Spherical fused silica compositions for injection-molded ceramic cores, and methods of making parts using such compositions
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-04-20
- Publication Date
- 2026-03-30
AI Technical Summary
Existing ceramic core compositions for casting processes exhibit instability at high temperatures and poor flow properties, limiting their ability to produce thin and precise ceramic parts.
A single crystal ceramic core composition comprising 85% inorganic portion (94-98% spherical fused silica and 2-6% zircon fines) and 15% organic portion (84-88% binder, 1-2% dye, 6-12% surfactant, and 1-5% polymer fiber) with spherical fused silica particles ranging from 0.58 to 296 microns, enhancing stability and flowability.
The composition provides improved thermal stability and flow properties, enabling the production of thinner and more precise ceramic cores with enhanced reproducibility and reliability.
Smart Images
Figure 2023160787000001 
Figure 2023160787000002 
Figure 2023160787000003
Abstract
Description
[Technical Field]
[0001] The present disclosure relates generally to compositions for injection-molded ceramic cores, and more particularly to spherical fused silica compositions for forming injection-molded ceramic cores for turbine blades, airfoils, and high-stage turbine components. [Background technology]
[0002] According to a typical casting process, a ceramic core mixture is provided as a composite of organic binder and ceramic particles, which is injected into a die with a specially designed profile. In the case of a turbine blade, the die is shaped to the desired interior profile of the turbine blade. Once the material solidifies to form the core, it is removed from the die and undergoes a firing process to remove the organics and sinter the core. The core is then inserted into a wax die that is molded to the desired exterior profile of the turbine blade. A gap is formed between the core and the wax die, and wax is injected into the gap and allowed to cool in the shape of the exterior profile. The wax is then cooled, and the die is opened to eject the binder-core composite.
[0003] The wax-coated ceramic core is then coated (e.g., dipped) with a ceramic shell slurry to form a solidified outer shell around the core. The wax is then removed (e.g., by melting), leaving a void between the solidified outer shell and the ceramic core. The void is then filled with a liquid metal of the composition desired for the final part. The liquid metal is cooled according to a predetermined method to form a cast part. For example, the cast part can be equiaxed (EQ), directionally solidified (DS), or single crystal, as known to those skilled in the art.
[0004] Once the liquid metal has cooled, the outer shell is hammered off the cast metal part and the core is chemically leached from the inside, leaving only the metal part, which can then be machined and coated to suit the application.
[0005] Various ceramic core compositions have been developed for use in casting processes. However, these compositions have inherent drawbacks. It would be beneficial to have a ceramic core composition for casting processes that has superior properties compared to prior art compositions. Summary of the Invention
[0006] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. The summary is not an extensive overview of the invention. It is not intended to identify essential elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a convenient form as a prelude to the more detailed description presented elsewhere herein.
[0007] In one embodiment, the single crystal ceramic core composition has an inorganic portion and an organic portion. The inorganic portion comprises approximately 85 wt% of the total weight of the ceramic core composition, and the organic portion comprises approximately 15 wt% of the total weight of the ceramic core composition. The inorganic portion includes approximately 94-98 wt% spherical fused silica and approximately 2-6 wt% fine zircon powder. The organic portion includes approximately 84-88 wt% binder, approximately 1-2 wt% dye, approximately 6-12 wt% surfactant, and approximately 1-5 wt% polymer fiber.
[0008] According to some embodiments of the present invention, the inorganic portion of the ceramic core composition comprises about 95-97 wt. % spherical fused silica and about 3-5 wt. % fine zirconium powder, and the organic portion of the ceramic core composition comprises about 86-87 wt. % binder, about 1.2-1.6 wt. % dye, about 8-10 wt. % surfactant, and about 2-4 wt. % polymer fiber.
[0009] In another aspect of the invention, the spherical fused silica comprises a plurality of particles having the following particle size distribution:
[0010] [Table 1]
[0011] According to a further aspect of the invention, the binder is a thermoplastic material. In some aspects, the thermoplastic material is a modified paraffin wax. In yet a further aspect of the invention, the surfactant comprises an effective amount of sodium stearate, an effective amount of aluminum stearate, and an effective amount of oleic acid.The polymeric fibers, according to yet another aspect of the invention, comprise rayon fibers.
