JPH107451A - Production of ceramic compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a method for producing ceramic compact, capable of remarkably shortening solid casting time and drying time and rapidly and safely producing dried compact comprising fine particles and having large size and complex shape. SOLUTION: This method for producing ceramic compact comprises solidifying ceramic slurry in a prescribed form by using a binder curable with a chemical reaction and charging the water-containing ceramic compact into a container having a structure capable of releasing gas in the system out of the system when the pressure in the system becomes atmospheric pressure or above and introducing water content into the container and/or dehydrating water-containing ceramic compact while keeping steam partial pressure in the container to atmospheric pressure by water content released from water-containing ceramic compact and keeping atmospheric temperature to 100 deg.C or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quickly and safely producing a large-sized ceramic molded body having a complicated shape.

[0002]

2. Description of the Related Art Casting molding is used to produce large-sized ceramic molded bodies having complicated shapes. However, the casting method using a plaster mold requires a long molding time and a remarkably dry time. For example, it takes a long time and its productivity is extremely low, which has been a factor of increasing the cost of ceramic products. In particular, when the raw material powder becomes submicron, the moisture transfer coefficient becomes small, so the productivity at the time of molding is poor, and the difference in moisture content between the inside and the surface layer becomes large during drying, so that dry cracking and dry deformation tend to occur, so to prevent this Required a significantly longer drying period. Humidity control drying and microwave drying using a thermo-hygrostat have been developed and commercialized to increase the moisture transfer coefficient during drying, but they are not yet sufficient.

Further, a heating steam drying method at atmospheric pressure has been proposed, and the drying speed at 100 ° C. or more has an advantage that it is extremely fast. However, drying shrinkage in the process of raising the temperature of the molded body to about 100 ° C. Deformation and cracking were caused by the low cost. This problem is particularly emphasized when the temperature unevenness of the molded article is large, such as when a large number of molded articles are put in a dryer. This is because it is necessary to dry with a steam pressure that does not cause dew condensation even in a low-temperature portion of the molded body, so that drying proceeds with a high-temperature molded body close to a heating source. In practice, there is a problem that the temperature needs to be raised to 100 ° C. over a long period of time at a slow rate so that temperature unevenness does not occur, and a more excellent drying method has been demanded.

[0004]

SUMMARY OF THE INVENTION The present invention eliminates the drawbacks of the conventional process of drying a molded article produced by casting using a hot-steam drying method, enables large-sized products to be molded quickly, and enables rapid temperature rise. It is an object of the present invention to provide a technique for greatly shortening the molding and drying time by using a heated steam drying technique.

[0005]

Means for Solving the Problems In a container having a structure capable of solidifying ceramic slurry into a predetermined shape by using a binder which is hardened by a chemical reaction and releasing gas in the system outside the system when the inside of the system becomes higher than atmospheric pressure. The water-containing molded body is put into the container, and water is introduced into the container, or the atmospheric temperature is maintained at 100 ° C. or higher while maintaining the partial pressure of water vapor in the container at atmospheric pressure with the water released from the water-containing ceramic body. The present inventors have experimentally found that by performing dehydration from the water-containing ceramic molded body while drying, the ceramic water-containing molded body can be quickly dried without causing dry cracking or deformation.

The details will be described below. A ceramic slurry containing a binder that hardens by a chemical reaction is solid-cast into a mold, a wooden mold, a plastic mold, a rubber mold, a gel mold, a conventional gypsum mold, etc., and solidified by a chemical reaction to form a water-containing ceramic molded body. Make it. As a binder hardened by a chemical reaction, ρ-alumina, hydraulic alumina, alumina cement, cement, gypsum, acryl, urethane, PVA + boric acid, etc. are those that solidify mud by chemical reaction and can be released and handled. The type does not matter. In addition, a material such as curdlan, agarose, agar or the like which can be given a form by gelation can also be used.

The obtained water-containing molded article is placed in a container capable of releasing gas when the internal pressure is equal to or higher than the atmospheric pressure, and a small amount of water is previously placed in the container to maintain the inside of the container at a saturated steam pressure. The container is held at 90 to 100 ° C. until the ceramics water-containing molded body reaches the vicinity of the temperature. Next, the container is kept at a set temperature equal to or higher than the boiling point of water, and water vapor is released outside the container using the water vapor pressure in the container which is higher than the atmospheric pressure. After the water vapor release at the set temperature is completed, the container is cooled to room temperature. In the cooling process, residual moisture inside the object to be dried is condensed on the container wall, and a dehydrated dried body is obtained.

