WO2014192820A1 - Core for precision casting, production method therefor, and mold for precision casting - Google Patents

Abstract

A core for precision casting, comprising a coating layer (19a) formed on the surface of a core main body (18a) for precision casting that is sintered using silica particles as the main component thereof, said coating layer being silicon alkoxide or a mixed alkoxide comprising silicon alkoxide and aluminum alkoxide. As a result holes (18c) formed on the surface are sealed. As a result, core breakage during casting can be prevented.

Description

Precision casting core and manufacturing method thereof, precision casting mold

The present invention relates to a core for precision casting, a manufacturing method thereof, and a mold for precision casting.

Examples of precision castings include moving blades used in gas turbines. In a gas turbine, a working fluid is burned in a combustor to form a high-temperature and high-pressure working fluid, and the turbine is rotated by the working fluid. That is, the working fluid compressed by the compressor is burned by the combustor, energy is increased, and the energy is recovered by the turbine to generate a rotational force, thereby generating electric power. The turbine section is provided with a turbine rotor, and at least one gas turbine rotor blade is provided on the outer periphery of the turbine rotor.

Here, the gas turbine blade is exposed to high temperature. As a countermeasure, a cooling medium for cooling is supplied to the gas turbine rotor blade. For this reason, the gas turbine rotor blade is provided with an internal cooling structure. In order to configure such an internal cooling structure, a core (core) having the same shape as the flow path of the cooling medium is disposed, and the core is removed after casting. The core is removed by dissolving and removing the core in an alkali (for example, NaOH or KOH) solution, thereby forming an internal cooling structure of the turbine rotor blade, for example.

As the core, a ceramic core using ceramic particles is conventionally used (Patent Document 1).

Here, the core for precision casting is obtained by molding a siliceous material such as fused silica (SiO ₂ ) by a method such as injection molding or slip casting, and then performing a heat treatment.
The injection molding method is a method of obtaining a molded product by kneading ceramic powder and wax, then injecting and injecting a material obtained by heating and melting the wax into a mold, and cooling and solidifying the material.
Slip cast molding is a method in which ceramic powder is mixed with water or the like to form a slurry, which is poured into a mold made of a material that absorbs a solution such as gypsum, dried, and molded.

JP-A-6-340467

By the way, since the present core is manufactured mainly for alkali solubility, there are problems such as low high-temperature strength. In addition, in the injection molding method, after the molding, the sintered core has a large number of holes on its surface, so the strength is low. There is a problem that there is a concern about the possibility of breaking.
Therefore, the appearance of a core for precision casting with improved high temperature strength is eagerly desired.

The present invention has been made in view of the above, and an object thereof is to provide a precision casting core having improved high-temperature strength, a method for producing the same, and a precision casting mold.

The first invention of the present invention for solving the above-mentioned problem is to form an alkoxide coating layer made of an alkoxide material on the surface of a sintered precision casting core body mainly composed of siliceous particles. The core for precision casting is characterized by

According to a second aspect of the present invention, there is provided an accurate alkoxide-silica fume coating layer comprising an alkoxide material and silica fume on the surface of a sintered precision casting core body mainly composed of siliceous particles. Located in the casting core.

The third invention is the precision casting core according to the first or second invention, wherein the alkoxide material is silicon alkoxide alone or mixed alkoxide of silicon alkoxide and aluminum alkoxide.

A fourth invention is a precision casting mold used for manufacturing a casting, the precision casting core of the first or second invention having a shape corresponding to a hollow portion inside the casting, and an outer periphery of the casting. And an outer casting mold corresponding to the shape of the surface.

According to a fifth aspect of the present invention, a sintered body of a core body for precision casting mainly composed of siliceous particles is immersed in an alkoxide material, then dried, and then subjected to heat treatment to obtain a surface of the core body for precision casting. A coating layer is formed on the precision casting core manufacturing method.

In a sixth aspect of the invention, the sintered body of the core body for precision casting mainly composed of siliceous particles is immersed in an alkoxide-silica fume material of an alkoxide material and silica fume, then dried, and then heat-treated. A method for producing a core for precision casting is characterized in that a coating layer is formed on the surface of a core body for precision casting.

According to a seventh invention, in the fifth or sixth invention, the alkoxide material is a silicon alkoxide alone or a mixed alkoxide of silicon alkoxide and aluminum alkoxide.

