The Blast Furnace

A blast furnace produced molten iron by combining iron ore, flux such as limestone and/or dolomite, coke, and hot air, creating molten slag and blast furnace gas as waste products. The molten iron and slag collected at the bottom and were drained off periodically, while gas left through the top and was routed to stoves and boilers for fuel. Furnace No. 1, one of two furnaces that operated at Sloss, replaced original furnaces built between 1881 and 1883 when the present structure was built in the late 1920s. The attached open-side cast shed was where molten iron was originally cast into bars called pigs. The furnace operated continuously, twenty-four hours a day and seven days a week, kept filled to a stock line about six feet from the top as new materials were added at the same rate that iron and slag were produced. It worked on a countercurrent principle, with iron ore, flux, and coke charged into the top while hot air was blown into the bottom through tuyeres. The coke descended largely unchanged until it reached the tuyeres, where it burned to form carbon monoxide and released intense heat. Rising hot gases heated the descending stock and reduced the iron oxides in the ore, freeing iron that trickled into a pool at the hearth, while the flux absorbed impurities from the ore and ash from the coke to form slag that floated on the molten iron. About every four hours, workers cast the furnace by opening the iron notch at the base, releasing molten iron to flow down a curved runner into a ladle car for transport to the pig casting machine, after which the notch was sealed again with clay using the mud gun, while slag was drained through a separate runner.

Birmingham, Alabama · United States