[0012] According to some embodiments, the spherical fused silica comprises a plurality of particles having the following particle size distribution:
[0013] [Table 2]
[0014] In yet a further aspect of the invention, the spherical fused silica comprises a plurality of particles having the following particle size distribution:
[0015] [Table 3]
[0016] In another embodiment of the present invention, a single crystal ceramic core composition includes an inorganic portion comprising approximately 85 wt. % of the total weight of the ceramic core composition and an organic portion comprising approximately 15 wt. % of the total weight of the ceramic core composition. The inorganic portion includes approximately 94-98 wt. % spherical fused silica and approximately 2-6 wt. % fine zircon. The organic portion includes approximately 84-88 wt. % binder and approximately 12-16 wt. % surfactant and dye.
[0017] According to some embodiments of the present invention, the surfactant comprises about 6-12% by weight of the organic portion, with the remainder of the organic portion being the dye. In one particular embodiment, the binder is a paraffin wax.
[0018] In a further aspect of the invention, the spherical fused silica comprises about 96% by weight of the inorganic portion, with the remainder of the inorganic portion being zircon. In yet a further aspect of the invention, the binder comprises about 86.5% by weight of the organic portion, with the remainder of the organic portion being surfactants and dyes.
[0019] According to one or more embodiments of the present invention, the surfactant comprises an effective amount of sodium stearate, an effective amount of aluminum stearate, and a fatty acid. In still a further aspect, the spherical fused silica comprises a plurality of particles having the following particle size distribution:
[0020] [Table 4]
[0021] According to yet another embodiment of the present invention, a method of forming a turbine blade includes: (a) injecting a single crystal ceramic core composition into a mold to form a core having an interior profile of a turbine blade; (b) removing the core from the mold; (c) subjecting the core to a firing process; (d) inserting the fired core into a die; (e) injecting liquid wax into the region formed between the fired core and the die, wherein the region formed between the fired core and the die has the exterior profile of the turbine blade; and (f) injecting the wax into the region formed between the fired core and the die. (g) forming a solidified ceramic shell around the wax-covered fired core from the die, (h) removing the wax from between the solidified shell and the fired core to form a void between the solidified shell and the fired core, (i) pouring molten metal into the void and allowing the molten metal to cool to form a turbine blade such that the fired core is located within the turbine blade, (j) removing the shell from the turbine blade, and (k) leaching the sintered core from within the turbine blade. The single crystal ceramic core composition includes an inorganic portion comprising about 94 to 98 wt% spherical fused silica, the inorganic portion comprising about 85 wt% of the total weight of the single crystal ceramic core composition, and an organic portion comprising about 85 to 89 wt% of a binder, the organic portion comprising about 15 wt% of the total weight of the single crystal ceramic core composition.
[0022] In some embodiments of the present invention, the inorganic portion of the single crystal ceramic core comprises about 96 wt.% silica and the organic portion of the single crystal ceramic core comprises about 87 wt.% binder. According to still further embodiments, the inorganic portion of the single crystal ceramic core composition comprises about 4 wt.% zircon and the organic portion of the single crystal ceramic core composition comprises about 13 wt.% surfactant, dye, and polymer fiber. [Brief explanation of the drawings]
[0023] [Figure 1] Figure 1 is a scanning electron microscope image of silica powder showing the distribution of needle-like glass fragments. [Figure 2] FIG. 2 is a photograph of a ceramic core component showing the stability of various silica core compositions. [Figure 3] FIG. 3 is a plot showing thermal expansion and sintering versus temperature for various silica core compositions. [Figure 4] FIG. 4 is a plot showing thermal expansion and sintering versus time for various silica core compositions. [Figure 5] FIG. 5 is a scanning electron microscope image of silica powder showing the distribution of spherical particles. [Figure 6] FIG. 6 is a plot showing the viscosity of various silica core compositions as a function of time. [Figure 7] FIG. 7 is another plot showing the viscosity of various silica core compositions as a function of time. DETAILED DESCRIPTION OF THE INVENTION
[0024] Embodiments of ceramic core compositions are described herein. As described in more detail below, the ceramic cores can be used to cast directionally solidified (DS) parts and / or single crystal (SX) parts. In some embodiments, ceramic cores having the compositions described herein can also be used to cast equiaxed castings. The ceramic core compositions described herein allow for thinner castings than were possible with previous core compositions and offer improved reproducibility compared to previous core compositions. Thus, the ceramic core compositions provide a means to produce parts with high reliability and consistency.
