History and Categories of Graphite Electrodes
Graphite electrode is a type of high-temperature resistant graphite electric conductive material made of petroleum coke and pitch coke as pellets, coal pitch as binder, by kneading, forming, calcining, graphitisation and machining. Graphite electrode is an important high-temperature conductive material for electric steelmaking...
In 2000, the world consumes graphite electrodes of about 1 million T, and China consumes about 250 thousand T graphite electrode in 2000. Graphite electrode is widely used in other industrial sectors because of its excellent physical and chemical properties. Carbon products industry, which mainly produces graphite electrode, has become an important part of the contemporary raw material industry.
As early as 1810, Humphry Davy used charcoal to make carbon electrodes that could produce arcs when electrified, opening up a broad prospect of using carbon materials as high-temperature conductive electrodes. In 1846, Stair and Edwards mixed coke powder and sucrose to form under pressure and baked at high temperatures to produce carbon electrodes. Another kind of carbon electrode, which was dipped in concentrated sugar water to increase its bulk density, was patented.
In 1877, C. F. Brush and W. H. Lawrence of Cleveland successfully developed low ash carbon electrode by calcined petroleum coke.
In 1899, O.G. Pritchard first reported the method of making natural graphite electrode from Ceylon natural graphite. In 1896, H.Y. Gastner patented the use of electricity to heat carbon electrodes directly to high temperatures to produce artificial graphite electrodes with better performance than natural graphite electrodes.
In 1897, E.G. Acheson of Carborundum Co. made the first batch of synthetic graphite electrodes using petroleum coke as raw material in a resistance furnace to produce diamond. The product specifications were 22 mm *32 mm X380 mm. The artificial graphite electrodes were then used in the electrochemical industry to produce caustic soda. On this basis, the "Acheson" was designed. The "Xun" graphitizing furnace will consist of a carbon electrode produced by petroleum coke and a small amount of resistance material (metallurgical coke particles) to form a "furnace core resistance". After being electrified, a high temperature will be generated, so that the carbon electrode made of Petroleum Coke will be "graphitized" at high temperature to obtain an artificial graphite electrode.
P.L.T. Heroult of France invented the direct electric arc furnace in the late 19th century and began to be used in the production of calcium carbide and ferroalloy. It was first used in steel making in 1899. The electric arc furnace needed a certain number of high-temperature conductive electrodes. Although Acheson Graphite Co. sold connectable electrodes around 1900, only small graphite electrodes could be produced.
In the early 20th century, carbon electrode with anthracite as raw material or natural graphite electrode with natural graphite as raw material were mainly used in EAF steelmaking. The process for producing carbon electrodes or natural graphite electrodes is relatively simple.
In 1910, the carbon electrode with diameter of 610mm has been supplied to the market. However, the excellent performance of graphite electrodes and the continuous improvement of manufacturing process, large-scale production of graphite electrodes and prices continue to decline, electric furnace steelmaking industry gradually changed to graphite electrodes, the use of carbon electrodes or natural graphite electrodes gradually decreased.
After 1960s, most of the electric arc furnaces used graphite electrodes.
The maximum diameter of graphite electrodes made in 1914~1918 years is only 356mm.
Graphite electrodes with a diameter of 406 mm were produced in 1924. In 1930, graphite electrodes with a diameter of 457 mm were expanded to 508 mm in 1937. Large-scale graphite electrodes with diameters of 559 mm, 610 mm, 660 mm, 711 mm and 762 mm were soon produced.
In 1980s, the graphite electrode diameter of 813mm was the largest arc furnace in the world. After the Second World War, the quality of raw materials, equipment and manufacturing process of graphite electrode were improved continuously. With the increasing demand of electric power input in electric furnace steelmaking, high power and ultra-high power graphite electrode were developed in the 1960s and 1970s.
Because of the continuous improvement of graphite electrode quality and the improvement of electric furnace steelmaking process, the consumption of graphite electrode per ton of electric furnace steel has been reduced from 6-8 kg in the 1970s to 4-6 kg in the 1980s (ordinary power electric furnace). The consumption of electrode per ton of steel in large electric furnace with ultra-high power graphite electrode has been reduced to about 2.5 kg and ultra-high power direct current has been used. The consumption of graphite electrode for each arc steel furnace (only 1 graphite electrodes) can be reduced to about 1.5kg. At the end of the 1980s, the tonnage of most electric furnaces in the steelmaking industry of the developed countries in the world has been increased to 80-200 t. Therefore, a large number of high-power or ultra-high-power graphite electrodes with diameters of 550-750 mm have been used.
According to the difference of raw materials and physical and chemical indexes of finished products, graphite electrode can be divided into three categories: ordinary power graphite electrode (RP grade), high power graphite electrode (HP grade) and ultra-high power graphite electrode (UHP grade). This is because the graphite electrode mainly supply arc furnace as conductive material. In the 1980s, the international EAF steelmaking industry classified EAF into three types according to the input power of transformer per ton of furnace capacity: ordinary power electric furnace (RP furnace), high power electric furnace (HP furnace) and ultra-high power electric furnace (UHP furnace). The input power of transformer per ton furnace capacity of ordinary power electric furnace above 20t is generally about 300 kW/t, that of high power electric furnace is about 400 kW/t, and that of 500-600 kW/t, 50-80t, 400-500 kW/t, and 350-450 kW/t is called ultra-high power electric furnace.
By the end of the 1980s, a large number of small and medium-sized ordinary electric furnaces with power below 50t were eliminated in developed countries. Most of the newly built ones were ultra-high-power and large-scale electric furnaces of 80-150t, and the input power was increased to 800kW/t. In the early 1990s, some of the ultra-high-power electric furnaces were further increased to 1000-1200kW/t. Graphite electrodes used in high and ultra-high power electric furnaces operate under more demanding conditions, due to the electrodes passing through them.