In the present invention, by forming a coating layer made of an alkoxide material on the surface of the sintered precision casting core body, the surface holes generated during sintering are sealed, and the strength of the core is reduced. While improving, since a hole is sealed, there exists an effect that it can prevent that a core breaks at the time of casting.

FIG. 1 is a cross-sectional configuration diagram of a precision casting core. FIG. 2 is a flowchart showing an example of the steps of the casting method. FIG. 3 is a flowchart showing an example of the steps of the mold manufacturing method. FIG. 4 is an explanatory view schematically showing a manufacturing process of the core. FIG. 5 is a perspective view schematically showing a part of the mold. FIG. 6 is an explanatory view schematically showing a wax mold manufacturing process. FIG. 7 is an explanatory diagram schematically showing a configuration in which slurry is applied to a wax mold. FIG. 8 is an explanatory view schematically showing a manufacturing process of the outer mold. FIG. 9 is an explanatory view schematically showing a part of the mold manufacturing method. FIG. 10 is an explanatory view schematically showing a part of the casting method.

Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following description. In addition, constituent elements in the following description include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range.

[First Embodiment]
FIG. 1 is a cross-sectional configuration diagram of a precision casting core.
The core for precision casting according to the present invention has two types of different particle diameters on the surface of a sintered core body for precision casting (hereinafter referred to as “core body”) mainly composed of siliceous particles. A coating layer of a siliceous material is formed.

As shown in the upper section of the cross-sectional view of the core body of the sintered body shown in FIG. 1, a large number of holes 18c are generated in the surface 18b of the core body 18a during sintering.
In the present invention, as shown in the lower part of FIG. 1, the hole 18c is sealed by covering the hole 18c formed on the surface with the coating layer 19a.

Here, the core body 18a contains siliceous particles as a main component, and is formed of fused silica (SiO ₂ ) such as silica sand or silica flour.
The core body 18a is manufactured by a known method, and uses, for example, silica flour (for example, 800 mesh (10 to 20 μm)) and silica sand (for example, 220 mesh (20 to 70 μm)) as siliceous particles. A wax is added to the mixture at a weight ratio of 1: 1 and heated and kneaded to obtain a compound.

The obtained compound is molded by injection molding to obtain a core molded body.
Thereafter, a degreasing process up to, for example, 600 ° C. is performed, and then a sintering process is performed at, for example, 1,200 ° C. to obtain the core body 18a.

In the present invention, the coating layer 19a is formed on the surface 18b of the core body 18a of the obtained sintered body.
The coating layer 19a uses an alkoxide material.
Here, the alkoxide material is silicon alkoxide alone or mixed alkoxide of silicon alkoxide and aluminum alkoxide.

Silicon ethoxide or silicon butoxide is used as the silicon alkoxide, and ethanol or butanol is used as the solvent.
When two types of alkoxide are mixed, a mixed alkoxide material of silicon alkoxide and aluminum alkoxide is used, and as the solvent, an alcohol solvent such as butanol is used.

When preparing a mixed alkoxide, a solution in which a mixed alkoxide of silicon ethoxide and aluminum isopropoxide is dissolved in butanol is prepared.
Here, the mixed alkoxide (silicon ethoxide + aluminum isopropoxide) is prepared so that the molar ratio = 2: 3, thereby preparing an organic mixed alkoxide.

After immersing the core specimen in the prepared alkoxide alone or mixed alkoxide, it is pulled up to form a silicon layer or silicon-aluminum alkoxide layer on the surface 18b of the core body 18a, and also in the hole 18c on the core surface. The silicon component or silicon-aluminum alkoxide component is deposited.
At the time of this immersion, since the alkoxide alone or the mixed alkoxide is dissolved in the alcohol solution, the penetration into the core body is good, and a good coating layer 19a is formed.

Then, it is dried and then heat-treated at, for example, 1,000 ° C. This heat treatment may be, for example, 1,000 ° C. or less as long as the coating layer 19a is formed on the surface.

In this heat treatment, in the case of the mixed alkoxide, the silicon-aluminum alkoxide layer is changed to a high melting point inorganic mullite (3Al ₂ O ₃ .2SiO ₂ ) by the reaction. The core 18 in which the core body 18a is covered with the mullitized coating layer 19a is obtained.
Here, since the melting point of mullite is 1,900 ° C., which is considerably higher than the melting point of silica (1,600 ° C.), it is possible to cope with a high casting temperature.
As described above, according to the present invention, since a large number of holes formed on the surface are sealed, it is possible to prevent the core from being broken at the time of casting by using such a hole as a starting point. Therefore, the high temperature strength of the core for precision casting is improved.

