Casting method and cast product

Abstract

[Problem] To provide a simple, quick, and low-cost casting method, with which a hole with a large aspect ratio and a bent hole can be easily produced, and which requires no large drawing force and enables compact equipment, and a casting obtained by such a casting method. [Solution] Ceramic fiber is impregnated with a binder and a resultant is solidified into a predetermined shape to prepare in advance a casting mold or core 3, which has shape retention. A molten material including a molten metal, semiconductor, or polymeric material is supplied to an inside of a mold in which the casting mold or core is provided, to form a solidified body 6 formed of the molten material. Subsequently, a binder dissolution solution 7 in which the binder is dissolved is allowed to permeate the casting mold or core 3, to soften the casting mold or core, and the casting mold or core 3, which has been softened, is separated from the solidified body 6 to obtain a casting 8 including the solidified body.

Description

TECHNICAL FIELD

[0001] The present invention relates to a casting method and a casting, for porous castings of metals, polymeric materials, or semiconductor materials, which can be effectively utilized as novel materials in various fields such as heat sinks, heat pipes, heat exchangers, aircraft engines, medical devices, machine tools, thermoelectric conversion materials, vibration damping materials, sound-absorbing materials, and shock-absorbing materials.BACKGROUND ART

[0002] Conventional techniques of perforating metals and other materials include methods of: (1) forming linear pores through solidification of a molten metal; (2) removing foreign metal wires embedded in metal and the like by chemical polishing; (3) mechanical perforation using drills; and (4) perforation by localized dissolution using lasers or electron beams. However, all of these methods involve complex processing, require a long time for the perforation, and incur high manufacturing costs.

[0003] In view of the above, heat-resistant metal wires each used as the core in a hole are drawn from solidified metal to produce a porous casting (see Patent Literature 1). However, the drawing of the heat-resistant metal wires requires a dedicated tensile testing machine. When the drawing is performed using a jig resembling a needle-point holder with numerous heat-resistant metal wires arranged, a large drawing force is required, necessitating the use of a larger testing machine. There has been also a problem that metal wires break in the middle when thin holes with a large aspect ratio (ratio of length to a diameter of the hole) or holes with complex shapes are formed. Furthermore, resistance during the drawing could damage the holes.CITATION LISTPATENT LITERATURE

[0004] [PTL 1] International Patent Application Publication No. WO2020 / 246588SUMMARY OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTION

[0005] In view of the aforementioned situation, a purpose of the present invention is to provide: a simple, quick, and low-cost casting method, with which a hole with a large aspect ratio, a bent hole, and a hole with a complex shape can be easily produced, and which requires no large drawing force, causes no damage to the holes, and enables compact equipment; and a casting obtained by such a casting method.SOLUTION TO THE PROBLEMS

[0006] In light of the situation, the inventor found the following after thorough examination. Specifically, ceramic fiber is solidified with a binder to form a casting mold or core, and then the binder is dissolved after the solidification of materials, to allow the casting mold or core made of the ceramic fiber to be softened. The softened casting mold or core could be easily and reliably removed without damaging the holes, even when holes with a large aspect ratio or complex shapes are formed. Thus, the present invention has been completed.

