Electric Arc FurnacePublished on 24/2/2012 and last updated on 9/8/2018
DC Electric Arc FurnaceDC Arc Furnace is recent and advanced furnace compared to AC Arc Furnace. In DC Arc Furnace, current flows from cathode to anode. This furnace has only a single graphite electrode and the other electrode is embedded at the bottom of the furnace. There are different methods for fixing anode at the bottom of the DC furnace.
The first arrangement consists of a single metal anode placed at the bottom. It is water cooled because it gets heated up fast. In the next one, the anode be the conducting hearth by C-MgO lining. The current is given to the Cu plate positioned at the bottom portion. Here, the cooling of anode is by the air. In the third arrangement, the metal rods act as anode. It is entrenched in MgO mass. In the fourth arrangement, the anode is the thin sheets. The sheets are entrenched in MgO mass.
Advantages of DC Electric Arc Furnace
- Decrease in electrode consumption by 50%.
- Melting is almost uniform.
- Decrease in power consumption (5 to 10%).
- Decrease in flicker by 50%.
- Decrease in refractory consumption
- Hearth life can be extended.
AC electric Arc FurnaceIn AC electric furnace, current flows between the electrodes through the charges in metal. In this furnace three graphite electrodes are used as cathode. The scrap itself acts as an anode. When compared to DC arc furnace, this is cost effective. This furnace is most commonly used in small furnaces.
Construction of Electric Arc FurnaceAs mentioned above, the electric furnace is a large firebrick lined erect vessel. It is demonstrated in figure 2. The main parts of electric furnace are the roof, hearth (lower part of a furnace, from where molten metal is collected), electrodes, and side walls. The roof consists of three holes through which the electrodes are inserted. The roof is made up of alumina and magnesite-chromite bricks. The hearth includes metal and slag. The tilting mechanism is used to pour the metal that is molten to the cradle by shifting the furnace. For the electrode removal and furnace charging (topping up scrap metals), roof retraction mechanism is incorporated. The provision for fume extraction is also given around the furnace considering the health of operators. In AC electric furnace, electrodes are three in number. These are round in section. Graphite is used as electrodes because of high electric conductivity. Carbon electrodes are also used. The electrodes positioning system helps to raise and lower the electrodes automatically. The electrodes get highly oxidized when the current density is high.
Transformer: - The transformer provides the electrical supply to the electrodes. It is located near to the furnace. It is well protected. The rating of large electric arc furnace may be up to 60MVA.