Method for Cleaning Aluminum or Aluminum Alloy Surfaces

Abstract

A method for cleaning a surface of an aluminum or aluminum alloy body of coatings, contaminants, dirt, or the like by immersing the surface in a basic aqueous electrolyte containing carbonate ions, connecting the body directly to the negative terminal of a DC current source and flowing DC current through the body. After a time, the flow of DC current is stopped and the surface is removed from the electrolyte. The surface is then rinsed off to remove the coating, dirt, contaminants, or the like from the surface. The cleaned surface may be recoated for reuse of the body

Claims

1. A method for cleaning a surface of an aluminum or aluminum alloy body, the method comprising the steps of: (a) wetting the surface of the body with an aqueous electrolyte, the electrolyte comprising dissolved potassium carbonate and having a pH generated by the dissolved potassium carbonate greater than 7; (b) connecting the body to a negative terminal of a DC current source and flowing DC current from the current source through the body concurrently with step (a), the flow of DC current being not less than 200 amperes; and (c) stopping the flow of the DC current after flowing the DC current for not less than 2 minutes.

2. The method of claim 1 further comprising the step of: (d) rinsing the surface with water after stopping the flow of DC current.

3. The method of claim 1 wherein step (b) comprises the step of flowing DC current for a sufficient length of time to coat the wetted surface with a coating of additional material.

4. The method of claim 3 comprising the step of: (d) removing the coating of additional material from the body.

5. The method of claim 1 wherein the electrolyte has a pH of between about 8 and about 13.

6. The method of claim 5 wherein the electrolyte has a pH of about 11.

7. The method of claim 1 wherein the electrolyte comprises dissolved trisodium phosphate.

8. The method of claim 7 wherein the trisodium phosphate is present in the electrolyte at a concentration of between 5% and 100% weight percent of the dissolved potassium carbonate.

9. The method of claim 1 wherein step (b) comprises the step of: flowing DC current of between about 200 amperes and about 5000 amperes.

10. The method of claim 0 wherein step (b) comprises the step of flowing DC current of about 1000 amperes.

11. The method of claim 1 wherein step (a) comprises maintaining the electrolyte wetting the surface at a temperature of no less than about 70 degrees Fahrenheit.

12. The method of claim 11 wherein step (d) comprises the step of maintaining the electrolyte at a temperature of no less than about 150 degrees Fahrenheit.

13. The method of claim 1 wherein step (b) comprises the step of continuously flowing the DC current through the body for not less than about 3 minutes and not more than about 30 minutes.

14. The method of claim 1 wherein step (b) comprises the step of applying a DC voltage of between about 3 volts and 200 volts to the body while flowing the DC current through the body.

15. The method of claim 1 comprising the step of: (d) rinsing the surface with a low pressure water spray after stopping the flow of DC current.

16. The method of claim 15 wherein step (d) comprises the step of rinsing the surface with the low pressure water spray no later than about 15 minutes after stopping the flow of DC current.

17. The method of claim 1 wherein the body has a surface coating to be cleaned from the surface, the method comprising the step of: (d) rinsing the surface coating off the surface with water after stopping the flow of DC current.

18. The method of claim 17 wherein the surface coating is a powder coating.

19. The method of claim 1 wherein the body is a wheel rim or a wheel hub of a motor vehicle.

20. The method of claim 1 comprising the steps of: (d) sequentially cleaning a plurality of aluminum or aluminum alloy bodies in the electrolyte by performing steps (a), (b), and (c) for each body over a period of time; (e) maintaining the pH of the electrolyte greater than 7 for the entire period of time; and (f) maintaining the temperature of the electrolyte at or above 70 degrees Fahrenheit for the entire period of time.

21. The method of claim 1 wherein step (a) comprises the step of immersing the body entirely or at least partially into a tank holding the electrolyte.

