Abstract:
Embodiments of the present invention include methods and systems for leaching material from an object. Examples include leaching ceramic from metallic components. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for leaching systems. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application No. 61/231,827, filed Aug. 6, 2009, and is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to material removal processing, and more particularly, to methods and systems for leaching a material from an object. 
       BACKGROUND 
       [0003]    Systems that effectively leach materials from objects, such as ceramic from metallic castings in a gas turbine engine, remain an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
       SUMMARY 
       [0004]    Embodiments of the present invention include methods and systems for leaching material from an object. Examples include leaching ceramic from metallic components. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for leaching systems. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      FIG. 1  illustrates an object in the form of a gas turbine engine blade casting in accordance with an embodiment of the present invention. 
           [0007]      FIG. 2  is a cross section of the object of the embodiment of  FIG. 1  illustrating a material in the form of a ceramic core that may be removed by leaching. 
           [0008]      FIG. 3  depicts a cutaway view gas turbine engine blade casting of the embodiment of  FIG. 1  illustrating portions of the ceramic core. 
           [0009]      FIG. 4  schematically illustrates a system for leaching a material from an object in accordance with an embodiment of the present invention. 
           [0010]      FIG. 5  illustrates the gas turbine engine blade casting of the embodiment of  FIG. 1  immersed in a superheated boiling leaching agent in accordance with an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0012]    Referring now to the drawings, and in particular  FIGS. 1-3 , there is illustrated a non-limiting example of an object. In one form, the object is a cast metallic component. In one particular form, the cast metallic component is a cooled gas turbine engine blade casting  10  having an internal cooling system (not illustrated) and a plurality of cooling air discharge apertures  12 . Although described herein as a cast gas turbine engine blade, it will be understood that the present invention is equally applicable to other types of objects  10 , formed by casting processes and/or other processes. The types of components that can be processed with forms of the present invention include virtually all fields and can be made of a great variety of materials and crystal configurations. The components can be formed of metallic and/or inter-metallic materials and have crystal structures and/or orientations consistent with single crystal, directionally solidified, and/or equiax. Gas turbine engine component designers are particularly interested in nickel and cobalt alloys and superalloys. However, all types of materials including, but not limited to, metallic and inter-metallic materials are contemplated herein. 
         [0013]    Casting  10  includes internal passageways and openings defined by a separate material, that is, a material different than that which forms casting  10 . In one form, the material is a ceramic core  14 . In other embodiments, other materials may be used, both internal and external to the casting  10 . In one form, core  14  includes protrusions  16  that extend through to the outer surface  18  of casting  10  and define apertures  12 . In one form, core  14  is exposed the environment external to casting  10  via apertures  12 . Core  14  is also exposed to the external environment via an opening (not shown) in the bottom surface  20  of casting  10 . The ceramic cores and/or ceramic material utilized to form internal passageways and/or openings in casting  10  can be provided in a variety of ways including, but not limited to, integral, individual and/or mechanically coupled. Materials contemplated for ceramic cores include all ceramic materials and mixtures thereof that are removable with a leaching agent. Ceramic materials contemplated herein include, but are not limited to, alumina, zirconia, silica, yttria, magnesia, and mixtures thereof. 
         [0014]    Aspects of the present invention include systems and methods for leaching the material (e.g., ceramic core  14 ) from casting  10 . However, it will be understood that the present invention is applicable to the removal of ceramic material and/or ceramic cores from a great variety of types of components and is not limited to gas turbine engine castings or components. While the embodiments of present invention are described herein with reference to a gas turbine engine blade it should be understood that the process is equally applicable to virtually any type of casting, as well as to components/objects that are formed by means other than casting. 
         [0015]    Referring now to  FIG. 4 , a non-limiting example of a system  30  for leaching ceramic core  14  from casting  10  in accordance with an embodiment of the present invention is schematically illustrated. The present invention is applicable for the removal of ceramic material and casting cores of any density. It will be understood that at least one form of the present invention contemplates the removal of the ceramic casting material and/or ceramic casting cores from casting  10  without any substantial deterioration and/or attack to casting  10 . 
         [0016]    In one form, system  30  includes a vessel  32 , an accumulator  34 , a valve  36 , a pressure reducing device  38 , a heater  40 , a cooling system  42  and a control system  44 . Vessel  32  is structured to contain casting  10  with core  14  disposed within a bath of liquid leaching agent  46  at and above atmospheric pressure. Core  14  is exposed to leaching agent  46  as set forth above, e.g., via apertures  12 . In one form, various components of system  30  are configured for automatic operation under the direction of control system  44 . In other embodiments system  30  may have greater or lesser degrees of automation, or may not have any automation. In one form, system  30  is operative to boil the leaching agent in order to increase the rate at which core  14  is leached from casting  10 . 
