WO2014057913A1 - 精密鋳造用鋳型及びその製造方法 - Google Patents
精密鋳造用鋳型及びその製造方法 Download PDFInfo
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- WO2014057913A1 WO2014057913A1 PCT/JP2013/077275 JP2013077275W WO2014057913A1 WO 2014057913 A1 WO2014057913 A1 WO 2014057913A1 JP 2013077275 W JP2013077275 W JP 2013077275W WO 2014057913 A1 WO2014057913 A1 WO 2014057913A1
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- mold
- slurry
- layer
- precision casting
- stucco
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
- B22C9/04—Use of lost patterns
- B22C9/043—Removing the consumable pattern
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
- B22C9/04—Use of lost patterns
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/10—Cores; Manufacture or installation of cores
Definitions
- the present invention relates to a precision casting mold and a manufacturing method thereof.
- a casting method for producing a casting there is a precision casting method used when producing a casting with high accuracy.
- slurry is applied around a vanishing model (wax mold) having the same shape as the molded part, and then the first layer stucco (flower) is adhered and dried. Let Thereafter, the three steps of slurry application, stucco attachment, and drying are repeated to produce a mold (outer mold) that covers the outside of the casting.
- a wax mold is attached to a slurry mainly composed of silica sol, and the slurry is attached to the surface of the wax mold and dried. Since only a small amount of slurry adheres to each operation and only a thin slurry can be formed, the thickness is increased by repeating several times to 10 to several times. Also, coarse particles called stucco material are sprinkled on and adhered to the surface of the slurry in order to speed up drying or to ensure a quick wall thickness in order to prevent dry cracking. Therefore, the mold cross-sectional structure is a dense layer and a layer of coarse particles.
- silica sol is a liquid in which spherical silica particles having a particle diameter of about 20 nm are dispersed.
- the silica ultrafine particles adhere to the surface of relatively fine particles (several to several tens of microns) and coarse particles (stucco) (several hundred microns to several mm) such as zircon and alumina contained in the slurry during the drying process.
- a mold using the above-mentioned silica sol (a liquid in which ultrafine particles of silica are dispersed) is sufficient.
- a molten metal is used to control the crystal precipitation direction. Hold.
- the holding time at a high temperature for example, about 1550 ° C.
- silica as a binder is softened and the mold is deformed.
- the mold is placed in a heater in a vacuum, heated and held at a temperature above the melting point of the molten metal, the molten metal is injected into the mold, and the mold is moved downward from the heater.
- the molten metal is manufactured by cooling and solidifying from one direction below by pulling out while controlling the pulling down.
- the present invention has been made in view of the above, and an object thereof is to provide a precision casting mold that does not deform even when kept at a high temperature for a long time, and a method for manufacturing the same.
- a first invention of the present invention for solving the above-described problems is a precision casting mold used for manufacturing a casting, wherein the core has a shape corresponding to a hollow portion inside the casting, and an outer peripheral surface of the casting.
- An outer mold corresponding to the shape of the outer mold, and the outer mold is formed of an alumina ultrafine particle having a particle size of 1.0 ⁇ m or less and a silica sol formed on the inner peripheral surface and a silica sol, and is fired.
- the precision casting mold slurry includes any one of zircon powder and alumina powder having an average particle size of 50 ⁇ m or less, and the stucco material has an average particle size of 0.5 mm.
- the present invention provides a precision casting mold characterized by being one of the above zircon stucco grains and alumina stucco grains.
- a third invention is the precision casting mold according to the first or second invention, wherein the prime layer has a stucco layer in which a stucco material is adhered to a slurry layer made of precision casting mold slurry. .
- a fourth invention is a method of manufacturing a precision casting mold used for manufacturing a casting, and includes a precision casting wax mold comprising alumina dispersed fine particles having a particle size of 1.0 ⁇ m or less and silica sol.
- a stucco material is sprinkled on the surface of the slurry, and then dried to form a backup layer, and the second film forming process.
- the step of forming the backup layer is repeated a plurality of times, and a molded body forming step for obtaining a molded body formed with a multilayer backup layer, and a dewaxing step for melting and removing wax-type wax from the obtained molded body And calcined molded body after dewaxing, in the production method of precision casting mold, characterized in that it comprises a mold sintering step of obtaining a template, the.
- a stucco layer is formed by adhering a stucco material to the slurry layer comprising the precision casting mold slurry in the first film forming step, and then drying. It is in the manufacturing method of the mold for precision casting characterized by the above.