[0007] The present invention encompasses the following inventions. (1) A casting method including: impregnating ceramic fiber with a binder and solidifying a resultant into a predetermined shape to prepare a casting mold or core, which has shape retention; supplying a molten material including a molten metal, a molten semiconductor, or a molten polymeric material to an inside of a mold in which the casting mold or core is provided, and forming a solidified body formed of the molten material; subsequently allowing a binder dissolution solution in which the binder is dissolved to permeate the casting mold or core, to soften the casting mold or core; and separating the casting mold or core, which has been softened, from the solidified body to obtain a casting including the solidified body. (2) The casting method described in (1) above, in which the ceramic fiber includes a ceramic fiber sheet, ceramic fiber bulk (cotton-like) material, ceramic fiber sewing thread (twisted yarn), ceramic fiber rope, ceramic fiber cord (solid wire material), or ceramic fiber sleeve (cylindrical hollow body). For the ceramic fiber sheet, ceramic fiber cloth, ceramic fiber tape, ceramic fiber nonwoven fabric (felt), ceramic fiber paper, and ceramic fiber knit are preferable. Furthermore, for the ceramic fiber bulk (cotton-like) material, ceramic fiber chopped fiber (short fiber body) is preferable. (3) The casting method according to (1), in which the casting mold or core includes a convex portion formed by solidifying the ceramic fiber into a convex shape, thereby forming a concave hole or a concave groove in the solidified body, the concave hole or the concave groove having a shape formed by transferring a shape of the convex portion. For example, the convex portion may be a rod-shaped or plate-shaped portion formed by solidifying the ceramic fiber into a rod-like or plate-like shape, and the concave hole or groove may be rod-shaped or plate-shaped holes formed by transferring shapes of the rod-shaped or plate-shaped portion. (4) The casting method according to (3), in which the ceramic fiber is a ceramic fiber sheet, and the ceramic fiber sheet is solidified, using the binder, into the rod-shape or plate-shape by rolling or folding the sheet, or stacking multiple sheets. (5) The casting method according to (3), in which the ceramic fiber is a ceramic fiber bulk material, and a ceramic fiber slurry using the binder as a solvent is applied to a rod-shaped or plate-shaped core material made of a heat-resistant rigid material, and the resultant is solidified into the rod-shape or plate-shape. (6) The casting method according to (5), in which fiber length of the ceramic fiber constituting the ceramic fiber bulk material is 100 µm or less, more preferably 50 µm or less, and further preferably 35 µm or less. (7) The casting method according to (1) in which the casting mold or core is subjected to machining after the ceramic fiber is solidified, to form one or more concave holes or grooves in the casting mold or core, thereby forming one or more convex portions in the solidified body, the one or more convex portions having a shape formed by transferring a shape of the one or more holes or grooves. For example, the concave holes or concave grooves include holes or wide grooves, while the convex portions include one or more rod-shaped or plate-shaped bodies formed by transferring shapes of the holes or wide grooves. (8) The casting method according to (1), in which the binder is a water-soluble binder, and the binder dissolution solution is water. (9) The casting method according to (7), in which the binder is polyvinyl alcohol, an alumina dispersion, a silica dispersion, a heat-resistant adhesive, or a combination thereof. (10) The casting method according to (1), in which the casting mold or core impregnated with the binder dissolution solution is pushed by a pressurized fluid consisting of the binder dissolution solution or air, to separate the casting mold or core from the solidified body. (11) A casting obtained by the casting method according to any one of (1) to (10). ADVANTAGEOUS EFFECTS OF THE INVENTION

[0008] According to the present invention above, a simple, quick, and low-cost casting method is provided with which a hole with a large aspect ratio, a bent hole, and a hole with a complex shape including a surface undulation can be easily produced, and which requires no large drawing force, causes no damage to the holes, and enables compact equipment.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [FIG. 1] FIG. 1 includes explanatory diagrams showing processes of a casting method according to a representative embodiment of the present invention. [FIG. 2] FIG. 2 includes explanatory diagrams showing processes following those shown in FIG. 1. [FIG. 3] FIG. 3 includes explanatory diagrams showing processes following those shown in FIG. 2. [FIG. 4] FIGS. 4A and 4B are both explanatory diagrams showing modified examples of the casting method. [FIG. 5] FIG. 5 includes explanatory diagrams showing processes of another modified example of the casting method. [FIG. 6] FIG. 6 includes explanatory diagrams showing processes of still another modified example of the casting method. [FIG. 7] FIG. 7 includes exemplary diagrams illustrating processes following those shown in FIG. 6. [FIG. 8] FIG. 8 includes exemplary diagrams showing a modified example of a casting mold or core. [FIG. 9] FIG. 9 includes explanatory diagrams showing another modified example of the casting mold or core. [FIG. 10] FIG. 10 includes explanatory diagrams showing still another modified example of the casting mold or core. [FIG. 11] FIG. 11 includes explanatory diagrams showing still another modified example of the casting mold or core. [FIG. 12] FIG. 12 shows an example of a vacuum suction device. [FIG. 13] FIG. 13 includes photographs of prototyped rod-shaped body and casting. [FIG. 14] FIG. 14 includes photographs of prototyped rod-shaped body and casting. [FIG. 15] FIG. 15 shows a photograph of a prototyped casting. [FIG. 16] FIG. 16A shows a photograph of a casting mold or core used for prototyping, while FIGS. 16B and 16C show photographs of prototyped castings. [FIG. 17] FIG. 17 shows photographs of a prototyped casting: the top image shows a casting before removing a casting mold or core, while the bottom image shows a casting after removal. [FIG. 18] FIG. 18 shows a photograph of a prototyped casting. [FIG. 19] FIG. 19 shows a photograph of a prototyped casting. [FIG. 20] FIG. 20 is an explanatory diagram showing processes of forming a rod-shaped body using a ceramic fiber cord. [FIG. 21] FIGS. 21A to 21D are explanatory diagrams showing ceramic fiber cords (solid wire materials) with different cross-sectional shapes. [FIG. 22] FIG. 22 is an explanatory diagram showing processes of forming a cylindrical body using the ceramic fiber cord. [FIG. 23] FIG. 23 includes explanatory diagrams showing processes of forming the rod-shaped bodies by respectively attaching ceramic fiber sleeves (cylindrical hollow bodies) to core materials. [FIG. 24] FIG. 24 includes photographs showing silica fiber sheets and alumina fiber sheets. Respective sheets include a sheet impregnated and solidified with polyvinyl alcohol (PVA) alone, and a sheet impregnated and solidified with PVA mixed with added alumina powder. DESCRIPTION OF EMBODIMENTS

