Abstract:
The present invention is a method of cleaning an object in an open aqueous cleaning system. The method is directed to an open cleaning vessel into which water used for cleaning a material or object can be introduced. A means is provided for introducing a reactant chemical to the vessel to form an aqueous solution. Cleaning of the surface is in the form of bubble formation on the part that vaporizes the chemical in order to react the oxidizer in the vapor state to the exposed surface at the bubble growth area. Treatment in the form of etching or any other process in which material is removed from a solid surface displaces the liquid residue from the surface. The resulting process produces no dissolution or emulsion of the contaminant and therefore can be easily separated from the chemical cleaner. The process also conserves chemistry, water, energy, and reduces pollution.

Description:
BACKGROUND OF THE INVENTION 
     In today&#39;s manufacturing environment there is an ever growing need to meet more stringent environmental regulations, an ever increasing need to reduce water use, an increasing need to reduce energy use and an overall need to increase quality control and cut costs. Parts&#39; cleaning is generally viewed as a simple process however quite often the lack of quality control in the parts&#39; cleaning process often leads to rejected end products or rework. Cleaning solutions are becoming more sophisticated and thus more expensive. Chemical discharge to public facilities and chemical evaporation to the environment is becoming a major issue in most countries. Energy conservation has become a major cost cutting avenue. 
     The present invention focuses upon a reduction in up front chemical costs, minimizing water use, limited air pollution, increased quality control and reduced energy costs for most manufacturing parts&#39; cleaning. The process often reduces the number of steps and process tanks required that could also lead to reduced capital costs. 
     The basic premise of the process is to chemically interact with the solid surface so as to reduce the physical wet ability of the residue fluid being removed. A fluid at its vapor pressure is vaporized at the solid surface either by heating the part or reducing the total pressure in the processing chamber. 
     A chemical, preferably an oxidizing agent, dissolved in the treating solution is vaporized and can rapidly diffuse to and oxidize the surface. The etching of the surface leads to a debonding of the fluid from the surface. The vapor being formed at the surface tends to lift the residue from the surface and transport the residue to the bulk liquid. The reacting chemical may also oxidize the liquid residue however the residue is not emulsified and rises to the surface to be physically removed from the vessel. The process fluid is essentially clean and can be recycled for reuse. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to a method of treating an object to remove residue in an open aqueous cleaning vessel. The vessel receives water used for cleaning a material or object. Means are provided for introducing a reactant chemical to the vessel to form an aqueous solution. Cleaning of the surface is in the form of bubble formation on the part that vaporizes the chemical in order to react the oxidizer in the vapor state to the exposed surface at the bubble growth area. Treatment in the form of etching or any other process in which material is removed from a solid surface displaces the liquid residue from the surface. Bubble growth and detachment provide for transport of the residue to the bulk liquid. Either transfer of heat from the preheated part or reducing the pressure in the vessel by continuously removing the vapor phase attains vaporization. Further steps recover residual contaminant from the vessel and may include recovering water from the object in order to dry the object. 
     A method of treating an object to remove residue in an open aqueous cleaning vessel, comprises the steps of: 
     (a) filling the cleaning vessel with water for cleaning; 
     (b) injecting a reactant chemical to the water to form an aqueous solution in the vessel; 
     (c) placing the object that may be preheated to be cleaned in the cleaning vessel; 
     (d) cleaning the object by allowing the liquid to heat or by pulling vacuum in the vessel to produce vapor bubbles at the surface of the object that reacts with the surface or the contaminant; 
     (e) recovering the contaminant from the cleaning vessel; and 
     (f) removing the cleaned object from the cleaning vessel. 
     The above-noted method can be effectively used to remove liquid or solid residue from a solid surface. The effectiveness is site insensitive since a pressure reduction or heat transfer is uniform throughout the system and thus the pressure or heat inside channels and pores is equal to the surface conditions. 