- the sixth invention is the method for producing a precision casting mold according to the fourth or fifth invention, wherein the precision casting mold slurry dispersant is a polycarboxylate.
- the heat-resistant temperature is improved with respect to the conventional use of silica sol by using alumina fine particles that become mullite having high heat resistance and silica sol, thereby increasing the heat-resistant temperature, for example, in the production of unidirectional solidified blades. Even when held for a long time at (° C.), there is an effect that a mold that does not deform is obtained.
- FIG. 1 is a configuration diagram of a dry molded body serving as an outer mold.
- FIG. 2 is a configuration diagram of another dry molded body serving as an outer mold.
- FIG. 3 is a flowchart showing an example of the process of the casting method.
- FIG. 4 is a flowchart showing an example of steps of the mold manufacturing method.
- FIG. 5 is an explanatory view schematically showing a core manufacturing process.
- FIG. 6 is a perspective view schematically showing a part of the mold.
- FIG. 7 is an explanatory view schematically showing a wax mold manufacturing process.
- FIG. 8 is an explanatory diagram schematically showing a configuration in which slurry is applied to a wax mold.
- FIG. 9 is an explanatory view schematically showing a manufacturing process of the outer mold.
- FIG. 10 is an explanatory view schematically showing a part of the mold manufacturing method.
- FIG. 11 is an explanatory view schematically showing a part of the casting method.
- FIG. 1 is a configuration diagram of a dry molded body serving as an outer mold.
- FIG. 2 is a configuration diagram of another dry molded body serving as an outer mold.
- the precision casting mold is a precision casting mold used for manufacturing a casting, and corresponds to the shape of the core corresponding to the hollow portion inside the casting and the shape of the outer peripheral surface of the casting.
- the outer mold is formed on the inner peripheral surface, and is dispersed in a single dispersion having a particle size of 1.0 ⁇ m or less (preferably 0.3 to 0.5 ⁇ m: described in the examples).
- a prime layer (first dry film) 101A made of a slurry film made of a precision casting mold slurry that is made of ultrafine alumina particles and silica sol, and becomes a mullite during firing, and the prime layer (first dry film).
- a first backup layer (second film) formed by drying a slurry layer 102 made of the precision casting mold slurry and a stucco layer 103 having a stucco material adhered to the slurry layer and dried. Dry film)
- the multi-layer backup layer 105A formed by multiple times 104-1 is formed.
- the high-purity ultrafine alumina particles which are the binder for forming the slurry in the present invention
- monodispersed means that, for example, when a slurry is formed using alumina fine particles having a particle size of about 0.5 ⁇ m, the result of the dispersion treatment is also monodispersed to 0.5 ⁇ m.
- the particle diameter of the alumina fine particles is 1.0 ⁇ m or less, more preferably in the range of 0.3 to 0.6 ⁇ m.
- the reason why the alumina fine particle is preferably 1.0 ⁇ m or less is that if it exceeds 1.0 ⁇ m, the result of bending test strength is not preferable.
- polycarboxylate for example, ammonium salt
- dispersant for example, ammonium salt
- dispersing means for example, a ball mill using balls having a diameter of 10 to 20 mm can be exemplified, but the dispersing means is not limited to this as long as it is a single dispersing means.
- the blending ratio of alumina fine particles monodispersed in 0.5 ⁇ m, for example, is large.
- the alumina particle diameter is 1.0 ⁇ m or less, preferably 0.3 to 0.6 ⁇ m.
- Silica sol is a uniform dispersion of 0.02 ⁇ m silica and is uniformly dispersed in an alumina slurry.
- the alumina fine particles having a predetermined particle diameter are made into a uniform dispersion, so that the reactivity with the silica sol in the baking process is good, and mullite can be formed at a lower temperature (for example, 1,000 ° C.). It becomes.
- the production cost can be reduced by adding silica sol to the alumina fine particles to form mullite at the time of firing.
- Zircon powder (for example, 350 mesh) is added as flour to the mixed slurry obtained by adding silica sol to the single dispersed alumina fine particle slurry to obtain a precision casting mold slurry. In the present invention, it is acceptable to add no flour.
- a precision casting mold slurry (hereinafter referred to as “slurry”) composed of ultra-fine alumina particles having a particle size of 1.0 ⁇ m or less and silica sol, which becomes mullite during firing. ),
- the wax mold 30 is dipped, pulled up, and excess slurry is dropped.
- a slurry film (first dry film) is obtained on the surface of the wax mold 30 by drying. This slurry film becomes a prime layer 101A in contact with the surface of the wax mold 30 in FIG.
