Fire-resistant cables refer to cables that can maintain safe operation for a certain period of time under the condition of flame burning. my country’s national standard GB12666.6 (such as IEC331) divides the fire resistance test into two grades, A and B. The flame temperature of grade A is 950~1000℃, and the continuous fire supply time is 90min. The flame temperature of grade B is 750~800℃, and the continuous fire supply time is 90 minutes. min, during the entire test period, the sample should withstand the rated voltage value specified by the product.
Fire-resistant cables are widely used in high-rise buildings, underground railways, underground streets, large power stations, important industrial and mining enterprises and other places related to fire safety and fire-fighting and lifesaving, such as power supply lines and control lines of emergency facilities such as fire-fighting equipment and emergency guide lights.
At present, most fire-resistant wires and cables at home and abroad use magnesium oxide mineral insulated cables and mica tape-wound fire-resistant cables; among them, the structure of magnesium oxide mineral insulated cables is shown in the figure.
Magnesium oxide mineral insulated cable is a kind of fire-resistant cable with better performance. It is made of copper core, copper sheath, and magnesium oxide insulating material. It is called MI (minerl insulated cables) cable for short. The fire-resistant layer of the cable is completely composed of inorganic substances, while the refractory layer of ordinary fire-resistant cables is composed of inorganic substances and general organic substances. Therefore, the fire-resistant performance of MI cables is better than that of ordinary fire-resistant cables and will not cause corrosion due to combustion and decomposition. gas. MI cables have good fire-resistant properties and can work at a high temperature of 250°C for a long time. At the same time, they are also explosion-proof, strong corrosion resistance, large carrying capacity, radiation resistance, high mechanical strength, small size, light weight, long life, and smokeless specialty. However, the price is expensive, the process is complicated, and the construction is difficult. In oil irrigation areas, important wooden structure public buildings, high-temperature places and other occasions with high fire resistance requirements and acceptable economy, this kind of cable with good fire resistance can be used, but it can only be used for Low voltage fire resistant cables.
The fire-resistant cable wrapped with mica tape is repeatedly wound with multiple layers of mica tape outside the conductor to prevent the flame from burning, thereby prolonging the safe operation time and keeping the line unblocked for a certain period of time.
magnesium oxide
White amorphous powder. Odorless, tasteless and non-toxic. It has strong high and low temperature resistance (high temperature 2500 ℃, low temperature -270 ℃), corrosion resistance, insulation, good thermal conductivity and optical properties, colorless and transparent crystal, melting point 2852 ℃. Magnesium oxide has high fire-resistant and insulating properties, and has a high melting point. Used in the production of magnesium oxide mineral insulated fire-resistant cables.
Mica tape
Mica is a flaky inorganic mineral material, which is characterized by insulation, high temperature resistance, luster, stable physical and chemical properties, good heat insulation, elasticity, toughness and non-combustibility, and it is stripped into elastic properties of transparent sheets.
Mica tape is made of flake mica powder into mica paper, which is adhered to glass fiber cloth with adhesive.
The glass cloth pasted on one side of the mica paper is called “one-sided tape”, and the one pasted on both sides is called “double-sided tape”. During the manufacturing process, several structural layers are glued together, dried in an oven, wound up, and slit into tapes of different sizes.
Mica tape, also known as fire-resistant mica tape, is made by (mica tape machine). It is a kind of fire-resistant insulating material. According to its use, it can be divided into: mica tape for motors and mica tape for cables. According to the structure, it is divided into: double-sided belt, single-sided belt, three-in-one belt, double-film belt, single-film belt, etc. According to mica, it can be divided into: synthetic mica tape, phlogopite mica tape, and muscovite tape.
(1) Normal temperature performance: synthetic mica tape is the best, followed by muscovite tape, and phlogopite tape is poor.
(2) Insulation performance at high temperature: synthetic mica tape is the best, followed by phlogopite mica tape, and muscovite tape is poor.
(3) High temperature resistance performance: Synthetic mica tape, does not contain crystal water, melting point 1375 ° C, the best high temperature resistance, phlogopite releases crystal water above 800 ° C, followed by high temperature resistance, muscovite releases crystals at 600 ° C Water, poor high temperature resistance.
Ceramic refractory silicone rubber
Due to the limitations of the process conditions, the fire-resistant cable wrapped with mica tape often causes defects in the joints. After ablation, the mica tape becomes brittle and easy to fall off, resulting in poor fire-resistant effect. Insulation, it is easy to fall off when it is shaken, so it is difficult to ensure the safe and smooth communication of long-term communication and power in case of fire.
Magnesia mineral insulated fire-resistant cables need to import special equipment, the price is very expensive, and the capital investment is large; in addition, the outer sheath of this cable is all copper, so the cost of this product also makes this product expensive; plus This kind of cable has special requirements in the process of production, processing, transportation, line laying, installation and use, and it is difficult to popularize and use it on a large scale, especially in civil buildings.
Post time: Mar-16-2023