         [0017]    Vessel  32 , accumulator  34 , valve  36 , pressure reducing device  38 , heater  40 , cooling system  42  and other components within the ceramic material leaching system  30  are formed of materials selected to withstand degradation from leaching agent  46 . In one form of the present invention, vessel  32  and system  30  components in fluid communication with leaching agent  46  are nickel-based materials. It will be understood that other materials may be employed in other embodiments. 
         [0018]    In one form of the present invention, vessel  32  is a pressure vessel. In one form, vessel  32  is about eighteen inches in diameter and twenty inches deep and is formed of nickel. In other embodiments, vessel  32  may be of any size in accordance with the needs of the particular application, and may formed of any material or combination of suitable materials, e.g., materials capable of withstanding exposure to the leaching agent at the desired pressures and temperatures. While the Figures herein illustrate the processing of one casting  10  at a time, it will be understood that a plurality of castings  10  can be placed within vessel  32  to facilitate bulk processing. Whether the parts can be stacked on top of the other or require the use of racks in vessel  32  will be determined based upon the geometry and properties of the individual castings  10 . 
         [0019]    Vessel  32  contains a sufficient quantity of leaching agent  46  to fill the vessel  32  to a suitable level, the closed vessel  32  forming all or a portion of a closed system. In one form, leaching agent  46  is one or more aqueous alkali hydroxides. In a particular example, the leaching material has the formula MOH, where M is selected from the group consisting of lithium, sodium, potassium, rubidium and cesium. In a more particular example, the leaching material is KOH or NaOH. In one embodiment of the present invention the leaching material is about 82.3 wt % KOH and the balance is water. However, the present invention contemplates other concentrations and types of leaching materials including, but not limited to, alkaline, acidic or solvents. 
         [0020]    Accumulator  34  is in fluid communication with vessel  32  via a fluid line  48 , valve  36  and a fluid line  50 . Fluid lines  48  and  50  are operative to transfer leaching agent  46  vapor from vessel  32  to accumulator  34 . In one form, fluid lines  48  and  50  are formed of nickel-based steel tubing. In other embodiments, fluid lines  48  and  50  may take any convenient form, including, for example, fluid passages in vessel  32  and accumulator  34 , pipes, flexible hoses, etc., and may be formed of any suitable material or combination of materials. Accumulator  34  is configured to serve as a pressure sink for vessel  32  for reducing pressure in vessel  32  by exposing vessel  32  to lower pressures in accumulator  34 . In one form, accumulator  34  is a vacuum reservoir configured to hold a partial or full vacuum. In other embodiments, accumulator  34  may be configured to hold a vacuum and/or pressures above atmospheric. 
         [0021]    Valve  36  is in fluid communication with vessel  32  and with accumulator  34 , and is operative to control the fluidic exposure of vessel  32  to accumulator  34 . Valve  36  has an open position to vent vessel  32  to accumulator  34 . In the open position, vessel  32  is exposed to the lower pressure of accumulator  34  to superheat and boil heated leaching agent  46  in vessel  32 . Valve  36  has a closed position to fluidly isolate vessel  32  from accumulator  34 . In one form, valve  36  is an electrically actuated valve that is automatically controlled by control system  44 . 
         [0022]    Pressure reducing device  38  is in fluid communication with accumulator  34 . Pressure reducing device  38  is structured to reduce the pressure in accumulator  34 . In particular, pressure reducing device  38  is structured to reduce the pressure in accumulator  34  to a desired pressure that is less than the pressure in vessel  32  in order to superheat and boil heated leaching agent  46  within vessel  32 . In one form, pressure reducing device  38  is a pump. In a particular example, pressure reducing device  38  is a vacuum pump. In one form, pressure reducing device  38  is structured to evacuate accumulator  34  to a desired pressure (vacuum) level. In other embodiments, other types of pressure reducing devices may be employed, for example and without limitation, such as a valve structured to vent accumulator  34  to a lower pressure sink or an ejector, such as a steam ejector. 
