A Brief History and Varieties of Graphite Electrodes

Graphite electrode is a high-temperature resistant graphite conductive material made by using petroleum coke and asphalt coke as particle materials, coal tar pitch as binder, and undergoing processes such as kneading, forming, roasting, graphitization, and mechanical processing. Graphite electrode is an important high-temperature conductive material for electric furnace steelmaking. Electric energy is input to the electric furnace through graphite electrode, and the high temperature generated by the arc between the electrode end and the furnace charge is used as a heat source to melt the furnace charge for steelmaking. Other electric smelting or electrolysis equipment also often uses graphite electrode as a conductive material. In 2000, the world consumed around 1 million tons of graphite electrodes, while China consumed around 250000 tons of graphite electrodes. The excellent physical and chemical properties of graphite electrodes have been widely used in other industrial sectors, and the carbon product industry, which mainly produces graphite electrodes, has become an important component of the contemporary raw material industry.

brief history

As early as 1810, Hanfley? Humphry Davy used charcoal to make a carbon electrode that can generate an electric arc 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, pressed and molded it, and baked it at high temperature to produce another type of carbon electrode. They then immersed this carbon electrode in concentrated sugar water to increase its bulk density, and obtained the right to produce this type of electrode.

In 1877, C.F. Brush and W.H. Lawrence from Cleveland, USA successfully developed a low ash carbon electrode using calcined petroleum coke

In 1899, O.G. Pritchard first reported the method of manufacturing natural graphite electrodes using Ceylon natural graphite as raw material. In 1896, H.Y. Gastner obtained the right to use electricity to directly heat carbon electrodes to high temperatures and produce artificial graphite electrodes with better performance than natural graphite electrodes.

In 1897, E.G. Acheson of Carborundum Co. in the United States manufactured the first batch of artificial graphite electrodes using petroleum coke as raw material in a resistance furnace for producing diamond. The product specifications were 22mm × 32mm X380mm. This artificial graphite electrode was used in the electrochemical industry to produce caustic soda. Based on this, the "Acheson" graphitization furnace was designed to form a "core resistor" consisting of carbon electrodes produced from petroleum coke and a small amount of resistance material (metallurgical coke particles). After being powered on, high temperatures were generated, causing the carbon electrodes made from petroleum coke to "graphitize" at high temperatures and obtain artificial graphite electrodes.

At the end of the 19th century, P.L.T. Heroult, a Frenchman, invented the direct electric arc furnace, which was used to smelt calcium carbide and ferroalloy. In 1899, it was first used to make steel. The electric arc furnace needs a certain number of heat-resistant conductive electrodes. Although Acheson Graphite Co. sold connectable electrodes around 1900, they could only produce small-sized graphite electrodes at that time,

In the early 20th century, electric furnace steelmaking mainly used carbon electrodes made from smokeless coal or natural graphite electrodes made from natural graphite. The process of producing carbon electrodes or natural graphite electrodes is relatively simple,

In 1910, carbon electrodes with a diameter of 610mm were already supplied to the market. However, the excellent performance of graphite electrodes and the continuous improvement of manufacturing processes have led to the mass production and decreasing prices of large-sized graphite electrodes. The electric furnace steelmaking industry is gradually switching to graphite electrodes, and the use of carbon or natural graphite electrodes is gradually decreasing,

Since the 1960s, the vast majority of electric arc steelmaking furnaces have used graphite electrodes.

The maximum diameter of graphite electrodes made between 1914 and 1918 was only 356mm,

Production of graphite electrodes with a diameter of 406mm began in 1924, and by 1930 it had expanded to 457mm. In 1937, it had increased to 508mm, and soon after, large-sized graphite electrodes with diameters of 559mm, 610mm, 660mm, 711mm, and 762mm were produced.

In the 1980s, the world's largest electric arc steelmaking furnace used graphite electrodes with a diameter of 813mm. After World War II, the quality of raw materials, equipment, and manufacturing processes for producing graphite electrodes continued to improve. With the increasing demand for input power in electric furnace steelmaking, high-power and ultra high power graphite electrodes were successfully developed in the 1960s and 1970s.

Due to the continuous improvement of the quality of graphite electrodes and the improvement of electric furnace steelmaking technology, the consumption of graphite electrodes 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 furnaces). The electrode consumption per ton of steel in large electric furnaces using ultra-high power graphite electrodes has been reduced to about 2.5 kg, while the graphite electrode consumption per ton of steel in ultra-high power DC arc furnaces (using only one graphite electrode) can be reduced to about 1.5 kg. In the late 1980s, the tonnage of most electric furnaces in the steelmaking industry of industrialized countries had increased to 80-200 tons, so high-power or ultra high power graphite electrodes with diameters of 550-750mm were widely used.

variety

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 a significant increase in current density passing through the electrodes,

The following issues arise as a result: (1) The electrode temperature increases due to resistance heat and hot air flow, leading to an increase in the thermal expansion of both the electrode and the joint, as well as an increase in 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 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. Table 1 lists the universal standard series and graphite electrode diameters used for three different power electric arc steelmaking furnaces in the late 1980s. In order to meet the needs of the large-scale development of high-power and ultra high power electric furnaces in steel mills, carbon factories in Europe, America, and Japan have mainly produced two quality standards of graphite electrodes since the 1980s, namely high-power graphite electrodes and ultra high power graphite electrodes. Ordinary power graphite electrodes are rarely produced due to limited sales. DC arc furnace with graphite electrodes is a new type of electric furnace steelmaking equipment that developed and matured in the early 1980s. The initial DC arc furnace was modified based on the original AC arc furnace, with some using three graphite electrodes and others using two graphite electrodes.

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