- the same operation as the second film forming step of the first backup layer 104-1 is repeated a plurality of times (for example, 6 to 10 times), and the slurry layer (n + 1 layer) 102 and the stucco layer (n layer) 103 are alternately arranged.
- a dry molded body 106A serving as an outer mold having a multilayer backup layer 105A having a predetermined thickness laminated on the substrate is obtained.
- This dried molded body is put into an autoclave at 150 ° C., for example, and the wax constituting the wax mold 30 is melted and discharged. Thereafter, this mold is heat-treated at 1,000 ° C. to obtain a precision casting mold in which the slurry constitutes mullite.
- the obtained mold for precision casting was high in strength without deformation in a 1500 ° C. strength test, as shown in a test example described later. On the other hand, the softening behavior was confirmed using the conventional silica sol.
- a stucco material may be attached to the prime slurry layer 101a to form the prime stucco layer 101b, and then dried to form the prime layer 101B.
- the number of times that the slurry layer of the multilayer backup layer 105B is stacked and the number of times that the stucco layer 103 is stacked are the same number (n layers).
- a dry molded body 106B serving as an outer mold having the layer backup layer 105B is obtained.
- zircon powder was used as the flour, but in addition to zircon powder, alumina powder was used, and even if alumina stucco particles were used instead of zircon stucco particles, the same precision casting mold was obtained. Can do.
- the relationship between the flour and the stucco material is not limited, and either zircon powder or alumina powder is used as the flour, and either zircon stucco particle or alumina stucco particle is used as the stucco material. Just do it.
- the particle size of the flour is 350 mesh, but the present invention is not limited to this.
- the stucco particles have a particle size of 0.8 mm, but the present invention is not limited to this. For example, particles having a diameter of about 0.4 mm to 2 mm and an average particle size of 0.5 mm or more should be used. Is preferred.
- FIG. 3 is a flowchart showing an example of the steps of the casting method.
- the casting method will be described with reference to FIG.
- the casting method of this embodiment produces a casting mold (step S1).
- the mold may be produced in advance or may be produced each time casting is performed.
- FIG. 4 is a flowchart showing an example of steps of the mold manufacturing method.
- the processing shown in FIG. 4 may be executed fully automatically, or may be executed by an operator operating an apparatus that executes each process.
- the mold manufacturing method produces a core (core) (step S12).
- a core is a shape corresponding to the cavity inside the casting produced with a casting_mold
- FIG. 5 is an explanatory view schematically showing a core manufacturing process.
- a mold 12 is prepared as shown in FIG. 5 (step S101).
- the mold 12 has a hollow area corresponding to the core.
- the portion that becomes the cavity of the core becomes the convex portion 12a.
- the mold 12 basically covers the entire circumference of the region corresponding to the core except for an opening for injecting material into the space and a hole for extracting air. It is hollow.
- the ceramic slurry 16 is injected into the mold 12 through an opening for injecting material into the space of the mold 12 as indicated by an arrow 14.
- the core 18 is produced by so-called injection molding in which the ceramic slurry 16 is injected into the mold 12.
- the core 18 is produced inside the mold 12, the core 18 is removed from the mold 12, and the removed core 18 is placed in the firing furnace 20 and fired. Thereby, the core 18 made of ceramic is baked and hardened (step S102).
- the core 18 is produced as described above.
- the core 18 is formed of a material that can be removed by a decore process such as a chemical process after the casting is solidified.
- an external mold is manufactured (step S14).
- the outer mold has a shape in which the inner peripheral surface corresponds to the outer peripheral surface of the casting.
- the mold may be made of metal or ceramic.
- FIG. 6 is a perspective view schematically showing a part of the mold. In the mold 22a shown in FIG. 6, the recess formed on the inner peripheral surface corresponds to the outer peripheral surface of the casting. In FIG. 6, only the mold 22 a is shown, but a mold corresponding to the mold 22 a and corresponding to the mold 22 a is also produced so as to close the concave portion formed on the inner peripheral surface.
- two molds are combined to form a mold whose inner peripheral surface corresponds to the outer peripheral surface of the casting.
- FIG. 7 is an explanatory view schematically showing a wax mold manufacturing process.
- the core 18 is installed at a predetermined position of the mold 22a (step S110).
- a mold 22b corresponding to the mold 22a is placed on the surface of the mold 22a where the recess is formed, the core 18 is surrounded by the molds 22a and 22b, and the core 18 and the molds 22a and 22b are separated.