<Test Example 1>
Hereinafter, test examples for confirming the effects of the present invention will be described.
In this test example, first, a wax is added to a mixture of silica flour (800 mesh) and silica sand (220 mesh) at a weight ratio of 1: 1, and heated and kneaded to obtain a compound. Here, the silica flower is “MCF-200C” (trade name) manufactured by Tatsumori, the silica sand is “RD-120” (trade name) manufactured by Tatsumori, and the wax is “Cerita Wax F30-” manufactured by Paramelt. 75 "(trade name) was used.
A molded body is obtained by injection molding of the obtained compound.
As an evaluation test body, width 30 × length 200 × thickness 5 mm was obtained.

Next, a degreasing process up to 600 ° C. and a sintering process at 1,200 ° C. were performed to obtain a test body for a core body.

(Coating layer 1)
Next, a solution in which silicon ethoxide is dissolved in ethanol is prepared. The core body specimen was immersed in the obtained silicon ethoxide, and then pulled up to form an alkoxide coating layer 19a on the surface. Next, after drying, heat treatment was performed at 1,000 ° C., and an inorganic silica coating layer 19a made of silicon ethoxide was formed on the core body surface 18b (test body 1).

(Coating layer 2)
Next, a solution in which mixed alkoxide of silicon ethoxide and aluminum isopropoxide is dissolved in butanol is prepared. Here, the mixed alkoxide (silicon ethoxide + aluminum isopropoxide) is prepared so that the molar ratio = 2: 3, thereby preparing an organic mixed alkoxide.

The core body specimen was immersed in the obtained mixed alkoxide and then pulled up to form a mixed alkoxide coating layer 19a on the surface. Next, after drying, heat treatment was performed at 1,000 ° C., and a coating layer 19a made of mullite formed by reaction of a mixed alkoxide of silicon ethoxide and aluminum isopropoxide was formed on the core body surface 18b (test body 2). .

As a comparative example, a comparative test body was formed without a coating layer.
The strength of these evaluation specimens was measured.
Here, the strength test was performed according to “Bending strength of ceramics (1981)” according to JIS R 1601.

The strength of the comparative test body in which the coating layer of the conventional method was not formed was 20 MPa, whereas the strength of the test body 1 of the silica coating layer of the core body coating layer 1 according to the present invention was 22 MPa. It was. As a result, a strength improvement of 10% was observed in the test body for the core body of the present invention.

Further, the strength of the test body 2 of the silica coating layer of the core body coating layer 2 according to the present invention was 24 MPa. As a result, the strength improvement of 20% was recognized in the test body for the core body of the present invention.
According to the test body 2 of the present invention, since the high temperature durability of the core is improved by mullite formation, no deformation occurs even if the core is kept at a high temperature (for example, 1,550 ° C.) for a long time, for example, in the manufacture of a unidirectional solidified blade. A mold can be obtained.

Hereinafter, a casting method using a mold in which the core for precision casting of the present invention is arranged will be described.

FIG. 2 is a flowchart showing an example of the steps of the casting method. Hereinafter, the casting method will be described with reference to FIG. Here, the processing shown in FIG. 2 may be executed fully automatically, or may be executed by an operator operating an apparatus that executes each process. 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.

Hereinafter, the mold manufacturing method of the present embodiment executed in the step S1 will be described with reference to FIGS. FIG. 3 is a flowchart showing an example of the steps of the mold manufacturing method. Here, the process shown in FIG. 3 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). The core has a shape corresponding to a cavity inside a casting made of a mold. That is, the core is arranged in a portion corresponding to the cavity inside the casting, thereby suppressing the metal that becomes the casting from flowing in at the time of casting. Hereinafter, the manufacturing process of the core will be described with reference to FIG.