[0025] According to some embodiments of the present invention, single crystal (SX) ceramic core compositions comprise a mix of conventional fused silica and mineralizers, including, but not limited to, aluminum and sodium compounds such as aluminum stearate and sodium stearate. Binders, including waxes, dyes, surfactants, and other organic compounds may also be added to the mix to control various aspects of the mixture. The fused silica contains a distribution of needle-like fragments based on a standard grade of high-purity fused silica with a high aspect ratio, as shown in the scanning electron microscope image in FIG. 1. When combined with silica, the elemental alkali mineralizer helps eliminate the instability exhibited by previous ceramic core compositions.
[0026] In embodiments, the fused silica comprises about 80-90% by weight of the total weight of the core mix. Effective amounts of organic components, including binder materials, dyes, and surfactants, are provided. In total, the organic components comprise about 10-20% by weight of the total weight of the core mix.
[0027] Figure 2 shows the stability of prior art ceramic core compositions compared to the SX ceramic core compositions described herein. As shown in Figure 2, the core bodies made with the prior art core mix (i.e., the two core bodies at the back of the figure) exhibit significant instability at 2850°F, with the core bodies clearly deforming. The core bodies made with the SX core mix (i.e., the four core bodies at the front of the figure) exhibit better stability at high temperatures, with a deflection of less than 0.020" at 2850°F.
[0028] Figures 3 and 4 further demonstrate the improved performance of the SX core mix. Figure 3 shows the expansion-temperature curves of a prior art hybrid core mix and an SX core mix during dilatometry. In Figure 3, the lower dashed line represents the expansion-temperature curve of a typical prior art hybrid core mix. At approximately 2850°F, or the casting temperature of the ceramic mix, the hybrid core mix exhibits severe shrinkage of the material, indicating a high degree of instability. In comparison, the SX core mix, shown by the solid line in Figure 3, exhibits almost no shrinkage. Generally, the less shrinkage, the more stable the material is at high temperatures. Thus, Figure 3 shows that the SX core mix exhibits significantly greater stability compared to the hybrid core mix.
[0029] Figure 4 shows the expansion-temperature curves as a function of time for the prior art hybrid and SX core mixes, again showing that the SX core mix exhibits greater stability over time and at various temperatures compared to the hybrid core mix.
[0030] While the SX core mix offers a clear improvement over the stability of conventional core mixes, it has been found that the SX core mix has poor flowability and cannot be poured for small, precision parts. Therefore, a core mix that exhibits further improved flowability and pourability compared to the SX core mix, but also has the same improved stability as the SX core mix, was desired. Surprisingly, it has been found that the use of spherical fused silica, rather than conventional fused silica powder, enhances the flowability of ceramic materials while maintaining the mixture's stability at high temperatures.
[0031] According to embodiments of the present invention, as further described herein, another SX ceramic core composition comprises an effective amount of an inorganic mixture including spherical fused silica and an effective amount of a binder including various mineralizers. In embodiments, the inorganic mixture comprises about 80-90 wt% of the total weight of the ceramic core composition. In some embodiments, the inorganic mixture comprises about 83-87 wt% of the total weight of the ceramic core composition. In still further embodiments, the inorganic mixture comprises about 84-86 wt%, or about 85 wt% of the total weight of the ceramic core composition.
