Method for cleaning molten metal and apparatus therefor

Abstract

Molten metal is put under pressure of up to 10 atmospheres in a covered ladle and a gas soluble in the metal is bubbled through the melt. Some gas goes into solution, while the remainder rises in bubbles and brings inclusions suspended in the molten metal up to the surface. Then the pressure is lowered, after which gas comes out of the solution in fine bubbles which also bring impurity inclusions up to the surface. In another method molten steel is refined at pressures not exceeding atmospheric pressure in a covered ladle equipped for evacuation and equipped for bubbling gas through the molten steel bath. Bubbling followed by pressure reduction can then be performed to form two stages of cleaning. Heat may be added for compensating the cooling effect of gas expansion. Instead of a closed ladle, an open ladle may be used, into which there can be dipped a chamber fitted for evacuation and having two large tubes at opposite sides of the chamber extending downwards to orifices that may be lowered into the molten metal in the ladle. The melt is then drawn up into the chamber by atmospheric pressure as the chamber is evacuated. Then bubbling may be performed in one connecting tube by injection of gas from the bottom of the ladle, or at a mid-level of the tube, to produce circulation of the molten metal up into the chamber and down through the other tube.