Abstract:
One embodiment of the present invention is a unique method for brazing an assembly. Another embodiment is a unique method of heat treating an object. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for heat treating and/or brazing. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of U.S. Provisional Patent Application No. 61/427,578, filed Dec. 28, 2010, entitled Heat Treating and Brazing of an Object, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to heat processing of objects, and more particularly, to heat treating and/or brazing objects. 
     BACKGROUND 
     The manufacture of objects, such as gas turbine engine components, by heat treating and/or brazing, remains 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 method for brazing an assembly. Another embodiment is a unique method of heat treating an object. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for heat treating and/or brazing. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will 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 some aspects of a non-limiting example of a system for brazing an assembly in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates some aspects of a non-limiting example of the assembly illustrated in  FIG. 1 . 
         FIG. 3  illustrates some aspects of a non-limiting example of the assembly of  FIG. 1  with a braze filler metal applied. 
         FIG. 4  illustrates some aspects of a non-limiting example of an assembly depicting braze filler metal having wetted undesirable portions of the assembly. 
         FIGS. 5, 5A and 5B  illustrate some aspects of non-limiting examples of heat shields for shielding a portion of an object or assembly. 
         FIG. 6  illustrates some aspects of a non-limiting example of an assembly having a portion shielded by a heat shield in accordance with an embodiment of the present invention, depicting braze filler metal having flowed into a braze joint. 
     
    
    
     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. 
     Referring to the drawings, in particular  FIG. 1 , a non-limiting example of a system  10  for treating an object  12  in accordance with an embodiment of the present invention is schematically depicted. System  10  includes a furnace  14  having heating elements  16 , and a controller  18 . Controller  18  is operative to control the amount of heat supplied to object  12  via furnace  14 , e.g., operative to control the temperature of heating elements  16 . In one form, controller  18  is also operative to control the duration of heating. In other embodiments, the duration of heating may be manually controlled or may be controlled by one or more other systems. 
     Heating elements  16  are operative to heat object  12  in furnace  14 . In one form, furnace  14  and heating elements  16  are configured to heat object  12  by radiation. In other embodiments, furnace  14  and heating elements  16  may be configured to heat object  12  by convection and/or conduction in addition to or in place of radiation. 
     In one form, furnace  14  is sized to heat a single object  12 . In other embodiments, furnace  14  may be configured to heat a plurality of one or more types of objects. In one form, furnace  14  is a vacuum furnace, in which case system  10  includes means for drawing a vacuum in furnace  14 . The vacuum may be a partial vacuum or a substantially full vacuum, depending upon needs of the particular application. In one form, system  10  includes a vacuum pump  20  operative to partially or substantially fully evacuate gases from furnace  14 . In other embodiments, other systems for evacuating or purging gases from furnace  14  may be employed. Although the example of furnace  14  is described herein as a vacuum furnace, in other embodiments, furnace  14  may be any furnace or autoclave, and may have little or no atmosphere, an inert and/or other gas atmosphere or an ambient air atmosphere. 
     Referring to  FIGS. 2-4 , some aspects of a non-limiting example of object  12  in accordance with an embodiment of the present invention are depicted. In one form, object  12  is a gas turbine engine component. In other embodiments, object  12  may be any device or structure. In one form, object  12  is an assembly that is to be brazed together, e.g., in furnace  14 . In other embodiments, object  12  may be one or more structures that are to be heat treated, e.g., in furnace  14 . In still other embodiments object  12  may be an object or assembly that is to be heat treated and brazed, e.g., in furnace  14 . In one form, object  12  is formed of a plurality of components or portions that are to be brazed together in furnace  14 . In the example illustrated in the drawings, e.g.,  FIG. 2 , object  12  is formed of portions  22  and  24  that are to be brazed together at a braze joint  26 . Portion  22  is relatively thin compared to portion  24 , and has a lower thermal mass than portion  24 . In other embodiments, object  12  may have any number of portions. 
     In order to braze portions  22  and  24  together, a braze filer metal  28  is applied to object  12  adjacent to braze joint  26 . Heating of portions  22  and  24  by heating elements  16  in furnace  14  raises the temperature of portions  22  and  24 , with the goal of melting braze filler metal  28  so that it flows into braze joint  26 . However, because portion  22  is thinner than portion  24 , portion  22  heats up faster than portion  24 , which results in braze filler metal  28  wetting the surface of portion  22  and flowing away from braze joint  26  because portion  22  reaches a temperature sufficient to melt braze filler metal  28  prior to portion  24  reaching the same temperature, which yields an undesirable result, depicted in  FIG. 4 . The melted braze filler metal  28  is depicted in  FIG. 4  as thicker lines on portion  22  of object  12 . In order to prevent the occurrence illustrated  FIG. 4 , it is possible to heat object  12  up to a temperature below the solidus point of braze filler metal  28  over a longer time period to allow portion  24  and portion  22  to achieve relatively similar temperatures just below the solidus point of braze filler metal  28 . Once the temperatures of portions  22  and  24  are just below the solidus point, furnace  14  may be operated to slowly increase the temperature of object  12  in an attempt to melt braze filler metal  28  and cause it to flow into braze joint  26 . However, such an approach is a time consuming process, resulting in higher energy costs and lower product throughput. 
