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Why are graphite electrodes indispensable for electric arc furnaces?

Graphite electrodes possess high electrical conductivity and have the high temperature resistance of carbon. Because of this, graphite electrodes have established themselves as the standard for melting in electric arc furnaces.

Why are graphite electrodes indispensable for electric arc furnaces?

Graphite electrodes possess high electrical conductivity and have the high temperature resistance of carbon. Because of this, graphite electrodes have established themselves as the standard for melting in electric arc furnaces. The electrodes are immersed in the scrap, passing large amounts of electric current through them, thus acting as a heat source. They are used for refining and smelting processes of scrap, iron ore and other raw materials.

Therefore, let's learn all about graphite electrodes, why they are used in furnaces, how they help the metallurgical industry and other facts that will allow you to make better use of these graphite elements.

What is an electric arc furnace?

They are furnaces for metal smelting, which convert electrical energy into heat during operation. Its construction is simple, having a vessel with a refractory cover and a lid through which the electrodes are introduced. As mentioned before, graphite electrodes have become the standard for this type of furnaces used in metallurgy in general.

In relation to the amount of electric current that is passed through the graphite electrodes, they reach temperatures in excess of 3500ºC. As a consequence, they are highly effective and graphite is an indispensable element for their operation.

According to the type of furnace construction, they can use alternating current (AC) or direct current (DC). In the case of steel, about 400 MWh of electrical energy is required for the production of a single ton of steel.

How are graphite electrodes used?

To start the furnace operation, the scrap or iron ore is introduced into the furnace and sealed with its lid to avoid accidents.

With the help of a hydraulic system, the electrodes are slowly introduced into the furnace chamber through openings in the lid.

It is worth mentioning that during the manufacturing process of the electrodes, they are machined and have threads on the ends. There are also graphite nipples to connect two or more electrodes one to another, so the final length of the electrode introduced into the furnace may vary.

The electrodes are screwed in a kind of sockets, like the incandescent bulbs we all know. In this way, the large amount of electric current required is passed through them.

At the end of the operation, the electrodes are removed by means of a hydraulic system and the molten metal is transferred or poured for the production of steel products.

Due to the extreme temperatures of the casting process, the graphite electrodes begin to degrade, or oxidize and sublimate into CO2 due to the presence of oxygen and the catalytic effect of the temperature. Therefore, these must be exchanged periodically for proper furnace operation.

Some important parameters of graphite electrodes are

  • Apparent density: Weight of the unit, the higher the weight the better mechanical properties.
  • Electrical resistance: When receiving an electric current, it has a resistance and depending on whether it is low or high, it guarantees its good performance.
  • Tensile and flexural strength: Force required to break the electrode nipple.
  • Coefficient of expansion: The expansion in the length of the graphite electrode according to the heat applied to it.
  • Young's modulus: Measure of resistance to change in electrode length under tensile force.
  • Grade: Quality of the graphite that makes up the electrode. This makes it the perfect material to meet the highest demands at high temperatures.

Conclusions

Finally, graphite electrodes are indispensable in the metallurgical industry. Their production is the task of large international corporations, as they require heavy investments. However, at ESGRAF we are ready to provide you with a wide range of solutions for handling, casting and molding in metallurgy in general. Contact our consultants for personalized advice.