Crucible furnace
A modern crucible furnace is an inductively heated furnace that is used in foundries to melt steel and cast iron , but also non-ferrous metals . Crucible furnaces were originally heated with solid fuel such as coke and were the first source of mild steel , which after the introduction of the Bessemer process , the Thomas process based on it and the Siemens-Martin process at the end of the 19th century, welded iron or displaced wrought iron produced by the puddle process .
Designs
Induction melting furnace
The modern crucible furnace essentially consists of the housing with tilting device and cover, the vertical stacks of sheet metal around a current-carrying coil, in the middle of which the crucible for holding the material to be melted is located. The electrical equipment includes a transformer , a frequency converter for higher frequencies than the mains frequency and a capacitor bank to compensate for the effects on the mains. The current in the coil induces strong eddy currents in the crucible filling , which melt and mix the contents. In addition to smaller furnace units (furnace content 60 kg to 6 t), furnaces with a content of up to 60 t have also been built since the 1960s.
A first electric induction melting furnace was built in Gysinge in 1899 based on a patent from the Swedish chemist Frederik Adolf Kjellin , and Hermann Röchling acquired the patent in 1901 for Völklinger Hütte .
Crucible shaft furnace (historical)
The British clockmaker Benjamin Huntsman developed the crucible steel process (Engl. Crucible steel ) in 1740 and ensured England through the closely guarded secret of production for a long time, the dominance of high quality steel. It was not until 1823 that Friedrich Krupp succeeded in producing high-quality mild steel in a crucible furnace in Germany as well.
In the crucible furnaces that were used in the 18th and 19th centuries to produce wrought iron ( i.e. steel ) , the steel made from cement steel (English blister steel ) was melted in refractory crucibles made from clay and graphite . Such a crucible is around 40 cm high and 18 cm wide and holds around 20 kg. Two of these crucibles are placed in a furnace shaft (A), several of which are arranged side by side in rows. The shafts are lined with fire-proof lining and are closed with a cover (K), which is approximately at the level of the hut hallway and is usually equipped with a chain hoist and counterweight for easier operation. The crucibles are placed in the furnace shaft from above and are also removed from above using special tongs after the melting process has been completed. The crucibles are slightly elevated in the shaft on a chamotte stone called "cheese" , which lies on a grate (B) that closes the furnace shaft at the bottom. In operation, the furnace shaft is completely filled with fuel (mostly coke , but also charcoal ). The ashes fall through the grate into the ash trap (C), which is to be emptied via the cellar corridor (D) running parallel to the row of ovens - the cellar corridor also supplies fresh air. The fireclay stone under the crucibles prevents the crucibles from coming into direct contact with the cold, fresh air. The exhaust gases from the ovens are led via a fox (E) to the forge (F), which can be cleaned via the ash trap at (M). Usually there is also a drying or firing furnace (Z) in the immediate vicinity of the crucible steel furnaces, in which the crucibles are dried or fired and the insert metal can be preheated.
These original crucible shaft furnaces were further developed in that they were given regenerative firing as crucible flame furnaces or the entire crucible with the furnace was rotatably mounted on a frame and the melting material could be emptied without removing the crucible.
literature
- William Henry Greenwood: Steel and Iron: comprising the practice and theory of the several methods pursued in their manufacture and of their treatment in the rolling mills, the forge, and the foundry , Second Edition, Cassell & Company, London 1884, p. 417 ff ( online at archive.org )
- Hermann Meyer: Textbook of the general mechanical technology of metals , Verlagbuchhandlung Max Jänecke, Hanover 1907, p. 9 f
- Adolf Ledebur : The processing of metals by mechanical means . Friedrich Vieweg and Son, Braunschweig 1877. Chapter The Melting of Metals - Crucible Furnaces , p. 218 ff ( online at archive.org , accessed on April 19, 2010)
Individual evidence
- ↑ Chronicle of the Völklinger Hütte , accessed on January 22, 2015