCX cable) is composed of an outer conductor 3 made of a copper or aluminum pipe and an outer conductor 3 made of an aluminum laminate tape vertically attached to the outer periphery of the inner conductor 1 and polyethylene. The protective sheath 4 has a structure provided in order, and a special radio wave leakage hole called a slot 5 for radiating an electromagnetic wave propagating through the cable is formed in the outer conductor 3 in a zigzag manner.
The insulator 2 is composed of, for example, a trapezoidal string (string-like insulator) 6 made of polyethylene and a tube-like insulator 7 made of polyethylene, and the string-like insulator 6 is spirally wound around the outer periphery of the inner conductor 1. After that, polyethylene was extruded onto the tube and immediately cooled through a cooling water bath.
[0005]
[Problems to be solved by the invention]
However, in the insulator of the conventional leaky coaxial cable formed in this way, as shown in FIG. 3, a dent 8 is formed in a portion where the string-like insulator 6 does not exist below the tubular insulator 7. It was easy.
[0006]
If the recess 8 is present on the outer peripheral surface of the tubular insulator 7 and the outer diameter of the tubular insulator 7 is not uniform in the longitudinal direction, the formability of the slot 5 in the outer conductor 3 is deteriorated. In addition, it is considered that VSWR (voltage standing wave ratio) and attenuation which are one of important electrical characteristics in the leaky coaxial cable are adversely affected. In particular, at the present time when the operating frequency of leaky coaxial cables is shifting to high frequencies in the GHz band, the outer diameter of the insulator 2 is required to be even more uniform.
[0007]
Conventionally, in the manufacture of a coaxial cable, the following method has been adopted in order to reduce irregularities on the surface of the tubular insulator 7 and to make the outer diameter uniform. That is, after the tubular insulator 7 is pushed out, it is first cooled with warm water through the first water tank and then cooled with normal temperature water through the second water tank, or spirally wound around the outer periphery of the inner conductor. After providing a layer of a flooring tape that is not softened and deformed at a normal extrusion temperature on a twisted polyethylene strap 6 (strand-like insulator), and extruding a tubular insulator 7 made of polyethylene thereon. A method of cooling by a conventional method is performed. However, in any of the methods, a sufficiently satisfactory effect has not been obtained.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method and an apparatus for forming an insulator having a uniform outer diameter without a dent in the outer peripheral surface in the manufacture of a coaxial cable.
[0009]
[Means for Solving the Problems]
The method for forming the insulator of the coaxial cable according to the present invention is to extrude a tubular insulator on a cord-like insulator wound spirally around the outer periphery of the inner conductor, and then cool it through cooling water. In a state where the cooling water is decompressed, the tubular insulator is cooled while passing through a forming pipe having a through-hole in its peripheral surface and disposed in the cooling water.
[0010]
Further, the coaxial cable insulator forming apparatus of the present invention includes an extruder for extruding an insulator in a tube shape on a string-like insulator wound spirally around an outer periphery of an inner conductor, and the extrusion A cooling water tank disposed on the downstream side of the machine, a molding pipe disposed in the introduction port of the cooling water tank, having a through-hole in the peripheral surface, and through which the tubular insulator passes, and the cooling And a decompression device for decompressing the cooling water stored in the water tank.
[0011]
In the method and apparatus for forming an insulator of a coaxial cable according to the present invention, after the insulator is extruded into a tube shape by an extruder on the cord-like insulator wound spirally around the outer periphery of the inner conductor. Then, it is immediately introduced into the cooling water tank and cooled by the cooling water while passing through the forming pipe having a through hole arranged at the inlet. At this time, since the cooling water stored in the cooling water tank is decompressed by the decompression device, the tubular insulator passing through the forming pipe is cooled while being sucked in the diameter expansion direction. As a result, the outer peripheral surface is not recessed even in a portion that is not supported by the cord-like insulator from the lower side, and a tubular insulator having a uniform outer diameter in the longitudinal direction is obtained. Therefore, the formability when forming the slot in the upper outer conductor is improved, and the VSWR, which is one of the important electrical characteristics in the leaky coaxial cable, can be stabilized.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 is a diagram schematically showing an embodiment of a molding apparatus used in a method for molding an insulator of a coaxial cable according to the present invention.
