Abstract:
A method and apparatus for cleaning conductive bodies using an electrolytic cleaning solution. An inverter power source is used to supply a high voltage, low current output for the electrolytic cleaning. The outside surfaces of a metallic body are cleaned by spraying the cleaning solution on to the body and passing a current through the cleaning solution on the conductive body, thereby causing the cleaning solution to electrolytically clean the body. The body is connected to the negative terminal of the power supply. The positive terminal of the power supply is connected to a spray nozzle and causes a current to pass through the spray to the cleaning solution on the body for the electroytic cleaning. Alternatively, a current can be induced in the cleaning solution on the body by placing a grid near the body and connecting the grid to the positive terminal, thereby generating an electric field.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to methods, equipment and solutions for electrolytic cleaning. Specifically, the present invention relates to a system and method of electrolytically cleaning conductive bodies using a power supply that has a high voltage and a low current output.  
           [0002]    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. Fabricated or machined metal products require cleaning, for example, prior to painting, coating, packaging or shipment. As another example, metal components, which are to be remanufactured for the after-market, almost always require some degree of cleaning.  
           [0003]    Rust, mill scale, embedded chips, core sand, scale, smut, petroleum-derived contaminants, oils, greases, flux, carbonization, nonmetallic coatings, corrosion, oxidation, paint, 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. Metal cleaning, including precision cleaning and light/heavy industrial cleaning, is particularly important in industries which are involved in the forming, casting, extruding and machining of ferrous and non-ferrous metals.  
           [0004]    Previously, cleaning of metals was typically accomplished using acidic cleaning solutions, preferably having a pH of 6.0 or less. Acidic solutions were most frequently used because of their relative low cost, and their substantial effectiveness (both in total cleaning ability, cleaning speed and cost) in removing metal oxides, scale and other contaminants prior to pretreatment or painting. Typically, such solutions included mineral acids, chromic acid, carboxylic acids and other organic acids. The use of acidic solutions, due to their very aggressive nature, resulted not only in the removal of the undesirable contaminants on the item being treated, but often had the negative effect of removing material from the item and potentially degrading the tank walls, pump components and other parts of the washer device itself. Further, the solution often had to be replaced due to the change in the pH of the solution over time, and as a result, disposal of the spent solution, which solution would almost certainly be classified as a hazardous substance, was necessary. Additionally, because of the chemical reaction, the spent solution invariably included heavy metals in solution as metallic ions.  
           [0005]    More recently, the metal cleaning industry began to utilize alkaline chemical solutions (having a pH of 8.0 or greater). These solutions typically use detergents and solvents, accompanied by high levels of agitation (such as by ultrasonic bath or high-pressure wash), to effect removal of contaminants. Alkaline cleaners have been formulated with such materials as sodium or potassium hydroxide, carbonate, bicarbonate, phosphate, silicate or other similar materials. The chemical reaction occurs via saponification with water-soluble soaps by neutralization of fatty acid soils. If the pH of the solution is kept between 8.0 and 13.0, these cleaners are somewhat successful in the removal of oils and greases. However, as with acidic solutions, the spent alkaline solutions must be frequently reprocessed, and further, they present similar hazardous waste disposal problems.  
           [0006]    To overcome some of the disadvantages of the above cleaning techniques, a variety of electrolytic cleaning systems were developed. Many of these systems use an electrolyte that is formed of a solution of potassium or sodium salt such as sodium carbonate, potassium carbonate, sodium chloride, sodium nitride, and other similar salts. Most types of electrolytic cleaning are conducted using either a bath or dip system where the body to be cleaned is immersed in the electrolyte or a spray system where the electrolyte is sprayed onto the body to be cleaned. However, other systems for electrolytic cleaning have also been used.  
           [0007]    The prior electrolytic cleaning processes used a rectifier or inverter power supply that output a low voltage, 350 volts or less, and typically an output of less than 50 volts. The power supply in the prior electrolytic cleaning processes typically also had a large current output. The large current output is necessary to generate a high current density in the electrolyte, which was required in many of the prior electrolytic cleaning processes. In addition, many of the prior electrolytic cleaning processes required the electrolyte to be heated for effective electrolytic cleaning.  
           [0008]    Some examples of prior electrolytic cleaning processes that used power supplies with low output voltages are U.S. Pat. No. 3,457,151 to Kortejarvi (0-24 VDC), U.S. Pat. No. 4,493,756 to Degen et al. (0-10 VDC), U.S. Pat. No. 5,776,330 to D&#39;Muhala (0-24 VDC), U.S. Pat. No. 5,227,036 to Gordon (12 VDC), and U.S. Pat. No. 6,045,686 to Fenton et al. (about 30 VDC). Some examples of prior electrolytic cleaning processes that used high current densities are U.S. Pat. No. 6,030,519 to Keller et al. (100 to 2000 amps/dm 2 ), U.S. Pat. No.  3 , 457 , 151  to Kortejarvi (10 to 35 amps/ft 2 ), U.S. Pat. No. 4,493,756 to Degen et al. (150 to 450 amps/ft 2 ), U.S. Pat. No. 5,840,173 to Waldmann (3 to 40 amps/dm 2 ), and U.S. Pat. No. 5,104,501 to Okabayashi (1 to 30 amps/dm 2 ).  
