graphite electrodes eaf
Brief history and varieties of graphite electrodes eaf development
Graphite electrodes eaf (graphite electrode) uses petroleum coke and pitch coke as granular materials, coal tar pitch as binder, and is made of high-temperature resistant graphite conductive material after kneading, molding, roasting, graphitization and mechanical processing . Graphite electrodes eaf is an important high-temperature conductive material for electric furnace steelmaking. Electric energy is input to the electric furnace through graphite electrodes eaf. The high temperature generated by the arc between the electrode end and the charge is used as the heat source to melt the charge for steelmaking. Other electric smelting or Electrolysis equipment also often uses graphite electrodes eaf as conductive materials. In 2000, the world consumed about 1 million tons of graphite electrodes eaf, and China consumed about 250,000 tons of graphite electrodes eaf in 2000. Utilizing the excellent physical and chemical properties of graphite electrodes eaf, it is also widely used in other industrial sectors. The carbon product industry, which mainly produces graphite electrodes eaf, has become an important part of the contemporary raw material industry.
As early as 1810, Humphry Davy used charcoal to make a carbon electrode that can generate an electric arc after being energized, opening up a broad prospect of using carbon material as a high-temperature conductive electrode. In 1846, Stair and Edwards mixed coke powder and sucrose, then pressed it into shape, and baked it at high temperature to make another kind of carbon electrode, and then immersed this kind of carbon electrode in concentrated sugar water to increase its bulk density. They obtained Granted the patent right to produce this electrode.
In 1877, C.F.Brush and W.H.Lawrence of Cleveland, USA, used calcined petroleum coke to develop a low-ash carbon electrode.
In 1899, O.G. Pritchard first reported a method of manufacturing natural graphite electrodes eaf using Ceylon natural graphite as a raw material. In 1896, H.Y.Gastner (H.Y.Gastner) obtained the patent right to use electricity to directly energize carbon electrodes to heat to a high temperature, and produce artificial graphite electrodes eaf with better performance than natural graphite electrodes eaf.
In 1897, EGAcheson of the American Carborundum Co. produced the first batch of artificial graphite electrodes eaf with petroleum coke as raw material in a resistance furnace for the production of emery. The product size is 22mm×32mmX380mm. Artificial graphite electrodes eaf was used in the electrochemical industry to produce caustic soda. The “Acheson” graphitization furnace designed on this basis will consist of carbon electrodes produced from petroleum coke and a small amount of resistance material (metallurgical coke particles) to form a “furnace core resistance” , The high temperature is generated after power on, so that the carbon electrode made of petroleum coke is “graphitized” at high temperature to obtain artificial graphite electrodes eaf.
At the end of the 19th century, the Frenchman P.L.T.Heroult invented the direct electric arc furnace and began to be used for the production of calcium carbide and ferroalloy. It was first used for steelmaking in 1899. The electric arc furnace required a certain number of high-temperature conductive electrodes. Although Acheson Graphite Co. sold connectable electrodes around 1900, only small-size graphite electrodes eaf could be produced at this time.
In the early 20th century, electric furnace steelmaking mainly used carbon electrodes made of anthracite or natural graphite electrodes eaf made of natural graphite. The process of producing carbon electrodes or natural graphite electrodes eaf is relatively simple,
Carbon electrodes with a diameter of 610mm have been supplied to the market in 1910. However, the excellent performance of the graphite electrodes eaf and the continuous improvement of the manufacturing process, the mass production of large-size graphite electrodes eaf and the declining prices, the electric furnace steelmaking industry gradually switched to the graphite electrodes eaf, the use of carbon electrodes or natural graphite electrodes eaf gradually reduce,
After the 1960s, most electric arc steelmaking furnaces use graphite electrodes eaf.
The maximum diameter of the graphite electrodes eaf made from 1914 to 1918 is only 356mm,
In 1924, it began to produce graphite electrodes eaf with a diameter of 406mm. In 1930, it was expanded to 457mm, and in 1937 it was increased to 508mm. Soon after, large-size graphite electrodes eaf with diameters of 559mm, 610mm, 660mm, 711mm, and 762mm were produced.
