Types of graphite electrodes

According to the different raw materials used and the differences in physical and chemical indicators of the finished products, graphite electrodes are divided into three varieties: ordinary power graphite electrodes (RP grade), high-power graphite electrodes (HP grade), and ultra-high power graphite electrodes (UHP grade).

This is because graphite electrodes are mainly used as conductive materials for electric arc steelmaking furnaces. In the 1980s, the international electric furnace steelmaking industry classified electric arc steelmaking furnaces into three categories based on the input power of transformers per ton of furnace capacity: ordinary power electric furnaces (RP furnaces), high-power electric furnaces (HP furnaces), and ultra-high power electric furnaces (UHP furnaces). The input power of a transformer with a capacity of 20 tons or more per ton of ordinary power electric furnace is generally around 300 kW/t; The high-power electric furnace has a capacity of around 400kW/t; Electric furnaces with an input power of 500-600kW/t below 40t, 400-500kW/t between 50-80t, and 350-450kW/t above 100t are referred to as ultra-high power electric furnaces. In the late 1980s, economically developed countries phased out a large number of small and medium-sized ordinary power electric furnaces with a capacity of less than 50 tons. Most of the newly built electric furnaces were ultra-high power large electric furnaces with a capacity of 80-150 tons, and the input power was increased to 800 kW/t. In the early 1990s, some ultra-high power electric furnaces were further increased to 1000-1200 kW/t. The graphite electrodes used in high-power and ultra high power electric furnaces operate under more stringent conditions. Due to the significant increase in current density passing through the electrodes, the following problems arise: (1) the electrode temperature increases due to resistance heat and hot air flow, resulting in an increase in thermal expansion of the electrodes and joints, as well as an increase in oxidation consumption of the electrodes. (2) The temperature difference between the center of the electrode and the outer circle of the electrode increases, and the thermal stress caused by the temperature difference also increases accordingly, making the electrode prone to cracking and surface peeling. (3) Increased electromagnetic force causes severe vibration, and under severe vibration, the probability of electrode breakage due to loose or disconnected connections increases. Therefore, the physical and mechanical properties of high-power and ultra high power graphite electrodes must be superior to ordinary power graphite electrodes, such as lower resistivity, higher bulk density and mechanical strength, lower coefficient of thermal expansion, and good thermal shock resistance.