[0010] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0011] In a casting method according to the present invention, a casting mold or core 3 having shape retention is formed in advance by impregnating a ceramic fiber 1 with a binder 110 and solidifying the resultant into a predetermined shape (a rod shape, in the present example), as shown in FIGS. 1A and 1B. The ceramic fiber 1 is a refractory insulation fiber that excels in high-temperature resistance among man-made mineral fibers composed primarily of alumina and silica, and is typically represented by amorphous ceramic fibers and crystalline alumina fibers.

[0012] For the ceramic fiber 1, a ceramic fiber sheet provides superior workability at formation of the casting mold or core 3. Furthermore, the ceramic fiber sheet is preferable in easy separation from the casting mold or core 3 at removal from a solidified body and in easy cleaning of the casting 8 after the removal, because the ceramic fiber sheet retains its sheet form even after being softened by a binder dissolution solution described later. It is also preferable that the ceramic fiber 1 is a ceramic fiber bulk material. A ceramic fiber slurry, in which the bulk material is dispersed in a binder, is applied to a core material (reinforcing structure) made of a heat-resistant rigid material, dried and solidified, to form the casting mold or core 3. This allows the core material (reinforcing structure) constituting the casting mold or core 3 to be easily separated at the removal from the solidified body.

[0013] Furthermore, the ceramic fiber 1, particularly crystalline alumina fiber, is available in various forms such as ceramic fiber cloth, ceramic fiber tape, ceramic fiber sewing thread (twisted yarn), ceramic fiber rope, ceramic fiber cord (solid wire material), ceramic fiber sleeve (cylindrical hollow body), ceramic fiber chopped fiber (short fiber body), ceramic fiber nonwoven fabric (felt), ceramic fiber paper, ceramic fiber knit, and other various forms. These various forms of the ceramic fiber 1 can be deformed or left in their original state, then impregnated with a binder in the same manner to be efficiently solidified into a predetermined shape, thereby forming the casting mold or core 3.

[0014] As the binder 110, it is preferable to use polyvinyl alcohol, an alumina dispersion solution, a silica dispersion solution, a heat-resistant adhesive, or a combination of them. Impregnation of the binder 110 into the ceramic fiber 1 can be achieved through spraying, dipping, or various other methods.

[0015] The casting mold or core 3 in the present example is provided with, as convex portions 310, a plurality of rod-shaped portions 31 each formed by solidifying the ceramic fiber 1 into a rod-like shape. The target casting 8 described later will have a plurality of rod-shaped holes 80 (concave holes) formed by transferring shapes of the rod-shaped portions 31 (convex portions 310). Each rod-shaped portion 31 can be easily formed by preparing a rod-shaped body 11 in processes of using a ceramic fiber sheet as the ceramic fiber 1, impregnating the ceramic fiber sheet with the binder 110, and then rolling or folding the sheet, or stacking multiple sheets to be bonded and solidified into a rod-shaped form, as shown in FIG. 1A.

[0016] In the example of FIG. 1A, the ceramic fiber sheet is used as the ceramic fiber 1. The ceramic fiber sheet is impregnated with the binder 110, rolled into a rod shape, and solidified to form the rod-shaped body 11. Here, a ceramic fiber cord (solid wire material) can be used as the ceramic fiber 1, and is simply impregnated with the binder 110 and solidified to thereby more easily prepare the rod-shaped body 11, as shown in FIG. 20. A plurality of ceramic fiber cords (solid wire material) can be twisted together to form a single cord for use.

