Precautions for Using Graphite Rods in High-Temperature Furnaces

Graphite rods are widely used in high-temperature furnaces due to their excellent high-temperature strength, which increases with temperature and surpasses that of all oxides and metals. Here are some important considerations when using graphite rods in high-temperature furnaces:

Current and Surface Temperature The larger the current applied to the graphite rod, the higher its surface temperature. It is recommended to use the smallest possible apparent load density (power). Note that the values recorded at the cold end of the graphite rod are the current and voltage at 1000°C in air, which correspond to actual applications. Generally, the surface power of the graphite rod is determined by the relationship between the furnace temperature and the surface temperature of the graphite rod. It is advisable to use surface power at 1/2 to 1/3 of the graphite rod’s limit density (w/cm²).

2.

Parallel Connection Graphite rods should be connected in parallel as much as possible. If the resistance values of the graphite rods differ, the load will concentrate on the rods with higher resistance when connected in series, causing a rapid increase in their resistance and shortening their lifespan.

3.

Oxidation Protection When heated in air, graphite rods form a dense silicon oxide film on their surface, creating an anti-oxidation protective layer that extends their lifespan. To prevent graphite rods from cracking, various coatings have been developed and applied to furnaces with different gases in recent years. These coatings help lubricate the graphite rods.

4.

Temperature Distribution The temperature distribution of graphite rods is critical. When newly installed, the reflectivity specifications within the effective length Δ should be within 60°C. However, as the rods age, the temperature distribution can increase up to 200°C. The detailed temperature distribution can also change due to variations in the furnace atmosphere and operational conditions.

5.

Resistance Increase When continuing to use graphite rods, it is advisable to gradually increase the resistance to maintain a longer lifespan.

6.

High Temperature Effects The higher the operating temperature, the shorter the lifespan of the graphite rods. When the furnace temperature exceeds 1400°C, the oxidation rate will accelerate, leading to a reduced lifespan. It is important to avoid excessively high surface temperatures during operation.

By following these precautions, you can optimize the performance and lifespan of graphite rods in high-temperature furnace applications.