JP2017198898A - Cable to be directly embedded - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cable to be directly embedded that achieves both impact strength and flexibility.SOLUTION: A cable 1 to be directly embedded includes: a first sheath (inner sheath 22) located inside; and a second sheath (reinforcement type outer coating 10) located outside that is loosely fitted to the first sheath. The second sheath is formed with high density polyethylene, and has an inner diameter within a range of 30±2 mm and a thickness within a range of 1.3 mm-1.4 mm. Preferably, a cross section of the second sheath in a longitudinal direction is formed in a wave form, and its crest parts and trough parts are alternately formed in the longitudinal direction of the second sheath.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cable, and more particularly, to a cable for direct embedding that is directly embedded in soil.

  In Japan, efforts are being made to eliminate the use of utility poles from the viewpoints of improving road disaster prevention, securing safe and comfortable traffic spaces, creating good landscapes and promoting tourism. Currently, a method of laying electric wires in underground pipes (also referred to as an electric wire co-groove method) is most often used for this effort to eliminate electric poles. However, this method is difficult to embed pipes on roads with narrow sidewalks or roads without sidewalks, and the application cost is limited due to high equipment costs.

One of the methods to solve the difficulty of burial of pipes and the increase in equipment costs in these undergrounding methods is the method of burying wires directly in the soil (especially because lower costs can be expected) The application of the direct burial method is also being considered.
However, when a communication cable is directly buried in the soil, there is a concern that the cable may be damaged or bent due to cable compression due to earth pressure, thereby adversely affecting the transmission characteristics and mechanical characteristics of the cable.

  For example, Patent Document 1 discloses a direct-embedded optical fiber cable in which an outer sheath formed by winding a high-hardness / high-rigidity plastic tape on a core cable and integrated with an outer sheath on the outer sheath is disclosed. Has been.

JP-A-7-33478

  However, the optical fiber cable described in Patent Document 1 is reinforced with a high-hardness plastic tape to withstand earth pressure, and the cable core is tightly fixed to the exterior. There was a problem that it was difficult to repair and maintain. That is, when repairing and maintaining the optical cable core, it is necessary to bury the entire cable after digging up a range corresponding to the entire length of the cable, and thus it may take a great deal of time and money to recover.

Also, when replacing only the repaired part with a new optical cable core, after excavating the range, install a new closure, etc., and install all the optical fiber of the optical cable core that will not be repaired and the optical fiber of the new optical cable core. Since it is connected, recovery in a short time becomes difficult. The communication service is stopped until it is restored, so there is a high possibility that it will not be allowed by the user.
In addition, there is a method of laying a hard duct and then laying an optical fiber cable in the duct, but in that case, the duct and the optical fiber cable are separately laid, and the laying man-hour is almost 2 Double.

  Therefore, it is conceivable that the optical cable core is kept loose relative to the exterior so that repair and maintenance can be completed in a short time, and the optical cable core can be easily pulled out and inserted from the exterior. Even so, it is desired that the exterior directly buried in the soil satisfy the impact strength and flexibility.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a cable for direct burying in which both impact strength and flexibility are achieved.

  A direct embedment cable according to one aspect of the present invention is a direct embedment cable that includes an inner first sheath and an outer second sheath, and the second sheath is loosely fitted to the first sheath. The second sheath is made of high-density polyethylene, has an inner diameter in the range of 30 ± 2 mm, and a thickness in the range of 1.3 mm to 1.4 mm.

  According to the above, it is possible to provide a cable for direct burying in which impact strength and flexibility are compatible.

It is a perspective view which shows an example of the cable for direct embedment concerning one embodiment of the present invention. It is a front view of the cable for direct burial. FIG. It is a figure explaining an impact strength test. It is a figure explaining a flexibility test. It is a table | surface explaining an evaluation result.

[Description of Embodiment of the Present Invention]
First, the contents of the embodiment of the present invention will be listed and described.
A direct embedment cable according to an aspect of the present invention includes (1) an inner first sheath and an outer second sheath, and the second sheath is loosely fitted to the first sheath. In the cable, the second sheath is made of high-density polyethylene, has an inner diameter in the range of 30 ± 2 mm, and a thickness in the range of 1.3 mm to 1.4 mm. If the second sheath is formed of high-density polyethylene and the wall thickness is within a range of 1.3 mm to 1.4 mm with respect to an inner diameter of 30 ± 2 mm, both impact strength and flexibility should be achieved. Can do.

(2) The longitudinal section of the second sheath is formed in a corrugated shape, and peaks and valleys are alternately formed along the longitudinal direction of the second sheath. In this way, if the corrugation is formed by alternately forming peaks and valleys along the longitudinal direction, it can withstand earth pressure and easily obtain the same flexibility as a general optical cable. It can be handled easily.

[Details of the embodiment of the present invention]
Hereinafter, a specific example of a direct burying cable according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing an example of a direct burying cable according to an embodiment of the present invention, and FIG. 2 is a front view of the direct burying cable.
The direct burying cable 1 includes an optical cable core 20 and a reinforced outer jacket 10 disposed outside the optical cable core 20.

