It refers to the heating element of the electric furnace made of graphite material. Graphite has excellent electrical and thermal conductivity, and is commonly used as a heating element in special industrial furnaces such as electric furnaces.
●In the early stage of industrial electric furnaces, graphite electrodes were used as heating elements, and later, high-density high-power electrodes were used as heating elements.
●In the development of semiconductor industry, the heating furnace for refining single crystal silicon, single crystal germanium, gallium arsenide, phosphorous indium and other materials selects high-purity fine-structure graphite and isotropic graphite as heating element.
● Some special industrial roads and test furnaces use carbon cloth or graphite cloth as heating element.
●The oxidation speed and volatilization speed of graphite affect the service life of the heating element. When the vacuum degree is 10~10 mmHg, the operating temperature should be below 2300℃. In the protective atmosphere (through H2, N2, Ar, etc.), the operating temperature can reach 3000 ℃. Graphite cannot be used in air, otherwise it will be consumed by oxidation. It reacts strongly with W above 1400°C to form carbides.
●The thermal expansion coefficient of graphite is small, and the dimension is stable when the temperature increases, which is one of the important characteristics in the structural design of the heating element.
●The mechanical strength of graphite is below 2500℃ and increases with the increase of temperature. When the temperature exceeds 2500℃, the strength decreases rapidly.
●The thermal conductivity of graphite decreases with the increase of temperature. When the furnace is running at high temperature and the wall thickness of the heating element is large, the temperature difference between the surface and the center of the heating element is large, resulting in a large thermal stress.
●Although the resistivity of graphite is large, in order to improve the strength of the heating element, the side wall should have a certain thickness. Therefore, the total resistance of the heating element is very low and varies with different batches of materials. A low-voltage, high-current transformer is required. Graphite has high mechanical strength, high thermal conductivity and small thermal expansion coefficient. Therefore, it has good thermal shock resistance and can reduce the occurrence of cracks at high temperature.
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