JP6206769B2 - Core manufacturing method - Google Patents

Description

The present invention relates to the production how the core for precision casting.

For example, since a moving blade of a gas turbine is exposed to a high-temperature working gas, a cooling medium is allowed to flow inside to cool the gas turbine moving blade to keep the temperature applied to the gas turbine moving blade lower. Is adopted.
An internal cooling structure is provided in the gas turbine rotor blade in order to allow the cooling medium to flow inside. When manufacturing a gas turbine rotor blade having an internal cooling structure, a core having the same shape as the flow path of the cooling medium is disposed, and the core is removed after casting.

  As such a core, a ceramic core using conventional ceramic particles is generally employed (for example, see Patent Document 1). Known ceramic molding methods include a slip casting method in which molding is directly performed from a slurry, and an injection molding method. The slip casting method is a method in which a ceramic core is produced by allowing a slurry to flow into a resin or metal mold, curing the slurry, and then drying and firing.

Japanese Patent Laid-Open No. 9-308941

However, the slip casting method is a method in which the solvent (water) is removed and solidified inside the mold, so that the dry shrinkage of the molded body is relatively large and it is difficult to obtain a precise shape. Moreover, a nest or a bubble is generated at the center of the molded body, which is not preferable as a core. In addition, there is a method in which the size of the core is increased in advance by taking account of the shrinkage of the molded body. However, since the degree of shrinkage is not uniform, it is difficult to manufacture a core with an accurate size.
Further, in the case of the injection molding method, since a large amount of wax is used as a binder, there is a problem that the firing time becomes long, for example, it takes about one week to remove the binder. There is also a problem that shrinkage proceeds in the degreasing step of removing the wax.

The present invention, in the manufacture of cores for precision casting, and an object thereof is to provide a manufacturing how shrinkage less core.

According to the first aspect of the present invention, a method for producing a core includes adding silica to a solution comprising a dispersant, a cured resin comprising an acrylamide monomer and N, N′methylenebisacrylamide , and water. The dispersant is 0.4 to 0.6 parts by weight, the acrylamide monomer is 5 to 10 parts by weight, and the N, N′methylenebisacrylamide is 0.4 to 0.6 based on 100 parts by weight of the silica. A slurry generation step for generating a slurry so that the water content is 20 to 30 parts by weight, and a curing accelerator for promoting the curing of the acrylamide monomer and the N, N′methylenebisacrylamide after the slurry generation step. After the curing accelerator addition step, after the curing accelerator addition step, after the mold curing step to introduce and cure the slurry into the mold, after the mold curing step A drying step of drying the molded body obtained by curing the slurry, and a baking step of heating and baking the molded body after the drying step, and the curing accelerator adding step includes ammonium persulfate, A step of dissolving tetramethylethylenediamine and water to form a solution, and 0.008 to 0.012 parts by weight of ammonium persulfate and 0.032 to 0 parts by weight of tetramethylethylenediamine with respect to 100 parts by weight of the slurry. Adding the solution to the slurry after weighing the solution to 0.048 parts by weight .

According to such a structure, shrinkage | contraction of a molded object can be suppressed by mixing a hardening accelerator with the slurry which added the hardening resin which consists of a water-soluble acrylic monomer and a crosslinking agent, and solidifying a slurry. When this molded body is fired, a degreasing step is unnecessary and a core with little shrinkage can be obtained.

  According to such a structure, since the ratio of the cured resin with respect to silica is small, shrinkage | contraction of a molded object can be suppressed more.

  According to this invention, shrinkage | contraction of a molded object can be suppressed by mixing a hardening accelerator with the slurry which added the hardening resin which consists of a water-soluble acrylic monomer and a crosslinking agent, and solidifying a slurry. When this molded body is fired, a degreasing step is unnecessary and a method for producing a core with little shrinkage can be obtained.

(First embodiment)
Hereinafter, the manufacturing method of the core of 1st embodiment of this invention and the core manufactured by this manufacturing method are demonstrated.
The core of the present embodiment is a core for precision casting, and is used together with a mold in wax mold injection molding in a mold manufacturing process.

  The core manufacturing method of the present embodiment includes a slurry generating step for generating a slurry, a curing accelerator adding step for adding a curing accelerator for promoting the curing of the water-soluble acrylic monomer and the crosslinking agent contained in the slurry, and the slurry. A mold curing process for introducing and curing the molded body, a drying process for drying the molded body obtained by curing the slurry, and a firing process for heating (sintering) the molded body.

