TREATMENT OF MOLTEN ALUMINUM WITH AN IMPELLER

• US 3,767,382 A
• Filed: 11/04/1971
• Issued: 10/23/1973
• Est. Priority Date: 11/04/1971
• Status: Expired due to Term

• Current Assignee: Burl L. Slaugenhaupt, Marshall J. Bruno, Noel Jarrett
• Original Assignee: Burl L. Slaugenhaupt, Marshall J. Bruno, Noel Jarrett
• Inventors: Bruno, Marshall J., Jarrett, Noel, Slaugenhaupt, Burl L.
• Primary Examiner(s): Rutledge, L. Dewayne
• Assistant Examiner(s): Andrews, M. J.
• Application Number:
  US05/195,772
• Time in Patent Office: 719 Days
• Field of Search: 75/68R,95AC,93R
• US Class Current: 75/678
• CPC Class Codes: C22B 21/062 using salt or fluxing agents C22B21/064, C22B21/066, and C22B21/068 take precedence
• CPC Class Codes: C22B 21/064 using inert or reactive gases C22B21/066 and C22B21/068 take precedence

Abstract

Molten aluminum is treated with selectively maintained salt flux in a compact efficient system to decrease its oxide, gas and sodium content. Gas removal is further aided by stripping with a non-reactive stripping gas. The system features an intensely agitated zone for contacting the metal and the salt flux followed by a quiet separation zone. Molten metal introduction, agitation and flux characteristics are utilized to achieve the required efficiencies.

Claims

2. The method according to claim 1 wherein said impeller is a vaned disc impeller having a substantially horizontal disc portion and upstanding radial vanes.

3. The method according to claim 2 wherein the disc of the impeller is situated at or below the static molten metal-salt flux interface, but not more than 8 inches below said interface, which prevails in said agitated zone if the agitator is not running.

4. The method according to claim 2 wherein said molten aluminum introduction is effected by causing a stream thereof to move downwardly a short distance of not more than 5 inches upon said impeller.

5. The method according to claim 1 wherein the agitated zone is maintained by the action of a rotary impeller having cavitation sites and provided with passages to convey gas from a blanket Maintained above said salt flux-molten aluminum mixture downwardly and toward said cavitation sites such that the cavitation action inducts said gas into said agitated zone.

6. The method according to claim 1 wherein in said step (c) said defined oxide content is maintained by periodically removing quantities of oxide from said floating flux-oxide layer.

7. The method according to claim 1 wherein in said step (c) said recirculated salt flux is maintained at a maximum oxide content of 5 percent.

8. The method according to claim 1 wherein the nominal residence time for the molten aluminum is the agitation zone is less than 5 minutes.

9. The method according to claim 1 wherein gas is introduced to said agitated zone to strip gases from said molten aluminum being treated therein.

10. The method according to claim 9 wherein said gas comprises a non-reactive gas comprising argon.

11. A continuous method of treating molten aluminum to decrease its content of oxide inclusions, hydrogen gas and sodium comprising the steps a. continuously introducing said molten aluminum into an agitated zone containing a mixture of said molten aluminum and a reactive salt flux containing magnesium chloride and not more than 1 percent moisture, b. the agitation being provided by the action of a rotating vaned disc impelled having a substantially horizontal disc portion and upstanding radial vanes, the molten aluminum being introduced substantially into the rotating impeller vanes, the disc of the impeller being situated at the static molten metal-salt flux interface which prevails in said agitated zone when the agitator is not running or below said interface but not more than 8 inches therebelow, c. continuously moving a mixture comprising molten aluminum and salt flux from said agitated zone to a separate quiet zone to substantially separate molten aluminum from the remainder of said mixture which remainder rises to form a floating salt flux-oxide layer above the separated molten aluminum, d. recirculating salt flux from said floating salt flux-oxide layer in said quiet separation zone to said agitated zone, e. removing oxide from said floating salt flux-oxide layer in said quiet separation zone to provide and maintain a maximum oxie content of 20 percent within the salt flux recirculated to said agitated zone, f. removing a purifieid molten aluminum product.

12. The method according to claim 11 wherein said disc of said impeller is situated beneath the static molten metal-salt flux interface by from 1 to 4 inches.

13. The method according to claim 11 wherein the molten metal introduction is arranged in cooperation with the rotating disc impeller such that molten metal is directed substantially downwardly to the upper faces of said disc.

14. The method according to claim 11 wherein said molten aluminum being treated contains up to 0.003 percnet sodium and where said removed purified aluminum product has a sodium content not exceeding 0.0002 percent.

15. The method according to claim 11 wherein the molten aluminum separated in said quiet zone is passed through a second quiet zone to facilitate further separation of residual salt flux values therefrom after which separation of the molten aluminum is removed.

16. The method according to claim 11 wherein in said step (e) said recirculated salt flux is maintained at a maximum oxide content of 5 percent.

17. The method according to claim 11 wherein the nominal residence time for the molten aluminum in the agitation zone is less than 5 minutes.

