What’s a dome oven?

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A cupola is a cylindrical furnace used to melt metals like iron and bronze. It is filled with alternating layers of metal and coke, and fluxing materials may also be added. Cupolas were used in China during the 3rd century BC and in Europe from the 17th century onwards. When in use, it is referred to as a campaign, and coke is ignited to create a blast furnace. The heat from the burning coke rises through the flask, melting the metal, which can be drained from a faucet at the bottom.

A cupola is a cylindrical device that is used to heat and melt metals such as iron and bronze. These blast furnaces are typically 1.5 to 13 feet (about 0.5 to four meters) in diameter and have the outward appearance of a smokestack. To operate a cupola, the cylinder is usually filled with alternating layers of metal and coke, and fluxing materials, such as lime or carbon makers, may also be added. As the metal melts, it flows down and can be released from a tap on the front of the furnace. After the run is complete, these furnaces can be emptied and prepared for future use by opening a dump gate at the bottom to remove remaining coke and other materials.

Archaeological evidence suggests that dome designs may have been used in China during the 3rd century BC The earliest examples of dome furnaces were used in China during the Chunqiu period to melt bronze. Dome furnaces were also used for cast iron in Europe from the 17th century onwards. Until the mid-20th century, the cupola remained the primary method of casting cast iron. Most foundries eventually switched to induction furnaces, although cupolas are still used in some cases.

When a cupola is in use, it is typically referred to as a campaign. At the start of a campaign, coke is placed in the furnace and then ignited. Ports called tuyeres are used to introduce air into the burning coke, which creates something of a blast furnace. Introducing air into the coke causes it to become very hot, at which point the metal can be set in the furnace. Additional layers of coke are added so that the heating process continues, and lime or other fluxing agents may be added to reduce oxidation.

The heat from the lower layers of burning coke typically rises through the flask, heating the upper layers of metal and melting them. The carbon in coke can bind to the liquid metal as it flows through the lower layers and accumulates at the bottom. In some cases, additives such as silicon carbide may be added to increase the carbon content. After enough molten metal has accumulated at the bottom of a cupola, the operator can turn on a faucet to drain it into a collection vessel. There is typically another spigot at a higher point on the back of the fixture that can drain the slag materials.

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