The graphite electrodes eaf used in the world’s largest electric arc steelmaking furnace in the 1980s was 813mm in diameter. After the Second World War, the quality of raw materials, equipment and manufacturing process for graphite electrodes eaf have been continuously improved. With the continuous increase in the input power of electric furnace steelmaking, high-power and ultra-high power were successfully developed in the 1960s and 1970s. graphite electrodes eaf.
Due to the continuous improvement of the quality of graphite electrodes eaf and the improvement of the electric furnace steelmaking process, the consumption of graphite electrodes eaf per ton of electric furnace steel has been reduced from 6～8kg in the 70s to 4～6kg (ordinary power electric furnaces) in the 1980s, using ultra-high power The graphite electrodes eaf’s large electric furnace has reduced the electrode consumption per ton of steel to about 2.5kg, and the ultra-high-power DC arc furnace (only 1 graphite electrodes eaf) can reduce the graphite electrodes eaf consumption per ton of steel to about 1.5kg. At the end of the 1980s, the tonnage of most electric furnaces in the electric furnace steelmaking industry in industrialized developed countries in the world has increased to 80-200t, so high-power or ultra-high-power graphite electrodes eaf with a diameter of 550-750mm are used in large quantities.
According to the difference of the raw materials used and the physical and chemical indicators of the finished product, the graphite electrodes eaf are divided into three types: ordinary power graphite electrodes eaf (RP grade), high power graphite electrodes eaf (HP grade) and ultra-high power graphite electrodes eaf (UHP grade). Variety. This is because graphite electrodes eaf mainly power arc steelmaking furnaces as conductive materials. In the 1980s, the international electric furnace steelmaking industry divided arc steelmaking furnaces into three categories according to the transformer input power per ton of furnace capacity: ordinary power furnaces ( RP furnace), high-power electric furnace (HP furnace) and ultra-high-power electric furnace (UHP furnace). The transformer input power per ton of furnace capacity for ordinary power furnaces above 20t is generally about 300kW/t; high-power furnaces are about 400kW/t; the input power of electric furnaces below 40t is 500～600kW/t, and the input power of electric furnaces is 50～80t. Electric furnaces with an input power of 350-450kW/t above 100t and 400-500kW/t are called ultra-high-power electric furnaces.
By the end of the 1980s, economically developed countries eliminated a large number of small and medium-sized ordinary electric furnaces below 50t. Most of the newly built electric furnaces were ultra-high-power large electric furnaces of 80-150t, and the input electric power was increased to 800kW/t. In the early 1990s, Some ultra-high power electric furnaces have been further increased to 1000～1200kW/t. The graphite electrodes eaf used in high-power and ultra-high-power electric furnaces operate under more demanding conditions. Due to the significant increase in the current density through the electrodes,
As a result, the following problems occur: (1) The temperature of the electrode increases due to resistance heat and hot air flow, which increases the thermal expansion of the electrode and the joint, and at the same time increases the oxidation consumption of the electrode.
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 increases accordingly, and the electrode is prone to cracks and surface peeling.
(3) The electromagnetic force is increased, causing severe vibration. Under severe vibration, the probability of the electrode breaking due to loose connection and tripping increases. Therefore, the physical and mechanical properties of high-power and ultra-high-power graphite electrodes eaf must be better than ordinary power graphite electrodes eaf, such as low resistivity, high volume density, high mechanical strength, low thermal expansion coefficient, and good thermal shock resistance performance. Table 1 lists the universal standard series of three different power arc steelmaking furnaces in the late 1980s and the diameter of the graphite electrodes eaf used. In order to meet the needs of steelmaking plants for the large-scale development of high-power and ultra-high-power electric furnaces, since the 1980s, carbon plants in Europe, America and Japan have mainly produced two quality standard graphite electrodes eaf, namely high-power graphite electrodes eaf and ultra-high power graphite electrodes eaf , Ordinary power graphite electrodes eaf are rarely produced due to the limited market.
Graphite electrodes eaf for DC electric arc furnace The DC electric arc furnace is a new type of electric furnace steelmaking equipment developed in the early 1980s. The initial DC electric arc furnace was modified on the basis of the original AC electric arc furnace, and some used 3 graphite electrodes. eaf, some use 2 graphite electrodes eaf.