  Although details of the optical cable core 20 are not shown, the optical cable core 20 has a core portion 21 of about 8 cores such as a drop cable for dropping a subscriber. The periphery of the core portion 21 is covered with an inner sheath 22 made of, for example, PE (polyethylene), PVC (polyvinyl chloride), or the like. The inner sheath 22 corresponds to the first sheath of the present invention.

The optical cable core 20 (inner sheath 22) has an outer diameter of about 10 mm to 20 mm, and the optical cable core 20 is formed in a round shape, for example.
The core portion 21 is a cable in which the outer side of a cable (for example, up to about 200 cores) bundled with multi-fiber optical fiber ribbons or the like, such as a low-comfort cable for a branch line, is held with a press-wound tape or the like. There may be.
The core portion 21 may be a slot cable or a slotless cable, and the shape thereof is not limited as long as it is a multi-core optical fiber cable.

The reinforced jacket 10 is loosely fitted to the optical cable core 20 and covers the periphery of the optical cable core 20 to protect the optical cable core 20. The reinforced outer jacket 10 corresponds to the second sheath of the present invention.
The reinforced outer jacket 10 is made of a hard plastic such as high density polyethylene (HDPE) having a density of 0.942 (g / cm ³ ) or more. If the reinforced casing 10 is made of HDPE, it can sufficiently withstand the compressive force and bending force applied to the cable due to earth pressure.

  As described above, the inner sheath 22 of the optical cable core 20 is loose with respect to the reinforced jacket 10, and the optical cable core 20 is easily pulled out of the reinforced jacket 10 when the optical cable core 20 is repaired or maintained. In addition, since the new optical cable core 20 can be easily inserted into the reinforced jacket 10, the optical cable core 20 can be repaired and maintained in a short time.

Further, the reinforced outer jacket 10 is formed in, for example, a bellows shape, and a longitudinal section thereof is formed in a waveform. If the reinforced outer sheath 10 is formed in a corrugated shape, it can withstand earth pressure, and has the same flexibility as that of a general optical cable due to the alternately formed ridge portions 11 having large diameter portions and valley portions 12 having small diameter portions. Therefore, the cable can be easily handled.
In addition, in the figure, although the example of the bellows-like reinforced type jacket in which the arrangement direction of the peaks and valleys is formed along the longitudinal direction has been described, the reinforced type jacket of the present invention has a longitudinal direction in which the arrangement direction of the peaks and valleys is the longitudinal direction. It is also possible to have a spiral bellows that intersects with each other, and it is also possible to form one of the outer peripheral surface and the inner peripheral surface of the reinforced outer jacket flat and make the other corrugated. However, from the viewpoint of flexibility, it is desirable to alternately form peaks and valleys in the direction along the longitudinal direction.

By the way, as described above, the reinforced jacket 10 needs to secure the same flexibility as that of a general optical cable. However, when the burying cable 1 is directly laid in the soil, it is positioned at the outermost periphery. The reinforced outer jacket 10 is also required to have a strength (also referred to as an impact strength) that can withstand excavation by a shovel or the like.
Therefore, in order to achieve both impact strength and flexibility, the inventors have conducted extensive investigations, and as a result, it has been found that the thickness of the reinforced outer jacket 10 should be defined within a certain range.

FIG. 3 is a partial cross-sectional view of the reinforced jacket.
The reinforced jacket 10 has an inner diameter D of 30 ± 2 mm, an outer diameter of 32 ± 2 mm at the valley 12, 37 ± 2 mm at the peak 11, and a height of the peak 11 of 2.5 mm. Further, the corrugated pitch P of the reinforced outer jacket 10 is 5.5 ± 0.5 mm, and the width of the peak portion 11 is 3.5 ± 0.5 mm. In FIG. 3, the thickness of the reinforced outer jacket 10 is indicated by t.

FIG. 4 is a diagram illustrating an impact strength test (excavator test).
In this test, an installation table 100, a shovel round shape 101, a weight 103, and a guide 102 are used. The excavator round shape 101 is of a predetermined standard (JIS A 8902 round shape No. 1), and is an excavator round shape with no deterioration or wear. The weight 103 is 10 kg, and a buffer material (chloroprene rubber (CR rubber) having a thickness of 10 mm or less) 104 is attached to the lower end of the weight 103. The reinforced outer jacket 10 has a length of 200 mm.

  The reinforced mold jacket 10 is placed on the installation table 100, the excavator round mold 101 is disposed at right angles to the axis of the reinforced mold jacket 10, and the tip of the excavator round mold 101 is attached to the peak portion of the reinforced mold jacket 10 (Tanibe). The weight 103 is naturally dropped from a height of 13 cm (indicated by Z in FIG. 4) along the guide 102, and a peak (or valley) of the reinforced jacket 10 is hit. When three reinforced outer jackets 10 are prepared and the crests and troughs of each of the three test pieces (the reinforced outer jacket 10) are hit, the tip of the excavator round mold 101 is placed on the inner surface of the reinforced outer jacket 10. Evaluate whether or not exposed.