     Referring to  FIG. 5 , in order to prevent portion  22  from achieving a temperature sufficient to melt braze filler metal  28  too soon, a heat shield  30  is employed. Heat shield  30  is formed and positioned on portion  22  to shield only portion  22  form heating elements  16 , and to not shield portion  24  from heating elements  16 . The radiation heat shield  30  may be positioned so that the radiation heat shield is supported by the assembly and the entire radiation heat shield  30  maintains a spaced-apart relationship with the braze filler metal  28  and the braze joint  26  both before and after melting the braze filler metal  28  to flow into the braze joint  26  as shown in  FIGS. 5 and 6 . In one form, heat shield  30  is configured to shield portion  22  from radiation emanating from heating elements  16  to reduce radiative heat transfer to portion  22 . Heat shield  30  may also be configured to shield portion  22  from conduction and/or convection heating in addition to or in place of radiation heating. In one form, heat shield  30  is configured to conform to the shape of portion  22 . In other embodiments, other shapes may be deployed. 
     Heat shield  30  is formed of one or more thin sheets of metal. The thickness of the sheet metal may vary with the needs of the application. In one form, sheet metal having a thickness in the range of 0.001″ to 0.010″ is employed. In other embodiments, other sheet metal thicknesses may be employed, including less than 0.001″ thickness and/or more than 0.010″ thickness. In one form, heat shield  30  is a layer of sheet metal. In one form, the material used to form heat shield  30  is a refractory metal, for example and without limitation, molybdenum, tantalum, niobium or their alloys. In other embodiments, other metals may be employed, including other refractory metals and/or their alloys, as well as common sheet metal materials, for example and without limitation, stainless steels or nickel alloys, in addition to or in place of refractory metals. In one form, heat shield  30  is laminated, being formed of a plurality of layers of sheet metal, for example and without limitation, sheet metal formed of one or more of the materials listed above. In one form, heat shield  30  is formed by wrapping portion  22  from a single sheet of sheet metal. In one form, the wrapping is performed in a spiral fashion, winding along a length and/or width of portion  22 . In one form, the layers are formed as concentric layers, e.g., individual sheets wrapped around portion  22  and around each other. In various embodiments, each layer may also be formed by various means, including laser cutting, water cutting, electrical discharge machining and/or other techniques. 
     Referring to  FIGS. 5A and 5B , in one form, heat shield  30  is configured to form a gap  32  between heat shield  30  and portion  22 , e.g., to prevent heat conduction from heat shield  30  to portion  22 . In one form, gap  32  is formed by one or more standoffs  34  disposed between heat shield  30  and portion  22 . In one form, standoff  34  is a ceramic powder or is formed of a ceramic powder. In other embodiments, standoff  34  may take other forms, for example and without limitation, ceramic rope and/or metallic wire. In still other embodiments, standoffs  34  may be formed in layers  36  that form heat shield  30 , e.g., dimples in one or more layers  36 . In yet other embodiments, heat shield  30  may not be configured to form a gap between heat shield  30  and portion  22 . 
     In one form, each layer  36  of heat shield  30  is also separated by a gap  32 , e.g., formed by standoffs  34 . In other embodiments, only some layers  36  may be separated to form gaps  32  therebetween. In still other embodiments, no gaps may be formed between layers  36  of heat shield  30 . In one form, heat shield  30  is configured to permit gases between heat shield  30  and object  12 , as well as between shield layers  36  to escape when a vacuum is drawn in furnace  14 . In one form, heat shield  30  is configured, e.g., by the number and locations of layers  36  and gaps  32 , to control the heat flux received by portion  22  from heating elements  16 , e.g., to achieve a desired heating rate and/or peak temperature of portion  22 . Heat shield  30  may also or alternatively be configured to control the cooling of portion  22  when furnace  14  is turned off and/or when object  12  is removed from furnace  14 , e.g., to yield a desired cooling rate of portion  22 . In various embodiments, one or more coatings, e.g., reflective and/or refractive coatings, may be deposited on one or more layers  36  in order to control the flow of heat to and/or from portion  22 . In addition, other materials, such as insulation materials or coatings may be deposited on heat shield  30  and/or between layers  36  of heat shield  30  in order to control the flow of heat to and/or from portion  22 . 
