With the development of the times, people have more and more strict requirements for environmental protection, and pay more and more attention to the problems of public places. Therefore, in modern high-rise buildings, subways, hospitals, colleges, shopping malls and other densely populated areas, such as emergency exit lighting, alarm systems and fire protection equipment, as well as ship and locomotive manufacturing, people require a more reliable and more reliable cable for energy transmission and measurement, which is different from ordinary PVC insulation -- low smoke halogen-free flame retardant and fire-resistant cable. The difference between LSZH flame retardant cable and fire-resistant cable is introduced by.
Low smoke halogen-free flame retardant and fire-resistant cable
The characteristics of low smoke halogen-free flame retardant cables and fire-resistant cables are to meet the requirements of people in electric energy transmission and measurement. Some multinational cable manufacturers, such as Alcatel (now renamed Nexant), have used newly developed raw materials to manufacture low smoke halogen-free flame retardant and fire-resistant cables more than ten years ago.
Compared with ordinary PVC insulated and sheathed cables, halogen-free cables are products that meet modern requirements. In case of fire, the smoke released when the cable is burned is non-toxic and corrosive, so the damage to human body and objects can be greatly reduced. At the same time, when halogen-free cables are in fire alarm, the amount and concentration of smoke released are very low, so people and firefighters can clearly find the source and outlet of the flame, and firefighters can quickly arrive at the fire scene to extinguish the fire.
In addition, in case of fire, the flame retardant components of flame retardant cable can play a role of flame retardancy, so that the cable will not become a channel for flame spread. At the same time, halogen-free flame-retardant cable can also adopt corresponding raw materials and structural design as required to make it have fire resistance. In case of fire alarm, such fire-resistant cable can still operate for a long time to provide electrical energy for rescue of personnel and equipment.
Main technical characteristics of low smoke halogen-free flame retardant cable and fire-resistant cable
1. Smoke dense polymer materials will produce some smoke more or less when burning. Smoke is a mixture of water vapor and gas as well as solid or liquid suspensions formed due to non combustion. The smoke density during cable combustion is evaluated by Ds (specific optical density at a given time) and Dm, which are used to measure the beam attenuation due to smoke accumulation under the test conditions of with optical method. Dm represents the total accumulation of smoke. The greater the Dm, the greater the smoke emission during combustion, and vice versa. When the cable is burned in a fire, the general PVC material will release high concentration and light tight smoke when burning. The reason is that the chlorine contained in PVC smoke will react with antimony in additives during combustion, resulting in non combustion and formation of antimony trichloride gas (the formation of this substance will greatly dilute the oxygen content in the air, thus suffocating the people in the fire), while releasing black smoke molecules (carbon molecules) that hinder light transmission. However, the above problems no longer exist in halogen-free cables.
2. When toxic and corrosive ordinary PVC cables are burned, chlorine and hydrogen in them will combine to release hydrogen chloride gas. When the cable is required not to produce excessive smoke and toxic substances, or its toxicity will not be enhanced when the temperature rises, PVC cable will be prohibited from use. While halogen-free cables use halogen-free polyolefin as the base material, which will not produce acid gas when burning, so its toxicity and corrosivity are much lower than ordinary PVC cables.
3. Flame retardant Although cables made of PVC and other halogen-containing materials have flame retardant properties, halogen-free flame retardant cables have become an inevitable choice in the modern society with increasingly high requirements due to their large smoke volume and toxic and corrosive gases. In halogen-free flame retardant, the flame retardant fillers mainly include aluminum or magnesium hydroxide filled in large quantities. This material can release crystal water when the cable is burned, absorb a lot of heat, thus inhibiting the rise of polymer temperature, delaying thermal decomposition, and reducing the burning speed. In addition, the water vapor generated by dehydration and decomposition can dilute the combustible gas, so as to have a flame retardant effect. Of course, excessive addition of combustible materials to organic matters will reduce the mechanical and electrical properties of materials. Therefore, how to make halogen-free materials not only have excellent flame retardancy, but also have good mechanical and electrical properties has once become a difficult problem to solve.
4. Fire resistance characteristics When the cable line can continue to play a role in the fire alarm, and when the cable inevitably needs to be erected on the line in the high-risk area, the cable has fire resistance performance. According to IEC331 standard, fire-resistant cables can operate for 90 minutes under 750 ℃. When the PVC cable burns, it will release corrosive and ionized gases that damage the mica edge sealing, creating a guiding environment. The halogen-free fire-resistant cables produced by a few cable manufacturers in the world that use halogen-free flame retardant materials and advanced fire-resistant structures have no such problem and can operate continuously for 3 hours at 1000 ℃.
