Fig. 158.—Another Cross Section of the Same.
183. The Bessemer Process.—This consists of blowing air through molten pig iron in a vessel called a converter, sectional views of which are shown in Figs. [157] and [158]. A converter is a pear-shaped structure hung on trunnions A, A, so that it can be tipped forward. The air is forced through one of the trunnions, which is hollow, and is connected with a pipe which conveys the air to the air chamber f at the bottom of the converter. The bottom grate or tuyère plate is located directly above the air chamber, and through the openings j, j, in the tuyère plate, the air passes up through the metal.
Fig. 159.—Pouring Metal into Molds.
Fig. 160.—Ingot Stripper.
The converter is tipped forward into a horizontal position while the molten metal is poured into it. The air is then turned on, and the converter is raised to a perpendicular position. The air passes up through the entire charge of iron; consequently the metal is thoroughly acted upon, while in the open-hearth process it is not. The Bessemer process is based on oxidation; it produces a very high temperature and keeps the charge in a liquid state during the time of blowing. This is continued until the sulphur and phosphorus are removed or the charge becomes decarbonized,—a condition termed burned steel, owing to the presence of dissolved oxygen. This condition is then changed or recarbonized by adding manganese alloys, such as spiegeleisen or ferromanganese, which give the necessary amount of carbon. By these additions the iron is changed into steel.
The Bessemer process requires a very short time in comparison with the puddling process. Three tons of pig iron can be refined in about twenty minutes, while by the puddling process the same amount of metal requires about twenty-four hours.
Fig. 161.—Lowering an Ingot into the Soaking Pit.