THE MACHINERY REQUIRED BY THE BESSEMER PROCESS.
The Bessemer process is exceedingly simple. The whole process rests upon the action which a strong current of air exerts upon the elements with which it meets when forced through a mass of melted pig iron. The stirring and combustion which it produces transform certain qualities of cast iron into a malleable metal that may be wrought like cast steel. The Bessemer process is, therefore, a method of refining. The opera tion is performed in a large egg-shaped vessel; the cast iron is poured in in a liquid con dition, and then the air is forced beneath it at a high pressure. The metallic mass re mains fluid while the air acts upon it. The resulting malleable product is obtained in certain cases by stopping the air while the process is yet incomplete, or, more generally, by prolonging its action until the iron is converted into a sort of burned or over-refined mass, and then transforming this product immediately into a malleable metal by means of the simple addition of a crystalline and steely iron. The process was at first carried on in a sort of fixed cupola-furnace, into which air was driven by tuyers passing through the bottom; but on account of the trouble caused by the tuyers clogging, another arrangement was substituted, where the vessel in which the process is executed is called the converter, and is a movable egg-shaped pot, with a short neck. It is made of plates of iron riveted together, and protected inside with a sheeting of refractory clay, 12 inches in thickness. At about the height of its centre of gravity this vessel is sus pended upon two trunnions, to which are geared wheels that enable the apparatus to be turned by hand or by machinery on a horizontal axis. An air-box which occupies the lower part of this converter communicates with the interior by means of a number of small holes passing through the fire-brick bottom. The air passes from the blowing engines through a hollow trunnion, thence into the bottom of the converter, and may be thrown in small jets into its interior, no matter in what position the vessel may be turned. The capacity of the converter is usually from five to six times the amount of
the cast iron to be treated. The throat should be large enough to let out the gases when the process is in operation, and to enable the fluid metal to be poured in and out without danger of obstruction. During the operation of converting, the mouth of the converter passes under a hood of sheet iron, which carries the fumes to a chimney. When the operation is terminated, the converter is turned over, and all the metal it contains is poured into a ladle, at the bottom of which is a hole, out of which the fluid mass can be tapped. The metal has a tendency to cool rapidly, and must be poured into the moulds soon, and with care that it shall not touch the walls of the mould. In order to accom plish this, a hydraulic crane is used, of which the pivot is a piston playing in a cylinder, and at the end of a horizontal arm extending from this pivot is fixed the ladle; the moulds are placed in a circle around the pivot at such distance that a hole in the bottom of the ladle can be brought directly over the centre of each of them by revolving the crane, while the height of the ladle above the mould may be fixed by raising or lowering its piston-pivot by hydraulic power.
The blowing-engines are of various patterns. The average pressure of the air should be from 15 to 25 pounds to the square inch, and it should be thrown into the converter through thirty-five tuyers, each inch in diameter.
It is, however, always best to have a considerable surplus of power in the blowing apparatus. When the cast iron is not taken directly from the blast-furnace in a liquid state, it is necessary to have a reverberatory or cupola-furnace for remelting it: this should be placed at such a height above the level of the converter that the liquid iron will flow readily from the former into the latter. It may be elevated in ladles, how ever, to the converter, as done at the Wyandotte Works, Michigan. The iron should be introduced into the converter as hot and fluid as possible.