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1 Types of graphite electrodes
Electric arc steel furnaces are generally divided into three categories, namely ordinary power electric furnaces, high-power electric furnaces and ultra-high power electric furnaces. Corresponding to the power level of electric furnace steelmaking, the graphite electrode is also divided into three varieties, namely ordinary power graphite electrode (code RP grade), high power graphite electrode (code HP grade) and ultra high power graphite electrode (code UHP grade). ). The nominal diameter of the electrodes ranges from 75mm to 700mm. The physicochemical properties of high-power and ultra-high-power graphite electrodes are superior to those of ordinary power graphite electrodes, such as low resistivity, high bulk density and high mechanical strength, small coefficient of linear expansion, and excellent oxidation resistance. The physical properties of the three types of graphite electrodes are shown in Table 1.
2 Selection of graphite electrode for AC arc steelmaking furnace
The electrode diameter of the AC arc steelmaking furnace is shown in Table 2. For electric furnaces with different powers, graphite electrodes of the corresponding type should be selected. For high-power electric furnaces, high-power electrodes should be used. Different power electric furnaces have different diameters for graphite electrodes. It is generally considered that ordinary power electric furnaces select 75-500mm RP electrodes; high-power electric furnaces select HPO electrodes with diameters larger than 300mm; ultra-high-power electric furnaces select UHP electrodes with diameters larger than 400mm.
Table 2 AC arc steelmaking furnace with graphite electrode diameter
Capacity, t transformer capacity kVA with electrode
Ordinary power furnace high power furnace ultra high power furnace
3 Conical joint connection electrode should pay attention to the problem
The biggest advantage of the conical joint is that the longitudinal section of the hole wall of the electrode receiving portion is tapered, the outer wall is thin, the inner wall is thick, the overall strength is large, and it is not easy to burst, and the middle portion of the joint has a large diameter and is not easily broken.
The use of graphite electrodes should pay attention to the following items: (1) When selecting the electrode type and diameter, you should refer to the capacity of the electric furnace and the capacity of the transformer. (2) During the loading and unloading and transportation process, the graphite electrode should be handled gently, protect the thread and prevent damage. (3) The graphite electrode should be protected from moisture during transportation and storage, otherwise it must be dried before use. (4) Before connecting, the dust in the thread of the electrode joint hole should be blown off with compressed air, and then the joint and the electrode should be tightened. The tightening force should meet the requirements. In order to ensure that the different specifications of the electrode can reach the required tightening force when connecting, some electric furnace steel mills have specially built a tightening wrench, and the tightening plate has a sign indicating the tightening torque to ensure correct operation. The holder should be clamped below or above the bottom of the electrode joint. (5) The electrode lifting device of the electric furnace should be flexible in response, and should not be shaken during operation to prevent the electrode or joint from being loosened and tripped. (6) When loading the furnace, the bulk material should be placed in the lower part to prevent the collapsed material from breaking the electrode during melting. (7) During the refining period, the electrode cannot be immersed in molten steel to increase the carbon, thereby preventing the electrode from being thinned, causing the electrode to break or the joint to fall. (8) In order to prevent the electrode connector from loosening or tripping, it is recommended to use the connector pin.