With the acceleration of urbanization in China, the development of urban rail transit has entered the fast lane. Urban rail transit requires a large number of wires and cables for various purposes, providing huge business opportunities for cable companies. Since most urban rail transit uses subways, the subway space is relatively closed, which places high requirements on fire safety. At the same time, rainy and humid areas in the south, harmful organisms such as rats and termites, pose greater risks to the safe operation of electrical facilities such as wires and cables. In addition to the requirements for ordinary cables, urban rail transit cables must also have the characteristics of environmental protection, low smoke and halogen-free, high flame retardant, waterproof, UV-proof, and rodent-resistant.

According to the special environment used by subways, in addition to meeting the requirements of GB / T12706-2008, these cables also have special requirements for anti-rat, anti-ant, waterproof, low-smoke and halogen-free products. The structure of this type of cable is as follows:

The quality control points of the 35kV low-smoke halogen-free Class A flame-retardant cable for rail transit are as follows:

1. Conductor twisting process: using high-quality bright electrolytic copper material, the conductor compression factor is not less than 0.9. The appearance of the conductor is smooth and burr-free. In the product structure, the conductor twisting adopts a high compression factor.

Can improve the roundness of the conductor surface to homogenize the electric field.

2, three-layer co-extrusion process: the use of imported insulation and shielding materials, XLPE has good and reliable insulation performance. The electric field distribution can be further improved by appropriately increasing the thickness of the inner shielding layer. The insulation eccentricity is controlled within 5%. During the production process, attention should be paid to the control of cleanliness, processing temperature and cross-linking degree. In terms of technology, by strengthening the purification treatment, strictly controlling the processing temperature, extrusion filtration system, cross-linking temperature and pressure control, cooling stress relaxation and other aspects to improve the level of cable partial discharge.

3. Metal shielding: Combined shielding with copper wire and copper tape to meet the short-circuit current requirements of the subway.

4. Aluminum-plastic comprehensive protective cover process: Use 0.3mm aluminum-plastic composite tape, and ensure that the overlapping width is more than 6mm. Pay attention to the control of the flatness and peel strength of the longitudinal package.

5. Oxygen barrier layer: It adopts high oxygen index material and has certain shell forming property, which can effectively prevent the external flame from spreading to the inside.

6. Rat-proof fireproof armoring layer: Copper tape rat-proof and high flame-retardant tape fireproof structure is adopted to further improve the overall flame-retardant performance of the cable.

7. Low-smoke and halogen-free rodent-proof and ant-proof sheath: adopting environmentally-friendly new rodent- and ants-resistant material, while satisfying the low-smoke and halogen-free flame-retardant performance, it has high halogen-free and low-smoke flame-retardant performance to meet the needs of the subway Flame retardant Class A requirements. Due to the addition of high loading inorganic materials such as aluminum hydroxide and magnesium hydroxide to the low-smoke halogen-free fuel, the polymer body is hardened and the strength is increased, the elongation and softness are reduced, the tear resistance and the crack resistance decline. Therefore, in the production, the extrusion speed should be reduced, and the extrusion temperature should be strictly controlled to prevent the degradation of metal hydroxides. At the same time, a special low compression ratio screw and an extruded tube die will be used to extrude. Reduce stress.