JP2014231080A - Core for precision casting, production method therefor, and mold for precision casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core for precision casting with improved high-temperature strength, a production method therefor, and a mold for precision casting.SOLUTION: A core for precision casting comprises a precision casting core main body formed as a result of mixing and sintering silica particles and silica fume. A precision casting core having silica fume added thereto has smaller resistance during heating/injection molding and improved fluidity as a result of silica fume addition. As a result, injection molding pressure when producing cores can be reduced because fluidity is improved. Furthermore, the present invention can be applied to thin-walled molded articles requiring improved fluidity and molded articles having a complicated shape.

Description

  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, since the turbine blades of the land gas turbine and the jet engine are exposed to a high temperature, they have a complicated cooling structure (air hole) for flowing a cooling medium (air) for cooling inside. In order to construct such an internal cooling structure, a core (silica) having the same shape as the flow path of the cooling medium is placed (installed) inside the mold, cast, and cooled, so that a cast metal article Is obtained. At this time, the outer shape can be obtained by breaking the mold, but the core remains in the mold. In order to remove this, dissolution and removal with an alkali (NaOH, KOH, etc.) is usually performed.

Therefore, the core needs to have solubility in alkali, and a siliceous material (SiO ₂ ) is 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, this siliceous material is generally produced by pulverizing an ingot obtained by electromelting quartz, so that there is a problem that the particle size is relatively coarse. A material obtained by molding such a material into a core shape by a method such as injection molding and heat-treating (firing) is used. However, since the particle size is coarse, the strength of the sintered body is low.
Moreover, since the fluidity | liquidity of the material at the time of injection molding is low, there exists a problem that a high injection pressure is required.

Furthermore, 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 of the present invention is to provide a precision casting core with good flowability and improved high-temperature strength, a method for producing the same, and a casting mold for precision casting. .

  A first invention of the present invention for solving the above-mentioned problems is for precision casting, characterized in that a siliceous particle and silica fume are mixed and sintered to form a core body for precision casting. In the core.

  A second invention is the precision casting core according to the first invention, wherein a coating layer is formed on the surface of the sintered precision casting core body.

  According to a third aspect of the present invention, there is provided a precision casting mold for use in manufacturing a casting, the core for precision casting according to claim 1 or 2 having a shape corresponding to a hollow portion inside the casting, and an outer peripheral surface of the casting. A precision casting mold characterized by having an outer mold corresponding to the shape.

  According to a fourth aspect of the invention, a sintered body of a precision casting core body mainly composed of siliceous particles is immersed in a coating material composed of a siliceous material and an alumina material, then dried, and then subjected to heat treatment. And a method for producing a core for precision casting, wherein a coating layer is formed on the surface of the core body for precision casting.

  According to a fifth aspect of the present invention, there is provided the method for producing a core for precision casting according to the fourth aspect, wherein the siliceous material is silica sol, and the alumina material is alumina sol.

  According to this invention, the fluidity | liquidity of the prepared compound improves by adding the silica fume of a spherical ultrafine particle to the siliceous particle | grains with a coarse particle size. Thereby, reduction of the injection molding pressure at the time of core manufacture can be aimed at.

  Furthermore, by forming a coating layer of two types of siliceous materials having different particle sizes on the surface of the sintered precision casting core body, the surface holes generated during sintering will be sealed, Since the strength of the core is improved and the hole is sealed, the core can be prevented from being broken during casting.

FIG. 1 is a graph showing the relationship between the amount of silica fume added in Test Example 2 and the strength. FIG. 2 is a graph showing the relationship between the amount of silica fume added in Test Example 3 and the strength. 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 manufacturing process of the core. 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. 12 is an explanatory diagram schematically showing a manufacturing process of the core according to the second embodiment. FIG. 13 is a cross-sectional configuration diagram of a precision casting core.

  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.

  The core for precision casting according to the present invention is obtained by mixing and sintering siliceous particles and silica fume (particle size: 0.15 μm) to form a core body for precision casting.

Here, the siliceous particles are formed of fused silica (SiO ₂ ) such as silica sand and silica flour.

The core body 18a is manufactured by a known method, and as siliceous particles, silica sand (220 mesh (20 to 70 μm) or 350 mesh (20 to 40 μm)) alone or, for example, silica flour (for example, 800 mesh). (10-20 μm)) and silica sand (for example, 220 mesh or 350 mesh) mixed at a weight ratio of 1: 1, silica fume (particle size 0.15 μm) is added, and wax is added thereto And knead to obtain a compound.
Here, the silica fume preferably has a particle size of 0.05 to 0.5 μm.

