What are the quality requirements of graphite electrode for DC arc furnace?

The graphite electrode used in DC arc furnace has no skin effect when the current passes through, and the current is evenly distributed on the current cross section. Compared with AC arc furnace, the current density through the electrode can be appropriately increased. For ultra-high power electric furnaces with the same input power, DC arc furnaces use only one electrode, and the diameter of the electrode is larger, such as 100t AC electric furnaces use electrodes with a diameter of 600mm, and 100t DC arc furnaces use electrodes with a diameter of 700mm, and larger DC arc furnaces even require electrodes with a diameter of 750-800mm. The current load is also getting higher and higher, so the following requirements are put forward for the quality of the graphite electrode:

(1) The positive rate of the electrode body and the joint should be smaller, such as the resistivity of the electrode body is reduced to about 5μΩ·m, and the resistivity of the joint is reduced to about 4μΩ·m. To reduce the resistivity of graphite electrode, in addition to selecting high-quality needle coke raw materials, the graphitization temperature should be increased accordingly.

(2) The linear expansion coefficient of the electrode body and the joint should be low, and the axial and radial linear expansion coefficient of the electrode body should maintain an appropriate proportional relationship with the corresponding thermal expansion coefficient of the joint according to the size of the passing current density.

(3) The thermal conductivity of the electrode should be high. The high thermal conductivity can make the heat transfer in the graphite electrode fast, and the radial temperature gradient is reduced, thus reducing the thermal stress.

(4) has sufficient mechanical strength, such as the bending strength of the electrode body reaches about 12MPa, and the strength of the joint is much higher than the electrode body, which should generally be about 1 times higher. For the joint, the tensile strength should be measured, and the rated torque should be applied after the electrode connection, so that the two ends of the electrode maintain a certain tight pressure.

(5) The porosity of the electrode should be low to reduce the oxidation consumption of the electrode surface.