Abstract:
One embodiment of the present invention is a unique filter and a method for manufacturing the same. Another embodiment is a unique system for casting a metallic object. Another embodiment is a unique method of filtering a molten metal. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for filtering molten metal. 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 
     The present application claims the benefit of U.S. Provisional Patent Application 61/291,042, filed Dec. 30, 2009, and is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to filters, and more particularly, to systems and methods for filtering molten metal. 
     BACKGROUND 
     Filtration systems for filtering liquids, e.g., molten metal, 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 
     One embodiment of the present invention is a unique filter and a method for manufacturing the same. Another embodiment is a unique system for casting a metallic object. Another embodiment is a unique method of filtering a molten metal. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for filtering molten metal. 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 
       The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
         FIG. 1  schematically illustrates a non-limiting example of a system for casting a metallic object in accordance with an embodiment of the present invention. 
         FIG. 2  schematically illustrates a non-limiting example of a stereolithography system for freeform fabrication of a ceramic filter in accordance with an embodiment of the present invention. 
         FIG. 3  schematically illustrates a non-limiting example of a ceramic filter in accordance with an embodiment of the present invention. 
         FIG. 4  depicts a non-limiting example of interconnected passages of a filter mesh in accordance with an embodiment of the present invention. 
         FIG. 5  depicts a non-limiting example of interconnected passages of a filter mesh in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Casting processes, e.g., investment casting and other casting processes produce components by pouring a liquid (often a metal) into a shaped cavity and subsequently allowing that liquid to solidify into the shape of the cavity. In many instances the liquid (or molten metal) may have impurities in the form of non-liquid contaminants within it. Such contaminants, or inclusions, may result in unacceptable defects if they are allowed to make their way into the castings. Effective filtration of the liquid can provide considerable improvements in process yield. However, traditional manufacturing techniques are typically unable form the complex paths desired for good filtration. An additional complication is that filtration of most molten metal requires a ceramic filter, and ceramics are difficult to form into the fine complex shapes required for filtering the molten metal. 
     Although it may be possible to manufacture a ceramic filter by infiltrating a volume of polystyrene foam spheres with ceramic slurry, and subsequently firing the ceramic slurry while burning out the polystyrene foam, such a manufacturing route results in a component wherein the ceramic ligaments have a varying cross-section. In particular, at locations where spheres were touching or in close proximity, the fired ceramic may be extremely thin. These thin sections may be fragile, and under investment casting conditions may break off thereby causing the filters themselves to become an inclusion source. Another technique that might yield a fine pore size may be to pack ceramic or polymeric particles to yield a filter made of the interstices. However, this approach would leave a large volume of the filter unavailable for use, since it is filled with the particles. The inventors address such concerns, in one aspect of the present invention, by controlling some or all aspects of the filter via an engineered and electronically defined geometry, e.g., including defining pore size and the tortuosity of the flow path(s) for the molten metal that is to be filtered. 
     Referring now to the drawings, and in particular,  FIG. 1 , there is schematically illustrated a non-limiting example of a system  10  for casting a metallic object, such as a gas turbine engine component, in accordance with an embodiment of the present invention. In one form, system  10  includes a crucible  12 , a ceramic filter  14  for filtering a molten metal  16 , and a mold  18 . In one form, crucible  12  is a transfer crucible that is operative to transfer molten metal  16  to mold  18  from another crucible that is used to melt a metal. In another form, crucible  12  is used to both melt the metal and transfer the molten metal to mold  18 . In one form, the metal is an alloy employed in creating a cast gas turbine engine component, such as an airfoil or a static structural component. The gas turbine engine component may be formed one or more alloys, such as a nickel-based superalloy, an aluminum alloy and/or a titanium alloy. 
