Thirty-eighth annual report [of the] Local Government Board. Supplement in continuation of the report of the Medical Officer of the Board for 1908-09, containing Reports and papers on the nature, uses and manufacture of ferro-silicon, with special reference to possible danger arising from its transport and storage / by S. Monckton Copeman, Samuel R. Bennett and H. Wilson Hake.

Date:
1909
Catalogue details

Licence: In copyright

Credit: Thirty-eighth annual report [of the] Local Government Board. Supplement in continuation of the report of the Medical Officer of the Board for 1908-09, containing Reports and papers on the nature, uses and manufacture of ferro-silicon, with special reference to possible danger arising from its transport and storage / by S. Monckton Copeman, Samuel R. Bennett and H. Wilson Hake. Source: Wellcome Collection.

    18/162 (page 8)
    (d.) It is used as an admixture in steel to produce certain important physical properties in the highest degree. These functions may be dealt with separately here, without entering on the details of actual manufacture. (a.) In the ordinary or acid Bessemer process the chief source of heat in the converter is that resulting from the oxidation of the silicon. Consequently the silicon content of the “ pig ” used must be kept within narrow limits, because if there be more than about 3 per cent, of silicon in the “ pig,” the “ blow ” will become too hot and the steel will be of inferior quality. Also the carbon, which is not oxidised out until after the silicon, may at very high temperatures, reduce the silica already formed. And as the “ blow ” is finished when the oxidation of the carbon is com- pleted, some silicon might yet remain unoxidised and objection- able excess of silicon in the steel would result. On the other hand, if there be not sufficient silicon in the “ pig,” the “ blow ” will be too cold, and there may be solidification of the external layer of metal in the converter—a result to be avoided at all hazards. The calorific value of silicon is approximately 14,000 British Thermal Units; that is to say, almost as great as that of carbon in being oxidised to C02> and nearly 3^ times the heat of formation of CO. So that the value of silicon in effecting a saving of fuel in Bessemer practice is easily understood; it is equivalent to about 10 cwt. of coal for a ten ton “ heat ” of less than twenty minutes duration. The silicon appears in the slag as silicate of iron, so that the greater the amount of silicon present the more is the waste of iron in the slag. It may be necessary to add ferro-silicon in the ladle, if a special quality of steel is desired, as from 0 2 or 0’3 per cent, of silicon raises the tensile strength of mild steel slightly, though it diminishes the ductility unless the percentage of carbon is very low. Occasionally, however, the ferro-silicon is run in from the spiegel cupola or added directly at the end of the “ blow.” In the basic Bessemer process the exothermic re-actions of silicon are not so important, because the amount of silicon in basic “pig” is much lower than in ordinary Bessemer “pig,” and the temperature does not rise so quickly at the beginning of the “ blow,” when the silicon is oxidised out. In fact, if there be a high percentage of silicon in the “ pig,” the “ blow ” is pro- tracted, and a large quantity of lime is necessary to combine with the silica formed in order to allow of the removal of phosphorus. In the open-hearth processes the temperatures realised are not usually so high as those obtainable in the Bessemer practice, con- sequently the calorific value of silicon is not considered to the same extent, but, as the silicon is almost completely eliminated in the slag, the use of a silicon alloy is almost a necessity. For, as Professor Turner, of Birmingham, has pointed out, the presence of silicon is necessary in steel if its important physical properties are to be realised to the utmost. In basic open-hearth working the silicon alloy is usually added in the ladle, so that, in order not to unduly chill the metal, the higher grades of ferro-silicon