     Another aspect of this invention is to clean parts without emulsifying or dissolving the liquid or solid residue thus allowing for waste-solution separation by floating, filtering or settling the contaminant. 
     Another aspect of this invention is to recycle the cleaning solution after separation of the contaminant so as to minimize water or chemical use. 
     Another aspect of this invention is to minimize energy use by recycling a heated cleaning solution minimizing the need to heat new makeup solution. 
     Another aspect of this invention is to use minimize cleaning chemical use by using small quantities of reactive chemicals as opposed to large quantities of surfactants or dissolution chemicals for cleaning. 
     Another aspect of this invention is to clean parts without using high energy consumption jets or ultrasonics for physical cleaning. 
     Another aspect of this invention is to clean parts without using air pollution chemicals such as often found in semi-aqueous and lipophilic solvents. 
     Another aspect of this invention is to rapidly dry parts by steam preheating followed by vacuum drying in order to shorten cycle time and prevent water spotting. 
     Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
         FIG. 1  is a schematic illustration of the open aqueous cleaning system as used in the method of the present invention; 
         FIG. 2  is a schematic illustration of a preferred embodiment of the open aqueous cleaning system of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an alternative embodiment of the open aqueous cleaning system of  FIG. 1 ; and 
         FIG. 4  is a schematic illustration of another alternative embodiment of the open aqueous cleaning system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, the method of cleaning an object in an open aqueous cleaning system of the present invention is illustrated and generally indicated at  10  in  FIG. 1 . In  FIG. 1 , the open aqueous cleaning system  10  for implementing the teachings of this invention includes a main processing chamber generally indicated at  12  that may or may not be heated. Other component parts of the system  10  will be described in connection with operation thereof. 
     On startup, water is introduced into the cleaning vessel by opening valve  40  and filling the vessel from water source  50 . After filling, valve  40  is closed and reactant chemical can be added to the water in the vessel from chemical source  46  by opening valve  44 . After chemical addition, a preheated object  18  is placed in the vessel on an appropriate holder  20  to submerge the object in the solution. The temperature of the object is above the boiling point of the solution and vapor bubbles will begin to form and detach from the object subjecting the object to regions of vapor solid contact. The vapor coming in contact with the solid surface will contain a reactant chemical that can now diffuse easily to the surface and react either with the solid surface or the contaminant on the surface. 
     The reactant chemical may include acids such as acetic acid, sulfuric acid, nitric acid, citrus acid, hydrofluoric acid, boric acid, oxalic acid and phosphoric acid; amines such as ethanol amine, ethyl diamine and diethanol amine; ketones such as acetone and metyl ethyl ketone; hydoxides such as sodium, potassium, ammonium and calcium hydroxide; peroxides such as hydrogen and benzoyl peroxide and other chemicals such as ozone and N-methylpyrrolidone or any other chemical that chemically reacts with the surface or the contaminant. 
     Upon cleaning, water is again introduced to the vessel  12  by opening valve  40  and excess water exits the vessel through overflow port  14  carrying floating contaminant from the water surface to the drain. 
     Referring now  FIG. 2 , the open aqueous cleaning system of the present invention is illustrated and generally indicated at  100  in  FIG. 2 . The system  100  for implementing the teachings of this invention includes a main cleaning vessel generally indicated at  12  that may or may not be heated. The main chamber  12  includes a lid  28 . Other component parts of the system  100  will be described in connection with operation thereof. 
     On startup of the process, the cleaning vessel  12  is charged with water from water source  50  through valve  40  and with chemical reactant from source  46  through valve  44 . In the preferred embodiment the charged chemical is hydrogen peroxide. The solution in vessel  12  may or may not be heated. 
     On startup of cleaning, a part  18  to be treated can be placed in the chamber  12  on an appropriate holder  20 . Closing lid  28  and vent valve  22  then seals the chamber  12 . Vacuum pump  32  is then activated, valve  34  is opened, and the chamber  12  is evacuated of essentially all the air. Typically, a mechanical dry pump can evacuate the vessel to pressures equal to the solution&#39;s vapor pressure. Other pumps such as liquid ring pumps, pneumatic pumps, diaphragm pumps or constant displacement, or other conventional vacuum pumps can also be used. 
