Cupola furnace

The cupola furnace is a shaft furnace, can be melted in the metals. Cupola furnaces are used for the production of cast iron from pig iron and scrap. The cupola furnace is similar in structure and operation of the strong blast furnace, is up to 20 meters high, but does not reach the temperatures needed for the reduction of metals from their ores.

History

The cupola furnace was invented in 1794 by the Englishman John Wilkinson ( 1727-1808 ). The cupola made ​​the cast iron from the blast furnace much larger independent, since it melts the iron was made possible without requiring much higher temperatures of a blast furnace. Cupola derives it from the dome from where the long furnace shaft still sticking out of the factory roof.

Design and function

To start the oven, a wood fire is lit and covered with coke at its base. With newer furnaces, coal is charged into the furnace and contacted with gas burners for annealing instead. The furnace is filled with burning embers with several layers of metal and coke and meanwhile blown with air. This results in the bottom of the furnace temperatures up to 1,600 ° C, which bring the metal to melt. Depending on whether the air is preheated introduced into the furnace or not, a distinction is made between hot air and cold wind cupola furnaces.

To remove the metal of the oven must be pierced somewhat above its base. To the bung includes a siphon, which has two outlets: through the top, the slag is discharged into a receptacle. By the other metal is pressed under the slag and may be passed for example to a Vorhalteofen. The function of the siphon is only possible due to a slight overpressure in the furnace. Correct adjustment of the slag and the Metallauslasses to ground level is a matter of experience.

Cast iron

Of special significance is the cupola furnace for cast iron production. He is charged with pig iron, steel scrap, recycled material and machine cast iron scrap. The setting of the carbon content of the cast iron is via the ratio scrap steel (low carbon content ) to machine cast iron scrap ( high carbon content ). An increased addition of coke also increases the carbon content. In addition, lime is added to neutralize the acid produced during the process slag and keep better flowable.

By blowing air with a higher oxygen content can be reduced, the carbon content of the cast iron.

Developments

So-called cokeless cupola furnaces are run solely on natural gas or oil and have a better heat balance and lower emissions. Because the coke is not necessarily required for a chemical reaction, in contrast to the blast furnace, this conversion is possible.

Cupola furnaces are replaced but increasingly also by induction, since these, unlike the koksgefeuerten cupola furnace slag and waste less produce, are more flexible in the use and composition of the melt product can be adjusted more accurately with them. However, they do not produce continuously melt. Disadvantage for the production of cast iron is the subsequent carburization of the melt in a channel induction furnace, induction furnaces can also be fed only with pretreated scrap. In large quantities, they are less economical than a cupola for their operation with electrical energy. However, the advantages of the induction furnace, the disadvantages in many applications.