           [0009]    The above mentioned conventional methods of cleaning metallic bodies can require extremely high operating temperatures, toxic chemicals and/or highly corrosive liquids and large output currents. Further, many of the techniques discussed above generate hazardous wastes that must be disposed of in compliance with environmental regulations and at high cost. In addition, there are a number of practical shortcomings which are present in the known methods, including limited effectiveness in removing contaminants, short solution life, and the tedious and time-consuming task of altering key variables (such as range of agitation, range of chemical ingredients of the cleaning solution, time and temperature requirements, etc.) in order to determine the optimum level of each variable that will effectively and efficiently accomplish the desired level of cleaning. These variables may vary dramatically, depending on the composition of the body being treated, and on the particular contaminants for which removal is desired. Treatment to clean the bodies should not cause a reaction with the bodies themselves, but rather, should attack only the contaminants and other materials of which removal is desired. Immersing the metallic body in the electrolyte may also be inefficient, as only a small number of bodies may be treated at a time.  
           [0010]    Therefore, what is needed is an improved method and apparatus for cleaning conductive bodies that is quick, efficient and economical. The improved method and apparatus for cleaning conductive bodies should operate at ambient temperature and have an electrolyte that has a substantially neutral pH so that hazardous wastes are not formed, although other electrolytes may be used. In addition, the improved method should be practical and permit the cleaning of a large number of bodies at the same time without attacking the bodies.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention is directed to a system and method for electrolytically cleaning conductive bodies.  
           [0012]    One embodiment of the present invention is an apparatus for cleaning the surfaces of a conductive body. The apparatus includes a supply of an electrolytic cleaning solution and at least one spray nozzle connected to the supply to permit the electrolytic cleaning solution to flow from the supply to the at least one spray nozzle. The apparatus also has a direct current power source having a high voltage and a low current output. The direct current power source has a positive output terminal and a negative output terminal. The positive output terminal is connected to the at least one spray nozzle and the negative output terminal is connected to the conductive body. Finally, when the direct current power source and the spray nozzle are activated, the electrolytic cleaning solution flowing through the at least one nozzle carries a current to the conductive body to clean the surface. Desirably, after application, the electrolytic cleaning solution can be collected and reused.  
           [0013]    Another embodiment of the present invention is an apparatus for cleaning the surfaces of a conductive body. The apparatus includes a first container having an electrolytic cleaning solution contained therein and a second container connected to the first container to permit the electrolytic cleaning solution to flow between the first container and the second container. At least one spray nozzle is disposed in the second container. The at least one spray nozzle is connected to the first container to permit the electrolytic cleaning solution to flow from the first container to the at least one spray nozzle. The apparatus also includes a direct current power source having a high voltage and a low current output. The direct current power source has a positive output terminal and a negative output terminal. A first grid is disposed in the second container and is connected to said positive output terminal. A second grid is disposed substantially parallel (either horizontally or vertically) to the first grid in the second container. The second grid is connected to the negative output terminal and has the conductive body positioned thereon. Finally, when the direct current power source and the spray nozzle are activated, the electrolytic cleaning solution flowing through the nozzle washes over the conductive body and the first grid and the second grid induce a current in the electrolytic cleaning solution washing over the conductive body to clean the surface.  
           [0014]    Still another embodiment of the present invention is a method of electrolytically cleaning the surfaces of an object. The method includes providing a container having an electrolytic cleaning solution therein and providing a spray washer having at least one spray nozzle. The method also includes connecting the container to the at least one spray nozzle to permit the electrolytic cleaning solution to flow from the container to the at least one spray nozzle and providing an inverter power source having a high voltage and a low current, direct current output. The inverter power source has a positive output terminal and a negative output terminal. The method further includes positioning the object in the spray washer, connecting the positive output terminal to the at least one spray nozzle and connecting the negative output terminal to the object. In addition, the method includes activating the inverter power source and the at least one spray nozzle to flow a current through the electrolytic cleaning solution sprayed by the at least one nozzle on to the object to clean the surfaces of the object and deactivating the inverter power source and the at least one spray nozzle when cleaning is completed. Finally, the method includes removing the object from the spray washer.  
           [0015]    Yet another embodiment of the present invention is a method of cleaning the surfaces of a conductive body. The method includes providing a container having an electrolytic cleaning solution therein and providing a spray washer having at least one spray nozzle. The method also includes connecting the container to the at least one spray nozzle to permit the electrolytic cleaning solution to flow from the container to the at least one spray nozzle and providing an inverter power source having a high voltage and a low current, direct current output. The inverter power source has a positive output terminal and a negative output terminal. The method further includes the steps of connecting the positive output terminal to a first grid positioned in the spray washer and connecting the negative output terminal to a second grid positioned substantially parallel (either horizontally or vertically) to the first grid in the spray washer. The conductive body is positioned on the second grid in the spray washer. The method additionally includes activating the inverter power source and the at least one spray nozzle to induce a current in the electrolytic cleaning solution washing over the conductive body from the at least one spray nozzle to clean the surfaces of the conductive body and deactivating the inverter power source and the at least one spray nozzle when cleaning is completed. Finally, the conductive body is removed from the spray washer.  
           [0016]    Still yet another embodiment of the present invention is an apparatus for cleaning the surface of a conductive body. The apparatus includes a container having an electrolytic cleaning solution therein and a direct current power source having a high voltage and a low current output. The direct current power source has a positive output terminal and a negative output terminal. The negative output terminal is operatively connected to the conductive body. The apparatus also includes an anode in contact with the electrolytic cleaning solution. The anode is connected to the positive output terminal of the power source. Finally, when the conductive body is at least partially immersed in the electrolytic cleaning solution, and when the power source is activated, current flows through the electrolytic cleaning solution to the conductive body to clean the surface.  
           [0017]    The electrolytic spray process permits larger bodies such as transformer cases, transmissions, 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 electrolytic spray process.  
