Patent Application
20100212854
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.
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.
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.
Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
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
Referring first to
Next, in box 11, a determination may be made for the size and location of one or more internal passages (shown as 56 in
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
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 69 core. 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
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
In box 14 of
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
In one exemplary embodiment, also shown in
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 materials 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
In an alternative arrangement to boxes 16 and 17, as shown in boxes 16A and 17A, the sand core 69, including the core inserts 20, may first, as shown in box 16A, 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 17A, the core inserts 20 may be removed in the manner described above in step 16 to create the internal passages 26 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.
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
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.
