Refractory cables refers to a cable that can maintain safe operation for a certain period of time in the case of flame burning. National standard GA 306.2-2007 classifies the fire resistance test into two grades, A and B. The flame temperature of Class A is 950~1000℃, and the continuous fire time is 90min. The flame temperature of Class B is 750~800℃, and the continuous fire time is 90 min. The whole test During this period, the sample shall withstand the rated voltage value specified by the product.
Fire-resistant cables are widely used in high-rise buildings, underground railways, underground streets, large power stations and important industrial and mining enterprises and other places related to fire safety and fire rescue. Therefore, their fire resistance performance has attracted much attention because even 1% of potential safety hazards exist for users It is 100% dangerous.
So how to improve the test pass rate of refractory cables? It should be analyzed from three aspects: raw materials, conductor structure and production process:
1. In terms of raw materials: the material of mica tape is divided into three types: synthetic mica, phlogopite and muscovite. Among them, the performance of synthetic mica is good, and the performance of muscovite is poor. For small-sized cables, synthetic mica tape must be selected for wrapping. It is worth noting that the mica tape stored for a long time is easy to absorb moisture, so the temperature and humidity of the surrounding environment must be considered when storing the mica tape.
2. Conductor structure: a round wire core with axial symmetry, the mica tape is tightly packed in all directions, so the conductor structure of the refractory cable should be a round compact conductor. Other users want to use bundled flexible conductors, but the soft structure bundles and double twisting can easily cause mica tape damage, so it is not desirable. The fan-shaped conductor is also not suitable for use, because the pressure distribution of the mica tape of the fan-shaped conductor is uneven, and the wrapped core passes through the guide wheel, the branch bar and the cable to the edge of the side plate of the tool wheel, and the insulation is squeezed into the back process When the mold core is used, it is easy to be scratched and bumped, which leads to a decrease in electrical performance.
In addition, from a cost perspective, the cross-sectional circumference of the sector-shaped conductor structure is larger than that of the circular conductor, adding valuable material mica tape. Although the outer diameter of the circular structure cable has increased, the amount of PVC sheath material has increased. But the overall cost of round structure fire-resistant cables is lower. Therefore, from a technical and economic point of view, the round structure of fire-resistant cable conductors is the best.
3. In terms of production process: when using mica tape wrapping equipment, the mica tape wrapping is even and tight. All the guide wheels and rods that touch the equipment must be smooth, the wiring is neat, and the tension should not be too large. And the cylinder is flat and smooth.
In summary, refractory cables are particular about raw materials, conductor structure and production technology, and manufacturers should strictly produce in accordance with specifications. When users choose fire-resistant cables, they can also analyze the performance of fire-resistant cables from the above angles.