There must be many friends who have the same question as us, that is, the direct-buried optical cable joint box is flooded without knowing what happened, and they do not know how to prevent the direct-buried optical cable joint box from entering the water. Let's talk about why the direct buried optical cable splice box enters the water and how to prevent the direct buried optical cable splice box from entering the water.
Why does the direct buried optical cable joint box enter the water?
1.1 The structural design of the splice box is not suitable for direct buried optical cables.
The cap-type splice box is mainly designed for laying optical cables in overhead and tunnels. It is used in direct buried lines that do not meet the waterproof requirements of the regulations, but the moisture-proof effect in the line is better. According to the regulations, the junction boxes of the other three common structures, such as the open type, are all used in direct burial, but the moisture-proof effect is poor.
Although the structure and scope of application of these four types of optical cable splice boxes are different, in terms of sealing process, there are only two parts that need to be waterproofed: the fold of the upper and lower covers of the splice box; the place where the line optical cable enters the splice box. introduction site.
The cap-type splice box is sealed with a heat-shrinkable sleeve at the introduction part of the optical cable into the splice box, which connects the line optical cable and the splice box into one, and squeezes the rubber ring against the upper and lower covers where the upper and lower covers are closed to waterproof. The other three joint boxes are sealed with non-vulcanized rubber tapes in these two parts, and water and moisture can only enter the joint box through these two channels. The fiber optic cable splice boxes of these three structures are all sealed with non-vulcanized rubber tape to prevent moisture.
The non-vulcanized rubber belt is a polymer material with a certain viscosity. When it is subjected to a large external force, it will deform and fill the gap between the objects to achieve the purpose of moisture resistance. However, it is a medium and low viscosity chemical substance, and its physical properties are easily affected by temperature changes, especially when other impurities are adhered, its sealing performance will drop sharply. In the cap-type splice box, the line optical cable enters the optical cable introduction part of the splice box, which is sealed with a heat-shrinkable sleeve. Compared with the non-vulcanized rubber belt, its physical properties are more stable, and the moisture-proof treatment process is more refined, so the occurrence of water ingress failures is avoided.
1.2 The handling of the cable entry part of the splice box is not standardized.
The water ingress failures caused by the improper handling of the line optical cables entering the splice box and the optical cable entry position accounted for 85.7% of the total water ingress failures, of which the water intake ratio of the three commonly used direct-buried optical cable splice boxes was as high as 88.3%. Carefully study the water ingress of the three commonly used direct buried optical cable splice boxes and optical cable entry parts, and found that there are three main reasons:
(1) The line optical cable is warped at the introduction part of the optical cable of the splice box;
(2) The non-vulcanized rubber tape used for sealing the joint box is stuck with impurities;
(3) The line optical cable is not completely shaved at the introduction part of the optical cable of the splice box.
How to prevent direct buried optical cable joint box from entering water
2.1 Handling of the lead-in part of the optical cable in the splice box
The commonly used optical cable splice box for direct burial, no matter what kind of structure, as long as it has a network access license, is equipped with attention instructions for its application characteristics. The operator should read this manual carefully before use, and pay close attention to the parts with high probability of problems, especially the introduction part of the line optical cable into the splice box. The handling of this part should be done as follows:
a. It must be ensured that the line optical cable is thoroughly roughened in this part to enhance the adhesion between the non-vulcanized rubber tape and the optical cable. In the project, No. 8 sandpaper is applied to the optical cable here, and the optical cable is used as the axis to be evenly roughened in a circular shape until the luster of the outer sheath of the optical cable disappears completely, and then the residual sandpaper particles on the outer sheath are removed with cotton yarn. Finally, the non-vulcanized rubber tape is stretched in the horizontal direction and evenly wound on the optical cable. The thickness of the winding should be higher than the extrusion recess between the upper and lower covers of the splice box. After the splice box is closed, the traces of the non-vulcanized rubber tape being pushed out of the box can be clearly seen from the outside of the splice box.
b. The cleanliness of the non-vulcanized rubber belt must be ensured. Due to the limitations of the outdoor geographical environment of some optical cable splicing points and the negligence of the operator, if the non-vulcanized rubber tape is stuck with impurities before use, its viscosity will decrease, resulting in a decrease in the moisture resistance of the splice box after packaging.
c. It is necessary to ensure that the non-vulcanized rubber belt stretches and wraps the operation specification. In order to ensure that the non-vulcanized rubber tape can connect the splice box and the line optical cable as a whole, and there is no gap between the layers of the non-vulcanized rubber tape, the operator should stretch it evenly when winding. If the tensile force is not enough, it is impossible to make it evenly wound, and there will inevitably be gaps after the joint box is packaged; if the tensile force is too large, it will break.
