Page 48 - Market Analysis Report of Optical Communications Field in China & Global market 2019

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the effects of different schemes on the flame-retardant standard of flame retardancy. The raw material of the
performance and air-blowing performance of the cable, sheathing layer needs to select low-smoke and halogen-
the optimal solution is determined, and finally it meets free with oxygen index ≥48%, and the dynamic friction
the requirements of air-blowing and CPR flame-retardant coefficient of the low-smoke halogen-free sheath material
performance. is <0.1 in order to ensure a certain air blowing distance of
the optical fiber cable.
2 Cable design
2.1 Cable structure design The hardness of the sheathing material also contributes to
The typical structure of the flame-retardant air-blowing the air blowing performance. The specific requirements
micro-cable is shown in Figure 1. The cable is composed of for the sheath of low-smoke halogen-free and filler rod
non-metallic strength member, gel-filling loose tube, water- materials are shown in Table 2 below.
blocking material, flame-retardant LSZH jacket. The semi-
dry structure design can make the cable easier to meet the Table 2.The specific requirements for the sheath of
flame retardant performance requirements. low-smoke halogen-free and filler rod materials

Fig.1. Typical structure of flame-retardant air-blowing
micro-cable

This paper designs three structural schemes and verifies the 3 Process control
routine performance, flame retardant performance and air 3.1 Second coating process
blowing performance of each, and finally selects the most Due to the small size and thin wall thickness of the air-
suitable scheme through comparative analysis. We divide blowing micro-tube, the fiber bundle has a small moving
the size of each component from small to large, in which space in the tube. Therefore, it is necessary to accurately
the loose tube size is divided into φ1 and φ2, the size of the control the PBT extrusion amount through the thin-wall
central strength member is divided into φ3 and φ4, the wall extrusion process method. At the same time, the gel pre-
thickness of the sheath is divided into φ5, φ6 and φ7 and coating process method is adopted to reduce the effect of
the outer diameter of the cable is divided into φ8 and φ9. the gel pressure on the fiber and keep the fiber in the proper
The specific test scheme is shown as follows: position of the tube to ensure good fiber transmission
performance. Of course, we also need to make a reasonable
Table1.Structural schemes of micro-cable selection of the process parameters such as the tension
of the secondary coating machine, the water temperature
of the water tank, and the number of tube turns on the
single wheel capstan, so as to obtain a suitable excess fiber
length. The anti-side pressure capability of the micro-
tube is relatively weak, and the excessive accumulation of
the tube on the take-up bobbin will make the fiber broken
easily, then the problem of poor fiber attenuation occurs.
Therefore, the pitch of the tube and the size of the bobbin
are proposed higher requirements. Unsuitable tube pitch
2.2 Filler rod and outer material selection or size of the bobbin will directly affect the quality of the
The flame retardant properties of the flame-retardant air- loose tube.
blowing micro-cable are achieved by improving the flame
retardant properties of the filler rod and the outer sheath. 3.2 Stranding process
The filler rod generally adopts a foamed filling rope, but The stranding process of the flame-retardant air-blowing
in order to improve the flame retardant performance of the micro-cable needs to focus on the tension of the yarn, the
optical cable, it is required to prepare a low-smoke halogen- tension of the tube, the tension of the strength member and
free sheathing material with its LOI≥38%. The sheathing the production speed. The tension of the yarn is controlled
material is critical to the flame retardant performance of between 1-3N. The tension of the tube is set to 1-1.5N with
the air-blowing micro-cable, which determines the highest precise control. The tension of the strength member and the
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