Why does the high temperature heating wire not short circuit?

- Aug 26, 2019-

Electric heating wire is a kind of functional alloy material that converts electric energy into heat energy. Its maximum working temperature is over 1 thousand degrees Celsius, and it is used to manufacture various electric heating elements in the fields of metallurgy, construction, military industry and home appliances. At present, electrothermal alloy materials have become an important engineering alloy material, occupying an important position in the national economy.


Iron-chromium-aluminum and nickel-chromium electrothermal alloys generally have strong oxidation resistance, but because the furnace contains various gases, such as air, carbon atmosphere, sulfur atmosphere, hydrogen and nitrogen atmosphere, etc., these gases are used under high temperature conditions. It has certain influence. Although all kinds of electrothermal alloys are treated with anti-oxidation treatment before leaving the factory, they will cause damage to components to a certain extent in transportation, winding, installation, etc., and reduce service life, in order to prolong service life. The customer is required to carry out pre-oxidation treatment before use. The method is to heat the installed electrothermal alloy component in the dry air to a temperature below 100-200 degrees of the maximum allowable temperature of the alloy, and keep it for 5-10 hours. The furnace can be cooled slowly.


High temperature electric wire


The electric heating wire must have a suitable electrical resistivity to achieve the purpose of energizing and heating. If the resistivity is too small or too small, a short or very long, very thin or very thick heating wire is required, so that the electric heater of the size and power has difficulty in manufacturing and using; the melting point is relatively high, and the melting can be performed without heating. At higher temperatures, the chemical stability is relatively high, and it cannot be oxidized very quickly and has a short life. Currently commonly used are: nickel-chromium wire, iron-chromium wire, pure nickel wire, constantan wire, karma, copper-nickel wire, stainless steel, Xinkang copper, manganese copper, Munnar and so on.


Some special electric heaters, such as electric blankets, require a large heat dissipation area and a low unit power. If ordinary nickel-chromium and iron-chromium-aluminum electric heating wires are used, a heating wire with a positive cross section is required, which cannot be produced at all. Therefore, the electric blanket is made of manganese copper wire, and the resistivity of the manganese copper wire is much smaller than that of the iron chromium aluminum, so that there is sufficient 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 heat and heat are balanced, the temperature is fixed.


The power of the resistance wire is determined by the thickness of the material and the resistance wire and the length. If it is the same material, the longer and thinner the resistance wire, the larger the resistance and the smaller the power. 220V/5A resistance wire, the power is 1100W. When designing the product, it is already determined.


The operating temperature of the resistance wire is also determined when the electric heating product is designed. For example, electric blanket, the design working temperature is only a few tens of degrees, and the power of the heating wire is selected according to the area of the electric blanket and the heat dissipation. If the use conditions are changed during use, such as folding the electric blanket to power up, the electric blanket is not well cooled, which is easy to cause a fire.


Short circuit refers to a state in which the current is infinitely large when the resistance approaches zero. The heating wire has a large resistance and a fixed melting point. The resistance can ensure that the electric heating circuit is not short-circuited, and if the melting point is reached, the circuit is broken. The current when the heating wire reaches the melting point is called the fusing current, but the circuit inside the electric heater can ensure that the current is less than the fusing current, so the electric heating wire in the electric heater can work normally.