Vacuum purification of liquid metal

A process for removing metallic impurities from steel comprising the steps of:

• subjecting a bath of liquid steel containing metallic impurities through a continuously decreasing pressure maintained at a level equivalent to about 60% to about 80% of the total vapor pressure of the liquid metal to create a bulk velocity of gasified vapors from the surface of the liquid metal,
• continuously lifting liquid steel from a lower level in the bath to at least the surface of the bath to create a circulation within the bath to maintain the surface free of contamination,
• continually condensing the rising gases remotely from the surface of the bath to prevent reflux of the impurities into the molten metal thereby to increase the speed of removal of the impurities,
• restoring the pressure to normal, and recovering the treated steel.

A process of removing metallic impurities from steel comrising the steps of:

• subjecting a bath of liquid steel containing more than 0.15% by weight of copper and more than 0.10% by weight of tin to a continuously decreasing pressure maintained at a level equivalent to 60% to 80% of the total vapor pressure of the liquid metal to create a bulk velocity of rising gasified vapors from the liquid metal surface,
• continually maintaining the surface of the molten metal substantially free of surface contamination to enhance the emission of the gases,
• continually condensing the rising gases remotely from the surface of the bath to prevent reflux of the impurities into the molten metal,
• carrying on the steps for a time of not more than 30 minutes until the treated steel contains less than 20% of the initial copper and tin,
• restoring the pressure to normal, and recovering the treated steel.

A process for producing steel, comprising,

• forming a bath of liquid steel from a steelmaking process, containing residual metallic impurities including more than 0.15% by weight of copper, eliminable gases, and manganese,
• subjecting a bath of such steel to vacuum treatment to remove the metallic impurities and eliminable gases and the manganese,
• recovering the vacuum treated steel and then subjecting it to an addition process to add required constituents including manganese,
• and directly casting the steel so treated.

A process for removing metallic impurities from steel, comprising the steps of:

• subjecting a bath of liquid steel containing metallic impurities including more than 0.15% copper to vacuum effective to cause emission from the metal surface of the metallic impurities as a bulk flow of rising gases,
• continually maintaining the surface of the molten metal substantially free of surface contamination to enhance the emission of gases,
• continually condensing the rising gases on condensing surfaces arranged remotely from the surface of the bath to prevent reflux of the impurities into the molten metal,
• continuously condensing the rising gases on said surfaces to prevent reflux of the impurities into the molten metal,
• continually adjusting the vacuum pressure to maintain it at a level equivalent to 60% to 80% of the total vapor pressure of the liquid metal thereby to maintain said bulk velocity if gasified vapor,
• adjusting the temperature of the condensing surfaces to maintain the liquidity of the condensed gases and continuously removing the liquid so formed on the surfaces to prevent return to the bath of molten metal.

An apparatus suitable for treating molten metal to remove impurities, comprising:

• a vacuum chamber having a receptacle for molten metal, a gas outlet and an outlet for liquid condensate,
• vacuum pump means for applying a vacuum to the gas outlet,
• two hollow legs leading downward from the bottom of said receptacle for immersion in a supply bath of molten metal,
• a condenser above the liquid metal level in said receptacle having surfaces for intercepting gases emitted from the molten metal and converting them to liquid condensate,
• means for receiving liquid condensate from said condenser and removing it through said outlet,
• means for continuously injecting lifting gas into one leg to provide upward circulation of metal therein and downward circulation in the other leg.

An apparatus suitable for treating molten steel to remove impurities, comprising:

• a vacuum chamber having a receptacle for molten metal, a gas outlet and an outlet for liquid condensate,
• vacuum pump means for applying a vacuum to the gas outlet,
• a first hollow leg leading downward from the bottom of said receptacle for immersion in a supply bath of molten metal,
• a second hollow leg extending from a position above the molten metal level in said receptacle to a position therebelow for immersion in said supply bath,
• means in the top of said second leg for releasing liquid metal and spraying it on the surface of the metal in said receptacle,
• a condenser above the liquid metal level in said receptacle having surfaces for intercepting gases emitted from the molten metal and converting them to liquid condensate,
• means for receiving liquid condensate from said condenser and removing it through said outlet,
• means for continuously injecting lifting gas into the second leg to provide upward circulation of metal therein and downward circulation in the first leg.

An apparatus for treating molten steel to remove impurities, comprising,

• means forming a vacuum chamber and a receptacle for molten metal, operatively connected
• said vacuum chamber having a gas outlet,
• vacuum pump means for applying a vacuum to the gas outlet,
• a condenser above the liquid metal level in said receptacle having surfaces for intercepting gases emitted from the molten metal and converting them to condensate,
• means for introducing gas into a lower part of the receptacle in quantities effective to cause circulation of the molten steel and to keep the surface free of contamination.

A process for removing metallic impurities from steel, comprising the steps of:

• subjecting a bath of liquid steel containing metallic impurities, to vacuum effective to cause emission from the metal surface of the metallic impurities as a flow of rising gases,
• continually maintaining the surface of the molten metal substantially free of surface contamination
• continually preventing return of impurities into the molten metal,
• maintaining the vacuum, throughout the treatment, at a level at which the emission is in the form of a bulk flow of rising gases which in combination with the continual freeing of the surface of contamination and the continual prevention of return of the impurities reduces the time of removal of the impurities substantially to a minimum,
• restoring the pressure to normal, and recovering the treated steel.

A process for recovering metallic impurities from steel, comprising the steps of:

• providing a body of liquid steel containing at least 0.15% by weight of copper and at least 0.1% by weight of tin at a temperature of at least 82.degree. to 100.degree. K. above its liquidus temperature and having an extensive free surface,
• subjecting said body to continuously decreasing pressure maintained at a level equivalent to 60% to 80% of the total vapor pressure of the liquid metal to create a bulk velocity of rising gasified vapors from the liquid metal surface, while continually maintaining the surface of the molten metal substantially free of surface contamination and continuously isolating the rising gases from the surface of the bath to prevent return of impurities to the molten metal,
• continuing the treatment until the treated steel contains less than 20% of the initial copper and tin,
• restoring the pressure to normal and recovering the treated steel.