18. The method according to claim 11 wherein at least 90 percent of the molten metal being introduced is fragmented into multiplicities of streams and particles each having a dimension under one-fourth inch.

19. A method according to claim 18 wherein said molten metal streams and particles are fragmented such that at least 60 percent have a dimension under one-eiGhth inch.

20. The method according to claim 11 wherein magnesium chloride is added to the salt flux in said floating flux-oxide layer in said quiet separation zone to provide and maintain in said salt flux in said mixing zone a MgCl2:

NaCl weight ratio of at least 4;

21. The method according to claim 20 wherein said weight ratio is at least 50:

1.

22. The method according to claim 11 wherein gas is introduced into said agitated zone to strip gases from said molten aluminum being treated therein.

23. The method according to claim 22 wherein said gas is a non-reactive gas comprising argon.

24. A continuous method of treating molten aluminum to decrease its content of oxide inclusions, hydrogen gas and sodium comprising the steps a. continuously introducing said molten aluminum into an agitated zone maintained by the action of a rotary impeller having cavitation sites and provided with passages to convey gas from a blanket maintained above said salt flux-molten aluminum mixture downwardly and toward said cavitation sites such that the cavitation action inducts said gas into said agitated zone, b. continuously moving a mixture comprising molten aluminum and salt flux from said agitated zone to a quiet zone to substantially separate molten aluminum from the remainder of said mixture which remainder rises to form a floating salt flux-oxide layer above the separated molten aluminum, c. recirculating salt flux from said floating said flux-oxide layer in said quiet separation zone to said agitated zone, d. removing a purified molten aluminum product.

25. A continuous method of treating molten aluminum to decrease its content of oxide inclusions, hydrogen gas and sodium comprising the steps a. continuously introducing said aluminum into an agitated zone maintained by the action of a submerged rotating impeller and containing a mixture of said molten aluminum and a reactive salt flux containing magnesium chloride, b. introducing into said agitated zone a non-reactive gas to strip gases from said molten aluminum being treated therein, c. continuously moving a mixture comprising molten aluminum and salt flux from said agitated zone to a separate quiet zone to substantially separate molten aluminum from the remainder of said mixture which remainder rises to form a floating salt flux-oxide layer above the separated molten aluminum, d. recirculating salt flux from said floating said flux-oxide layer in said quiet separation zone to said agitated zone, e. removing a purified molten aluminum product.

26. A method of treating molten aluminum to decrease its content of oxide inclusions, hydrogen gas and sodium comprising the steps a. introducing said aluminum into an agitated zone maintained by the action of a submerged rotating impeller and containing a mixture of said molten aluminum and a reactive salt flux containing magnesium chloride, b. introducing into said agitated zone a gas to strip dissolved gases from said molten aluminum being treated therein, c. continuously moving a mixture comprising molten aluminum and salt flux from said agitated zone to a quiet zone, separated from said agitated zone, to substantially separate molten aluminum from the remainder of said mixture which remainder rises to form a floating salt flux-oxide layer above the separated molten aluminum, d. recirculating salt flux from said floating salt flux-oxide layer in said quiet separation zone to said agitated zone, e. removing a purified molten aluminum product.

27. The method according to claim 26 wherein said gas comprises a non-reactive gas.

28. A method of treating molten aluminum to decrease its content of oxide inclusions, hydrogen gas and sodium in a level pour system having an inlet and an outlet disposed not more than 3 inches below said inlet and comprising the following steps a. introducing said aluminum through said inlet into an agitated zone containing a mixture of said molten aluminum and a reactive salt flux containing magnesium chloride and not more than 1 percent moisture, b. the agitation being provided by the action of a rotating vaned disc impeller having a substantially horizontal disc portion and upstanding radial vanes, the disc of the impeller being situated at or below the static molten metal-salt flux interface which prevails in said agitated zone when the agitator is not running, c. said molten metal introduction being arranged in cooperation with the rotating disc impeller such that it falls downwardly a distance of up to 5 inches upon the upper faces of said rotating disc and wherein at least 90 percent of the molten metal being introduced is fragmented into particles and streams each having a dimension under one-fourth inch, d. continuously moving a mixture comprising molten aluminum and salt flux from said agitated zone to a quiet zone to substantially separate molten aluminum from the remainder of said mixture which remainder rises to form a floating salt flux-oxide layer above the separated molten aluminum, e. recirculating salt flux from said floating said flux-oxide layer in said quiet separation zone to said agitated zone, f. removing oxide from said floating salt flux-oxide layer in said quiet separation zone to provide and maintain a maximum oxide content of 20 percent within the salt flux recirculated to said agitated zone, g. removing a purified molten aluminum product through said outlet.

29. The method according to claim 28 wherein the nominal residence time for the molten aluminum in the agitation zone is less han 5 minutes.

30. The method according to claim 28 wherein in said step (f) said recirculated salt flux is maintained at a maximum oxide content of 5 percent.