[0017] At solidification, dimensional accuracy can be maintained by placing the material in a predetermined mold. Furthermore, during the solidification, it is preferable to apply pressure simultaneously with drying of the binder 110, thereby forming the solid casting mold or core 3 that conforms with design dimensions. In the present example, after preparation of such multiple rod-shaped bodies 11, a base 32 is molded using, for example, heat-resistant thermoplastic resin 320, cast iron, heat-resistant alloy steel, graphite, or refractory ceramics, as shown in FIG. 1B, thereby forming the casting mold or core 3 including a plurality of rod-shaped portions 31 as the convex portions 310, which are integrally connected to the base 32 serving as a proximal end portion of the casting mold or core 3, as shown in FIG. 1C.

[0018] Next, as shown in FIGS. 2A and 2B, a molten material 600, such as a molten metal (e.g., aluminum alloy), a semiconductor, or a polymeric material, is supplied (injected) into a mold 4 (crucible) with the casting mold or core 3 arranged as a template, and solidified, thereby forming a solidified body 6 formed from the molten material and integrated with the casting mold or core 3. The mold 4 illustrated is made of heat-resistant thermoplastic resin, cast iron, heat-resistant alloy steel, graphite, or refractory ceramics. The mold 4 includes a combination of a plate mold 40 that has a plate-like shape and forms a bottom surface of a casting and supports the casting mold or core 3 on its upper surface, and an outer mold 41 that has a container-like shape, houses the casting mold or core 3 and forms an outer peripheral surface of the casting.

[0019] Various materials can be used as the "metal" or the "semiconductor material" for the molten material 600, including: aluminum, copper, magnesium, iron, cobalt, nickel, manganese, beryllium, chromium, zinc, titanium, zirconium, vanadium, niobium, molybdenum, palladium, silver, gold, cadmium, indium, tin, platinum, hafnium, tungsten, tantalum, lead, bismuth, and alloys thereof; silicon, germanium, and compounds thereof; and various other metals or semiconductor materials. Additionally, various thermoplastic synthetic resins and thermosetting synthetic resins can be used as a "polymeric material". It is preferable that the molten metal, molten semiconductor, or molten polymeric material in the molten material 600 is degassed prior to the supply, in order to control the generation of excess gas bubbles. For example, in the case of an aluminum alloy, argon bubbles can be generated in the aluminum alloy in a molten state through a nozzle, to thereby perform the degassing processing.

[0020] Next, as shown in FIGS. 3A and 3B, a binder dissolution solution 7, in which the binder 110 is dissolved, permeates the casting mold or core 3, to thereby soften the casting mold or core 3. For the binder dissolution solution 7, water can be used when the binder 110 is a water-soluble binder, such as polyvinyl alcohol. The permeation of the binder dissolution solution 7 into the casting mold or core 3 may be achieved by spraying or other methods in addition to the immersion.

[0021] The ceramic fiber constituting the casting mold or core 3 integrated with the solidified body 6 are preferably exposed on a surface of the solidified body 6. When the solidified body 6 integrated with the casting mold or core 3 is immersed in the binder dissolution solution 7, the above configuration enables the binder dissolution solution to permeate the exposed ceramic fiber on the surface of the solidified body 6 and soften the casting mold or core 3. If the ceramic fiber is not exposed, the solidified body should be cut to form a groove or a hole should be drilled, until the ceramic fiber is exposed, and then the binder dissolution solution 7 is supplied. In the present example, a tip of the rod-shaped portion is exposed on the surface, and the binder dissolution solution 7 permeates from the tip.

[0022] Then, as shown in FIGS. 3C and 3D, the casting mold or core 3 softened by the permeation of the binder dissolution solution 7 is separated from the solidified body 6, thereby obtaining the casting 8 made of the solidified body. The solidified body (casting 8) is provided with rod-shaped holes 80 (concave holes) formed by transferring shapes of the rod-shaped portions 31 of the casting mold or core 3.

[0023] The casting mold or core 3 may be drawn from the solidified body 6 as shown in FIG. 3C, or a fluid (e.g., liquid or air) may be supplied under pressure from a distal end side opposite the base 32 in the casting mold or core 3 as shown in FIG. 4A, thereby pushing the casting mold or core 3 toward a proximal end side of the casting mold or core 3 from each of the holes 80 in the solidified body 6. Here, if the binder dissolution solution 7 is used as the supplied fluid, it is also preferable to omit the pre-permeation process and instead soften the casting mold or core 3 through the pressurized supply of the fluid while the casting mold or core 3 is simultaneously pushed out. In this case, the base 32 should be removed first. If the base 32 is also composed of the ceramic fiber and the binder, the casting mold or core 3 will be pushed out while fiber fragments scatter, as shown in FIG. 4B, and will be rendered unrecognizable after removal.