[0008] The container used in this method does not need to be specially manufactured. If there is no clear gap between the container and the lid, the container with the lid placed thereon or the container opening may be removed. It is sufficient to use a material which is sealed with a wrap or the like and a small hole is formed in the wrap with a wire, and it is not necessary to set the inside of the container to a strict water vapor partial pressure equal to the atmospheric pressure. Further, the container is not particularly limited because a drying device capable of releasing steam to the outside at 1 atm or more may be used. In addition, in the method of storing the ceramic hydrate molded article to be dried in the container, it is preferable to place a ceramic ball or the like on the bottom surface of the container so that the dried object does not directly contact the bottom surface or wall surface of the container.

If the material to be dried is small compared to the size of the container, rapid evaporation of water occurs during the temperature rise process, which tends to cause dry cracking and deformation. It is important to blow water and steam.

The present invention is characterized in that the container is maintained at a set temperature equal to or higher than the boiling point of water, and steam is released to the outside of the container by utilizing the steam pressure in the container.
50 ° C. is preferred. For example, in the case of a molded body composed of submicron fine raw material powder, since the boiling point of water is high in a portion having a small radius of curvature between raw material particles, it is preferable to gradually increase the set temperature. When the temperature is 150 ° C. or higher, the amount of heat transferred to the object to be dried is large, and the amount of evaporation of water is large, so that the internal vapor pressure becomes high, and the dryness of water vapor in the atmosphere in the container becomes high. The portion is too dry, and it is difficult to relieve the stress, so that cracks and explosions are likely to occur.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, first, a ceramic slurry containing a binder hardened by a chemical reaction is solid-cast into a mold, a wooden mold, a plastic mold, a rubber mold, a gel mold, a conventional plaster mold and the like. It is characterized by making a ceramics water-containing molded body by solidification by a chemical reaction, but it is not a method of solidifying the slurry by dehydration with a mold as in the conventional solid casting and casting, so the solidification time of the molded body is chemical Because it is limited by the reaction speed and not by the shape,
The molding solidification time does not change even when the size is increased. For this reason, the effect of shortening the molding time increases as the size of the molded body increases.

The following drying method is a kind of the superheated steam drying method, and it is generally accepted that the heated steam drying method causes bumping of water when H ₂ O is liquid. However, by controlling the heat transfer rate below the critical speed at which bumping occurs, it was possible to perform dehydration in the form of steam without bumping by balancing the latent heat of vaporization and the amount of heat transferred. Confirmed. Fortunately, since the latent heat of vaporization of water is large, the choice of heat transfer is wide, and the partial differential equations for heat conduction and diffusion in the material to be dried are of the same form. Since the amount of heat transferred can be automatically balanced, it is theoretically supported that dehydration can be easily performed in the form of steam without causing bumping in the material to be dried.

In the case of ceramics, the drying speed is also important, but it is most important that the ceramics be dried without drying cracks and drying deformation. When the superheated steam drying method under atmospheric pressure is applied to a ceramics water-containing molded body, most of the drying distortion, drying deformation, and drying cracks occur in the temperature raising process, and the tendency is more remarkable as the drying shrinkage ratio is larger. If it is possible to keep the inside of the container at the saturated water vapor partial pressure of the molded body surface temperature during the temperature rise process, it is possible to prevent condensation on the molded body surface and evaporation from the surface,
In practice, especially when a large number of products are stored in a container, unevenness in the temperature of the molded body occurs, so that evaporation occurs in a high-temperature portion and dew condensation occurs in a low-temperature portion. This tendency is promoted as the heating rate increases.

In the case of a water-containing molded product obtained by solidifying a ceramic slurry into a predetermined shape by using a binder hardened by a chemical reaction,
Since there is no problem even if there is dew condensation, it is possible to use saturated steam at the temperature of the heat receiving portion or the heating portion of the container. The latent heat associated with the condensation of water vapor can also be used to transfer heat to the low-temperature part of the molded body, so that evaporation from the molded body surface is suppressed, as in a steamer for cooking, and there is little temperature unevenness and rapid temperature rise is possible. is there. In addition, in the case of the molded article, since the molded article is solidified by a binder, it is characterized by a small drying shrinkage. Even if evaporation occurs from the surface of the molded article in the process of raising the temperature, drying distortion, drying deformation, and drying cracks are reduced. Less likely. For this reason, it is possible to quickly raise the temperature to the limit where destruction due to stress caused by the temperature difference between the surface of the molded body and the inside does not occur, and the diameter of the molded body can be reduced to 10 mm.
Even when the temperature of the heating part of the container was suddenly set to 100 ° C., no problem such as cracking or deformation was observed even in the cylindrical molded body having a height of 12 cm.

