Cupola Furnace 5 Parts Working Principle, Construction, Pros & Cons, Applications [PDF]

In this article, we shall discuss the working principle, construction, advantages, disadvantages, and applications of Cupola Furnaces. We have also provided a PDF for the same. A Cupola furnace is one of the furnaces where we melt different types of metal some are cast iron, some are maybe bronze.

What is the Cupola Furnace

A Cupola furnace is a melting device. We used this device in the forging operation where Cast Iron, Bronze, and other alloying elements are melted. This is a very old device we used in manufacturing for melting because this system produces good cast iron from Pig Iron. The shape of this device is cylindrical but others size is also available. While choosing a them we keep some valid factors such as Melting Point Temperature, Shapes, and many more.

Cupola Furnace
Photo by Viktor Macha

Construction of Cupola Furnace

The Cupola Furnace is consists of the following

  • Legs
  • Slag Hole
  • Sand Bed
  • tuyeres
  • Preheating Zone
  • Melting Zone
  • Charging Door
  • Brick lining
  • Spark Arrester


Legs are provided for supporting purposes.

Slag Hole or Slag spout

The slag hole is used for removing or extracting the slag from the melting iron.

Sand Bed

This is in taper form and from this, the melted iron comes out easily.


By tuyeres, we enter the gas to the proper burn of fuel.

Preheating Zone

In the Preheating zone, the heating process started and heats the metal charge to about 1090 degrees Celsius.

Melting Zone

In the melting zone, we do not provide much heat to melt the metal charge because it’s already melted in the preheating zone with a temperature of about 1090 degrees Celsius.

Charging door

From here we supply the charge to the furnace. The various charges for the cupola furnace are Pig Iron, Coke, and limestone.

Brick lining and Steel shell

The shell of the cupola furnace is usually made of steel and it’s called a steel shell.

Spark Arrester

This device is used in the system for preventing emissions from the fireplace.

The Schematic Diagram of the Cupola Furnace

Cupola Furnace diagram
Schematic Diagram of Cupola Furnace

Working Principle of Cupola Furnace

The Cupola furnace works on the principle where we generate heat from burning coke and when the temperature of the furnace is above the melting point of the metal then the metal is melted. The charge introduced in the cupola consists of pig iron, scrap, casting rejection, coke, and flux. Coke is the fuel and limestone are added as a flux to remove undesirable materials like ash and dirt. The scrap consists of Steel and cast iron rejections.

Here Over the sand Bottom, Coke is in charge of extending up to a predetermined height. This serves as the coke bed within which the combustion takes place. The Cupola operation is started by igniting the coke bed at its bottom. After the Coke bed is properly Ignited, alternate charges of limestone, pig iron, and coke are charged until the level of the charging Door. Then the air blast is turned on and combustion occurs rapidly within the coke bed. Within 5 to 10 minutes after the blast is turned on the first molten cast iron appears at the tap hole.

Cupola Furnace
working of Cupola Furnace photo by shubham kola

Usually, the first iron which comes out will be too cold to pour into sand molds. During the cupola operation, molten metal may be tracked every 10 minutes depending on the melting rate and the capacity. All the oxygen in the air blast is consumed by the combustion, Within the combustion zone. The chemical reaction takes place which is,

C + O2 (from the air) →  CO2 + Heat

This is an exothermic reaction. The temperature in this zone varies from 1550 to 1850 degrees Celsius.

Then hot gases consisting principally of Nitrogen and carbon dioxide moved upward from the combustion zone, where the temperature is 1650 degree Celsius. The portion of the coke bed if the combustion zone is reducing zone. It is a protective zone to prevent the oxidation of the metal charge above and while dropping through it. As the hot carbon dioxide gas moves upward through the hot coke, some of it is reduced by the following reaction.

3Fe + 2CO → Fe3C + CO2

This is an endothermic reaction.

The first layer of iron above the reducing zone is the melting zone where the solid iron is converted into the molten state. A significant portion of the carbon that is picked up by the metal also takes place in this zone. The hot gas is passed upward from the reducing and melting zones into the preheating zone which includes all layers of charge above the melting zone up to the charging Door. Since the layer of the charge is preheated by the outgoing gases which exist at the top of the cylindrical shell. The temperature is this zone is around 1090 degrees Celsius.

Video by Shubham Kola

Advantages of Cupola Furnace

  • For operation purposes, this is a simple and economical device.
  • A wide range of materials can be melted.
  • This device is used for removing the slag present in the Iron.
  • Comparison of electric furnaces This is very less harmful.
  • This is having high melting heat i.e. 100 tones/hr.
  • The floor space required is less and to perform the operation skilled operator not required.
cupola furnace advantages
Photo by Viktor Macha

Disadvantages of Cupola Furnace

  • The main disadvantage is that sometimes unable to main a close temperature.
  • Inconsistent quality
  • Environmental impact
  • High energy consumption
  • Limited flexibility
  • Labor intensive
  • Maintenance and repair
  • Safety concerns

Applications of Cupola Furnace

  • The main application is different types of cast iron produced from this device Malleable, Grey cast iron, and copper base alloy is also manufactured by this device.
  • Cost-effective: They are relatively inexpensive to build and operate, making them a cost-effective option for small to medium-sized foundries.
  • High production rate: These have a high melting rate, allowing for the production of large quantities of molten metal in a short amount of time.
  • Versatile: They can melt a wide variety of metal alloys, making them suitable for producing a range of products.
  • Minimal preheating: It does not require extensive preheating, which can save time and reduce energy costs.
  • Recyclability: Cupola furnaces can melt scrap metal, which can be recycled and reused in the production process.
  • Minimal emissions: Cupola furnaces produce minimal emissions compared to other types of furnaces, making them a more environmentally friendly option.
  • Ease of operation: These are relatively easy to operate, requiring less skill and training compared to other types of furnaces.


In conclusion, a cupola furnace is a popular melting furnace used in foundries for melting various types of metals such as cast iron, brass, and aluminum. The furnace works on the principle of combustion of coke, which generates heat to melt the metal charge in the furnace.

The construction of the furnace involves a cylindrical shell, refractory lining, tuyeres, and a charging door. Cupola furnaces are widely used in the production of automotive parts, pipes, and agricultural equipment. However, the use of has declined in recent times due to the increasing popularity of electric arc furnaces, which are more energy-efficient and environmentally friendly.


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