Cupola is an important equipment for melting cast iron in foundry refractory. The cast iron block is melted into molten iron and then poured into the sand mold to be cooled and then opened to obtain castings. Cupola is a vertical cylindrical smelting furnace, which is divided into front furnace and rear furnace. The forehearth is further divided into a tap hole, a slag outlet, a hearth in front of the furnace cover and a bridge. The rear furnace is further divided into three parts, the top furnace, the waist furnace and the hearth. The waist furnace is separated from the hot air surrounding pipe, closed after repairing the furnace, and sealed with mud. On the top furnace is a heat exchanger. It is mainly used in the production of cast iron castings, and is also used in conjunction with converter steelmaking. Because the top of the furnace opens upward, it is called a cupola.
The working process of the cupola: first put a certain amount of coal into the furnace as the bottom coke, and its height is generally more than one meter. After ignition, add the bottom coke to the specified height, from the tuyere to the top surface of the bottom coke is the bottom coke height. Then according to the melting rate of the furnace, the prepared limestone, metal charge and layer coke are added in batches from the feeding port in order. Keep the top surface of the charge at the lower edge of the charging port during the entire furnace opening process. The air blown into the furnace through the tuyere undergoes a combustion reaction with the bottom coke, and the generated high-temperature furnace gas flows upward to heat the charge and melt the first batch of metal charge on the top surface of the bottom coke. As the molten iron droplets fall to the hearth, they are further heated by the hot furnace gas and the hot coke, a process called superheating. With the loss of bottom coke and the melting of metal charge, the charge layer gradually declines. After each batch of charge is melted, the fuel is supplemented by the additional layer coke, so that the height of the bottom coke remains basically unchanged, and the whole melting process is carried out continuously. Application field: Cupola is mainly used in steel, metallurgy, mining and other industries.
The limestone in the charge is decomposed into lime and carbon dioxide under the action of high temperature furnace gas. Lime is an alkaline oxide, which can combine with ash in coke, impurities in charge, metal oxides and other acidic substances to form slag with a lower melting point. The molten slag also falls to the hearth and floats on the molten iron.
In the cupola, three important processes of bottom coke combustion, heat transfer and metallurgical reaction are carried out at the same time. According to the different physical and chemical reactions, the cupola takes the combustion zone as the core and is divided into five zones from top to bottom: the preheating zone, the melting zone, the reduction zone, the oxidation zone and the hearth. Due to the action of furnace gas, coke and slag, the molten metal composition also changes to some extent. Among the five elements of cast iron, carbon and sulfur generally increase, silicon and manganese generally burn, and phosphorus does not change much. The final chemical composition of molten iron is the comprehensive result of the original composition of the metal charge and the composition changes during the smelting process.
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