22. The method of claim 1 wherein step (a) comprises the step of spraying the electrolyte on the surface.

23. The method of claim 1 comprising the steps of: (d) drying the body after cleaning, and then (e) coating the surface with a powder coating or other surface coating after drying the body.

24. The method of claim 1 comprising the step of: (d) ultrasonic cleaning the body after stopping the flow of DC current.

25. The method of claim 1 wherein step (d) comprises ultrasonic cleaning at a frequency of 25 kHz.

Description

BRIEF SUMMARY OF THE DRAWING

[0043] FIG. 1 is a schematic view of a metal alloy wheel immersed in an electrolyte for cleaning in accordance with an embodiment of the disclosed method of cleaning.

[0044] FIG. 2 is an enlarged view of a portion of the wheel shown in FIG. 1.

DETAILED DESCRIPTION

[0045] FIG. 1 illustrates a used truck or airplane wheel 10 totally immersed in an electrolyte 12 for cleaning in accordance with the disclosed method. The wheel 10 is a conventional aluminum wheel that has a powder coating 14 on an external surface 16 of the wheel. See FIG. 2. It is desired to remove the powder coating 14 and surface contaminants 18 on the powder coating from the surface 16 to enable recycling and reuse of the wheel.

[0046] The wheel 10 is connected electrically in series to the negative terminal 20 of a DC current source 22 by a conductor 24. A steel or iron electrode 26 is also immersed in the electrolyte 12 and is connected in series to a positive terminal 28 of the current source 22 by a conductor 30. The wheel 10 and the electrode 26 are electrically connected by the electrolyte 12.

[0047] The illustrated electrolyte 12 is an aqueous basic electrolyte formed by dissolving only potassium carbonate (K.sub.2CO.sub.3) in water. The potassium carbonate is preferably food-grade potassium carbonate.

[0048] The pH of the electrolyte is about 11. The temperature of the electrolyte is about 130 degrees Fahrenheit.

[0049] In the illustrated embodiment the wheel 10 is immersed into a 200 gallon bath of electrolyte 12.

[0050] The DC current source 18 is energized and flows 1000 amperes of DC current from the negative terminal 16, through the wheel 10 and to the electrode 26, and back to the positive terminal 22.

[0051] The current source 18 is energized and supplies the 1000 ampere current through the wheel 10 continuously for five minutes. The current source 18 is then shut off and the wheel 10 is removed from the electrolyte 12.

[0052] While the DC current is flowing through the wheel 10, an additional layer of material is deposited on wetted surfaces of the wheel 10. The electrolyte 12 also darkens. It has been found that the wheel 10 does not appreciably heat while the DC current is flowing. It may even be necessary to heat the electrolyte 12 to maintain a desired electrolyte temperature while the DC current is flowing.

[0053] In the illustrated embodiment it is not necessary to treat the electrolyte in response to the electrolyte darkening. Additional potassium carbonate and/or water may be added to the electrolyte to maintain the desired pH. The electrolyte may be filtered in a conventional manner to remove dirt, soil, or other contaminants introduced into the electrolyte by the bodies being cleaned.

[0054] After the current source 18 is shut off, the wheel 10 is removed from the electrolyte 12. The wheel 10 is then rinsed or otherwise cleaned using water or water and soaps or detergents to remove the additional material deposited on the wheel.

[0055] The wheel 10 may be rinsed with a low pressure water jet spray to remove the additional material deposited on the wheel 10. In the illustrated embodiment the wheel 10 is sprayed with a 2000 psi water jet spray not more than 5 minutes after removal of the wheel from the electrolyte.

[0056] The jet spray also removes the powder coating 14 and the contaminants 18 from the wheel surface 16. After rinsing, the wheel 10 has a clean wheel surface 16 capable of accepting application of a new powder coating and/or alternative surface coatings.

