Electrolytic cleaning of conductive bodies

Details Electrolytic cleaning of conductive bodies Electrolytic cleaning of conductive bodies

1998-09-18

2001-03-20

Phasge, Arun S. (Department: 1741)

Electrolysis: processes, compositions used therein, and methods

Electrolytic material treatment

Metal or metal alloy

C205S712000, C204S242000, C204S275100, C204S22400M

Reexamination Certificate

active

06203691

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to methods and equipment for cleaning electrically conductive bodies.
BACKGROUND OF THE INVENTION
Bodies capable of conducting electricity, including bodies made entirely of metal and bodies having both metallic and nonmetallic portions, often have outer surfaces that need to be cleaned. Rust, scale, smut, petroleum derived contaminants, flux, carbonization, nonmetallic coatings, corrosion, dirt and the like may form or be deposited on the surface of the body. These surface deposits or contaminants must be removed so that the body may be recycled and reused or to prepare the body for subsequent surface treatment. Examples of metallic bodies that may require cleaning include grocery carts, metallic brake shoes, jewelry, and electronic circuit boards.
An early method of cleaning metal bodies immerses the bodies in a high temperature cyanide bath. Major ingredients of the cyanide bath include caustic soda and sodium cyanide or potassium cyanide. The bath is heated to a temperature in excess of 700 degrees F. All of the cyanide and alkali materials are limited in life and have to be discarded and entirely fresh bath solutions made. The cyanide bath has the potential of liberating deadly cyanide gas, and the cyanide bath itself is a hazardous waste that requires special and expensive waste treatment and disposal.
To overcome the disadvantages of the cyanide bath, a variety of electrolytic cleaning systems were developed. Many of these systems use caustic soda (NaOH) to form a highly alkaline caustic soda bath. Caustic soda attacks galvanized steel, brass, bronze, copper, aluminum, magnesium, titanium and other metals. The caustic soda attacks the metal itself. Even if the metal could withstand immersion in the caustic soda bath, subsequent brushing or spraying treatments may be needed to remove tenacious impurities. The caustic soda bath is highly corrosive and requires special care in handling and disposal.
Other electrolytic cleaning systems have been proposed. One electrolytic system uses an electrolyte solution containing ferric sulfate and ammonium bifluoride. This system may generate objectionable fumes. The system does not de-scale or de-smut. A sludge containing insoluble salts of such metals as aluminum, copper, brass and bronze is generated that must be disposed of as a hazardous waste. Another electrolytic system uses an electrolyte solution composed of a phosphate alkaline material heated to 160-190 degrees F. Metallic ions, such as lead, tin, zinc or cadmium ions act as catalysts in the solution for removal of scale from stainless steel. These metallic ions remain in the spent electrolyte and require hazardous waste treatment and disposal. A film of metal may be deposited on the surface of the treated object. The film may be acceptable in cleaning stainless steel, but would be totally unacceptable in cleaning surfaces of other metallic objects such as circuit boards.
Yet another known method of cleaning is directed to consumer cleaning of gold, silver, coins and jewelry. The object to be cleaned is immersed in an electrolyte and a relatively low voltage and amperage electric current is passed through the electrolyte solution. The method is designed specifically to remove tarnish, which are sulfides of gold and silver. During cleaning, hydrogen sulfide gas is created. Hydrogen sulfide is a noxious, poisonous gas that would present a serious problem in commercial operation.
The above conventional methods of cleaning metallic bodies require extremely high operating temperatures, toxic chemicals or highly corrosive liquids. These conventional methods are designed primarily to remove rust, scale or smut from iron or steel bodies, and are not suitable for cleaning of other types of metallic bodies. The methods generate hazardous wastes that must be disposed of in compliance with environmental regulations and at high cost. Immersing the metallic body in the electrolyte may also be inefficient, as only a small number of bodies may be treated at a time.
Thus, there is a need for an improved method and apparatus for conductive cleaning bodies. The improved method should clean a wide variety of bodies, and should not be limited to iron or steel. The improved method should use non-toxic materials that are non-hazardous to personnel and should not require special disposal. The improved method should be efficient and allow the cleaning of a large number of bodies at the same time. Treatment to clean the bodies should not harm the bodies.
SUMMARY OF THE INVENTION
The present invention is an improved electrolytic method and apparatus for cleaning conductive bodies. Two embodiments are disclosed.
In the first embodiment, a conductive body to be cleaned is immersed in a specialized basic electrolytic bath and connected to the cathode of a direct current power source. The anode of the source is immersed in the bath. The resulting electrolysis weakens the attachment of deposits and contaminants to the outer surfaces of the body. The cleaned body may be lightly rinsed after removal from the bath to remove any debris remaining on the body.
In the second embodiment, the specialized basic electrolyte is sprayed from one or more spray nozzles onto the body to be cleaned. The body is connected to the cathode of a direct current power source. The anode of the source is connected to each spray nozzle. The metallic body is washed in a continuous stream of electrolyte. Resulting electrolysis weakens the attachment of foreign matter to the outer surfaces of the article. The electrolyte spray may wash off foreign matter from the metallic body. Electrolyte sprayed on the body is collected, filtered and recycled.
The electrolyte spray allows larger bodies such as transformer cases, shopping carts, extruded and sheet steel, boilers and the like to be cleaned on site. It is not necessary to transport the bodies to a bath. Bodies that are too large to be immersed in a bath or which cannot be moved to a bath can be cleaned using an electrolyte spray.
If desired, a plurality of metallic bodies can be electrolytically spray cleaned at the same time. The bodies are placed in electrical contact with each other and one body is attached to the cathode. Electrolyte spray is sprayed onto all the bodies for simultaneous electrolysis and cleaning of all the bodies. The bodies could move through an electrolyte spray on a conveyor belt to spray clean a continuous stream of bodies.
In both embodiments, the electrolyte is an aqueous solution of disodium phosphate and sodium bicarbonate having a pH greater than 7 and less than 9.0, preferably in the pH range of 8.0 to 8.5. In this pH range the electrolyte is not corrosive, is non-hazardous to personnel and is environmentally friendly. The electrolyte can be disposed of by conventional means, and does not have to be treated and disposed of as a hazardous waste.
Temperature ranges for successful cleaning of metallic bodies extend from just above the freezing point of the electrolyte to just below the boiling point of the electrolyte. The preferred operating temperature of the electrolyte is between about 55 degrees F. and 90 degrees F.
The electrolyte has a long useful life, whether used in the bath or discharged as a spray. The liquid component of the electrolyte needs replenishment only due to the evaporation of liquid from the electrolyte. Other components of the electrolyte are replenished as needed to maintain the specific gravity of the electrolyte. The specific gravity of the electrolyte can range from between about 1.5 to about 2.50, and is preferably between about 1.86 to about 2.15.
Cleaning of metallic objects does not contaminate the electrolyte. When used as a bath, metal oxides and other metallic residues removed from the metallic bodies sink to the bottom of the bath. Nonmetallic residues float on the surface of the bath. Both residues can be easily removed from the electrolyte bath by occasionally collecting each into separate containers. Sprayed electrolyte can be collected, filtered to remove residues and then

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