Molten metal degassing device and impellers therefor

A device for releasing gas into molten metal contained within a vessel having a vessel wall and a vessel bottom, said device comprising:

• (a) a drive source;
• (b) a shaft having a first end, a second end and a passage for transferring gas, the first end connected to the drive source;
• and
• (c) a dual-flow impeller including a bottom surface and a plurality of vanes, wherein each of the vanes includes:
• (i) a first surface for moving molten metal downward towards the vessel bottom, the first surface being formed at an angle other than vertical;
• (ii) a second surface for moving molten metal outwards away from the impeller, the second surface being positioned closer to the vessel bottom than the first surface;
• and
• (d) one or more gas-release openings.

A device for releasing gas into molten metal contained in a vessel, the vessel having a bottom, the device comprising:

• (a) a shaft having a first end, a second end and a passage therein for the transfer of gas;
• (b) a tri-flow impeller comprising:
• (i) a connective portion connected to the second end of the shaft;
• (ii) a plurality of vanes wherein:
• (1) at least one vane includes a first surface for moving molten metal downward towards the vessel bottom, the first surface being formed at an angle other than vertical;
• (2) at least one vane includes a second surface for moving molten metal outward away from the impeller;
• and
• (3) at least one vane includes a third surface for moving molten metal upward away from the vessel bottom, the third surface being formed at an angle other than vertical;
• (c) one or more gas-release openings in communication with the passage;
• and
• (d) a drive source connected to the first end of the shaft, the drive source for rotating the shaft and the impeller.