GB460138A - Improvements in and relating to the manufacture of iron - Google Patents

Abstract

In the production of pig iron in a blast furnace, the ores and fluxing media are mixed in such proportions as to form slags of relatively low melting point and in which the ratio of lime to silica is decreased progressively below the usual limits of 1,65 to 1,25 as the alumina content of the slag formed increases upwards from 15 per cent. For example with a slag containing 20 per cent of alumina, the ratio of lime to silica is from 1,125 to 0,85 and for a slag containing 30 per cent of alumina, the ratio is from 0,95 to 0,75. The molten metal tapped from the furnace into a ladle or another inactive receptacle is treated for the removal of sulphur and/or oxides slags or gases. The smelting is carried out in the furnace to produce a low silicon iron, and a high sulphur content. To remove the sulphur &c., the hydrogen gas or a gas containing a considerable quantity of hydrogen is bubbled through the molten iron, or a desulphurizing agent such as alkali, e.g. in the form of soda ash, is added to the iron, the alkali being preferably placed in the ladle &c. before the iron is run in. The ladle may also be preheated and provided with a cover to conserve the heat during the desulphurization. After the addition of alkali, the slag is thickened by the addition of lime so that it can be skimmed off or water is added to the molten slag which is decomposed by the steam formed, and certain of the products of the reaction volatilized leaving the metal clean and ready for pouring. The desulphurization may be assisted by agitation of the metal in the ladle during its travel from the furnace to the steel plant or by blowing gases through the molten metal. Before the desulphurization as described above, especially when the original charge contains manganese, the metal from the furnace is poured into a hot container and allowed to stand, any manganese sulphide forming being removed before the iron is refined further. The atmosphere above the metal may be converted into an oxidizing one, to accelerate the desulphurization. In carrying out the smelting, the furnace is burdened with ores irrespective of their manganese content and the manganese required, if any, to attain the desired specification is added to the desulphurized iron in the ladle &c. in the form of manganese alloys or otherwise, e.g. ferromanganese or spiegel. The iron produced may be converted into steel, e.g. by the basic Bessemer or Thomas process. Specification 454,562 is referred to.