Patent Publication Number: US-8540009-B2

Title: Hollow sand cores to reduce gas defects in castings

Description:
TECHNICAL FIELD 
     The technical field generally relates to mold casting techniques and, in particular, to the introduction of hollow sand cores to reduce gas defects in castings. 
     BACKGROUND 
     Casting is a manufacturing process by which a liquid material is (usually) poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solid casting is then ejected or broken out to complete the process. 
     Sand casting is one type of casting process in which a cast part is produced by forming a mold from an assembly of sand cores and pouring molten liquid metal into the cavity of the mold. The mold and metal are then cooled until the metal has solidified. In the last stage the casting is separated from the mold. 
     Cold box and no bake technologies are types of sand casting processes that use organic and/or inorganic binders that strengthen the sand core by chemically adhering to the sand. In cold box and no bake technologies, the resin is cured using a catalyst reaction to harden the entire core inside and out prior to the introduction of liquid material that is cast to a desired shape. Green sand technology uses clay to bind the sand and is used for making molds where sand cores, if required, are placed into. 
     SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
     One exemplary method includes forming a core insert, forming a sand core around the core insert, and creating at least one passage within the sand core by removing or otherwise transforming a portion of the core insert, wherein at least one passage includes an exit point. 
     Another exemplary method includes forming a core insert, forming a sand core around the core insert, creating at least one passage within the sand core by removing or otherwise transforming a portion of the core insert, wherein at least one passage includes an exit point, introducing the sand core as part of a casting mold assembly having a vent, wherein the vent is coupled to the exit point, and casting a part within the casting mold assembly, wherein the gas generated during the casting process escapes the sand core through the passages to the exit point and the vent. 
     Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a logic flow diagram for forming a sand core within a core box system, and subsequently using the formed sand core to form a cast part, in accordance with an exemplary method; 
         FIG. 2  is a schematic illustration of a pair of sand core inserts according to one exemplary embodiment; 
         FIG. 3A  is a schematic illustration of a sand core precursor formed within a core box system according to one exemplary embodiment and including the sand core inserts of  FIG. 2 ; 
         FIG. 3B  is a section view of the sand core of  FIG. 3A  taken along line  3 B- 3 B; 
         FIG. 4A  is a schematic illustration of a sand core formed from the sand core precursor of  FIG. 3A  after ejection from the sand core box; 
         FIG. 4B  is a sectional view taken along lines  4 B- 4 B of  FIG. 4A . 
         FIG. 5  is a schematic illustration of a casting mold assembly including multiple sand cores according to one exemplary embodiment; and 
         FIG. 6  is a close-up view of a portion of  FIG. 5  within circle  7 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description of the embodiment(s) is merely exemplary (illustrative) in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring first to  FIG. 1 , an exemplary method for forming a sand core within a core box system, and the subsequent production of a cast part utilizing the sand mold, is illustrated in a logic flow diagram. Supplementary  FIGS. 2-6  aid in explaining the formation of the cast part at various stages from a sand core and sand core precursor formed in accordance with one exemplary embodiment. 
     Referring first to  FIG. 1 , the method begins, as shown in box  10 , by determining a size and shape of a sand core (shown as  69  in  FIGS. 4A ,  4 B, and  5 ) that may be subsequently used to form a cast part in a sand mold. 
     Next, in box  11 , a determination may be made for the size and location of one or more internal passages (shown as  56  in  FIGS. 4A and 4B ), including one or more exit points (shown as  58  in  FIG. 4A ), to be introduced within the sand core  69  to provide a passageway for the escape of gases during the subsequent casting process. 
     Next, in box  12 , one or more core inserts  20  may be formed roughly corresponding in approximate size and shape to each of the internal passages  56  as determined in box  11 . 
     Referring now to  FIG. 2 , one exemplary embodiment of a pair of formed core inserts  20  may be illustrated for use in one exemplary sand core. The core inserts  20  may include any variety of spokes  21  that may be interconnected at coupling points  22 . The spokes  21  may be of any defined dimension and shape and may include at least one end  23  that will define an exit point  58  for gases in the subsequently formed sand core  69 . 
     The core inserts  20  may be formed from a wide variety of materials utilizing a wide variety of different formation methods. The materials may be at least partially thermally or chemically degradable to create the passages  56  within the sand core  69 . In addition, the materials of the core inserts  20  may have a different reactivity than the resin component  66  to allow then to remain in their original state (i.e. not chemically or thermally degrade) when the resin component  66  may be hardened or cured as described above in box  15 . 
