Since fire-resistant cables are now used more and more widely, many manufacturers are producing them, but often the quality is not guaranteed. Therefore, under normal circumstances, when developing fire-resistant cable products, enterprises are first trial-produced a product, and sent to the relevant national testing institutions. After obtaining the test report, they will carry out batch production. A few cable manufacturers have established their own fire test. Room, we all know that the fire test is for the test of the production process results of the cable. The same process plan and the performance of the cable produced in different periods have certain differences. For the enterprises producing fire-resistant cables, if the fire-resistant test of the fire-resistant cable With a pass rate of 99%, there is a 1% safety hazard for the fire resistant cable, which is 100% dangerous for the user. Then how to improve the pass rate of fire-resistant cable fire test, from the raw material, conductor selection, production process control and other aspects to make a description:
1. Mica has three kinds of synthetic mica, phlogopite and muscovite. Their respective quality properties are the best for synthetic mica, and the muscovite is the worst. For small-sized cables, synthetic mica tape must be selected for wrapping, mica tape layering cannot be Use, 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 the mica tape.
2. When using mica tape wrapping equipment, the stability should be good. The wrapping angle is preferably 300--400. The mica tape wrapping is even and tight, and all the guide wheels and rods that touch the equipment must be smooth. The cable is neat, the tension is not too large, and the side plates and the cylinder of the wire-removing tool are smooth and smooth.
3. For the circular wire core with axial symmetry, the mica tape is tight in all directions after wrapping, so it is preferable to use a circular pressing conductor for the conductor structure of the fire resistant cable. The reasons are as follows:
①Some users have proposed that the conductor is a bundle of soft-structured conductors, which requires the enterprise to change from the reliability of the cable to the user to a circularly-pressed conductor, and the soft-structured bundle and the double-twisted are easy to cause damage to the mica tape. The conductor is not desirable, but some manufacturers believe that the user needs any kind of fire-resistant cable, the manufacturer should meet the user's needs, I think the user is not very clear about the details of the cable, the cable is closely related to human life. Therefore, cable manufacturers must make relevant technical issues clear to users.
②Fan-shaped conductors are also not suitable, because the winding pressure of the mica tape of the fan-shaped conductor is unevenly distributed. As shown in the figure, it can be seen from the figure that the pressure of the fan-shaped core wrapped mica belt at its three fan-shaped corners is the largest. Since mica is a sheet silicate polymer, its interlayer molecular attraction is much weaker than that of the s1-0 covalent bond in the crystal. The interlayer is easy to slide, bonded by silicon, but the bonding strength is low. When it is scraped and squeezed by external force, it is easy to fall off and crack. Especially when the fan-shaped structure is adopted, the core after winding passes through the guide wheel, the branching rod and the cable to the edge of the side plate of the tooling wheel, and the subsequent process. When the package is insulated and enters the core, it is easy to be scratched and bumped, resulting in a decrease in electrical performance. In addition, from the perspective of cost, the cross-sectional circumference of the fan-shaped conductor structure is larger than the circumference of the circular conductor, thereby increasing the precious material mica tape. Although the outer diameter of the circular structure cable is increased, the amount of the PVC sheathing material is increased, but the rounded structure cable is still saved in terms of the overall cost compared with the total cost of the product material. Based on the above description, from the technical and economic analysis, the conductor of the fire-resistant power cable is preferably a circular structure.
Yangzhou Fongming Cable Factory, a special cable expert around you.
