Fiber optic cable water leakage does not cause significant problems during initial use, but over long-term use, water or moisture can enter the interior of the cable and react chemically with the cable components, producing hydrogen molecules or hydroxide ions, which can cause hydrogen damage to the fiber optic cable in this environment. Hydrogen loss refers to the significant increase in the H peak or OH peak of a fiber optic cable during use due to the combination of hydrogen molecules or hydroxide ions with the molecular network structure of the fiber, resulting in an overall shift in the attenuation spectrum. This can also cause microcracks on the surface of the fiber optic cable to continuously propagate until it breaks, seriously affecting the performance and service life of the cable. In addition, if the overall water resistance performance of the optical cable does not meet the requirements, water vapor will gather inside the cable and infiltrate the terminal equipment connected on both sides of the cable, causing incalculable losses and extremely serious consequences. Therefore, the water blocking measures of optical cables are important issues that must be considered in the design process of optical cables.
What are the ways of fiber optic cable water penetration?
The main ways of water leakage in optical cables include: gaps between sleeves and armor layers, gaps between loose sleeves or filling units, gaps between loose sleeves or filling units and reinforcement components, steel aluminum tape overlaps, gaps between reinforcement components and sheath materials, gaps between reinforcement components and armor layers, gaps between inner sheath layers and armor layers, and water leakage in the cushion layer of reinforcement components.
During the production process, over 90% of water penetration in optical cables mainly occurs at the overlap of steel and aluminum strips, while the probability of other water penetration situations is relatively small.
Several situations and solutions for water penetration in optical cables
Normally, when water penetration occurs, we can divide it into two types based on the location of occurrence: cable core water penetration and overlapping water penetration. There is also a third type of penetration caused by raw material defects, mainly including defects in oil paste performance and structural defects in reinforcement components.
Cable Core Water Penetration
Cable core water penetration mainly refers to the gaps between loose sleeves or filling units, as well as the gaps between loose sleeves or filling units and reinforcing components. During the production process, we will fill the cable core with grease and add water blocking strips on the outer layer of the cable core to ensure the water leakage of the cable core. However, cable core water leakage still occurs.
The water penetration between the loose casing and the filling unit, and the water penetration between the loose casing or the filling unit and the reinforcing component, first needs to control the outer diameter size of the loose casing and the filling unit, and try to minimize the water penetration caused by insufficient filling of the water blocking paste due to large structural gaps caused by size deviation. The intermittent water blocking paste filling between the reinforcing component and the loose casing can be filled in the cable forming process or in the sheath process. In the sheath process, the filling pressure of the water blocking paste needs to be increased. If the filling pressure of the water blocking paste is too small, it will not reach the center intermittent position, causing water penetration;Moreover, for the typical layer twisted fiber ribbon cable with 4 large and 4 small structures, filling the sheath with grease will generally result in incomplete filling and water leakage. So our company recommends filling water blocking oil during the cable forming process to ensure saturation.
Overlapping Water Penetration
Metal plastic composite with steel plastic and aluminum-plastic mainly plays a mechanical guarantee role while also being waterproof and moisture-proof. The peeling strength between metal tape and plastic film, the bonding strength between composite tape and sheath, etc. are all related to the water permeability of optical cables. From the actual production situation, the metal tape coating mold cannot fully achieve the expected effect. Therefore, how to control the water penetration at the edge of the metal tape is a concern for optical cable manufacturers.
The identification of water penetration at the overlap of the optical cable requires a water penetration test after production is completed. The factory generally uses a 1m optical cable for the water penetration test. Before the test, both ends of the optical cable need to be tested to ensure the test effect. If there is water penetration at the 1m optical cable, a 3m optical cable is used to repeat the test to determine the result. If there is water penetration, the location of the water penetration in the optical cable needs to be identified. For water penetration at the overlap, our company usually removes the protective layer of the overlap and opens the overlap to clearly distinguish the water penetration. Dyeing agents can also be added to the water.
Based on the analysis of the water penetration situation above, the water penetration at the overlap of the optical cable is the main cause. The main solutions to the water penetration at the overlap are as follows:
1. The appropriate ratio of oil paste mold and sizing mold is used to control the water penetration at the overlap. The ratio during the control process needs to be adjusted according to the actual size of the cable core. If the sizing mold does not change, if the oil paste mold is too small, it will prevent the oil paste from entering the overlap position, causing water penetration. If the oil paste mold is too large, it will cause the oil paste to overflow from the overlap position, resulting in the sheath being wrapped or small holes at the overlap. Moreover, in the actual production process, changes in the outer diameter of the cable core have a direct impact on the filling of the grease. So in the actual production process, the control ability of using this method is not very good ideal. 2. Fill hot melt adhesive at the overlap of metal strips, and the amount of hot melt adhesive is greatly affected by human control during the process of controlling the filling of hot melt adhesive. Insufficient filling of hot melt adhesive can result in insufficient filling degree and also cause water leakage during overlapping; Excessive filling of hot melt adhesive can cause the hot melt adhesive to overflow from the overlapping position. The overlapping area of the hot melt adhesive overflow will result in the sheath being wrapped or the overlapping area having small holes. The overflow to the overlapping area will cause the metal composite tape to adhere to the cable core or fail the drip test.
Raw Material Defects
The material issue of filling ointment
There is a problem with the material. There are two reasons for water penetration caused by quality issues with the oil paste. One is that the oil paste is too thin, resulting in less oil paste filling the cable and causing water penetration; Another reason is that the expansion speed of the ointment is slow, which can also cause water penetration.
Strengthen the structural defects of components
Water penetration in the steel wire cushion layer usually occurs in steel wire cushion layers with an extrusion thickness of more than 2mm. The main reason is that when the extrusion thickness is thick, there will be small gaps between the steel wire and the sheath material, causing water penetration. Main solution: Divide into two extrusions. If you want to extrude a 6.5m cushion layer, first extrude it to around 4.0mm, and then extrude it to 6.5m. Preheat the steel wire and reduce the extrusion production speed.
References
YD/T 901-2009 outdoor optical cable for twisted communication
YD/T 769-2010 Outdoor optical cable for central tubular communication
SHP, LHQ, The impact of water penetration on the lifespan of optical cables. Research on Optical Communication - 2007.1.
ZJJ, The evolution of the principle and solution of fiber optic cable water penetration. Network Telecommunications - 2008.10.