BESSEMER PROCESS. The most eommon steel making process is the Bessemer process, which may be subdivided into the acid Bessemer and the basic Bessemer process. The apparatus used is the same for both the acid and the basic proc ess, and the general process is the same up to a certain point. The chemical reactions differ substantially, however. Briefly described. the Itessemer process consists in charging molten pig iron into a vessel called a eonverter. forcing a blast of air through it until the silicon. man ganese. and carbon are burned out, and restoring a definite portion of manganese and carbon by adding a recarburizing material. This is the process in skeleton; it divides itself for the pur pose of a detailed consideration into the tollow lug divisions; Apparatus and mechanical ma nipulations and chemical reactions.
The central feature of the plant for making Bessemer steel is the converter. This is a pear shaped or jug-shaped vessel a refractory material. trig. 2 shows a modern American Bessemer converter in cross-section. The vessel is mounted on a horizontal axis. consisting of two hollow gudgeons. through which the air-blast enters the bottom of the con verter. An automatic valve shuts off the air when the converter is turned on its side, and admits it when the converter is upright. The blast is fur nished by a blowing engine which keeps the pressure at from '25 pounds to 30 pounds per square inch. The Cunt viler lining is about one foot thick, :Ind consists of a siliceous eompo-,i tion or stone in the acid process. and of dolomite or liniestohe in the basic process. The converter is so equipped that it can be rotated from a to a horizontal position and back in either direction. In operation the molten pig iron is charged into the converter them it ill/H7.0111:11. lit 11 the molten metal is taken directly from the blast-furnace it is usually brought to the converter in ladles: but in case the iron is nielttd in cupola furnaces these are so placed that they discharge directly into the converter. As soon as the charge has been run
into the converter it is turned into an upright position, the opt ration automatically turning on the blast. The blowing continues from seven to twelve minutes, and then the converter is turned upon its side and the recarburizing material in molten form is added. The charge is then ready for casting. This operation consists first in drawing the contents of the converter into a ladle, which is swung into position under the nose of the converter by a crane, the converter being tipped so as to empty. Sometimes the molds are set in a row around the perimeter of a circular pit, and the ladle is swung around in a circle by the (-rant. to fill one mold after another; but more often. in American practice, the molds are mounted in little platform which are hauled past the ladle and filled one at a time, the same ears taking the filled molds to the rolling-mill. where they are stripped from the ingots. Practieally all the mechanical operations, like the tilting of the converter and ladles, are performed by power.
The elletnioal reactions which take place in the converter differ according to whether the converter is acid- or basic- lined. In both eases the object is to burn away the silicon and carbon of the pig iron, and then to edit carbon in the proper proportions to make steel. The reason for this seemingly inconsistent practice of first burning away the carbon and then adding the same material is as follows: Pig iron eontains varying quantities of ea•bon. and to burn away just would necessitate a different length of the blowing for each charge of iron, thus introducing complications difficult to handle. It was Bessemer's original plan to do this, how ever, and it delayed the general introduction of the until the remedy was found by Mushet. This consisted in burning out the im purities and then adding a definite amount of carbon and manganese in the form of molten spiegeleisen or ferromanganese.