  Here, the silica fume to be blended with the siliceous particles is 5% by weight or more, preferably 10% by weight or more, and more preferably 20% by weight or more, as shown in Test Examples described later. This is because the addition of less than 5% by weight does not contribute much to the improvement of the core strength.

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.

  By adding silica fume of spherical ultrafine particles to siliceous particles having a coarse particle size, the fluidity of the prepared compound is improved. Thereby, reduction of the injection molding pressure at the time of core manufacture can be aimed at.

<Test Example 1>
Test examples showing the fluidity effect of the present invention will be described.
A comparison was made of the fluidity of the compounds to improve the injection moldability.
10% by weight of wax (thermoplastic) is added to siliceous particles (for example, 220 mesh), kneaded to form a compound, which is used as a comparative compound.
Silica particles (for example, 220 mesh) are mixed with silica fume at a weight ratio of 9: 1, 10% by weight of wax (thermoplastic) is added and kneaded to form a compound, which is used as a compound for this test.

  Each compound of the conventional silica fume not added (comparative product compound) and the silica fume added (test product compound) was put into an injection molding machine, and the pressure when heated and injected was compared.

  Assuming that the conventional comparative compound containing only siliceous particles is 100, the resistance of the test product compound to which 10% by weight of silica fume was added was 85, and the improvement in fluidity was confirmed by the addition of silica fume.

  As a result, in the test compound, the fluidity was improved, so that it was possible to reduce the injection molding pressure when the core was manufactured. In addition, it can be applied to thin-walled molded products with improved fluidity and molded products with complex shapes.

<Test Example 2>
Test examples showing the effect of the strength of the present invention will be described.
In this test example, wax was added to silica sand (220 mesh: 20 to 70 μm) added with 10%, 20%, 30%, and 40% silica fume, and kneaded by heating. Get a product compound. Here, “RD-120” (trade name) manufactured by Tatsumori Co., Ltd. was used as the silica sand.
A molded body is obtained by injection molding using each of the obtained test product compounds.
As each evaluation specimen, width 30 × length 200 × thickness 5 mm was obtained.

Next, degreasing treatment up to 600 ° C. and sintering treatment at 1,200 ° C. were performed to obtain an evaluation test body for the core body.
The strength of the obtained evaluation specimen was measured.
Here, the strength test was performed according to “Bending strength of ceramics (1981)” according to JIS R 1601.

The test result of Test Example 2 is shown in FIG. FIG. 1 is a graph showing the relationship between the amount of silica fume added in Test Example 2 and the strength.
As shown in FIG. 1, the bending strength increased with an increase in the amount of silica fume added and increased to 20% by weight. In addition, about 20 weight% or more addition, the ratio of strength improvement was small.

  As a result, the silica fume to be blended is a fine particle, and if the addition amount is too large, the densification becomes intense and there is a concern that it takes time to dissolve the core with alkali. It was confirmed that the addition amount of is preferably in the range of 5 to 30% by weight, and preferably in the range of 10 to 30% by weight.

  As described above, it was confirmed that the core material was densified and the bending strength was improved by adding a spherical ultrafine silica fume to a coarse siliceous particle and preparing a compound. .

<Test Example 3>
In Test Example 2, a bending test was performed in the same manner as in Test Example 2 except that the silica sand particles were 350 mesh (20 to 40 μm).
The test result of Test Example 3 is shown in FIG. FIG. 2 is a graph showing the relationship between the amount of silica fume added in Test Example 3 and the strength.
As shown in FIG. 2, since the silica sand was made finer than in Test Example 2, the value of the initial bending strength was high. Moreover, with the increase in the amount of silica fume added, the bending strength increased and increased to 20% by weight. In addition, about 30 weight% or more addition, the ratio of strength improvement was small. 2. From FIG. 2, it was confirmed that the addition amount of silica fume is preferably in the range of 5% by weight to 30% by weight, and preferably in the range of 10% by weight to 30% by weight for improving the strength of the core.

  Hereinafter, a casting method using a mold having the precision casting core of the present invention will be described.

