Page:The American Cyclopædia (1879) Volume XV.djvu/371

 STEEL 359 process is briefly as follows : On Oct. 17, 1855, Henry Bessemer patented a process of blowing air or steam through molten pig iron in cruci- bles, until the metal was decarburized to any desired extent. At this time he recognized the fact that while steam cooled the metal, air increased the heat from red to white. A pat- ent in December of the same year specified a circular or elliptical vessel provided with a re- fractory lining and hung on trunnions, which could be filled and emptied by means of a lipped opening. In this patent the essential features of the process were fully developed. A patent of Feb. 12, 1856, indicated that the heat developed in the process was sufficient without the additional use of fuel, and that, according to the duration of the blowing, steel or soft iron might be produced. In July, 1856, Bessemer read a paper before the British association at Cheltenham on the " Manufac- ture of Iron and Steel without Fuel," which created an intense interest. But the subse- quent trials did not yield uniformly satisfactory results, and except by the inventor the process was practically abandoned. Patient and care- ful experiments showed that not all pig irons were adapted to the process ; that sulphur and phosphorus were not eliminated, and conse- quently pig irons containing a notable propor- tion of these substances could not be used. Again, the interruption of the process at the precise point of decarburization desired was found to be impracticable, owing to lack of trustworthy indications. Further, it was found that the process was not adapted to making the finer and harder steels, but had its chief application in the production of low steels or soft iron. The absorption of oxygen, anfl the consequent red-shortness of the metal when the pig iron was blown to nearly complete decarburization, was overcome by the addi- tion of spiegeleisen, a white pig iron contain- ing from 7 to 12 per cent, of manganese. This was a suggestion of Robert Mushet, and to it the practical success of the Bessemer pro- cess is largely due. After conquering all the obstacles to success, Bessemer did not find a ready acceptance of his process owing to the distrust caused by his previous failures. He therefore started in 1859 a small establishment of his own in Sheffield for the regular manu- facture of his steel. His commercial success soon led to the general adoption of his pro- cess throughout the civilized world, more par- ticularly at first in Sweden, where the pure ores and fuels furnished a pig iron admirably adapted to the process. In 1867 there were in England 52 Bessemer converters, in Prussia 22, in France 12, in Austria 14, in Sweden 15, and in Belgium 2. In 1873 Germany alone had 70 converters, and the number had risen in England to 105. The production in Eng- land has increased from 6,000 tons in 1867 to 540,000 tons in 1874. The Bessemer pro- cess consists, first, in melting the pig iron; second, transferring the molten metal to the converter, where it is subjected to the action of the blast of air ; third, pouring the finished product into a ladle ; and fourth, pouring from the ladle into the mould. The metal when solid, but while still hot, is taken from the moulds and worked by rolling or hammering into the desired form. Pig iron is in some cases used direct from the blast furnace, but remelting is generally found advantageous. The furnaces now used for this purpose are generally cupolas, which melt quicker and are more economical, although the direct contact of the iron with the fuel may cause a deterio- ration of the metal if the fuel is impure. The reverberatory furnace is not open to this objec- tion, but the pig iron may here suffer a loss of silicon and manganese, owing to the oxidizing atmosphere. The molten metal is either run in troughs directly from the furnace to the converter, or is first run into ladles where it can be weighed, and thence carried to the con- verter. The latter is a pear-shaped vessel, sometimes called the retort or simply the ves- sel, consisting of an iron mantle lined with a refractory silicious material. It is usually made in two parts, upper and lower, for con- venience of lining. The bottom, which con- tains the tuyeres, is made in a separate conical piece, and inserted from below. The size of the converter is usually calculated for a charge of five to six tons of pig iron. This amount of metal occupies but a small part of the ves- sel, as is indicated in the accompanying figures. The greatest external diameter is about 8 ft., with a total height of from 12 to 15 ft. The silicious material of the lining usually con- tains a little alumina. The so-called "ganis- ter" used in England for this purpose is a ground sandstone found in the coal forma- tion, containing 93 per cent, of silica, 4 per cent, of alumina, and 1 to 2 per cent, of oxide of iron. The lining is made by ramming the material in a moist condition around a form placed in the converter. It is usually about 12 in. thick. The greatest attention must be paid to the selection of the material for the FIG. i. lining and to its thorough consolidation, for upon the lining the success of the process largely depends. The tuyeres, from 7 to 12