Method for Cleaning Metal or Metal Alloy Surfaces

Abstract

A method for cleaning a surface of a metal or metal alloy body by immersing the surface in a basic aqueous electrolyte containing carbonate ions, and flowing DC current through the body to make the body anodic. 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 dirt, corrosion, coatings, and the like from the surface. The surface can then be dried and, if desired, coated for reuse of the body

What is claimed is: 
     
         1 . A method for cleaning a surface of a metal or metal alloy body, the method comprising the steps of:
 (a) wetting the surface of the body with an aqueous electrolyte, the electrolyte comprising a dissolved carbonate salt and having a pH greater than 7;   (b) making the body anodic by flowing DC current 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  wherein step (c) comprises 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  wherein step (c) comprises 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 carbonate salt comprises potassium carbonate. 
     
     
         8 . The method of  claim 7  wherein the electrolyte comprises water and dissolved potassium carbonate. 
     
     
         9 . The method of  claim 8  wherein the electrolyte comprises dissolved trisodium phosphate. 
     
     
         10 . The method of  claim 9  wherein the trisodium phosphate is present in the electrolyte at a concentration of between 5% and 100% weight percent of the potassium carbonate. 
     
     
         11 . The method of  claim 1  wherein step (b) comprises the step of:
 (e) flowing DC current of between about 200 amperes and about 5000 amperes. 
 
     
     
         12 . The method of  claim 11  wherein step (b) comprises the step of:
 (f) flowing DC current of about 1000 amperes. 
 
     
     
         13 . The method of  claim 1  wherein step (a) comprises:
 (d) maintaining the electrolyte wetting the surface at a temperature of no less than about 70 degrees Fahrenheit. 
 
     
     
         14 . The method of  claim 13  wherein step (d) comprises the step of:
 (e) maintaining the electrolyte at a temperature of no less than about 150 degrees Fahrenheit. 
 
     
     
         15 . The method of  claim 1  wherein step (b) comprises the step of:
 (d) continuously flowing the DC current through the body for not less than about 3 minutes and not more than about 30 minutes. 
 
     
     
         16 . The method of  claim 1  wherein step (b) comprises the step of:
 (e) applying a DC voltage of between about 3 volts and 200 volts to the body while flowing the DC current through the body. 
 
     
     
         17 . The method of  claim 1  comprising the step after step (c) of:
 (d) rinsing the surface with a low pressure water spray. 
 
     
     
         18 . The method of  claim 17  wherein step (d) comprises the step of:
 (e) rinsing the surface no later than about 10 minutes after stopping the flow of DC current. 
 
     
     
         19 . The method of  claim 1  wherein the body is a steel body, an aluminum body, an aluminum alloy body, a manganese body, a manganese alloy body, or a cast metal body. 
     
     
         20 . 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. 
 
     
     
         21 . The method of  claim 20  wherein the surface coating is a powder coating. 
     
     
         22 . The method of  claim 1  wherein the body is a wheel rim or a wheel hub of a motor vehicle. 
     
     
         23 . The method of  claim 22  wherein the wheel rim or wheel hub comprises aluminum or an aluminum alloy. 
     
     
         24 . The method of  claim 1  comprising the steps of:
 (d) sequentially cleaning a plurality of 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. 
 
     
     
         25 . The method of  claim 1  wherein step (a) comprises the step of:
 (d) immersing the body entirely or at least partially into the electrolyte. 
 
     
     
         26 . The method of  claim 1  wherein step (a) comprises the step of:
 (d) spraying the electrolyte on the surface. 
 
     
     
         27 . 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 coating for reuse of the body.