     In one exemplary embodiment, the core insert  20  may be formed from a foam material having a low collapse temperature. A collapse temperature, by definition for the purposes herein, is a temperature in which a material at least partially degrades, shrinks, or is otherwise acted upon to create a passage (shown as  56  in  FIG. 4A ) within the hardened sand core  69 . The collapse temperature may be greater than any temperature increase associated with hardening or curing the resin component  66  to form the hardened sand mold  69  as described below in box  17 . 
     Non-limiting exemplary foam materials that may form the core insert include Styrofoam™, methyl methacrylate foam, polystyrene foam, and polyalkylene carbonate foam. In addition, these foam materials may be reinforced with fibers such as carbon fibers, aramid fibers, glass fibers or other polymeric and non-polymeric fibrous materials to provide some degree of structural reinforcement. 
     In another exemplary embodiment, the solid core insert  20  may be formed from a meltable or sublimable material that melts, or sublimes, to form the passage  56 . As with the foam materials, the meltable or sublimable temperature of these materials may be greater than any temperature increase associated with hardening or curing the resin component  66  to form the sand core  50  as described below in box  15 . 
     Exemplary meltable materials may be utilized include wax, polymers having a melting point below about 200 degrees Celsius, inorganic materials such as salts, or ultra low melting alloy materials such as solders. In addition, these meltable materials may be reinforced with fibers such as carbon fibers, aramid fibers, glass fibers or other polymeric and non-polymeric fibrous materials to provide some degree of structural reinforcement. Moreover, other meltable composite materials, or meltable organic or inorganic materials including filler materials, may also be utilized. 
     Sublimable materials may include any material that sublimates below about 200 degrees Celsius. Exemplary sublimable materials include organic polymers such as camphor. 
     Of course, other polymeric and non-polymeric materials may also be contemplated herein to form the core insert  20 , provided that they can be removed or otherwise acted upon to create the passages  56  without adversely affecting the surrounding sand core  69 . Moreover, similar to the foam materials, meltable materials, and sublimable materials described above, these other materials may not degrade or otherwise be transformed to create the passages  56  at or below the temperature associated with hardening or curing the resin component  66  to form the hardened sand core  69  as described below in box  17 . 
     Referring back to  FIG. 1 , in box  13 , the one or more core inserts  20  may be introduced into the interior  54  of a core box system  52  at predetermined locations. 
     In box  14  of  FIG. 1  and as shown in  FIGS. 3A and 3B , a mixture  62  of sand  64  and resin  66  may be blown into the interior  54  of the core box system  52  to fill the interior region  54  around the one or more core inserts  20  to form a sand mold precursor  50  in such a way so that the ends  23  of the spokes  21  of the core inserts  20  are not covered (i.e. they are exposed) with sand  64  and resin  66 . 
     In box  15 , the resin component  66  of the mixture  62  may be hardened around the one or more core inserts  20 , therein forming the sand core  69  as shown in  FIGS. 4A and 4B  from the sand mold precursor  50 . This hardening step may be performed in such a way as to not adversely affect the one or more core inserts  20 . In many exemplary embodiments, the hardening step coincides with the curing of the resin component  66 . 
     In one exemplary embodiment, also shown in  FIG. 3A , triethylamine gas  65  may be introduced within the interior  54  of the core box system  52 . The gas  65  may be blown through the sand mold precursor  50  to cure the resin component  66  to form the sand core  69 , wherein the resin component  66  is a polyurethane material. The curing of the polyurethane material  66  may cause the resin component  66  to harden and, in essence, fuse or otherwise couple together the sand component  62  and resin component  66  in an integral structure. 
     In other exemplary embodiments (not shown), other types of curing mechanisms such as heat or radiation may be used to harden the resin component  66  without adversely affecting the one or more core inserts  20 . 
     In still other exemplary embodiments (not shown), the hardening may be accomplished without an associated curing step (i.e. the resin hardens without curing). For example, a catalyst (not shown) may be mixed with the resin component  66  that causes the resin component  66  to cure within a specific period of time to fuse together the sand component  62  and resin component  66  without adversely affecting the sand core inserts  20 . 