FIG. 4 is an explanatory view schematically showing the manufacturing process of the core. In the mold manufacturing method, a mold 12 is prepared as shown in FIG. 4 (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. In FIG. 4, the cross section of the mold 12 is shown. However, the mold 12 basically has an entire circumference corresponding to the core except for an opening for injecting material into the space and a hole for extracting air. It is a covering cavity. In the mold casting method, 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. Specifically, the core 18 is produced by so-called injection molding in which the ceramic slurry 16 is injected into the mold 12. In the mold manufacturing method, when 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 formed of ceramics is baked and hardened (step S102). Here, “alkoxide material” was used as the ceramic slurry 16 material.

Next, in order to form a coating layer on the surface of the core 18, the sintered core 18 is immersed in the storage portion 17 in which the slurry 19 is stored, taken out, and then dried (step S 103). Next, the immersed core 18 is taken out, placed in the firing furnace 20, and fired. Thereby, the coating layer 19a is formed on the surface of the core 18 made of ceramics (step S104).
The mold casting method produces the core 18 on which the coating layer 19a is formed as described above. The core 18 is formed of a material that can be removed by a core removal process such as a chemical process after the casting is solidified.

In the mold manufacturing method, after the core 18 is manufactured, 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 ceramics. FIG. 5 is a perspective view schematically showing a part of the mold. As for the metal mold | die 22a shown in FIG. 5, the recessed part formed in the internal peripheral surface respond | corresponds to the outer peripheral surface of a casting. In FIG. 5, only the mold 22a is shown, but a mold corresponding to the mold 22a and corresponding to the mold 22a is also produced so as to close the recess formed on the inner peripheral surface. In the mold manufacturing method, two molds are combined to form a mold whose inner peripheral surface corresponds to the outer peripheral surface of the casting.

In the mold manufacturing method, when an external mold is manufactured, a wax mold is manufactured (step S16). Hereinafter, a description will be given with reference to FIG. FIG. 6 is an explanatory view schematically showing a wax mold manufacturing process. In the mold manufacturing method, the core 18 is installed at a predetermined position of the mold 22a (step S110). Thereafter, a mold 22b corresponding to the mold 22a is placed on the surface of the mold 22a where the recess is formed, and the core 18 is surrounded by the molds 22a and 22b, and the core 18 and the molds 22a and 22b are surrounded. A space 24 is formed between the two. 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. In the mold manufacturing method, the entire space 24 is filled with the WAX 28 (step S113). Thereafter, the wax 28 is solidified to form the wax mold 30 in which the core 18 is surrounded by the wax 28. The wax mold 30 basically has the same shape as the casting for which the part formed by the WAX 28 is manufactured. Thereafter, in the casting manufacturing method, 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. As described above, the mold manufacturing method produces the solder mold 30 including the core 18 inside and formed of the WAX 28 having the same shape as the casting.

In the mold manufacturing method, when the wax mold 30 is produced, slurry application (dipping) is performed (step S18). FIG. 7 is an explanatory diagram schematically showing a configuration in which slurry is applied to a wax mold. FIG. 8 is an explanatory view schematically showing a manufacturing process of the outer mold. In the mold manufacturing method, as shown in FIG. 7, the wax mold 30 is immersed in the storage part 41 in which the slurry 40 is stored, and is taken out and then dried (step S19). Thereby, the prime layer 101 </ b> A can be formed on the surface of the wax mold 30.
Here, the slurry applied in step S <b> 18 is a slurry applied directly to the wax mold 30. As the slurry 40, a slurry in which alumina ultrafine particles are monodispersed is used. In the slurry 40, it is preferable to use refractory fine particles of about 350 mesh, such as zirconia, as flour. Moreover, it is preferable to use polycarboxylic acid as a dispersing agent. Further, it is preferable to add a small amount, for example, 0.01%, of an antifoaming agent (silicon-based substance) or a wettability improving agent to the slurry 40. By adding the wettability improving agent, the adhesion of the slurry 40 to the wax mold 30 can be improved.

In the mold manufacturing method, as shown in FIG. 7, slurry application is performed with the slurry 40, and then the wax mold having the prime layer (first dry film) 101A is further applied with slurry (dipping) (step S20). . Next, as shown in FIG. 8, 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). After that, the surface of the slurry layer with the stucco material 54 attached is dried, and the first backup layer (second dry film) 104-1 is formed on the prime layer (first dry film) 101A (step S22). .
A determination is made to repeat the same operation as that for forming the first backup layer (second dry film) 104-1 a plurality of times (for example, n: 6 to 10 times) (step S23). 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.

