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1. Furnaces for casting
 A furnace
 A furnace is a device used for high-
temperature heating. The heat energy to
fuel a furnace may be supplied directly by
fuel combustion, by electricity such as the
electric arc furnace, or through induction
heating in induction furnaces.

2. A cupola furnace
 A cupola or cupola furnace is a melting
device
 used to melt cast iron, Ni-resist iron and
some bronzes. The cupola can be made
almost any practical size.

3. Construction of copula furnace
 Shell:
 Foundation:
 Tuyeres:
 Wind box:
 Blower:
 Slag Hole:
 Tap Hole (Molten Metal Hole):
 Charging Door:
 Chimney:

5. Operation of Cupola Furnace:
 (i) Preparation of Cupola:
 A newly built cupola should be thoroughly dried before
firing.
 Any slag around the tuyeres from previous run are cleaned.
 Any broken bricks are repaired with a mixture of silica sand
and fire clay
 A slag hole opening of about 30 to 35 mm diameter and a
tap hole of about 25 mm diameter is provided

6.  (ii) Firing of Cupola:
 A fire of wood is ignited on the sand bottom.
 coke is dumped on the bed well from top.
Make sure that the coke begins to burn too.
 A bed of coke about 40 inches thick, slightly
above the tuyeres.
 The air blast is turned on at a lower blowing
rate than normal for igniting the coke

7.  (iii) Charging the Cupola:
 Next, the charge is fed into the cupola
through the charging door.
 Coke fuel, limestone flux, metal.

8.  (iv) Soaking of Iron:
 After charging the furnace fully, it is
allowed to remain as such for about 1—
1.5 hr. During this stage charge slowly
gets heated up because the air blast is
kept shut this time and due to this the iron
gets soaked.

9.  (v) Starting the Air Blast:
 The air blast is opened at the end of the soaking
period. The top opening is kept closed till the
metal melts and sufficient metal is collected. As
melting proceeds, the contents of the charge
move gradually downwards. The rate of
charging must be equal to the rate of melting so
that the furnace is kept full throughout the heat.

10. CHEMICAL REACTIONS
 Combustion
C(coke) + 02 (from air) -> C02 + Heat
Si+ o2 - sio2 +heat
2Mn + o2 - 2Mno
 Reducing zone
C02 + C2 -» CO – Heat
 Melting zone
3 Fe + 2 CO -» Fe3C + C02

11.  (vi) Closing the Cupola:
 When no more melting is required, the
feeding of charge and air blast is stopped.

12. Zones of Cupola
Furnace

13. Zones of Cupola Furnace
 The cupola furnace is divided in a number of
zones where a number of chemical reactions
take place.
 The following are the six important zones

14. Direct fuel fired furnace

15. Construction:
The Hot Air Generator is solid fuel fired medium air
temperature hot air generator, which is very
compact in construction of VERTICAL design, with
External bottom furnace.
The main body of the Generator is of sturdy
Construction made out of heavy gauge steel and
Structure. The body is painted with epoxy paint to
combat corrosive industrial atmosphere.

16. Salient Features:
1. Clean, Uncontaminated Hot Air available
Economically.
2. Hot Air available at temperature up to 1700 C.
3. Multiple passes on air side ensure high thermal
efficiency.
4. Lowest operating costs, compared to Electricity,
Steam & thermic oil heating.
5. Vertical design, requires very low floor space.
6. Low motive power requirements.

17. Direct fired heaters
 Direct fired heaters are similar to a gas
barbecue grill or your gas stove top. With
propane or natural gas heating, units force air
directly through the flame to heat the air.

18. Direct fired heaters
diagram

19. Benefits to using direct fired heaters include:
1. Efficiency – Direct fired heaters convert 100% of the
fuel being used to direct heat which lowers fuel
consumption and operating Costs
2. Easy to Transport – Direct fired heaters are fairly
simple pieces of equipment that can be moved to
where heat is needed
3. Some units do not require electricity
4. Lower rental costs – Direct Fired Heaters are less
expensive
5. Lower Maintenance Costs – Easier to maintain

20. Some drawbacks to using direct fired heaters are:
1. Adds moisture and carbon monoxide into the
air.
2. Low Operation Cost
3. The rising prices of the fuel oil have made the
use of oil as a heating medium prohibitively
costly. In these times of highly competitive
markets, it has become necessary to look at
the other fuel options available.

21. Trouble free Operation:
The Unit is of Sturdy construction and also
there are very few moving parts; this ensures
long life & trouble free operation of the unit.

22. INDUCTION FURNACE

23. What is induction furnace?
 Induction Furnace
 An induction furnace is an electrical furnace in
which the heat is applied by induction heating of
metal.
 Induction furnace capacities range from less than one
kilogram to one hundred tonnes capacity and are used
to melt iron and steel, copper, aluminium and precious
metals.

24. Construction
 An induction furnace consists of a nonconductive crucible
holding the charge of metal to be melted, surrounded by a
coil of copper wire.
 A powerful alternating current flows through the wire. The
coil creates a rapidly reversing magnetic field that
penetrates the metal. The magnetic field induces
eddy currents, circular electric currents, inside the metal, by
electromagnetic induction. The eddy currents, flowing
through the electrical resistance of the bulk metal, heat it by
Joule heating.

25.  Principle
 The principle of induction heating is based on the
following two laws:
 1. Electromagnetic induction
 2. The joule effect (the heating that occurs when an
electric current flows through a resistance.)
 The principle of induction melting is that a high voltage
electrical source from a primary coil induces a low
voltage, high current in the metal or secondary coil.
Induction heating is simply a method of transferring heat
energy.

26. Important points
 The inductor is usually made of copper in order to limit the
electric losses.
 In this furnace type, the charge is melted by heat
generated from an electric arc.
 The coil carries the high frequency current of 500 to 2000
Hz.

29. Advantages
 · Induction furnace does not need electrodes like electric
arc furnace.
 · Better control of temperature
 · Better control of composition of the melt

30. Disadvantages
 Disadvantages:
 · An induction installation usually implies a big investment
that must be considered and compared to alternative
heating techniques.
 · Induction heating is preferably used for heating relatively
simple shapes.

31. Types of induction furnaces
 Coreless induction furnaces
 The heart of the coreless induction furnace is the coil,
which consists of a hollow section of heavy duty, high
conductivity copper tubing which is wound into a helical
coil.
 To protect it from overheating, the coil is water-cooled, the
water bing recirculated and cooled in a cooling tower.

32.  Channel induction furnaces
 The channel induction furnace consists of a
refractory lined steel shell which contains the
molten metal. Attached to the steel shell and
connected by a throat is an induction unit which
forms the melting component of the furnace. The
induction unit consists of an iron core in the form of
a ring around which a primary induction coil is
wound.

33. ELECTRIC ARC
FURNACE

34. 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..

35. 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

37. Operation:
The electric arc furnace operates as a
batch melting process.
 Furnace Charging
 Melting
 Tapping
 Furnace turn-around

38. 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.

39.  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.

40. 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.

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