Little knowledge about terminal box plastic coating process

The small residual length of the communication fiber is the key to process control in the production process of the plastic coating process. The so-called residual length is: the difference between the optical fiber length and the loose sleeve length and the fraction of the loose sleeve length:

As for the way of generating the residual length in the production, this paper focuses on the control of temperature difference residual length, which is widely used at present. The following are the factors that affect the residual length:

① Pay-off tension. ② Loosening the traction tension and take-up tension of the casing, the smaller the tension, the PBT pipe is more likely to cool and shrink in the second tank, thus increasing the residual length. ③ Water temperature difference, the greater the temperature difference, the greater the residual growth. The number and diameter of the traction wheel will have a certain impact on the size of the residual length. ⑤ The faster the speed of the production line, the greater the residual growth. The viscosity of optical fiber ointment, the greater the viscosity under a certain shear force, the greater the residual growth. ⑦ Whether the needle configuration is reasonable or not is also crucial to the control of residual length. ⑧ Lay distance and speed of SZ.

Among the above eight factors, especially the water temperature difference has the greatest influence on the residual length. In actual production, the other seven factors are basically stabilized and the water temperature difference is adjusted to change the residual length. Considering that the bending radius of the optical fiber should not be too small, the gap between the inner diameter of the casing and the optical fiber should be reasonably designed. If the pipe diameter is small and the residual size is long, the bending radius of the fiber is too small, although there is a good stress-strain curve, it will affect the low temperature performance and the service life of the cable.

Since the control of the residual length is so important for the coating and even the entire cable, the accurate measurement of the residual length is very critical. The determination of the residual length value can not only guide the coating process, but also provide the basis for the structure of the cable and the production of the next process. The fiber residual length in the finished optical cable can be basically determined by the fiber tensile strain test, that is, the fiber residual length can be more accurately obtained by the difference between the cable strain and the fiber strain. However, it is more difficult to determine the remaining length of the plastic coating, because the ambient temperature during the plastic coating production is constant temperature, while the cable forming process is generally the natural temperature, and the temperature changes greatly, which makes the sleeve after the plastic coating into the cable when a temperature difference, and the production of the later process will have a certain force on the sleeve, so that the remaining length of the fiber has a certain change. The length of the fiber is not easy to measure directly, and the length difference with respect to the sleeve is more difficult to determine. At present, most optical cable manufacturers use the following measurement methods:

1. For the newly produced casing, place it at a room temperature of about 20℃ for about one hour until the casing is fully cooled.

2. Measure the casing 4 to 6m away from the outer end of the casing, and remove both ends with a blade.

3. Remove the optical fiber from the tube and measure its length.

4. Calculate the residual length according to the residual length formula. In the test, both the casing length and the fiber length must be precisely measured.

Residual length testing is very important for several reasons, the first is that the difference is very small and difficult to determine when cutting short casing measurements. In order to reduce the measurement error, the measurement length should generally be above 4m. The second is that when the casing is intercepted, the casing should be in a free state and not affected by external forces in the longitudinal direction. Both ends are cut quickly and simultaneously, the cutting knife should be perpendicular to the casing, and the knife edge should be sharp. If the cutting is not simultaneous and rapid, the residual length will change because the fiber is loose in the bushing. If the knife edge is not vertical, it will cause the casing bevel, and it is difficult to determine the length value. The knife edge is not sharp, which will make the casing section uneven. The third is the length measurement of casing and optical fiber. Since the casing we intercept is generally not straight, it must be straightened to measure.