JPH04224044A - Production of high strength mold for precision casting - Google Patents

Abstract

PURPOSE:To provide a mold improving high temp. creep strength and having a little high temp. deformation by blending binder to filler having the specific grain distribution to form slurry, alternately coating this slurry and fine grain refractory on surface of a pattern and sintering. CONSTITUTION:The above filler is composed of Al2O3 grains having grain diameter in the range of 0.5-40mum and this grain distribution satisfies the equation. This filler is blended into the binder of a colloidal silica at 60 to 90% ratio to form above slurry. This slurry and the fine grain refractory are alternately coated on the surface of pattern and sintered. The filler contains at least one kind among TiO2, MgO, ZrO2, etc., and the grain size distribution is satisfied as the above. The fine grain refractory is composed of at least one kind of Al2O3, TiO3, MgO, etc. By this method, as the mold improving the high temp. creep strength and having a little high temp. deformation is provided, unidirectional solidifying allay and single alloy are cast by using this mold.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high-strength precision casting mold suitable for manufacturing precision castings made of super heat-resistant alloys, particularly directionally solidified alloys or single crystal alloys.

0002

BACKGROUND OF THE INVENTION Conventionally, first-stage rotor blades for gas turbines have been precision cast products made of super heat-resistant alloys that have excellent high-temperature strength such as creep strength. The mold is made of ZrO2, which has suitable high-temperature properties for normal casting, where the casting temperature and time are 1400-1500°C and 10-20 minutes, respectively.
System particles (ZrO2, SiO2) are used as fillers, and mullite (3Al2O3,
2SiO2) was applied. However, a high-temperature gas turbine plant is being planned in which the gas temperature is increased to approximately 1500° C. in order to improve the power generation efficiency of the gas turbine. In order to increase high-temperature strength, this gas turbine rotor blade material is made of a directionally solidified alloy in which the crystal growth direction matches the direction of centrifugal stress generation, or a crystal grain It is necessary to apply a single crystal alloy that does not contain fields. Casting of unidirectionally solidified alloys and single crystal alloys aligns the crystals in one direction by applying a larger thermal gradient than in normal casting. Therefore, the mold environment is high and for a long time, and in order to suppress mold deformation during pouring and prevent reactions between the molten metal and the mold, it is necessary to use a mold that has even better high-temperature strength than conventional molds. . As a technique for this purpose, as described in JP-A-61-46346, a mold in which a slurry formed from Al2O3 powder and colloidal silica, ZrO2, etc. is alternately and repeatedly coated, and a method for manufacturing the same have been proposed. ing.

0003

[Problems to be Solved by the Invention] In the conventional manufacturing method of high-strength molds for precision casting, materials with excellent properties are selected to obtain high-temperature strength, but particles in the slurry Particle size distribution has not been studied. Therefore, in order to obtain strength, it is necessary to increase the proportion of filler added in the slurry, but there is a problem in that sufficient strength cannot be obtained due to constraints on optimizing the viscosity of the slurry.

An object of the present invention is to provide a method for manufacturing a high-strength mold for precision casting that improves high-temperature strength without impairing the viscosity of the slurry and is excellent for casting directionally solidified alloys and single-crystal alloys. There is a particular thing.

[0005] Still another object is to provide a gas turbine for power generation comprising blades made of a directionally solidified alloy and a single crystal alloy manufactured by the same mold.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing a high-strength mold for precision casting according to the present invention is to form a slurry by blending a binder with a filler, and to mix the slurry with fine particles. In a method for manufacturing a high-strength mold for precision casting in which a refractory is alternately applied to the model surface and sintered, the filler is made of Al2O3 particles with a particle diameter in the range of 0.5 to 40 μm, and The distribution is

[0007]

[Math 3]

CPFT: Cumulative weight (%) D: Particle diameter Ds: Minimum particle diameter DL: Maximum particle diameter n: 0.1 to 1, and this filler is colloidal at a blending rate of 60 to 90%. The composition is such that it is mixed with a silica binder to form a slurry.

[0009]The filler is TiO2, MgO, Z
rO2, HfO2, Y2O3, CaO, La2O3, C
The structure includes at least one of eO2, BaO, and Cr2O3 and satisfies the above particle size distribution.

[0010] Furthermore, the slurry has a Ds of 0.5 to 10 μm.
, DL is 10 to 40 μm, and viscosity is 100 to 200
It may be formed of 0 cP, and after alternately applying the slurry and the fine grain refractory, it may be preheated or fired at a temperature of at least 1500°C.

[0011] Furthermore, after applying the slurry to the first layer,
It may also be possible to mix a fine-grained refractory into a slurry and apply the mixture.

After applying the slurry to the first layer,
The particle size distribution of the slurry is

[0013]

[Math 4]

[0014] CPFT: Cumulative weight (%) D: Particle diameter Ds: Minimum particle diameter DL: Maximum particle diameter n: Mix fine-grained refractories that satisfy the following: 0.2 to 3, and apply the mixture. It can also be a configuration.

