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Different kinds of graphite electrodes

Release time:2019-11-04 From: Zhengnai Industry in China


Graphitization is a change in solid phase at high temperature. Based on the motion caused by thermal energy, the structure of carbon element microcrystalline transits from disorder to ordered state, which is the structural change of physical properties, mainly the growth of crystals and the orderly superposition of inner layers of crystals.
How to reduce power consumption under the premise of ensuring product quality is also an important task of the graphitization process.


Graphitization process

The graphitization process can be roughly divided into two stages. The first stage is carried out between 1000° C and 1800 ° C. At this stage, the graphitization of amorphous carbon does not start, in fact, the chemical reaction is mainly used; The stage is above 1800 °C and rises to 3000 °C. The temperature is 1800~2000 °C as the limit, and the heat treatment temperature is further increased. The difference between easily graphitized carbon and non-graphitizable carbon begins to become apparent.

Graphitization process is related to density

The density of petroleum coke is increased after calcination, but it is generally reduced after graphitization, with the exception of some bituminous coke, which is related to the increase of true density and volume change of coke during graphitization.

The lattice parameter can measure the degree of graphitization

The closer the lattice parameter of artificial graphite is to the lattice parameter of ideal graphite, the higher the degree of graphitization. When high-quality raw materials (such as needle coke) are used to increase the graphitization temperature, artificial graphite with a lattice parameter very close to ideal graphite can be obtained.


The graphite electrodes used are divided into three varieties.

According to the power level of electric furnace steelmaking, our company also divides the graphite electrodes used into three grades: regular power graphite electrode (codenamed RP grade), high power graphite electrode (codenamed HP grade) and ultra high power graphite electrode. (codenamed UHP grade). Among them, the current density of graphite electrodes used in high-power and ultra-high-power electric furnaces is significantly increased.

Different kinds of graphite electrodes

HP graphite electrode is superior to ordinary graphite electrodes
The physicochemical properties of high-power and ultra-high-power graphite electrodes must be superior to those of ordinary power graphite electrodes, such as lower resistivity, higher bulk density and higher mechanical strength, lower linear expansion coefficient, oxidation resistance and thermal shock resistance. Excellent to meet the requirements of high power or ultra high power electric furnace.

Index of UHP/HP/RP Graphite electrode

Item Unit UHP HP RP
300-600mm 650-800mm 300-800mm 300-800mm
Electric resistivity Electrode μΩm 4.8-5.8 4.6-5.8 5.8-6.6 7.8-8.8
Nipple 3.8-4.5 3.8-4.5 4.2-5.0 5.0-6.5
Flexural strength Electrode Mpa 10.0-14.0 10.0-14.0 10.0-13.0 7.0-12.0
Nipple 20.0-26.0 22.0-26.0 18.0-22.0 15.0-20.0
Elastic modulus Electrode Gpa 9.0-13.0 10.0-14.0 8.0-12.0 7.1-9.3
Nipple 15.0-18.0 15.0-18.0 14.0-16.0 12.0-14.0
Bulk density Electrode ≥g/cm3 1.68-1.74 1.70-1.74 1.62-1.66 1.53-1.56
Nipple 1.77-1.82 1.78-1.84 1.74-1.80 1.70-1.74
CTE(100-600℃) Electrode x10-6/℃ 1.1-1.4 1.1-1.4 1.6-1.9 2.2-2.6
Nipple 0.9-1.2 0.9-1.2 1.1-1.4 2.0-2.5
Ash   0.3 0.3 0.3 0.5


Characteristics of graphite electrode for DC arc furnace

The graphite electrode used in the DC arc furnace has no skin effect when the current passes, and the current is evenly distributed on the cross section of the electrode. Therefore, compared with the AC arc furnace, the current density through the electrode can be appropriately increased, and the same input power is super high. In the case of a power electric furnace, a DC furnace using only one graphite electrode has a larger electrode diameter and a higher current load, so the quality of the graphite electrode is more severe. When the resistivity is low, the power loss is small, and the resistivity of the finished product is lowered. In addition to selecting a high-quality raw material, the graphitization temperature must be increased accordingly.

The linear expansion coefficient of the electrode body and the joint is low.

The thermal conductivity of the electrode is high, and the high thermal conductivity enables the heat transfer in the graphite electrode body to be fast, the radial temperature gradient is reduced, and the thermal stress is lowered.

To have sufficient mechanical strength.

the porosity should be low in order to reduce the oxidation rate of the electrode surface.


Regular graphite electrode raw materials and properties

Regular power graphite electrode, produced by ordinary grade petroleum coke, has a low graphitization temperature, so its physical and chemical properties are poor, such as high resistivity, large linear expansion coefficient, poor thermal shock resistance, and less allowable current density.

High power graphite electrode raw materials and performance

High-power graphite electrodes are produced using high-quality petroleum coke (or low-grade needle coke), which has better physicochemical properties than ordinary power graphite electrodes, such as low resistivity, allowing for greater current density.

UHP graphite electrode raw materials and performance

The ultra-high power graphite electrode is produced using high-grade needle coke. The graphitization temperature is as high as 2800~3000°C, so the resistivity is lower, the current density is allowed to pass, the coefficient of linear expansion is smaller, and the thermal shock resistance is excellent. .