JPH09308941A - Manufacture of ceramic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the manufacturing efficiency of a core of excellent dimensional accuracy by forming a core for precision molding of the slurry made of raw material ceramic powder, colloidal silica and gypsum powder. SOLUTION: The colloidal silica of 30-50 pts.wt. is mixed to the raw material ceramic powder of 100 pts.wt. in which the molten quartz powder and zircon powder, the gypsum power of 40-70 pts.wt. is added to the colloidal silica of 100 pts.wt. and mixed. The slurry is poured into a metallic mold, and after the slurry is hardened through gelation, it is dried and burned to form a core. The zircon powder of 20-50 pts.wt. is preferably mixed in the molten quartz powder of 100 pts.wt. Because the colloidal silica affects the fluidity of the slurry, and the gypsum powder affects the slurry hardening time and the contraction ratio in the burning, the mixing quantity is adjusted in the above range according to the shape of the core and the working condition or the like.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a ceramic core for precision casting.

[0002]

2. Description of the Related Art Ceramic cores used in precision casting are manufactured by various methods. The main manufacturing methods are as follows.

(1) Casting method (strip casting method) Casting method into resin or metal mold Casting a slurry obtained by adding ethyl silicate or colloidal silica to a raw material ceramic powder as a binder is poured into a resin or metal mold. After curing and molding, the molded product is taken out of the mold, dried and baked. Casting method into a gypsum mold Pour slurry into raw ceramic powder with water or alcohol as a solvent, cast into a gypsum mold, solidify by water absorption of gypsum and mold, then remove from mold, dry,
Bake.

(2) Injection Molding Method A slurry in which a raw material ceramic powder is mixed with a thermoplastic resin as a binder is injection-molded in a mold at a high pressure, then taken out of the mold, degreased (removal of the binder) and baked.

[0005]

The above-described method for manufacturing a ceramic core has the following problems.

(1) Casting method Casting method using resin or metal mold-Since ethyl silicate or colloidal silica is used as a binder, the curing speed is slow, especially when thick cores are manufactured. It takes a long time and is not suitable for mass production. Casting method into a plaster mold i) Not suitable for the production and mass production of thick and large cores because it takes a long time to solidify the slurry. ii) Since a mold made of gypsum is used, it is difficult to mold a core having a complicated shape, and the dimensional accuracy of the core becomes poor. iii) Cracks and deformations tend to occur during drying.

(2) Injection molding method i) Since a large amount of a binder of a thermoplastic resin is used when the raw material ceramic powder is slurried, cracks are likely to occur during degreasing, and therefore degreasing must be performed over a long period of time. ii) Since the upper limit of the wall thickness that can be manufactured is about 10 to 15 mm, it is difficult to manufacture a thick core having a larger size. iii) Since a thermoplastic resin is used as a binder, it is likely to be deformed during degreasing and the dimensional accuracy may be deviated.

In view of the above, an object of the present invention is to provide a ceramic core manufacturing method capable of efficiently manufacturing a highly accurate ceramic core even with a thick wall or a large size.

[0009]

A method of manufacturing a ceramic core according to the present invention for attaining the above-mentioned object comprises:
The raw material ceramic powder, colloidal silica, and gypsum powder are mixed, poured into a mold, cured and molded, and then taken out from the mold, dried, and fired.

In the above-mentioned method for producing a ceramic core, the content of the colloidal silica is 30 to 50 parts by weight with respect to 100 parts by weight of the raw material ceramic powder, and the content of the gypsum powder is the colloidal silica 10 described above.
It is characterized in that it is 40 to 70 parts by weight with respect to 0 parts by weight.

The above-mentioned method for producing a ceramic core is characterized in that the raw material ceramic powder is a mixture of fused quartz powder and zircon powder.

In the above-mentioned ceramic core manufacturing method, the blending amount of the zircon powder is the fused silica powder 1
20 to 50 parts by weight with respect to 00 parts by weight.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for manufacturing a ceramic core according to the present invention will be described with reference to FIG. In addition,
FIG. 1 is a flowchart showing the procedure.

As shown in FIG. 1, zircon powder is added to and mixed with fused silica powder (raw ceramic powder).
After adding colloidal silica to knead to form a slurry, and further adding gypsum powder to knead, pour into a mold to cure and mold, then take out from the mold, dry and bake to achieve high efficiency and high accuracy. You can get a good core. The reason for this will be described below.