[0032] Silica constitutes about 90-99 wt% of the inorganic portion of the ceramic core composition (or about 76-84 wt% of the total weight of the SX ceramic core composition). In embodiments, silica forms about 94-98 wt% of the inorganic portion of the ceramic core composition (or about 80-83 wt% of the total weight of the composition), about 95-97 wt% of the inorganic portion of the ceramic core composition (or about 81-82 wt% of the total weight of the composition), or about 96 wt% of the inorganic portion of the ceramic core composition (or about 81.6 wt% of the total weight of the composition).
[0033] Figure 5 is a scanning electron microscope image showing spherical fused silica particles according to an embodiment of the present invention. Figure 5 shows that the spherical fused silica particles are provided in a variety of particle sizes. According to various embodiments of the present invention, the plurality of spherical fused silica particles present in the composition comprises particles ranging in size from about 0.58 microns to about 296 microns. According to some embodiments, the composition has the following particle size distribution, all reported as percentages by volume: Approximately 0-3% of the particles are less than 1.16 microns, approximately 0-1.5% of the particles are 1.16-1.64 microns, approximately 0-1.8% of the particles are 1.64-2.31 microns, approximately 1.4-2.4% of the particles are 2.31-3.27 microns, approximately 1.6-2.6% of the particles are 3.27-4.62 microns, approximately 2.0-3.0% of the particles are 4.62-6.54 microns, approximately 2.9-3.9% of the particles are 6.54-9.25 microns, approximately 4.4-5.4% of the particles are 9.25-13.08 microns, approximately 6.6-7.6% of the particles are 13.08-18.50 microns, and approximately 9.2-10. 2% of the particles are between 18.50 and 26.16 microns, about 12.7 to 13.7% of the particles are between 26.16 and 37.00 microns, about 16.9 to 17.9% of the particles are between 37.00 and 52.33 microns, about 16.7 to 17.7% of the particles are between 52.33 and 74.00 microns, about 9.6 to 10.6% of the particles are between 74.00 and 104.7 microns, about 3.9 to 4.9% of the particles are between 104.7 and 148.0 microns, about 1.4 to 2.4% of the particles are between 148.0 and 209.3 microns, about 1.4 to 2.4% of the particles are between 209.3 and 296.0 microns, and about 0 to 2% of the particles are greater than 296 microns.
[0034] In some embodiments, about 0-2.8% of the particles are less than 1.16 microns, about 0.3-1.2% of the particles are 1.16-1.64 microns, about 0.4-1.5% of the particles are 1.64-2.31 microns, about 1.7-2.1% of the particles are 2.31-3.27 microns, about 1.9-2.3% of the particles are 3.27-4.62 microns, about 2.3-2.7% of the particles are 4.62-6.54 microns, about 3.2-3.6% of the particles are 6.54-9.25 microns, about 4.7-5.1% of the particles are 9.25-13.08 microns, and about 6.9-7.3% of the particles are 13.08-18.50 microns. About 9.5-9.9% of the particles are between 18.50 and 26.16 microns, about 13.0-13.4% of the particles are between 26.16 and 37.00 microns, about 17.2-17.6% of the particles are between 37.00 and 52.33 microns, about 17.0-17.4% of the particles are between 52.33 and 74.00 microns, about 9.9-10.3% of the particles are between 74.00 and 104.7 microns, about 4.2-4.6% of the particles are between 104.7 and 148.0 microns, about 1.7-2.1% of the particles are between 148.0 and 209.3 microns, about 1.7-2.1% of the particles are between 209.3 and 296.0 microns, and about 0-1.5% of the particles are greater than 296 microns.