           [0018]    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 connected to the negative terminal of the power supply. 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.  
           [0019]    Temperature ranges for successful cleaning of metallic bodies extend from just above the freezing point of the electrolytic solution to just below the boiling point of the electrolytic solution. The preferred operating temperature of the electrolyte is between about 50 degrees F. and 150 degrees F.  
           [0020]    In each embodiment, a method or apparatus is provided for cleaning items that is more efficient (in cleaning ability, cleaning time, and cost) than existing methods, such as ultrasonic bath or high-pressure aqueous wash systems because of the high voltage, low current power supply that is used, although certain embodiments, such as the submersion embodiments, may be used in conjunction with ultrasonic baths and other embodiments, such as the spray embodiments, may be used in conjunction with high pressure wash systems.  
           [0021]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a schematic diagram of one embodiment where a plurality of objects are sprayed with electrolyte for cleaning the exposed surfaces of the objects.  
         [0023]    [0023]FIG. 2 is a schematic diagram of a surface of an object being cleaned by the sprayed electrolyte.  
         [0024]    [0024]FIG. 3 is a schematic diagram of another embodiment where a plurality of objects are sprayed with electrolyte for cleaning the exposed surfaces of the objects.  
         [0025]    [0025]FIG. 4 is a schematic diagram of one embodiment where an object is immersed in an electrolyte for cleaning.  
         [0026]    [0026]FIG. 5 is a schematic diagram of another embodiment where an object is immersed in an electrolyte for cleaning.  
         [0027]    [0027]FIG. 6 is a schematic diagram of still another embodiment where an object is immersed in an electrolyte for cleaning.  
         [0028]    [0028]FIG. 7 is a graph showing the relationship between voltage and time required to remove contaminants of the same type and degree in Examples 1-13.  
         [0029]    Whenever possible, the same reference numbers will be used throughout the figures to refer to the same parts. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    [0030]FIG. 1 illustrates one configuration of a system for the electrolytic cleaning of objects. One or more objects  100  are located or placed in a spray washer  102  for cleaning the exposed surfaces of the objects  100 . The objects  100  are preferably any type of electrically conductive objects, but are typically metallic objects, and can include machined, milled or cast automotive parts, such as engine blocks, manifolds and heads, transformer cases and extruded and sheet steel. The objects  100  are placed in the spray washer  102  to remove any surface contamination present on the objects  100  prior to any subsequent processing or treatment procedures required for the objects  100 . The surface contamination present on the objects  100  can include rust, mill scale or oxidation, core sand, embedded chips, paint, oil or grease, dirt and any other similar type of surface contaminant.  
         [0031]    Spray washer  102  includes a reservoir  104  with a supply of cleaning solution  106 . The cleaning solution  106  can be any type of electrolytic cleaning solution, including very acidic solutions and very basic solutions. However, the cleaning solution  106  is preferably an aqueous basic solution made of water, disodium phosphate (Na 2  HPO 4 ) and baking soda (sodium bicarbonate, NaHCO 3 ) with a pH greater than 7.0 and less than about 10.0 and preferably between 8.0 and 8.5 inclusive.  
         [0032]    The disodium phosphate is preferably food grade disodium phosphate, and more preferably is a granular form of food grade disodium phosphate. Disodium phosphate in the powder form may also be used. The amount of disodium phosphate that is used in the cleaning solution  106  is about 0.0375 pounds per gallon of water to about 1.33 pounds per gallon of water. The amount of baking soda that is used in the cleaning solution  106  is about 0.0125 pounds per gallon of water to about 0.444 pounds per gallon of water. While any combination of disodium phosphate and baking soda within these respective ranges will produce cleaning results without creating any negative environmental implications, it is preferable for the solution to contain approximately three times as much disodium phosphate as baking soda, that is, a ratio of disodium phosphate to baking soda of approximately 3 to 1. Most preferably, approximately 0.075 pounds of disodium phosphate and 0.025 pounds of baking soda are dissolved in each gallon of water to form the cleaning solution  106 .  
         [0033]    In addition, when the amount of disodium phosphate is less than 0.15 pounds per gallon of water and the amount of baking soda is less than 0.05 pounds of baking soda per gallon of water, the cleaning solution  106  does not leave a residue of disodium phosphate and baking soda on the object  100  being cleaned. These relatively low concentrations of the cleaning solution  106  also do not have a crystallization problem at lower temperatures due to the oversaturation of the cleaning solution  106 .  
         [0034]    A supply or feed line  108  extends from reservoir  104  to a plurality of spray nozzles  110  that spray the cleaning solution  106  on the objects  100 . The nozzles  110  are preferably adjustable to provide several different types of output spray characteristics for the cleaning solution  106 . For example, the nozzles  110  can have a substantially closed configuration, which results in a narrow or focused output spray of cleaning solution  106 , or the nozzles  110  can have a substantially open position, which results in a wide output spray of cleaning solution  106 . A supply or feed pump  112  is located in the supply line  108  to pump cleaning solution  106  from the reservoir  104  to the spray nozzles  110 . The feed pump  112  can be adjusted to vary the amount of cleaning solution  106  sprayed from the nozzles  110  and to vary the pressure with which the cleaning solution  106  is sprayed from the nozzles  110 .  
         [0035]    The feed pump  112  can preferably produce an output of about 25 to 375 gallons per minute (gpm) of cleaning solution  106  at each of the nozzles  110  and an output pressure of cleaning solution  106  of about 10 to 150 pounds per square inch (psi) from each of the nozzles  110 . While any combination of output pressure and output flow within these respective ranges will produce cleaning results, it is preferable for the feed pump  112  to generate an output ratio at each of the nozzles  110  of about 1 psi of pressure for about each 2.5 gpm of flow of cleaning solution  106  from each of the nozzles  110 . In a preferred embodiment, the feed pump  112  generates an output at each of the nozzles  110  of 100 gpm and 40 psi.  