After the completion of the temperature increase, in consideration of the industrial advantages, a heating steam drying test was performed at atmospheric pressure without restrictions on devices such as a decompression device, a decompression container, and a pressurized container. It was recognized that the drying period was at the center of the material to be dried, which was maintained at about 100 ° C. for a long time, and then the temperature started to rise to the later stage of drying. From this, the outer layer of the object to be dried is water vapor, and the inside of the object is kept in the state of liquid water. It is thought that it will go.
When dried under these conditions, even in the case of a water-containing ceramic compact made of a submicron raw material powder, one of the conventional drying methods can be used.
It has been demonstrated that safe drying can be performed without causing dry cracking or dry deformation in an extremely short time of about / 10 to 1/100. As described above, it was recognized that drying cracks did not occur even when the outer layer of the material to be dried was quickly dried while maintaining the state of water vapor and liquid water inside. Environmental water vapor pressure is about 7
It is estimated that this is due to the fact that the water film covering the constituent particles of the material to be dried is thick and easy to relieve stress, and the distance between the particles is not too short due to capillary force. The fact that it is in the rate drying period is considered to be a proof.

After dehydration and drying, if the container is immediately opened and the molded body is taken out, in the case of a large ceramic molded body using fine powder raw materials, hair cracks are liable to enter the surface layer. This is because the part having a small radius of curvature, such as the contact point of the raw material particles, has a high boiling point because the water is dried under a high steam pressure, and the molded body is not completely dried. Is thought to be due to rapid evaporation. Because of the small amount of water, it is presumed that a large crack is not formed and a hair crack is formed. To prevent this, there are two methods. One is to increase the degree of dehydration of the molded body by gradually increasing the drying atmosphere temperature to a higher temperature after dehydration, or if the sintering process is necessary, use a heat-resistant material. In this case, the process directly proceeds to the firing step. The second is a method in which after the release of water vapor at the set temperature is completed, when the entire container is cooled to room temperature, the water vapor inside the molded body is condensed on the container wall in the cooling process, and a dewatered dry molded body is obtained. . Which method should be used should be determined from the viewpoint of economy and equipment.

[0017]

【Example】

(Example 1) 3600 gr of α-alumina (trade name: AES11C) having an average particle diameter of 0.4 to 0.5 μm and an average particle diameter of 2 μm
400 g of hydraulic alumina (trade name BK103), 4 gr of citric acid, 440 gr of pure water and ammonium polycarboxylate dispersant (trade name: SN Dispersant 5)
468) 10 gr was mixed, and a slurry was prepared using an alumina pot mill for 2 hours in an atmosphere at 15 ° C. The slurry viscosity at that time was 760 cP. Inner diameter 10
Inject the slurry into the mold into a mold with a height of 20 cm and a diameter of 20 cm,
Hold at 60 ° C for 1 hour, outer diameter 10cmφ, height about 12cm
Was obtained. After placing 30 cc of hot water at 80 ° C. into the bottom of a vacuum desiccator having an internal volume of about 10 liters, the molded body was placed on a partition plate, and a lid was inserted into the opening with a rubber stopper into which a Teflon tube having an inner diameter of 5 mmφ was inserted. 10
In order to prevent water vapor scattering below 0 ° C as much as possible,
Ceramic beads of 7 mmφ were placed on a Teflon tube. This desiccator was placed directly in a drier set at 98 ° C. and left for 1 hour.
After drying at 130 ° C. for 1 hour and at 130 ° C. for 15 hours, the product was taken out of the dryer and allowed to cool naturally for 4 hours, and then a molded product at about 50 ° C. was taken out. As a result of the inspection, no dry crack was observed.
The time from molding to removal of the dried body was about one day.
No abnormalities were observed after standing for 48 hours, and the weight was measured to conversely adsorb moisture in the air and increase the amount by 0.2 gr.
On the other hand, as a control, a water-containing molded product which had been shaded in a room at about 25 ° C. and a relative humidity of about 60%, was dried at a constant rate for 5 days, and was shifted to a reduced rate drying on the 6th day. Was observed. Since then, the cracks have grown and the number of cracks has increased. After 15 days, the width of the cracks on the outer surface of the cylinder became small, and the cracks became inconspicuous.
After 21 days, a crack occurred at the center of the upper surface of the cylinder, and the width and length of the crack increased with time.

