With the development of the times, people have more more strict requirements for environmental protection, pay more more attention to the safety of public places. Therefore, in modern high-rise buildings, subways, hospitals, colleges, shopping malls other crowded places, such as emergency exit lighting, alarm systems fire-fighting equipment, in the shipbuilding locomotive manufacturing industry, people require a more safe reliable, more environmentally friendly transmission power measurement cable, which is different ordinary PVC insulation - low smoke, halogen-free, flame-retardant fire-resistant cable.
1、 Characteristics of low smoke halogen-free flame-retardant cable fire-resistant cable
In order to meet people's requirements for safety environmental protection in power transmission measurement, some leading multinational cable manufacturers, such as Alcatel (now renamed nexen), have used the newly developed raw materials to manufacture low smoke, halogen-free, flame-retardant fire-resistant cables more than ten years ago. Compared with ordinary PVC insulated sheathed cable, halogen-free cable is an environmental protection product that meets the modern safety requirements. In case of fire, the smoke emitted the burning of cables is non-toxic corrosive, so the damage to human body objects can be greatly reduced. At the same time, the amount concentration of smoke released by halogen-free cable are very low in case of fire. The crowd firefighters can clearly find the source outlet of the fire, the firefighters can also quickly arrive at the scene of the fire to put out the fire. In addition, in case of fire, the flame-retardant components of the flame-retardant cable can play a role of flame-retardant, so that the cable will become a channel for flame spread.
At the same time, the halogen-free flame-retardant cable can also use the corresponding raw materials structural design according to the requirements to make it have the fire performance. In case of fire, the fire-resistant cable can continue to operate safely for a certain period of time, providing electric energy for the rescue of personnel equipment.
2、 Main technical characteristics of low smoke halogen-free flame-retardant cable fire-resistant cable
1. Smoke density
When polymer materials burn, some smoke will be produced more less. Smoke is a mixture of water vapor gas, as well as solid liquid suspension formed by incomplete combustion.
The smoke density of the cable during combustion is evaluated by DS (specific optical density at a given time) DM (maximum specific optical density). Under certain test conditions, with the help of optical method, it measures the beam attenuation caused by smoke accumulation. DM represents the total smoke accumulation. The higher DM is, the more smoke is emitted when burning, vice versa.
When the cable is burned in the fire, the PVC material will release very high concentration opaque smoke. The reason is that the chlorine contained in PVC smoke will react with antimony in additives during combustion, resulting in incomplete combustion the formation of antimony trichloride gas (the formation of the substance will greatly dilute the oxygen content in the air, thus suffocating the people in the fire), while releasing the black smoke molecules (carbon molecules) that hinder the light transmission. The above problems no longer exist in Halogen-free cables.
2. Toxicity corrosiveness
When the ordinary PVC cable burns, the chlorine hydrogen in it will combine to release hydrogen chloride gas. PVC cables will be used when they are required to produce excessive smoke toxic substances, when their toxicity will be enhanced when the temperature rises. However, halogen-free polyolefin is used as the base material for halogen-free cable, which will produce acid gas during combustion, so its toxicity corrosiveness are much lower than ordinary PVC cable.
3. Flame retardant
Although PVC other halogen-containing materials have certain flame-retardant properties, but due to their large smoke toxic corrosive gases, in the modern society, with higher higher requirements for safety environmental protection, halogen-free flame-retardant cable has become an inevitable choice.
In halogen-free flame retardant, the main flame retardant is a large number of filled aluminum magnesium hydroxide other flame retardant fillers. The substance can release crystal water absorb a lot of heat when the cable is burned, thus inhibiting the rise of polymer temperature, delaying thermal decomposition reducing combustion speed. In addition, the water vapor produced by dehydration decomposition can dilute the combustible gas, so as to achieve the flame retardant effect.
Of course, adding too much combustible materials to organic materials will greatly reduce the mechanical electrical properties of materials. Therefore, how to make halogen-free materials only have excellent flame-retardant performance, but also have better mechanical electrical properties has become a difficult problem. However, some foreign cable manufacturers, such as Alcatel / nexen, rely on their strong R & D capabilities to make it possible earlier. Their halogen-free products have already met the requirements of iec332 standards 20 years ago.
4. Fire resistance characteristics
When the cable line must be able to continue to play a role in case of fire, when the cable inevitably needs to be erected on the line in the high-risk area, the cable must have fire resistance performance.
According to the latest iec331 standard, the fire-resistant cable must be able to operate safely under 750 ℃ for 90 minutes. When the PVC cable burns, it will release corrosive ionic gas which will destroy the mica edge, resulting in a guiding environment. The halogen-free fire-resistant cable produced by a few world-famous cable manufacturers with halogen-free flame-retardant materials advanced fire-resistant structure has no such problem can operate safely for 3 hours under 1000 ℃.
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