(1) Operating temperature
The higher the temperature of the silicon carbon rod, the shorter the life. Especially after the furnace temperature exceeds 1600 °C, the oxidation rate is accelerated, and the service life of the silicon carbon rod becomes shorter, so please try not to let the surface temperature of the silicon carbon rod be too high, that is, it is necessary to reduce the difference between the furnace temperature and the temperature of the silicon carbon rod.
(2) Surface load
Surface load density refers to the rated power per unit surface area of the heating section of the rod.
Surface load density = rated power (W) / heating section surface area (cm2)
Practice has proved that the difference between the surface temperature of the heating element and the furnace temperature is also large when the load density is large. If the load density is large, the surface temperature of the rod body is high, the resistance growth is fast, and the life of the SIC rod is short. Therefore, the surface temperature load density, furnace atmosphere, and temperature of silicon carbon rod are directly proportional to the aging speed of SIC rod and inversely proportional to the life of SIC rod.
Furnace temperature vs. surface load density
The usage range curve shown in the figure is the critical line of surface load density, in practice, please maintain 1/2-1/3 of the surface load of the critical line.
(3) Furnace atmosphere
In the firing process, the reaction between the silicon carbon rod and many chemicals volatilized by the firing material will occur, and if it comes into contact with gases such as water, hydrogen, nitrogen, sulfur, halogen, and molten aluminum, alkali, salt, molten metal, and metal oxide, reaction, corrosion or oxidation will also occur.
(4) Kiln operation mode
Silicon carbon rods have a longer life in continuous kilns and batch kilns. The silicon carbon rod is oxidized on the surface to form a silicon dioxide film during use, and the silicon dioxide film increases due to long-term use, and the resistance of the silicon carbon rod also increases. The silica film expands and contracts abnormally near the crystallization critical point (270 °C). Because intermittent use in the intermittent kiln always fluctuates up and down at this temperature, the silica film is repeatedly broken to accelerate oxidation. Therefore, when the temperature of the power failure furnace drops to room temperature, the resistance often increases sharply.
(5) Wiring method
If the resistance of silicon carbon rods is different, the load of silicon carbon rods with high resistance is concentrated in series, which can easily lead to a rapid increase in resistance and shorter life of a silicon carbon rod. Silicon carbon rods are generally used in series and parallel wires. It is recommended to use 2 roots in series as a group and then multiple groups in parallel. Especially when the temperature in the furnace exceeds 1350 °C, it must be connected in parallel. For three-phase wiring, it is recommended to use open delta wiring.