JP2013193412A - Method for manufacturing dry ceramic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a dry ceramic molding that can manufacture the dry ceramic molding of high quality with a high yield by uniformly drying the ceramic molding in a short time without causing fissures and cracks in the surface of the molding in drying the ceramic molding.SOLUTION: A method for manufacturing a dry ceramic molding includes placing a wet ceramic molding 1 in a sealed container 3 sealed except for a steam discharge port 4, placing the internal space of the sealed container 3 into a superheated steam atmosphere with moisture produced from the wet ceramic molding 1 by heating the sealed container 3 from the outside, and drying while maintaining this state.

Description

  The present invention relates to a method for producing a dried ceramic molded body that can complete the drying step in a short time and that does not cause cracks or cracks in the dried molded body.

  Various ceramic products are manufactured through a molding process of molding using ceramic raw materials, a drying process of drying the molded body, a firing process of firing the dried molded body, and a cooling process of cooling the fired body. Among these steps, the drying step or the cooling step may be due to natural drying or natural cooling, but a separate heating means or cooling means may be used for the purpose of shortening the time.

  However, in the case of drying ceramic thick molded bodies, if a large change in the amount of moisture contained between the surface and the interior due to a rapid drying operation in the drying process or a sudden temperature difference occurs, cracks and cracks will occur on the surface. There was a problem that occurred. For this reason, it has not been possible to achieve a sufficient reduction in production time only by a conventional drying method using simple heating means.

  In order to solve such problems, various methods using various techniques have been proposed. For example, a method called moisture conditioning drying is performed in which a ceramic molded body is dried while adjusting the external humidity to be constant. However, even in this humidity control drying method, if the external humidity is lowered to increase the drying speed, a large difference in moisture content occurs between the inside and outside of the molded body, and cracks and cracks occur in the molded body. There was a problem. Therefore, in the case of drying a ceramic thick molded body containing clay as a component, this humidity control drying method is carried out under the condition that the internal temperature of the molded body is about 40 ° C. A long period of 3 weeks is required.

  In order to shorten the drying time, a method using superheated steam has been implemented (see Patent Documents 1 and 2). This is a method of drying in a state where the external atmosphere of the ceramic molded body is filled with superheated steam. By drying in a superheated steam atmosphere, the moisture content distribution inside and outside the ceramic molded body is reduced, and the moisture in the molded body is reduced. The diffusion rate can be increased and the temperature in the molded body can be kept relatively high. For example, the internal temperature of the molded body is about 40 ° C. in the humidity drying method, but the temperature is about 100 ° C. in the method using superheated steam.

  According to the normal drying method for ceramic molded bodies, the evaporation rate of moisture from the surface of the molded body is larger than the diffusion rate of moisture inside the molded body. Cracks and cracks occur on the body surface. However, in the above-described method using superheated steam, the evaporation of moisture from the surface is suppressed, and the internal temperature of the molded body can be increased to about 100 ° C., so that the diffusion rate of moisture increases and the evaporation of moisture occurs. Drying can proceed while the speed is almost the same as the diffusion speed inside the molded body, and therefore, cracks and cracks are less likely to occur on the surface of the molded body.

  Furthermore, this method using superheated steam has the advantage that surface hardening is unlikely to occur because condensed water adheres to the surface of the molded body. In addition, since it has far-infrared radiation, it has an advantage that heat transfer penetrates into the inside and cracks are hardly generated on the surface.

  Such a method of drying an article using superheated steam is used not only for drying ceramic molded bodies but also for drying meat and fish, for example. Specifically, meat or fish meat is dried in a stable and high quality state in a short time (see Patent Document 4), or it is used for heat treatment of wood to prevent warping due to heating of wood. It is used for obtaining products (see Patent Document 5).

  However, this method using superheated steam requires special equipment such as a superheated steam generator for the drying operation, which increases the equipment cost and also requires the superheated steam generation cost during its operation. There is a problem of becoming expensive.

JP 2008-229872 A JP 2007-230796 A JP-A-5-43300 JP 2006-262706 A JP 2007-136881 A

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to dry the ceramic molded body, particularly in the case of a thick ceramic molded body, on the surface of the molded body. An object of the present invention is to provide a method for producing a dry ceramic molded body capable of producing a high-quality dry ceramic molded body with good yield by drying uniformly and uniformly in a short time without generating cracks or cracks.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have heated the ceramic molded body before drying from the outside in a sealed state without using a special superheated steam generator or the like. The present invention has been completed by finding that the ceramic molded body can be dried quickly and uniformly by proceeding with the superheated steam atmosphere with the steam generated from the molded body.

  That is, according to this invention, the manufacturing method of the dry ceramic molded object shown below is provided.