         [0036]    The number, location and orientation of spray nozzles  110  in the spray washer  102  can be varied to conform to the size and shape of the object or objects  100  being cleaned. The spray nozzles  110  are preferably positioned in the spray washer  102  to assure wetting of the entire surface of the object  100  with cleaning solution  106 . The spray nozzles  110  are also preferably positioned at a distance from the object  100  to perform “wash-off” cleaning of the object  100  from the spray and to maintain electrical conductivity in the spray as discussed in more detail below. As the amount of cleaning solution  106  sprayed from the nozzles  110  is increased and the pressure of cleaning solution supplied to the nozzles  110  is increased, the distance between the nozzles  110  and the objects  100  can be increased.  
         [0037]    In an embodiment of the present invention, the objects  100  being cleaned could be placed on a conveyor to move through the electrolyte spray and the spray washer  102 . The objects  100  would be exposed to the spray for a sufficient time to be cleaned. Alternatively, the nozzles  110  could move and the objects  100  being cleaned could remain stationary. In still another embodiment, the spray washer  102  could be mounted on a truck to allow spray washing of large or immobile objects such as over-the-road trailers and aircraft. In yet another embodiment, one or more spray nozzles  110  could be attached to a flexible supply line to permit an operator to direct the electrolyte spray where needed.  
         [0038]    After the cleaning solution  106  is sprayed on the objects  100  in the spray washer  102 , a drain basin in the spray washer  102  collects sprayed cleaning solution  106 . The collected cleaning solution  106  flows through return line  114  to filter  116  for filtering and removal of contaminants. The collected and filtered cleaning solution  106  is then pumped by drain pump  118  through return line  114  to reservoir  104 . The cleaning solution  106  can be continuously pumped out of the reservoir  104 , sprayed onto the objects  100  and returned to the reservoir  104 .  
         [0039]    The electrolytic cleaning process illustrated in FIG. 1 also includes a power supply  120 . The power supply  120  has a positive terminal  122  that is connected to the nozzles  110  to form the anodes for the electrolytic cleaning process. In an alternate embodiment, the positive terminal  122  of the power supply  120  can also be connected to a manifold (not shown) for several of the nozzles  110 . The power supply  120  also has a negative terminal  124  that is connected to the objects  100  to form the cathodes of the electrolytic cleaning process. Each nozzle  110  (or manifold) can be directly connected to the positive terminal  122  of the power supply  120  or, more preferably, one nozzle  110  (or manifold) can be connected to the positive terminal  122  of the power supply  120  and the remaining nozzles  110  (or manifolds) can be connected or jumpered by jumpers  126  to the nozzle  110  connected to the positive terminal  122  of the power supply  120  as shown in FIG. 1. Similarly, each object  100  can be directly connected to the negative terminal  124  of the power supply  120  or, more preferably, one object  100  can be connected to the negative terminal  124  of the power supply  120  and the remaining objects  100  can be connected or jumpered by jumpers  128  to the object  100  connected to the negative terminal  124  of the power supply  120  as shown in FIG. 1 or can be in contact with the object  100  connected to the negative terminal  124  of the power supply  120 . Alternatively, each object  100  in the spray washer  102  can be placed on a grid or plate (not shown) that is connected to the negative terminal  124  of the power supply  120 .  
         [0040]    Any suitable power supply can be used to provide the voltage necessary to accomplish electrolytic cleaning. For example, power supply  120  may be one that produces a high voltage direct current (DC) output of 70 volts (V) to over 115 kilovolts (kV). Preferably, the output voltage from the power supply  120  is over 350 V and more preferably over 1000 V. The higher the output voltages from the power supply  120 , the higher the cleaning ability of the spray washer  102 . In addition, the maximum output voltage output from the power supply  120  can be a large as the power supply  120  can generate. In other words, the maximum voltage output from power supply  120  for electrolytic cleaning is limited only by the mechanical ability of the power supply  120  to generate that desired maximum voltage. With regard to the current output from the power supply  120 , the power supply  120  can output a DC current of between 10 amps (when the output voltage is about 140 V) and 0.0005 amps (when the output voltage is about 115 kV). In a preferred embodiment, as the output voltage from power supply  120  is increased, the output current from power supply  120  is decreased. However, it is to be understood that the output current from power supply  120  may stay relatively constant or possibly even increase and still provide effective electrolytic cleaning as the output voltage from power supply  120  is increased. A small current ouptut from power supply  120  is preferred to reduce the possibility of the cleaning solution  106  being heated during the cleaning process. Furthermore, the output voltage and output current from the power supply  120  preferably has substantially constant magnitude throughout the cleaning procedure to provide consistent and effective cleaning. Fluctuations in the output voltage magnitude from power supply  120  can reduce the cleaning effectiveness of the cleaning system  102  during those fluctuations.  
         [0041]    It has been found that inverter power sources or supplies which have traditionally only been used in connection with welding machines and plasma cutters, when used with the methods, equipment and solutions of the present invention, provide excellent results in terms of increased efficiency, effectiveness and cleaning power over known methods for cleaning conductive bodies. For example, power supply  120  can be a Spectrum 3080 power source manufactured by Miller Electric Manufacturing of Appleton, Wis. However, it is to be understood that any other suitable power supply may be used, for example, a rectifier power source.  
