With the speeding up of urbanization in our country, urban rail transit development into the fast lane. Urban rail transit needs a large number of various USES of wire and cable, provides cable companies with huge business opportunities. Due to the urban rail transit are mostly used the subway, the subway space is relatively closed, puts forward higher requirements on fire safety, southern rainy and wet at the same time, the mouse and termites and other harmful organisms to the safe operation of wire and cable and other electrical facilities hidden trouble, so the urban rail transit with cable in addition to have common cable requirements, also must have a high environmental protection, low smoke, zero halogen flame retardant, waterproof, uv protection, rat character such as ants.

　　According to the use of the special environment of subway, this kind of cable should meet the requirements of GB/T12706-2008, is the product of rat, termite resistant, waterproof, as well as low smoke zero halogen, etc, are put forward special requirements. This kind of cable structure diagram is as follows:

　　Rail transit 35 kv low smoke zero halogen class A flame retardant cable manufacturing quality control points in the process has the following several aspects:

　　1, conductors twisted process: made of high quality light electrolytic copper, conductor compression coefficient is not less than 0.9. Conductor appearance is smooth, without burr. On the product structure, use high compression coefficient stranded conductors,

　　The roundness of the conductor surface can be improved to homogenize the electric field.

　　2, three-tier co-extrusion process: imported described.properties insulating and shielding materials, has a good and reliable insulation performance. Can be appropriately increased, shielding layer thickness to further improve the electric field distribution in the insulation eccentricity control within 5%, pay attention to cleanliness in the process of production, processing temperature and the control of the crosslinking degree. On craft, through strengthening the purification treatment, strictly control the processing temperature, extrusion filtering system, crosslinking temperature and pressure control, cooling the stress relaxation of improving cable bureau level.

　　3, metal mask: the copper wire and copper tape screen, can satisfy the demands of the subway short-circuit current.

　　4, lu: su composite armor layer process: using 0.3 mm aluminum-plastic composite belt, and ensure the overlapping width 6 mm above. Pay attention to the longitudinal package control of flatness and peel strength.

　　5, oxygen insulation layer: use data of high oxygen index, as part of the shell, which can effectively prevent external to internal flame spread.

　　6, rat fire armoured layer: the copper strip rat covering fire prevention structure and high flame retardant, further improve the flame retardant performance of cable as a whole.

　　7, low smoke zero halogen rat termite sheath layer: use environmentally friendly rat termite, new materials to meet at the same time, the performance of low smoke zero halogen flame retardant has high low smoke zero halogen flame retardant performance, meet the requirements of subway fire retardant class A. Due to low smoke zero halogen resistance fuel by adding aluminium hydroxide, magnesium hydroxide filling amount of inorganic material, hardening and strength increase, lead to aggregation object reduced elongation and softness, tear resistance and resistance to cracking down. Therefore should reduce the extrusion speed in the production, strictly control the extrusion temperature, prevent the degradation of metal hydroxide, screw using special low compression ratio at the same time, squeeze tube die extrusion, stretching ratio control within 2.0, prevent degumming and reduce stress.