Fiber Optic Cable Technology-microtube Air Blowing Technology

1. Micro-tube

1.1 types of micro-Tubes

Microtubes are an important part of the air blowing system. Just like a city road, the microtubes must be laid to the destination before the microcables are laid, and must be laid in place at a time. Because 1st laying of micro-tubes and 2nd laying of micro-tubes may be entangled, in a protective tube (protection tube: protection tube refers to the pipe that protects the micro-tube, this type of pipe can be gas-blown Silicon core pipe, PVC pipe for traction, sub-pipe for municipal pipeline, grid pipe, and other pipelines for laying optical cables). Micro-tubes cannot be laid in batches, at present, there are about two types of micro-tubes at home and abroad by structure:

1.1.1 cluster management

The Bundle Tube (see Figure 1) is a bit like the honeycomb tube commonly used in our municipal pipeline. It is a combination of a micro tube and an external jacket consisting of a loose microtube unit, but between the micro-tube and the micro-tube, the micro-tube unit and the Outer Sheath cannot be attached, and there can be relative displacement. The advantage of the bundle tube is that the pipe has a high density and can accommodate the largest number of microtubes in an effective space. The disadvantage is that the flexibility is poor, the pipeline is not convenient to open the section (refers to the thick wall of the Outer Sheath), the inner tube is difficult to split, and the Impact Resistance is also poor, because the micro-tube is tightly wrapped together by the protection tube, the deformation of the protection tube can directly cause the micro-tube deformation. See figure 2.

Currently, according to different engineering purposes, the bundle tubes are classified into direct buried, pipe, bundle, flat, overhead, fire-retardant, anti-termite and armor. The bundle tubes are circular, polygon, square, and flat shapes. Most of the circular bundle tubes are thick-walled Outer Sheath bundle tubes. The polygon bundle tubes are generally Thin-Walled Outer Sheath bundle tubes, the square and flat bundle tubes have thick-walled and thin-walled outer casings, as shown in figure 3 and figure 4.

Directly Buried cluster tube:The Directly Buried bundle tube is composed of a micro-tube unit with a thick-wall outer sheath and a standard wall thickness, or a Thin-Wall Outer Sheath and a thick-wall micro-tube unit, to solve the problem of difficult opening and cutting of the bundle tube with Thick Wall Outer Sheath and improve the flexibility of the bundle tube, the bundle tube with Thick Wall Outer Sheath begins to change to the bundle tube with Thin Wall Outer Sheath. Directly Buried bundle tubes can be directly purchased from the channels.

Pipe-type Bundle Tube:The pipe-type bundle tube is composed of a thin-walled outer sheath and a micro-tube unit with a standard wall thickness. It is suitable for laying in buildings and air blowing or traction in pipes with protective tubes.

Bundle type micro Tube Bundle:Bundle-type bundle tubes are bundled with fine nylon ropes to combine micro-tube units. They can be used for traction, air blowing, and direct burial, it depends on the wall thickness of the micro-tube unit and the material of the protection tube. This shape of the bundle tube can maximize the use of the protective tube and channel space, the combination of a flexible way. In one 40/33-mm protective tube, four groups can be blown by air, and each group has 6 4/3mm micro-tube units.

Flat cluster tubes:Flat-shaped bundle tubes are used in standard channels for mechanical excavation in the urban area. The width of such channels is very narrow. Therefore, flat-shaped bundle tubes are very suitable for such channels, at the same time, there is no problem at the horizontal turning point of the line. However, for high and low ups and downs of lines, it is difficult to lay such a bundle tube at a change point in the direction. To solve this problem, a flat cluster tube that can be squashed into a circular shape has been launched.

Overhead Bundle Tube:The overhead type bundle tube is a 8-character structure of the bundle tube. The manufacturers combine the bundle tube and the strengthen unit of the overhead support, which is suitable for access and downloading.

Flame Retardant Bundle Tube:The flame-retardant bundle tube consists of low halogen, smoke-free, micro-tube unit and External Sheath, used for direct laying in buildings.

Anti-termite Bundle Tube:The outer jacket of the anti-termite bundle tube is an external jacket that can enhance the mechanical strength of the pipe and provide chemical protection materials to prevent the destruction of the termite.

Armored bundle tubes:A corrugated steel belt is used in the outer sheath to protect the micro-tube bundle, which can effectively prevent animal bites.

A Directly Buried Bundle Tube formed by a combination of wall-thick outer sheath and standard wall-thickness micro-tube units. the pipe-type bundle pipe composed of units has no outer jacket, all the standard wall-wall micro-tube units are bundled with a thin rope.

A flat-shaped Bundle Tube composed of a thin-walled outer sheath and a thick-walled microtube unit is a new flat Bundle Tube composed of a thick-walled microtube unit of the same diameter or a thick-walled microtube unit of different diameters, the "8" character overhead Bundle Tube combined with a thick-wall outer jacket and a hanging wire or an overhead microtube unit for the next user.