In general, a slurry containing colloidal silica as a binder loses the charge balance of the colloidal silica and gels (solidifies) when dried, so that the ceramic core can be easily molded. However, if the ceramic core is thick or large, it takes a long time to dry, that is, to evaporate the water content in the colloidal silica. It is difficult to mass-produce cores efficiently.

By the way, in colloidal silica, negatively charged tens of nanometer-sized silica particles are dispersed in water to form a colloidal state, that is, --SiOH groups and --OH ions are present on the surface of the silica particles. The electric double layer is formed by the alkali ions, so that the particles are repulsed and stabilized. When gypsum (CaSO ₄ .0.5 to 2H ₂ O) powder having a small ionic-oxygen attractive force is added to the slurry containing such a colloidal silica as a binder, a polyvalent polyvalent metal is obtained as shown in the following formula (1). Due to the generation of the metal ions, the charge balance of the colloidal silica is disturbed, the silica particles approach each other, and gel, that is,
It will solidify.

[Chemical formula 1] CaSO ₄ → Ca ²⁺ + SO ₄ ² -... (1)

The gelation thus occurring occurs in a much shorter time than the gelation caused by drying,
The molding time is short. In addition, since the molded product gelled as described above has a large bonding force between particles, even if it is dried relatively quickly, the pressure of the generated steam causes cracking or deformation, or it causes large shrinkage. There is nothing to do. Furthermore, since the time required for the gelation can be adjusted by the blending amount of the gypsum powder, the workability can be easily improved. Therefore, according to the method for producing a ceramic core as described above, it is possible to efficiently produce a highly accurate ceramic core even if it is thick or large.

In order to confirm the optimum conditions of the method for manufacturing such a ceramic core, the following examination experiment was conducted.

[Experiment 1] -Amount of colloidal silica (lower limit) <Experimental method> The following amount of colloidal silica was added to the raw ceramic powder obtained by mixing zircon powder with fused silica powder and kneaded. Slurry is obtained, and the thickness that can be filled when the slurry is poured into a mold having a predetermined cavity thickness is obtained.

<Experimental conditions> -Fused silica powder-average particle size: 20 μm-Zircon powder-particle size: 44 μm or less Blending amount: 40 parts by weight per 100 parts by weight of fused silica powder-Colloidal silica-silica content: 30 parts by weight Blending amount: 25, 30, 40, 50 parts by weight with respect to 100 parts by weight of raw material ceramic powder

<Experimental Results> The results are shown in FIG. As can be seen from FIG. 2, when the content of colloidal silica is 30 parts by weight or less, the castable thickness of cavities becomes extremely large, that is, the viscosity of the slurry becomes extremely large, and molding becomes difficult. found. From this, it is judged that the compounding amount of colloidal silica is preferably 30 parts by weight or more with respect to 100 parts by weight of the raw material ceramic powder.

[Study 2] ・ Amount of gypsum powder (upper limit) <Experimental method> Colloidal silica was added to the raw material ceramic powder prepared by mixing zircon powder with fused silica powder, and the amount shown below was obtained. After each of the gypsum powders of No. 1 is added, the time until the slurry is kneaded to gel the slurry, that is, the flowable time (usable time, pot life) of the slurry is obtained.

<Experimental conditions> -Fused silica powder-Same as study experiment 1-Zircon powder-Same as study experiment 1-Colloidal silica-Blending amount: 40 parts by weight relative to 100 parts by weight of raw material ceramic powder Other conditions: Study experiment Same as 1.-Gypsum powder-compounding amount: 20, 40, 60, 70, 80 parts by weight with respect to 100 parts by weight of colloidal silica

<Experimental Results> The results are shown in FIG. As can be seen from FIG. 3, when the blending amount of the gypsum powder exceeds 70 parts by weight, the flowable time of the slurry becomes 3 minutes or less, that is,
It was found that the gelation of the slurry was significantly accelerated, causing a problem in workability. From this, it is judged that the blending amount of the gypsum powder is preferably 70 parts by weight or less with respect to 100 parts by weight of colloidal silica.

[Experimental Experiment 3] ・ Amount of plaster powder (lower limit) <Experimental method> Colloidal silica was added to the raw material ceramic powder prepared by mixing zircon powder with fused silica powder, and after kneading, the amount shown below was obtained. Gypsum powder is added to each, the kneaded slurry is poured into a mold, and the time from the pouring to the hardening, that is, the hardening time is determined.