     Upon evacuating all the air, vacuum pump  32  now begins to remove evaporating water vapor from the vessel. Removal of the vapor reduces pressure within the system  100 , and since the solvent in the chamber  12  is under vacuum, vapor bubbles will begin to nucleate at the solid surfaces including the surface of the part  18 . If the vacuum pump  32  continues to evacuate vapors, the vapor bubbles at the surface will grow, detach from the solid surface and rise to the top of the vessel  12  to replenish the vapor being removed by the vacuum pump  32 , thus maintaining the chamber at or around the vapor pressure of the solution. Such a condition will continually allow replenishment of the surface with fresh solution at the region where vapor bubbles are detached, i.e. the bubbles create a desired solution flow over the surface of the part  18 . These regions will thus experience a rapid increase in vapor concentration at the solid surface. 
     In one embodiment, the vapor coming in contact with the solid surface will contain hydrogen peroxide or ozone that can diffuse rapidly to the surface and chemically react with the solid surface or contaminant. Other solutions including mineral acids, amines, hydroxides, ketones or any other chemical that can react with the object&#39;s surface or with the contaminant on the surface can be used in place of hydrogen peroxide. The reaction can be in the form of surface etching and carbon bond attack on the solid surface and contaminant respectively. Other surface reactions such as oxidation, anodic reactions, ion exchange and any other reaction that alters the surface chemistry can be used. Contaminant reactions could be saponification, hydrolysis, cracking and any other reaction that alters the contaminant chemistry. 
     The resulting reactions debond the liquid contaminant from the surface and the vapor bubbles detaching from the surface transports the contaminant to the bulk fluid. Because of the difference in fluid density and the continuous upward flow of vapor bubbles, the contaminant floats to the solution surface and accumulates with time. Heavier contaminants could also be removed and may either float to the surface attached to vapor bubbles or settle to the vessel bottom to be remove through a bottom port. 
     Upon completion of cleaning of object  18 , valve  34  is closed and vacuum pump  32  is turned off. Valve  22  is opened to return chamber  12  to atmospheric pressure. Valve  40  is again opened and additional water from water source  50  is introduced to chamber  12 . Excess water and floating contaminant now begins to enter overflow port  14  to be sent to the drain. Upon completing the contaminant skimming, valve  40  is closed. Lid  28  can now be opened and object  18  can be removed from cleaning vessel  12 . 
     Now referring to  FIG. 3 , a number of options are depicted that are easily adapted to the open aqueous cleaning system. For enhanced bubble formation, the object  18  can be preheated within vessel  12 . In one embodiment, on startup, a part  18  to be cleaned can be placed in the vessel  12  on an appropriate holder  20 . Closing lid  28  and vent valve  22  then seals the chamber  12 . Vacuum pump  32  is then activated, valve  34  is opened, and the chamber  12  is evacuated of essentially all the air. 
     To initiate cleaning, valve  42  is opened and since the vessel is free of air, the steam from steam source  16  flashes into the processing chamber  12  and increases the pressure in chamber  12 . Condensing steam heats the part  18 , holder  20  and vessel  12  to a temperature above ambient temperature. Other types of heating such as light, radiation and non-condensable heated gas circulation can be used to preheat the object  18 . Upon heating the part  18 , valve  42  is closed and cleaning can proceed as described above in the preferred embodiment. 
     It may be desirable to conserve water use. To accomplish this tank  26  and pump  38  are added to the system in order to assist in recycling water as depicted in  FIG. 3 . After preheating the object  18 , water is introduced to the cleaning vessel  12  by opening valve  40  and activating pump  38  to fill the vessel from water tank  26 . Water tank  26  may be as shown with electric heater  52 . Optionally, steam heaters or direct steam injection can be used. During filling, reactant chemical can be added to the incoming stream from chemical source  46  by opening valve  44 . Optionally the chemical can be added to the cleaning vessel  12  directly as above or can be added to water tank  26  prior to filling vessel  12 . 
