Flame-retardant cable refers to the cable that is burned under the specified test conditions. After the test fire source is removed, the flame spreads only within the limited range, and the residual flame or residual burn can be extinguished by itself within a limited time. The fundamental characteristic is that it may be burnt out in the event of a fire and cannot operate, but it can prevent the spread of fire. In layman's terms, in the event of a fire, the wires can be confined to a local extent without spreading, and other equipment can be saved to avoid further losses.
Flame-retardant wire and cable types can be divided into: ordinary flame-retardant wire and cable, low-smoke flame-retardant wire and cable, low-smoke halogen-free flame-retardant wire and cable, fluoroplastic flame-retardant wire and cable.
1. Ordinary flame retardant wire and cable
Ordinary flame-retardant wire and cable insulation and sheathing materials are generally made of halogen-containing (or modified with halogen-containing flame retardants) polymer materials, the most commonly used is polyvinyl chloride (PVC) materials. Ordinary PVC resin has high electrical insulation, chemical resistance, wear resistance, aging resistance, and low price. It has become the most used cable material in China, but it releases hydrogen chloride when it burns. , toxic and harmful gases such as carbon monoxide, carbon dioxide, various aromatic hydrocarbons, and chlorine-containing compounds.
2. Low smoke type flame retardant wire and cable
Low-smoke type flame-retardant wire and cable can be added with inorganic hydroxide flame retardant such as aluminum hydroxide or magnesium hydroxide in the insulation and sheath material. The flame retardant principle is the principle of condensed phase flame retardant: aluminum hydroxide and magnesium hydroxide are thermally decomposed to release moisture, while absorbing heat reduces the actual temperature of the insulation and sheath material, inhibits the decomposition of the material and releases the combustible gas. The resulting metal oxide is a refractory material, and covering the surface of the material can improve the ability of the insulation and the sheath to resist the flame, and the purpose of isolating the air from combustion. The advantages of aluminum hydroxide and magnesium hydroxide as flame retardants are as follows: non-toxic, non-volatile, inexpensive, flame retardant, and smoke-free. However, it has poor compatibility with the matrix resin. When it is used as a flame retardant, it must be added in a large amount to achieve a certain flame retardant level. A large amount of addition may easily lead to a decrease in material formability and mechanical properties.
Low-smoke flame-retardant cables can also incorporate lanthanide compounds into the material. The lanthanide compound itself is not a flame retardant, but a flame retardant synergist. It is often used in combination with a halide. At high temperature, antimony trioxide reacts with a halide to form lanthanum trihalide or lanthanum oxyhalide. The flame retardant principle is The principle of gas phase flame retardation: the trihalide bismuth vapor can stay in the combustion zone for a long time, and can dilute the flammable gas. The trihalogenated ruthenium has a high vapor density and covers the surface of the polymer, which can play the role of heat insulation and oxygen barrier. The combustion of the material is very effective; the decomposition of bismuth oxyhalide is an endothermic reaction, which can effectively reduce the temperature and decomposition rate of the flame retardant material; the surface effect of the liquid and solid lanthanum trihalide particles can reduce the flame energy; the antimony trihalide can Promoting the char formation reaction of the condensed phase, relatively retarding the thermal decomposition and oxidative decomposition of the flammable gas-generating material, and the formed carbon layer prevents the combustible gas from entering the flame zone and protecting the underlying material from damage.
3. Low-smoke halogen-free flame-retardant wire and cable
The insulation and sheathing materials of low-smoke and halogen-free flame-retardant wire and cable are mostly thermoplastic elastomer materials. The materials do not contain halogen elements such as chlorobromobromoiodine, etc., and mercury, chromium, cadmium and lead are excluded in the production process. Heavy metal elements with large pollution in the environment, often used as polyamide. The flame retardant mechanism of this cable is to interrupt the exchange of flame retardant mechanism. Interrupted exchange of flame retardant means that part of the heat generated when the flame retardant material is burned away, so that the material cannot maintain the thermal decomposition temperature, and thus the combustible gas cannot be continuously generated, so that the combustion self-extinguishes. For example, when the flame retardant material is heated or burned, it can be melted, and when the molten material drops, most of the heat can be carried away, causing the combustion to be delayed, and finally the combustion may be terminated. These cables are extremely corrosive to equipment and buildings after combustion, thus minimizing economic losses and providing high safety. However, the dripping hot droplets can ignite other substances and increase the risk of fire. Therefore, anti-melt drops should be considered when using flame retardants.
4. Fluoroplastic flame retardant wire and cable
Fluoroplastic flame-retardant wire and cable is inherently flame retardant due to the special chemical structure of its materials. This kind of material does not need modification or flame retardant treatment, and has the characteristics of high temperature resistance, oxidation resistance, non-flammability, high oxygen index, self-extinguishing, etc. It is an ideal line for optical fiber communication cables. However, the cost of such flame-retardant wire and cable exceeds the above three types of cables, and there is no price competitive advantage in the mass market, so it is currently only used in national security projects.
The above is about the types of flame-retardant wire and cable in wire and cable.