In the mold manufacturing method, after obtaining the dry molded body 106A on which a plurality of layers of the prime layer 101A and the multilayer backup layer 105A are obtained, 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. Hereinafter, a description will be given with reference to FIG. FIG. 9 is an explanatory view schematically showing a part of the mold manufacturing method. In the mold manufacturing method, as shown in step S130, 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 the space between the dry molded body 106A serving as the outer mold and the core 18 is filled with space as shown in step S131. A mold 72 in which 64 is formed is produced. Thereafter, in the mold manufacturing method, as shown in 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. As a result, 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. In the casting manufacturing method, the mold 72 is produced as described above.

The explanation of the casting method will be continued using FIG. 2 and FIG. FIG. 10 is an explanatory view schematically showing a part of the casting method. In the casting method, when the mold is produced in step S1, the mold is preheated (step S2). For example, the mold is placed in a furnace (vacuum furnace, firing furnace) and heated to 800 ° C. or higher and 900 ° C. or lower. By performing 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.

In the casting method, when the mold is preheated, pouring is performed (step S3). That is, as shown in step S <b> 140 of FIG. 10, 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.

In the casting method, 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. 10, when the molten metal hardens 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.

As for the casting method, when the outer mold 61 is removed from the casting 90, the core removal process is performed (step S5). That is, as shown in step S142 of FIG. 10, the casting 90 is put into the autoclave 92 and the core removal process is performed to melt the core 18 inside the casting 90, and the melted melting core 94 is removed. It discharges from the inside of the casting 90. 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.

In the casting method, after the removal of the core, the finishing process is performed (step S6). That is, a finishing process is performed on the surface and inside of the casting 90. In the casting method, the casting is inspected together with the finishing process. Thereby, as shown to step S143 of FIG. 10, the casting 100 can be manufactured.

As described above, the casting method of the present embodiment produces a casting by using a lost wax casting method using WAX (wax) to produce a casting. Here, the mold manufacturing method, the casting method, and the mold according to the present embodiment include an outer mold that is an outer portion of the mold, and a prime layer (first layer that is the first layer) that forms an inner peripheral surface using alumina 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.

In the casting method of this embodiment, since the coating layer is formed on the surface of the core, the dimensional accuracy is improved, and the durability is improved even when the casting temperature is high.
Even when the casting process takes a long time, since it is a high-strength core, the degree of freedom in casting design (for example, setting the pulling speed low) is improved.
Furthermore, it is possible to reduce the thickness of the product and manufacture a precision casting such as a turbine rotor blade having good thermal efficiency.

Examples of precision castings according to the present invention include gas turbine stationary blades, gas turbine combustors, gas turbine split rings and the like in addition to gas turbine rotor blades.

[Second Embodiment]
In this embodiment, since it is the same as that of the core for precision casting of the first embodiment, description will be made with reference to the drawings (FIGS. 1 and 2) described in the first embodiment.
FIG. 1 is a cross-sectional configuration diagram of a precision casting core.
The core for precision casting according to the present invention has two types of different particle diameters on the surface of a sintered core body for precision casting (hereinafter referred to as “core body”) mainly composed of siliceous particles. A coating layer of a siliceous material is formed.

As shown in the upper section of the cross-sectional view of the core body of the sintered body shown in FIG. 1, a large number of holes 18c are generated in the surface 18b of the core body 18a during sintering.
In the present invention, as shown in the lower part of FIG. 1, the hole 18c is sealed by covering the hole 18c formed on the surface with the coating layer 19a.

Here, the core body 18a contains siliceous particles as a main component, and is formed of fused silica (SiO ₂ ) such as silica sand or silica flour.
The core body is manufactured by a known method and uses, for example, silica flour (for example, 800 mesh (10 to 20 μm)) and silica sand (for example, 220 mesh (20 to 70 μm)) as siliceous particles. A wax is added to the mixture at a weight ratio of 1 and the mixture is heated and kneaded to obtain a compound.

The obtained compound is molded by injection molding to obtain a core molded body.
Thereafter, a degreasing process up to, for example, 600 ° C. is performed, and then a sintering process is performed at, for example, 1,200 ° C. to obtain the core body 18a.

In the present invention, the coating layer 19a is formed on the surface of the core body 18a of the obtained sintered body.
The covering layer 19a is an alkoxide-silica fume material made of an alkoxide material and silica fume.
Here, the alkoxide material is silicon alkoxide alone or mixed alkoxide of silicon alkoxide and aluminum alkoxide.

