Ladle Metallurgy Furnaces Steel Foundations
A Ladle Metallurgy Furnace, better known as the LMF, 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 main functions of a ladle furnace are:
- Reheating of liquid steel by electric power which is conducted by graphite electrodes.
- Homogenization of steel temperature and chemistry through inert gas stirring.
- Formation of slag layer that protects refractory from arc damage, concentrates and transfers heat to the liquid steel, trap inclusions and metal oxides, and provides means for desulphurization.
- Additions of ferro alloys to provide for bulk or trim chemical control.
- Cored wire addition for trimming and morphology control.
- Provide a means for dephosphorization or deep desulphurization.
- Act as a buffer for downstream equipment and process.
- A Ladle Metallurgy Furnace uses three large, graphite electrodes to reheat the steel bath in the ladle.
Molten 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 surface of the molten steel. At the surface, they are absorbed into the slag layer, leaving the steel “clean” of impurities.
The steel chemistry can be further modified by adding calcium, aluminum, or other ferroalloys as needed. The 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, although some LMFs also use electromagnetic stirring.
The Ladle Metallurgy Furnace (LMF) and refining station are similar in purpose, with their function being to relieve the primary steelmaking furnace of most secondary refining operations. They also act as a time buffer for subsequent steelmaking processes.