Both types of furnace comprise of a refractory lined vessel into which either mixed liquid iron/solid scrap or solid charges of scrap are added together with slag making materials essentially made up of lime with small quantities of fluorspar. The process is then maintained in conditions, which promote the removal of unacceptable levels of impurities such as sulphur, phosphorous and excess carbon, silicon and manganese.

 

In the pneumatic BOS process, excessive furnace slag, oxidising in nature with a high FeO content, is extremely detrimental to both final cleanliness and efficiency of desulphurisation efficiency in the ladle as well as overall reaction predictability. The yield of deoxidising elements such as aluminium and silicon and recovery alloying elements is significantly decreased by the presence of carryover slag in the ladle.

 

Several slag retention techniques have been developed to reduce or eliminate this slag carryover. The least costly method of slag control is to quickly tilt the vessel back at the first sign of slag entering the ladle at the end of tap. Other more costly but more efficient systems include electromagnetic slag detectors, tap hole slide gates and eccentric bottom tapping (EBT) in electric arc furnaces.

 

Another very efficient but less expensive system is the use of slag balls and slag floats. Foseco Steel has developed a system called the RAMTAP/SWIMTAP slag retention system for the control of the pre-tap and post-slag during tapping of the BOS furnace. Under careful supervision and applied using mechanical applicators, the use of both RAMTAP and SWIMTAP can ensure almost slag free tapping.