         [0023]    Although one embodiment of the present application employs accumulator  34 , valve  36  and pressure reducing device  38  to reduce the pressure in vessel  32  to superheat and boil heated leaching agent  46  within vessel  32 , other embodiments may employ other means for reducing the pressure in vessel  32  to superheat and boil heated leaching agent  46  within vessel  32 . For example and without limitation, some embodiments may include a piston/cylinder, diaphragm and/or bellows arrangement in fluid communication with vessel  32 , wherein the piston/cylinder, diaphragm and/or bellows arrangement may be employed to draw down on vessel  32  to reduce the pressure in vessel  32 . 
         [0024]    Heater  40  is structured to heat leaching agent  46 . In one form of the present invention the heater  40  is a strap resistance heater that provides the required heating energy to vessel  32 . However, the present invention contemplates a variety of heaters including, but not limited to, molten metal bath heaters, resistant heaters, radiant quartz heaters, induction heaters and flame heaters. The present invention contemplates a heater having the capacity to heat the vessel  32 , leaching agent  46  and casting  10  to predetermined temperatures in specified times, which may vary with the needs of the particular application. 
         [0025]    Cooling system  42  is structured to condense into a liquid the leaching agent  46  vapor that is produced by boiling leaching agent  46  during the operation of system  30 . In one form, cooling system  42  includes a cooling loop  52  located in the headspace above the liquid leaching agent  46  inside vessel  32 . In one form, cooling loop  52  circulates a coolant inside vessel  32 , such as water, to condense the leaching agent  46  vapor. Other arrangements for condensing leaching agent  46  vapor are contemplated in other embodiments. 
         [0026]    Control system  44  includes a controller  54  and one or more sensors that are structured to sense a control parameter associated with the boiling of leaching agent  46 . Controller  54  is communicatively coupled to pressure reducing device  38 , and is operative to control pressure reducing device  38  based on an output from one or more sensors. Controller  54  is configured to execute program instructions to vary the pressure in accumulator  34  using pressure reducing device  38  based on the sensed control parameter, in order to control the amount of boiling of leaching agent  46 . In one form, controller  54  is a proportional integral derivative (PID) controller. Other types of controllers may be employed in other embodiments. In one form, controller  54  is a microprocessor based, and the program instructions are in the form of software stored in a memory (not shown). However, it is alternatively contemplated that the controller and program instructions may be in the form of any combination of software, firmware and hardware, including state machines, and may reflect the output of discreet devices and/or integrated circuits, which may be co-located at a particular location or distributed across more than one location, including any digital and/or analog devices configured to achieve the same or similar results as a processor-based controller executing software or firmware based instructions. 
         [0027]    In one form, the operation of system  30  includes exposing core  14  to liquid leaching agent  46  in vessel  32 , and heating leaching agent  46  using heater  40 . In one form, core  14  is exposed to leaching agent  46  by submerging casting  10  in the bath of leaching agent  46  inside vessel  32 . The temperature to which leaching agent  46  is heated depends upon various factors, such as the type and concentration of leaching agent  46 , the material used to form core  14 , the pressure within vessel  32  and the material used to form casting  10 . In one example, leaching agent  46  is heated to approximately 220° C. In a particular example, leaching agent  46  is heated to approximately 250° C. During the heating of leaching agent  46 , vessel  32  is isolated from accumulator  34  by valve  36 , e.g., under the direction of controller  54 . In some embodiments, vessel  32  includes a pressure relief valve that vents excess pressure in vessel  32 , e.g., to accumulator  34  or another pressure sink. Because vessel  32  is a closed system, the pressure inside vessel  32  increases with the heating of leaching agent  46 . In some embodiments, the pressure in vessel  32  may be further increased, e.g., using a pressure source external to vessel  32 . 
         [0028]    Prior to or during the heating and pressurization of leaching agent  46  in vessel  32 , the pressure in accumulator  34  is reduced to a pressure less than that in vessel  32  having the heated leaching agent  46 . The pressure in accumulator  34  is set to a value that will superheat leaching agent  46  under selected temperature conditions inside vessel  32  by venting vessel  32  to accumulator  34 . The reduced pressure set point value for accumulator  34  may vary, for example, with system loading, leaching agent  46  type and concentration, the operating pressure and temperature of vessel  32  with leaching agent  46  in the heated condition, and/or leaching agent  46  depletion resulting from reaction with core  14 . Leaching agent  46  is considered to be superheated when its pressure is reduced to a value lower than that required for thermodynamic equilibrium, such that the temperature of the liquid leaching agent  46  is higher than the boiling point of the liquid leaching agent  46 . The pressure in accumulator  34  may vary with the application. In one form, the pressure in accumulator  34  is determined by pressure differential relative to the pressure in vessel  32 . Although described herein as being less than atmospheric pressure, it will be understood that in some embodiments, accumulator  34  may be at a pressure greater than or equal to atmospheric. 
