2. 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.
3. 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
4.
5. 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.
6. Operation:
The electric arc furnace operates as a batch melting
process.
Furnace Charging
Melting
Tapping
Furnace turn-around
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