- a space 24 is formed therebetween.
- the mold manufacturing method starts injection of WAX 28 from the pipe connected to the space 24 toward the inside of the space 24 as indicated by an arrow 26 (step S112).
- WAX 28 is a substance having a relatively low melting point, such as wax, which melts when heated above a predetermined temperature.
- the entire space 24 is filled with the WAX 28 (step S113).
- the wax 28 is solidified to form the wax mold 30 in which the WAX 28 surrounds the core 18.
- the wax mold 30 basically has the same shape as the casting for which the part formed by the WAX 28 is manufactured.
- the wax mold 30 is separated from the molds 22a and 22b, and the gate 32 is attached (step S114).
- the gate 32 is a port into which molten metal, which is a metal melted during casting, is charged.
- the mold manufacturing method produces the wax mold 30 including the core 18 inside and formed of the WAX 28 having the same shape as the casting.
- FIG. 8 is an explanatory diagram schematically showing a configuration in which slurry is applied to a wax mold.
- the wax mold 30 is immersed in the storage portion 41 in which the slurry 40 is stored, and is taken out and then dried (step S19).
- the prime layer 101 ⁇ / b> A can be formed on the surface of the wax mold 30.
- the slurry applied in step S ⁇ b> 18 is a slurry applied directly to the wax mold 30.
- the slurry 40 is composed of ultrafine alumina particles and silica sol, and uses a casting slurry for precision casting that becomes mullite during firing.
- a casting slurry for precision casting that becomes mullite during firing.
- refractory fine particles of about 350 mesh, such as zirconia, as flour.
- polycarboxylate as a dispersing agent.
- slurry application is performed with the slurry 40, and the solder mold having the prime layer (first dry film) 101A is further applied with slurry (dipping) (step S20).
- stuccoing is performed by sprinkling zircon stucco grains (average particle size 0.8 mm) as the stucco material 54 on the surface of the wet slurry (step S21).
- the slurry layer with the stucco material attached thereto was dried to form the first backup layer (second dry film) 104-1 on the prime layer (first dry film) 101A (step S22).
- a predetermined number (n) of n-th backup layers 104-n are stacked (step S23: Yes) to obtain a dry molded body 106A that is an outer mold having a thickness of, for example, 10 mm on which the multilayer backup layer 105A is formed.
- step S24 the dry molded body 106A is subjected to heat treatment (step S24). Specifically, WAX between the outer mold and the core is removed, and the outer mold and the core are further fired.
- FIG. 10 is an explanatory view schematically showing a part of the mold manufacturing method.
- a dry molded body 106A serving as an outer mold in which a plurality of layers of the prime layer 101A and the multilayer backup layer 105A is formed is placed in the autoclave 60 and heated.
- the autoclave 60 heats the wax mold 30 in the dry molded body 106A by filling the interior with pressurized steam. As a result, the WAX constituting the wax mold 30 is melted, and the molten WAX 62 is discharged from the space 64 surrounded by the dry molded body 106A. In the mold manufacturing method, the melted WAX 62 is discharged from the space 64, so that, as shown in step S131, an area filled with WAX between the dry molded body 106A serving as the outer mold and the core 18 is filled with the space 64. A mold 72 in which is formed is produced.
- step S132 the mold 72 in which the space 64 is formed between the dry molded body 106A serving as the outer mold and the core 18 is heated in the firing furnace 70.
- the mold 72 removes the water component and unnecessary components contained in the dry molded body 106 ⁇ / b> A serving as the outer mold, and is further cured by firing to form the outer mold 61.
- the mold 72 is produced as described above.
- FIG. 11 is an explanatory view schematically showing a part of the casting method.
- the mold is preheated (step S2).
- the mold is placed in a furnace (vacuum furnace, firing furnace) and heated to 800 ° C. or higher and 900 ° C. or lower.
- a furnace vacuum furnace, firing furnace
- preheating it is possible to prevent the mold from being damaged when molten metal (melted metal) is injected into the mold at the time of casting production.
- step S3 when the mold is preheated, pouring is performed (step S3). That is, as shown in step S ⁇ b> 140 of FIG. 11, a molten metal 80, that is, a molten casting material (for example, steel) is injected between the outer mold 61 and the core 18 from the opening of the mold 72.
- a molten metal 80 that is, a molten casting material (for example, steel) is injected between the outer mold 61 and the core 18 from the opening of the mold 72.