         [0029]    After leaching agent  46  is heated to the desired temperature and the pressure in accumulator  34  is at the desired value, a boiling cycle is performed. Valve  36  is opened to vent vessel  32  to the lower pressure of accumulator  34 . Exposure of the contents of vessel  32  to the lower pressure of accumulator  34  superheats the liquid leaching agent  46 , causing the liquid leaching agent  46  to boil. 
         [0030]    Referring now to  FIG. 5 , casting  10  with core  14  is depicted as being submerged in a superheated boiling leaching agent  46 . It will be understood that  FIG. 5  illustrates a transient condition during the process of leaching core  14  from casting  10 , wherein the superheated leaching agent  46  is causing the nucleation of boiling bubbles  46 A all over the internal and external surfaces of casting  10  and core  14  that are disposed in contact with leaching agent  46 . Boiling bubbles  46 A form along the inner and outer surfaces of the cast component  10  and on core  14  and protrusions  16  that are in fluid communication with the leaching agent  46 . 
         [0031]    The plurality of boiling bubbles  46 A creates areas of local agitation and fluid movement to displace the liquid leaching agent  46  at the bubble nucleation site and refill the area with other liquid leaching agent  46 . The agitation serves to replenish leaching agent  46  in the vicinity of casting  10  and core  14 . For example, it is recognized that during the core  14  removal process, there is often leaching agent  46  adjacent to core  14  that is at least partially depleted (due to it reacting with core  14 ) in comparison with the bulk leaching material in the vessel. This partially depleted leaching agent  46  is often present at the core  14 —leaching agent  46  interface. The presence of this at least partially depleted leaching agent  46  at the core  14 —leaching agent  46  interface slows the process of removing core  14  from the casting  10 . The boiling bubbles  46 A function to drive the at least partially depleted leaching agent  46  from the core-leaching interface and facilitate replacement with other leaching agent  46 . 
         [0032]    Referring again to  FIG. 4 , in one aspect of the present invention, the amount of boiling of leaching agent  46  is controlled, e.g., to enhance the efficiency of the process of removing core  14  from casting  10 . In one form system  30  maintains a constant degree of agitation (resulting from boiling leaching agent  46 ) during each boiling cycle, regardless of varying system conditions, such as variation in leaching agent  46  concentration and depletion of leaching agent  46  that may occur during the leaching process. As set forth herein, in one form, the constant degree of agitation is obtained by controlling the boiling of leaching agent  46 . In other embodiments, the degree of agitation may be varied, e.g., as between boiling cycles. In still other embodiments, the degree of agitation may vary throughout a given boiling cycle, e.g., by varying the amount of boiling in a given boiling cycle, which may be achieved, for example, by varying the flow area through which vessel  32  is vented to accumulator  34 . 
         [0033]    It is recognized that the boiling action of leaching agent  46  is the means by which the superheated leaching agent  46  reduces its energy. As such, the boiling leaching agent  46  is undergoing a cooling process. The cooling occurs, in part, as a result of vapor formation within the fluid, which is a volumetric reaction. Thus, the degree of agitation produced by the nucleation of the leaching agent  46  is related to the degree of cooling experienced by the liquid leaching agent  46 . Given a constant initial pressure (e.g., the pressure in vessel  32  after heating leaching agent  46 , but before venting vessel  32  to accumulator  34 ), for a given temperature drop of the liquid leaching agent  46  resulting from the boiling of the superheated liquid leaching agent  46 , the amount of vapor formed during the boiling process is relatively constant. As such, for a given temperature drop, the degree of agitation per unit volume of leaching agent  46  is also relatively constant. Thus, by controlling the temperature drop of the liquid leaching agent  46  that results from the boiling of the superheated liquid leaching agent  46 , the volumetric amount of boiling may be controlled. 
