JP2777674B2 - Manufacturing method of ceramic sintered body - Google Patents

Description

The present invention relates to a method for producing a ceramic sintered body, and more specifically, to a method for producing a ceramic sintered body having a degreasing step that does not cause a defect in a thick-walled central portion. It relates to a manufacturing method. INDUSTRIAL APPLICATION This invention is utilized for manufacture of ceramic products, such as a turbine rotor, especially the ceramic product which has a thick part.

[Conventional technology]

In recent years, applications of ceramic materials, such as automobile parts, heat-resistant materials, electronic materials, and machine tools, have been rapidly expanding, and accordingly, the shape of ceramic products has become more complicated. For this reason, the injection molding method is frequently used as a method for accurately and efficiently molding a ceramic material into a molded article having a complicated shape.
A degreasing step is required after molding in order to add and mold an organic binder such as an organic binder, a plasticizer, a lubricant, etc., which is close to (about 30% by weight).

In order to prevent the surface layer portion from being rapidly degreased due to a large temperature difference between the surface layer portion and the inside of the molded body, and to prevent the degreased body from being sharpened, the ceramic molded body is made of an alumina powder. A method of embedding in a filling material and degreased is known (JP-A-57-100973, etc.).

Further, in order to prevent the binder from being decomposed during the heat degreasing to generate gas, and to prevent the volume of the formed body from expanding due to the gas pressure and causing cracks in the formed body, a method of degreasing the formed body under pressure is used. Is known (JP-A-60-118675). Furthermore, a method is known in which a compact is buried in ceramic powder and the rate of decompression is adjusted to suppress the occurrence of cracks due to gas expansion in the compact during depressurization (Japanese Patent Laid-Open No. 2-172853). .

[Problems to be solved by the invention]

However, in the above-mentioned conventional method, when the molded body is embedded in the embedding material and degreased, the organic binder is uniformly decomposed and diffused from the surface of the molded body into the embedding material. Due to expansion, shrinkage at the time of disassembly, etc., sharpening is likely to occur in the maximum thickness portion of the molded body during this degreasing. Similarly, in the case of degreasing under a pressurized atmosphere, if the thickness of the molded body is increased, degreased cracks may occur in the thickest part of the molded body.

Further, in the degreasing step, usually, a long time (for example, a wall thickness of 10 mm
(Approximately one week) and heating is performed, which can be said to be inefficient.

The present invention solves the above-mentioned problems, and covers a part of the surface of the ceramic molded body with a film such as a resin to regulate the diffusion direction of the decomposed binder component. It is an object of the present invention to provide a method for producing a ceramic sintered body that can be quickly degreased without generating defects or the like.

[Means for solving the problem]

The method for producing a ceramic sintered body according to the first invention is as follows.
A method for producing a ceramic sintered body, in which a sintered body is obtained by sintering after firing a molded body made of a ceramic powder and an organic binder, wherein a part of the surface of the molded body is melted or pyrolyzed at the organic binder. coated with a film made of resin or rubber has a melting point or thermal decomposition temperature than, then, at 1 atm or more 10 kg / cm ² less than in the gas atmosphere, the melting point or thermal decomposition of the resin or rubber constituting said coating Performing a preliminary degreasing step of removing the organic binder until the porosity at the center of the molded body becomes 25% or more by heating to a temperature lower than the temperature, and then heating to a temperature equal to or higher than the melting point or the thermal decomposition temperature of the film. Then, after the film is removed, or after the film is removed, the main degreasing step of removing the remaining organic binder is performed.

The melting point of “resin or rubber” (hereinafter, referred to as a coating material) constituting the coating is equal to or higher than the melting point or the thermal decomposition temperature of the binder. Examples of the resin include vinyl acetate, acrylic, polyurethane, silicone, epoxy, polyester, and phenol resin, and examples of the rubber include
SBR (styrene butadiene rubber), natural rubber, silicone rubber, chloroprene rubber and the like can be used. Here, the reason why the melting point of the coating material is set to “not less than the melting point or the thermal decomposition temperature of the binder” is to prevent the coating from being removed before the completion of the preliminary degreasing step.