- step S4 After the molten metal 80 poured into the mold 72 is solidified, the outer mold 61 is removed (step S4). That is, as shown in step S141 of FIG. 11, when the molten metal 80 is solidified into the casting 90 inside the mold 72, the outer mold 61 is crushed and removed from the casting 90 as a broken piece 61a.
- the core removal process is performed (step S5). That is, as shown in step S142 of FIG. 11, the casting 90 is put into the autoclave 92 and the core removal process is performed by melting the core 18 inside the casting 90, and the molten core 94 is dissolved in the casting 90. Drain from inside. Specifically, the casting 90 is put into an alkaline solution inside the autoclave 92, and the melting core 94 is discharged from the casting 90 by repeating pressurization and decompression.
- a finishing process is performed (step S6). That is, a finishing process is performed on the surface and inside of the casting 90.
- the casting is inspected together with the finishing process. Thereby, as shown to step S143 of FIG. 11, the casting 100 can be manufactured.
- a casting mold is manufactured by using a lost wax casting method using WAX (wax).
- the mold manufacturing method, the casting method, and the mold according to the present embodiment include an outer mold, which is an outer portion of the mold, and a prime layer (first layer that is the first layer) that becomes an inner peripheral surface using zirconia ultrafine particles as a slurry.
- (Dry film) 101A is formed, and a plurality of backup layers 105A are formed outside the prime layer 101A to form a multilayer structure.
- the prime layer 101B including the prime slurry layer 101a to which the stucco material is added and the prime stucco layer 101b may be used as the prime layer (see FIG. 2).
- the wax mold before the outer mold is formed is a member having a width of 30 mm, a thickness of 8 mm, and a length of 300 mm, and this wax mold has a prime layer (first dry film) made of a slurry layer, A mold was prepared by forming a multilayer backup layer of slurry and stucco material.
- a slurry of high-purity ultrafine alumina (Al 2 O 3 , specific surface area 10 m 2 / g, particle size of about 0.5 ⁇ m) is kneaded for 24 hours using a ball mill and a slurry using ammonium polycarboxylate as a dispersant. Turned into.
- the solid content concentration of the obtained alumina slurry is 30 wt%.
- silica sol SiO 2 , particle size 0.02 ⁇ m, solid content concentration 30%
- the slurry was blended in advance. At this time, no precipitation was observed even when mixed.
- 350 mesh zircon powder was added as a flour to obtain a precision casting mold slurry.
- 0.01% silicon-based antifoaming agent and 0.01% wettability improving agent were added to prepare slurry for use.
- a wax body having a prime layer was immersed in the slurry, and then the excess used slurry was dropped.
- Zircon stucco grains having an average grain size of 0.8 mm were adhered to the wet slurry and then dried to form a second dry film (first backup layer).
- test A strength test piece of 10 mm ⁇ 50 mm and a thickness of 5 mm was processed from the obtained mold of Example 1 and the comparative mold, and a high-temperature strength test was performed. In the strength test at 1500 ° C., the softening behavior was confirmed using the conventional silica sol. As a result, the test piece of the comparative example was not clearly cut and bent. On the other hand, the test piece using the slurry (zircon grains as the stucco material) blended as mullite (3Al 2 O 3 .2SiO 2 ) of the present example was not deformed and fractured at 100 MPa.
- the strength test was performed according to “Bending strength of ceramics (1981)” according to JIS R 1601.
- the conventional silica sol is used by making the binder into a slurry that becomes mullite (melting point: 1,885 ° C.) with high heat resistance during firing and stucco material as zircon grains (melting point: 2,715 ° C.).
- the heat resistant temperature was improved, and a mold that did not deform even when kept at a high temperature (1550 ° C.) for a long time in the production of a unidirectionally solidified blade could be obtained.
- Example 2 In Example 1, 350 mesh alumina powder was added as flour instead of zircon powder to obtain a precision casting mold slurry. Further, a mold of Example 2 was obtained in the same manner as in Example 1 except that alumina stucco particles having an average particle diameter of 0.8 mm were used as the stucco material.
- test A strength test piece of 10 mm ⁇ 50 mm and a thickness of 5 mm was processed from the obtained mold of Example 2 and the mold of Comparative Example, and the same high-temperature strength test as in Example 1 was performed.
- the test piece using the slurry (alumina particles as the stucco material) serving as the mullite of this example was not deformed and was broken at 100 MPa.
- the conventional silica sol is used by making the binder into a slurry that becomes mullite (melting point 1,885 ° C.) with high heat resistance during firing and the stucco material as alumina particles (melting point 2,070 ° C.).
