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1. The number of wrapping layers should generally be 50% for two layers or 5% for four layers.

2. Select the correct refractory mica tape and analyze it according to combustion performance. There are the following models. The double-sided synthetic mica tape has the best fire resistance (refractory temperature 1000). The key project recommends the use of single-sided synthetic mica tape with better fire resistance (refractory temperature 1000). The key project recommends the use of double-sided synthetic mica tape. The fire resistance is slightly better (refractory temperature 800) It is recommended to use single-sided phlogopite tape for general engineering. The fire resistance is slightly better (refractory temperature 800). General engineering is recommended to use single-sided phlogopite tape. Use mica tape, non-cable use, it is recommended not to use.

3. The wrapping process is also very important, you must be very careful and operate carefully. The production of refractory wire and cable itself is not complicated, but it is not easy to produce fully qualified products.In addition to the selection of mica tape, cable manufacturers' own winding production must be controlled well.

I will give you some information, I hope it will help you:

c) Wrap around refractory mica tape

In the production of refractory cables, the wrapping process is the most critical.The wrapping machine can be divided into two types: vertical machine and horizontal machine according to the structure.It can be divided into high-speed wrapping machine and low-speed wrapping machine according to the speed, but there are few cable production plants The special wrapping machine with mica tape is mostly made by using the existing paper wrapping machine to properly modify the wrapping head of the cable twisting machine. No matter what equipment is used, the operator is required to be careful and responsible. Under the guidance of technical personnel, the operator adjusts and masters the winding tension and winding angle according to the test results, and no tape breakage or leakage may occur, so that the surface of the insulated wire core after the winding is smooth and flat without mica falling off, and The joints must be handled carefully to prepare for the next process. It should be particularly pointed out that when winding small cross-section wires, the mica may easily fall off due to the small radius of curvature of the wrap. Even if the synthetic mica tape does not fall off, synthetic mica is more brittle than phlogopite and can easily cause mica fracture, so it is very easy to cause the fire resistance characteristics of the refractory cable to be unqualified. , Continuously explore experience, adjust and improve. The key process, wrapping, must be strictly controlled to greatly improve the pass rate of finished products. As long as we solve the problem of wrapping, several other processes have relatively little effect on the fire resistance. The conductor wrapped around the mica tape should be evenly wound on the spool. Care should be taken not to scratch the mica layer, especially the refractory cable with a larger cross section should avoid the event of scratching the mica layer due to the two conductors scratching each other.

d) The number of winding layers and overlapping rate of mica tape

For the wrapping of mica tape, it is difficult to give a certain amount of data on the number of layers of wrapping, and it is difficult to give a definite data. Generally, the manufacturer of mica tape will recommend 2 layers of wrapping. However, due to differences in material properties and model specifications of cable products, how much wrapping or lamination can pass the fire resistance test, and only the designer of the product can give a certain value based on the results of multiple tests. Of course, the more the number of wrap layers, the higher the pass rate of the product, and vice versa, but this not only wastes mica tape, but also makes the insulation of the cable and the outer diameter of the sheath increase, accordingly increasing the plastic quota and increasing the The manufacturing cost reduces the competitiveness of the product, so the number of winding layers should be determined according to the user's requirements, the structure of the cable, the complicated procedures, the withstand voltage level and the test conditions. At the same time, under a certain number of cladding layers, the overlap rate is also a very important indicator, which determines the actual number of cladding layers. If the lap pressure rate of the first layer is 50%, the actual number of cladding layers is 2; if the lap pressure rate is less than 50%, assuming the lap pressure rate is 25%, the actual cladding layer is 1.5 layers, that is, there are The place is 2 layers, and some places are 1 layer.It is obvious that the 1st layer is easy to break down; if the two-layer mica tape is wrapped and the overlap pressure is less than 50%, then there is a single layer around the inner and outer cladding. It may overlap together, which results in there are only two layers of mica tape, so it is easier to break down than the fourth layer. It is difficult to ensure that the overlap rate is exactly 50%. In actual use, due to bending and other reasons, the overlap rate will also be less than 50%. Therefore, in actual production, the optimal overlap rate should be controlled to be slightly greater than 50%.

e) Matters needing attention when wrapping mica tape

Because the conductor diameter of the small-section power cable is small, the width of the mica tape selected is relatively narrow. Under high temperature conditions, the insulation resistance of the mica tape drops sharply, and it is easy to flash (electric flashover) between the winding gaps. Too many times of flashover, causing the fast fuse to blow, but no breakdown point can be found when analyzing the cause.In this case, in addition to the appropriate increase in the number of cladding layers, as long as the production conditions allow, Use a wide range of mica tape as much as possible, while staggering the wrapping gap. The problems with refractory cables with large cross-sections are not great. As long as attention is paid to the manufacturing process, the mica tape will not be damaged, and the pass rate of the finished cable is high. Since the refractory mica tape is very easy to damage, it is important to note that the preservation of the refractory mica tape is as important as its use.The transfer and storage of the refractory mica tape during the winding process must prevent collision, scratch (scratch) and damage to the mica tape, and the finished semi-finished products Arrange the extrusion insulation as soon as possible to prevent moisture absorption. In the process of extrusion insulation, the radius of curvature of the guide wheel should be avoided to be too small. At the same time, the extrusion die should not scratch the mica layer.

4. General requirements for refractory mica tape

The refractory mica tape is an electrical insulation material made of glass fabric or plastic film and powder mica or synthetic mica, impregnated and bonded with high temperature resin glue. Its melting point is 1200 ~ 1300 ℃. In order to ensure that the cable can continue to run within a certain time after the fire. The selection of refractory mica tape should be based on the actual requirements. The actual requirements of the selected refractory mica tape should meet the requirements of the fire resistance characteristics of the refractory cable.

a) The production process of refractory mica tape shall comply with the International Electrotechnical Standard IEC 371-3- 8: 1995

b) The nominal thickness of refractory mica tape is from 0.05mm to 0.15mm mica tape.

c) Each roll of refractory mica tape from