<Experimental conditions> -Fused quartz powder-Same as study experiment 1-Zircon powder-Same as study experiment 1-Colloidal silica-Same as study experiment 2-Gypsum powder-compounding amount: 100 parts by weight of colloidal silica , 20, 30, 40, 60, 70, 80 parts by weight

<Experimental Results> The results are shown in FIG. As can be seen from FIG. 4, it was found that when the amount of the gypsum powder blended was less than 40 parts by weight, the slurry curing time was remarkably lengthened, resulting in poor efficiency. From this, the amount of gypsum powder blended is 4 with respect to 100 parts by weight of colloidal silica.
It is considered preferable that the amount is 0 parts by weight or more.

[Study Experiment 4] -Amount of Colloidal Silica (Upper Limit Value) <Experimental Method> The following amounts of colloidal silica were added to the raw material ceramic powder prepared by mixing zircon powder with fused silica powder and kneaded. To form a slurry, add gypsum powder to each of these slurries and knead them, then pour each into a mold, cure and mold, then take out from the mold, dry and bake, and obtain the long side of each test piece. Determine the dimensional shrinkage of each.

<Experimental conditions> -Fused quartz powder-same as study experiment 1-Zircon powder-same as study experiment 1-Colloidal silica-blending amount: 30, 40, 50, 60 with respect to 100 parts by weight of the raw material ceramic powder , 70 parts by weight Other conditions: The same as in Study Experiment 1-Gypsum powder-Amount: 60 parts by weight per 100 parts by weight of colloidal silica-Mold-Cavity size: 20 mm x 40 mm x 200 mm-Curing time-about 10 minutes- Drying conditions-Atmosphere: Air Temperature: 120 ° C Time: 3 hours-Firing conditions-Atmosphere: Air Temperature: 1100 ° C Time: 1 hour

<Experimental Results> The results are shown in FIG. As can be seen from FIG. 5, it was found that the dimensional shrinkage ratio exceeded 2% when the amount of the gypsum powder blended exceeded 50 parts by weight.
From this, it is judged that the amount of the gypsum powder is preferably 50 parts by weight or less with respect to 100 parts by weight of the raw material ceramic powder.

[Study Experiment 5] Amount of Zircon Powder (Lower Limit Value) <Experimental Method> Raw ceramic powders prepared by mixing fused silica powders with the amounts of zircon powders shown below were prepared. After adding colloidal silica, test pieces are manufactured by the same operation as the above-described study experiment 4, and the three-point bending strength of each obtained test piece is determined.

<Experimental conditions> -Fused quartz powder-the same as in Study Experiment 1-Zircon powder-Blending amount: 10, 20, 30, 40, 50, 60, 70 parts by weight, etc. relative to 100 parts by weight of fused silica powder Conditions: Same as Study Experiment 1-Colloidal silica-Same as Study Experiment 2-Gypsum powder-Same as Study Experiment 4-Mold-Cavity size: 10 mm x 20 mm x 60 mm-Curing time-Same as Study Experiment 4-Drying conditions- Same as Study Experiment 4 ・ Firing conditions-Same as Study Experiment 4

<Experimental Results> The results are shown in FIG. As can be seen from FIG. 6, it was found that when the amount of zircon powder blended was less than 20 parts by weight, the three-point bending strength was less than 60 kgf / cm ² . From this, it is judged that the amount of zircon powder blended is preferably 20 parts by weight or more with respect to 100 parts by weight of fused silica powder.

When the content of zircon powder exceeds 50 parts by weight with respect to 100 parts by weight of fused silica powder, the elution properties of the ceramic core in the autoclave after casting tend to deteriorate. From this, it is judged that the amount of zircon powder blended is preferably 50 parts by weight or less with respect to 100 parts by weight of fused silica powder.

Therefore, 20 to 50 parts by weight of zircon powder is added to 100 parts by weight of fused silica powder, and 30 to 50 parts by weight of colloidal silica is added to 100 parts by weight of this raw material ceramic powder. 4 parts of gypsum powder to 100 parts by weight of silica
By adding 0 to 70 parts by weight, it becomes possible to more efficiently obtain a highly accurate ceramic core.