(Slurry production process)
The slurry which melt | dissolved the dispersing agent, the water-soluble acrylic monomer, the crosslinking agent, and water with respect to silica material (powder) is produced | generated. Among these, the water-soluble acrylic monomer functions as a main material of the skeleton for suppressing the shrinkage of the silica material. Moreover, a crosslinking agent is a crosslinking agent which couple | bonds water-soluble acrylic monomers.
Specifically, a silica material is gradually added to a solution of a dispersant, a water-soluble acrylic monomer, a crosslinking agent, and water, and the mixture is sufficiently kneaded to form a slurry.

  As the dispersant, ammonium polycarboxylate (Poise 532A (trade name, manufactured by Kao Corporation)) can be used. By containing the dispersant in the slurry, the silica material is well dispersed in water without agglomeration. As the dispersant, a dispersant other than ammonium polycarboxylate can be appropriately used as long as the silica material can be dispersed in water.

The water-soluble acrylic monomer is an acrylic soluble in water, and an acrylamide monomer can be adopted.
As the crosslinking agent, an amide-based crosslinking agent, for example, N, N′methylenebisacrylamide can be employed.

The amount of the slurry is, for example, 200 g of silica material, dispersant: 0.8 g to 1.2 g, acrylamide monomer: 10 g to 20 g, N, N′methylenebisacrylamide: 0.8 g to 1.2 g, water : 40 g to 60 g is preferable.
The amount of the slurry is more preferably 200 g of the silica material, dispersant: 1 g, acrylamide monomer: 15 g, N, N′methylenebisacrylamide: 1 g, and water: 50 g. That is, with respect to 100 parts by weight of the silica material, dispersant: about 0.5 parts by weight, acrylamide monomer: about 7.5 parts by weight, N, N'methylenebisacrylamide: about 0.5 parts by weight, water: about 25 parts It is preferable to use parts by weight.
The acrylamide monomer may be 10% by weight or less of the silica material.

The acrylamide monomer is a monomer that functions as a main material of the skeleton that suppresses the shrinkage of the silica material when mixed with the silica material.
N, N′methylenebisacrylamide is a crosslinking agent having a function of changing the hardness and strength of a skeleton that suppresses shrinkage of the silica material by being added to the silica material together with the acrylamide monomer. By changing the amount of N, N′methylenebisacrylamide added, the hardness and strength of the molded product can be changed.

(Curing accelerator addition process)
Next, a curing accelerator comprising an amine and persulfate that accelerates the curing of the acrylamide monomer and N, N′methylenebisacrylamide is added to the slurry. The amine functions as a catalyst for the curing accelerator. When the persulfate is added to the catalyst, it functions as a reaction initiator that initiates a reaction as a curing accelerator.
The curing accelerator addition step includes an amine dissolution step for dissolving amine in the slurry, and a persulfate addition step for adding persulfate to the slurry after the amine dissolution step. After the persulfate is added, the slurry is thoroughly mixed.

As the amine, for example, tetramethylethylenediamine can be employed. As the amine, not only tetramethylethylenediamine but also tetraethylenediamine and triethanolamine can be used.
For example, ammonium persulfate can be used as the persulfate. As the persulfate, any persulfate having an effect of generating oxygen radicals may be used. For example, sodium persulfate may be employed.

As a compounding quantity of the hardening accelerator with respect to a slurry, when it is set as about 250g of slurry, it is preferable to set it as amine: 0.08g-0.12g and persulfate: 0.02-0.03g. More preferably, the amine is 0.1 g and the persulfate is 0.025 g.
That is, it is preferable to use 0.04 parts by weight of amine and 0.01 parts by weight of persulfate with respect to 100 parts by weight of the slurry. By setting it as such a compounding quantity, the hardening time of a slurry can be made into about 3 minutes.

If the amount of amine and persulfate is less than this blending amount, the time required for curing becomes longer. On the other hand, when the amounts of amine and persulfate are increased, it is not preferable because curing is accelerated and working time for molding is eliminated.
By controlling the amount of amine and persulfate added according to the size of the core, the operation can be facilitated. For example, when the core is large, it is preferable to reduce the amount of amine and persulfate to increase the time required for curing.

(Mold curing process)
Next, the slurry is introduced into a mold and cured. In the curing accelerator addition step, when persulfate is added to the slurry and mixed, when about 30 seconds have elapsed, curing starts with light heat generation, and thus the slurry needs to be poured into the mold within about 30 seconds. That is, after about 30 seconds elapses after the curing accelerator addition step, the slurry viscosity increases and solidifies, so that it is not preferable to pour the slurry after about 30 seconds elapses.