[0024] In the present example, each of the rod-shaped portions 31 of the casting mold or core 3 has the distal end protruding as a free end, like a pin, from the base 32 at the proximal end. However, as shown in FIG. 8A, it is also preferable to provide a plate-shaped connecting portion 34 that connects the distal ends of the respective rod-shaped portions 31 in the distal end, similarly to the base 32. With such a configuration, each rod-shaped portion 31 is held in a stable state in which both ends of the rod-shaped portion 31 are bridged and supported between the base 32 and the connecting plate portion 34 in the mold 4, as shown in FIG. 8, thereby preventing the rod-shaped portions 31 from bending under pressure of the flowing molten material 600 and causing the holes to have a shape deviated from a designed shape when the molten material 600 is injected. Accordingly, a casting with high precision can be obtained.

[0025] In this case, the removal of the casting mold or core 3 can be easily performed by first removing the connecting plate portion 34 impregnated with the binder dissolution solution, and then drawing the remaining portion impregnated with the binder dissolution solution from the base 32 side, as in the above example.

[0026] Alternatively, as shown in FIGS. 9B and 10B, it is also preferable to provide a core material 35 having relatively high bending strength in a core portion of the rod-shaped portion 31 serving as the convex portion 310. Specifically, as shown in FIG. 9A, the base body 30 of the casting mold or core, in which the core material 35 protrudes from the base 32, is composed of a heat-resistant rigid material such as heat-resistant thermoplastic resin, cast iron, heat-resistant alloy steel, graphite, or refractory ceramics. A sheet of the ceramic fiber 1 is then wrapped around the core material 35 and solidified with the binder 110. In addition, as shown in FIGS. 10A and 10B, the core material 35 can be coated with a ceramic fiber slurry 111 in which ceramic fiber bulk material is dispersed in the binder, and the resultant is dried and solidified. In the example of FIG. 9, it is preferable to apply the binder 110 to the core material 35 before the sheet is wrapped around. Furthermore, as another example, a ceramic fiber sleeve (cylindrical hollow body) having an inner diameter corresponding to an outer diameter of the core material 35 can be used as the ceramic fiber 1, as shown in FIG. 23. The sleeve is fitted to the core material 35 and is solidified with the binder 110, thereby performing the process with improved workability.

[0027] The above items can also be removed by softening a sheath layer 12 composed of the ceramic fiber surrounding the core material 35 with the binder dissolution solution, thereby allowing the rod-shaped portions 31 to be easily drawn from the solidified body. Furthermore, even with a cantilevered protruding shape, reinforcement by the core material 35 ensures that the shape of the rod-shaped portions 31 remains stable without bending deformation under the pressure of the flowing molten material 600, enabling the production of a casting with holes maintaining their designed shapes. Furthermore, when forming a casting with a bent hole formed using a bent rod-shaped portion 31, for example, the method is preferable since the bent rod-shaped portion 31 can be easily formed by wrapping a sheet of the ceramic fiber 1 around a bent core material 35, applying a ceramic fiber slurry in which the ceramic fiber bulk material is dispersed in the binder to the bent core material 35, or fitting the ceramic fiber sleeve (cylindrical hollow body) to the bent core material 35.

[0028] As described with reference to FIG. 10, etc., the ceramic fiber slurry in which the ceramic fiber bulk material is dispersed in the binder is applied to the core material 35, and thus a thin rod-shaped portion 31 with a diameter of 10 mm or less is formed. When a corresponding thin hole is formed, it is preferable to use ceramic fiber chopped fiber (short fiber) as the ceramic fiber bulk material. In this case, length of the fiber is preferably 100 µm or less, more preferably 50 µm or less, and further preferably 35 µm or less. When the fiber exceeds 100 µm in length, it becomes difficult to apply the ceramic fiber slurry to a surface of the thin core material 35 with uniform thickness. As a result, irregularities tend to form on the outer surface of the rod-shaped portion 31, and the molded hole also tends to have an irregular shape in its inner surface.