  FIG. 3 is a flowchart showing an example of the process 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. 4 is a flowchart showing an example of steps of the mold manufacturing method. Here, 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). 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. 5 is an explanatory view schematically showing a manufacturing process of the core. In the mold manufacturing method, 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. In FIG. 5, the cross section of the mold 12 is shown, but the mold 12 basically has the entire circumference of the region corresponding to the core other than the opening for injecting the material into the space and the 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).

  In the mold manufacturing method, when 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. 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. 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.

  After producing the external mold, the mold manufacturing method produces a wax mold (wax mold) (step S16). Hereinafter, a description will be given with reference to FIG. FIG. 7 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. 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. In the mold manufacturing method, as shown in FIG. 8, 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). 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. 8, 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). . Next, as shown in FIG. 9, 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 the n-th backup layers 104-n are stacked (step S23: Yes) to obtain a dry molded body 106A which 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. 10 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 106 serving as an outer mold in which a plurality of layers of a prime layer 101A and a 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 106 by filling the interior with pressurized steam. As a result, the wax forming the wax mold 30 is melted and the molten wax 62 is discharged from the space 64 surrounded by the dry molded body 106.
In the mold manufacturing method, the melted WAX 62 is discharged from the space 64, so that the space between the dry molded body 106 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 S <b> 132, the mold 72 in which the space 64 is formed between the dry molded body 106 serving as the outer mold and the core 18 is heated in the firing furnace 70. As a result, the mold 72 is cured by firing by removing water components and unnecessary components contained in the dry molded body 106 serving as the outer mold, and the outer mold 61 is formed. In the casting manufacturing method, the mold 72 is produced as described above.

  The description of the casting method will be continued with reference to FIGS. FIG. 11 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. 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.

  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 in FIG. 11, 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.

  In 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. 11, 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 core removal process is performed, a 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. 11, 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.

  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.

Next, the second precision casting core will be described. FIG. 13 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. 13, 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. 13, the hole 18c formed on this surface is covered with the coating layer 19a, thereby sealing the hole 18c.

In this example, the siliceous particles obtained in Example 1 and silica fume (particle size 0.15 μm) are mixed and sintered to form a coating layer 19a on the surface of the core body 18a of the sintered body. To do.
For example, the coating layer 19a uses two types of siliceous materials having different particle diameters.
Here, two types of siliceous materials having different particle diameters use silica sol (SiO ₂ is 30 wt%) as the first material and silica fume (particle diameter 0.15 μm) as the second material.

In the present invention, silica fume is added to and dispersed in the silica sol to prepare a silica sol-silica fume slurry.
Here, the silica sol and the silica fume are kneaded at a weight ratio of 1: 1 to 4: 1. The ratio of silica fine particles in the silica sol when kneaded at 2: 1 is sol solid content: silica fume = 30: 50.

The sintered core body is immersed in the obtained silica sol-silica fume slurry, and then pulled up to form a coating layer 19a made of silica sol-silica fume on the surface of the core body 18a. When this coating layer 19a is formed, the slurry component penetrates into the holes 18c on the surface of the core, and after drying, the component of silica sol-silica fume precipitates in the holes of the core material.
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.

The obtained coating layer 19a is in a state in which a silica sol having a small particle size is filled in a gap between silica fume having a large particle size of a siliceous material, which is a constituent material, so that the dense coating is formed. Become.
In addition, since silica fume is spherical, silica sol having a small particle size can easily enter gaps between particles of silica fume having a large particle size, so that fine packing is further enhanced. Furthermore, the fine-particle silica sol improves the adhesion between the particles, and thus contributes to the strength improvement.

  Thus, according to the present invention, the high temperature strength of the core for precision casting is improved.

In addition, a siliceous material and an alumina material are used as the second material for forming the coating layer.
Here, the siliceous material is silica sol (SiO ₂ is 30 wt%), and the alumina material is alumina sol (Al ₂ O ₃ ).
Mixing silica sol (SiO ₂ ) and alumina sol (Al ₂ O ₃ ) is prepared so that the molar ratio = 2: 3, thereby preparing a mixed sol (silica-alumina sol).

After immersing the core specimen in the prepared silica-alumina sol, it is pulled up to form a silica-alumina sol layer on the surface 18b of the core body 18a, and the silica-alumina sol component is also present in the holes 18c on the core surface. Precipitate.
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.

In this heat treatment, the silica-alumina sol is converted into a high melting point 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 18c 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.

Further, as the third material for forming the coating layer, the coating layer 19a is made of 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 test 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 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.

