1. Select graphite rods with good uniform heating in the heating zone. Poor uniformity of heating will affect furnace temperature uniformity and shorten the rod's lifespan. During use, the uniformity of heating will gradually deteriorate, potentially leading to rod breakage in severe cases.
2. The lifespan of graphite rods decreases with increasing operating temperature, especially when the surface temperature exceeds 1500°C, as the oxidation rate accelerates and the lifespan shortens. During use, try to avoid excessively high surface temperatures of the graphite rods.
3. When heated in air, a dense silicon oxide film forms on the surface of the graphite rod, acting as an anti-oxidation protective layer and extending its lifespan. Intermittent use, with fluctuations in furnace temperature, can cause the protective film on the rod surface to crack, weakening the protective effect and accelerating the increase in the rod's resistance.
To ensure stable furnace temperature and meet the requirements of rapid heating, the supporting electrical control system should have sufficient voltage adjustment margin – that is, with new rods, the furnace design and operating power can be met at a lower voltage; as the usage time increases, the rod resistance increases, requiring a corresponding increase in voltage to meet the furnace design and operating power.
Voltage margin value: The voltage in the later stages of graphite rod use is generally 1.5-1.7 times the voltage used with new rods. Depending on the voltage regulation method and wiring method, the upper limit of the later stage voltage is generally calculated as 220V or 380V.
For adjusting the power of the graphite rods, it is recommended to adjust the power by adjusting the voltage. Thyristor voltage regulation or transformer voltage regulation is recommended for graphite rod voltage adjustment. Adjusting the power by changing the frequency is generally not recommended.
4. Generally, the surface load density of the graphite rod is determined by the relationship between the furnace temperature and the graphite rod surface temperature. It is recommended to use a power value of 1/2 to 1/3 of the maximum surface load density of the graphite rod. The greater the current applied to the graphite rod, the higher the surface temperature of the graphite rod. It is recommended to use the smallest possible surface load density (power).
Please note that the values recorded on the cold end of the graphite rod are the current and voltage measured in air at 1050℃ ± 50℃, and may not necessarily correspond to actual use.
5. When using graphite rods continuously, it is recommended to increase the voltage gradually to maintain a longer lifespan.
6. Graphite rods should be connected in parallel whenever possible. If the resistance values of the graphite rods differ, connecting them in series will concentrate the load on the rod with the highest resistance, leading to a rapid increase in resistance and a shorter lifespan for that rod.
Therefore, it is necessary to strengthen the matching of resistance values, ensuring that the resistance values of rods in the same group are as close as possible. Generally, the resistance value deviation of rods in the same group should be within 10%-15% for parallel connection, and within 5%-10% for series connection. The higher the furnace temperature, the smaller the required resistance value deviation should be.