[0029] FIG. 13A is a photograph of the rod-shaped portion 31 formed by coating and solidifying a ceramic fiber slurry composed of ceramic fiber bulk material (ceramic fiber chopped fiber (short fiber)) with an average fiber length of approximately 20 mm onto a surface of a metal wire having a diameter of 1.0 mm. FIG. 13B is a photograph of holes in a casting formed using the obtained rod-shaped portions 31. FIG. 14A is a photograph of the rod-shaped portion 31 formed by coating and solidifying a ceramic fiber slurry composed of bulk material further pulverized with a mortar and pestle to obtain a fiber length of 30 µm or less onto the surface of the same metal wire having the diameter of 1.0 mm. FIG. 14B shows a photograph of holes formed in a casting using the obtained rod-shaped portions 31. It was confirmed that shortening the fiber length eliminates surface irregularities on each rod-shaped portion 31, resulting in the formation of clean circular holes.

[0030] Instead of, or in addition to the reinforcement by the core material 35 as described above, it is also preferable to improve strength of the rod-shaped portion 31 by adding and mixing ceramic powder to the binder, and then applying and solidifying the mixture onto the ceramic fiber. FIG. 24 shows photographs of silica fiber sheets (manufactured by SAKAGUCHI ELECTRIC HEATERS CO., LTD.) (the upper side of the chart) and alumina fiber sheets (manufactured by NITIVY CO., LTD.) (the lower side of the chart), which were prepared as ceramic fibers. The respective photographs show that each of the silica fiber sheet and the alumina fiber sheet was impregnated solely with a binder (polyvinyl alcohol (PVA)) and then solidified (left side of the chart), and each of them was impregnated and solidified with a binder mixed with alumina powder (right side of the chart). The results of hardness measurements performed on these four samples using a durometer (rubber hardness tester) (Type A conforming to JIS K 6253) are shown in Table 1 below. [Table 1]Ceramic fiberBinderPoint of durometerIncrease rate due to addition (%)Silica fiberOnly PVA48.2 ± 2.7Alumina powder added to PVA79.1 ± 1.664.1Alumina fiberOnly PVA95.9 ± 1.0Alumina powder added to PVA97.4 ± 1.01.6

[0031] The alumina fiber showed a slight increase in hardness of 1.6%, whereas the silica fiber exhibited a significant effect, with increase in hardness of 64.1% due to the addition of the ceramic powder. The alumina fiber inherently possesses superior tensile and bending strength compared to the silica fiber. Therefore, it was found that adding the ceramic powder enhances the strength of the silica fiber, in particular. The principle behind the increased strength is that infiltration of the ceramic powder into voids in the fiber leads to the reinforcement.

[0032] Although the above embodiments have described examples where the rod-shaped portions 31 are provided on the casting mold or core 3 to form the rod-shaped holes 80 in the solidified body 6 (casting 8), the present invention is not limited to providing such rod-shaped holes 80. For example, as shown in FIGS. 5A to 5C, the plate-shaped portions 31A formed by solidifying the ceramic fiber into a plate shape can be provided in the casting mold or core 3. With this casting mold or core 3, the solidified body 6 (casting 8) having the plate-shaped holes 80A each having a shape transferred by an outer shape of the plate-shaped portions 31A, as shown in FIG. 5E. The photograph in FIG. 15 shows a prototyped casting actually produced using the casting shown in FIG. 5E. Thickness of each plate portion 31A of the casting mold or core 3 was set to 1.0 mm, and thickness of each hole 80A in the produced casting was 1.0 mm.

[0033] Here, the plate-shaped portions 31A of the casting mold or core 3 can be formed by: stacking multiple ceramic fiber sheets and solidifying them with a binder to create plate-like bodies 11A, as shown in FIG. 5A; preparing multiple such plate-like bodies 11A; and molding the base 32 using a heat-resistant thermoplastic resin 320, as shown in FIG. 5B. In the present example as well, similar to the example shown in FIG. 9 above, it is also preferable to provide a core material having a relatively high bending strength, such as a thin stainless steel foil (e.g., 0.1 mm thick), in the core portion of each of the plate-shaped portions 31A to thereby enhance the bending strength for the reinforcement. As shown in FIG. 11, another preferred example involves sandwiching multiple metal wires 5 as the core material between sheets of the ceramic fiber 1 and solidifying the resultant with the binder 110. FIG. 16 includes photographs showing a prototyped casting actually produced using the casting mold or core shown in FIG. 11. The prototyped casting was manufactured by using the casting mold or core that was prepared by sandwiching stainless steel wires each having a diameter of 0.8 mm φ between two ceramic fiber sheets each having a thickness of 1 mm and solidifying the resultant with a polyvinyl alcohol binder.

