Apparatus for gas treatment of molten metals

• US 5,656,236 A
• Filed: 09/09/1996
• Issued: 08/12/1997
• Est. Priority Date: 02/04/1994
• Status: Expired due to Term

• Current Assignee: Alcan Incorporated (Rio Tinto Limited)
• Original Assignee: Alcan Incorporated (Rio Tinto Limited)
• Inventors: Dumont, Robert, Waite, Peter D.
• Primary Examiner(s): ANDREWS, MELVYN J
• Application Number:
  US08/711,062
• Time in Patent Office: 337 Days
• Field of Search: 266/225, 266/226
• US Class Current: 266/225
• CPC Class Codes: C21C 7/072 Treatment with gases C21C7/06, C21C7/064, C21C7/068 take precedence
• CPC Class Codes: C22B 21/064 using inert or reactive gases C22B21/066 and C22B21/068 take precedence
• CPC Class Codes: C22B 9/05 Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
• CPC Class Codes: C22B 9/055 while the metal is circulating, e.g. combined with filtration

Abstract

A method of and apparatus for treating molten metal to achieve effective removal of such unwanted inclusions as gases, alkali metals, entrained solids, and the like. The method comprises introducing molten metal into a trough, such as the trough provided between a melting furnace and a casting machine, providing at least one mechanically movable gas injector submerged within the metal in the trough and injecting a gas into the metal in a part of the trough forming a treatment zone through the injector(s) to form gas bubbles in the metal while moving the injector(s) mechanically to minimize bubble size and maximize distribution of the gas within the metal. The injectors are preferably rotated and comprise a rotor body having a cylindrical side surface and a bottom surface, at least three openings in the side surface spaced symmetrically around the rotor body, at least one opening in the bottom surface, and at least one internal passageway for gas delivery and an internal structure for interconnecting the openings in the side surface, the openings in the bottom surface and the internal passageway. The internal structure is adapted to cause gas bubbles emanating from the internal passageway to break up into finer bubbles and to cause a metal/gas mixture to issue from the openings in the side surface in a generally horizontal and radial manner.

Claims

1. Apparatus for treating a molten metal with a treatment gas, comprising:

a container forming an elongated trough defining a channel for holding and conveying a molten metal, having a bottom wall and opposed side walls;

at least one gas injector in use positioned in said container submerged in said metal;

means for moving said gas injector selected from the group consisting of means for rotating said gas injector about a central vertical axis thereof, means for vibrating said gas injector, and means for oscillating said gas injector about a central vertical axis thereof; and

means for conveying gas to said injector for injection into said metal;

wherein a portion of said trough adapted for containing said molten metal has a transverse vertical cross-sectional area centred on each said injector and a maximum width at a midpoint of said injector, and wherein the product of said transverse vertical cross-sectional area and said maximum width does not exceed 0.2 m².

2. Apparatus according to claim 1 wherein said injector includes a rotor having a smooth cylindrical outer surface provided with inwardly directed openings which generate metal flow in an outward radial and substantially horizontal direction when said rotor is immersed in said molten metal and rotated;

said rotor having a lower end surface provided with at least one opening communicating with said openings in said cylindrical surface, a gas injection port for introducing said treatment gas into said metal flow, and a channel for conveying said gas to said gas injection port.

3. Apparatus according to claim 1 wherein each said injector has a rotor body including a cylindrical side surface and a bottom surface, with at least one opening on said bottom surface, at least three openings in said side surface symmetrically disposed around the surface, and an internal structure providing passages within the rotor for movement of molten metal between the bottom and side openings, and at least one gas injection port located within the body of the rotor and communicating with the said passages;

said internal structure in use causing gas entering by the gas injection port to mix with molten metal within the body of the rotor so as to form bubbles; and

said internal structure in use also causing the molten metal and gas bubbles to flow from the side openings in a radial and substantially horizontal manner.

4. Apparatus according to claim 3 further comprising means for rotating each said rotor such that gas bubbles within said radial and substantially horizontal metal flows encounter a tangential shear gradient in said molten metal as said flows exit said rotor effective to breakup said bubbles into finer bubbles, such that said radial and substantially horizontal metal flows have sufficient momentum to disperse said metal flows and finer gas bubbles throughout said treatment segment but without causing substantial splashing at walls of said trough, and such that bubbles breaking said metal at an upper surface are substantially uniformly distributed without concentrations of bubbles at said gas injector or said walls of said trough.

5. Apparatus according to claim 2 wherein said rotor has at least three openings in said side surface spaced symmetrically around the rotor.

6. Apparatus according to claim 2 wherein said rotor has a generally flat horizontal upper surface centrally connected to a shaft for supporting and rotating said rotor.

7. Apparatus according to claim 2 wherein said rotor has a frusto-conical, upwardly tapering surface merging with a shaft for supporting and rotating the rotor.