         [0042]    Electrolytic cleaning using a conventional rectifier power source requires alternating or reversing the polarity of the cathode and anode, not only to maintain a stable electric field, but also to prevent corrosive deterioration of the cathode and anode, as well as to prevent smut from being attracted to the cathode and anode. While conventional rectifier power sources may be used, in the preferred embodiment an inverter power source is used. It has been found that by using an inverter power source with the cleaning solution, apparatuses and methods of the present invention, as well as with known electrolytic cleaning solutions, apparatuses or methods (whether environmentally friendly or not), the electrolytic cleaning process decreases the time in which debonding and removal of surface materials, contaminants, etc. are removed from metal bodies. Further, there is no need to reverse the polarity of the cathode and anode. As such, the process of the preferred embodiment does not deteriorate or degrade the cathode or anode. Further, an inverter power source allows the cleaning process to be performed at a much lower solution temperature than a conventional rectifier power source. The inverter power source is particularly preferred when electrolytic cleaning via a spray system is desired. In all electrolytic cleaning systems, the higher frequency, more defined direct current produced by an inverter system allows the de-bonding of rust and paint from the metal to a significantly larger degree than that which is achieved using a conventional rectifier power source.  
         [0043]    In an inverter power source from a welding machine, the input alternating current voltage is rectified into an unregulated direct current voltage by means of a diode rectifier. Subsequently, the power converter must take the unregulated direct current and convert it to regulated direct current with a lower voltage level. This is accomplished by a high-frequency bridge, wherein switching causes the generation of a high frequency square wave alternating current. The high frequency alternating current is transferred to the secondary side by means of an isolation transformer, which is then rectified and filtered to produce the regulated high current, low voltage direct current output. By controlling the switching of the high frequency bridge, the output is thereby regulated.  
         [0044]    In contrast, the more preferred inverter power source is from a plasma cutter. The input alternating current (AC) line power is changed into full-wave rectified DC by a silicon-controlled rectifier (SCR) or Integrated Rectifier using thyristors. The output from the SCR is then filtered by capacitors and the peak current from the SCR and the capacitors is limited by inductors. Next, insulated gate bipolar transistor (IGBT) modules convert the DC output into AC through very fast on/off switching of the IGBT modules. This AC can be a high frequency square wave alternating current due to the rapid on/off switching. The AC from the IGBT modules is then used to activate the primary of a transformer. The transformer then supplies power to the cutting circuit from its secondary. The output from the transformer is then rectified using diodes to generate a high voltage, low current DC output.  
         [0045]    The temperature of cleaning solution  106  may range from just above the freezing point of the cleaning solution  106  to just below the boiling point of the cleaning solution  106 . The preferred temperature of cleaning solution  106  is between 55 degrees F. and 160 degrees F. An external source of cooling or heating is not provided and the temperature of the cleaning solution  106  does not vary greatly because of the limited amount of electric current which is passing through the cleaning solution  106 .  
         [0046]    The streams of electrolyte spray electrically connect the anodes to the metallic body or bodies  100  being cleaned by spray washer  102 . It is important that the electrolyte discharged from the nozzles  110  be in continuous streams extending from the anode to the metallic body  100 . The length of the streams from the nozzles  110  to the body being cleaned  100  can range from about two inches or less to about eighteen inches depending on the output voltage from the power supply  120 . The higher the output voltage from the power supply  120 , the larger the distance can be between the nozzles  110  and the object  100  being cleaned. The higher output voltages can maintain the electrical continuity in the stream for the larger distances. In another embodiment of the present invention, when the power supply  120  has an output voltage of over 100 kV, the length of the streams from the nozzles  110  to the body  100  being cleaned can be extended to twenty six inches for the cleaning of rust, oxidation, embedded chips and paint.  
         [0047]    [0047]FIG. 2 illustrates in greater detail the electrolytic treatment of the surface of an object  100 . Nozzle  110  flows a continuous stream  202  of cleaning solution  106  onto a surface  204  of an object  100 . The stream  202  directly impacts or impinges on a small area  206  of surface  204 . Impingement area  206  forms part of the cathode and is electrically connected to the anode by stream  202 . Electrolytic cleaning takes place on surface area  204 .  
         [0048]    Some electrolyte bounces off surface  204  and forms a mist or fog  208  surrounding the impact area  206 . The electrolyte mist  208  is sufficiently dense to be electrically conductive and forms a portion of the electrical circuit between the anode and cathode. Other electrolyte  210  from the streams from impact area  206  flows along surface  204  and wets a surface area considerably larger than the area of impingement  206 . The surface electrolyte  210  flowing from area  206  remains in fluid connection with electrolyte stream  202  and remains a part of the electrical circuit between the anode and the cathode so that a greatly enlarged surface area is cleaned. Electrolytic activity occurs on surface area  212  of surface  204  in contact with electrolyte mist  208  and the wetted portion of surface  214  in contact with the stream  210 . These areas can greatly increase the area of electrolytic cleaning around area  206 .  
         [0049]    The surface area cleaned by a stream  202  is not limited to the surface area  206  directly impinged by the stream  202 . The nozzles  110  are preferably arranged to maximize the surface areas  212 , 214  wetted by electrolyte and electrically connected with the anode, and to overlap these areas so that the entire surfaces  204  of the objects  100  are electrolytically cleaned. Wetting of the surfaces  204  of the objects  100  is aided by gravity flow of electrolyte down the objects  100  and by surface tension wetting of recesses and valleys on the surfaces  204  of the objects  100 .  
