General electric wires and cables are insulated and she […]
General electric wires and cables are insulated and sheathed with plastic and rubber. These materials are all conventional materials, have abundant sources, can meet mass production, and the cost is relatively low. But for some special industries such as petrochemical, steel, aerospace, shipbuilding, military industry, pharmaceuticals, food, plastic machinery, boilers and other industries related to heat and high temperature, wires and cables that can withstand a certain higher temperature are required. Ordinary wires Obviously, cables cannot be used, and temperature-resistant wires and cables are required to ensure the safe operation of their power and signals.
With the rapid development of my country’s economy, the demand for high-temperature cables in special industries has shown rapid growth. Heat-resistant and high-temperature cables are growing at a rate of 20% every year. As an important part of special cables, high-temperature cables have strong vitality. In short supply, my country imports about 2 billion yuan from abroad every year for domestic construction.
Let's take a look at what kind of working temperature is called heat-resistant and high-temperature cable.
The wire and cable insulation and sheath we generally use are ordinary engineering rubber and plastic as the basic resin, but the requirement is insulation level. Common rubber materials for cables include: butadiene rubber, ethylene-propylene rubber, natural rubber and chlorosulfonated polyethylene, etc., and the working temperature is (60～75) ℃; common cable plastic materials include polyvinyl chloride, polyethylene (including The working temperature is (70～90)℃. It can be seen that these cables are not strictly heat-resistant or high-temperature cables.
Heat-resistant cables generally refer to cables at (90～155)℃ and below, while high-temperature cables are cables at 180℃ and above. To solve the problem that ordinary cables are not resistant to high temperatures, it is necessary to improve the materials, or use insulating materials that can withstand high temperatures.
2. Main features of heat-resistant and high-temperature wires and cables
Heat-resistant and high-temperature wires and cables are generally determined by two requirements. The first is the high ambient temperature of the wire and cable, and the cable can normally transmit signals or electric energy under high temperature for a long time; the other is the power transmission cable, which is mainly for increasing the interception capacity.
Cable working in high temperature environment. Ordinary cables are prone to insulation aging and scorching at high temperatures, and the use of cables loses performance, is damaged and cannot be used. The high temperature cable can work normally and stably under the rated high temperature, the signal or power transmission performance is not affected, and the cable has a long service life. This type of functional cable is the most common type of high-temperature cable, and its use characteristics are also the easiest to understand.
The load-increasing type high-temperature cable is mainly to reduce the outer diameter and weight of the cable under the prerequisite of current-carrying, and to develop towards light weight. Generally speaking, the higher the operating temperature of the cable, the greater the current carrying capacity of the cable of the same cross-section. For occasions like airplanes and automobiles, weight reduction is of great significance. The use of high-temperature cables greatly reduces the cross-section. When the operating temperature rises from 90°C to 155°C, the current-carrying capacity increases by 50%. At the same current-carrying capacity, the weight of the cable is reduced by half and the cost is also reduced. Of course, at the same time as high current interception, the power loss of most insulating materials will also increase.
Three, heat-resistant wire and cable
Heat-resistant wires and cables are divided into two types: heat-resistant materials and heat-resistant modification of common materials.
(1) Wire and cable made of heat-resistant materials
Heat-resistant wire and cable are insulated and sheathed materials. The body resin has heat-resistant properties. The main varieties are: polyurethane (up to 155°C), polyester (up to 135°C), polyvinylidene fluoride (150°C) ) And nylon (up to 115°C) insulation or sheath material. Commonly used in industries such as communications, automobiles, motors, and construction.
(2) Ordinary cable materials are modified in various ways to achieve heat resistance:
1. Heat-resistant modification of rubber materials
Due to its poor heat resistance, rubber materials have a small margin for increasing the working temperature. Ordinary rubber can only reach 90°C with more heat stabilizers and cross-linking treatment, so it cannot be called heat-resistant cables, such as styrene butadiene rubber, Neoprene rubber, chlorosulfonated polyethylene, etc. Mainly used in rubber-insulated mobile flexible wires, rubber-insulated flexible power cables and control cables.
However, EPDM rubber can be modified to increase the temperature resistance level to 135°C. In addition, it has better insulation properties, so it has a better development prospect in rubber.
2. Modification of PVC cable
The working temperature of ordinary PVC cable is 70℃. The high miscibility of PVC cable material makes it possible to modify it. The use of a large amount of heat stabilizer can facilitate the heat resistance of PVC from 70℃ to 90℃. ℃ or 105℃, which greatly expands the applicability of PVC, an old-fashioned material. Perhaps this is one of the reasons why PVC cables will last? For power, control and electrical equipment cables, due to the modification of PVC, the use of PVC cable materials that could be obsolete will continue for a long time in the sheath. The main component of polyvinyl chloride butyronitrile compound is PVC, so it has the same modified properties as polyvinyl chloride butyronitrile compound cables and PVC insulated cables.
3. Modification of polyethylene cable
The plasticity of polyethylene material is better, but its fillability is poor, so it cannot be filled with heating stabilizer to increase the heat resistance temperature. Polyethylene cables can be used for DCP dry chemical crosslinking and silane warm water crosslinking to increase the working temperature to 90℃. The former is used for medium and high voltage power cables and the latter is used for low voltage cables. But another cross-linking method—irradiation cross-linking modification can greatly increase the working temperature of polyolefin (mainly polyethylene). The irradiated insulating material can vary according to the conditions, and the temperature resistance can reach 105 ℃, 125℃, 135℃, 150℃, foreign countries can increase to 180℃. It is mainly through the conversion of high-energy electrons into stable bond energy to enhance the thermal stability of its molecular structure. At the same time, it is equipped with an appropriate thermal stabilizer. According to the energy level and the performance of the thermal stabilizer, it is divided into different heat resistance levels.
The commonly used processing equipment in the radiation cross-linking industry is an electron accelerator, which increases the energy of the electron beam at high pressure to achieve the purpose of cross-linking polyolefin materials. The energy level of the accelerator commonly used in electricity processing is 1.0 ~ 3MeV. Irradiation crosslinking can also crosslink materials such as rubber, PVC and fluoroplastics. Irradiation cross-linked polyolefin wires and cables are mainly used for heat-resistant building wires, automotive wires, aviation wires, locomotive wires and electrical and electrical lead wires.
A heat-resistant cable is a medium-temperature cable with a certain degree of heat resistance and can adapt to a certain temperature environment. The most widely used is that in power transmission cables, it is of great significance to increase the current-carrying capacity of the cable and reduce the weight and cross-section of the cable while ensuring the insulation performance.