2.2 Prevent the warping of the optical cable at the introduction part of the optical cable of the splice box
After the optical cable splice box is encapsulated, the backfilling and covering soil is generally not taken seriously, but the unqualified backfilling method is the root cause of the warping of the line optical cable at the cable entry part of the splice box. According to statistics, 59% of the direct buried optical cable splice box water is caused by this. This is mainly because the openings of all direct-buried optical cable splice boxes into the optical cable are located in the middle of the longitudinal thickness of the splice box.
Before backfilling the splice box with soil, if there is no bottom of the optical cable here, use a hard object to cushion the optical cable to the same height as the opening of the splice box, which will inevitably make the optical cable in the suspended state. In particular, when the loose backfill soil sinks and becomes compact, the optical cable at that place will not be able to withstand the huge sinking force of the backfill soil and will warp, which will drive the original sealing winding deformation of the non-vulcanized rubber belt, and finally Causes water to enter the joint box. Therefore, before backfilling the fiber optic cable splice box, use a hard stone piece to solidify the bottom of the fiber optic cable at the introduction part of the fiber optic cable of the splice box, so that the cable can be at the same height as the opening of the splice box when backfilling the soil. Do not smash the fiber optic cable in this part.
2.3 Enhance the moisture resistance of the direct buried optical cable splice box
On the basis of maintaining the structure of the existing optical cable splice box, the non-vulcanized rubber tape is replaced by the expansion water-blocking yarn tape as the sealing material to improve the moisture-proof performance of the splice box. The water-blocking function of the swelling water-blocking gauze tape is to use the water-blocking gauze tape body to rapidly expand to form a large volume of gel when it encounters water (the water absorption can reach dozens of times its own volume, and the first minute it encounters water) The inner diameter can be rapidly expanded from about 0.5 mm to about 5.0 mm), and the water-retaining capacity of the jelly is quite strong, blocking the water channel space between the optical cable splice box and the outside world, preventing the continuous infiltration and diffusion of water.
Compared with the non-vulcanized rubber tape, the water-blocking yarn tape has the following characteristics: a. It can be reused, which reduces the operation and maintenance cost of the optical cable. b. Good chemical stability, no corrosive ingredients, resistant to bacteria and mold. c. It has a certain mechanical strength, which can prevent the damage to the sealing performance of the joint box caused by vibration or terrain changes. d. Sealing requirements and procedures and operation methods are the same as non-vulcanized rubber belts, no special skills are required.
2.4 Improve the structure of the direct buried optical cable splice box
In terms of the sealing performance of the four structural splice boxes, different sealing processes are used for the introduction of optical cables into the splice box, resulting in different moisture-proof effects. The cap-type splice box uses a heat-shrinkable sleeve for waterproofing at the optical cable introduction part of the splice box; the open type and other three commonly used direct-buried optical cable splice boxes use non-vulcanized rubber tape to prevent moisture in this part. From the overall effect, it is obvious that the moisture-proof effect of the heat-shrinkable sleeve is better than that of the non-vulcanized rubber belt.
To this end, the heat-shrinkable sleeves originally used for cap-type splice closures were used for three other direct-buried fiber optic splice closures. The improved splice box is the same in structure as the original splice box. The biggest difference from the original splice box is that the length of the bayonet opening of the upper and lower covers of the original splice box is extended, and it is integrated with the upper and lower covers. In order to facilitate the sealing of the heat-shrinkable sleeve, the length of its extension should generally not be less than 4-6 cm. In this way, P-type or W-type heat-shrinkable sleeves can be used when sealing the joint box, and the parts that need to be sealed with non-vulcanized rubber tapes can be easily sealed with heat-shrinkable sleeves, thereby further improving direct burial. Moisture resistance of fiber optic splice closures.
The above is why the direct buried optical cable joint box enters the water and how to prevent the direct buried optical cable joint box from entering the water. Presumably after reading this article, you have a certain understanding of why the direct buried optical cable joint box enters the water and how to prevent the direct buried optical cable joint box from entering the water. , I hope you can help.