         [0034]    In one form, control system  44  controls the amount of boiling of leaching agent  46  by controlling the temperature drop within the liquid leaching agent  46  that occurs as a result of the superheated boiling of the leaching agent  46 . In a particular form, the temperature control is accomplished by varying the pressure or degree of vacuum in accumulator  34  prior to equalization with vessel  32  via valve  36  and fluid lines  48 ,  50 , which may be referred to herein as the pre-boiling cycle pressure. In one form, the boiling is terminated after equalization at a desired point by re-pressurizing vessel  32 . In some embodiments, the temperature may be controlled by varying the flow area through which vessel  32  is vented to accumulator  34 . In other embodiments, the temperature may be controlled by other means, including by adding heat to leaching agent  46  during the boiling process while venting vessel  32  to accumulator  34 . 
         [0035]    In order to control the amount of boiling, embodiments of control system  44  include one or more sensors. The sensor(s) provide feedback information associated with the boiling of leaching agent  46 , which is used as a control parameter. Embodiments of the present invention sense one or more control parameters associated with the boiling of leaching agent  46 , which is used by controller  54  to vary the pressure in accumulator  34  to control the amount of boiling. In one form, the control parameters are sensed prior to, during and/or after the previous boiling cycle, and are used to determine the pressure in accumulator  34  for a subsequent boiling cycle. In one form, the pressure in accumulator  34  is varied to control the duration of the boiling cycle. For example, the greater the pressure differential between vessel  32  and accumulator  34  prior to a boiling cycle, the greater the degree of superheat of leaching agent  46  upon the venting of vessel  32  to accumulator  34 . Under otherwise similar conditions, a greater superheat results in a longer duration of boiling, as well as a more virulent boil. The process of heating leaching agent  46 , reducing the pressure in accumulator  34 , performing a boiling cycle, sensing control parameters and varying the pre-boiling cycle pressure in accumulator  34  is repeated until core  14  has been leached from casting  10  completely, or to a desired degree. 
         [0036]    Illustrated in  FIG. 4  are exemplary sensors, including a temperature sensor  56 , a nucleation sensor  58 , a temperature sensor  60 , a temperature sensor  62 , a pressure sensor  64  and a pressure sensor  66 , which are each communicatively coupled to controller  54  via a communications link  68 . Valve  36 , pressure reducing device  38 , heater  40  and cooling system  42  are also each communicatively coupled to controller  54  via a communications link  68 . The operations of valve  36 , pressure reducing device  38 , heater  40  and cooling system  42  are each directed by controller  54  via the respective communications links  68 . In one form, communications link  68  is a wired connection. Other types of communications links are contemplated in other embodiments, including digital and analog links, and wireless links. The type of communications link  68  may vary with the particular sensor or other component that is coupled thereby with controller  54 . Embodiments of the present invention include one or more of sensors  56 ,  58 ,  60 ,  62 ,  64  and  66 , as described herein. 
         [0037]    In one form, control system  44  includes temperature sensor  56  and pressure sensor  66 . Temperature sensor  56  is operative to sense the temperature of the liquid leaching agent  46 . In particular, sensor  56  is operative to sense the temperature drop in boiling superheated leaching agent  46  during the boiling cycle. More particularly, sensor  56  senses the temperature drop in the previous boiling cycle, which is used by controller  54  to set an accumulator  34  initial pressure value for the subsequent boiling cycle, i.e., the pre-boiling cycle pressure. In one form, temperature sensor  56  is disposed within vessel  32 , e.g., in the bath of liquid leaching agent  46 . In other embodiments, the location of temperature sensor  56  may vary. Temperature sensor  56  provides signals indicative of the temperature drop as feedback to controller  54 . Pressure sensor  66  is operative to sense the pressure in accumulator  34 . Pressure sensor  66  provides a signal indicative of accumulator  34  pressure as feedback to controller  54 . 
         [0038]    Controller  54  is configured to execute program instructions to compare the temperature drop in the liquid leaching agent resulting from boiling of the liquid leaching agent  46  with a selected temperature value. In one form, the selected temperature value is a predetermined fixed value. In other form, the selected temperature value is determined by controller  54 , e.g., based on other parameters, such as leaching agent  46  concentration or leaching agent  46  depletion parameters. In one form, the temperature drop is a temperature drop in the liquid leaching agent  46  resulting from boiling of the leaching agent in the previous boiling cycle. That is, in one form, the sensed value from one boiling cycle is used to set the accumulator pressure for the next boiling cycle. In one form, controller  54  is configured to execute program instructions increase the pre-boiling cycle pressure in accumulator  34  in response to a temperature drop reaching or exceeding the selected value, and to reduce the pre-boiling cycle pressure in accumulator  34  in response to the temperature drop being less than the selected value. 