     Ceramic filter  14  is operative to receive molten metal  16 , capture impurities that might otherwise form inclusions in the cast metallic object, and discharge molten metal  16 . In particular, filter  14  is operative to capture impurities from molten metal  16  prior to molten metal  16  entering the one or more cavities in mold  18  that define the cast metallic object. Ceramic materials used to form ceramic filter  14  contemplated herein include, but are not limited to, alumina, zirconia, silica, yttria, magnesia, and mixtures thereof. In one form, filter  14  is formed separately from both crucible  12  and mold  18 . In other embodiments, filter  14  may be formed integrally with one or both of crucible  12  and mold  18 . In one form, filter  14  is fitted to a portion of crucible  12 . In other embodiments, filter  14  may be fitted to a portion of mold  18  or otherwise disposed in an arrangement suitable for receiving molten metal  16  from crucible  12  and for discharging molten metal  16  for reception into mold  18 . 
     Mold  18  includes one or more internal cavities  20 , such as chambers and/or passages that define the internal and/or external geometry of the cast metallic object. In one form, one or more of cavities  20  are defined at least in part by a core, such as a ceramic core (not shown). Mold  18  may also include one or more gates and risers, e.g., to accommodate the flow of the molten metal, to help ensure adequate filling of cavities  20  with molten metal, and to backfill molten metal  16  to accommodate shrinkage during the solidification of molten metal  16  in various parts of mold  18 . Mold  18  is operative to receive the filtered molten metal  16  and form the cast metallic object. 
     In one form, system  10  also includes a stereolithography system  22  operative to fabricate ceramic filter  14  based on an electronic model  24 . In one form, stereolithography system  22  is operative to form ceramic filter  14  in the form of a green body, which is sintered prior to use as a filter. Filter  14  is electronically defined e.g., using commercially available stereolithography computer aided design (CAD) software to generate electronic model  24 , e.g., in the form of an STL (.stl) file. Electronic model  24  is supplied to system  22 , which fabricates filter  14 . 
     Referring to  FIG. 2 , there is schematically illustrated a non-limiting example of stereolithography system  22  for freeform fabrication of ceramic filter  14  in accordance with an embodiment of the present invention. In one form, system  22  is a selective laser activation (SLA) stereolithography system. Selective laser activation is based upon a stereolithography process that utilizes resins which solidify when exposed to an energy dose. While the present application will be generally described with respect to an SLA stereolithography system, it is equally applicable to other stereolithography systems, such as flash cure systems and other forms of scanned cure systems. 
     System  22  is operable to create ceramic filter  14  from electronic model  24  as a three dimensional ceramic component formed of a plurality of layers, some of which are labeled as layers  26 ,  28 ,  30  and  32 . In one form, stereolithography system  10  employs a ceramic loaded resin  34  disposed in a resin containment reservoir  36 ; an elevation-changing member  38 ; a laser source  40  and a scanning device  42  operative to scan a laser beam  44  across elevation changing member  38 ; and a controller  46 . 
     Resin containment reservoir  36  is filled with a quantity of ceramic loaded resin  34  from which ceramic filter  14  is fabricated. In one form, ceramic loaded resin  34  includes the ceramic material used to create filter  14  in the form of ceramic particles mixed with a photo-polymerizable monomer(s) and/or oligomer(s). The present application contemplates the use of an oligomer(s) resin alone or in combination with a monomer resin. In one form, ceramic loaded resin  34  contains a photoinitiator. In another form, ceramic loaded resin  34  contains a dispersant in addition to the photoinitiator. 
     Controller  46  is communicatively coupled to elevation changing member  38 , laser source  40  and scanning device  42 . Controller  46  is configured to execute program instructions to form filter  14  using elevation changing member  38 , laser source  40  and scanning device  42 . In one form, controller  46  is microprocessor based and the program instructions are in the form of software stored in a memory (not shown). However, it is alternatively contemplated that controller  46  and the 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. 
     Controller  46  is operative to control the operation of elevation changing member  38 , laser source  40  and scanning device  42  to form each layer of ceramic filter  14  based on electronic model  24  by selectively providing polymerizing energy doses to each layer. Scanning device  42  scans laser beam  44  from laser source  40  across ceramic loaded resin  34 , e.g., on a surface  48  of ceramic loaded resin  34 , in the desired shape to form each layer of ceramic filter  14 . The ceramic particles contained in ceramic loaded resin  34  ultimately form ceramic filter  14 . 
