Field of the Disclosure

The disclosure relates generally to cleaning of metal or metal alloy surfaces, and more specifically, to electrolytic cleaning of metal or metal alloy surfaces.

Background of the Disclosure

Surfaces of metal bodies or components must be returned to a clean, bare metal surface for recycling and reuse. Metal alloy wheels of trucks and airplanes, for example, may be sold with a powder coating on wheel surfaces. Powder coating is a thermoplastic or polymer coating that creates a hard finish that is tougher than conventional paints. The powder coating is applied electrostatically to the surface and then cured to form a protective skin over the surface. The powder coating, along with brake dust, road grime, oil, and other surface contaminants or coatings must be removed from the wheel before the wheel can be reused.

It is known to remove contaminants from surfaces of metal or metal alloy bodies using electrolysis. The surface to be cleaned is wetted by the electrolyte and DC current is passed through the body acting as a cathode in the electroyte. The inventors' US Patent 6,203,691 fully incorporated herein by reference discloses methods of cleaning metal bodies using a basic aqueous electrolyte containing disodium phosphate and sodium bicarbonate. The cleaning methods disclosed in the '691 patent, although well-suited for many cleaning needs, do not efficiently remove powder coatings or other specialized coatings found on wheels.

Conventional methods to remove powder coatings from the surfaces of metal or metal alloy bodies include use of specific solvents, heating the powder coating to high temperatures, or abrasive blasting. Methylene chloride, benzyl alcohol, and acetone are generally effective solvents for removing powder coating. Alternatively, the body may be placed in an oven heated to a temperature of between 300 degrees Centigrade - 450 degrees Centigrade for several hours to burn off the powder coating. Abrasive blasting mechanically removes the powder coating.

Conventional methods to remove powder coatings have disadvantages. Some solvents are suspected carcinogens. Heating components to hundreds of degrees Centigrade may warp the body or may adversely impact heat treatments of metal alloys. Abrasive blasting may remove metal as well as damage or roughen the surface. And conventional cleaning methods either take a long time to remove the powder coating or require extensive manual labor and handling.

Thus there is a need for an improved method to clean surfaces of metal or metal alloy bodies that can remove powder coatings and other surface coatings or contaminants.

Summary of the Disclosure

Disclosed is a method for electrolytic cleaning of surfaces of metal components or bodies well suited for removing powder coatings as well as other surface coatings and contaminants. The electrolyte used in possible embodiments of the disclosed method is inexpensive, environmentally friendly, and non-hazardous.

A method for cleaning a metal surface of a metal or metal alloy body in accordance with the present disclosure includes 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 sufficient to thereby coat the wetted surface with a coating of additional material; and

(c) stopping the flow of the DC current after performing step (b) and removing the additional coating from the surface, thereby cleaning the surface. The surface of the body in embodiments of the disclosed method can be wetted by immersing the body in the electrolyte or by spraying the body with the electrolyte.

Contaminants or coatings that can be cleaned from surfaces of metal or metal alloy bodies in accordance with the disclosed method include, but are not limited to, carbonization, surface powder coatings, paints, petroleum based or hydrocarbon (organic) based materials, environmental contaminants including dirt, soil, dust, or smut.

The inventors have found that applying a DC current making the body anodic deposits a coating of an additional material on the portion of the body wetted by the electrolyte. Without being bound by or limited to any theory or explanation, the inventors herein theorize as to the creation and cleaning benefits of the additional material coating. The additional material is not believed to be generated by either reduction or oxidation of metal or metal compounds forming the body but is believed to be created by oxidation of the carbonate ions in the electrolyte. The oxidized carbonate ions form the coating on the portion of the body immersed in or wetted by the electrolyte. The additional material coating is visible as a substantially gray to black coating that covers the entire outer surface of the portion of the body immersed in or wetted by the electrolyte. The additional material coating appears to physically or chemically break down coatings and contaminants (including but not limited to powder coatings) that are on the immersed or wetted surfaces without harming the body, and without removing or otherwise affecting metal or metal alloys of the body.

The electrolyte also darkens with creation of the additional material, but the darkening of the electrolyte does not appear to adversely impact the cleaning process.

After removal from the electrolyte, the additional material coating can be rinsed off with water. Rinsing off the additional material also removes the contaminants on the immersed surfaces (including powder coatings if present) , resulting in clean surfaces suitable for recycling.

In a possible embodiment of the disclosed method, a low pressure water jet is used to rinse off the additional material. "Low pressure water jet" as used herein means use of a water jet in which the pump pressure is less than 5,000 psi (340 bar) . Rinsing using a low pressure water jet of about 2,000 psi has been found effective in embodiments of the disclosed method in removing the additional coating and, along with the additional coating, powder coatings and other contaminants without damage to the body.