         [0039]    In another form, control system  44  includes nucleation sensor  58 , a timer  70 , e.g., a built-in timer in controller  54 , and pressure sensor  66 . Nucleation sensor  58  is operative to detect nucleation in the boiling leaching agent  46 , e.g., the acoustic noise and/or vibrations indicative of boiling of the leaching agent  46 . In one form, nucleation sensor  58  is mounted on vessel  32 . In other embodiments, the location of nucleation sensor  58  may vary. In one form, nucleation sensor  58  is a microphone. In another form, nucleation sensor  58  is an accelerometer. In other embodiments, other types of nucleation sensors may be employed. Nucleation sensor  58  provides a signal indicative of boiling in leaching agent  46 . Controller  54  measures the duration of boiling based the output of nucleation sensor  58 . Pressure sensor  66  is operative to sense the pressure in accumulator  34 . Pressure sensor  66  provides a signal indicative of accumulator  34  pressure as feedback to controller  54 . 
         [0040]    Controller  54  is configured to execute program instructions to compare the duration of boiling with a selected value. In one form, the selected duration value is a predetermined fixed value. In other form, the selected duration value is determined by controller  54 , e.g., based on other parameters, such as leaching agent  46  concentration or leaching agent  46  depletion parameters. In one form, the sensed boiling duration is the duration of the previous boiling cycle. That is, in one form, the sensed value from one boiling cycle is used to set the accumulator pressure for the next boiling cycle. In one form, controller  54  is configured to execute program instructions increase the pre-boiling cycle pressure in accumulator  34  in response to the duration of boiling in the previous boiling cycle reaching or exceeding the selected value, and to reduce the pre-boiling cycle pressure in accumulator  34  in response to the duration being less than the selected value. 
         [0041]    In yet another form, control system  44  includes temperature sensors  60 ,  62 . Temperature sensors  60 ,  62  are operative to sense the temperature of the coolant of cooling system  42 . In particular, sensors  60 ,  62  are operative to sense the coolant temperature rise in cooling loop  52  that results from cooling loop  52  condensing the leaching agent  46  vapor generated by boiling the liquid leaching agent  46 . More particularly, sensors  60 ,  62  sense the temperature rise in the previous boiling cycle, which is used by controller  54  to set an accumulator  34  initial pressure value for the subsequent boiling cycle, i.e., the pre-boiling cycle pressure. In one form, temperature sensors  60 ,  62  are disposed along cooling loop  52 . In other embodiments, the locations of temperature sensors  60 ,  62  may vary. Temperature sensors  60 ,  62  provide signals indicative of the temperature rise as feedback to controller  54 . Pressure sensor  66  is operative to sense the pressure in accumulator  34 . Pressure sensor  66  provides a signal indicative of accumulator  34  pressure as feedback to controller  54 . 
         [0042]    Controller  54  is configured to execute program instructions to compare the coolant temperature rise with a selected temperature rise value. In one form, the selected temperature rise value is a predetermined fixed value. In other form, the selected temperature rise value is determined by controller  54 , e.g., based on other parameters, such as leaching agent  46  concentration or leaching agent  46  depletion parameters. In one form, the temperature rise is the coolant temperature rise in the previous boiling cycle. That is, in one form, the sensed value from one boiling cycle is used to set the accumulator pressure for the next boiling cycle. In one form, controller  54  is configured to execute program instructions increase the pre-boiling cycle pressure in accumulator  34  in response to a temperature rise reaching or exceeding the selected value, and to reduce the pre-boiling cycle pressure in accumulator  34  in response to the temperature rise being less than the selected value. 
         [0043]    In still another form, control system  44  includes pressure sensor  64 . Pressure sensor  64  is operative to sense the pressure in vessel  32 . In particular, pressure sensor  64  is operative to sense the pressure increase that results from boiling the liquid leaching agent  46 . More particularly, pressure sensor  64  senses the pressure increase in the previous boiling cycle, which is used by controller  54  to set an accumulator  34  initial pressure value for the subsequent boiling cycle, i.e., the pre-boiling cycle pressure. In one form, pressure sensor  64  is in fluid communication with vessel  32 . In one form, pressure sensor  64  is disposed in vessel  32 . In other embodiments, the location of pressure sensor  64  may vary. Pressure sensor  64  provides signals indicative of the pressure increase as feedback to controller  54 . Pressure sensor  66  is operative to sense the pressure in accumulator  34 . Pressure sensor  66  provides a signal indicative of accumulator  34  pressure as feedback to controller  54 . 
