Design requirements for new high temperature conductors
High-temperature resistant conductors can be used to transmit analog signals, electrical pulses, control currents, etc. in various types of transformers, transformers, and sensors. High-temperature coaxial cables that operate in closed electromagnetic field transmission can be used to transmit high-frequency signals at high temperatures. In general, high-frequency signals of higher power are transmitted. With the continuous development of technology, the requirements for the use temperature of high temperature resistant wires are getting higher and higher, and the wire size is getting smaller and smaller.
Material selection and structure of new high temperature resistant conductors
a. Reasonably choose the structure of the high temperature resistant wire to meet the requirements of wire use temperature, insulation resistance and mechanical properties. The principle of structural dimension determination is to enlarge the insulation outer diameter of the core wire as much as possible under the total outer diameter of the defined high temperature resistant wire to reduce the DC resistance of the high temperature wire.
b. Strengthen process control and take special and effective process measures to ensure the electrical performance and continuous manufacturing length of high temperature resistant wires.
The conductor base of the high temperature resistant wire is generally copper, and the surface thereof may be plated with a high temperature resistant metal plating. At high temperatures, the surface of the copper conductor increases with temperature and time, and the process of accelerating aging becomes more and more serious. The aging process eventually reduces the transmission capacity of the conductor, which is undesirable. When selecting a conductor material of a new high temperature resistant wire, it is necessary to consider not only that a large current must be transmitted, but also that a large current causes the wire to heat up. In order to avoid and delay this process, a relatively stable molecular metal such as silver or nickel may be plated on the surface of the copper conductor. In order to ensure the conductivity of the new high temperature resistant wire at high temperature, we used a soft copper wire with a diameter of 0.75 mm for nickel plating. The wire after nickel plating was overmolded with a wire drawing die with a hole diameter of 0.70 mm. In order to ensure that the core diameter is between (O.7O ± 0.02) mm. According to the relevant tests, the thickness of the nickel-plated layer of nickel-plated copper wire must be greater than 3 p. m, and the wire after overmolding is preferably no longer bent.
Because high silica glass fiber yarn (glass filament) has good insulation and excellent high temperature resistance, it is one of the preferred insulating materials for high temperature resistant wires. The temperature resistance grade of the high silica glass fiber yarn and its specification count are usually selected according to the specifications of the high temperature wire. The larger the count, the finer and softer the high silica glass fiber yarn, but its tensile strength is relatively poor. Conversely, the smaller the count, the thicker the high silica glass fiber yarn, and the greater the tensile strength. , but the softness is poor.
Ordinary high silica glass fiber insulation high temperature resistant wire can be used at around 400 °C, or in special high temperature (such as 800 °C instantaneous). However, if it is used in an excessively high temperature state for a long time, its electrical properties and mechanical properties will be destroyed, which will affect its normal use in severe cases. It can be seen from Table 1 that the new high temperature resistant wire has a small specification, a thin insulating layer, and needs to work at a temperature of 500 ° C or higher for a long time, and the insulation resistance must reach 50 MΩ (50 O V) at such a high temperature. High silica glass fiber yarns are difficult to meet these requirements through conventional processes. Although the domestic high-silica glass fiber yarn has been greatly improved in quality, some technical indicators have gradually stabilized, but the sample performance indicators provided by the manufacturer are unknown, and some are even blank. For example, a high-silicone glass fiber yarn (performance index shown in Table 2) produced by a professional manufacturer using ternary system glass manufacturing equipment has high mechanical strength and high temperature resistance. Long-term operation in 500 ° C environment; but when the temperature is about 400 ° C, its insulation performance is reduced due to the increase in temperature, when the temperature is 500 ° C, its insulation resistance is almost zero.
Obviously, the high-temperature wires made of this high-silica glass fiber yarn and the conventional process can only meet the mechanical performance requirements, and it is difficult to meet the requirements of the insulation performance. Through many practices, we used a high-temperature coating with high insulation properties and baked in high silica glass fiber yarns to achieve insulation resistance of 50 MΩ (500 V) at 500 °C. Requirements. Therefore, the high silica glass fiber yarn we choose must be able to withstand high temperatures of 500 ° C, can be easily coated with high temperature resistant coating, and the coated wire should be able to withstand the high temperature furnace drying of the wire surface and after Winding.