JPH0482083B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a ceramic molded article. [Prior art] In recent years, ceramic molded products made from fine ceramic powder have attracted attention for their superior mechanical, chemical, and thermal properties compared to molded products made of metal or organic materials. Applications are being developed in the following fields. Therefore, in order to improve the mechanical and thermal properties of a ceramic molded product, a sintered body with a homogeneous, dense, and fine crystal structure is required. It is necessary that the powder be fine, and as a result, the ceramic raw material is required to be made into a finer powder. On the other hand, one of the traditional methods for molding ceramics is the slurry casting method, and this molding method is suitable for molding ceramic moldings of large size and complicated structure, and its importance is being reaffirmed. [Problems to be Solved by the Invention] As described above, in order to improve the mechanical and thermal properties of ceramic molded products, it is necessary to pulverize the ceramic raw material, but it is necessary to finely powder the ceramic raw material. The finer the raw material, the more difficult it is to mold it. In particular, in the slurry casting method, the finer the ceramic raw material, the more difficult it is to obtain a relatively uniform molded product with few internal defects, resulting in the following problems. (a) Generally, in the slurry casting method, an organic binder (peptizer, binder, etc.) is added to the ceramic powder.
Add water to make a slurry, and use this slurry to make plaster,
It is molded by being cast into a casting mold made of resin, etc. Prior to casting, the slurry is subjected to pretreatment such as deaeration in order to prevent the occurrence of internal defects due to pores etc. in the molded product. Ru. however,
Even when a molded body formed by such a method is dried and fired, characteristics such as bulk density and strength are not sufficiently developed. In particular, when compared with a sintered body obtained by press molding, the strength properties are inferior, and a 5 to 20% decrease in properties is observed in a sintered body obtained by cast molding. The cause of this property deterioration is that when water in the slurry is absorbed into the casting mold during casting molding and solidifies as a molded object, and when moisture existing between raw material particles is scattered during the drying process, inside the molded object. This is presumed to be because fine pores remain as internal defects. (b) In the slurry casting method, the molded product is likely to break due to shrinkage during demolding and drying, causing damage such as cracks. In particular, the larger the molded product is complex and has a large difference in wall thickness, the more likely the density of the molded product is uneven.Due to the density difference, the molded product solidifies, shrinkage rate differs during drying, and damage such as breakage and cracks occurs. Likely to happen. (c) Cast molded bodies are often calcined when a large amount of organic binder is used, but in this case, when the added organic binder burns and generates gas, the molded body may be cut, causing damage such as cracks. Likely to happen. This tendency is particularly strong as the ceramic raw material becomes finer powder. Accordingly, an object of the present invention is to establish a method for manufacturing ceramic molded articles with excellent mechanical and thermal properties even if they are large and have a complicated structure. [Means for Solving the Problems] The first object of the present invention is a method for manufacturing a ceramic molded article, which comprises the following steps (a) to (e). (a) A process of granulating raw material powder for ceramics. (b) A process of adjusting the slurry by adding an organic binder to the granules obtained in the granulation process. (c) A process of casting the slurry obtained in the slurry preparation process into a mold. (d) A process of drying the molded body obtained in the casting process and subjecting it to an isostatic press. (e) A process of firing the molded body obtained in the isostatic pressing process. Further, the present invention is a manufacturing method in which the molded body obtained in the casting process is dried, then calcined, and subjected to an isostatic press. In the granulation step (a) of the present invention, the following known methods can be employed as the granulation method. In other words, (1) a rolling granulation method in which humidified powder is given rolling action to agglomerate into spherical particles; (2) a certain amount of raw material powder is compression-molded into a certain size and shape. Compression granulation method to create granules, (3) fluidized bed granulation method in which powder is fluidized and then sprayed with liquid from a spray nozzle to coat the particle surface with liquid, and (4) slurry is added. Injection granulation method, in which the powder is pulverized using a pressure type nozzle or a two-fluid nozzle, and then air-cooled and solidified in a granulation tower to obtain spherical granules. (5) Spray drying, in which the raw material powder is slurried, spray-dried, and granulated at the same time. A granulation method etc. can be adopted. Among these granulation methods, spray drying granulation method and fluidized bed granulation method are preferred. Further, the shape of the granules is not particularly limited, but is preferably spherical, and has an average particle diameter of 10 to 1000 μm, particularly preferably 20 to 100 μm. If the average particle diameter is less than 10 μm, the time required for ink forming during casting will be long, and the internal solidification will be slow, making it impossible to obtain a uniform molded product. Also,
During drying and calcining, the scattering of moisture and generated gas becomes insufficient. On the other hand, if the average particle size exceeds 1000 μm, it is difficult to adjust the slurry, making casting impossible. In the slurry adjustment step (b), the slurry is adjusted by adding an organic binder using the granules described above, and in the casting step (c), the slurry is poured into a mold made of gypsum, resin, etc. under normal pressure. Or cast under pressure. If the mold is released when the predetermined thickness is reached, a molded product can be obtained.