It is desirable that the area of the surface covered with the coating in the total surface area of the molded body is 50 to 90% of the total surface area. The reason will be described below. That is, when the ratio of the surface to which the coating material is not applied (hereinafter, referred to as an exposed surface) is too small, it takes a long time to scatter the organic binder in the preliminary degreasing step. On the other hand, if the ratio of the exposed surface is too large, it is difficult to control the moving direction of the binder, and a defect is likely to occur at the center of the thickness. Further, when the treatment is performed in a pressurized atmosphere, a portion that is difficult to be uniformly compressed by the molded body increases. Therefore, the area of the exposed surface needs to be individually and specifically examined according to the product shape. In the case of an injection-molded product, a defect can be generally eliminated if it is 50 to 90% of the total surface area, and It is also possible to shorten the degreasing time.

It is preferable that the surface to be reprocessed (polished or the like) after firing is set as the exposed surface. In the case of a molded body having a thin part and a thick part, this coating is usually provided so as to cover the entire thin part and a part of the thick part. That is, it is preferable that the coating covers the molded body so as to expose a part of the thick portion. In the method for manufacturing a ceramic sintered body according to the second invention, after embedding the molded body coated with the resin or rubber film in an embedding material made of embedding ceramic particles, the preliminary degreasing step is performed. Do
Next, the main degreasing step is performed.

The type, shape, presence or absence of granulation, size, etc. of this "embedding material" are not particularly limited, but, for example, alumina, cordierite,
Various kinds of ceramic powders such as zirconia, amorphous silica and hollow silica can be selected and used depending on the purpose and application.

The reason for using the embedding material in this way is as follows. That is, when the molded body has a thick part so as to exceed 20 mm,
If the embedding material is not used, the decomposition product of the binder is gasified in the vicinity of the surface of the molded product, causing a large volume change in the decomposition product in the molded product, and thereby many defects are easily generated.
On the other hand, if the embedding material is used, the decomposition product of the binder moves from the surface of the molded body into the embedding material in a state of a high molecular weight (liquid, etc.) and is gasified in the embedding material. The change in volume of the decomposition product in the body can be suppressed to a small value. Therefore, by using the embedding material as in the second aspect of the present invention, it is possible to obtain a degreased body having no or few defects even in a relatively thick molded body. In addition, the thickness of the molded body is about
If it is up to about 20 mm, even if the molded body is not embedded in the embedding material, it only covers a part of the molded body as described above and regulates the moving direction of the decomposition gas of the binder, and there is no defect. A defatted body can be obtained.

In the “preliminary degreasing step”, the molded body is heated to a temperature lower than the melting point or decomposition temperature of the coating material. For example, when coated with natural rubber, silicon rubber, or the like, the heating temperature is up to about 200 ° C.

This preliminary degreasing step, in order to suppress the occurrence of sharp due to pressure increase in the molded body portion due to volume expansion during decomposition of injection molding an organic binder, may be treated with a pressurized gas atmosphere of less than 10 kg / cm ² desirable. Where the upper pressure limit is 10
The reason for setting it to be less than kg / cm ² is that it is advantageous in handling the device.

According to the method of the present invention, in the pre-degreasing step, the speed at which the binder at the center of the molded body comes off differs from the conventional method, and is almost the same as other parts of the molded body. Also,
This preliminary degreasing step is performed until the porosity formed after the binder is removed at the center of the molded body becomes 25% or more. This “porosity 25%” is the minimum value that connects the voids. After the center of the molded body is degreased until it reaches this porosity in a state where a part of the molded body is covered, degreasing is continued in the following main degreasing process By doing so, the decomposed gas of the remaining binder can be smoothly scattered in the main degreasing step. When a non-oxide ceramic material is used, degreasing is usually performed in a non-oxidizing gas atmosphere such as nitrogen or argon in order to suppress oxidation.

