Abstract: The carbon and dissolved oxygen contents of molten steel are reduced by a vacuum degassing treatment which may employ oxygen blowing. A determination is made of the idealized trajectory or path reflecting the change in carbon content and dissolved oxygen content, between atmospheric pressure and a preselected sub-atmospheric pressure at which the vacuum degassing treatment occurs. The idealized trajectory also reflects the effect of extraneous factors on the carbon content, dissolved oxygen content and temperature of the molten steel during the treatment. A selection is made of the boundaries of the idealized trajectory based upon the permissible limits of carbon content, dissolved oxygen content and temperature at the end of the vacuum degassing treatment. Adjustments are made at the beginning of the treatment and periodically throughout the treatment to maintain all three parameters, carbon content, dissolved oxygen content and temperature, within the boundaries of the idealized trajectory.

Abstract: A method for improving separation of the flotable phase from the non-flotable phase of a slurry of particulate material in a froth flotation machine comprising a tank, an upper outlet port for discharge of the flotable phase, and a mechanism for delivering air to the slurry in the tank to form a froth which includes a mixture of air bubbles and the flotable phase from the slurry, with the rate and selectivity of separation of the flotable phase from the slurry for predetermined size particles of the flotable phase and at a predetermined concentration of the flotable phase being dependent on the total volume and size distribution of the air bubbles generated in the slurry, the method of this invention comprising the steps of providing a quantity of slurry in the tank, generating air bubbles of relatively small size and relatively large size, and controlling the volume of air as small bubbles and the volume of air as large bubbles in response to the concentration of the flotable phase of the slurry for enhanced