Example 2 Average particle size 0.4-0.5 μm
Alumina (trade name AES11C) 3600 gr and hydraulic alumina having an average particle diameter of 2 μm (trade name BK103)
400 gr, pure water 440 gr and ammonium polycarboxylate dispersant (trade name: SN Dispersant 54)
68) 10 gr was mixed, and a slurry was prepared using an alumina pot mill for 2 hours in an atmosphere at 15 ° C. The slurry viscosity at that time was 860 cP. Inner diameter 10c
The slurry was poured into a mold having an mφ height of 20 cm and kept at 60 ° C. for 60 minutes to obtain a cylindrical water-containing molded body having an outer diameter of 10 cm and a height of about 12 cm. A 7 mm ceramic bead was spread on the bottom surface of a stainless steel container having an internal volume of about 3 liters, and the formed body was put in the container. The lid was covered with a stainless steel plate having a thickness of 2 mm. This stainless steel container was placed in a drier set at 98 ° C., left for 20 minutes, and then left at 110 ° C. for 1 hour, 120 ° C. for 2 hours, 13 ° C.
After drying at 0 ° C. for 12 hours, the container was kept at 200 ° C. for 1 hour, the container was taken out of the drier, immediately opened, and allowed to cool naturally. As a result, no cracks were found.

(Example 3) A commercially available porcelain potter's clay (for terracotta) of 5 cm x 10 cm x 18 cm was placed in the bottom of a vacuum desiccator having an internal volume of about 10 liters, and 30 cc of warm water at 50 ° C was placed. Then, alumina beads were laid on the partition plate. The molded body was placed thereon, and a lid with a rubber stopper in which a Teflon tube having an inner diameter of 5 mm was inserted into the opening was placed. Ceramic beads having a diameter of 7 mm were placed on a Teflon tube in order to prevent water vapor from scattering at a temperature of 100 ° C. or lower as much as possible. The desiccator was heated to 95 ° C. for 10 hours, left at the same temperature for 1 hour, dried at 110 ° C. for 8 hours, 120 ° C. for 5 hours, 130 ° C. for 5 hours, taken out of the dryer and allowed to cool naturally,
The molded body at about 50 ° C. was taken out. As a result of a visual inspection of the drying state of the molded product, cracks were already observed on the surface of the molded product in the latter stage of the temperature raising process.

[0020]

According to the method for producing a ceramic molded body of the present invention, the molding time does not become long even when the product becomes large, and even if a rough heating operation is performed, the drying time is 1/10 to the conventional drying time. Inexpensive and safe products can be dried in a short time of about 1/100 without drying cracks or dry deformation. In particular, the release time and drying time of solid casting are too long, and industrially impossible to produce large-sized cast molded products using submicron raw materials, which could not be produced industrially. It is thought to give bright light to the development and application of high-quality fine ceramics large members. Also, there is no limitation on the mold used for molding, and a special device such as a decompression device, a decompression container, a pressurization device, a pressurization container, and a microwave generator is not required for drying, so that a wide range of application is possible.

As described above, according to the present invention, it is possible to extremely quickly, safely and inexpensively form a ceramic molded body which cannot be formed and dried by conventional techniques such as a large product and a large-sized uneven thickness product without using a special device. Since it can be manufactured, it can be widely applied to the field of ceramics molding and is extremely useful in industry.

Claims (2)

[Claims] 1. A container having a structure capable of solidifying ceramic slurry into a predetermined shape by using a binder hardened by a chemical reaction and releasing gas in the system outside the system when the pressure of the system exceeds atmospheric pressure. Putting the molded body and introducing water into the container, and / or maintaining the ambient temperature above 100 ° C while maintaining the atmospheric partial pressure of water vapor in the container with the moisture released from the ceramic-containing molded body, and forming the ceramic with water. A method for producing a ceramic molded body, comprising dehydrating a molded body. 2. The binder hardened by a chemical reaction includes ρ alumina, hydraulic alumina, alumina cement, cement,
2. The method of claim 1, wherein one or more selected from gypsum, acrylic, urethane, PVA and boric acid are used.