Electric Arc Furnace

Introduction: Electric Arc Furnace is a furnace that heats the

charged material by mean of an electric arc. Arc Furnace range in size from small units of

approximately one ton capacity up to 400 tons. industrial arc furnace can be heat up to 1800°C.

Arc Furnace is different from induction furnace because charge material is directly exposed to an electric arc furnace, and the current in the furnace terminals passes through the charged material.

Construction:

The furnace consists of a spherical hearth (bottom), cylindrical shell and a swinging water-cooled dome-shaped roof.

The roof has three holes for consumable graphite electrodes held by a clamping mechanism.

This mechanism provides independent lifting and lowering of each electrode

Furnace is split into three sections

The “shell”, which consist of the sidewalls and lower steel bowl.

The “Hearth”, Which consist of the refractory that lines the lower bowl.

The “roof”, which may be refractory lined or water cooled, and can be shaped as a section of sphere, or as a conical section.

Operation:The electric arc furnace operates as a batch melting process.

Furnace Charging Melting Tapping Furnace turn-around

Furnace Charging: The first step is “charging”. The roof and electrode are raised and are swung

to the side of the furnace to allow the material to be charged. When the charging is complete the roof and electrodes swing back into place

over the furnace. The roof is lowered and then the electrodes are lowered to strike an arc on the charged material.

The heat produce by electrode is primarily dependent on volume and density of charge.

Melting:

The melting period is a heart of Electric arc furnace. The EAF has evolved into a highly efficient melting apparatus and modern design are focused on maximizing is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical.

Electrical energy is supplied via graphite electrodes and is usually the largest contributor in melting operations. Initially, an intermediate voltage tap is selected until the electrodes bore into the scrap. usually light scrap is placed on top of the charge to accelerate bore-in. approximately 15% of scrap is melted during the initial bore-in period.

after a few minutes, the electrodes will have penetrated the material sufficiently so that a long arc tap can be used without fear of radiation damage to the roof.

The long arc maximizing the transfer of power to the material and a liquid pool of a metal will form in the furnace hearth. At the start of melting the arc is unstable. As the atmosphere of furnace is heated up the arc stabilizes and once the molten pool is formed, the arc become stable and the average power input increases.

Chemical energy is supplied via several sources including oxy-fuel burners and oxygen lances. Oxy-fuel burners burn natural gas using oxygen or a blend of oxygen and air.

Heat is transferred to charge material by flame radiation and convection by the hot products of combustion. Heat is transferred within the charged material by conduction.

Large pieces of scrap take longer time to melt into the bath than smaller pieces. In some operations oxygen is injected via a consumable pipe lance to “cut” the charged material and burns iron to produce intense heat.

This oxygen will react with several components in the bath including, aluminum , silicon , manganese , phosphorous , carbon , and iron all these reactions are exothermic.

Tapping: Once the charged material has been melted, the tap hole of

furnace is opened, the furnace is tilted, and molten metal is pours into a ladle.

Furnace turned around: It is the period after completion of tapping until the furnace is

recharged for the next heat. During this period the electrodes and roof are raised and furnace

lining is inspected for refractory damage.

Advantage: Electric arc furnace can be used as heat treatment furnace. It can be used for melting. EAF is used for production of steel making by pig iron Electric arc furnace provides flexibility, EAFs can be rapidly started

and stopped.

Disadvantages: A lot of electricity consumption.