Patent Publication Number: US-2011048665-A1

Title: Corrosion resistance for a leaching process

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application 61/232,454, filed Aug. 9, 2009, and is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to leaching devices used to remove a core/mold/shell from a cast component, and more particularly, but not exclusively, to corrosion resistance for the cast component during a leaching process. 
     BACKGROUND 
     Protecting cast component parts during a leaching process remains an area of interest. Some existing systems have various shortcomings relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
     SUMMARY 
     One embodiment of the present invention is a unique ability to provide corrosion resistance to a cast component during a leaching process. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for providing corrosion resistance during a core/mold leaching process from a cast component part. 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 FIGURES 
         FIG. 1  depicts one form of the present application. 
         FIG. 2  depicts an article having an object and a mold/core. 
         FIG. 3  depicts one form of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     For the 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 nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     In one aspect of the present application a mold used to receive a molten metal in an investment casting process is removed by a leaching process to reveal a cast article. The present application will be describe with reference to metals however it is contemplated herein as useful with elemental metals, alloys, superalloys and intermetallic materials unless specifically provided to the contrary. The mold can be made of a ceramic material and in one form is alumina. The leaching process utilizes a leaching fluid that interacts with and removes the mold material, but in so doing the leaching fluid in the vicinity of the ceramic being leached can become less reactive. To replenish its effectiveness, the leaching fluid can be boiled to sweep away the depleted solution and allow fresh leaching fluid to take its place. The leaching fluid can either be boiled through a conversion of liquid to vapor at, for example, a heat flux surface, or the leaching fluid can be placed in a superheated state where vapor can nucleate on a variety of surfaces within the system. Such a superheated state can be accomplished by, for example, suddenly dropping system pressure when the leaching fluid is at or near an equilibrium state. 
     An electric power supply is used to create an electrolytic cell which discourages corrosion or other attacks of the cast article from the leaching fluid. The power supply is used to provide a potential difference in the electrolytic cell in which the cast article can be configured as either an anode or a cathode. In some embodiments multiple cast articles can be used in the system, some of which are configured as an anode and others as a cathode. As will be described further below the power supply can be activated at any time and in one form in particular when the leaching fluid is being boiled to remove the ceramic mold. 
     With reference to  FIG. 1 , an electrolytic device  50  is shown that is capable of protecting an object from corrosion when the object is at least partially immersed in a working fluid  52 . The object can take a variety of forms in various embodiments. To set forth just a few non-limiting examples, the object can be metallic, it can take the form of an alloy, and it can be produced using a casting process such as, but not limited to, investment casting. Other forms and variations of the object are also contemplated. In some applications the working fluid  52  can be a caustic fluid used as a leachant in an investment casting mold removal process, an example of which will be described further below. In one particular form the working fluid can be KOH. The working fluid  52  can also be NaOH, or mixtures of NaOH and KOH, among other possibilities, combinations, and mixtures. The electrolytic device  50  includes an anode  54  and a cathode  56  that can be driven to a potential difference by a power supply (not shown). Either the anode  54  or the cathode  56  can be coupled with such things as the object, a container that holds the working fluid  52 , or with any other of a variety of structures. It will be appreciated, therefore, that any of the object, container, or other structures can themselves serve as the anode  54  or the cathode  56  of the electrolytic device  50 . It will also be appreciated that whatever the ultimate form, either or both the anode  54  or the cathode  56  can be immersed completely into the working fluid or have a surface directly in contact with the working fluid  52 . Some embodiments of the electrolytic device  50  are described further below. 
       FIG. 2  depicts one form of an article  58  that can be used with the electrolytic device  50 . In the illustrated form the article  58  includes an object  60  coupled with a mold  62 . The term mold as used herein can include a shell and/or a core, and each can be used interchangeably. The object  60  can be a cast metallic alloy and the mold  62  can be an alumina mold. The present application contemplates a wide variety of ceramic materials for the shell and/or core. Further, the shell and core can be formed of dissimilar material. The present application contemplates materials other than ceramics for use as the shell and/or core. Other variations either in the composition of the object  58  or the type of mold  62  are also contemplated herein. If made of a metallic alloy, the object  60  can be produced using a variety of techniques such as directional solidification, and can also take on crystal structures such as single crystal. Other forms of the object  60  are also contemplated. The metallic alloy can be a nickel based alloy, among other possibilities. In one form the mold  62  is produced using free-form fabrication techniques, such as but not limited to virtual pattern casting, laser stereolithography, and others. In one embodiment the mold  62  can be used to create a cast shape of the object  60  in the form of an aircraft gas turbine engine blade. 
