What is Cupola Furnace?
- The cupola furnace is a melting device used to melt cast iron, bronze, and other alloying elements.
- It is mainly used to convert iron to cast iron.
- The Kapila furnace was first built in China during the period of the Warring States (403 –221 BCE). The cupola furnace is cylindrical in shape, and the equipment of this furnace is fitted vertically inside this cylindrical shell with a door.
- For many years the cupola furnace was used to melt iron in iron castings as it produces a better cast iron than pig iron.
- The top of the cupola furnaces is sometimes fitted with a cap to avoid gases harmful to the environment, and this cap also protects from rainwater.
- The cupolas shell is made of steel and consists of refractory brick and plastic refractory patching materials.
- The bottom of this shell is lined with a mixture of clay and sand and is a temporary lining. Sometimes coal is mixed with the soil lining so that when the coal is heated, it rots, and the bond becomes brittle.
Cupola furnace design
- The outermost part of the cupola furnace is a cylindrical steel shell.
- The diameter of this shell ranges from 1.5 to 13 feet, depending on the furnace’s size.
- They are lined with an inner edge of furnace Refractory brick and plastic refractory patch material.
- These furnaces is supported on cast iron legs mounted on a concrete base.
- At the bottom of the furnace, two cast iron doors are hinged with the bedplate of the furnace.
- Near the bottom, it has sent a bed above, which has a flow of molten iron.
- This sand bed is taped.
- Near the higher part of the taped sand bed, slag holes exist through which slag made of impurities come out.
- Below the down bed, there exists a tap hole through which molten iron comes out.
- Above the sending bed, tuners exist through which air reaches the furnace and helps in combustion.
- A cap or cap is present at the top of the furnace spark, which traps burning particles and releases only gases into the environment.
- Near the top of the furnace, a charging door exists through which metal, coke, and limestone are fed into the furnace.
Purpose of cupola
- Similar to the blast furnaces, the cupola is a refractory-lined steel stack 20 to 35 feet (6 to 11 m) high, resting on a cast iron base plate with four steel legs.
- Below the cupola furnace are two hinged doors supported in a closed position by a center prop. Coking beds, molten metal, and closed sand are molded to support successful charges.
- The air forced into the combustion enters the cupola through the openings (tires) around the rim of the lower part of the cupola.
Working Principle of Cupola Furnace:
- The wood is first ignited over a bed of sand.
- When the wood starts burning properly, the coke is thrown from the top to the well at a predetermined height of about 40 inches. This makes a 40-inch coke bed.
- Then the combustion begins in the coke bed using fire from the burning wood and air from the trees.
- At this time, aerial explosions have flown at lower than normal rates to provoke coke.
- When the coke starts to burn properly after about 3 hours of burning, alternating layers of limestone, pig iron, and coke are charged until it reaches the level of the charging door.
- At this time, an air blast is carried out at a normal blowing rate, and combustion occurs more rapidly in the coke bed.
- All the oxygen from the air blast is consumed by combustion in the combustion zone.
- The chemical reaction that occurs is C + O2 -> CO2 + Heat.
- It is an exothermic reaction, and the temperature in the combustion zone varies from 1150 to 1850 ° Celsius.
- The portion of the coke bed above the combustion zone is a reducing zone.
- This region prevents oxidation of the metal charge while leaving it over and through.
- Ho carbon dioxide goes up through this region; some of it is reduced by the following reaction, CO2 + C -> 2CO
- The zone of dilution of iron above the zone is a melting zone where solid iron is converted into molten iron.
- This molten iron falls down through the coke bed and collects in the well.
- In this region, sufficient carbon compacts are extracted by the molten metal and are characterized by the following chemical reaction: – 3 Fe + 2 CO -> Fe3 C + CO2
- Above the melting zone, there is a preheating zone, where the inward gases are preceded by and the temperature of this zone is about 1900 degrees Celsius.
- In addition to limestone, fluorspar and soda ash are also used as flux materials.
- The main function of the flux is to remove impurities from the iron and protect the iron from oxidation.
- For normal blast rates, the first molten iron appears in the tap hole within 5 to 10 minutes after the start of the air blast.
- The charging door remains closed until the metal melts.
- The content of the charge goes down as the melting proceeds.
- The rate of charging, i.e., the rate of adding layers of charge, is equal to the rate of melting. The furnace is kept throughout the process.
- When the melting process is over and no more molten irons are required, the charge feeders stop, and the air blast also stops.
- The bottom plate opens when the prop is removed, and the slag is removed.
- The copula furnace is generally not used for more than 4 hours but may be used for 10 hours of continuous operation.
- The cupola furnace operates on a simple principle that produces carbon dioxide and heat from the combustion of coke and causes iron to melt.
- Iron melts when it flows downwards.
Advantages of Cupola Furnace
- Simple in Construction.
- A wide range of materials can be melted.
- Less floor space is required.
- Very skilled operators are not required.
- It can be easily operated by low skilled person.
- Low cost of operation.
- Low cost of maintenance.
- Low cost of construction.
Also, Read: What Is a Comparator | Types of Comparators
Disadvantages of Cupola Furnace
- The main disadvantage is that sometimes it is very hard to control the temperature in this furnace.
- Metal elements are converted to their oxide, which is not suitable for casting.
Applications of Cupola Furnace
- It is mainly used to convert pig irons to molten irons.
- More types of cast irons are produced from this furnace-like malleable and grey cast iron.
- The copper base alloy is also manufactured by this device.