Characteristics of low smoke halogen-free flame retardant cable

Author：hlyb Add Time：2016-03-03 15:54:24

Hazardous substance content requirements. At present, the so-called ordinary environmental protection wire and cable refers to the cable whose content of lead, cadmium, * * *, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ethers is within the range specified by EU ROHS. Moreover, wires and cables shall not contain environmental hormones and shall not pollute soil and water sources. Flame retardant performance: the flame retardant performance of environment-friendly flame retardant wires and cables is good. In case of flame and fire source, it can prevent the rapid spread and diffusion of flame, control it in a limited area and reduce the loss to * * * low. Advanced environmental protection flame retardant wire: refers to halogen-free environmental protection flame retardant wire, which does not fully meet the requirements of ordinary environmental protection flame retardant wire, and does not contain halogen, and will not produce harmful gas and corrosive gas after combustion. According to the requirements of environmental protection, flame retardant wires ensure that the gas released during combustion has the characteristics of low smoke, halogen-free and low toxicity without reducing the flame retardant grade. In case of fire, in order to ensure that all personnel have the opportunity to escape, the visual distance shall not be less than 15m. The visual distance when some environmental protection wires and cables burn and smoke can reach 97m, while the visual distance of general cables * * * is 5 ~ 8m. The cable insulation layer is usually burned by fire. The high-grade environmental protection conductor emits white smoke, mainly water vapor, and the amount of smoke is very small.

The temperature resistance grade is improved and the ampacity is increased. Generally, the temperature resistance grade of ordinary PVC conductor is 70 ℃, while that of environmental protection conductor is 105 ℃, 125 ℃, 150 ℃, which is 30 ℃ ~ 60 ℃ higher than that of ordinary cable. Through relevant tests, the current carrying capacity of environmental protection wires with the same specification section can be increased by more than 30% ~ 50% and the crosslinking degree can even reach more than 80%. Halogen free environment-friendly conductors are usually cross-linked products, * * * in recent years, the cable industry generally adopts the irradiation cross-linking process. Through the specific nuclear technology and high-energy electron irradiation processing, the molecular structure of polyolefin materials is changed from the original linear structure to network structure. This technology can improve the operating temperature of cables and the ability to resist instantaneous high current carrying capacity in case of short circuit, Greatly improve the temperature resistance grade. Although the cost of advanced environmental protection and flame retardant wires increases, considering the increase of current carrying capacity, the cost performance of advanced environmental protection and flame retardant wires is higher, that is, the cost price of advanced environmental protection and flame retardant wires is lower at the same current carrying capacity.

So, what is the development status of low smoke halogen-free flame retardant cables?

In the 1980s, the international community began to develop low smoke halogen-free flame retardant materials for wires and cables. The advantages of this material are low smoke and non-toxic. When it is burned by open fire, it will produce metal oxides and water vapor. Low smoke halogen-free flame retardant cable takes halogen-free polyolefin as the matrix, kneads a large amount of magnesium hydroxide or aluminum hydroxide activated by EVA (ethylene vinyl acetate copolymer) into polyethylene matrix, and uses hydroxide to decompose into metal oxide and water when burned and heated to achieve the purpose of flame retardant. The reaction formula is as follows:

Mg (OH) 2 → MgO + H2O endothermic

2Al (OH) 3 → Al2O3 + 3H2O endothermic

The low smoke halogen-free flame retardant cable is flame retardant by endothermic and metal oxide oxygen isolation methods. Its flame retardant mechanism: first, when the wire and cable are burned, the surface hydroxide decomposes. This reaction is an endothermic reaction, which absorbs a large amount of heat in the surrounding air and reduces the surface temperature of the wire and cable; Second, the generated water molecules also absorb a lot of heat on the surface of wires and cables, and the water vapor also isolates oxygen; Third, the metal oxide crusts produced prevent oxygen from contacting with organic matter again.

Developed countries have developed halogen-free low smoke cables in the 1980s, and strongly recommend the use of such harmless wires and cables to replace and gradually abandon the use of toxic PVC wires and cables. That is to say, the toxicity released by halogen-containing cables in the fire is very terrible. If the toxicity index of the gas concentration that can cause death in 30 minutes is determined as 1, the toxicity index of PVC is 15.01 and the toxicity index of halogen-free polyolefin is 0.79. People can only survive in the smoke of PVC for 2 minutes, but if halogen-free materials are replaced, people's survival in the smoke can be extended to 40 minutes, which greatly increases the escape time in case of fire. In addition, according to relevant materials, the light transmittance of smoke emitted by flame-retardant PVC cable during combustion is less than 15%, that is, in this concentration of smoke, the naked eye sight distance is about 2m. Therefore, in the fire, the strong smoke makes the victims dizzy and unable to distinguish the direction, prolonging the stay time in the fire, resulting in further inhalation of smoke and toxic gas and suffocation.

In a large number of tests, it is found that the smoke density and volatile amount of halogen acid gas released during combustion of materials with polyolefin as base material and hydrated metal compound Al (OH) 3 or Mg (OH) 3 as flame retardant can meet the requirements of IEC standard. Al (OH) 3 or Mg (OH) 2 is an inorganic hydroxide, which has excellent flame retardancy, low toxicity, smoke suppression and low corrosion. It has good smoke suppression, because smoke suppression and flame retardancy are equally important.

Developed countries have always attached great importance to the R & D and promotion of low smoke halogen-free flame retardant cables and related materials, especially in important buildings and facilities with relatively closed or concentrated personnel, such as high-rise buildings, subways, stations, airports, power stations and shopping malls. In recent years, developed countries have restricted the use of heavy metals such as lead and cadmium and bromide such as polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) in electrical and electronic equipment. Electronic and electrical giants in developed countries have formulated their own "green plans" to prohibit or restrict the use of heavy metals and halogens harmful to human body and the environment, and have carried out a lot of research and development work, Many series of "green" wires and cables for electronic appliances have been launched. Some countries, such as Switzerland and Germany, strongly oppose the application of PVC, and have formulated strict laws to restrict and eliminate the application of PVC.

The development and application of low smoke halogen-free flame retardant cables and related materials in China lags behind developed countries for about ten years. It was not until 2000 that we gradually got rid of the situation of complete dependence on imports. At present, the performance of domestic low smoke halogen-free flame retardant cables and related materials has met the relevant national and international standards, but people's awareness of environmental protection and safety still needs to be improved, and the products need to be vigorously promoted.

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Characteristics of low smoke halogen-free flame retardant cable