     As used herein, the term “aircraft” includes, but is not limited to, helicopters, airplanes, unmanned space vehicles, fixed wing vehicles, variable wing vehicles, rotary wing vehicles, unmanned combat aerial vehicles, tailless aircraft, hover crafts, and other airborne and/or extraterrestrial (spacecraft) vehicles. Further, the present inventions are contemplated for utilization in other applications that may not be coupled with an aircraft such as, for example, industrial applications, power generation, pumping sets, naval propulsion, weapon systems, security systems, perimeter defense/security systems, and the like known to one of ordinary skill in the art. 
     Turning now to  FIG. 3 , one embodiment of a corrosion resistance system  64  is shown. The corrosion resistance system  64  includes a container  66  having the working fluid  52  and article  58  disposed within it. In one embodiment the container is made of nickel. In the illustrative form the corrosion resistance system  64  also includes an inert gas purge  68  operable to provide an inert gas within the container  66  above the working fluid  52 , and a pump system  70  capable of withdrawing a gas, whether inert or otherwise, from within the container  66 . Not all embodiments need have the one or both of the inert gas purge  68  or the pump system  70 . The corrosion resistance system  64  includes an electrode  72  coupled with a power supply  75 . In one form the electrode is metal which can made from platinum, among possible others. In the illustrative embodiment the electrode includes an end at least partially submerged within the working fluid  52 . 
     In some embodiments of the instant application the corrosion resistance system  64  can be used in conjunction with a process to leach a ceramic core from the article  58 . Such a leaching process can use heater  74  useful in providing a heat for a leaching process and to boil the working fluid  52  and leach the mold  62 . Other mechanisms in addition or alternative to the heater  74  can also be used to heat and/or boil the working fluid  52 . For example, a pressure of the working fluid  52  can be lowered to a point in which the working fluid  52  is at a superheated state thus encouraging nucleation and subsequent boiling of the working fluid  52 . Mechanisms such as pumps can be used to change the pressure in the working fluid  52 . For example, the pump system  70  can be used in some embodiments to not only withdraw a gas, whether inert or otherwise, from the container  66 , but can also be used to provide a gas, whether inert or otherwise, into the container  66  to change the pressure of the working fluid  52 . It will be appreciated, therefore, that either the inert gas purge  68  or the pump system  70  can be used to vary the pressure of the working fluid  52 . 
     The power supply  75  can take the form of any variety of devices capable of providing and/or regulating a voltage or current. In one form the power supply  75  can be a DC power supply. In the illustrative embodiment the power supply is electrically coupled with the container  66 . In one form the power supply  75  is further electrically coupled with the article  58  to provide either anodic or cathodic protection. In some embodiments the power supply  75  can be electrically coupled with the article  58  through a wire  76  extending between the article  58  and the container  66 . Such a wire can be fixed within the container  66  by drilling and taping a hole. Alternatively and/or additionally, in still further embodiments the power supply  75  can be electrically coupled with the article  58  through a basket  78 , such as a wire frame basket. The basket  78  can be electrically coupled with the power supply by contacting the container  66  or through an intervening conductor such as the wire  76 . 
     If operated to provide anodic protection, a potential difference can be provided by the power supply  75  and the article  58  configured to be operated as an anode. As the potential difference is increased above a certain value the material of the article  58 , and specifically the object  60 , enters a passive region in which relatively little or no corrosion process is present. 
     If operated to provide cathodic protection, a potential difference can be provided by the power supply  75  and the article  58  configured to be operated as a cathode. 
     In some embodiments multiple articles  58  can be disposed within container  66  and the corrosion resistance system  64  can be operated to provide anodic or cathodic protection. In some embodiments, one or more articles  58  can be configured as an anode and one or more articles  58  can be configured as cathodes. 
     In still other embodiments, operating the corrosion resistance system  64  for an extended period of time can be useful in removing or mitigating oxide coatings on the inside of the container  66  and/or on the basket  78 . 
     The inert gas purge  68  can include the devices depicted in  FIG. 3  but not all embodiments need include each of the devices. The inert gas purge  68  can provide a gas to the container  66  at a variety of pressures and temperatures. The inert gas purge  68  can deliver a gas such as, but not limited to, argon. 
     The pump system  70  can include the devices depicted in  FIG. 3  but not all embodiments need include each of the devices. The pump system can be used to extract a gas such as hydrogen from the container  66 . 
     In some forms of the corrosion resistance system  64 , an oxygen getter can be used to remove oxygen present within the container  66 . Such an oxygen getter can take the form of, but not limited to, titanium, wood chips, etc. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the inventions are desired to be protected. It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the 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,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.