Next, the coating material is heated to a temperature at which the coating material is melted or thermally decomposed or higher, and after the coating is removed or the coating is removed, the main degreasing step of removing the remaining organic binder at the end of the preliminary degreasing step is performed. Do. At this time, two-stage heating of heating mainly for the purpose of removing the film and heating mainly for the purpose of main degreasing may be performed (corresponding to the case where the remaining binder is removed after removing the film).
These may be performed almost simultaneously in parallel (corresponding to the case where the film is removed and the remaining binder is removed). By this heating, the coating material can be removed from the molded body, and the organic binder and the like remaining in the preliminary degreasing step can be almost completely scattered and removed through the entire surface of the molded body including the coated portion.
According to the production method of the present invention, even if this heating is performed relatively rapidly, no sharpness is generated at the center of the thickness of the molded body. This is because the amount of the binder in the center of the thickness of the molded body has already been greatly reduced in the preliminary degreasing step as compared with the binder in other parts of the molded body.

Incidentally, the method of the present invention is particularly preferably used in the production of injection molded articles using a large amount of molding binder,
It can be used for an extruded product, a molded product or the like having a thick portion.

[Action]

Hereinafter, a method for producing a sintered body according to the present invention will be described by taking a spherical molded body as an example.

In the conventional degreasing method, when the molded body is heated and the decomposition of the binder starts from the molded body surface, the binder melted inside the molded body moves to the vicinity of the molded body surface. At that time, the ceramic powder slightly moves along with the movement of the binder in the center of the thickness, so that a defect easily occurs in the center of the thickness.

On the other hand, in the present invention, as shown in FIG. 1, first, the surface of the molded body 1 excluding the exposed surface is covered with a film 2 such as a resin, and if necessary, the molded body 1 with the film is embedded with an embedding material. 3
The molded body 1 with the coating is then heated at a temperature lower than the melting point or the decomposition temperature of the coating material to perform a preliminary degreasing step. At this time, since the surface of the molded body is covered with the film 2 except for the exposed surface, the thermal decomposition product of the organic binder moves toward the exposed surface and is removed from the outside of the molded body. As a result, the moving direction of the thermal decomposition product of the organic binder in the degreasing low temperature range is regulated as shown in FIG. 2, so that the remaining amount of the organic binder in the center part of the thickness is reduced in other parts (particularly, in the coated area). (Surface portion of the molded body).

After performing this preliminary degreasing step until the porosity of the center of the thickness becomes 25% or more, the process proceeds to the following main degreasing step. That is, the molded body is heated to a temperature higher than the temperature at which the coating material is thermally decomposed,
The coating covering the surface of the molded body is decomposed and removed, and the degreasing is performed simultaneously or thereafter to decompose and remove the binder from the entire surface of the molded body as shown in FIG. Thereby, a defatted body having no defect can be obtained. The arrows in FIGS. 2 and 3 show the moving state of the binder.

Further, according to the present invention, the heating for the main degreasing is performed relatively rapidly in order to decompose and remove the remaining binder after setting the amount of the binder in the central portion of the maximum thickness to be smaller than the amount of the binder in the other portions of the molded body. This can shorten the degreasing time.

〔Example〕

 Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 First, for 100 parts by weight of silicon nitride powder having an average particle diameter of 1 μm (hereinafter simply referred to as “parts”), 5 parts of alumina (average particle diameter of about 1 μm) and 5 parts of yttria (average particle diameter) were used as sintering aids. 5 parts (about 1 μm) were added to prepare a silicon nitride mixture for sintering. This mixture was added with ethylene-
5 parts of a vinyl acetate copolymer resin, 15 parts of microcrystalline wax, and 4 parts of diethyl phthalate as a plasticizer were added and heated and kneaded to prepare a ceramic material for injection molding.

Then, using a predetermined mold, the ceramic material was molded by an injection molding method to produce 20 spherical molded bodies (30 mmφ) 1. 80% of the surface area of the molded body 1 is covered with a natural rubber film (thickness of 1 mm or less) 2, and then the molded body with the film is embedded in a sagger 4 for degreasing (alumina, average particle size). (Diameter: 100 μm) 3 (FIG. 1).
Next, vibration was applied to the sagger 4 for degreasing to increase the bulk density of the embedding material 3.

