The Robert Process.— In this process a rotary converter was with horizontal tuyeres placed tangentially, in order to impart a rotary motion to the metal. The tuyeres were submerged, but near to the surface of the bath. Whilst the loss was greater than in the ordinary vessel, a hotter steel was made, which was suitable for steel castings, and for this purpose it was almost exclusively used.
The Tropenas Process.— This has been by far the most successful development of the Bessemer process for casting work, introducing the idea that the violent mechanical disturbance of the bath is unnecessary and that the more tranquil the bath is the purer, sounder and better will be the steel. A rotary, side blown converter of two tons capacity is used, and the tuyeres are arranged in a symmetrical posi tion from the centre tuyere in order that any tendency to stirring or rotation may be neutral ized. The tuyers, moreover, are never beneath the surface of the metal, though they approach it very closely. A second row of tuyeres is placed a few inches higher than and parallel with the lower tuyeres, and when the carbon flame appears these tuyeres are opened, admit ting air to complete the combustion of carbon from CO to CO:. The result of this is to increase the temperature of the bath by radia tion. A high silicon, high manganese mixture is used in the converter, and results in exceed ingly hot and fluid steel, which can be car ried around in hand ladles and poured into very small and complicated shapes.
When the blast is first started the surface only of the metal is oxidized, three pounds pressure of air being used, and by dilution and change of specific gravity a fresh surface is constantly presented to the action of the blast without any mechanical disturbance whatever. In this way the possibility of occluded gases is reduced to a minimum, no more air being intro duced than is necessary for the chemical re action. The fact remains, however, that for casting basic open hearth steel is greatly pre ferred.
The Roll of history of the de velopment of the Bessemer process in the United States is the history of a company of the brightest minds this country has produced. There is no doubt that the Bessemer process is worked more perfectly in America than else where, and the credit must be given to those brilliant men who in the early days gave their great intellects to its problems and overcame them. The most important work has been done by A. L. Holley, John and George Fritz, Wil liam R. Jones and Robert W. Hunt. To Alex ander Lyman Holley one of, if not the fore most American engineers, were granted 10 pat ents in connection with the Bessemer process alone, some of them being raised converters, hydraulic cranes, accumulating ladles and con verter bottoms. Holley investigated the Besse
mer process in England in 1863 and realizing its possibilities and also its defects obtained the only American license, and set to work to perfect its machinery. The latest and most im portant of the modern improvements is the Jones metal mixer, which is a large storage re ceiver in which the various quantities of iron direct from the blast furnace are stored and equalized, so that the silicon is uniform in the converter. One of the most important links in this perfectly welded chain was the work of Robert Mushet, who developed the method of recarburizing the iron after blowing in the con verter. The Swedish method of checking the blowing when the carbon had been reduced to the proper percentage proved too slow and uncertain. Mushet's plan was to burn out all the carbon and restore a right proportion by the addition of a quantity of melted spiegeleisen (about 10 per cent) after the blow. Without his method the Bessemer process could not have been a commercial success. Considerable trouble was caused in the early days by the con fliction of the Bessemer and Kelly patents. The Winslow, Griswold and Holley Company at Troy had control of the Bessemer patents covering the important and essential machinery, and the owners of the Kelly and Mushet patents could not operate without the use of this ma chinery. In fact each side was necessary to the other and naturally this resulted in an agree ment by which a joint-stock company of all the pneumatic steel manufacturers was made. All the patents on these processes have now ex pired. According to the 1914 census of manu factures there were in the United States in that year 9,146 plants engaged in the mAnufac ture of Bessemer steel. Their combined prod uct was 6,219,304 tons of ingot steel and 43,437 tons of castings. The decline in the use of Bessemer steel in favor of open hearth steel is markedly indicated by the decrease of nearly 3,000,000 tons in the annual production for the census period 1909-14 for the former and an equal gain for the latter. The production of open hearth steel in 1914 was over 17,000,000 tons — nearly three times that of the Bessemer product. See STEEL - OPEN HEARTH MANU FACTURE. Consult Hall, J. H., The Steel Foundry' (New York 1914) ; Harbord, F. W., and Hall, J. W., The Metallurgy of Steel' (London 1918) ; Stoughton, B., The Metal lurgy of Iron and Steel' (New York 1913).