[0015] Further, fine grain refractories include Al2O3, TiO2
, MgO, ZrO2, HfO2, Y2O3, CaO, L
a2O3, CeO2, CeO3, BaO and Cr2O3
A configuration consisting of at least one of these may also be used.

Furthermore, in high-strength molds for precision casting,
The structure is manufactured using a manufacturing method for high-strength molds for precision casting.

[0017] The gas turbine for power generation is configured to include blades formed of a directionally solidified alloy or a single crystal alloy cast using a high-strength precision casting mold. [Operation] It is known that the viscosity of a slurry generally changes depending on the blending ratio of filler and caking agent, and that the viscosity increases as the amount of filler increases. However, as shown in FIG. 3, it has become clear that the viscosity also depends on the particle size distribution of fillers A and B, and the viscosity of the slurry for the same blending ratio changes significantly depending on the difference in particle size distribution. Figure 4
3 shows the particle size distribution of each filler A and B used in the experiment shown in FIG. Filler A, which has a high viscosity, has a smaller variation in particle size distribution than Filler B, and has a particle size of approximately 20 μm.
exist concentrated on. On the other hand, filler B has a particle size of 5 to 30
Each particle size is distributed almost uniformly in the μm range.

According to Furnas, the particle size distribution can generally be summarized by equation (1).

[0019]

[Math 5]

(1) Here, CPFT is the cumulative percentage of particles having a particle size of D or less, Ds is the minimum particle size, DL is the maximum particle size, and n is an index. If formula (1) is applied to each filler shown in FIG. 4, n of fillers A and B is 5.6 and 0.0, respectively.
7, and the effective n value for reducing viscosity is 0 for fillers.
．． It became clear that it was 1 to 1.

[0021] Also, the strength σ of the caking material made of fine-grained refractories
It is known that f follows equation (2).

[0022]

[Math 6]

-αp σf/σ0=e (2) Here, σ0 and α are constants, and p is the porosity. Therefore, the smaller p is, the higher σf is and excellent strength can be obtained. In order to reduce this p, n in formula (1) is also relevant, and high strength can be obtained when n is in the range of 0.2 to 3. Therefore, the particle size distribution (particle size distribution) of fine-grained refractories is particularly important when n is 0.
It is effective to limit it to a range of 2 to 3. Furthermore, if the filler has a minimum particle size of 0.5 μm or less, no improvement in strength can be expected, and if the minimum particle size exceeds 10 μm, the viscosity of the slurry will be significantly impaired, and if the maximum particle size is 4.
If it exceeds 0 μm, the viscosity increases, so the minimum and maximum particle diameters of the particles are 0.5 to 10 μm and 10 to 10 μm, respectively.
It should be limited to a range of 40 μm.

[0024]

[Embodiment] An embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, mold No. 1 and no.
11 is the mold of the present invention, and mold No. 11 is the mold of the present invention. 111 and no
．． 1V is a comparative mold. Mold No. 1, both the filler and the fine refractory (stucco) are Al2O3,
Further, the blending ratio of filler and binder (caking agent) was about 80%, and the index n of formula (1) was about 0.4. In addition, the minimum particle size and maximum particle size of the filler are each approximately 5 μm.
and 30 μm, and the viscosity of the slurry was approximately 800 cP.

[0026] After the wax model was immersed in this slurry, fine-grained refractories were sprinkled on it and dried for about 1 hour. After repeating the same process seven times to form a mold, the wax model was removed at a high temperature and fired in a heating furnace. The firing temperature was approximately 1550°C. Mold No. 11 is mold No. 11 as a slurry. The same alumina slurry as in 1 was made using mullite for stucco. The process is based on mold No.
It is the same as 1. Note that the firing treatment was performed at a temperature of 1450°C. Mold No. The slurry and stucco of No. 111 were prepared using mold no. The same alumina particles as in 1 were applied. However, the blending ratio of filler and binder in the slurry was about 70%, and the index n in formula (1) was 5.6. In addition, the maximum particle size and minimum particle size of the filler are approximately 15 μm each.
m and 25 μm, and the viscosity at this time was approximately 800 cP.

Using the filler and stucco described above, mold No. Mold No. 1 in the same process as 1. 111 was produced. The firing temperature at this time was about 1550°C. Mold No.
1V uses zircon as a filler, mullite for stucco, and mold No. It was produced using the same method as No. 11. This is a comparison mold with a firing temperature of about 1450°C.

FIG. 2 shows the creep strength of the four types of molds described above. The test was conducted at 1450°C, the applied stress was varied, and the creep rate at each stress was measured. The test was conducted using a four-point bending creep test device. Mold No. according to the present invention. 1 and no. 11 indicates excellent creep strength, especially mold No. 1 has a stress of about 6Kgf/cm2
It was found that almost no creep deformation occurred even under load. Also, mold No. 11 is mold No. 1
Although the amount of deformation is larger than that of the mold, the amount of deformation is about 1/10 of that of the comparative mold. As described above, the mold according to the present invention has excellent high-temperature strength, and can provide a mold suitable for casting directionally solidified alloys and single-crystal alloys that have a high casting temperature and a long holding time. Also, Al2O3
Compared to ZrO2, ZrO2 has a lower dissociation pressure and is expected to react less with the alloy composition, and has superior properties to the comparative molds in this respect as well.