     Ceramic filter  14  is freeform fabricated by system  22  in layer-by-layer fashion by applying the energy dose to cure a film of ceramic-laden photo-polymerizable resin into a polymerized layer; lowering elevation changing member  38  and applying a new film of the resin; and applying an energy dose sufficient to both photo-polymerize the new film of resin into a new layer and to provide an overcure to bind the new layer to the previous layer. In one form, each new resin film is formed over the topmost polymerized layer by lowering elevation changing member  38  to submerge the topmost polymerized layer in the ceramic loaded resin  34  in reservoir  36 . The process is repeated to form a plurality of polymerized layers, i.e., layers of ceramic particles that are held together by a polymer binder, e.g., such as the illustrated layer  26 ,  28 ,  30  and  32 . The successively formed cured layers ultimately form the three-dimensional shape of ceramic filter  14  having the desired three-dimensional features formed therein. 
     In one form, each polymerized layer is on the order of 0.05 mm (0.002 inches) thick. Thinner or thicker layers may be employed in other embodiments. For example, the thickness of each layer may vary with the needs of the particular application, including the desired resolution of the ceramic filter  14 . It should be understood that embodiments of the present application may have any number of layers or thickness of layers. In addition, although only a single ceramic filter  14  is illustrated, it will be understood that in various embodiments, a plurality of ceramic filters  14  of the same and/or different configuration may be formed as a batch in system  22 . In addition, although the present embodiment is described with respect to a ceramic filter for filtering molten metal, it will be understood that other embodiments include other filter types. 
     After the formation of ceramic filter  14 , additional processing may be performed prior to use. In one form, ceramic filter  14  is subjected to burnout processing and sintering. In other embodiments, other additional processes may be performed in addition to or in place of burnout processing and sintering. 
     Referring now to  FIG. 3 , there is schematically illustrated a non-limiting example of ceramic filter  14  in accordance with an embodiment of the present invention. Ceramic filter  14  includes a filter mesh  50 . In one form, filter  14  also includes an integral solid shell  52 . In other embodiments, filter  14  may not include an integral shell. In one form, shell  52  includes an opening  54  and an opening  56 . Opening  54  is operative to receive molten metal  16  from crucible  12 . Opening  56  is operative to discharge the molten metal  16  into mold  18 , in particular, cavities  20 . 
     Filter mesh  50  is electronically defined in electronic model  24 , e.g., using commercially available stereolithography computer aided design (CAD) software to generate electronic model  24  in the form of an STL (.stl) file. In one form, shell  52  is also electronically defined in electronic model  24 . Electronic model  24  is supplied to system  22  and employed by controller  46  to direct the operations of laser source  40  and scanning device  42  to selectively cure and overcure subsequent layers in order to yield the desired three-dimensional filter  14 . In one form, electronic model  24  provides point-by-point definition for each geometric feature of filter mesh  14 , e.g., wherein each point is governed by the diameter of laser beam  44 . Hence, in some embodiments, the diameter of laser beam  44 , in conjunction with the thickness of each polyermized layer, determines the resolution of the geometric features of filter mesh  14 . 
     In one form, filter mesh  50  is defined in electronic model  24  to include a plurality of three-dimensional interconnected passages having a geometry configured to capture contaminants from molten metal  16 , e.g., based on velocities of the molten metal within filter mesh  50 , the pore size and the tortuosity of the passages. In one form, anisotropic shrinkage of filter  14 , in particular filter mesh  50 , is controlled. In addition, structural aspects of filter mesh  50  are designed to withstand the loads and temperatures associated with filtering molten metal  16 . In one form, the structural aspects include defining a minimum thickness of ceramic walls and/or ceramic ligaments within filter mesh  50 . 
     Referring now to  FIG. 4 , a non-limiting example of the interconnected passages of filter mesh  50  in accordance with an embodiment of the present invention is depicted. In the depiction of  FIG. 4 , the interconnected passages of filter mesh  50  are in the form of a plurality of pores  58  defined by a plurality of ceramic ligaments  60 . The thickness  62  of ceramic ligaments has a minimum defined value designed to withstand the pressures associated with filtering molten metal  16 . In the embodiment of  FIG. 4 , the size, shape and number of pores  58  and ligaments  60  are designed to control the velocity at which molten metal  16  flows through filter  14  and pores  58 , and to capture contaminants in molten metal  16  as if flows through pores  58 . 
