Introduction of flame retardant cable types and related properties

Mar 13, 2020

Flame retardant cable refers to the cable whose flame spread is only within the limited range after the test sample is burned under the specified test conditions and the residual flame or ignition can extinguish itself within the limited time after the test fire source is removed. The basic feature is that it may be burnt out in case of fire, but it can prevent the spread of fire. Generally speaking, in case of a fire, the electric wire can limit the combustion within the local scope without spreading, so as to protect other equipment and avoid greater losses.
Flame retardant wire and cable product drawing
The types of flame-retardant wire and cable 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 wires and cables
The common flame-retardant wire and cable insulation and sheath materials are generally high polymer materials containing halogen (or modified by adding halogen flame retardant), the most commonly used is PVC materials. The common PVC resin has the characteristics of high electrical insulation, chemical resistance, wear resistance, excellent aging resistance, and low price, so it has become the most widely used cable material in China. However, when PVC is burned, it will release toxic and harmful gases such as hydrogen chloride, carbon monoxide, carbon dioxide, various aromatic hydrocarbons, chlorinated compounds and so on.
2. Low smoke flame retardant wire and cable
Aluminum hydroxide, magnesium hydroxide and other inorganic hydroxide flame retardants can be added to the insulation and sheath materials of low smoke flame retardant wires and cables. The flame-retardant principle is condensed phase flame-retardant principle: aluminum hydroxide and magnesium hydroxide decompose and release water when heated, while absorbing heat to reduce the actual temperature of insulation and sheath materials, and inhibit the decomposition of materials and release of combustible gases. The generated metal oxide is also a refractory material, covering the surface of the material can improve the ability of insulation and sheath to resist the flame, and play the purpose of isolating air and preventing combustion. The advantages of aluminum hydroxide and magnesium hydroxide as flame retardants are as follows: non-toxic, non-volatile, cheap, flame retardant, smoke. However, it has poor compatibility with the matrix resin, so it is necessary to add a large amount of flame retardants to achieve a certain level of flame retardancy. A large amount of addition is easy to lead to the reduction of the material’s molding processability and mechanical properties.
Antimony compounds can also be added to the low smoke flame retardant cable. Antimony compounds are not flame retardants, but flame retardant synergists. They are often used in combination with halides. At high temperature, antimony trioxide reacts with halides to form antimony trihalide or antimony halide. The flame retardant principle is gas-phase flame retardant principle: Antimony trihalide steam can stay in the combustion area for a long time, diluble combustible gas, high density of antimony trihalide steam, covering polymer The decomposition of antimony oxyhalide into endothermic reaction can effectively reduce the temperature and decomposition rate of the flame retardant material; the surface effect of liquid and solid antimony trihalide particles can reduce the flame energy; Antimony trihalide can promote the carbonization reaction of the condensed phase, relatively delay the thermal decomposition and oxidative decomposition of the materials that generate combustible gas, and the generated carbon layer can prevent the escape of combustible gas into the flame area, and protect the lower materials from damage.
3. Low smoke halogen-free flame-retardant wire and cable
The insulation and sheath materials of low smoke and halogen-free flame-retardant wires and cables are mostly thermoplastic elastomer materials, which do not contain halogens such as fluorine, chlorine, bromine and iodine. Heavy metal elements such as mercury, chromium, cadmium and lead, which pollute the environment greatly, are excluded in the manufacturing process. Polyamide is often used as the material. The flame retardant mechanism of the cable is interrupt exchange flame retardant mechanism. Interrupted exchange flame retardant is to take away part of the heat generated during the combustion of flame retardant materials, so that the materials can not maintain the thermal decomposition temperature, and thus can not continuously generate combustible gas, so the combustion is self extinguishing. For example, when the flame-retardant material is subjected to strong heat or combustion, it can melt, and when the molten material drips, most of the heat can be taken away, resulting in delayed combustion, and finally the combustion may be terminated. This kind of cable has very low corrosiveness to equipment and buildings after combustion, so it can reduce the economic loss to the maximum extent and has high safety performance. However, the dripping hot liquid drop can ignite other substances, which increases the risk of fire. Therefore, anti droplet should be considered when selecting flame retardant.
4. Fluoroplastic flame retardant wire and cable
Due to the special chemical structure of fluoroplastic flame-retardant wire and cable, it has flame retardancy. This material does not need to be modified or treated as flame retardant. It has the characteristics of high temperature resistance, oxidation resistance, nonflammability, high oxygen index, self extinguishing, etc. it is an ideal line for optical fiber communication cable. But the cost of this kind of flame-retardant wire and cable is more than the above three kinds of cables, so it has no price competitive advantage in the mass market, so it is only used in the national security engineering at present.

 
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