The silica fume of the inorganic material uses, for example, a spherical body having a particle size of 0.15 μm.
Here, the silica fume preferably has a particle size of 0.05 to 0.5 μm.
The dispersion ratio of silica fume is 5 to 40% by weight, preferably around 20% by weight.

Silicon ethoxide or silicon butoxide is used as the silicon alkoxide, and ethanol or butanol is used as the solvent.
When two types of alkoxide are mixed, a mixed alkoxide material of silicon alkoxide and aluminum alkoxide is used, and as the solvent, an alcohol solvent such as butanol is used.

When preparing a mixed alkoxide, a solution in which a mixed alkoxide of silicon ethoxide and aluminum isopropoxide is dissolved in butanol is prepared.
Here, the mixed alkoxide (silicon ethoxide + aluminum isopropoxide) is prepared so that the molar ratio = 2: 3, thereby preparing an organic mixed alkoxide.

After immersing the core test body in the prepared single-piece alkoxide or mixed alkoxide in which the silica fume is dispersed, the core specimen is pulled up to form a silicon layer or silicon-aluminum alkoxide layer containing silica fume on the surface 18b of the core body 18a. A silicon layer containing silicon fume or silicon-aluminum alkoxide component also deposits in the hole 18c on the core surface.
At the time of this immersion, since the alkoxide alone or the mixed alkoxide is dissolved in the alcohol solution, the penetration into the core body is good, and a good coating layer is formed.

Thereafter, drying is performed, and then heat treatment is performed at 1,000 ° C., for example. This heat treatment may be, for example, 1,000 ° C. or less as long as the coating layer 19a is formed on the surface.
After this drying, the alkoxide and silica fume components are deposited in the holes 18c on the surface of the core body 18a. At this time, a mixed layer of a large particle size silica fume layer and a fine and dense alkoxide layer is formed.
Then, the heat treatment at 1000 ° C. causes the alkoxide layer to become inorganic ceramics, and the voids of the large particle size silica fume layer are filled with a dense ceramic layer to improve the adhesion between the particles.

In this heat treatment, when a mixed alkoxide is used, the silicon-aluminum alkoxide layer containing silica fume changes to a high melting point inorganic mullite (3Al ₂ O ₃ .2SiO ₂ ) by the reaction. The core 18 in which the core body 18a is covered with the coating layer 19a in which the voids of the silica fume layer having a large particle diameter are filled with a dense mullite layer and the adhesion between the particles is improved is obtained.
Here, since the melting point of mullite is 1,900 ° C., which is considerably higher than the melting point of silica (1,600 ° C.), it is possible to cope with a high casting temperature.
As described above, according to the present invention, since a large number of holes formed on the surface are sealed, it is possible to prevent the core from being broken at the time of casting by using such a hole as a starting point. Therefore, the high temperature strength of the core for precision casting is improved.

In addition, since silica fume has a large particle size, thermal contraction is small even in heat treatment at 1,000 ° C.

<Test Example 2>
Hereinafter, test examples for confirming the effects of the present invention will be described.
In this test example, first, a wax is added to a mixture of silica flour (800 mesh) and silica sand (220 mesh) at a weight ratio of 1: 1, and heated and kneaded to obtain a compound. Here, the silica flower is “MCF-200C” (trade name) manufactured by Tatsumori, the silica sand is “RD-120” (trade name) manufactured by Tatsumori, and the wax is “Cerita Wax F30-” manufactured by Paramelt. 75 "(trade name) was used.
A molded body is obtained by injection molding of the obtained compound.
As an evaluation test body, width 30 × length 200 × thickness 5 mm was obtained.

Next, a degreasing process up to 600 ° C. and a sintering process at 1,200 ° C. were performed to obtain a test body for a core body.

(Coating layer 3)
Next, a solution in which silicon ethoxide is dissolved in ethanol is prepared. Silica fume (for example, a particle size of 0.15 μm; spherical body) is blended in an amount of 20% by weight with the obtained silicon ethoxide to obtain a silicon ethoxide slurry blended with silica fume.
The core body test specimen was immersed in the silicon ethoxide slurry containing this silica fume and then pulled up to form an alkoxide coating layer 19a containing silica fume on the surface. Next, after drying, heat treatment was performed at 1,000 ° C., and an inorganic silica coating layer 19a made of silicon ethoxide containing silica fume was formed on the core body surface 18b (test body 3).