[0034] Here, a plate-shaped ceramic fiber cord (solid wire material) is used as the ceramic fiber 1, for example, as shown in FIG. 21A, thereby more easily forming the plate-shaped body 11A simply by impregnating the cord with the binder 110 and solidifying the resultant.

[0035] The above embodiments have described examples where the rod-shaped or plate-shaped holes 80 (80A) are formed for the casting 8. Here, it is also possible to provide concave holes or grooves having shapes transferred by outer shapes of a box-shaped body, partially spherical body, cylindrical body, or a body having another shape, in addition to rod-shaped or plate-shaped bodies, as the convex portions 310. Furthermore, the cross-sectional shape of the convex portion can also be varied to suit a desired shape of the target concave hole or groove. It is difficult to form cross-sectional shapes such as squares, triangles, or irregular shapes, for example, by winding ceramic fiber sheets as the ceramic fiber 1. However, as shown in FIGS. 21B to 21D, a ceramic fiber cord (solid wire material) having the desired cross-sectional shape is used as the ceramic fiber 1, thereby easily forming the rod-shaped body 11 having such cross-sectional shapes. As shown in FIG. 22, a cylindrical ceramic fiber sleeve (cylindrical hollow body) is used as the ceramic fiber 1, thereby providing a hole with the convex protrusion at its center.

[0036] Furthermore, as shown in FIG. 7, machining is performed on the casting mold or core 3 after the ceramic fiber is solidified, to provide one or more concave holes 33 or grooves. With such a casting mold or core 3, a casting 8B having protrusions 81, such as rod-shaped or plate-shaped protrusions as a single or multiple convex portions 810 with outer shapes transferred by shapes of the holes 33 or grooves, can be formed as shown in FIG. 7E.

[0037] Such a casting is formed by first stacking multiple ceramic fiber sheets 1 and bonding / solidifying the stacked sheets with the binder 110 to create a three-dimensional base body 11C for a base of the casting mold or core 3, as shown in FIGS. 6A and 6B. The holes 33 or wide grooves are then formed in this base body through machining or another process. The holes 33 or wide grooves may have penetrating forms or non-penetrating forms (with a bottom).

[0038] Next, as shown in FIGS. 7A and 7B, the molten material 600, such as molten metals (e.g., aluminum alloy), semiconductors, or polymeric material, is supplied (injected) into the mold 4 (crucible) set up with the casting mold or core 3 as a template, and then solidified to form a solidified body 6B made of the molten material integrated with the casting mold or core 3. The mold 4 in the present example includes: a first outer mold 42, which has a container shape, houses the casting mold or core 3, and forms an outer peripheral surface of the casting; and a second outer mold 43, which has also a container shape and forms a main body portion 82 of the casting. If an inner diameter of each hole 33 is small, the molten material will not enter such a pore due to its surface tension and viscosity. Therefore, as shown in FIG. 12, it is preferable to adopt a vacuum suction method of vacuum-drawing during supply of the molten material 600 to draw the molten material into the pores. The reference sign 50 in the drawing denotes a heat-resistant porous material such as ceramic fiber usable for reduced-pressure suction, while 51 denotes an exhaust pipe. An unillustrated suction pump is installed ahead of the exhaust pipe 51, forming a device that performs downward vacuum suction.

[0039] Next, as shown in FIG. 7C, the binder dissolution solution 7 permeates the casting mold or core 3 to allow the casting mold or core 3 to be softened. Then, as shown in FIGS. 7D and 7E, the casting mold or core 3 softened by the permeation of the binder dissolution solution 7 is separated from the solidified body 6B, thereby obtaining the casting 8B formed of the solidified body. The plurality of rod-shaped protrusions 81 formed by transferring shapes of the holes 33 in the casting mold or core 3 are formed on the casting 8B in a protruding manner.

