What is a Refining Station? Steel Foundations
A Refining Station is used to refine molten steel into specialty grades while remaining in the ladle. This relieves the primary steelmaking furnace of most secondary refining operations.
The Refining Station and the Ladle Metallurgy Furnace (LMF) are similar in purpose, with their function being to relieve the primary steelmaking processes of most secondary refining operations. They also act as a time buffer for subsequent steelmaking processes. Unlike the Ladle Metallurgy Furnace, a refining station can utilize an oxygen lance and powdered aluminum additions to reheat the steel bath via the energy resulting from the oxygen/aluminum chemical reaction, in addition to external burners.
In the refining station, the liquid steel is stirred by bubbling an inert gas such as argon up from the bottom of the ladle. The inert gas is introduced either by an opening in the bottom of the ladle or by bringing a lance (tube) in from the top. As the argon gas bubbles float to the surface of the liquid steel, impurities, such as inclusions and metal oxides, attach themselves to the bubbles and float to the steel surface. At the surface, they are absorbed into the slag layer, leaving the steel “clean” of impurities.
Steel chemistry can be further modified by adding calcium, aluminum, or other ferroalloys as needed. Chemistry modifications are typically introduced by pushing thin, hollow wires filled with the necessary addition into the liquid steel. However, modifications can also be added by more standard methods such as dumping buckets or bags of materials into the steel. The stirring and agitation produced by the inert gas bubbling up from the bottom ensures that the chemistry and temperature of the liquid steel is homogenized throughout the ladle, however some stations also use electromagnetic stirring.
Since the slag layer protects the liquid steel from contact with the oxygen in the atmosphere, the flow of the argon gas is typically limited, so it does not disrupt or open the slag layer. However, for more efficient alloy additions, some refining stations may utilize a Composition Adjustment by Sealed argon bubbling with Oxygen Blowing (CAS-OB) system. The CAS-OB system allows for much more aggressive argon flow and faster/better mixing by lowering a refractory bell into the steel surface of the ladle, where the increased argon flow has opened an “eye” in the slag layer. Inside the refractory bell of the CAS-OB there is an inert atmosphere to ensure that the agitated surface of the steel bath does not contact the outside atmosphere.