The carbonate salt must be dissolvable in water. Preferred carbonate salts are potassium carbonate and sodium carbonate, the most preferred is potassium carbonate.

The electrolyte is a basic electrolyte. The electrolyte in embodiments may be mildly alkaline or may be highly alkaline. The electrolyte in embodiment may have a pH greater than 7, or a pH from greater than about 8 to not more than about 13, or a pH of about 11.

The electrolyte may be maintained at a temperature not less than about 70 degrees Fahrenheit to not more than the boiling point of the electrolyte, or may be maintained at between not less than about 150 degrees Fahrenheit and the boiling point of the electrolyte.

The DC current applied to the body in embodiments may be about 200 amperes or greater, may be between about 200 amperes and about 5000 amperes, and may be about 1000 amperes.

The DC current applied to the body in embodiments may be applied for between about 2 minutes and about 15 minutes, may be applied for between about 3 minutes to about 5 minutes, and may be applied for about 5 minutes.

The DC voltage applied to the body to induce current flow in embodiments may be less than or equal to about 200 volts, and the applied DC voltage may be equal to or more than about 3 volts. The additional material may be rinsed off the body in embodiments no more than about 15 minutes after removal from the electrolyte, and is preferably rinsed off not more than about 10 minutes after removal from the electrolyte, and most preferably is rinsed off not more than about 5 minutes after removal from the electrolyte.

It has been observed that the additional material coating hardens after removal from the electrolyte and after time may become so hard that it becomes relatively difficult to remove. The sooner after the body is removed from the electrolyte that the body is rinsed to remove the additional material, the easier it is to remove the additional material. In an embodiment of the disclosed method a low pressure water jet has been found effective for removing the additional material and contaminants if the rinse is started within about 15 minutes after stopping the DC current .

A suitable source of DC current for use in embodiments of the disclosed methods includes, but is not limited to, the Model No. 43pl-00 im-048 rectifier manufactured by Process Electronics Corp, Mt Holly, NC 28120 USA. This rectifier can provide 1000 DC amperes at 48 amperes with a continuous duty cycle .

Powder coatings have been successfully removed from motor vehicle wheel hubs and rims made from aluminum alloy, steel, and manganese alloys. Other bodies that have been successfully cleaned using the disclosed methods include cast iron and stainless steel bodies.

The disclosed method for cleaning has a number of advantages. Potassium carbonate and sodium carbonate electrolytes are inexpensive and environmentally friendly. Food grade potassium carbonate and food grade sodium carbonate are available and are non-toxic. Rinsing the bodies to remove the additional coating and contaminants can be automated, is not labor intensive, and can generate high production rates of cleaned bodies as compared to conventional cleaning methods (particularly when removing powder coatings) .

A further advantage of the disclosed method for cleaning when cleaning aluminum or aluminum alloy bodies is that the body is not discolored after cleaning. Conventional cleaning of aluminum or aluminum alloy bodies in a strong alkaline solution may discolor the body. Rubin et al . US Patent 4,457,332 for example suggests adding metasilicate salt to a strongly basic aqueous solution to avoid discoloration of aluminum bodies . The inventors have found that soft metal or metal alloy bodies such as aluminum and aluminum alloy bodies cleaned in accordance with the disclosed method do not discolor even when cleaned using a highly alkaline aqueous electrolyte that includes only carbonate salts.

Other objects and features of the disclosure will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing sheets illustrating one or more illustrative embodiments.

Brief Summary of the Drawing

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.

Fig. 2 is an enlarged view of a portion of the wheel shown in Figure 1.

Detailed Description

Figure 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 alloy wheel that has a powder coating 14 on an external surface 16 of the wheel. See Figure 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.

The wheel 10 is connected electrically in series to an anode terminal 20 of a DC current source 22 by a conductor 24. A steel or iron cathode 26 is also immersed in the electrolyte 12 and is connected in series to a cathode terminal 28 of the current source 22 by a conductor 30. The wheel 10 and the cathode 26 are electrically connected by the electrolyte 12.

The illustrated electrolyte 12 is an aqueous basic electrolyte formed by dissolving potassium carbonate (K ₂ C0 ₃ ) in water. The potassium carbonate is preferably food-grade potassium carbonate.

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

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

The DC current source 18 is energized and flows 1000 amperes of DC current from the anode terminal 16, through the wheel 10 and to the cathode 26, and back to the cathode terminal 22. The impressed DC current makes the wheel 10 anodic, that is, anodic with respect to the electrolyte 12.

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.

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.

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. After the current source 18 is shut off, the wheel 10 is removed from the electrolyte 12. The wheel 10 is 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.

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 .

After rinsing, 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.

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.

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 connect the body as anode with the cathode and must conduct sufficient DC current to create the additional material coating.

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. 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) .

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

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 .