- the stucco material as alumina particles
- the binder is made of ultra-fine alumina particles with a particle size of 1.0 ⁇ m or less and silica sol, and the mold slurry for precision casting that becomes mullite with high heat resistance at the time of firing is used as the slurry.
- the heat resistance temperature of the obtained mold is improved compared to the case of using conventional silica sol, and the mold is kept at a high temperature (1,550 ° C.) for a long time in the production of a unidirectional solidified blade. In some cases, a mold that does not deform was obtained.
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Abstract
Description
1回の操作では付着するスラリーが少なく、薄いものしかできないので、数回~10数回繰返して厚さを稼いでいる。また、乾燥を早くするため、あるいは、早く肉厚を確保するため、乾燥割れを防止するため、スタッコ材と呼ばれる粗い粒子をスラリー表面にふりかけ、付着させている。そのため、鋳型の断面構造は緻密層、粗い粒子の層の繰り返しとなっている。
例えばシリカゾルは粒径20nm程度の球状シリカ粒子が分散された液である。このシリカ超微粒子が、乾燥の過程でスラリーに含まれるジルコン、アルミナなどの比較的細かい粒子(数ミクロンから数十ミクロン)及び粗い粒子(スタッコ)(数百ミクロン~数mm)の表面に付着し、乾燥、熱処理により固く結合することにより、鋳型の形状が保たれると同時に強度を保有し、鋳型として利用できるようになっている。
図1に示すように、精密鋳造用鋳型は、鋳物の製造に用いる精密鋳造用鋳型であって、前記鋳物の内部の空洞部分に対応する形状のコアと、前記鋳物の外周面の形状に対応する外側鋳型と、を有し、前記外側鋳型は、内周面に形成され、粒径1.0μm以下(好適には0.3~0.5μm:実施例に記載)の単一分散してなるアルミナ超微粒子とシリカゾルとからなり、焼成の際ムライトとなる精密鋳造用鋳型スラリーを用いて乾燥してなるスラリー膜からなるプライム層(第1乾燥膜)101Aと、前記プライム層(第1乾燥膜)101Aの外側に形成され、前記精密鋳造用鋳型スラリーからなるスラリー層102と、該スラリー層にスタッコ材を付着したスタッコ層103とにより形成し、乾燥してなる第1バックアップ層(第2乾燥膜)104-1を、複数回形成してなる複層バックアップ層105Aと、からなるものである。
ここで、単一分散されているとは、例えば粒径が約0.5μmのアルミナ微粒子を用いてスラリーを形成する場合、分散処理をした結果においても、0.5μmに単一分散されている状態をいう。
ここで、アルミナ微粒子の粒径としては、1.0μm以下、より好ましくは0.3~0.6μmの範囲とするのが良い。
これらの配合比率は以下の範囲とするのが好ましい。
Al2O3/SiO2=1.5(モル比)
なお、本発明では、フラワーを添加しない場合も許容されうる。
(第1成膜工程)
先ず、この第1成膜工程では、この粒径1.0μm以下の単一分散してなるアルミナ超微粒子とシリカゾルとからなり、焼成の際ムライトとなる精密鋳造用鋳型スラリー(以下「スラリー」という)を用いて、ろう型30を浸漬させ、引き上げ、余分なスラリーを落下させる。その後、乾燥させることで、ろう型30表面に、スラリー膜(第1乾燥膜)を得る。
このスラリー膜が、図1において、ろう型30の表面と接するプライム層101Aとなる。
次いで、このプライム層101Aを有するろう型30を、スラリーに浸漬させた後、引上げ、余分なスラリーを落下させ、スラリー層(2層目)102を形成する。この濡れているスラリー層(2層目)102にスタッコ材としてジルコンスタッコ粒(平均粒径0.8mm)を振掛けて(スタッコイングして)、スタッコ材を付着させたスタッコ層(1層目)103を形成する。このスラリー層(2層目)102とスタッコ層(1層目)103との積層体を乾燥して、プライム層(第1乾燥膜)101Aの上に第1バックアップ層(第2乾燥膜)104-1を形成する。
