Main factors affecting the life of SiC rod

① Service temperature

The higher the temperature is, the shorter the life is. Especially after the furnace temperature exceeds 1600 ℃, the oxidation speed is accelerated, and the service life of the silicon carbide rod is shortened. Therefore, please try not to let the surface temperature of the silicon carbide rod be too high, that is, it is necessary to reduce the difference between the furnace temperature and the temperature of the silicon carbide rod.

② Surface load

Surface load density refers to the rated power allowed to be carried by the unit surface area of the heating part of the rod.

Surface load density = rated power (W) / surface area of heating part (cm2)

It has been proved that the difference between the surface temperature of the heat generator and the furnace temperature is also large when the load density is large. When the load density is high, the surface temperature of the rod is high, the resistance increases fast, and the life of SiC rod is short. Therefore, the surface temperature, load density, furnace atmosphere and temperature of SiC rod are directly proportional to the aging speed of SiC rod and inversely proportional to the service life of SiC rod.

③ Furnace atmosphere

In the process of sintering, the reaction between the silicon carbide rod and many chemicals volatilized from the sintering materials will occur. If the silicon carbide rod contacts with water, hydrogen, nitrogen, sulfur, halogen and molten aluminum, alkali, salt, molten metal and metal oxide, the reaction, corrosion or oxidation will also occur.

④ Kiln operation mode

The service life of SiC rod is longer in continuous kiln and intermittent kiln. The surface of silicon carbide rod is oxidized to form silicon dioxide film in use. The long-term use of silicon dioxide film increases the resistance of silicon carbide rod. The abnormal expansion and contraction of silica film occurred near the critical point of crystallization (270 ℃). Because of the fluctuation of the temperature in the intermittent kiln, the silicon dioxide film is broken repeatedly to accelerate the oxidation. Therefore, when the furnace temperature drops to room temperature, the resistance often increases sharply.

⑤ Wiring method

If the resistance value of the silicon carbide rod is different, the load of the silicon carbide rod with high resistance in series is relatively concentrated, which is easy to cause the resistance of a certain silicon carbide rod to increase rapidly and the service life to become shorter. The silicon carbide rod is generally used in series and parallel connection. It is suggested to use two in series as a group and then multiple in parallel. Especially when the temperature in the furnace exceeds 1350 ℃, it must be connected in parallel. Open delta connection is recommended for three-phase connection.