1.1.2 micro-tube unit

A micro-tube unit is composed of a silicon core layer added to the inner wall of HDPE material. Generally, the inner wall with a diameter of more than 5mm has a flow channel, the inner wall of the microtube diameter below 5mm does not have a flow channel. At present, the external diameter of the micro-tube generally ranges from 3mm to 16mm. The number of fiber cores that can be accommodated in one microtube ranges from 1 core to 288 cores or even higher. When the optical fiber single element and micro-cable are blown by air, the silicon core layer is mainly used to reduce the friction coefficient between the cable pipes. After air blowing, the silicon core layer remains on the inner wall of the microtube, which is conducive to future maintenance and cable replacement. The micro-tube unit has a standard wall thickness and a reinforced micro-tube. The micro-tube with a standard wall thickness can be used for traction and gas blowing, and the reinforced micro-tube unit can be used for direct burial. See Figure 5.

In the silicon core tube of 1 to 40/33, four groups of gas are blown, each group of 6, A total of 24 4/3mm bundle type bundle tubes in one 40/33-mm Silicon core tube air blow 5 10/8 microtube units.

The advantages of micro-tube units include:

1. simple and flexible Laying Methods:

If the protection tube is a silicon core tube, a certain number of micro-tubes can be blown into the laid protection tube according to the mold Shape Based on the diameter of the protection tube. If the protection pipe is another pipe, such as a PE pipe, grid pipe, or PVC pipe, you can also use the traction technology or water laying technology to lay the micro tube into the existing pipe. If there is no blank protection tube, the expansion technology of the micro-tube can also be based on the internal diameter of the protection tube and the ratio of the existing optical fiber diameter in the protection tube to determine whether it can also be blown, laid or pulled by water, and how many microtubes can be blown or pulled. See Figure 6.

2. As long as there is no protection tube available, you can upgrade and expand the pipeline:

Gas Blowing micro-tube control can make full use of existing pipeline resources for Pipeline Expansion, especially in the Old City and the lack of pipeline resources. As long as there is an empty protection tube, the pipe can be expanded to 3-5 or more. The capacity of the expansion depends on the inside diameter of the protection tube and the outer diameter of the micro-tube. For details about the relationship between the protection tube and the gas blow tube unit, refer to 1.3.

3. The combination of micro-tube control can be selected as needed:

During Air Blowing and traction, we can select the microtube units with different diameters according to the requirements of the number of microcable cores. As shown in the table above, five 40/33-mm microtubes can be laid in one 10/8-mm protective tube, and two 12/10-mm and one 14/12-mm microtubes can be laid, however, different combinations of these two groups of micro-bundle can have a great impact on the number of cores of the gas blow micro-cable. The combination of 5 10/8 microtubes can accommodate a maximum of 480 cores, but the combination of 2 12/10 and 1 14/12 microtubes can accommodate a maximum of 720 cores.

4. Pipeline upgrade can be synchronized with development:

Because the micro-tube system has a strong ability of parallel upgrade and vertical upgrade, the micro-tube direct joint and the different joints of the protection tube can be installed and connected anytime, anywhere, allows a micro-tube to quickly connect to any location of the network. After the micro-cables are laid, the micro-cables can be laid into the micro-Tubes in batches according to market requirements, without the need to predict the future market, you do not need to overwrite networks that are on demand or not on demand.

5. Minimize resizing costs and maximize pipeline utilization:

As the pipeline creation cost increases, Pipeline Expansion in many places has become impossible. Using the resizing technology of micro-tube not only can increase the utilization rate of the pipe quickly, but also can greatly increase the number of fiber cores in each micro-tube. For example, a 192-core optical fiber cable with a diameter of 14.5mm is usually a 40/33-core silicon tube with only one air-blown optical fiber cable, and a 96-core microcable, the typical diameter is 6.5mm. Five 96-core microcables can be laid in one 40/33-mm Silicon core tube, and the number of fiber cores can reach 480 cores, in addition, the 480-core micro-cables do not need to be laid once. They can be laid in stages according to market requirements, saving the initial investment cost of the market.

6. Better protection for micro-cables:

For air-blown micro-tubes and micro-cables, both micro-tubes and micro-cables are relaxed in the protection tube and have no stress. When the protection tube is subjected to external tensile force, the remaining length of the micro-tube and micro-cable in the protection tube can automatically compensate for the deformation of the protection tube. According to the air blowing principle, the micro-tube bundle cannot fill the whole pipe. Therefore, a certain amount of space is required between the micro-tube and the protection tube. This space also enhances the mechanical strength of the micro-tube, this ensures that when the surface of the protection tube is slightly deformed, the micro-tube unit can avoid deformation through displacement in the deformation protection tube without directly causing damage to the micro-tube. Because the gas blow micro tube is relaxed in the protection tube, when the protection tube is affected and stretched by the outside, the micro tube has a high buffer capacity.

7. Most convenient network maintenance and fastest cable replacement:

When the microcable in the microtube system fails, you can use the air blow Method to quickly blow the reservation of the microcable in the line to the obstacle point. You only need one access box to fix the obstacle points. However, the traditional line requires two head boxes and one optical cable. When the microcables in the network need to be replaced, the gas blowing technology can also quickly blow out the old microcables and the new microcables.