     Next, in box  16 , the one or more core inserts  20 , or at least a portion of the one or more core inserts  20 , are removed or otherwise transformed to create a corresponding located internal passage  56  within the hardened sand core  69 . The end portion  23  of the one or more core inserts  20  may be removed or transformed to create the corresponding exit point  58 . 
     The precise method for removal or transformation of the one or more inserts  20  to create the passages  56  and exit points  58  may be determined by the composition of the one or more core inserts  20  as described above. 
     For example, core inserts  20  formed from collapsible materials, such as the foam materials described above, may be transformed to create the passages  56  by heating the sand core  69  to an elevated temperature (i.e. above the collapse temperature for the material) sufficient to cause the core inserts  20  to collapse (i.e. breaks down or otherwise be altered) to create voids representing the passages  56 . 
     Core inserts  20  formed from meltable materials, by contrast, may be melted by raising the temperature of the sand core  69 . The melted material may primarily then travel through the passages  56  created towards the exit points  58 , either by gravity or through vacuum assist. The melted core materials may then be collected as it exits through the exit points  58  by a collection device (not shown). 
     Sublimable materials may be sublimed by raising the temperature above the subliming temperature of the material, therein transforming the solid core material to a gas. The gas (not shown) may travel primarily through the passages  56  created towards the exit points  58  and exit the sand core  69 . The gas may be collected as it exits through the exit points  58  by a collection device (not shown) or simply allowed to enter the atmosphere. 
     Referring back to  FIG. 1 , in box  17 , the sand core  69  having the internal passages  56  may be ejected from the core box system  52 . The resultant sand core  69  having the passages  56  and exit points  58  may be illustrated in one embodiment in  FIGS. 4A and 4B . 
     In an alternative arrangement to boxes  16  and  17 , as shown in boxes  16 A and  17 A, the sand core  69 , including the core inserts  20 , may first, as shown in box  16 A, be ejected from interior  54  of the core box system  52  prior to the removal or transformation of the core inserts  20 . 
     Next, as shown in box  17 A, the core inserts  20  may be removed in the manner described above in step  16  to create the internal passages  56  and exit points  58 . 
     Next, in box  18 , the sand core  69  may be used to form a cast part. 
     In one exemplary embodiment, a single sand core  69 , or multiple sand cores  69  formed as described above, may be introduced with an interior region  102  of a casting mold assembly  100  including a vent  106 .  FIGS. 5 and 6  illustrate such an exemplary embodiment wherein multiple sand cores  69  are introduced within the casting mold assembly  100 . 
     The casting mold assembly  100  may be formed from one or more pieces, here shown as multiple pieces  101 , of a sand core material. The composition, and method of manufacturing of the one or more pieces  101 , may be substantially similar to the sand core  69 , but without passages  58  formed by the removal of core inserts  20 . The casting mold assembly  100  may be formed of additional or other materials as well, such as core pieces formed by green sand technology or the like, and are thus not limited to any particular arrangement and material composition of the pieces  101  as shown in  FIGS. 5 and 6 . The casting mold assembly  100  may also include an outer jacket (not shown) formed of metal, a polymer, or the like that contains the sand core pieces  101  and one or more sand cores  69 . 
     Next, a liquid material  104  may be introduced within a casting mold assembly  100  to fill the interior region  102  not otherwise occupied by the sand core  69  and sand core pieces  101 . The liquid material  104  therein solidifies within the interior region  102  of the casting mold assembly  100  around the sand core  69  and pieces  101  to form a cast part (not shown). As the liquid material  104  is introduced, gas  110  may be generated due to the decomposition of the resin component  66  of the sand core  69  and pieces  101 . This gas  110  follows the path of least resistance, mainly through the internal passages  56  in the sand core  69 , and exits the sand core  69  through the one or more exit points  58 , which may be strategically coupled with a corresponding vent  106  within the remainder of the casting mold assembly  100 . A vacuum  108  may also be coupled to the vents  106  to hasten the removal of the generated gas  110 . Thus, the liquid material  104  may solidify without the substantial introduction of gas  110  there through, which may result in less defects, on a macroscopic and microscopic level, in the cast part associated with the gas evolution. In this way, a complex cast part may be produced in a single casting operation with fewer gas related defects. 
     In alternative arrangements (not shown), the sand core or cores  69  form the entirety of the casting mold assembly  100 . In other words, additional pieces  101  of sand core coupled together, or other materials noted above, that surround the sand core  69  may not be utilized. 
     The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.