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Induction Melting of Metals in Cold, Self-lined Crucibles.
U S Pat 3 775 091 1973 Nov; :
Refractory metals, such as ti, zr, and their alloys, are induction melted in a crucible having liquid-cooled cu walls and bottom, formed by the cooled melt, that is lowered as melting takes place near the top. The crucible and ingot formed in the bottom are enclosed by a gas tight shield except for a rod through the bottom to lower the ingot. To begin the melt, a solid ingot-shaped block having a smaller diameter than the crucible cavity is held in the crucible by the rod, with powdered caf2 above it. When the top of the block is heated by induction, it melts the caf2, which flows down around the block, forming an insulating layer so that the upper part melts without contact with the cooled cu. Additional metal, such as ti sponge, may then be charged into the crucible with additional caf2, and a continuous metal ingot with a protective caf2 coating is lowered from the crucible as melting takes place. For effective induction heating inside the cooled cu crucible, it must be separated lengthwise into at least 2 water-cooled cu segments with ceramic insulation between them and solid caf2 to seal cracks. The water-cooled cu coils carrying the A.C. for induction heating surround only the upper parts of the segments. Without addition of caf2, melting was slow and incomplete, and the crucible was damaged.
U.S. Pat. 3,775,091; Nov. 27, 1973; Chem. Abstr. 80:62,888F
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