Metal furnaces are selected based on criteria like the metal's melting point, required quantity and purity, pouring type, maximum temperature, and cost factors. Common furnace types include crucible, pot, rotary, and electric furnaces. The crucible furnace uses a crucible container and can be coke, gas, or oil fired. The pot furnace contains molten metal in a pot to avoid smoke impurities. The rotary furnace rotates horizontally for homogeneous melting. Electric furnaces like direct arc, indirect arc, and induction furnaces provide high purity but at a higher cost. The cupola furnace is a cylindrical furnace that produces molten cast iron. It operates

2. Metal Furnaces
• The selection of furnace is depend on below
mentioned criteria:
(1) Type of pouring metal and its melting point.
(2) Quantity required
(3) Percentage of purity required
(4) Type of pouring
(5) Maximum temperature
(6) Investment cost of furnace, repair cost and
maintenance cost.
(7) Type of fuel used in furnace and also whether it is
available.

3. Different types of furnaces
The following are the furnace used for
melting metals
(A) Crucible furnace
(1) Coke fired pit furnace
(2) Stationary gas or oil fired crucible
furnace
(3) Crucible furnace of tilting type
(B) Pot furnace
C) Rotary furnace
(D) Electric furnace
(1) Direct arc furnace
(2) Indirect arc furnace
(3) Induction furnace
(E) Cupola furnace

4. Working of various types of Furnace
• A) Crucible furnace :
1.It is used for small jobs, crucible is used in
this type of furnace.
2.Crucible is made from Granite, silicon carbide
like refracting material.
3.Coke, oil or gas is used to heat crucible as a
fuel.
4.The size of crucible is measured from 1 to 400
unit, this unit is used to identify the quantity
or capacity of crucible.
5.This is used for ferrous and non-ferrous
material.
 Advantages of Crucible
1. It is economic and initial cost is
low.
2. Easy to operate
3. Low cost fuel can be used.

5. (A) Crucible Furnace
(1) Coke fired pit furnace:
1. It is constructed in a pit dug in the
ground. In this furnace coke is
used as a fuel.
2. The coke bed is formed, ignited
and allowed to burn.
3. Now coke from the center of the
coke bed is removed and crucible
with lid containing the metal
charge is placed.
4. It is used for cast iron, nonferrous
metal and alloys. It is not costly
and with low maintenance.

7. (A) Crucible Furnace
(2) Stationary gas or oil fired crucible
furnace:
1. In this furnace as a fuel, gas or oil is
used.
2. Crucible is placed inside the furnace
with oil or gas it is heated at definite
temperature and metal is melt.
3. Applications are similar to coke fired
pit furnace

8. (A) Crucible Furnace
(3) Crusible furnace of tilting type:
1. Large amounts of metal are melted.
2. Crucible is permanently cemented in
place.
3. The furnace is made of sheet metal is
lined with refractory (Fire) bricks.
4. Oil or Gas is used as fuel.
5. Application: 50kg – 1500kg metal
1. Used for aluminium, copper, magnenise.
6. Fast, economic and temperature is
maintained homogeneously

9. (B) Pot Furnace
• Furnace pot is made from Cast Iron or
Steel.
• A metal is placed inside the pot and heat is
applied to its surrounding with coke or gas
or oil firing.
• In this furnace the developed smoke will
not come in contact with molten metal, so
impurities are minimum or less.
• aluminum, tin, magnesium, lead, zink,
cadmium are melted

10. (C) Rotary Furnace
• Cylindrical in shape and rotate
horizontally with its axis.
• Capacity: 500kg to 2000kg
• One end is heated with fuel,
generated heat melts the metal,
burning gas comes out from
second end.
• Furnace is rotated with electric
motor and gear mechanism.
• Homogeneous mixture is achived.
• Ease of loading and unloading

11. (D) Electric Furnace
• Advantages compared to other furnace:
1.Purity in molten metal is maximum
2.Temperature control in furnace is
maintained
• Cost of electricity increases the cost of
furnace.

12. (D) Electric Furnace
• (1) Direct Arc Furnace(three
phase)
1.Steel Scrap is placed on the
hearth of the furnace.
2.An arc is Drawn between
electrodes and the surface of the
metal charge by lowering the
electrodes down till the current
jumps.
3.Capacity: upto 50 tonns
4.Purity of metal is kept easily
5.Investment is higher

14. (D) Electric Furnace
• (2) Indirect arc furnace (single
phase)
1.Electrodes do not come in
contact with molten metal.
2.Electrodes forms arc above the
molten metal.
3.Furnace is mounted on rollers
which is driven by rocking unit
to rock the furnace back and
forth during melting.

16. (D) Electric Furnace
• (3) Induction furnace:
1. Copper coil is arranged around
crucible and current is passed
through this coil.
2. This coil works as primary coil
of transformer and crucible as
secondary coil.
3. Due to high resistance around
50 to 60 minutes for melting
metal.
4. Frequency of electric current is
1000 per second.

17. (E)
Cupola
Furnace

18. (E) Cupola Furnace
• (1) Furnace construction:
1. The cupola furnace is a cylinder type furnace for producing molten
cast iron.
2. Dimensions:
1. Vertical cylinder shell thickness: 6-12 mm
2. Diameter of shell: 1-2 meters
3. Height of shell: 3-5 meters
3. The bottom of cupola is provided with drop bottom door through
which debris consist of slag, coke etc. can be removed at the end of
melt.
4. Cone shape spark arrester is provided at top of the furnace which
discard gases developed in the furnace and keeps spark and dust
inside the furnace.

19. (E) Cupola Furnace
• (2) Cupola furnace operations:
1. Preparation of cupola: Acidic refractory brick lining is patch.
2. Lightening the cupola: By gas or electric spark igniters.
3. Charging of cupola: Coke and pig iron is charged in alternative layers.
1. Fluxing material : fluorspar , soda ash
4. Melting: Soaking for half an hour, blower is operated for 10-15 min.
5. Slagging and metal tapping: This process is done for 4 to 6 hours.
6. Closing the cupola : prop/probe is removed from bottom and door is
opened so dust, slag, burnt metal parts and coke comes out.

20. Zones of Cupola
1. Crucible zone:
1. It is between the top of the sand and bottom of the tuyeres.
2. Combustion zone: located above the tuyeres where the combustion
of the fuel takes place by oxygen of the air blast and temperature is
around 1540℃ to 1870℃.
1. .
2. .
3. .
3. Reducing zone: CO2 produced come contact with hot coke and is
reduced to CO.

21. Zones of Cupola
4. Melting Zone: It is the First layer of coke bed. Temp: 1700℃. Iron is
melted.
5. Preheating Zone: It located above melting zone to the charging door.
Iron and coke are preheated in this Zone. The temperature is around
1100° C.
6. Stack Zone: Carrier gases from preheating zone to atmosphere.

22. Advantages and limitations of Cupola Furnace
• Advantages
1. Simple design and easy construction.
2. Initial cost is low compared to other.
3. Maintenance is easy and economic.
4. Operation cost is low.
5. Low space is required compare to other.
6. Run for long time.
• Limitations
1. Metal purity cannot be maintained.
2. Temperature is difficult to control.

23. Efficiency of Cupola