Graphite electrode application technology and selection in arc steelmaking furnace

01 Variety of graphite electrode

Electric arc steelmaking furnace is generally divided into three categories: regular power electric furnace, high power electric furnace and ultra-high power electric furnace. Corresponding to the power level of electric furnace steelmaking, graphite electrode is also divided into three varieties: regular power graphite electrode (RP level), high power graphite electrode (HP level) and ultra-high power graphite electrode (UHP level). The nominal diameter of the electrode ranges from 75mm to 700mm. The physical and chemical properties of HP and UHP graphite electrodes are better than RP graphite electrodes, such as low resistivity, high bulk density, high mechanical strength, low linear expansion coefficient, excellent oxidation resistance and so on. The physical properties of three kinds of graphite electrodes are shown in Table 1.

02 Selection of graphite electrode for AC arc steelmaking furnace
The electrode diameter of AC arc steelmaking furnace is shown in Table 2.  Different power electric furnace should be selected with the corresponding varieties of graphite electrode, such as high power electric furnace should be selected high power electrode. The diameter of graphite electrode is also different for different power electric furnaces. It is generally considered that RP electrode with diameter of 75 ~ 500mm is selected for RP electric furnace; HP electrode with diameter greater than 300mm shall be selected for HP electric furnace; UHP electrode with diameter greater than 400mm shall be selected for UHP electric furnace.

Table 2 Diameter of graphite electrode for AC arc steelmaking furnace

03 Problems needing attention in using conical nipple connecting electrode

The biggest advantage of the conical nipple is that the longitudinal section of the hole wall at the electrode hole is conical, the external wall is thin, the inner wall is thick, the overall strength is large, it is not easy to expand and crack, and the middle diameter of the nipple is large, so it is not easy to be broken.

The following precautions shall be taken for the use of graphite electrode:

• (1) When selecting electrode type and diameter, the capacity of electric furnace and equipped transformer should be referred to.

• (2) The graphite electrode shall be handled with care during loading, unloading and transportation, and the thread shall be protected to prevent damage.

• (3) Graphite electrode shall be protected from moisture during transportation and storage, otherwise it must be dried before use.

• (4) Before connection, the dust in the thread of electrode nipple hole must be blown off with compressed air, and then the nipple and electrode shall be tightened, and the tightening distance shall meet the requirements. In order to ensure that the required tightening force distance can be reached when connecting electrodes of different specifications, some electric furnace steel plants have specially manufactured a tightening wrench, which is marked with the size of tightening torque to ensure correct operation. The holder shall be clamped below or above the bottom of the electrode nipple hole.

• (5) The electrode lifting device of the electric furnace shall respond flexibly and shall not shake during operation to prevent breaking of the electrode or loosening and tripping of the nipple.

• (6) When charging into the furnace, large pieces of material shall be placed at the lower part to prevent material collapse from breaking the electrode during melting.

• (7) During the refining period, the electrode shall not be immersed in molten steel for carburization, so as to prevent the electrode from thinning, resulting in electrode breaking or nipple falling.

• (8) In order to prevent the electrode nipple from loosening and tripping, it is recommended to use the nipple pin, more graphite electrode news talk with us.