Suggested as far back as 1856 by Sir Henry Bessemer, the Basic Oxygen process of steelmaking consisted of blowing high purity oxygen onto the surface of a bath, or mixture of scrap metal and molten pig iron. The resulting violent reaction and intense heat accelerated the refining of steel. By the time CF&I began utilizing the method in 1961, the time it took to make a batch of steel was shorted from 10 hours to 60 minutes.
The Basic Oxygen furnaces used at CF&I’s Pueblo Plant consisted of two 120 ton capacity refractory-lined pear shaped vessels mounted on pivots on either side so that they could be tilted a full 360 degrees if needed. Due to the intense heat, one vessel operated while the other one was relined with bricks or repaired if needed.
Scrap metal, about 30% of the total batch, was loaded first into the vessel with a long cylinder shaped tool called a charger, then hot metal known as pig iron created in the blast furnace was poured into the opening of the tilted vessel. After loading, the vessel was tipped upright. A water cooled, copper tipped oxygen carrying lance was lowered to a point four to eight feet above the bath. Oxygen was then blown onto the surface of the metal, igniting the heat below to blazing glare.
Reaction started immediately and the temperature at the center of the vessel climbed to iron’s boiling point of about 3,000 degrees Fahrenheit. Unneeded naturally occurring minerals such as carbon, manganese and silicon within the scrap metal were oxidized at this point. Lime and fluxes were added which kept impurities such as phosphorus and sulphur in slag form. The slag floated to the top and was poured off as waste to be reused at a later date.
When the refining process was over, the vessel was “tapped” or emptied. The molten steel ran into a ladle and later was poured into ingot molds for shaping.
In the late 1960s, the basic oxygen furnace could produce 100,000-110,000 tons of steel per month. The Basic Oxygen Furnace was used until the mid-1970s when CF&I replaced the technology with the more efficient and environmentally friendly Electric Arc furnaces.