この第1バックアップ層104-1の第2成膜工程と同様の操作を複数回(例えば6~10回)繰り返し、スラリー層(n+1層目)102とスタッコ層(n層目)103とが交互に積層された所定厚みの複層バックアップ層105Aを有する外側鋳型となる乾燥成形体106Aを得る。
その後、この型を1,000℃で熱処理し、スラリーがムライトを構成した精密鋳造用鋳型を得る。
なお、このプライム層101Bのように、スタッコ材を付着させた場合には、複層バックアップ層105Bのスラリー層の積層回数と、スタッコ層103の積層回数とは共に同数(n層)からなる複層バックアップ層105Bを有する外側鋳型となる乾燥成形体106Bを得ることとなる。
なお、フラワーとスタッコ材との関係は、限定されるものではなく、フラワーとしてジルコン粉、アルミナ粉のいずれかを用いると共に、スタッコ材として、ジルコンスタッコ粒、アルミナスタッコ粒のいずれかを用いるようにすれば良い。
ここで、ステップS18で塗布するスラリーは、ろう型30に直接塗布されるスラリーである。このスラリー40は、アルミナ超微粒子とシリカゾルとからなり、焼成の際ムライトとなる精密鋳造用鋳型スラリーを用いる。このスラリー40には、フラワーとして350メッシュ程度の耐火性の微粒子、例えばジルコニアを用いることが好ましい。また、分散剤としてポリカルボン酸塩を用いることが好ましい。また、スラリー40には、消泡剤(シリコン系の物質)や、濡れ性改善剤を微量、例えば0.01%添加することが好ましい。濡れ性改善剤を添加することで、スラリー40のろう型30への付着性を向上させることができる。
この第1バックアップ層(第2乾燥膜)104-1の形成工程と同様の操作を複数回(例えばn:6~10回)繰り返す判断を行う(ステップS23)。所定回数(n)の第nバックアップ層104-nを積層させ(ステップS23:Yes)、複層バックアップ層105Aが形成された厚みが例えば10mmの外側鋳型となる乾燥成形体106Aを得る。
鋳型製造方法は、溶けたWAX62を空間64から排出することで、ステップS131に示すように、外側鋳型となる乾燥成形体106Aと、コア18との間のWAXが充填されていた領域に空間64が形成された鋳型72が作製される。その後、鋳型製造方法は、ステップS132に示すように、外側鋳型となる乾燥成形体106Aとコア18との間に空間64が形成された鋳型72を、焼成炉70で加熱する。これにより、鋳型72は、外側鋳型となる乾燥成形体106Aに含まれる水成分や不要な成分が除去され、さらに、焼成されることで硬化され、外側鋳型61が形成される。鋳物製造方法は、以上のようにして鋳型72を作製する。
なお、前述したように、プライム層として、スタッコ材を添加したプライムスラリー層101aとプライムスタッコ層101bとからなるプライム層101Bとしてもよい(図2参照)。
以下、実施例を用いて、本実施形態の鋳型製造方法及び鋳造方法について説明する。なお、以下の実施例では、外側鋳型が形成される前のろう型を幅30mm、厚さ8mm、長さ300mmの部材とし、このろう型にスラリー層からなるプライム層(第1乾燥膜)、スラリーとスタッコ材による複層のバックアップ層を形成して鋳型を作製した。
このアルミナスラリーでは、分散処理の結果、アルミナ粒子は0.5μmに単一分散されていることが確認された。
また、シリカゾル(SiO2、粒径0.02μm、固形分濃度30%)を準備した。
焼成の際、ムライト(3Al2O3・2SiO2)の配合になるように、アルミナスラリー:シリカゾル=306:120(3Al2O3の分子量は3×102=306、2SiO2の分子量は2×60=120)になるように配合したスラリーをあらかじめ調合した。
このとき、混合しても沈殿の発生は認められなかった。
この配合スラリーに、フラワーとして350メッシュのジルコン粉を添加して、精密鋳造用鋳型スラリーとした。
また、同時に、消泡剤としてシリコン系のものを0.01%、濡れ性改善剤を0.01%添加して、使用スラリーとした。
濡れているスラリーに、平均粒系0.8mmのジルコンスタッコ粒を付着させた後乾燥し、第2乾燥膜(第1バックアップ層)を形成した。
この得られた乾燥成形体を150℃のオートクレーブに入れて、ワックスを融解し、排出した。
次いで、この型を1000℃で熱処理し、実施例1の鋳型を得た。
