Industry experts talk about how to improve the pass rate of cable fire resistance tests

Because fire-resistant cables are now used more and more extensively, many manufacturers are producing, but often the quality is not guaranteed
.
Therefore, in general, when enterprises develop fire-resistant cable products, they are first trial-produced a section of products, sent to the relevant national testing agencies, after obtaining the test report, they will be produced in batches, and a small number of cable manufacturers have established their own fire resistance test testing room, as we know, the fire resistance test is for the production of cable process results of the test, the same process program, in different periods of the production of cable performance has a certain difference, for the production of fire-resistant cable enterprises if the fire resistant cable fire test pass rate of 99% , then fire-resistant cable has a 1% safety hazard risk, which is 100% danger for users, in response to these problems, industry experts on how to improve the fire resistant cable fire test pass rate, from raw materials, conductor selection, production process control and other aspects of the explanation:

1.
Mica with three kinds, synthetic mica, phlogopite, muscovite, their respective quality performance is synthetic mica is the best, muscovite is the worst, for small specifications of the cable must be selected synthetic mica tape for wrapping, mica tape layering can not be used, long-term storage of mica tape is easy to absorb moisture, so the temperature and humidity
of the surrounding environment must be considered when storing mica tape.

2.
When selecting mica tape wrapping equipment, it should adopt good stability performance, the wrapping angle is best in 300--400 wrapping, its mica tape winding is uniform and tight, all guide wheels and rods that touch with the equipment must be smooth, the line is neat, the tension is not easy to be too large, and the side plate and barrel of the winding tooling wheel are smooth and smooth
.

3.
For the circular core with axial symmetry, the mica tape is tight in all directions after wrapping, so the circular tight conductor should be used for the conductor structure of the fire-resistant cable
.
The reasons for this are as follows:

(1) Some users propose that the conductor is a bundle twisted soft structure conductor, which requires the company to communicate with the user from the reliability of the use of the cable to a circular tight conductor, soft structure bundle line, complex twisting is easy to cause mica belt damage, as a fire-resistant cable conductor is not desirable, but some manufacturers think that users need what kind of fire-resistant cable, manufacturers should meet user needs, I think users after all the details of the cable are not very clear, cables are closely related to human life, Therefore, cable manufacturers must clearly explain the relevant technical problems to users
.

(2) The sector conductor should not be used, because the sector conductor its mica band wrapping pressure is unevenly distributed, as shown in the figure, from the figure it can be seen that the pressure at the three sector corners of the sector core wrapped mica tape is the largest, because the mica is a sheet silicate polymer, its interlayer molecular attraction is far weaker than the bond force of the S1-0 covalent bond in the crystal.
The layers are easy to slide, relying on silicon bonding, but the bonding strength is also low, in the external force scraping, extrusion is easy to fall off, crack, especially when using a sector structure, the wrapped wire core through the guide wheel, distribution rod and cable to the edge of the side plate of the tooling wheel, and the post-process squeeze insulation into the mold core, are easy to scratch and bruise, resulting in a decline
in electrical properties.

In addition, from the cost point of view, the cross-sectional circumference of the sector conductor structure is greater than the cross-sectional circumference of the circular conductor, which increases the precious material mica belt, although the outer diameter of the circular structure cable increases.
The amount of PVC sheath material has increased, but compared with the total cost of product materials, circular structure cables are still economical
in terms of comprehensive cost.
Based on the above description, from the technical and economic analysis, the conductor of the fire-resistant power cable adopts a round structure as the best
.