How to choose the fiber optic cable casing material? Optical fiber ribbon casing size design, optical fiber ribbon can be divided into two types of structure, namely edge bonding type and overall coating type, the overall coating type structure is relatively thicker and wider than the edge bonding type structure. Considering the actual production and use of optical fiber ribbon cables, in order to improve the lateral pressure resistance and torsion resistance of optical fiber ribbons, domestic optical cable manufacturers currently choose to produce optical fiber ribbons with integral coating structures.
For the identification of the optical fiber in the optical fiber ribbon, it is generally recommended to select the full color spectrum to identify, so as to facilitate the on-site management of engineering connection and future optical fiber distribution. Optical fiber ribbons can be stacked to form an optical fiber ribbon matrix.
The inner diameter of the casing is usually approximated by the following formula
The equivalent size of the optical fiber ribbon matrix, where the width and height of the optical fiber ribbon matrix determine the length of the diagonal of the matrix, and its length is the basis for our design of the sleeve size.
The formula for casing inner diameter is as follows:
Among them, the value of K is related to the control of the production process. If the value of K is considered large, the space for the optical fiber stack to move in the sleeve will be large, and the quality of the optical fiber stack in the sleeve will be more guaranteed. If the diameter design is too large, the cost of the optical cable will increase significantly.
The inner diameter of the sleeve determined by the above formula is designed based on a completely ideal rectangular optical fiber stacked ribbon, but from the anatomical results of the actual optical fiber ribbon cable, the optical fiber stacked ribbon is rhombus in the sleeve, and there is a certain gap between each ribbon . Therefore, the model of the corrected fiber lapping should be the lapping under deformation.
Design of casing wall thickness
The design of the wall thickness of the casing needs to take into account the flattening resistance, torsion resistance and bending performance of the casing. The test results of these properties are related to the side pressure, bending and torsion that the casing needs to bear when passing the runner, stranding head, etc. during the processing. Industry standards have specified the corresponding test methods.
In order to facilitate the design, the relationship between the wall thickness of the casing and the lateral compressive strength and bending strength can be theoretically estimated by the structural strength factor and material strength factor of the casing. The structural strength factor of the casing is related to the inner space and wall thickness of the casing, while different materials have different material strength factors, and the material strength factor is linearly related to the compression modulus and bending modulus of the material.
Based on experience, the casing wall thickness is generally designed to be 5% to 10% of the casing diameter, and the casing wall thickness is generally controlled at 0.45 to 0.85mm in the actual production process. As long as the sleeve designed in this way can withstand a crushing force greater than 400N, it is relatively safe in the actual production process.
Therefore, according to the design of the inner diameter and wall thickness of the casing above, the outer diameter of the casing can be obtained.
Fiber Ribbon Sleeve Material Selection
The optical fiber ribbon casing needs to be filled with fiber paste. The filling of the fiber paste can ensure the change of the roundness of the inner diameter of the casing, and at the same time meet the water blocking requirements of the casing. Non-polar filling fiber paste is used for polar polymer casing materials, and polar filling fiber paste is used for non-polar polymer casing materials to ensure good compatibility between casing materials and filling fiber paste.
Currently, the commonly used optical fiber ribbon casing materials are modified polypropylene (PP) and polybutylene terephthalate (PBT).
The PP optical fiber ribbon casing material is generally a high-impact copolymerized non-polar polypropylene modified by adding a nucleating agent. During the crystallization and nucleation process of PP, the polymer segment forms more molecules by adsorbing PP molecules on the surface of the nucleating agent. , Thermodynamically stable micro-crystal nuclei; this micro-crystalline structure makes the crystallinity of the PP material greater, resulting in better impact resistance properties of the product. The quality of this kind of crystallization can be evaluated by measuring the after-shrinkage phenomenon of the sleeve after extrusion. The material with severe after-shrinkage phenomenon has a small proportion of crystallites, which corresponds to the impact resistance, tensile yield strength and compressive strength of the sleeve. Performance is poor.
PBT is a polar polyester polymer material, which is formed by polycondensation of terephthalic acid monomer with hard segment structure and 1,4-butanediol monomer with soft segment structure. The hard segment structure provides sufficient tensile strength and bending strength of the material, and the soft segment structure provides certain flexibility. Its crystallization process is very fast, which makes the sleeve have better surface gloss and dimensional stability, but crystallization at different cooling rates will form crystals with different densities and structures, resulting in changes in the mechanical properties and shrinkage characteristics of the sleeve.
