Working Mode Classification
According to the different ways of electric energy conversion, electric heating is usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating, and dielectric heating.
Resistance Heating Coil
Using the Joule effect of current to convert electrical energy into thermal energy to heat objects. It is usually divided into direct resistance heating and indirect resistance heating. In the former, the power supply voltage is directly applied to the object to be heated. When current flows, the object itself generates heat. Objects that can be directly resistance heated must be conductors but have high resistivity. Since heat is generated within the object itself, it is internal heating with high thermal efficiency. Indirect resistance heating requires special alloy materials or non-metallic materials to make heating elements, which generate heat and transfer it to the object through radiation, convection, and conduction. Since the object and the heating element are separate, the type of object is generally not limited, and operation is simple.
The materials used for heating elements in indirect resistance heating generally require high resistivity, low temperature coefficient of resistance, small deformation at high temperatures, and not easy to embrittle. Commonly used are metal materials such as iron-chromium-aluminum alloys and nickel-chromium alloys, and non-metallic materials such as silicon carbide and molybdenum disilicide. The maximum working temperature of metal heating elements can reach 1000~1500°C depending on the material; non-metallic heating elements can reach 1500~1700°C. The latter is easy to install and can be replaced in a hot furnace, but it requires a voltage regulating device during operation and has a shorter lifespan than alloy heating elements. It is generally used in high-temperature furnaces, places where the temperature exceeds the maximum working temperature allowed for metal heating elements, and some special occasions.