1.2 effect of air blow indexes and structures of micro-tube units on air blow

According to the standards of the Gas Blowing System, the technical requirements for the micro-tube construction are as follows:

1.2.1 dimensions

The micro-tube must be round and the size is as follows:

For the gas blow micro-tube, it is very important to keep the size of the micro-tube within the deviation range of the above table. If the positive deviation of the micro-tube diameter increases, it is difficult for a micro-tube to pass through or cannot pass through the sealing Guide of the air blow machine. Generally, the lower deviation of the air blow machine sealing guide is only 0.2 greater than that of the micro-tube. Because the sealing Guide adopts the Labyrinth Sealing Principle, if the deviation of the sealing guide increases, the effect of the Labyrinth Sealing will decrease or fail to seal. In addition, the micro-tube adopts a plug-in connection mode, and the outer diameter deviation of the micro-tube increases, which makes the micro-tube connection and disassembly difficult or cannot be connected. If the negative deviation of the outer diameter of the micro-tube increases, the sealing effect of the micro-tube orientation will become worse when it passes through the sealing guide. At the same time, the force of the micro-pipe joint on the outer diameter of the micro-tube will also decrease, it will lead to the micro-cable in the air blowing, the micro-pipe joints will be removed from the tube under the high pressure, the micro-cable may be removed from the connector, causing a discount on the micro-cable. If the micro-tube is not circle, it will produce a lot of friction resistance on the sealing guide, leading to the failure of Gas Blowing Pipe. In addition, it may cause difficulties and air leaks in the connection of micro-tubes.

1.2.2 Chromatography

Based on IEC-304 standard using full chromatography, 10 micro tube selected the following color:

For gas blowing micro-tube bundles, chromatography is very important to differentiate the microtubes. Because when a microtube is blowing, its unit is arranged randomly in the pipe. If chromatographic differentiation is not required, a large amount of work will be added to distinguish the microtube units of the same chromatography. For the bundle tube, because the arrangement of the micro-tube unit is regular, the micro-tube unit in the cluster tube does not need to consider full chromatography, but only needs to understand the arrangement rules of the micro-tube unit in the cluster tube, during the laying of the bundle tube, chromatography is required to identify the and B ends, and the gas blow tube unit is not required.

1.2.3 identifier

The Bundle Tube and microtube unit should have a readable and traceable tag every one meter, including the production date, trademark, and microtube length.

The length and size of the micro-tube are very important. Whether it is air blowing, direct burial or traction, record the size band of each microtube to facilitate the configuration of the microcable.

1.2.4 pressure

At 20 C, the microtube must be able to withstand the pressure of 12 bar, lasting for 30 minutes.

Currently, this stress indicator has been upgraded to 15 bar in many projects. The larger the pressure that a micro-tube can withstand, the farther the micro-cable can be laid. Because the high-pressure air flowing at high speed in the micro-tube will form a thrust on the surface of the micro-cable, the higher the pressure, the greater the thrust, the more conducive to the increase of the air blowing length. When users are very concerned about how to increase the core number of the microcable to the maximum extent within the limited space of the micro-tube, the diameter of the micro-cable and the diameter ratio of the micro-tube will exceed the theoretical limit of 80% blow, the air blow effect will decrease a lot. If 15 bar air pressure is adopted under the same conditions, the air blow effect will be improved in the air blow Effect of 12 bar pressure.

1.2.5 Friction Coefficient

The friction coefficient of the micro-tube cannot exceed 0.1 when measured by the drum method.

The friction coefficient is also a very important indicator for air blowing. The lower the friction coefficient, the smaller the friction between the wall of the micro-tube and the wall of the micro-cable, then, the longer the air blow length, when the thrust of the same airflow is applied. For the drum method, the friction test is based on the theory of traction. for gas blowing, the effect of the flow of air in the pipeline on the Friction cannot be reflected, but it can be used as a reference, it is used to compare the friction coefficient of micro-tubes of different manufacturers in the traction mode.

1.2.6 micro-disk

Micro-tubes can be packed in paper, wooden, or iron discs. However, wooden discs are currently popular in the world. The inner end of the micro-tube must bring out the outside of the disk and prevent impact protection, so as to facilitate the inflation and gas filling of the tube during air blowing.

The tube tray made of cardboard is not easy to store. If the tube tray is damp and drenched, the tube tray will be damaged immediately. At the same time, if the axis hole of the paper tube disk does not adopt the central positioning card, the axis hole will be damaged during the rotation of the tube disk, resulting in the tube disk cannot be rotated. The price of an iron pipe tray is high, and the weight and transportation cost of the tube tray will be increased. The strength of a wooden tube disk is higher than that of a paper tube disk. However, it is recommended that a central positioning card be used to prevent the shaft hole from breaking during the rotation of the tube disk.

The shaft hole of the center positioning card and fixed tube disk for the lifting frame with a central positioning card.