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How is the graphite electrode consumed in steelmaking?

Graphite electrode

Electric arc furnace steelmaking is to generate an arc between the graphite electrode and the loaded scrap steel. The heat source of the arc dissolves the scrap steel, oxidizes and removes impurities in molten steel, adjusts the composition, and then produces steel. Graphite electrodes are essential in the process of steelmaking.

Graphite electrodes consumption

Furnace structure, operation, AC/DC mode, and graphite electrode quality will directly affect electrode consumption. Generally, in production, the electrode consumption per ton of steel is 1-4kg.

We found that the consumption of graphite electrodes for steelmaking usually includes end consumption, side consumption, and loss. End loss is mainly due to sublimation and slag erosion caused by high-temperature arc heat at the end.

For example, in the AC ultra-high voltage operation refining process, the terminal consumption caused by high current increases, accounting for 50% of the total consumption. In the recently applied large-scale DC electric furnace, while using high current, the diameter of the electrode also increases accordingly, so the end loss caused by thermal shock becomes the primary consumption.

Graphite electrode vice consumption

Side consumption, and oxidation consumption, account for 50% of the total consumption of  AC electric furnaces. Unlike terminal consumption, terminal consumption also occurs during power outages.

This consumption depends on electrode surface temperature, furnace surface area, gas composition and flow, and steel-making time. Generally, the bulk density of electrodes is increased to densify them to reduce oxidation consumption.

Graphite electrode for steelmaking damage consumption

Damage consumption is an abnormal consumption different from the previous two consumptions and belongs to electrode accidents. Disconnection accidents include disconnection at the electrode hole, connector disconnection, and body disconnection. Coupled with loose tripping, the blocking material loss caused by the crack expansion at the end generally accounts for 0-10%.

After the graphite electrode for steel making is energized, it will vibrate violently due to electromagnetic force and other reasons. At this time, if an external pressure exceeding the strength of the electrode is applied to generate thermal stress, the connection wire under the electrode’s main handle will break, significantly reducing production efficiency and increasing electrode consumption. You should avoid it as much as possible.

Graphite electrode usage-for steelmaking furnace

Properties of graphite electrodes

The selection of graphite electrodes is essential in the steelmaking process. Properly maintaining the electrical load (current density) is crucial to reducing the consumption of graphite electrodes. At the same time, the electrode consumption is also closely related to the operating conditions of the electric furnace.
The graphite electrode for steelmaking consumption of a DC electric furnace is 5%-30%, lower than that of an AC electric furnace. DC furnaces usually use one electrode, and AC furnaces use three electrodes.
The properties required to reduce graphite electrode consumption are
1. Low resistivity and sufficient current capacity;
2. Low thermal expansion coefficient and good thermal shock performance;
3. High density and good oxidation resistance;
4. High mechanical strength, not easy to break, etc.

Specific ways to reduce consumption

DC furnaces operating at high currents must have good thermal shock resistance, which prevents thermal spalling of the arcing electrode ends. We can take some measures to reduce the unit consumption of graphite electrodes.
On the one hand, it is to reduce the consumption rate. Specifically, energize the furnace with the same power, high voltage, and low current; for the design of the furnace, Reduce the height of the furnace shell, and you need to choose a suitable graphite electrode for steel making; the atmosphere inside the furnace is airtight; the electrode material has good mechanical, electrical and thermal properties. On the other hand, it can achieve low consumption by shortening the refining time,  continuous operation, and reducing accidents, improving the steel making yield.

Inclusion

Graphite electrodes in steel making include arc light consumption, chemical consumption, and oxidation consumption. The quality of graphite electrodes has a direct impact on production consumption. Resistivity, bulk density, mechanical strength, and nipple quality are all related to consumption. Graphite electrode manufacturers improve product quality, improving steel mills’ production efficiency.
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