[0057] Alternatively, ultrasonic cleaning may be used to remove the additional material deposited on the wheel 10. With ultrasonic cleaning, the wheel 10 is removed from the electrolyte and then immersed in a liquid in which high frequency sound waves agitate the liquid for cleaning. The liquid is preferably an aqueous solution containing a cleanser compatible with aluminum. Examples of ultrasonic cleansers for cleaning aluminum that can be adapted for use with the disclosed method include TRANSBRITE ultrasonic cleaning liquid solution distributed by Allen Woods & Associates, Arlington Heights, Ill., PELCO KLEENSONIC CDC ultrasonic cleaning solution distributed by Ted Pella, Inc., Redding, Calif. 96049, and equivalents.

[0058] Ultrasonic cleaning is itself conventional and so will not be described in further detail. The inventors have found that ultrasonic cleaning at 25 kHz frequency has provided good results in removing the additional material as well as removing powder coating after the electrolytic cleaning if originally present.

[0059] After cleaning the wheel 10 is dried. The wheel 10 may then be powder coated or otherwise coated or painted for return to the aftermarket and reuse.

[0060] In alternative embodiments of the disclosed method, some, but not all, surfaces of the metal or metal alloy body require cleaning. In such embodiments, the body may only be partially immersed in the electrolyte 12 if total immersion is not required to wet the surfaces to be cleaned.

[0061] In other alternative embodiments of the disclosed method, surfaces to be cleaned may be wetted by spraying electrolyte on the surfaces to be cleaned instead of being wetted by immersion in a tank. The electrolyte spray must electrically complete the circuit in the same manner as the electrolyte in the tank and must conduct sufficient DC current to create the additional material coating.

[0062] In alternative embodiments of the disclosed method, some, but not all, surfaces of the metal or metal alloy body require cleaning. In such embodiments, the body may only be partially immersed in the electrolyte 12 if total immersion is not required to wet the surfaces to be cleaned.

[0063] In other alternative embodiments of the disclosed method, surfaces to be cleaned may be wetted by spraying electrolyte on the surfaces to be cleaned. The electrolyte spray must electrically complete the circuit from the body to the electrode as previously described and must conduct sufficient DC current to create the additional material coating.

[0064] In a further alternative embodiment of the disclosed method, trisodium phosphate (TSP) was added to the potassium carbonate based electrolyte and wheels similar to the wheels 10 were cleaned using different concentrations of trisodium phosphate in the electrolyte.

[0065] A TSP concentration of 1% or less (calculated as the weight of TSP divided by the weight of the potassium carbonate in the electrolyte and expressed as a percentage) had no appreciate effect on the cleaning of the wheel.

[0066] A TSP concentration of 5% had a positive effect, increasing the shine of the cleaned wheel, but the shine would not be considered very bright.

[0067] A TSP concentration of 50% resulted in good brightness of the cleaned wheel.

[0068] A TSP concentration of 100% (equal weights of TSP and potassium carbonate) had the best brightness.

[0069] It is contemplated that bodies may be cleaned by automating the disclosed method. For a nonlimiting example, metal or metal alloy bodies to be cleaned may be conveyed to an electrolysis station for immersion in or wetting with the electrolyte and application of DC current. Application of the DC current may stop after a predetermined time, or if a computerized optical monitoring system determines that the surface of the body has been adequately coated with the additional material to end application of DC current.

[0070] After the application of DC current stops, the body is moved from the electrolysis station to a rinse station for rinsing. The electrolyte is continuously filtered to remove contaminants in the electrolyte. The pH, temperature, and volume of electrolyte is monitored and maintained within predetermined limits by an automatic control system (not shown).

[0071] Features recited in a claim may, in embodiments of the disclosed method, be found in combination with features recited in the claims.

[0072] While one or more embodiments have been disclosed and described in detail, it is understood that this is capable of modification and that the scope of the disclosure is not limited to the precise details set forth but includes modifications obvious to a person of ordinary skill in possession of this disclosure and also such changes and alterations as fall within the purview of the following claims.