         [0044]    Controller  54  is configured to execute program instructions to compare the pressure increase with a selected pressure increase value. In one form, the selected pressure increase value is a predetermined fixed value. In other form, the selected pressure increase value is determined by controller  54 , e.g., based on other parameters, such as leaching agent  46  concentration or leaching agent  46  depletion parameters. In one form, the pressure increase is a pressure increase in the previous boiling cycle. That is, in one form, the sensed value from one boiling cycle is used to set the accumulator pressure for the next boiling cycle. In one form, controller  54  is configured to execute program instructions increase the pre-boiling cycle pressure in accumulator  34  in response to a pressure increase reaching or exceeding the selected value, and to reduce the pre-boiling cycle pressure in accumulator  34  in response to the pressure increase being less than the selected value. 
         [0045]    In yet still another form, controller  54  determines the amount of energy required to reheat leaching agent  46  in vessel  32  up to a desired temperature subsequent to the previous boiling cycle. That is, in one form, the sensed value from one boiling cycle is used to set the accumulator pressure for the next boiling cycle. In one form, controller  54  includes timer  70 , and calculates the amount of energy based on the power supplied to heater  40  and the amount of time the power is supplied. In other embodiments, the amount of energy required to reheat leaching agent  46  may be determined via other means. Pressure sensor  66  is operative to sense the pressure in accumulator  34 . Pressure sensor  66  provides a signal indicative of accumulator  34  pressure as feedback to controller  54 . 
         [0046]    Controller  54  is configured to execute program instructions to compare the amount of energy required to re-heat the leaching agent with a selected value. In one form, the selected energy value is a predetermined fixed value. In other form, the selected energy value is determined by controller  54 , e.g., based on other parameters, such as leaching agent  46  concentration or leaching agent  46  depletion parameters. In one form, controller  54  is configured to execute program instructions increase the pre-boiling cycle pressure in accumulator  34  in response to the amount of energy reaching or exceeding the selected value, and to reduce the pre-boiling cycle pressure in accumulator  34  in response to the amount of energy being less than the selected value. 
         [0047]    Embodiments of the present invention include a method for leaching a material from an object, comprising: exposing the material to a liquid leaching agent in a vessel; heating the leaching agent; reducing a first pressure in an accumulator to less than a second pressure in the vessel with the heated leaching agent; performing a boiling cycle by venting the vessel to the accumulator to superheat and boil the leaching agent; sensing a control parameter associated with boiling of the leaching agent; and varying the first pressure in the accumulator based on the sensed control parameter to control an amount of boiling of the leaching agent. 
         [0048]    In a refinement, the first pressure is varied based on sensing the control parameter during a previous boiling cycle. 
         [0049]    In another refinement, the first pressure is varied to control a duration of boiling. 
         [0050]    In yet another refinement, the embodiment further comprises repeating the heating the leaching agent, the reducing the first pressure in the accumulator and the performing the boiling cycle until the material is leached from the object. 
         [0051]    In still another refinement, the object is a metallic cast component, and wherein the material is a ceramic core. 
         [0052]    In yet still another refinement, the control parameter is a temperature of the liquid leaching agent. 
         [0053]    In a further refinement, the temperature is a temperature drop in the liquid leaching agent resulting from boiling of the leaching agent in a previous boiling cycle. 
         [0054]    In a yet further refinement, the method further comprises reducing the first pressure in the accumulator in response to the temperature drop being less than or equal to a selected value. 
         [0055]    In a still further refinement, the control parameter is a plurality of control parameters, including an acoustic noise indicative of boiling of the leaching agent and including a duration of boiling determined based on the acoustic noise. 
         [0056]    In a yet still further refinement, the method further comprises reducing the first pressure in the accumulator in response to the duration of boiling in a previous boiling cycle being less than or equal to a selected value. 
         [0057]    In an additional refinement, the boiling leaching agent produces a leaching agent vapor, further comprising using a coolant to condense the leaching agent vapor into liquid form, wherein the control parameter is a temperature rise of the coolant resulting from condensing the leaching agent vapor. 
         [0058]    In another additional refinement, the method further comprises reducing the first pressure in the accumulator in response to the temperature rise of the coolant being less than or equal to a selected value. 
         [0059]    In yet another additional refinement, the control parameter is a pressure in the vessel. 
         [0060]    In still another additional refinement, the pressure is a pressure increase resulting from superheated boiling of the leaching agent. 