         [0050]    After cleaning of the objects  100  in spray washer  102 , power supply  120  is deactivated. The objects  100  are disconnected from the negative terminal  124  of the power supply  120  and are removed from spray washer  102 .  
         [0051]    [0051]FIG. 3 illustrates another configuration of a system for the electrolytic cleaning of objects. In this embodiment, as shown in FIG. 3, the spray washing system  302  has a spray washer  303  that is placed inside the reservoir  104  of cleaning solution  106 . In another embodiment, the spray washer  303  is connected to the reservoir  104  similar to the spray washer  102  in FIG. 1. The positive terminal  122  of the direct current power source  120  is connected, not to each spray nozzle as in FIG. 1, but rather, to a first metal grid, mounting or cage  304  that is provided in the spray washer  303  to form the anode for electrolytic cleaning. The negative terminal  124  of the power source  120  is connected to a second metal grid, mounting or plate  306  to form the cathode for electrolytic cleaning. The second grid, mounting or plate  306  is positioned adjacent and substantially parallel (either in a horizontal direction or a vertical direction) to the first grid or mounting  304 . The first grid  304  and the second grid  306  are separated and are not in contact with one another. The second grid  306  is preferably located about 0.25 inches to about 0.5 inches from the first grid  304 . The object or body to be cleaned  100  is placed on, and in direct contact with, the second grid  306 . The first grid  304  and the second grid  306  are constructed from a conductive material and are preferably perforated steel plates. In addition, the second grid  306  has to be constructed from a material that can also support the weight of the object to be cleaned  100 . The first grid  304  and the second grid  306  can be mounted in any suitable way in the spray washer  303  that does not reduce the conductive properties of the first and second grids  304  and  306  and maintains the positions of the first grid  304  and second grid  306 . In another embodiment of the present invention, there can be one or more first grids or mountings  304  and second grids or mountings  306  used in the spray washer  303 .  
         [0052]    The container  104  holds an amount of cleaning solution  106  that is sufficient to accomplish cleaning of the metal body  100 . When the spray washer  303  is positioned within the container  104 , as shown in FIG. 3, the level of cleaning solution  106  in container  104  remains below that of the first metal grid  304  so that the cleaning solution  106  does not come into contact with the first metal grid  304 , the second metal grid  306  or object  10 . In the embodiment where the spray washer  303  is not positioned in the container  104 , the level of cleaning solution  106  may be higher.  
         [0053]    Spray washer  303  includes a plurality of spray nozzles  110 , and is arranged in relation to the first and second grids  304  and  306  so as to spray the cleaning solution  106  from the spray nozzles  110  towards the object  100 . Spray nozzles  110  can be positioned above the object  100 , as shown in FIG. 3, or may be positioned below the object  100  (not shown), or both. Additional spray nozzles  110  may be placed around the body  100  to be cleaned in any desired fashion. For example, the spray nozzles  110  can be positioned along the sides of the object  100 , that is, in a perpendicular direction to any spray nozzles  110  that are above and/or below the object  100 . Further, spray washer  303  can be adapted so as to rotate around the object  100  during cleaning, thereby assuring that cleaning solution  106  is directed at the entire surface area of the object  100 .  
         [0054]    A supply line  108  extends from cleaning solution  106  to the spray washer  303 . Power supply  120  is energized to generate an electric field with the first and second grids  304  and  306  to induce an electric current in the cleaning solution  106  sprayed onto the surface of the object  100  for electrolytically cleaning the outer surface of the object  100 . Feed pump  112  in supply line  108  pumps cleaning solution  106  to spray nozzles  110 , which then spray cleaning solution  106  onto the body to be cleaned  100  and wash the object  100  in a continuous stream of cleaning solution  106 . Cleaning solution  106  sprayed on the body  100  passes through second grid  306  and first grid  304  and from the spray washer  303 , into the bottom of container  104 , where the initial supply of cleaning solution  106  is stored. Cleaning solution  106  is then filtered (not shown) and recycled by being continuously drawn through supply line  108  by feed pump  112 . In the embodiment of the present invention, where the spray washer  303  is not positioned in the container  104 , the spray washer  303  can included a drain to collect the cleaning solution  106  that has been sprayed onto the object  100  and piping to return the cleaning solution  106  to the reservoir  104 , in a manner similar to that shown in FIG. 1.  
         [0055]    In another embodiment of the present invention, an insulating material can be positioned directly between first metal grid  304  and second metal grid  306 . The insulating material is porous enough to permit cleaning solution  106  to pass through, and yet still provide the necessary separation between the anode and cathode (i.e., first grid  304  and second grid  306 ).  
         [0056]    The electrolytic cleaning process of the present invention can also be implemented as a dip or bath process. FIGS.  4 - 6  illustrate different embodiments that can be used for the dip or bath procedures. FIGS.  4 - 6  illustrate an object  100  immersed in a cleaning solution  106  for cleaning the outer surfaces of the object  100 . A power supply direct current source  120  having a positive terminal  122  and a negative terminal  124  is used to supply the power for the electrolytic cleaning process.  
         [0057]    During normal electrolytic cleaning, the power supply  120  is energized for an appropriate time to remove surface contaminants from the object  100 . During the cleaning process, bubbles of CO 2  gas are evolved. The bubbles agitate the cleaning solution  106  adjacent the part  100 . The agitation may help in mechanically removing surface contaminants and may aid in cleaning the object  100 . Agitation of the solution may also be accomplished by a pump or other mechanical method, or by an ultrasonic method No toxic or environmentally hazardous gases are evolved, if the preferred cleaning solution  106  is used. Most surface contaminants removed from the object  100  sink to the bottom of container or vat  104  and form a sludge. Other surface contaminants may float on the top of cleaning solution  106 . The sludge and floating residue are physically removed by occasionally collecting each into separate containers. The sludge and floating residue are non-hazardous and may be disposed of through normal channels.  