Further, these are heated at a rate of 5 ° C./hour between 100 ° C. and 180 ° C. in a nitrogen atmosphere at 1 atm using a hot air circulation type electric furnace, and then maintained at 180 ° C. for 10 hours. By heating at a rate of 10 ° C./hour between 180 and 500 ° C., preliminary degreasing, film decomposition and main degreasing were performed to obtain a degreased body.

With respect to the 20 degreased bodies thus produced, the presence or absence of sharpness was observed using microfocus X-rays.

Example 2 A degreased body was prepared in the same manner as in Example 1 except that the area covered with the natural rubber film was set to 60% of the surface area of each molded body, and the sharpness was reduced in the same manner. The occurrence was observed.

Example 3 Example 1 was the same as Example 1 except that the area covered by the natural rubber film in the surface area of each molded product was 90%, and the temperature rising rate between 100 and 180 ° C. was 2 ° C./hour. A defatted body was prepared in the same manner as in Example 1, and the presence or absence of sharpness was observed in the same manner.

Example 4 A degreased body was prepared in the same manner as in Example 1 except that the ratio of the surface area of each molded body covered with the natural rubber film was set to 50%, and generation of sharpness was performed in the same manner. Was observed.

Example 5 This example is an example in which the degreasing step is performed under pressure, and the temperature is increased at a higher temperature than in the above example. That is, in a pressurized degreasing furnace, under a nitrogen atmosphere of 5 atm.
Heat at a rate of 8 ° C / hour between 0 and 180 ° C, then
After maintaining at 180 ° C. for 5 hours, degreasing was performed by heating at a rate of 15 ° C./hour between 180 and 500 ° C. Other than these points,
A degreased body was prepared in the same manner as in Example 1, and the presence or absence of sharpness was observed in the same manner.

Example 6 A degreased body was produced in the same manner as in Example 1 except that the molded body had a diameter of 15 mmφ and the molded body with a coating was not embedded in an embedding material, and was cleaned in the same manner. Was observed.

Comparative Example 1 A degreased body was prepared in the same manner as in Example 1 except that the molded article was not covered with the natural rubber film, and the presence or absence of sharpness was observed in the same manner. .

Comparative Example 2 A degreased body was prepared in the same manner as in Example 4 except that the molded article was not covered with the natural rubber film, and the presence or absence of sharpness was observed in the same manner. .

Comparative Example 3 In this comparative example, a molded body not covered with a film was heated at a slower rate than in Example 1. That is, heating was performed at a rate of 2 ° C./hour between 100 and 200 ° C., and then at a rate of 3 ° C./hour between 200 and 500 ° C. Except for these points, a degreased body was prepared in the same manner as in Example 1, and the presence or absence of sharpness was observed in the same manner.

Comparative Example 4 A degreased body was prepared in the same manner as in Example 6 except that the molded article was not covered with the natural rubber film, and the presence or absence of sharpness was observed in the same manner. .

The results of the above observations are shown in the table together with the degreasing time and the like.
In the table, “coverage” refers to the total surface area of each molded product as 100%.
In this case, the surface area ratio (%) of each molded body covered with the film is shown. In addition, the presence or absence of the use of the embedding material is also shown in the table. Further, in the same table, "no generation of sharpness" means both the case where no sharpness was found inside the degreased body by microfocus X-ray and the case where no sharpness was found on the surface of the degreased body by magnifying examination. Is satisfied. On the other hand, "sharp" means that a sharp is found in any of the above-described tests.

According to the above results, when no coating was applied (Comparative Examples 1 to 5)
In 4), the incidence of sharpness is high. This is considered to be because the moving direction of the binder was not sufficiently regulated in the preliminary degreasing step. In addition, in order to prevent the occurrence of sharpness in a conventional degreasing method using a molded body that is not coated with a film (Comparative Example 3), it is necessary to reduce the heating rate and increase the degreasing time to 150 hours. . Moreover, even in this case, 15% of the defatted bodies are sharp.