[0035] In still other embodiments, about 0-2.7% of the particles are less than 1.16 microns, about 0.9-1.1% of the particles are 1.16-1.64 microns, about 1.2-1.4% of the particles are 1.64-2.31 microns, about 1.8-2.0% of the particles are 2.31-3.27 microns, about 2.0-2.2% of the particles are 3.27-4.62 microns, about 2.4-2.6% of the particles are 4.62-6.54 microns, about 3.3-3.5% of the particles are 6.54-9.25 microns, about 4.8-5.0% of the particles are 9.25-13.08 microns, about 7.0-7.2% of the particles are 13.08-18.50 microns, and about 1.64-2.31 microns. 9.6-9.8% are between 18.50 and 26.16 microns, about 13.1-13.3% of the particles are between 26.16 and 37.00 microns, about 17.3-17.5% of the particles are between 37.00 and 52.33 microns, about 17.1-17.3% of the particles are between 52.33 and 74.00 microns, about 10.0-10.2% of the particles are between 74.00 and 104.7 microns, about 4.3-4.5% of the particles are between 104.7 and 148.0 microns, about 1.8-2.0% of the particles are between 148.0 and 209.3 microns, about 1.8-2.0% of the particles are between 209.3 and 296.0 microns, and about 0-1.3% of the particles are greater than 296 microns.
[0036] In still other embodiments, about 0% of the particles are less than 1.16 microns, about 1.0% of the particles are between 1.16 and 1.64 microns, about 1.3% of the particles are between 1.64 and 2.31 microns, about 1.9% of the particles are between 2.31 and 3.27 microns, about 2.1% of the particles are between 3.27 and 4.62 microns, about 2.5% of the particles are between 4.62 and 6.54 microns, about 3.4% of the particles are between 6.54 and 9.25 microns, about 4.9% of the particles are between 9.25 and 13.08 microns, and about 7.1% of the particles are between 13.08 and 18.50 microns. Approximately 9.7% of the particles are between 18.50 and 26.16 microns, approximately 13.2% of the particles are between 26.16 and 37.00 microns, approximately 17.4% of the particles are between 37.00 and 52.33 microns, approximately 17.2% of the particles are between 52.33 and 74.00 microns, approximately 10.1% of the particles are between 74.00 and 104.7 microns, approximately 4.4% of the particles are between 104.7 and 148.0 microns, approximately 1.9% of the particles are between 148.0 and 209.3 microns, approximately 1.9% of the particles are between 209.3 and 296.0 microns, and approximately 0% of the particles are greater than 296 microns.
[0037] According to yet another embodiment, about 0% of the particles are less than 1.16 microns, about 1% of the particles are between 1.16 and 1.64 microns, about 1% of the particles are between 1.64 and 2.31 microns, about 2% of the particles are between 2.31 and 3.27 microns, about 2% of the particles are between 3.27 and 4.62 microns, about 3% of the particles are between 4.62 and 6.54 microns, about 3% of the particles are between 6.54 and 9.25 microns, about 5% of the particles are between 9.25 and 13.08 microns, and about 7% of the particles are between 13.08 and 18.50 microns. , about 10% of the particles are between 18.50 and 26.16 microns, about 13% of the particles are between 26.16 and 37.00 microns, about 17% of the particles are between 37.00 and 52.33 microns, about 17% of the particles are between 52.33 and 74.00 microns, about 10% of the particles are between 74.00 and 104.7 microns, about 4% of the particles are between 104.7 and 148.0 microns, about 2% of the particles are between 148.0 and 209.3 microns, about 2% of the particles are between 209.3 and 296.0 microns, and about 0% of the particles are greater than 296 microns.
[0038] Spherical fused silica may include combinations of various forms of silica, for example, spherical fused silica may include an amount of fused silica, either alone or together with other forms of silica, such as cristobalite.
[0039] Silica is mixed with zircon in an amount ranging from about 1% to about 10% by weight of the inorganic portion of the ceramic core composition (or about 0.8% to 8% by weight of the total weight of the SX ceramic core composition). In embodiments, zircon is combined with silica in an amount ranging from about 2% to 6% by weight of the inorganic portion of the ceramic core composition (or about 1.7% to 5.1% by weight of the total weight of the SX ceramic core composition), or about 3% to 5% by weight of the inorganic portion of the ceramic core composition (or about 2.5% to 4.2% by weight of the total weight of the SX ceramic core composition). In yet other embodiments, zircon is present in the inorganic portion of the ceramic core composition in an amount equal to about 4% by weight of the inorganic portion of the ceramic core composition (or about 3.4% by weight of the total weight of the SX ceramic core composition).
