When each heat leaves the Ladle Metallurgy Furnace, it is the proper chemistry and temperature for casting.
Steel pours from the ladle into the tundish, which serves as a reservoir to allow multiple heats to be sequentially cast. The tundish maintains a constant ferro static pressure, which insures consistent flow into the mold. Finally, the liquid flow in the tundish is used to help remove inclusions from the steel.
The steel flows from the tundish into the mold through the submerged entry nozzle or the SEN. The SEN delivers the steel beneath a layer of mold powder. The mold powder protects it from re-oxidation in the air and regulates heat transfer to the mold walls. The mold powder also lubricates the slab mold interface to ensure good surface quality.
The cast slab thickness at an integrated steel maker is between eight and twelve inches. Conversely, mini mills cast between two and three inches. This allows for greater energy efficiency and cost effectiveness in the hot rolling process.
As the slab leaves the mold, it enters a water spray chamber. After the slab is sheared to length at the end of the caster, it goes into a tunnel furnace.
In the tunnel furnace the slab temperature is equalized to approximately 1,900° Fahrenheit. It takes approximately 15 minutes for each slab to make its way through a tunnel furnace.
Each slab is transported from the tunnel furnace to the rolling mill by a “shuttle furnace.” After the shuttle furnace each slab goes through a de-scaling process where high-pressure water jets remove the scale from the top and bottom of the slab at approximately 3,200 psi.
From the de-scaler the coil heads into the hot-strip mill where the steel is rolled to customer gauge or pre-cold rolled thickness.