![]() ![]() This is referred to as the “hot metal” process. At composite works, where blast-furnace metal is available, molten pig iron is employed. In many cases, cold or solid pig iron is charged into the furnace and the process is referred to as “the cold pig and scrap” process. As far as possible, Siliceous materials should be avoided because an excessive lime is required to neutralize the silica formed, and if the slag becomes too siliceous the removal of sulfur and phosphorus is hindered and the basic lining of the furnace is attacked. The addition of Limestone forms a basic slag that affects the removal of sulfur and phosphorus. In the basic process, a wider range of raw materials may be employed. The carbon escapes as carbon monoxide gas, while the silica and manganese oxide passes into the slag, which is virtually a ferrous-manganous silicate. The carbon, silicon, and manganese present in the charge are oxidized by these ore additions. The pig iron and scrap are charged, and when melted the slag is rendered fluid and oxidized by iron-ore additions. The maintenance of an acid slag prevents the elimination of these elements. The raw materials for the acid process are of a siliceous nature, but low in sulfur and phosphorus.
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