         [0058]    After completion of the cleaning process, the power supply  120  is deactivated. The object  100  is removed from cleaning solution  106  and disconnected from the negative terminal  124  (if connected). The object  100  may be lightly rinsed with water to remove any loose debris still adhering to the object  100 . After rinsing, the outer surfaces of the object  100  have been cleaned and are ready for any post-cleaning surface treatment.  
         [0059]    In the embodiment illustrated in FIG. 4, a nonmetallic container or vat  104  is used to hold the cleaning solution  106  and the object  100 . The positive terminal is connected to one or two anodes  402  that are at least partially submersed in the cleaning solution  106 . The object  100  is immersed in the cleaning solution  106  and is connected to the negative terminal  124  to form a cathode.  
         [0060]    [0060]FIG. 4 illustrates a single object  100  immersed in cleaning solution  106  for cleaning. However, a number of objects  100  in electrical contact with each other can be immersed in cleaning solution  106  for simultaneous cleaning of the objects. One of the objects  100  is connected to the negative terminal  124 . The other objects  100  touch the object  100  connected to the negative terminal  124  or form a series of objects  100  that contact one another and include the object  100  connected to the negative terminal  124 . Alternatively, vat  104  could be made from stainless steel and connected to the negative terminal  124  of power supply  120  to form the cathode. The objects  100  would contact vat  104  to be connected to the cathode.  
         [0061]    Alternatively, as shown in FIG. 5, a metal grid or plate  502  is positioned in the container  104  and submersed in the cleaning solution  106 . The grid  502  is connected to the negative terminal  124  of power source  120 . In this alternative embodiment, the object  100  is placed on, and in direct contact with the grid  502 . The grid  502  and anodes  402  must not come into contact with one another, and an insulating material (not shown) may be provided between grid  502  and anodes  402  to avoid such contact. The insulating material is positioned so as to allow for sufficient contact between anodes  402  and cleaning solution  106 , as well as between grid  502  and cleaning solution  106 .  
         [0062]    In still another embodiment, as shown in FIG. 6, the container  104  can be made of metal and connected, such as by bolting, to the positive terminal  122  of power source  120 . In this embodiment, the anodes  402  are not used and have been replaced by the connection to the container  104 . Grid  502  and container  104  must not come into contact with one another, and an insulating material (not shown) may be provided between grid  502  and container  104  to avoid such contact. The insulating material is positioned so as to allow for sufficient contact between container  104  and cleaning solution  106 , as well as between grid  502  and cleaning solution  106 .  
         [0063]    When the anodes  402  are made from stainless steel, they generally are not sacrificed during electrolysis and are used continuously. Other types of anodes may act as sacrificial anodes and should be inspected and replaced as necessary.  
         [0064]    In all of the embodiments, the cleaning solution and the process steps used result in a method for removing materials and contaminants from conductive bodies in a manner that is economical and efficient. The present invention removes a wide variety of materials, including mill scale, core sand, embedded chips, rust, scale, smut, petroleum derived contaminants, oils, greases, flux, carbonization, nonmetallic coatings, corrosion, paint, dirt, and oxides, without any degradation or discoloration of the surface of the body being cleaned. All ferrous and nonferrous metals may be treated using the present invention to successfully clean and remove contaminants and other materials therefrom. The preferred cleaning solution is long-lasting, and requires replacement or replenishment on a very infrequent basis. Further, by utilizing an inverter power source from a plasma cutter, the process of the present invention accomplishes a level of cleaning which is equal to or better than known electrolytic cleaning techniques (including those techniques which today are considered to be not environmentally friendly, caustic, inefficient, non-economical, etc.), and does so in a manner which is equal to or faster than known methods.  
         [0065]    The following examples of cleaning metallic bodies further illustrate the invention.  
       EXAMPLE 1  
       [0066]    An electrolyte solution was prepared by dissolving disodium phosphate at a concentration of about 0.75 pounds per 10 gallons of water and sodium bicarbonate at a concentration of about 0.25 pounds per 10 gallons of water. The volume of electrolyte was sufficient to fill a 50-gallon holding tank attached to a pump supplying a spray system mounted in another tank. The pump was configured to provide an output of  100  gallons per minute (gpm) at a pressure of 40 pounds per square inch (psi) of electrolyte from each of a series of spray nozzles in the spray system. A head casting contaminated with core sand was placed in the tank for cleaning by the spray system at a distance of two inches from the series of spray nozzles. An inverter power supply from a plasma cutter was used to supply 140 volts (V) and 10 amperes (A) to the spray system. The negative terminal of the inverter power supply was connected to the casting. The positive terminal of the inverter power supply was connected to the series of nozzles positioned to flow streams of electrolyte on the casting. The power supply was activated along with the spray system. The stream pattern of the nozzles wetted all of the casting surfaces. Excess electrolyte was drained from the tank, filtered and pumped to the pump holding tank for reuse. After 18 minutes, the core sand was released from the casting and the bare metal exposed. The power supply and spray system were deactivated and the casting removed.  
       EXAMPLE 2  
       [0067]    The same arrangement as in Example 1 was used, except that the inverter power supply was used to supply 115 kilovolts (kV) and 0.0005 A to the spray system and the casting was placed at a distance of 18 inches from the series of spray nozzles. After 220 seconds, the core sand was released from the casting and the bare metal exposed.  
