Graphite electrodes carry the electricity that melts scrap iron and steel, and sometimes direct-reduced iron (DRI), in electric arc furnaces, which are the vast majority of steel furnaces. They are made from petroleum coke after it is mixed with coal tar pitch. They are then extruded and shaped, baked to carbonize the binder (pitch), and finally graphitized by heating it to temperatures approaching 3000 °C, at which the carbon atoms arrange into graphite. They can vary in size up to 3.5 m (11 ft) long and 75 cm (30 in) in diameter. An increasing proportion of global steel is made using electric arc furnaces, and the electric arc furnace itself is becoming more efficient, making more steel per tonne of electrode. An estimate based on USGS data indicates that graphite electrode consumption was 197,000 Tonnes in 2005.
Electrolytic aluminum smelting also uses graphitic carbon electrodes. On a much smaller scale, synthetic graphite electrodes are used in electrical discharge machining (EDM), commonly to make injection molds for plastics.
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Graphite Electrodes are used primarily in electric arc furnace steel manufacturing.
Graphite electrodes can provide high level of electrical conductivity and capability of sustaining the extremely high levels of generated heat. Graphite electrodes are also used in the refinement of steel and similar smelting processes.
Carbon-graphite electrodes are also used in gouging operations such as in the forming of bevel or groove, removing defects in casting or weldments by an arc or gas process. Arc gouging removes material by melting it with the heat of an arc struck between a carbon-graphite electrode and the base metal. Compressed air or nitrogen simultaneously blows the molten metal away.
Graphite electrodes are selected based on some of the following application:
- Furnace design
- Scrap requirement
- Charging practice
- Burner/Oxygen usage
- Water spray rings
- Fume control system
- Meltdown/Refine/Tap-to-Tap Time
- Power level
- Slag practice
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