Main performance of graphite heater
The service life of the heater is affected by the oxidation rate and volatilization rate of graphite. When the vacuum is 10–3–10–4 mm Hg column, the service temperature should be below 2300 C. When the atmosphere is protected (H2, N2, Ar, etc.), the temperature can reach 3000 degrees Celsius. Graphite can not be used in air, otherwise it will oxidize and consume. Carbides are strongly reacted with W at temperatures above 1400 C.
Graphite has a small thermal expansion coefficient and a stable size when the temperature rises, which is one of the important characteristics in the structure design of heater.
The mechanical strength of graphite below 2500 degrees Celsius increases with the increase of temperature. When the temperature exceeds 2500 degrees, the strength drops rapidly.
The thermal conductivity of graphite decreases with increasing temperature. When the furnace is in high temperature operation and the wall thickness of the heater is large, the temperature difference between the surface and the center of the heater is large, resulting in a large thermal stress.
Although the resistivity of graphite is large, the sidewall should have a certain thickness in order to improve the strength of the heating body. Therefore, the total resistance of the heating body is very low, and varies with different batches of material. Transformer with low voltage and high current 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 temperatures.
Optimal design of graphite heater
By comparing the simulation results of graphite heater before and after structural improvement, the following conclusions are drawn:
1. After improving the structure of graphite heater, the uniformity of temperature field in graphite tube is obviously improved.
2. After the structure of graphite heater was improved, the temperature of sintered products near the graphite cylinder door was greatly improved.
The temperature difference between the sintered products near the graphite rod cylinder door and other places is small, and the uniformity of the surface temperature of the sintered products is improved, which plays an important role in guaranteeing the quality of the sintered products.
3. Although the surface temperature of sintered products is still high outside and low inside after the structure of graphite heater is improved, the highest temperature area is no longer the top-middle sintered products, which plays an important role in increasing the surface temperature of sintered products near the furnace door area and greatly reduces the place where the heater is not arranged because of the furnace door. The influence on the surface temperature of the sintered product is improved.