Cupola furnaces construction and its working principle

Cupola Furnace 

                       This type of furnace is used for melting cast iron. 

                      It is a vertical, cylindrical shell made of 10mm thick steel plate. It is lined with refractory bricks inside. Two bottom doors close the bottom of the cupola. A sand bed is laid over the bottom doors sloping towards the tap hole. Molten metal stays over this bed. The 1egs are set at the bottom of the furnace using a concrete. There is a faucet hole for taking the melted metal. A plug made of clay closes the tap hole. The Slag hole is provided in the shell above the tap hole. The slag floating Over the molten metal is removed through this slag hole. The opening called tuyeres are provided one meter above the bottom. Fuel is supplied through these tuyeres for making complete combustion of fuel. There is a wind box and blower for the supply of air into the furnace. For charging the metal and fuel into the furnace, a separate charging door is made. 

Preparation: 

                     The slag and waste from previous melting are cleaned. Broken bricks are repaired or replaced, if necessary. Then bottom doors are closed. A sand bed with sloping towards tap hole is prepared up to a height of 200 mm. A tap hole is made and lined with clay. Then a slag hole is prepared. F inally, the cupola is dried thoroughly. 

Firing:

                       Oil waste and wooden pieces are placed at the bottom and the tire is started. Now, the sufficient amount of air is supplied when the wood starts burning. The coke is charged at several portions. Now, the coke bums. More coke is poured up to the tuyere level. The blast is turned off. Coke is again added up to the level of bed charge. Then, the coke is allowed to burn for half an hour. Finally, the charging is done through the changing door. 

Charging and Melting: 

                     Pig iron and iron scrap are charged into the furnace through the charging door. Then coke 13 charged alternatively. Limestone is added to the charge to remove impurities and also to ensure thorough mixing of molten metal. The ratio of pig iron to limestone and pig iron to coke are 25:1 and 10:1 respectively. The cupola is fully charged. Then, the iron is soaked for one hour. After that, the blast is turned on. The molten metal will begin to collect at the sand bed. After melting enough quantity of molten metal, clay plug is removed and collected in ladles.

              Then the molten metal can directly be poured into moulds. The floating slag on the tap layer of the molten metal is tapped out through the slag hole. Again the furnace should be charged to the full level for repeating the same procedure. 

                  At the end, the cupola is shut off by stepping the air blast. Then, the remaining molten metal is removed, the bottom doors are opened, the wastes are dropped down and they are quenched by water. 

Application:

      

         Cupola is used to melt cast iron. 

Advantages: 

1. Initial cost is comparatively less than other type of furnaces. 

2. It is simple in design. 

3. It requires less floor area. 

4. Operation and maintenance are simple. 

5. It can be operated continuously for many hours.