(Coating layer 4)
Next, a solution in which mixed alkoxide of silicon ethoxide and aluminum isopropoxide is dissolved in butanol is prepared. Here, the mixed alkoxide (silicon ethoxide + aluminum isopropoxide) is prepared so that the molar ratio = 2: 3, thereby preparing an organic mixed alkoxide.
Silica fume (for example, particle size 0.15 μm; spherical body) is blended with the obtained mixed alkoxide at 20% by weight to obtain a mixed alkoxide slurry blended with silica fume.
The core body specimen was immersed in the mixed alkoxide slurry containing silica fume and then pulled up to form a mixed alkoxide coating layer 19a on the surface. Next, after drying, heat treatment was performed at 1,000 ° C., and a coating layer 19a made of mullite containing silica fume formed by reaction of a mixed alkoxide of silicon ethoxide and aluminum isopropoxide was formed on the core body surface 18b (test). Body 4).

As a comparative example, a comparative test body was formed without a coating layer.
The strength of these evaluation specimens was measured.
Here, the strength test was performed according to “Bending strength of ceramics (1981)” according to JIS R 1601.

The strength of the comparative test body in which the coating layer of the conventional method was not formed was 20 MPa, whereas the strength of the test body 3 of the silica coating layer of the core body coating layer 3 according to the present invention was 23 MPa. It was. As a result, a strength improvement of 15% was recognized in the test body for the core body of the present invention.
Further, the strength of the test body 4 of the silica coating layer 4 of the core body coating layer 4 according to the present invention was 25 MPa. As a result, the core body test specimen of the present invention was found to have a strength improvement of 25%.

According to the test body 4 of the present invention, since the high temperature durability of the core is improved by mullite formation, for example, no deformation occurs even if the core is kept at a high temperature (for example, 1,550 ° C.) for a long time in the manufacture of a unidirectional solidified blade. A mold can be obtained.

Here, regarding the casting method using the mold in which the core for precision casting according to this embodiment is arranged, the “alkoxide material” which is the material of the ceramic slurry 16 used in the method of the first embodiment is referred to as “alkoxide material”. Since the operation is the same except that the alkoxide-silica fume material made of silica fume is changed, the description thereof will be omitted.

12, 22a, 22b Mold 12a Convex 14, 26 Arrow 16 Ceramic slurry 18 Core (core)
18a Core body 18b Surface 18c Hole 19 Slurry 19a Coating layer 20, 70 Firing furnace 24, 64 Space 28 WAX (Wax)
30 Wax mold 32 Gate 40 Slurry 60, 92 Autoclave 61 Outer mold 61a Debris 62 Molten WAX
72 Mold 80 Molten metal 90, 100 Casting 94 Melting core 101A Prime layer

Claims (7)

1. On the surface of a sintered precision casting core body mainly composed of siliceous particles,
   A precision casting core comprising an alkoxide coating layer made of an alkoxide material.
2. On the surface of a sintered precision casting core body mainly composed of siliceous particles,
   A precision casting core comprising an alkoxide-silica fume coating layer comprising an alkoxide material and silica fume.
3. In claim 1 or 2,
   A precision casting core, wherein the alkoxide material is silicon alkoxide alone or mixed alkoxide of silicon alkoxide and aluminum alkoxide.
4. A mold for precision casting used in the manufacture of castings,
   The core for precision casting according to claim 1 or 2 having a shape corresponding to a hollow portion inside the casting,
   A precision casting mold comprising: an outer mold corresponding to a shape of an outer peripheral surface of the casting.
5. A sintered body of a core body for precision casting mainly composed of siliceous particles,
   Soak in alkoxide material,
   A method for producing a core for precision casting, which is then dried and then heat-treated to form a coating layer on the surface of the core body for precision casting.
6. A sintered body of a core body for precision casting mainly composed of siliceous particles,
   Immersion in alkoxide-silica fume material of alkoxide material and silica fume,
   A method for producing a core for precision casting, which is then dried and then heat-treated to form a coating layer on the surface of the core body for precision casting.
7. In claim 5 or 6,
   A method for producing a core for precision casting, wherein the alkoxide material is silicon alkoxide alone or a mixed alkoxide of silicon alkoxide and aluminum alkoxide.

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