[0040] The zircon may comprise a zircon powder, wherein the zircon particles comprising the powder are all substantially the same size. In some embodiments, the zircon powder may comprise a first portion of zircon particles having a size slightly larger than the size of a second portion of the zircon particles.
[0041] Moving forward, the binder (or organic portion) comprises approximately 15 wt. % of the total weight of the SX ceramic core composition. The binder comprises a binder material, a dye, one or more surfactants, and may also comprise fibers. Of the organic portion, the binder material comprises approximately 80-90 wt. % (or approximately 12-13.5% of the total weight of the SX ceramic core composition). In some embodiments, the binder material comprises approximately 82-89 wt. % of the organic portion (or approximately 12.3-13.3% of the total weight of the SX ceramic core composition), approximately 84-88 wt. % of the organic portion (or approximately 12.6-13.2% of the total weight of the SX ceramic core composition), approximately 85-87.5 wt. % of the organic portion (or approximately 12.75-13.1% of the total weight of the SX ceramic core composition), or approximately 86-87 wt. % of the organic portion (or approximately 12.9-13.05% of the total weight of the SX ceramic core composition). In a further embodiment, the binder comprises about 86.6% by weight of the organic portion (or about 13% of the total weight of the SX ceramic core composition). In an embodiment, the binder material is a thermoplastic material. The thermoplastic material may be, for example, a paraffin wax.
[0042] The organic portion of the SX ceramic core composition may further comprise a dye. The dye may comprise about 1-2 wt. % of the organic portion (or about 0.15-0.3% of the total weight of the SX ceramic core composition). In embodiments, the dye comprises about 1.2-1.6 wt. % of the organic portion (or about 0.18-0.24% of the total weight of the SX ceramic core composition). In yet further embodiments, the dye comprises about 1.4 wt. % of the organic portion (or about 0.22% of the total weight of the SX ceramic core composition).
[0043] In addition to the binder material and dye, the organic portion of the ceramic core composition may include one or more surfactants. The surfactant may aid in controlling the high-temperature stability of the fired ceramic material. According to embodiments of the present invention, the surfactant may include one or more stearates. Stearates may include, but are not limited to, sodium stearate and / or aluminum stearate. In some embodiments, the surfactant may include effective amounts of both sodium stearate and aluminum stearate. In further embodiments, the surfactant may additionally or alternatively include an effective amount of a fatty acid. The fatty acid may be, for example, palmitic acid, stearic acid, lauric acid, myristic acid, capric acid, linoleic acid, oleic acid, myristoleic acid, palmitoleic acid, arachidonic acid, erucic acid, or the like.
[0044] In combination, the surfactant comprises about 6-12 wt% of the organic portion (or about 0.9-1.8 wt% of the total weight of the SX ceramic core composition). In embodiments, the surfactant may comprise about 7-11 wt% of the organic portion (or about 1.1-1.7 wt% of the total weight of the SX ceramic core composition), or about 8-10 wt% of the organic portion (or about 1.2-1.5 wt% of the total weight of the SX ceramic core composition). According to further embodiments, the surfactant comprises about 9 wt% of the organic portion (or about 1.35 wt% of the total weight of the SX ceramic core composition).
[0045] According to some embodiments, the surfactant comprises sodium stearate, aluminum stearate, and / or oleic acid. In some embodiments, the sodium stearate comprises about 1-5 wt. % of the organic portion (or about 0.15-0.75 wt. % of the total weight of the SX ceramic core composition). In some embodiments, the sodium stearate may comprise about 2-4 wt. % of the organic portion (or about 0.6-0.6 wt. % of the total weight of the SX ceramic core composition). According to further embodiments, the sodium stearate may comprise about 3 wt. % of the organic portion (or about 0.45 wt. % of the total weight of the SX ceramic core composition).
[0046] In embodiments, aluminum stearate comprises about 0.5-4 wt. % of the organic portion (or about 0.01-0.6 wt. % of the total weight of the SX ceramic core composition), or about 1-3 wt. % of the organic portion (or about 0.15-0.45 wt. % of the total weight of the SX ceramic core composition). According to some embodiments, aluminum stearate may comprise about 2 wt. % of the organic portion (or about 0.3 wt. % of the total weight of the SX ceramic core composition).