     In order to braze portions  22  and  24  together, braze filler metal  28  is positioned adjacent to braze joint  26 . Heat shield  30  is then positioned on portion  22 , and object  12  is placed into furnace  14 . In one form, a vacuum is drawn in furnace  14 , although in other embodiments a vacuum may not be drawn. In some embodiments, furnace  14  may be purged with an inert gas prior to heating. Heating elements  16  are activated to heat object  12  with heat shield  30 . Heat shield  30  prevents portion  22  from heating up too quickly, e.g., promoting a more uniform temperature distribution as between portion  22  and portion  24 . As a result, both portions  22  and  24  achieve a sufficient temperature to melt braze filler metal  28  so that it flows into braze joint  26 , e.g., as depicted in  FIG. 6 , wherein the thick lines represent braze filler metal  28  within braze joint  26 . After braze filler metal  28  has flowed into braze joint  26 , the temperature inside furnace  14  is reduced, allowing object  12  to cool. Furnace  14  is then re-pressurized, e.g., brought up to atmospheric pressure, and object  12  is removed from furnace  14 . Heat shield  30  is then removed from object  12 . In some embodiments, heat shield  30  is configured to be reusable for subsequent objects  12 , e.g., of the same configuration. 
     In some embodiments, a heat shield such as heat shield  30  may be configured to control the heating rate and/or cooling rate of portion  22  of object  12  during heat treating of object  12  in order to obtain a desired microstructure in the portion covered by heat shield  30 , e.g., portion  22 , that is different from the microstructure of other portions of object  12 , e.g., portion  24 . This may be performed as a heat treat operation alone or in conjunction with a brazing operation. 
     Embodiments of the present invention include a method for brazing an assembly in a furnace, comprising: applying a braze filler metal adjacent to a joint in the assembly; providing a radiation heat shield conforming to a shape of only a portion of the assembly, wherein the radiation heat shield is configured to reduce radiative heat transfer to the portion of the assembly; positioning the radiation heat shield on the assembly; placing the assembly and the radiation heat shield in the furnace; and heating the assembly and the radiation heat shield in the furnace to melt the braze filler metal into the joint. 
     In a refinement, the method further comprises positioning the radiation heat shield to shield only the portion of the assembly from heating elements of the furnace. 
     In another refinement, the method further comprises configuring the radiation heat shield to form a gap between the radiation heat shield and the portion of the assembly. 
     In yet another refinement, the method further comprises supplying a standoff to form the gap. 
     In still another refinement, the standoff is formed in the radiation heat shield. 
     In yet still another refinement, the method further comprises forming the radiation heat shield as a plurality of layers, each layer being separated by a gap. 
     In a further refinement, the method further comprises forming each layer from sheet metal. 
     In a yet further refinement, the method further comprises providing standoffs configured to form the gap between each layer. 
     Embodiments of the present invention include a method for treating an object, comprising: supplying a laminated heat shield conforming to a shape of a portion of the object; positioning the laminated heat shield on the portion of the object; placing the object and the laminated heat shield in a furnace; heating the object and the laminated heat shield in the furnace; and cooling the object and the laminated heat shield, wherein the laminated heat shield is configured to control a cooling rate of the portion of the object shielded by the laminated heat shield. 
     In a refinement, the method further comprises drawing a vacuum in the furnace. 
     In another refinement, the laminated heat shield is formed from a refractory metal. 
     In yet another refinement, the laminated heat shield is formed of a plurality of layers of a sheet metal. 
     In still another refinement, the method further comprises forming the layers by wrapping the portion with a sheet of sheet metal. 
     In yet still another refinement, the wherein the wrapping is performed in a spiral fashion. 
     In a further refinement, the layers are concentric. 
     In a yet further refinement, the method further comprises forming a different microstructure in the portion of the object than the balance of the object. 
     Embodiments of the present invention include a method for treating an object, comprising: wrapping a selected portion of the object in a plurality of layers of a sheet metal; separating at least a portion of each layer of the sheet metal from an adjacent layer of the sheet metal; placing the object in a furnace; and heating the object in the furnace to braze the object and/or heat treat the object. 
     In a refinement, the method further comprises forming standoffs in at least one layer of the sheet metal. 
     In another refinement, the method further comprises applying a braze filler metal adjacent to a joint in the object. 
     In still another refinement, the method further comprises further comprising selecting the number of layers based on a desired cooling rate for the portion of the object. 
     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.