[0036]

EXAMPLE An example of a method for producing a ceramic core according to the present invention will be described below. [Manufacturing of ceramic core] <Manufacturing method> Colloidal silica is added to raw material ceramic powder in which zircon powder is mixed with fused quartz powder to knead to form a slurry, and gypsum powder is added to the slurry and kneaded into a mold. After being poured into a mold, cured and molded, the mold was taken out from the mold, dried and fired to manufacture a ceramic core used for casting an asymmetric bifate tube for a boiler.

[0037]

<Production Result> The obtained ceramic core is shown in FIGS. The obtained ceramics core 1 can be manufactured in a short time even though it is relatively large and thick, and furthermore, it is free from cracks and deformation.
The dimensional accuracy was good. Therefore, it was confirmed that a ceramic core with good dimensional accuracy can be produced in a short time without cracking or deformation even if it is relatively large and thick.

[Precision Casting Using Ceramics Core] <Casting Method> The ceramics core manufactured as described above is placed in a mold of an asymmetric bifate tube for a boiler, and wax is injection-molded. As in the precision casting of, a wax model is assembled to make a shell mold,
After the wax is dissolved in the autoclave, the mold integrated with the ceramic core is fired to immediately cast the low alloy cast steel.

[0040]

<Casting Results> The obtained asymmetric bifate tubes are shown in FIGS. The precision-cast biphacate tube 2 did not have casting defects (dimensional defects, cracks, gas defects, etc.) due to the ceramic core 1 produced as described above. Also,
The ceramic core 1 could be easily eluted with an autoclave using potassium hydroxide. Therefore, it was confirmed that the precision casting can be very favorably performed by using the ceramic core 1 manufactured as described above.

[0042]

According to the method for producing a ceramic core of the present invention, the following effects can be obtained. (1) Since the curing time can be significantly shortened as compared with the conventional casting method, the manufacturing can be efficiently performed. (2) Degreasing is unnecessary compared to the conventional injection molding method,
The manufacturing period can be greatly shortened, the cost is low, and mass production is easy. (3) Since the core has high strength even before firing, it is easy to handle and excellent in manufacturability. (4) The core is not cracked during the drying and firing steps. (5) The core is not deformed in the drying and firing steps, and the shrinkage rate is small, so that the dimensional accuracy of the core is good. (6) Even a relatively large and thick core can be manufactured. (7) Since the solidification time and the strength of the core can be easily controlled by adjusting the blending amount,
The manufacturability and performance of the core can be flexibly set.

[Brief description of drawings]

FIG. 1 is a flow chart showing a procedure of an embodiment of a method for manufacturing a ceramic core according to the present invention.

FIG. 2 is a correlation diagram between the compounding amount of colloidal silica and the thickness that can be filled in a mold.

FIG. 3 is a correlation diagram between the compounding amount of gypsum powder and the flowable time.

FIG. 4 is a correlation diagram between the compounding amount of gypsum powder and the setting time.

FIG. 5 is a correlation diagram between the compounding amount of colloidal silica and the shrinkage rate of the core.

FIG. 6 is a correlation diagram between the compounding amount of zircon powder and the three-point bending strength of a core.

FIG. 7 is a plan view of an example of a ceramic core for an asymmetric bifate tube manufactured based on the method for manufacturing a ceramic core according to the present invention.

8 is a view taken along the line VIII-VIII of FIG.

FIG. 9 is a plan view of an asymmetric bifate tube precision-cast using the ceramic core of FIGS.

FIG. 10 is a view taken along line XX of FIG. 9;

[Explanation of symbols]

 1 Ceramics core 2 Asymmetric bifate tube

Claims (4)

[Claims] 1. A method for producing a ceramic core, which comprises mixing raw ceramic powder, colloidal silica, and gypsum powder, pouring the mixture into a mold, curing and molding, and then taking out from the mold, followed by drying and firing. . 2. The compounding amount of the colloidal silica is 30 to 50 parts by weight with respect to 100 parts by weight of the raw material ceramic powder, and the compounding amount of the gypsum powder is 40 to 70 parts by weight with respect to 100 parts by weight of the colloidal silica. The method for producing a ceramic core according to claim 1, wherein the method is a part. 3. The method for producing a ceramic core according to claim 1, wherein the raw material ceramic powder is a mixture of fused quartz powder and zircon powder. 4. The method for producing a ceramic core according to claim 3, wherein the amount of the zircon powder blended is 20 to 50 parts by weight with respect to 100 parts by weight of the fused silica powder.