         [0061]    In yet still another additional refinement, the method further comprises reducing the first pressure in the accumulator in response to the pressure increase in a previous boiling cycle being less than or equal to a selected value. 
         [0062]    In another further refinement, the control parameter is an amount of energy required to re-heat the leaching agent subsequent to a previous boiling cycle, further comprising reducing the first pressure in the accumulator in response to the amount of energy being less than or equal to a selected value. 
         [0063]    In yet another further refinement, the method further comprises re-pressurizing the vessel to terminate the boiling. 
         [0064]    Embodiments of the present invention also include a system for leaching a material from an object, comprising: a pressure vessel structured to contain the object with the material exposed to a liquid leaching agent; a heater structured to heat the leaching agent; an accumulator; a valve in fluid communication with the pressure vessel and the accumulator, wherein the valve has an open position to vent the pressure vessel to the accumulator to superheat and boil the leaching agent in the vessel, and wherein the valve has a closed position to fluidly isolate the pressure vessel from the accumulator; a pressure reducing device in fluid communication with the accumulator, wherein the pressure reducing device is structured to reduce pressure in the accumulator to a first pressure less than a second pressure in the pressure vessel; a sensor structured to sense a control parameter associated with boiling of the leaching agent; and a controller communicatively coupled to the pressure reducing device and the sensor and operative to control the pressure reducing device based on an output from the sensor, wherein the controller is configured to execute program instructions to vary the first pressure in the accumulator based on the sensed control parameter to control an amount of boiling of the leaching agent. 
         [0065]    In a refinement, the sensor is a temperature sensor operative to sense a temperature of the liquid leaching agent; and the controller is configured to execute program instructions to increase the first pressure in the accumulator in response to a temperature drop resulting from boiling the liquid leaching agent reaching or exceeding a selected value. 
         [0066]    In another refinement, the sensor is a plurality of sensors including a nucleation sensor and a timer; the control parameter is a plurality of control parameters, including acoustic noise indicative of boiling of the leaching agent and including a duration of boiling determined based on the acoustic noise; and the controller is configured to execute program instructions to increase the first pressure in the accumulator in response to the duration of boiling in a previous boiling cycle reaching or exceeding a selected value. 
         [0067]    In yet another refinement, wherein the boiling leaching agent produces a leaching agent vapor, the method further comprises: a cooling system structured to condense the leaching agent vapor using a coolant, wherein: the sensor is a temperature sensor operative to sense a temperature of the coolant; the control parameter is a temperature rise of the coolant resulting from condensing the leaching agent vapor; and the controller is configured to execute program instructions to increase the first pressure in the accumulator in response to the temperature rise of the coolant reaching or exceeding a selected value. 
         [0068]    In still another refinement, the sensor is a pressure sensor operative to sense the pressure in the pressure vessel; the control parameter is a pressure increase resulting from superheated boiling of the leaching agent; and the controller is configured to increase the first pressure in the accumulator in response to the pressure increase in a previous boiling cycle reaching or exceeding a selected value. 
         [0069]    In yet still another refinement, the control parameter is an amount of energy required to re-heat the leaching agent subsequent to a previous boiling cycle; and the controller is configured to increase the first pressure in the accumulator in response to the amount of energy reaching or exceeding a selected value. 
         [0070]    In a further refinement, in the pressure reducing device is a pump. 
         [0071]    Embodiments of the present invention also include a system for leaching a material from an object, comprising: means for containing the object and a liquid leaching agent; means for heating the leaching agent; means for reducing pressure in the means for containing to superheat and boil the leaching agent; means for varying pressure in the means for reducing pressure based on a control parameter associated with boiling of the leaching agent to control an amount of boiling of the leaching agent. 
         [0072]    In a refinement, the means for varying pressure includes means for comparing a temperature drop in the liquid leaching agent resulting from boiling of the liquid leaching agent with a selected value. 
         [0073]    In another refinement, the means for varying pressure includes means for comparing a duration of boiling with a selected value. 
         [0074]    In yet another refinement, the system further comprises means for condensing a leaching agent vapor using a coolant, wherein the means for varying pressure includes means for comparing a temperature increase of the coolant with a selected value. 
         [0075]    In still another refinement, the means for varying pressure includes means for comparing a pressure increase resulting from superheated boiling of the leaching agent with a selected value. 
         [0076]    In yet still another refinement, the means for varying pressure includes means for comparing an amount of energy required to re-heat the leaching agent with a selected value. 
         [0077]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.