Aluminum may be added to the furnace, ladle, Ladle Furnace, caster tundish or ingot mold. Each type of addition has its specific purpose, and each will produce characteristic results. Aluminum is a very powerful deoxidizer but poses problem because of its low density and lower melting point. It has been estimated that the density of liquid aluminum at steelmaking temperatures (1600°C) is only about 2 g/cm3. Steel's density at this temperature is greater than 7 g/cm3, depending on composition. Therefore, when aluminum is added to the bath, it will float at the steel/slag interface, where it quickly oxidizes. Relatively small amounts actually make contact with the steel. The recovery of Al by notch bar/ shot addition is therefore low and erratic as its loss by burning in atmosphere is high and unpredictable.
Wire feeding has overcome this disadvantage by force feeding the aluminum deep into the bath. The aluminum wire is introduced in to ladle from top through slag at a speed ranging from 100-300 meters/minute depending upon the ladle size. The main objective of wire feeding is to increase the residence time of solid aluminum before melting and release of aluminum at a depth of 0.5-1.5 meters from top so that aluminum reacts with steel before floating to the top The depth of Al wire melting is dependent on Al wire diameter, wire feeding speed, bath temperature etc. The amount added depends on composition, temperature, and tap carbon. The recovery of Aluminum is more than double of recovery achieved with Notch Bars/Shot additions. The normal Al level in Al/Al-Si killed steel is 0.02-0.05%.The deoxidation of slag by reducing its FeO and MnO content is also necessary for preventing Al fading (Loss of Aluminum) between Ladle furnace and caster. Aluminum contents over 0.01% can cause nozzle blockage in open stream continuous billet casting machines.
The solution lies in use of Sub merged entry nozzle and proper calcium treatment of steel.