[0047] Embodiments of the present invention may include oleic acid in an amount ranging from about 2-6 wt. % of the organic portion (or about 0.3-0.9 wt. % of the total weight of the SX ceramic core composition), or about 3-5 wt. % of the organic portion (or about 0.45-0.75 wt. % of the total weight of the SX ceramic core composition). In embodiments, oleic acid may comprise about 4 wt. % of the organic portion (or about 0.6 wt. % of the total weight of the SX ceramic core composition).
[0048] The binder may further comprise an effective amount of a polymeric material to further strengthen the final core product made with the SX ceramic core composition described herein. In embodiments, the polymeric material may be, for example, polyamide nylon, polyester, modal, bamboo fiber, rayon fiber, diacetate fiber, and / or triacetate fiber.
[0049] Embodiments of the present invention may include the polymeric material in an amount ranging from about 1 to 5 weight percent of the organic portion (or about 0.15 to 0.75 weight percent of the total weight of the SX ceramic core composition), or about 2 to 4 weight percent of the organic portion (or about 0.3 to 0.6 weight percent of the total weight of the SX ceramic core composition). In embodiments, the polymeric material may comprise about 3 weight percent of the organic portion (or about 0.45 weight percent of the total weight of the SX ceramic core composition).
[0050] Core components fabricated using the SX ceramic core compositions containing spherical fused silica described herein were tested to determine the strength and flow characteristics of the compositions. Figure 6 shows that the viscosity of the SX ceramic core compositions containing spherical fused silica remained relatively constant over time, indicating that the compositions were relatively stable. In contrast, previous core compositions (i.e., the upper group of lines in Figure 6) showed a significant decrease in viscosity over time until glass shards (in compositions containing needle-shaped glass fragments) became aligned with the direction of fluid movement. Furthermore, Figure 6 also shows that the viscosity of the SX ceramic core compositions containing spherical fused silica was significantly lower than that of the other core compositions. The lower viscosity of the SX ceramic core compositions containing spherical fused silica indicates significantly improved flow characteristics compared to the other core compositions.
[0051] Figure 7 is another graph showing the viscosity of spherical fused silica core compositions compared to previous compositions. In Figure 7, the lower line represents the viscosity of the SX ceramic core composition containing spherical fused silica, and the upper line represents the conventional core mix. It can be seen that at an injection temperature of about 150°F, the conventional mix exhibits a higher viscosity than the core mix described herein. Again, the lower viscosity of the SX ceramic core composition containing spherical fused silica indicates significantly improved flow characteristics compared to other core compositions, particularly at injection temperatures.
[0052] It has been discovered that, due at least in part to the improved flow characteristics of the spherical fused silica core composition, the composition can be used to form ceramic cores that are significantly thinner than possible with previously available core mixes. According to one embodiment, it may be possible to produce cores having thicknesses of about 0.012", a feature that has previously been extremely difficult, if not impossible, to achieve. Importantly, the lower viscosity of the spherical fused silica core composition does not preclude the ability to produce large components. For example, cores having trailing edge features of greater than 20" in length and about 0.040" in thickness have been successfully injection molded and cast using the spherical fused silica core composition described herein. Thus, the core compositions of the present invention can be used to form cores of a wide variety of sizes and shapes.
[0053] It is well known that ceramic materials shrink when heated at a certain rate, known as the shrinkage factor. The shrinkage factor is specific to each material composition, and knowing the shrinkage factor of that material composition, specifically the ceramic core mix, is necessary to ensure that the final ceramic core is the correct size. If the shrinkage factor is known, the mold into which the ceramic core mix is poured can be oversized to account for the shrinkage factor so that when the ceramic core mix is fired (which will inevitably shrink), the final ceramic core removed from the mold will be the desired size. Interestingly, the inventive ceramic core mixes described herein are unique in that the particle size distribution of the silica in the mix can be slightly modified to increase or decrease the shrinkage factor as needed. This can be particularly useful when tooling is developed for compositions with shrinkage factors greater (or less) than is typical for the spherical fused silica SX ceramic core compositions described herein.