In this heat treatment, in the case of the mixed alkoxide, the silicon-aluminum alkoxide layer is changed into 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.

In addition, as the fourth material for forming the coating layer, an alkoxide-silica fume material composed of an alkoxide material and silica fume is used.
Here, the alkoxide material is silicon alkoxide alone or mixed alkoxide of silicon alkoxide and aluminum alkoxide.

For example, silica fume, which is an inorganic material, has a particle size of 0.15 μm and a spherical body.
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 about 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 single alkoxide or mixed alkoxide in which the prepared silica fume is dispersed, the core specimen is pulled up, and a silicon layer containing silicon fume or a silicon-aluminum alkoxide layer is formed on the surface 18b of the core body 18a. The 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 18b 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.
The heat treatment at 1,000 ° C. causes the alkoxide layer to become inorganic ceramics, filling the voids of the silica fume layer having a large particle size with a dense ceramic layer and improving 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.

  Further, as the fifth material for forming the coating layer, a siliceous material, an alumina material and silica fume are used.

Here, the siliceous material is silica sol (SiO ₂ is 30 wt%), and the alumina material is alumina sol (Al ₂ O ₃ ).
Here, the dispersion ratio of the silica fume dispersed in the siliceous material and the alumina material is 5 to 40% by weight, preferably about 20% by weight.
Silica fume preferably has a particle size of 0.05 to 0.5 μm.

Here, the mixing of the silica sol (SiO ₂ ) and the alumina sol (Al ₂ O ₃ ) is prepared so that the molar ratio = 2: 3, and the mixed sol (silica-alumina sol) is prepared (the particle diameter of the dispersed particles). : 1 to several 100 nm).
Silica fume is added and dispersed in the prepared silica-alumina sol to prepare a silica-alumina sol-silica fume slurry.

After immersing the core specimen in this prepared silica-alumina sol-silica fume slurry, it is pulled up to form a layer of silica-alumina sol-silica fume on the surface 18b of the core body 18a, and in the holes 18c on the core surface. Also, silica-alumina sol-silica fume components are deposited.
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.

In this heat treatment, the silica-alumina sol is converted into a high melting point 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 4>
Hereinafter, test examples for confirming the effects of the present invention will be described.
In this test example, a wax is added to silica sand (220 mesh) to which 20% by weight of silica fume is added, and the mixture is heated and kneaded to obtain a compound.
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.

Next, silica fume (particle size is 0.15 μm, spherical) was added to and dispersed in the silica sol (SiO ₂ 30 wt%) to prepare a silica sol-silica fume slurry (silica sol and silica fume in a weight ratio of 2: 1). Kneaded). At this time, the ratio of silica fine particles in the silica sol was sol solid content: silica fume = 30: 50.
The core body specimen was immersed in the obtained silica sol-silica fume slurry, and then pulled up to form a silica sol-silica fume coating layer 19a on the surface. Next, after drying, heat treatment was performed at 1,000 ° C. to form a coating layer 19a made of silica sol-silica fume on the core body surface 18b.

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 23 MPa, whereas the strength of the test body for the core body according to the method of the present invention was 29 MPa. As a result, the core body test specimen of the present invention was found to have a strength improvement of 25%.

Hereinafter, a casting method using a mold having the precision casting core of the present invention will be described.
In addition, the process same as the casting method of Example 1 is abbreviate | omitted, and only a "core manufacturing process" is demonstrated with reference to FIG.
FIG. 12 is an explanatory diagram schematically showing a manufacturing process of the core according to the second embodiment. In the mold manufacturing method, a mold 12 is prepared as shown in FIG. 12 (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. 12, the cross section of the mold 12 is shown, but the mold 12 basically has the entire circumference corresponding to the core other than the opening for injecting the material into the space and the 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).
Up to this point, the process is the same as that of the first embodiment.

Next, as shown in FIG. 12, 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 S103). 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 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.

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, 101B Prime layer

Claims (5)

  A core for precision casting, wherein a core body for precision casting is formed by mixing and sintering siliceous particles and silica fume. In claim 1,
A core for precision casting, wherein a coating layer is formed on the surface of the sintered core body for precision casting. 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. A sintered body of a core body for precision casting mainly composed of siliceous particles,
Immerse in a coating material consisting of siliceous material and alumina 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. In claim 4,
A method for producing a core for precision casting, wherein the siliceous material is silica sol and the alumina material is alumina sol.

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