       EXAMPLE 3  
       [0068]    The same arrangement as in Example 1 was used, except that the head casting was contaminated with mill scale. After 17 minutes, the mill scale was removed from the casting and the bare metal exposed.  
       EXAMPLE 4  
       [0069]    The same arrangement as in Example 3 was used, except that the inverter power supply was used to supply 250 V and 1.76 A to the spray system and the casting was placed at a distance of 4 inches from the series of spray nozzles. After 14.5 minutes, the mill scale was removed from the casting and the bare metal exposed.  
       EXAMPLE 5  
       [0070]    The same arrangement as in Example 3 was used, except that the inverter power supply was used to supply 500 V and 0.976 A to the spray system and the casting was placed at a distance of 6.5 inches from the series of spray nozzles. After 12.75 minutes, the mill scale was removed from the casting and the bare metal exposed.  
       EXAMPLE 6  
       [0071]    The same arrangement as in Example 3 was used, except that the inverter power supply was used to supply 115 kV and 0.0005 A to the spray system and the casting was placed at a distance of 18 inches from the series of spray nozzles. After 2.15 minutes, the mill scale was removed from the casting and the bare metal exposed.  
       EXAMPLE 7  
       [0072]    The same arrangement as in Example 1 was used, except that the casting was contaminated with embedded chips and the inverter power supply was used to supply 70 V and 15.7 A to the spray system. After 12 minutes, the embedded chips were removed from the casting and the bare metal exposed.  
       EXAMPLE 8  
       [0073]    The same arrangement as in Example 7 was used, except that the inverter power supply was used to supply 250 V and 1.76 A to the spray system and the casting was placed at a distance of 4 inches from the series of spray nozzles. After 9.5 minutes, the embedded chips were removed from the casting and the bare metal exposed.  
       EXAMPLE 9  
       [0074]    The same arrangement as in Example 7 was used, except that the inverter power supply was used to supply 500 V and 0.976 A to the spray system and the casting was placed at a distance of 6.5 inches from the series of spray nozzles. After 7 minutes, the embedded chips were removed from the casting and the bare metal exposed.  
       EXAMPLE 10  
       [0075]    The same arrangement as in Example 7 was used, except that the inverter power supply was used to supply 115 kV and 0.0005 A to the spray system and the casting was placed at a distance of 18 inches from the series of spray nozzles. After 1.3 minutes, the embedded chips were removed from the casting and the bare metal exposed.  
       EXAMPLE 11  
       [0076]    The same arrangement as in Example 1 was used, except that the casting was contaminated with oxides and rust and the inverter power supply was used to supply 100 V and about 10 A to the spray system. After 2 minutes, the oxides and rust were removed from the casting and the bare metal exposed.  
       EXAMPLE 12  
       [0077]    The same arrangement as in Example 11 was used, except that the inverter power supply was used to supply 500 V and 0.976 A to the spray system and the casting was placed at a distance of 6.5 inches from the series of spray nozzles. After 15 seconds, the oxides and rust were removed from the casting and the bare metal exposed.  
       EXAMPLE 13  
       [0078]    The same arrangement as in Example 11 was used, except that the inverter power supply was used to supply 115 kV and 0.0005 A to the spray system and the casting was placed at a distance of 18 inches from the series of spray nozzles. The oxides and rust were removed from the casting and the bare metal exposed essentially on contact by the electrolytic spray.  
         [0079]    [0079]FIG. 7 shows the relationship between voltage and time for removal of the various contaminants set forth in Examples 1-13. Generally, increasing the voltage decreases the cleaning time. Below 1 kV, the relationship is substantially linear for contaminants of the same type and degree. As the voltage increases, the relationship will become asymptotic. However, higher voltages may be beneficial and desirable when the scale or material to be removed is very heavy or severe.  
       EXAMPLE 14  
       [0080]    A second test was conducted at Ingersoll Cinetic facilities in Livonia, Mich. using a “Halo” test cell outfitted with the present invention. An electrolyte solution was prepared by dissolving disodium phosphate at a concentration of about 0.50 pounds per 1 gallons of water and sodium bicarbonate at a concentration of about 0.25 pounds per 1 gallons of water. The volume of electrolyte was sufficient to fill a 500-gallon holding tank attached to a pump supplying the Halo test cell. The pump was configured to provide an output of 250 gallons per minute (gpm) and a pressure of 150 pounds per square inch (psi) of electrolyte to a series of 32 spray nozzles in the Halo test cell. A “cast iron” V-6 cylinder head was soiled with embedded chips and oil to simulate the part after a milling process. The cylinder head was placed in the Halo test cell with the joint face down and the rear leading at a distance of four inches from the series of spray nozzles for cleaning by the Halo test cell. An inverter power supply from a plasma cutter was used to supply 500 volts (V) and 2.9 amperes (A) to the Halo test cell. The negative terminal of the inverter power supply was connected to the cylinder head. The positive terminal of the inverter power supply was connected to the series of nozzles positioned to flow streams of electrolyte on the cylinder head. The power supply was activated along with the Halo test cell, which resulted in the series of spray nozzles being oscillated over the cylinder head. The stream pattern of the nozzles wetted all of the cylinder head surfaces. After 1 minute, 28 seconds, the power supply and the Halo test cell were deactivated and the cylinder head was removed with no rinsing. A metal port test was conducted on the cylinder head as removed from the Halo test cell and with no rinsing of the cylinder head. The metal port test revealed that no oil or metallic contaminants remained on the cylinder head. The only residue present on the cylinder head was disodium phosphate from the electrolyte.  
         [0081]    While the invention has been illustrated and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.