     Referring now to  FIG. 5 , a non-limiting example of the interconnected passages of filter mesh  50  in accordance with another embodiment of the present invention is depicted. In the depiction of  FIG. 5 , the interconnected passages of filter mesh  50  are in the form of a plurality of interconnected openings  64  defined in solid ceramic structure  66 . The wall thickness  68  of structure  66  between openings  64  has a minimum defined value designed to withstand the pressures associated with filtering molten metal  16 . In the embodiment of  FIG. 5 , the size and shape of openings  64  are designed to control the velocity at which molten metal  16  flows through filter  14  and openings  64 , and to capture contaminants in molten metal  16  as if flows through openings  64 . In one form, the size and shape of each opening  64  varies although the length of each opening  64 . In another form, the size of each opening  64  is constant along its length, e.g., wherein openings  64  are in the form of interconnecting holes of constant cross section extending through structure  66 . In yet another form, structure  66  may be in the form of diagonally intersecting rods having a desired cross section, wherein openings  64  are defined by the spaces between the intersecting rods. 
     Embodiments of the present invention include a method of manufacturing a ceramic molten metal filter, comprising: defining a filter mesh having a plurality of three-dimensional interconnected passages with a geometry configured to capture contaminants from a molten metal; freeform fabricating the filter mesh using a polymerizable ceramic loaded resin; and sintering the filter mesh. 
     In a refinement, the method also includes defining a minimum thickness in the filter mesh, wherein the minimum thickness is designed to withstand pressures associated with filtering the molten metal. 
     In another refinement, the method also includes defining the plurality of interconnected passages to control a velocity of a flow of the molten metal. 
     In yet another refinement, the method also includes defining an integral shell disposed around the plurality of interconnected passages. 
     In still another refinement, the method also includes defining the shell to include a first opening operative to receive the molten metal, and to include a second opening operative to discharge the molten metal. 
     In yet still another refinement, the polymerizable ceramic loaded resin contains alumina. 
     Embodiments of the present invention include a method of filtering a molten metal, comprising: defining a filter mesh having a geometry operative to withstand loads and temperatures associated with filtration of the molten metal and to capture contaminants from the molten metal; operating a stereolithography machine to fabricate the defined filter mesh using a photo-polymerizable ceramic loaded resin; sintering the filter mesh; and pouring the molten metal through the filter mesh. 
     In a refinement, the filter mesh includes a plurality of interconnected passages. 
     In another refinement, the plurality of interconnected passages are defined by a plurality of intersecting holes in a solid matrix. 
     In yet another refinement, the plurality of interconnected passages include a passage having a size that varies along a length of the passage. 
     In still another refinement, the filter mesh is defined by a plurality of ceramic ligaments and a plurality of pores. 
     In yet still another refinement, the method further includes defining a minimum ligament thickness. 
     In a further refinement, the minimum ligament thickness is designed to withstand pressures associated with filtering the molten metal. 
     In a yet further refinement, the method includes controlling anisotropic shrinkage. 
     Embodiments of the present invention include a system for casting a metallic object from a molten metal, comprising: at least one of a crucible and a mold; and a ceramic filter operative to receive the molten metal and to capture impurities from the molten metal prior to the molten metal entering one or more cavities in the mold that form the metallic object, the ceramic filter having an electronically defined ceramic filter mesh operative to remove contaminants from the molten metal. 
     In a refinement, the system also includes a stereolithography system operative to fabricate the electronically defined ceramic filter mesh using a photo-polymerizable ceramic loaded resin. 
     In another refinement, the system also includes a controller configured to execute program instructions to direct the stereolithography system to form the ceramic filter based on an electronic definition of the electronically defined ceramic filter mesh. 
     In yet another refinement, the electronically defined ceramic filter mesh is structured to withstand pressures associated with filtering the molten metal. 
     In still another refinement, the system includes an integral shell disposed around the electronically defined ceramic filter mesh. 
     In yet still another refinement, the shell includes a first opening operative to receive the molten metal, and includes a second opening operative to discharge the molten metal. 
     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.