     Upon completing the cleaning step, contaminant can now be recovered from the vessel  12  by opening valve  22  to return vessel  12  to atmospheric pressure. Valves  24  and  40  are opened and pump  38  is activated to introduce additional water to vessel  12  from tank  26 . Excess fluid and floating contaminant now begins to enter overflow port  14  to be returned to a separation section in the tank  26 . Floating contaminant overflows from tank  26  to waste oil tank  36  to be separated from water to be recycled. Upon completing the contaminant skimming, valves  24  and  40  are closed and pump  38  is turned off. Valve  30  is then opened and the processing solution is drained from the chamber  12  to tank  26 . Upon draining, valve  30  is closed. 
     It may also be desirable to dry object  18  prior to removal from cleaning tank  12 . To accomplish this valve  22  is closed and valve  34  is opened and vacuum pump  32  is turned on and chamber  12  is again reduced in pressure. Reducing pressure may suffice to vacuum dry object  18  however to enhance drying it may be desirable to preheat the object  18 . Upon evacuating vessel  12 , pump  32  is turned off and valve  34  is closed. 
     To enhance drying, valve  42  is opened and steam from steam source  16  flashes into the cleaning vessel  12  and increases the pressure in vessel  12 . Condensing steam heats the object  18 , holder  20  and vessel  12  to a temperature above ambient temperature. Upon heating the object  18 , valve  42  is closed. 
     Valves  22  and  30  are now opened to drain excess steam condensate from chamber  12 . Upon draining the condensate, valves  22  and  30  are closed and valve  34  is opened and vacuum pump  32  is turned on and chamber  12  is again reduced in pressure. The excess condensate on the chamber  12 , part  18  and holder  20  flashes from the chamber and dries the chamber, object and holder. Valve  22  and lid  28  are now opened and object  18  is removed from vessel  12 . 
     Now referring to  FIG. 4 , a system  120  is shown for continuous removal of floating contaminant from the vessel  12 . On startup after object  18  is placed in vessel  12  and lid  28  and valve  22  are closed, the cleaning vessel  12  is charged with water from water source  50  through valve  40  and with chemical reactant injected into the inlet stream from source  46  through valve  44 . Opening valve  48  and heating the solution in heat exchanger  26  with steam from steam source  16  can preheat the aqueous solution formed. In one embodiment the charged chemical is hydrogen peroxide for moderate cleaning or ozone for more aggressive cleaning. 
     Following filling the vessel  12 , enclosed water tank  58  and vessel  12  are both evacuated of air by opening valves  34  and  62  and activating vacuum pump  32 . After evacuating all the air, vapor bubbles will begin to form and contaminant will be removed from the surface of object  18  and float to the top of vessel  18  as described above 
     Contaminant can now be continuously removed from the vessel  12  through overflow port  14  by opening valves  24 ,  60  and  40  and activating circulation pump  38  to recirculate water to vessel  12  from water tank  58 . Contaminant leaving port  14  can be separated in water tank  58  by using a water separation section  66 . Floating contaminant is collected in the water tank  58  in the separation section during recirculation of water. Upon completion of cleaning object  18 , Valves  34 ,  24 ,  62 , and  40  are closed and pumps  32  and  38  are turned off. Water tank  58  and vessel  12  are brought back to atmospheric pressure by opening valves  22  and  34 . Water is drained from vessel  12  by opening valve  30  and sent to drain or recovered and contaminant is drained to waste drum  36  by opening valve  62 . 
     It can therefore be seen that the present invention provides a unique method for cleaning an object in an open aqueous cleaning system that conserves chemistry, water, and energy while reducing pollution. 
     While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.