比較のため、従来と同様のシリカゾル(粒径20nm程度の球状シリカ粒子が分散された液)を使用したスラリーを用い、実施例と同様の操作を行い比較例の鋳型も同時に試作した。
得られた実施例1の鋳型及び比較例の鋳型から、10mm×50mm、厚さ5mmの強度試験片を加工し、高温強度試験を実施した。
1500℃の強度試験では、従来のシリカゾルを使用したものでは軟化の挙動が確認された。
また、その結果、比較例の試験片の切断は明瞭でなく、曲がってしまった。
これに対し、本実施例のムライト(3Al2O3・2SiO2)となる配合のスラリー(スタッコ材としてジルコン粒)を使用した試験片は変形もなく、100MPaでの破断であった。
ここで、強度試験は、JIS R 1601による「セラミックスの曲げ強さ(1981)」に準拠しておこなった。
実施例1において、フラワーとして、ジルコン粉の代わりに、350メッシュのアルミナ粉を添加して、精密鋳造用鋳型スラリーとした。
また、スタッコ材として、平均粒径0.8mmのアルミナスタッコ粒を用いた以外は、実施例1と同様に操作して、実施例2の鋳型を得た。
得られた実施例2の鋳型及び比較例の鋳型から、10mm×50mm、厚さ5mmの強度試験片を加工し、実施例1と同様の高温強度試験を実施した。
本実施例のムライトとなるスラリー(スタッコ材としてアルミナ粒)を使用した試験片は変形もなく、100MPaでの破断であった。
12a 凸部
14、26 矢印
16 セラミックスラリー
18 コア(中子)
20、70 焼成炉
24、64 空間
28 WAX(ろう)
30 ろう型
32 湯口
40 スラリー
60、92 オートクレーブ
61 外側鋳型
61a 破片
62 溶融WAX
72 鋳型
80 溶湯
90、100 鋳物
94 溶解コア
101A、101B プライム層
102 スラリー層
103 スタッコ層
104-1 第1バックアップ層
104-n 第nバックアップ層
105A、105B 複層バックアップ層
Claims (6)
- 鋳物の製造に用いる精密鋳造用鋳型であって、
前記鋳物の内部の空洞部分に対応する形状のコアと、
前記鋳物の外周面の形状に対応する外側鋳型と、を有し、
前記外側鋳型は、内周面に形成され、粒径1.0μm以下の単一分散してなるアルミナ超微粒子とシリカゾルとからなり、焼成の際ムライトとなる精密鋳造用鋳型スラリーを用いて乾燥してなるスラリー膜からなるプライム層と、
前記プライム層の外側に形成され、前記精密鋳造用鋳型スラリーからなるスラリー層と、該スラリー層にスタッコ材を付着したスタッコ層とにより形成し、乾燥してなるバックアップ層を、複数回形成してなる複層バックアップ層と、からなることを特徴とする精密鋳造用鋳型。 - 請求項1において、
前記精密鋳造用鋳型スラリーに平均粒径が50μm以下のジルコン粉、アルミナ粉をいずれか一方を含み、
前記スタッコ材が、平均粒径が0.5mm以上のジルコンスタッコ粒、アルミナスタッコ粒のいずれか一方であることを特徴とする精密鋳造用鋳型。 - 請求項1又は2において、
前記プライム層が、精密鋳造用鋳型スラリーからなるスラリー層に、スタッコ材を付着したスタッコ層を有することを特徴とする精密鋳造用鋳型。 - 鋳物の製造に用いる精密鋳造用鋳型の製造方法であって、
精密鋳造用ろう型を、粒径1.0μm以下の単一分散してなるアルミナ超微粒子とシリカゾルとからなり、焼成の際ムライトとなる精密鋳造用鋳型スラリーに浸漬し、引き上げた後乾燥して、ろう型の表面にスラリー膜からなるプライム層を形成する第1成膜工程と、
前記プライム層を形成したろう型を、前記精密鋳造用鋳型スラリーに浸漬し、引き上げた後、スラリー表面にスタッコ材を振掛け、その後乾燥してバックアップ層を形成する第2成膜工程と、
前記第2成膜工程のバックアップ層を形成する工程を複数回繰り返し、複層バックアップ層を形成した成形体を得る成形体形成工程と、
得られた成形体からろう型のワックスを融解・除去する脱ワックス工程と、
脱ワックス後の成形体を焼成処理し、鋳型を得る鋳型焼成工程と、を有することを特徴とする精密鋳造用鋳型の製造方法。 - 請求項4において、
前記第1成膜工程の際、前記精密鋳造用鋳型スラリーからなるスラリー層に、スタッコ材を付着してスタッコ層を形成し、その後乾燥することを特徴とする精密鋳造用鋳型の製造方法。 - 請求項4又は5において、
前記精密鋳造用鋳型スラリーの分散剤がポリカルボン酸塩であることを特徴とする精密鋳造用鋳型の製造方法。
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