A Cupola is a type of furnace that is very much alike to blast furnace. The Cupola furnace is refractory lined, stack of steel that is around 20 to 35 feet high. It rests on a base plate that is made of cast iron and has four legs. The casting that is obtained from the cupola furnace is known as a cupola casting.



Cupola Furnace: The Cupola furnace is one of the oldest forms of furnace that have been used by the iron and metal foundries. The Cupola furnace is the crudest and the simplest furnace that has been used by the industries. However, the cupola's use is declining and the furnace is fast being extinct.

Merits of the Cupola Furnace: Though the electric or the blast furnace has started replacing the Cupola Furnace, it has some special benefits of its own. The Cupola furnace can always remain continuously in action. The furnace also offers a very high melting rate. The most important merit of the furnace is that it has relatively very low melting cost. The furnace has also permits a lot of ease of operation.

However, due to the invention and development of the electric furnace, the use of Cupola furnaces has substantially declined. The electric furnace melts a much larger amount of metal. The operation cost of the electric furnace is also very low. The electric furnace also emits a much smaller level of smoke heat and also pollutants.

Construction of the Cupola furnace: The Cupola furnace is constructed in a crude and simple manner. The Cupola furnace is a vertical structure like a steel shell. The steel is lined with refractory bricks from the inside. The furnace has an opening half way in the vertical shaft. The charge is introduced through the opening. The charge is divided into different layers. It contains the metal that is to be melted. The metal is mixed with coke, fuel, and lime stone flux. The fuel is burnt directly into the air and is introduced in to the furnace through the tuyeres which are positioned above the hearth. The hot gases that have been produced ascend and pre heat the charge.

The cupolas in majority of the cases have drop down doors. The bottoms can be dropped down to facilitate the cleaning and the repairs. At bottom in front of the furnace is a tap hole. The molten metal is removed from the tap hole. At the rear there is also another slag hole. The top of the stag is covered with a spark or fume arrester.

Usually the cupola has a diameter of 405 to 2000 mm. It is operated on varying fuels for different metal ratios. The molten metal that can be produced in the copula of this size at a speed of 1 to 30 tones per hour.

Continuity of process: After the process of melting has ended, the charging is halted. However, the blast of hot air is always maintained till all the metal has been melted and has been taken out from the tap hole. When the air cools down, the doors at the bottom are opened and the residue that has been left behind is removed.