cupola
The cupola furnace is a shaft furnace in which metals can be melted. Cupolas are used to manufacture cast iron from pig iron and scrap. The cupola furnace is very similar in structure and mode of operation to the blast furnace , is up to 20 meters high, but does not reach the temperatures necessary to reduce metals from their ores .
history
The cupola furnace was invented in 1794 by the Englishman John Wilkinson (1727-1808). The cupola made iron casting independent of the much larger blast furnace, as it enabled iron to be smelted without the need for the much higher temperatures of a blast furnace.
The name "cupola furnace" is derived from the dome in which the long furnace shaft protruded from the factory roof.
Layout and function
To start the furnace, a wood fire is lit at the bottom and covered with coke . In newer furnaces, coal is instead filled into the furnace and made to glow with gas burners . Then the furnace is filled with several layers of metal and coke while the embers are burning and air is blown at the same time. This creates temperatures of up to 1,600 ° C at the bottom of the furnace, which melt the metal. Depending on whether the air is preheated and fed into the furnace or not, a distinction is made between hot-blast and cold-blast cupolas.
To remove the metal, the furnace must be pierced slightly above its bottom. A siphon with two outlets connects to the bunghole : the slag is drained through the upper one into a receptacle. Through the other, the metal is pushed through under the slag and can, for. B. be passed into a holding furnace. The function of the siphon is only possible due to a slight overpressure in the furnace. The correct setting of the slag and metal outlet to the floor level is a matter of experience.
cast iron
The cupola furnace is of particular importance for the manufacture of cast iron. It is loaded with pig iron, steel scrap, recycled material and broken machine castings. The setting of the carbon content of the cast iron takes place via the ratio of steel scrap (low carbon content) to machine castings (high carbon content). Increasing the addition of coke also increases the carbon content. Furthermore, lime added to the resulting acid in the process slag to neutralize and to keep better flowable.
The carbon content of the cast iron can also be reduced by blowing in air with an increased oxygen content.
Further developments
So-called coke-free cupolas are operated purely with natural gas or oil and have a better heat balance and lower emissions. Since, in contrast to the blast furnace, the coke is not absolutely necessary for a chemical reaction, this changeover is possible.
Cupola furnaces are also increasingly being replaced by induction furnaces , since, in contrast to coke-fired cupolas, they produce less slag and waste, are more flexible in use and with them the composition of the melted product can be adjusted more precisely. However, they do not continuously produce melt. The subsequent carburization of the melt in a channel induction furnace is disadvantageous for the production of cast iron, and induction furnaces can only be charged with pre-treated scrap. In large quantities, they are less economical than a cupola because of their electrical operation. However, the advantages of the induction furnace outweigh the disadvantages in many applications.
literature
- Karl-Heinz Caspers: Beginning and development of melting in the cupola furnace. In: Landschaftsverband Rheinland, Rheinisches Industriemuseum , Thomas Schleper, Burkhard Zeppenfeld (Hrsg.): St. Antony - the cradle of the Ruhr industry, a "business crime" about the first ironworks in the area . Book accompanying the exhibition in the St. Antony Hut . Aschendorff, Münster 2008, pp. 122-124, ISBN 978-3-402-12764-3 .
- Carl Irresberger : Kupelofenbetrieb (= workshop books for company officials, foremen and skilled workers, booklet 10). Julius Springer, Berlin 1922 ( digitized ).
Web links
- Coke-free cupola furnace - the environmentally friendly smelting unit Functional description of gas-heated cupola furnaces on the website of the Dueker.de foundry, accessed on October 18, 2012.
- Operation of a cupola furnace in an iron foundry Daily routine in an iron foundry in 1989 with a focus on the furnace team. Landschaftsverband Rheinland, accessed on March 10, 2020.
swell
- ↑ LKG technical terms "Eisenkunstguss" ( Memento of the original from 23 September 2015 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
