Degassing of molten alloys with the assistance of ultrasonic vibration

• US 20070235159A1
• Filed: 08/16/2005
• Published: 10/11/2007
• Est. Priority Date: 08/16/2005
• Status: Active Grant

• Current Assignee: University of Tennessee Research Foundation (University of Teesside), UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Meek, Thomas, Han, Qingyou, Xu, Hanbing
• Granted Patent: US 7,682,556 B2
• Time in Patent Office: Days
• US Class Current: 164/66.100
• CPC Class Codes: B22D 1/00 Treatment of fused masses in the ladle or the supply runners before casting for continuous casting B22D11/10; metallurgical processing, e.g. refining of iron or other metal C21, C22, C25C
• CPC Class Codes: C22B 21/06 refining electrolytic refining C25C; C22B21/0046, C22B21/0061 take precedence
• CPC Class Codes: C22B 21/064 using inert or reactive gases C22B21/066 and C22B21/068 take precedence
• CPC Class Codes: C22B 9/02 Refining by liquating, filtering, centrifuging, distilling, or supersonic wave action including acoustic waves; C22B9/003, C22B9/006, C22B9/05, C22B9/22 take precedence
• CPC Class Codes: Y02P 10/20 Recycling

Abstract

An apparatus and method are disclosed in which ultrasonic vibration is used to assist the degassing of molten metals or metal alloys thereby reducing gas content in the molten metals or alloys. High-intensity ultrasonic vibration is applied to a radiator that creates cavitation bubbles, induces acoustic streaming in the melt, and breaks up purge gas (e.g., argon or nitrogen) which is intentionally introduced in a small amount into the melt in order to collect the cavitation bubbles and to make the cavitation bubbles survive in the melt. The molten metal or alloy in one version of the invention is an aluminum alloy. The ultrasonic vibrations create cavitation bubbles and break up the large purge gas bubbles into small bubbles and disperse the bubbles in the molten metal or alloy more uniformly, resulting in a fast and clean degassing.

Claims

1. An apparatus for degassing a liquid, the apparatus comprising:

an ultrasonic transducer; and

a radiator coupled to the ultrasonic transducer such that activation of the ultrasonic transducer creates ultrasonic vibration in the radiator,

wherein the radiator has a hollow shell defining a fluid flow path for transporting a purge gas, the shell including at least one throughhole that extends from the fluid flow path to an outer surface of the radiator.

2. The apparatus of claim 1 wherein:

the shell of the radiator comprises a cylindrical outer wall and an end wall extending inward from the outer wall, and

a plurality of throughholes extend through the end wall from the fluid flow path to the outer surface of the radiator.

3. The apparatus of claim 1 further comprising:

a container for the liquid,

wherein the radiator is positioned in a wall of the container such that the outer surface of the radiator can contact liquid in the container.

4. The apparatus of claim 3 wherein:

the container is a refractory ladle, or a holding furnace of molten metal or metal alloy, or a reservoir in a trough for transporting molten metal or metal alloy.

5. The apparatus of claim 3 further comprising:

a cooling jacket surrounding the radiator for lowering the radiator temperature.

6. The apparatus of claim 3 wherein:

the outer surface of the end wall of the radiator has a coating that protects the outer surface of the radiator from dissolving into liquid in the container.

7. The apparatus of claim 3 further comprising:

means for lowering air pressure above liquid in the container.

8. The apparatus of claim 3 wherein:

wherein the radiator is positioned in the wall of the container such that the outer surface of the radiator is below liquid in the container.

9. The apparatus of claim 3 wherein:

the container includes an inlet and an outlet for the liquid, and

the outlet is positioned above the inlet.

10. The apparatus of claim 3 further comprising:

means for regulating humidity above liquid in the container.

11. A method for degassing a liquid, the method comprising:

providing a radiator coupled to an ultrasonic transducer, wherein the radiator has a hollow shell defining a fluid flow path for transporting a purge gas and the radiator also has at least one throughhole that extends from the fluid flow path to an outer surface of the radiator;

contacting the liquid with the outer surface of the radiator;

activating the ultrasonic transducer to create ultrasonic vibration in the radiator; and

introducing purge gas into the liquid through the at least one throughhole.

12. The method of claim 11 wherein:

purge gas is introduced into the liquid at a rate of 30 cubic feet per hour or less.

13. The method of claim 11 wherein:

the ultrasonic vibration creates cavitation bubbles in the liquid and breaks up bubbles of the purge gas into smaller bubbles.

14. The method of claim 11 wherein:

bubbles of the purge gas collect ultrasonically induced cavitation bubbles thereby making the ultrasonically induced cavitation bubbles survive in the liquid.

15. The method of claim 11 wherein:

acoustically induced acoustic streaming disperses bubbles of the purge gas and ultrasonically induced cavitation bubbles in the liquid.

16. The method of claim 11 further comprising:

providing a container for the liquid; and

positioning the radiator in a wall of the container such that the outer surface of the radiator can contact liquid in the container.

17. The method of claim 16 further comprising:

creating a vacuum above liquid in the container.

18. The method of claim 16 further comprising:

regulating humidity above liquid in the container.

19. The method of claim 16 further comprising:

providing a coating that protects the outer surface of the radiator from dissolving into the liquid.

20. The method of claim 16 wherein:

wherein the radiator is positioned in the wall of the container such that the outer surface of the radiator is below liquid in the container.

21. A method for removing a dissolved gas from a molten metal or molten metal alloy, the method comprising:

providing a radiator coupled to an ultrasonic transducer, wherein the radiator has a hollow shell defining a fluid flow path for transporting a purge gas and the radiator also has at least one throughhole that extends from the fluid flow path to an outer surface of the radiator;

providing a container for the molten metal or molten metal alloy;

positioning the radiator in a wall of the container such that the outer surface of the radiator can contact molten metal or molten metal alloy in the container;

activating the ultrasonic transducer to create ultrasonic vibration in the radiator; and

introducing purge gas into the molten metal or molten metal alloy through the at least one throughhole.

22. The method of claim 21 wherein:

the molten metal or molten metal alloy is selected from metals and metal alloys that are prone to porosity formation upon solidification from a melt.

23. The method of claim 21 wherein:

the molten metal or molten metal alloy is selected from aluminum, aluminum alloys, magnesium, magnesium alloys, steels, or cast iron, and

the dissolved gas is hydrogen in aluminum, aluminum alloys, magnesium, and magnesium alloys, and the dissolved gas is nitrogen or carbon containing gases in steels and cast irons.

24. The method of claim 21 wherein:

the radiator is positioned in the wall of the container such that the outer surface of the radiator is below the molten metal or molten metal alloy in the container.

25. The method of claim 21 further comprising:

providing a coating that protects the outer surface of the radiator from dissolving into the molten metal or molten metal alloy.