Furthermore, mold No. 1 has a particle size of approximately 100
A slurry was prepared by adding about 30 wt % of fine-grained refractory made of alumina of 200 μm to the filler, and mold No. V was created. The manufacturing process uses mold No. It is the same as 1. Mold No. The creep rate of V is the stress 0.2
Approximately 0.0 at 5Kgf/cm2 and temperature 1450℃
The speed was 15 mm/h. This strength is based on mold No. The strength exceeded that of No. 1, indicating that the strength can be improved by adding fine-grained refractories to the slurry.

According to the present invention, the high-temperature creep strength can be improved by about 10 times compared to conventional molds, and therefore a mold with low high-temperature deformation can be provided. Therefore, compared to the normal casting method, the casting temperature is higher and the holding time is longer, making it suitable for molds that are applied to unidirectional solidification and single crystal casting made of Fe, Ni, and Co-based heat-resistant alloys. Moreover, this unidirectional solidification and production of single crystals makes it possible to produce large-sized gas turbine rotor blades, and by increasing the gas temperature, power generation efficiency can be dramatically improved.

[0031] The present mold has significantly higher high-temperature strength than conventional molds, and is suitable for manufacturing large-sized cast members that are used at high temperatures. It is also applicable to the manufacturing process of unidirectionally solidified alloys and single crystal alloys of heat-resistant materials with higher melting points, such as intermetallic compounds.

[0032]

Effects of the Invention According to the method of manufacturing a high-strength mold for precision casting of the present invention, it is possible to provide a mold with improved high-temperature creep strength and less high-temperature deformation. It becomes possible to cast crystalline alloys, and the power generation efficiency of power generation gas turbines can be improved by providing blades made of these alloys.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a mold showing an example of the present invention and a comparative mold.

FIG. 2 is a graph showing the creep strength of the mold of the present invention.

FIG. 3 is a graph showing changes in viscosity with changes in the blending ratio of filler and colloidal silica.

FIG. 4 is a graph showing the cumulative weight percentage with respect to filler particle size.

Claims (8)

[Claims] 1. A method for manufacturing a high-strength mold for precision casting, in which a binder is mixed with a filler to form a slurry, and the slurry and a fine-grained refractory are alternately applied to the surface of a model and sintered. The filler consists of Al2O3 particles with a particle diameter in the range of 0.5 to 40 μm, and the particle size distribution is as follows:
[Equation 1] CPFT: Cumulative weight (%) D: Particle diameter Ds: Minimum particle diameter DL: Maximum particle diameter n: Satisfies 0.1 to 1, and contains this filler at a blending rate of 60 to 90%. A method for producing a high-strength mold for precision casting, comprising mixing colloidal silica with the caking agent to form the slurry. Claim 2: The filler is TiO2, MgO, Zr
O2, HfO2, Y2O3, CaO, La2O3, Ce
Claim 1, characterized in that it contains at least one of O2, BaO and Cr2O3, and satisfies the particle size distribution.
The method for manufacturing the high-strength mold for precision casting described above. Claim 3: The slurry has a Ds of 0.5 to 10 μm.
, DL is 10 to 40 μm, and viscosity is 100 to 200
3. The production of a high-strength mold for precision casting according to claim 1 or 2, wherein the slurry and the fine-grained refractory are alternately applied and then preheated or fired at a temperature of at least 1500°C. Law. 4. The high-strength mold for precision casting according to claim 1 or 2, wherein after applying the slurry to the first layer, a fine grain refractory is mixed with the slurry and the mixture is applied. manufacturing method. 5. After applying the slurry to the first layer, the particle size distribution of the slurry is as follows: [Formula 2] CPFT: Cumulative weight (%) D: Particle diameter Ds: Minimum particle diameter DL: Particle The method for manufacturing a high-strength mold for precision casting according to claim 1 or 2, characterized in that fine-grained refractories satisfying a maximum diameter n of 0.2 to 3 are mixed and the mixture is applied. [Claim 6] The fine grain refractory is Al2O3, TiO2
, MgO, ZrO2, HfO2, Y2O3, CaO, L
a2O3, CeO2, CeO3, BaO and Cr2O3
The method for manufacturing a high-strength mold for precision casting according to any one of claims 1, 2, 3, 4, or 5, characterized in that the mold is made of at least one of the following. 7. A high-strength mold for precision casting manufactured using the method for manufacturing a high-strength mold for precision casting according to any one of claims 1 to 6. 8. A gas turbine for power generation, comprising blades made of a directionally solidified alloy or a single crystal alloy cast by the high-strength precision casting mold according to claim 7.