[0014]
As shown in the drawing, the molding apparatus of the example includes an extruder 9 for extruding a tubular insulator on a string-like insulator wound spirally around the outer periphery of an inner conductor, and a downstream side of the extruder 9. The cooling water tank 10 is arranged on the travel path, and the cooling water tank 10 is divided into a first cooling part 10 a and a second cooling part 10 b by a partition wall 11. And in the 1st cooling part 10a of the cooling water tank 10, the shaping | molding pipe 13 by which the several through-hole 12 was formed in the zigzag shape in the perimeter surface at the inlet part of a tubular insulator is provided. In addition, the first cooling unit 10a is provided with a decompression pump 14 having a structure in which water intrusion is sealed (water-sealed type).
[0015]
In the molding apparatus of the embodiment configured as described above, a cable core 15 in which a cord-like insulator such as a polyethylene trapezoidal cord is spirally wound around the outer periphery of an inner conductor made of a copper or aluminum pipe is an extruder. After passing through 9, an insulator made of polyethylene is extruded into a tube shape on the string-like insulator, and then immediately introduced into the cooling water tank 10. Then, the tubular insulator 16 is cooled while being sucked in the diameter expansion direction while passing through the forming pipe 13 disposed in the introduction port portion of the first cooling portion 10a.
[0016]
As a result, the outer peripheral surface of the portion that is not supported by the cord-like insulator from the lower side is prevented from being dented, and the tubular insulator 16 having a uniform outer diameter in the longitudinal direction can be formed. Therefore, the moldability when forming the slot in the upper outer conductor is improved, and the VSWR, which is one of important electrical characteristics in the leaky coaxial cable, can be stabilized.
[0017]
In addition, although the above Example demonstrated the example which provided the partition 11 in the cooling water tank 10, and installed the decompression device 14 in the 1st cooling part 10a divided | segmented by the partition 11, this invention is such a structure. It is not limited to this, The whole may be made into one water tank without providing a partition, and a decompression device may be installed in this water tank. Further, the water flow holes 12 of the molded pipe 13 are not limited to a staggered shape, and may be any arrangement shape, or may be formed in a wire mesh shape as a whole. Furthermore, the molding method and the molding apparatus of the present invention are not limited to the molding of an insulator of a leaky coaxial cable, and the insulator can be molded in the same manner in a normal coaxial cable having a low dielectric constant structure.
[0018]
【The invention's effect】
As described above, according to the molding method and apparatus of the present invention, in a coaxial cable such as a leaky coaxial cable, an insulator having a uniform outer diameter without a dent on the outer peripheral surface can be obtained. It is possible to maintain the characteristics as described above.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an embodiment of a forming apparatus used in a method for forming an insulator of a coaxial cable according to the present invention.
FIG. 2 is a perspective view showing an example of the structure of a leaky coaxial cable.
FIG. 3 is a partial cross-sectional view showing a state of an insulator of a conventional leaky coaxial cable.
[Explanation of symbols]
9 ... Extruder 10 ... Cooling water tank 11 ... Partition 13 ... Molded pipe 14 ... Water-sealed vacuum pump 16 ... Tubular insulator

Claims (2)

  After the tubular insulator is extruded on the string-like insulator spirally wound around the outer periphery of the inner conductor, the tube-like insulator is cooled in a state where the cooling water is decompressed in cooling through the cooling water. A method for forming an insulator for a coaxial cable, wherein the insulator is cooled while passing through a forming pipe having a through hole in its peripheral surface and disposed in the cooling water. An extruder for extruding the insulator into a tube shape on a string-like insulator wound spirally around the outer periphery of the inner conductor, a cooling water tank disposed on the downstream side of the extruder, and the cooling water tank Provided with a molding pipe having a through-hole in the peripheral surface thereof, through which the tubular insulator passes, and a decompression device for decompressing the cooling water stored in the cooling water tank. An apparatus for forming an insulator for a coaxial cable, characterized by comprising:

Images