Dec 07, 2020
Why does the high temperature resistance wire not short circuit
Electric resisitance wire is a functional alloy material that converts electrical energy into heat. Its maximum operating temperature can reach over 1,000 degrees Celsius. It is used to manufacture various electrical heating elements in the fields of metallurgy, construction, military industry, and home appliances. At present, electric heating alloy materials have become an important engineering alloy material and occupy an important position in the national economy.
Iron-chromium-aluminum and nickel-chromium electric heating alloys generally have strong oxidation resistance, but because the furnace contains various gases, such as air, carbon atmosphere, sulfur atmosphere, hydrogen, nitrogen atmosphere, etc., these gases affect the components under high temperature use. All have a certain impact. Although all kinds of electric heating alloys have been treated with anti-oxidation before leaving the factory, they will cause component damage to a certain extent during transportation, winding, and installation, which will reduce the service life and extend the service life. , The customer is required to perform pre-oxidation treatment before use. The method is to energize and heat the installed electric heating alloy components in dry air to 100-200 degrees below the allowable maximum use temperature of the alloy, and keep it for 5-10 hours. Slowly cool the furnace.
The resistance heating wire must have a suitable resistivity to achieve the purpose of heating. If the resistivity is too large or too small, you need a very short or very long, very thin or very thick heating wire, so that it is difficult to manufacture and use electric heaters of large and small power; the melting point should be relatively high, and it will not melt when it generates heat. When the temperature is high, the chemical stability is relatively high, and it cannot oxidize quickly and has a short life. Currently commonly used are: nickel-chromium wire, iron-chromium wire, pure nickel wire, constantan wire, kama wire, copper-nickel wire, stainless steel, new constantan, manganese copper, Monel, etc.
Some special electric heaters, such as electric blankets, require a large heat dissipation area and low unit power. If you use the usual nickel-chromium and iron-chromium-aluminum heating wires, you need an electric heating wire with a thin section, which is impossible to make. Therefore, the electric blanket is made of manganese-copper wire. The resistivity of the manganese-copper wire is much smaller than that of iron-chromium-aluminum, so that it has enough length.
When the voltage is constant, as the temperature increases, the resistance of the resistance wire will increase, and the power will decrease somewhat. When the heat and heat are in balance, the temperature is fixed. The power of the resistance wire is determined by the material, the thickness and length of the resistance wire. If it is the same material, the longer and thinner the resistance wire, the greater the resistance and the lower the power. The power of 220V/5A resistance wire is 1100W. When designing the product, it has been determined. The working temperature of the resistance wire is determined during the design of the electric heating product. For example, electric blankets have a designed working temperature of only tens of degrees.
The power of the electric resistance heating wire is selected according to the area and heat dissipation of the electric blanket. If the conditions of use are changed during use, such as folding the electric blanket to energize, the electric blanket will not dissipate smoothly, which will easily cause a fire.
Short circuit refers to the state where the current is infinite when the resistance approaches zero. The resistance heating wire has a larger resistance and a fixed melting point. The resistance can ensure that the heating circuit is not short-circuited, and if it reaches the melting point, it will open. The current when the heating wire reaches the melting point is called the fuse current, but the circuit inside the electric heater can ensure that the current is less than the fuse current, so the heating wire in the electric heater can work normally.