The obtained molded body is dried and dried at a temperature of 600 to 800
It is calcined at ℃ and subjected to an isostatic press. In the isostatic press process (d),
Prior to pressing, latex or the like is applied to the entire surface of the molded product, dried, and coated over the entire surface.
Place in an isostatic press at a pressure of 1000Kg/ ^cm2 . In the final firing step (e), the pressed compact is fired by a conventional method, and the firing conditions are appropriately selected depending on the desired characteristics. [Operations and effects of the invention] According to this manufacturing method, since granules are used as the ceramic raw material, the plasticity of the cast molded product is increased, and even if the molded product is complex and has different wall thicknesses, There is less occurrence of damage such as unattached parts and cuts during mold release. In addition, since the gaps between particles in the molded body are relatively large, the moisture in the dried molded body is easily evaporated and scattered, and the amount of shrinkage accompanying the evaporation of moisture is small, resulting in damage such as cuts and cracks in the molded body during drying. Less is. The cast molded body is placed in an isostatic press and equiaxially pressed from all sides, so it is firmly bonded.
The ceramic molded product, which is a sintered body obtained by firing this, has excellent mechanical and thermal properties. Even in molded bodies that require calcination, the gaps between particles within the molded body are relatively large, making it easy for gas generated by combustion of the organic binder to scatter, resulting in damage such as cuts and cracks caused by gas generation. Occurrence is also low. Example 1 Al ₂ O ₃ with an average particle size of 0.4 μm and 0.8 μm and 3 mol% Y ₂ O ₃ containing 2 wt% clay-based sintering aid as raw material powder
A total of four types of ZrO ₂ with average particle diameters of 0.4 μm and 0.8 μm including Granulated powder with a diameter of 80 μm is obtained. In the granulation methods (1) and (2), an organic binder (carboxylic acid binder 1wt%, wax 0.5wt%) is used in a dedicated granulation device, and in the granulation method (3), each raw material is It is packed in an ice bag and subjected to an isostatic press (CIP) at a pressure of 1000 kg/cm ² , then crushed and classified using a sieve to obtain a granulated powder. For comparison, (4) ungranulated powder is also used. Organic binders (carboxylic acid binder 0.01 to 0.9 wt%, acrylic acid binder 0.01 wt%) are used to adjust the slurry.
~0.9 wt%) and 0.05 wt% of an antifoaming agent, each granulated powder is mixed and dispersed in a kneader to form a slurry, and the ungranulated powder is mixed and dispersed in a pot mill to form a slurry. Mixing and dispersing granulated powder in a pot mill is undesirable because there is a risk that the granulated powder may be destroyed, and mixing and dispersing ungranulated powder in a kneader makes it difficult to mix uniformly. The test mold for casting is shown in Fig. 1a, upper mold 1.
and lower mold 2, and using the same test mold, 5 kg/
Pressure casting is performed at a pressure of cm ² G, and the resulting cast body is dried under constant temperature and humidity conditions of 80°C or less and humidity of 60% or more, and the humidity is gradually lowered to dry. . After drying, latex is applied to the molded product, dried, the entire surface is covered with a rubber film, and then subjected to CIP at a pressure of 2000 kg/cm ² . The molded body is subjected to CIP at 1400℃
A ceramic molded article 10 having the shape and dimensions shown in FIG. 1b is obtained. Such a molded article 1
A sample of the center part 11 and outer peripheral part 12 was cut out from 0, and the bending strength of the sample before and after heat treatment was measured.
