Graphite electrode is an important high temperature conductive data of electric furnace steelmaking.electric energy is input to the electric furnace through graphite electrode, and the high temperature of arc between electrode point and burden is used as heat source to melt the burden for steelmaking
graphite electrode With petroleum coke and asphalt coke as granule materials and coal asphalt as binder, it is a kind of high temperature resistant graphite conductive data made by kunpining, molding, roasting, graphitization and mechanical processing. Graphite electrode is an important high temperature conductive data of electric furnace steelmaking. electric energy is input to the electric furnace through graphite electrode, and the high temperature of arc between electrode point and burden is used as heat source to melt the burden for steelmaking. In 2000, about 1 million t of graphite electrodes were used in the world, and 250,000 t of graphite electrodes were used in China. The use of graphite electrode with excellent physical and chemical properties is also widely used in other industrial parts, to produce graphite electricity is the main type of carbon products industry has become an important part of the contemporary information industry.
A brief history: as early as 1810, Humphrey David (Sir Humphrey Davy) use charcoal is made of carbon electrode arc can occur after the power supply, opened up by using carbon materials as a broad vision, high temperature conductive electrode 1846 Tate (Stair) and Edward (Edwards) the use of coke powder and sugar blend extrusion forming, and calcined at high temperature to produce another kind of carbonaceous electrode, then the carbon electrode immersed in concentrated sugar water to increase its volume density, they obtained from the electrode of the patent right.
In 1877, C.F.Brush and w.H.Lawrence of Cleveland of the United States made a success of using calcined petroleum coke to develop carbon electrode with low ash content.
In 1899, O.G.Pritchard first reported how to make natural graphite electrodes from Ceylon natural graphite.
In 1896 H.Y.Gastner patented an artificial graphite electrode that used electricity to heat the carbon electrode directly to a high temperature, producing a better performance than the natural graphite electrode
Emery companies in the United States in 1897 (Carborundum Co.) the acheson (E.G.A cheson) in the production of silicon carbide resistance furnace produced the first batch of petroleum coke as the material of artificial graphite electrode, the product standard is 22 mm x 32 mmx380mm, the artificial graphite electrode was used in the electrochemical industry produce caustic soda, on the basis of the design of “acheson graphitization furnace, petroleum coke produced by the carbon electrode, and a few resistors (smelting Jin Jiao grain) constitute” resistance furnace core “, electricity after high temperature, The carbon electrode made of petroleum coke is graphitized at high temperature to obtain the artificial graphite electrode.
In the late 19th century, the Frenchman P.L.T.Heroult developed direct electric arc furnaces, which began to be used for smelting calcium carbide and ferroalloy production.
First used in steel making in 1899, electric arc furnaces required a certain number of heat-resistant conductive electrodes.Although Acheson Graphite Co., a company, sells electrodes that can be connected, around 1900, only small standard Graphite electrodes are produced.
In the early 20th century, the carbon electrode made from anthracite or natural graphite electrode made from natural graphite was mainly used in electric steelmaking.The process of producing carbon electrodes or natural graphite electrodes is relatively simple,
In 1910, carbon electrodes with diameters up to 610mm were supplied to the market.However, the excellent performance of graphite electrode and the continuous improvement of production technology, large quantities of large standard graphite electrode production and price continues to decline, electric steelmaking industry gradually converted to graphite electrode, using carbon electrode or natural graphite electrode gradually cut.
Since the 1960s, most electric arc furnaces have used graphite electrodes.
1914～1918The graphite electrode was made with a maximum diameter of only 356mm
In 1924, the graphite electrode with a diameter of 406mm was produced. In 1930, it was expanded to 457mm, and in 1937, it was increased to 508mm. Before long, the large standard graphite electrode with a diameter of 559mm, 610mm, 660mm, 711mm and 762mm was produced.
The world’s largest arc furnace used graphite electrodes with a diameter of 813mm in the 1980s.After the second world war, the raw material quality, equipment and production technology of graphite electrode were improved constantly. With the continuous improvement of input power of electric steelmaking, high power and ultra-high power graphite electrode was developed in the 1960s and 1970s.Because the quality of graphite electrode constant progress and improvement of electric furnace steelmaking process, electric furnace steel per ton of graphite electrode cost has been reduced from 6 to 8 kg in the 70 s to 80 s in 4 ~ 6 kg (general power electric furnace), using high power graphite electrode of large electric furnace electrodes each tonne of steel cost has been reduced to 2.5 kg, and ultra high power dc arc furnace (only 1 graphite electrode) each tonne of steel graphite electrode cost can be reduced to 1.5 kg.At the end of 1980s, the tonnage of most electric furnaces in the developed countries in the world has been improved to 80 ~ 200t, so many use of the diameter of 550 ~ 750mm high power or ultra-high power graphite electrode.
According to the different raw materials used and the different physical and chemical objectives of the finished products, graphite electrodes are divided into three varieties: general 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 is mainly used to supply arc steelmaking furnace as a conductive material. In the 1980s, the world’s electric steelmaking industry divided the arc steelmaking furnace into three categories according to the transformer input power of each ton of furnace capacity: general power electric furnace (RP furnace), high power electric furnace (HP furnace) and ultra-high power electric furnace (UHP furnace).The transformer input power of the furnace capacity per ton is generally about 300kW/t.The high power electric furnace is about 400kW/t;The input power of the electric furnace below 40t is 500 ~ 600kW/t, the input power of the electric furnace of 50 ~ 80t is 400 ~ 500kW/t, and the input power of the electric furnace above 100t is 350 ~ 450kW/t.
At the end of 1980s, many small and medium-sized general power electric furnaces under 50t were eliminated in economically developed countries, and most of the newly built electric furnaces were ultra-high power electric furnaces of 80-150t, and the input electric power was improved to 800kW/t. In the early 1990s, some ultra-high power electric furnaces were further improved to 1000-1200kw /t.The graphite electrodes used in high – and ultra-high – power furnaces operate under more demanding conditions because the current density through the electrodes increases significantly,
The following problems occurred:
(1) the temperature of electrode increases due to resistance heat and hot air flow, which increases the thermal expansion of electrode and joint, and the oxidation consumption of electrode also improves.
(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 improves correspondingly.
(3) it increases the electromagnetic force and causes violent oscillation. Under the violent oscillation, the probability of electrode breaking due to loose connection and tripping increases. Therefore, the physical and mechanical functions of high power and ultra-high power graphite electrode are necessary to be better than those of general power graphite electrode, such as low resistivity, large volume density, high mechanical strength, small thermal expansion coefficient, and good thermal shock resistance. Table 1 lists the general standard series and graphite electrode diameters for three different power arc furnaces in the late 1980s.In order to get used to steel mills and many of the development of high power and ultra-high power furnace needs, since the 1980s, the European and American, Japanese carbon plant mainly produces two kinds of quality standard graphite electrode, namely high power graphite electrode and ultra-high power graphite electrode, general power graphite electrode because of little market and very little production. The graphite electrode dc arc furnace is a new type of steel making equipment developed in the early 1980s. The initial dc arc furnace is transformed from the original communication arc furnace. Some use 3 graphite electrodes, some use 2 graphite electrodes.