The mold is preferably configured to be divided into two or more so that the molded body can be taken out later.
After the slurry is introduced into the mold, curing of the slurry is completed in about 3 minutes. After curing is complete, the mold is split and the compact is removed.

(Drying process)
Next, the molded body is dried. That is, the water in the silica is evaporated. As a drying method, for example, a method of introducing a molded body into a predetermined moisture drying furnace can be employed. As drying conditions, for example, temperature: 120 ° C., time: 3 hours can be set.
The drying method is not limited to the hot air drying method described above, and for example, a hot air drying method in which hot air generated by a gas burner is introduced for drying or a natural drying method in which the air is allowed to stand at room temperature may be employed.

(Baking process)
Next, the molded body is heated and fired. That is, the compact is heated below the melting point, and the powders are combined to advance and promote densification, thereby obtaining a sintered body having no pores. As a firing method, a method of introducing a compact into a predetermined firing furnace can be employed. As the firing conditions, for example, the temperature can be 1200 ° C. and the time can be 1 hour.
A ceramic core sintered body can be obtained through the above steps.

(Example)
A simulated molded body intended for a core having a diameter of 200 mm and a thickness of 100 mm was prototyped using the above core manufacturing method.
The dimensional change of the molded body was 199 mm in diameter when demolded, 198.5 mm in diameter when dried, and 198 mm in diameter after sintering at 1200 ° C. The magnitude of shrinkage is 0.25% for dry shrinkage and 0.25% for sintering shrinkage.
For reference, the core produced by the inventors in the past was shrunk by 1% by sintering at 1200 ° C., but the sintered shrinkage of the molded body produced from the above production method was compared with this. It was very small.

According to the said embodiment, shrinkage | contraction of a molded object can be suppressed by mixing a hardening accelerator with the slurry which added the hardening resin which consists of a water-soluble acrylic monomer and a crosslinking agent, and solidifying a slurry. That is, since the cured resin functions as a silica skeleton, silica shrinkage can be suppressed.
When this molded body is fired, a degreasing step is unnecessary and a core with little shrinkage can be obtained.
Further, since the ratio of the cured resin to the silica is small, the shrinkage of the molded body can be further suppressed.

(Second embodiment)
Hereinafter, the manufacturing method of the core of 2nd embodiment of this invention is demonstrated. In the present embodiment, differences from the first embodiment described above will be mainly described, and description of similar parts will be omitted.
In the curing accelerator adding step of the core manufacturing method of the first embodiment, tetraethylenediamine: 0.1 g was dissolved in 250 g of slurry, and then ammonium persulfate: 0.025 g was added.

  In this embodiment, 1 g of ammonium persulfate and 4 g of tetraethylenediamine were dissolved in 10 g of water. When 1 g of this solution was added to the slurry produced in the slurry production step of the first embodiment, curing was confirmed in about 3 minutes.

  In the case of this embodiment, compared with the first embodiment, about four times the amount of ammonium persulfate and tetraethylenediamine is required, but because the reaction rate is slowed because it is diluted with water, The effect was recognized.

According to the embodiment, ammonium persulfate by dissolving in water, it is possible to accurately meter the amount. That is, ammonium persulfate is powdery, it is difficult to simply weighing accurately small amounts, by diluting dissolved in water, so that accurate weighing.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible. Further, the present invention is not limited by the embodiments, and is limited only by the scope of the claims.

Claims (1)

Silica is added to a solution comprising a dispersant, a cured resin composed of an acrylamide monomer and N, N′methylenebisacrylamide , and water, and the dispersant is 0.4 to 100 parts by weight based on 100 parts by weight of the silica. A slurry is produced so that 0.6 parts by weight, 5-10 parts by weight of the acrylamide monomer, 0.4-0.6 parts by weight of the N, N′methylenebisacrylamide, and 20-30 parts by weight of water. A slurry generation step;
After the slurry generation step, a curing accelerator addition step of adding a curing accelerator that accelerates the curing of the acrylamide monomer and the N, N′methylenebisacrylamide ,
After the curing accelerator addition step, a mold curing step for introducing and curing the slurry into a mold,
After the mold curing step, a drying step of drying the molded body obtained by curing the slurry;
A baking step of heating and baking the molded body after the drying step;
The curing accelerator addition step includes
Dissolving ammonium persulfate, tetramethylethylenediamine, and water to form a solution;
The slurry is weighed so that the ammonium persulfate is 0.008 to 0.012 parts by weight and the tetramethylethylenediamine is 0.032 to 0.048 parts by weight with respect to 100 parts by weight of the slurry. And a step of adding to the core.