Measured using JISR1601 4-point bending test method. The results are shown in Table 1, and the bending strength values of the samples obtained by press molding are shown as criteria. The heat treatment was performed in an autoclave at 250° C. and saturated steam pressure, and the heat treatment time was 500 hours for Al ₂ O ₃ and 250 hours for ZrO ₂ . Referring to the same table, when using granulated powder, the strength before and after heat treatment is higher than when using ungranulated powder. Strength equivalent to that of a molded body can be obtained. Regarding CIP, although it is an ungranulated powder, there is a significant difference in strength depending on the presence or absence of CIP, and it can be seen that the entire surface is compressed firmly by CIP and the strength is improved. Regarding the average particle diameter of the raw material powder, it can be seen that the μm strength is higher when the particle diameter is 0.4 μm than when it is 0.8 μm.

[Table] Example 2 Figure 2 a and b using the slurry prepared in Example 1.
Pump impeller 20, No. 3, with the shape and dimensions shown in
Butterfly valve body 30 with the shape and dimensions shown in figures a and b
Ceramic molded bodies with large and complicated structures such as
It was formed by pressure casting and drying, and the casting ability was evaluated. Performance evaluation was performed by observing the external appearance of each molded product for damage such as cuts and cracks during the molding and drying process, and the results are shown in Table 2. In addition, damaged parts 21 to 24 are damaged parts of the impeller 20 shown in FIG. 2, and damaged parts 31 and 32 are damaged parts of the valve body 3 shown in FIG.
This is the damage site of 0. Casting ability depends on the type of raw material powder (Al ₂ O ₃ ,
There is no difference depending on ZrO ₂ ), but there is a difference depending on the presence or absence of granulation and the granulation method. Regarding the granulation method, good results are obtained when spray drying granulation method and fluidized bed granulation method are used, and even in compression granulation method, when a material powder with an average particle size of 0.8 μm is used as the raw material powder, the results are good. In good condition. When ungranulated powder was used, drying and shrinkage occurred from the inked surface layer before the center part was fully inked during molding, and some products collapsed even after being released from the mold in the middle. This means that
Although the casting test mold of Example 1 is fully capable of casting even when ungranulated powder is used, the present invention is not suitable for casting molding of compacts with complex structures, large sizes, and large differences in wall thickness. This means that the manufacturing method is extremely effective.

【table】 [Brief explanation of drawings]

Figure 1a is a longitudinal cross-sectional view of a casting test mold, Figure 1b is a side view of a ceramic molded product using the test mold in casting, and Figure 2a is a ceramic molded product formed by casting and drying. Molded body (impeller for pump)
FIG. 3B is a longitudinal sectional view of the molded body, FIG. 3A is a plan view of another molded body (butterfly valve body), and FIG. 3B is a side view of the molded body. Explanation of symbols: 10...Molded product, 20...Pump impeller, 30...Butterfly valve body.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a ceramic molded article, comprising the following steps (a) to (e). (a) A process of granulating raw material powder for ceramics. (b) A process of adjusting the slurry by adding an organic binder to the granules obtained in the granulation process. (c) A process of casting the slurry obtained in the slurry preparation process into a mold. (d) A process of drying the molded body obtained in the casting process and subjecting it to an isostatic press. (e) A process of firing the molded body obtained in the isostatic pressing process. 2. The manufacturing method according to item 1, wherein the molded product obtained in the casting step is dried, then calcined, and subjected to an isostatic press.