FIG. 5 is a diagram for explaining the flexibility test.
In this test, a fixed base 200, a gripper 201, a free end support base 203, and a weight 204 are used. The weight 204 is 0.5 ± 0.01 kg. The reinforced outer jacket 10 has a length of 1.2 m (indicated by L in FIG. 5A), and is used that has been left at room temperature for 2 hours or more.
As shown in FIG. 5A, the reinforced outer jacket 10 is placed on the fixing base 200, and one end (fixed end) of the reinforced outer jacket 10 is fixed to the grip portion 201. The distance from one end of the reinforced outer jacket 10 to the fulcrum 202 of the fixed base 200 (indicated by L1 in FIG. 5A) is 500 mm, and the other end (free end) of the reinforced outer jacket 10 from the fulcrum 202. The distance up to (indicated by L2 in FIG. 5A) is 700 mm.

  On the other hand, the other end of the reinforced outer jacket 10 is supported by a free end support base 203. The weight 204 is suspended at a position within 50 cm from the other end of the reinforced outer jacket 10 (indicated by L3 in FIG. 5A). After the weight 204 is suspended, the free end support base 203 is quickly removed from the other end of the reinforced casing 10 and the amount of bending of the other end of the reinforced casing 10 after 10 seconds (see FIG. 5B). Flexibility is evaluated by whether or not (shown by y) is 8 cm or more.

FIG. 6 is a table for explaining the evaluation results.
The thickness of the reinforced outer jacket 10 was changed from 1.1 mm to 1.5 mm in increments of 0.1 mm, and impact strength (excavator test) and flexibility were evaluated. The physical properties of the reinforced outer jacket 10 other than the thickness are bending elasticity of 1350 MPa, density of 0.96 g / cm ³ , and Shore D hardness of 70. ^3. Same as Shore D hardness 67-71).

When the wall thickness was 1.1 mm (referred to as Sample 1), cracks were confirmed in all three reinforced outer jackets. In this case, since the tip of the excavator round mold 101 described with reference to FIG.
When the wall thickness was 1.2 mm (referred to as Sample 2), pinholes were confirmed in all three reinforced outer jackets. In this case, the tip of the excavator round shape was not exposed on the inner surface of the reinforced outer jacket, but it was determined that the required strength was not satisfied.

On the other hand, when the wall thickness was 1.3 mm (referred to as Sample 3), no damage was observed in any of the three reinforced outer jackets, so it was determined that the required strength was satisfied. In addition, when the wall thickness is 1.4 mm (referred to as Sample 4) and the wall thickness is 1.5 mm (referred to as Sample 5), no damage was observed in the reinforced outer jacket, so the required strength It was determined that
Thus, the required impact strength could not be obtained when the thickness of the reinforced outer jacket 10 was less than 1.3 mm, but the required impact strength could be obtained when the thickness was 1.3 mm or more. .

Then, the evaluation result of flexibility is demonstrated. The amount of deflection of the sample 1 described above was 350 mm. Since it was 8 cm or more, it was determined that flexibility was secured. Further, the deflection amount of the sample 2 was 300 mm, the deflection amount of the sample 3 was 200 mm, and the deflection amount of the sample 4 was 100 mm.
On the other hand, the amount of deflection of the sample 5 is 60 mm and not more than 8 cm, so it was determined that the flexibility was not ensured.

As described above, the necessary flexibility can be obtained when the thickness of the reinforced outer jacket 10 is less than 1.5 mm, but the necessary flexibility can be obtained when the thickness is 1.5 mm or more. It wasn't.
Therefore, if the reinforced outer jacket 10 is made of HDPE and the wall thickness is within a range of 1.3 mm to 1.4 mm with respect to an inner diameter of 30 ± 2 mm, both impact strength and flexibility can be achieved. Can be achieved.

  In addition, although the case where this invention was applied to the optical cable core was demonstrated as embodiment, a metal cable core may be sufficient instead of an optical cable core.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 ... Cable for direct embedment, 10 ... Reinforced type jacket, 11 ... Mountain part, 12 ... Valley part, 13 ... Open end part, 20 ... Optical cable core, 21 ... Core part, 22 ... Inner sheath, 30 ... Adhesive part, DESCRIPTION OF SYMBOLS 31 ... Adhesive member, 100 ... Installation stand, 101 ... Excavator round shape, 102 ... Guide, 103 ... Weight, 104 ... Buffer material, 200 ... Fixing stand, 201 ... Holding part, 202 ... Supporting point, 203 ... Free end support stand 204 ... Weight.

Claims (2)

A direct embedment cable comprising an inner first sheath and an outer second sheath, wherein the second sheath is loosely fitted to the first sheath;
The second sheath is a direct embedment cable made of high-density polyethylene, having an inner diameter in the range of 30 ± 2 mm and a thickness in the range of 1.3 mm to 1.4 mm. The cable for direct embedment according to claim 1, wherein a longitudinal section of the second sheath is formed in a corrugated shape, and peaks and valleys are alternately formed along the longitudinal direction of the second sheath. .

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