[0054] Many different arrangements of the various components shown, and even components not shown, are possible without departing from the spirit and scope of the present disclosure. The embodiments of the present disclosure have been described with the intention of being illustrative and not limiting. Alternative embodiments that do not depart from its scope will become apparent to those skilled in the art. Those skilled in the art will develop alternative means of implementing the improvements described above without departing from the scope of the present disclosure. It is understood that certain features and subcombinations are useful and may be employed without reference to other features and subcombinations and are contemplated to be within the scope of the present disclosure. All steps listed in the various figures need not be performed in the specific order described. The specification should not be limited to the specifically described embodiments.
Claims
1. A single-crystal ceramic core composition, The inorganic portion comprising approximately 85% by weight of the total weight of the ceramic core composition, Approximately 94-98% by weight of spherical fused silica, and Approximately 2-6% by weight of zircon, The inorganic part, The organic portion comprising approximately 15% by weight of the total weight of the ceramic core composition, Binders of approximately 84-88% by weight, Approximately 1-2% by weight of dye, Approximately 6-12% by weight of surfactant, and Approximately 1-5% by weight of polymer fibers, The organic part includes, A single-crystal ceramic core composition containing [the specified element].
2. The inorganic portion of the ceramic core composition is 95-97% by weight of spherical fused silica, and 3-5% by weight of zircon, Includes, The organic portion of the ceramic core composition is Binder with 86-87% weight, 1.2 to 1.6% by weight of dye, 8-10% by weight of surfactant, and 2-4% by weight of polymer fibers, A ceramic core composition according to claim 1, comprising:
3. The spherical fused silica is as follows: Table 1 The ceramic core composition according to claim 2, comprising a plurality of particles having a particle size distribution.
4. The spherical fused silica is as follows: Table 2 The ceramic core composition according to claim 1, comprising a plurality of particles having a particle size distribution.
5. The ceramic core composition according to claim 4, wherein the binder is a thermoplastic material.
6. The ceramic core composition according to claim 5, wherein the thermoplastic material is a paraffinic wax.
7. The ceramic core composition according to claim 5, wherein the surfactant comprises sodium stearate, aluminum stearate, and oleic acid.
8. The ceramic core composition according to claim 7, wherein the polymer fibers include rayon fibers.
9. The spherical fused silica is as follows: Table 3 The ceramic core composition according to claim 1, comprising a plurality of particles having a particle size distribution.
10. The spherical fused silica is as follows: Table 4 The ceramic core composition according to claim 1, comprising a plurality of particles having a particle size distribution.
11. A single-crystal ceramic core composition, The inorganic portion comprising approximately 85% by weight of the total weight of the ceramic core composition, Approximately 94-98% by weight of spherical fused silica, and Approximately 2-6% by weight of zircon, The inorganic part, The organic portion comprising approximately 15% by weight of the total weight of the ceramic core composition, A binder of approximately 84-88% by weight, and Approximately 12-16% by weight of surfactants and dyes, The organic part includes, A single-crystal ceramic core composition containing [the specified element].
12. The ceramic core composition according to claim 11, wherein the surfactant constitutes 6 to 12% by weight of the organic portion.
13. The ceramic core composition according to claim 12, wherein the binder is a paraffinic wax.
14. The ceramic core composition according to claim 11, wherein the spherical fused silica constitutes 96% by weight of the inorganic portion, and the remainder of the weight of the inorganic portion is zircon.
15. The ceramic core composition according to claim 14, wherein the binder constitutes 86.5% by weight of the organic portion, and the remainder of the weight of the organic portion is a surfactant and a dye.
16. The ceramic core composition according to claim 11, wherein the surfactant comprises sodium stearate, aluminum stearate, and a fatty acid.
17. The spherical fused silica is as follows: Table 5 The ceramic core composition according to claim 11, comprising a plurality of particles having a particle size distribution.