[0040] FIGS. 17 to 19 are photographs showing actually prototyped samples of the casting 8B shown in FIG. 7E. The upper photograph in FIG. 17 shows that the casting mold or core 3 and the solidified body 6 are integrated and solidified, viewed from a hole-opening side. Distal end surfaces of a solidified aluminum alloy in the holes are visible. The lower photograph in FIG. 17 shows the casting after the casting mold or core has been removed. The protrusions (pins) are set to 22 mm in height, and to multiple different values in thickness (outer diameter). FIG. 18 shows a similar sample with protrusions set to 20 mm in height and 1.7 mm φ in thickness (outer diameter). The sample has an arrangement in a staggered pattern. FIG. 19 shows a photograph of a sample with fine protrusions (pins) formed using the vacuum reduced-pressure suction method. The pins each have a thickness (outer diameter) of 0.6 mm φ and are arranged in a grid pattern. Such fine protrusions (thickness (outer diameter) of 1.5 mm or less) can be easily achieved by using the vacuum reduced-pressure suction method.

[0041] Although the embodiments of the present invention have been described as above, the present invention is not limited to these examples. The invention may be implemented in various forms within the scope of the essence of the invention.

[0042] Although the holes 80, 80A and protrusions 81 in the casting described in the above examples are straight, for example, the present invention also enables forming curved holes and protrusions by configuring shapes of the convex portions 310 (rod-shaped portions 31) or the holes 33 in the casting mold or core 3 as a curved shape. Similarly, the shapes of the convex portions 310 (rod-shaped portions 31) and the holes 33 are formed to fit a corresponding shape, thereby making the cross-sectional shapes of holes or protrusions into polygonal shapes other than circular, such as triangular, square, pentagonal, or hexagonal, as well as elliptical, flat plate-shape (rectangular cross-section), L-shape, V-shape, Y-shape, or U-shape.

[0043] Furthermore, it is also possible to form holes or protrusions with non-uniform cross-sectional areas that are not constant along the axial direction, such as tapered shapes where the cross-sectional area gradually decreases (or increases). Furthermore, it is possible to form shapes or protrusions with periodically varying thicknesses. Furthermore, instead of having holes or protrusions extending in only one direction, the convex portions 310 (rod-shaped portions 31) or holes 33 can be formed as multiple convex portions 310 (rod-shaped portions 31) or holes 33 extending in different directions. This allows a casting having multiple holes or protrusions extending in different directions to be formed. Furthermore, it is also easily possible to form a hole that branches off internally by configuring a branching rod-shaped portion 31. Furthermore, the present invention is not limited to forming "holes" or "protrusions," but can form various shapes.DESCRIPTION OF THE REFERENCE CHARACTERS

[0044] 1ceramic fiber 3core 4mold 5wire 6, 6Bsolidified body 7binder dissolution solution 8, 8Bcasting 11rod-shaped body 11Aplate-shaped body 11Cbase body 12sheath layer 30base body 31rod-shaped portion 31Aplate-shaped portion 310convex portion 32base 33hole 34connecting plate portion 35core material 40plate mold 41outer mold 42, 43second outer mold 80, 80Ahole 81protrusion 810convex portion 82main body portion 110binder 320thermoplastic resin 600molten material

Claims

1. A casting method comprising: impregnating ceramic fiber with a binder and solidifying a resultant into a predetermined shape to prepare a casting mold or core, which has shape retention; supplying a molten material including a molten metal, a molten semiconductor, or a molten polymeric material to an inside of a mold in which the casting mold or core is provided, and forming a solidified body formed of the molten material; subsequently allowing a binder dissolution solution in which the binder is dissolved to permeate the casting mold or core, to soften the casting mold or core; and separating the casting mold or core, which has been softened, from the solidified body to obtain a casting including the solidified body.

2. The casting method according to claim 1, wherein the casting mold or core includes a convex portion formed by solidifying the ceramic fiber into a convex shape, thereby forming a concave hole or a concave groove in the solidified body, the concave hole or the concave groove having a shape formed by transferring a shape of the convex portion.

3. The casting method according to claim 1, wherein the casting mold or core is subjected to machining after the ceramic fiber is solidified, to form one or more concave holes or concave grooves in the casting mold or core, thereby forming one or more convex portions in the solidified body, the one or more convex portions having a shape formed by transferring a shape of the one or more holes or grooves.

4. The casting method according to claim 1, wherein the binder is a water-soluble binder, and the binder dissolution solution is water.

5. The casting method according to claim 4, wherein the binder is polyvinyl alcohol, an alumina dispersion, a silica dispersion, a heat-resistant adhesive, or a combination thereof.

6. The casting method according to claim 1, wherein the casting mold or core impregnated with the binder dissolution solution is pushed by a pressurized fluid consisting of the binder dissolution solution or air, to separate the casting mold or core from the solidified body.

7. A casting obtained by the casting method according to any one of claims 1 to 6.

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