8. Apparatus according to claim 2 wherein said openings in said side surface occupy and area of said outer surface corresponding to less than 60% of a total area swept by said openings upon rotation of said rotor.

9. Apparatus according to claim 2 wherein said rotor has a diameter in the range of 5 to 20 cm.

10. Apparatus according to claim 2 wherein said internal structure consists of vanes and passageways separating said vanes.

11. Apparatus according to claim 2 wherein said internal structure comprises at least six vanes.

12. Apparatus according to claim 1 further comprising a plurality of generally vertical stationary vanes separated by channels around each said rotor for receiving said radial and substantially horizontal metal flows.

13. Apparatus according to claim 1 wherein said trough has a depth in the range of 15 to 50 cm and width in the range of 10-40 cm.

14. Apparatus according to claim 1 wherein a plurality of said gas injectors are provided in said trough and said injectors are separated by baffles arranged transversely of said trough for controlling flow of metal through said trough.

18. Apparatus according to claim 1 wherein said treatment segment has a volume not exceeding 0.07 m³.

19. Apparatus according to claim 1 wherein said trough has a depth of less than about 50 cm.

15. Apparatus for introduction into a molten metal-conveying trough for treating molten metal in said trough with a treatment gas, comprising:

at least one gas injector;

means for rotating said at least one gas injector about a central vertical axis thereof;

support means for said at least one gas injector; and

means for moving said support means for moving said at least one gas injector into and out of molten metal in said trough;

wherein a portion of said trough adapted for containing said molten metal has a transverse vertical cross-sectional area centred on each said injector and a maximum width at a midpoint of said injector, and wherein the product of said transverse vertical cross-sectional area and said maximum width does not exceed 0.2 m³.

16. Apparatus according to claim 15 wherein each said gas injector comprises a rotor having a smooth cylindrical outer surface provided with inwardly directed openings which generate metal flow in an outward radial and substantially horizontal direction when said rotor is immersed in said molten metal and rotated, said rotor having a lower end surface provided with openings communicating with said indentations in said cylindrical surface;

a gas injection port positioned on said rotor for introducing a treatment gas into said metal flow; and

a channel for conveying a gas under pressure to said gas injection port.

17. Apparatus according to claim 15 comprising a plurality of said injectors separated by baffles arranged transversely of said trough for controlling flow of metal through said trough.

20. Apparatus for treating a molten metal with a treatment gas, comprising:

a container forming an elongated trough defining channel for holding and conveying said molten metal, having a bottom wall and opposed side walls;

at least one gas injector in use positioned in said container submerged in said metal;

means for rotating said gas injector about a central vertical axis thereof; and

means for conveying gas to said injector for injection into said metal;

wherein said injector is a rotor having;

a projection-free cylindrical side surface, a projection-free and unbroken upper surface, and a bottom surface;

a plurality of openings in said side surface spaced symmetrically around the rotor, said openings occupying an area of said outer surface corresponding to less than 60% of a total area swept by said openings upon rotation of said rotor;

at least one opening in the bottom surface, and

at least one internal passageway for gas delivery and an internal structure for interconnecting said openings in said side surface, said at least one opening in said bottom surface and said at least one internal passageway;

said internal structure in use being at least partially filled with molten metal or metal/gas mixtures, and being adapted to cause gas emanating from said internal passageway to break up into bubbles to form metal/gas mixture and to cause said metal/gas mixture to issue from said openings in said side surface in a generally horizontal and radial manner, said side surfaces being adapted on rotation of said rotor in said molten metal to cause said gas bubbles to be broken up into finer bubbles.

21. Apparatus according to claim 20 wherein a portion of said trough adapted for containing a molten metal has a transverse vertical cross-sectional area centred on each said injector and a maximum width at a midpoint of said injector, and wherein the product of said transverse vertical cross-sectional area and said maximum width does not exceed 0.07 m³.

22. Apparatus according to claim 20 wherein said trough has a depth of less than about 50 cm.

23. Apparatus for treating a molten metal with a treatment gas, comprising:

a container forming an elongated trough defining a channel for holding and conveying said molten metal, having a bottom wall and opposed side walls, said trough having a width in the range of 10 to 40 cm and a depth in the range of 15 to 50 cm;

at least one gas injector in use positioned in said container submerged in said metal;

means for moving said gas injector selected from the group consisting of means for rotating said gas injector about a central vertical axis thereof, means for vibrating said gas injector, and means for oscillating said gas injector about a central vertical axis thereof; and

means for conveying gas to said injector for injection into said metal;

wherein a portion of said trough adapted for containing said molten metal has a transverse vertical cross-sectional area centred on each said injector and a maximum width at a midpoint of said injector, and wherein the product of said transverse vertical cross-sectional area and said maximum width does not exceed 0.2 m³.