Slag free tapping

Priamary steelmaking slag contains   and CaO.
FeO content varies form 15-18 %. These slags are oxidizing in nature. During tapping, carry-over of slag should be avoided for the following reasons:

• During ladle treatment impurities can revert back from slag to metal.
• During synthetic slag practice in ladle, composition of slag will be altered which will affect secondary steelmaking refining operations like desulphurization, deoxidation etc. This will lead to increased consumption of deoxidizers
• Carried-over slag can increase the refractory wear.
• FeO and MnO of slag react with Al and forms   which is a solid inclusion at the steelmaking temperature, this will affect steel cleanliness.

Mechanism of slag carry-over 

Slag can be carried-over from converter to ladle in the initial stage when converter is tilted. As tapping proceeds converter is tilted further which leads to formation of vortex and top slag is carried into the ladle. During up-tilting, part of the slag may be carried into ladle.
The amount of drained slag depends on tilting speed of converter, bath level, drain velocity

Prevention of slag carry-over

Several methods are developed and in use to minimize slag carry-over. Tap-hole plug, slag cut ball pneumatic slag stopper and slag detection methods are commonly is use. The interested reader may look into the references given at the end of the lecture