Ferroalloys are also added during tapping from bof see bof process link from description. Additions from bof are kept minimum due to their low recovery and balance additions at LRF done to save costly ferroalloys. There are also other factors.

The plug on the tap hole is usually made so that it will not dissolve until the heated steel gets to it. Since the slag is of cooler temperature than the steel itself, you can tip it and the plug will hold until enough of the liquid metal moves over the hole. Essentially the plug acts as delay timer giving you time to tip the furnace enough to submerge the path to the hole in molten steel before it gives way. Then you tap as normal.

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Ld furnace shell is lined with magnesite based refractory bricks. They are prone to thermal cycle, chemical attack and mechanical impact. To reduce wear rate of bricks, slag coating is done after every tap. Left over slag inside furnace is splashed by blowing nitrogen and a layer of slag deposited on bricks.

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Density of slag stopper is in between metal and slag densities. It floats at the interface of slag and metal. As metal drains out and slag about to come, stopper closed tap hole opening.

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