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Tuesday, 19 December 2017
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Graphite for steel production Print E-mail
Furnace linings made from carbon and graphite are applied for the production of primary iron.
Graphite electrodes and nipples (connecting pins) are applied for the production of steel.
Their production is similar to the graphite production. After the baking process (for carbon material) and/or the graphitization process (for graphite) the material is machined within well- defined tolerances on length and diameter. The nipples and sockets are threaded to assure optimal electrode- nipple joining.
• Steel is one of the most important and widely used products in the world. Currently, the steel industry is undergoing a process of change. As a result of ongoing technical and economic developments, the production and use of electric arc furnace (EAF) steel is, beneath the steel production in a blast furnace, becoming increasingly important, continuously gaining share of world-wide steel production over the past 30 years.
• For the manufacture of graphite electrodes for the use in the EAF selected coal-tar or petrol cokes are crushed, milled and sieved to sort it by the specific different particle size fractions. Depending on the end use different fractions are mixed together with a liquid coal tar pitch as a binder. This mix is extruded into a green product with the near final shape and dimension of the resulting electrode. This rods are baked to approx.. 800°C - 1000°C and according to the needs for the final quality of the electrode impregnated with an petroleum pitch and rebaked. Than the graphitization step follows where the material is graphitized by heating it up to 3000°C.

Requirements for graphite electrodes
1. Good electrical conductivity in order to withstand the high current density required by the metallurgical process
2. High thermal conductivity to minimize the temperature differences inside the electrodes when in use and, consequently, to reduce internal stresses
3. Low thermal expansion resulting in high thermal stress resistance
4. Strength at high temperatures to withstand the stresses when in use
5. Chemical inertness and non-wetting to glass and most metals

Material Parameter
Graphite electrode
(top performance 800mm)
Carbon electrode
(typical values)
Apparent density
1.69 – 1.75 g/cm3
1.6 – 1.7 g/ cm3
Flexural Strength
10 – 14 N/mm2
4 – 7 N/mm2
Spec. electric resistance
4.0 – 4.8 Ohm m10-622 – 36 Ohm m10-6
Coefficient of thermal expansion
0.3 – 0.6 10-6K-1
1.2 – 2.5 10-6K-1
 
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