On the other hand, among the degreased bodies obtained using the degreasing method according to the present invention, when the coverage is 60 to 90% (Examples 1 to 3 and Examples 5 to 6), generation of sharpness is not observed at all. I could not do it. Further, when the coverage was 50% (Example 4), although slight cracking occurred, the cracking rate was 50% of that of the degreased body (Comparative Example 1) according to the conventional method. It is halved, and it can be said that the result is satisfactory if the degreasing time is also considered. That is, in the case of a covering rate of 50%, if the degreasing time is set to about 82 hours in Example 3, it is apparent that generation of sharpness is further reduced. Furthermore, even when no embedding material was used (Example 6), better results were obtained as compared with Comparative Example 4.

As described above, the use of the degreasing method of this example significantly reduces the occurrence of sharpness as compared with the comparative method (Comparative Examples 1 to 4).
It was also found that the degreasing time was significantly improved.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention according to the purpose and application. That is, the present manufacturing method is not limited to the spherical molded body as in the present embodiment, but can be used for various shapes. In particular, it is suitable for manufacturing a ceramic product having a complicated shape having a thick portion and a thin portion such as a turbine rotor. In this case, it is preferable that the coating be provided so as to cover the entire thin portion of the molded body and further cover a part of the thick portion. The molded body may be made of a material other than those described above, and the organic binder may be of a type other than those described above, an added amount thereof, or the like. In addition, organic plasticizers, lubricants, and other various additives can also be used. Furthermore, degreasing conditions (degreasing temperature, degreasing speed, type of atmosphere, etc.) are variously selected depending on the materials used.

〔The invention's effect〕

According to the manufacturing method of the present invention, as shown in the above operation, it is possible to prevent the occurrence of a degreasing defect at the center portion of the thickness. Further, by using the present manufacturing method, the degreasing time can be shortened, and the manufacturing time of the sintered body can be shortened.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a state in which a molded body is embedded in an embedding material in an embodiment, FIG. 2 is an explanatory view showing a moving state of a binder at the time of preliminary degreasing, and FIG. FIG. 4 is an explanatory diagram showing a moving state of the camera. 1; spherical molded body, 2;
Natural rubber film, 3; embedding material, 4; sagger for degreasing.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C04B 35/00-35/22 C04B 35/622-35/657

Claims (5)

(57) [Claims] 1. A method for producing a ceramic sintered body in which a molded body comprising a ceramic powder and an organic binder is degreased and then fired to obtain a sintered body, wherein a part of the surface of the molded body is made of the organic binder. coated with a film made of resin or rubber has a melting point or thermal decomposition temperature than the melting point or thermal decomposition temperature, at then 1 atm or 10 kg / cm ² less than in the gas atmosphere,
Performing a preliminary degreasing step of heating to a temperature lower than the melting point or thermal decomposition temperature of the resin or rubber constituting the film and removing the organic binder until the porosity in the center of the molded body becomes 25% or more; Next, a ceramic sintering step is performed, in which the coating is heated to a temperature equal to or higher than the melting point or the thermal decomposition temperature of the coating to remove the coating or remove the coating and remove the remaining organic binder to remove the remaining organic binder. How to make the body. 2. A molded body covered with a film made of the resin or rubber is embedded in an embedding material made of ceramic particles for embedding, and then, in a gas atmosphere of 1 atm or more and less than 10 kg / cm ² ,
Performing a preliminary degreasing step of heating to a temperature lower than the melting point or thermal decomposition temperature of the resin or rubber constituting the film and removing the organic binder until the porosity in the center of the molded body becomes 25% or more; 2. The ceramic sintering process according to claim 1, wherein the degreasing step is performed after heating the coating to a temperature equal to or higher than the melting point or the thermal decomposition temperature to remove the coating or remove the coating and remove the remaining organic binder. How to make the body. 3. The method for producing a ceramic sintered body according to claim 1, wherein an area of a surface covered with the resin or rubber coating is 50 to 90% of a total surface area of the molded body. 4. In the main degreasing step, at least a part of the organic binder is removed from a part of the surface of the molded body covered with the film during the preliminary degreasing step, to the outside of the molded body. A method for producing the ceramic sintered body according to claim 1. 5. The method for producing a ceramic sintered body according to claim 1, wherein the coating is coated so as to expose a part of a thick portion of the molded body.