(1) Moisture generated from a ceramic molded body in which the wet ceramic molded body is placed inside a sealed sealed container except for the water vapor outlet and the internal space of the sealed container is wetted by heating from the outside of the sealed container. The manufacturing method of the dry-ceramics molded object made into superheated steam atmosphere by this, and making it dry, maintaining this state.

(2) The method for producing a dried ceramic molded body according to (1), wherein the temperature of the internal space of the sealed container is maintained at 100 ° C to 130 ° C and dried.

(3) The method for producing a dried ceramic molded body according to (1), wherein the temperature of the internal space of the sealed container is maintained at 101 ° C to 120 ° C and dried.

(4) The method for producing a dried ceramic molded body according to any one of (1) to (3), wherein the sealed container is a metal container or a heat-resistant resin container.

(5) The method for producing a dried ceramic molded body according to any one of (1) to (4), wherein the sealed container is provided with a water vapor outlet at a lower part thereof.

(6) The method for producing a dried ceramic molded body according to any one of (1) to (5), wherein the heating means from the outside of the sealed container is hot air.

(7) The method for producing a dried ceramic molded body according to any one of (1) to (6), wherein the ceramic molded body before drying has a thickness of 10 mm or more.

  According to the method for producing a dry ceramic molded body of the present invention, a superheated steam atmosphere is formed inside the sealed container by the moisture of the wet ceramic molded body itself without using a special superheated steam generator. Drying can proceed, and a dry ceramic molded article of good quality free from cracks and cracks can be produced in a short drying time with good yield.

It is explanatory drawing which shows an example of the drying apparatus used for this invention. 3 is a graph showing the results of temperature measurement in Example 1. 3 is a graph showing the results of moisture measurement in Example 1. It is a graph which shows the result of the temperature measurement of Example 2. 6 is a graph showing the results of temperature measurement in Example 3.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that modifications, improvements, and the like appropriately added to the embodiments described above fall within the scope of the present invention.

  In general, a method for producing ceramics comprises a molding step of molding using a ceramic raw material, a drying step of drying the molded body, a firing step of firing the dried molded body, and a cooling step of cooling the fired body. Various ceramic products are manufactured through such processes. The method for producing a dried ceramic molded body of the present invention is characterized in that the molded body is dried using a superheated steam atmosphere in the drying step in the ceramics production process.

  In the method for producing a dried ceramic molded body of the present invention, the ceramic molded body in a wet state before firing formed by various ceramic raw materials is placed inside a sealed container other than the water vapor outlet, The method includes a method of obtaining a dry ceramic molded body by making a superheated steam atmosphere with moisture generated from a ceramic molded body in which the internal space of the sealed container is moistened by heating from the outside of the closed container and maintaining this state.

  That is, in the present invention, using a sealed container other than the water vapor outlet, a ceramic molded body in a wet state before firing is placed inside and heated from the outside of the sealed container. The water held by the body itself is evaporated to form a superheated steam atmosphere in the internal space of the sealed container, and the ceramic molded body is dried while maintaining this superheated steam atmosphere.

  In order to form a superheated steam atmosphere in the internal space of the sealed container, it is preferable to maintain the temperature of the internal space in a temperature range of 100 ° C. to 130 ° C. by heating from the outside, and a temperature range of 101 ° C. to 120 ° C. It is further preferable to maintain the above. By maintaining the temperature of the internal space of the sealed container at such a temperature, moisture is supplied to the surface of the molded body by the moisture diffusing from the inside of the ceramic molded body, and this moisture evaporates and the inside of the sealed container is The space can be an atmosphere of superheated steam. By setting such a heating temperature, the diffusion of moisture from the inside of the molded body and the evaporation of the surface are performed in a well-balanced manner. As a result, a sufficient superheated steam atmosphere is formed in the internal space of the sealed container and is relatively short It dries efficiently over time and does not crack or crack on the surface of the molded body.

  However, if the temperature of the internal space of the sealed container is less than 100 ° C., the drying does not proceed because the inside of the sealed container is a saturated water vapor atmosphere.

  The heating time from the outside of the sealed container is appropriately determined depending on the size, thickness and shape of the ceramic molded body to be dried. For example, in the case of a ceramic molded body having a rectangular parallelepiped shape (100 × 100 × 80 mm) generally having a thickness of 80 mm, drying can be completed in a heating time of about 30 hours. The drying time can be greatly shortened compared with the case where a long time of 60 hours is required when a ceramic molded body having the same shape is dried by a conventional humidity control drying method.

  When the ceramic molded body wetted by the method of the present invention is dried, the moisture distribution inside and on the surface of the molded body can be kept small at every stage during the drying process. For example, in the case of the above-mentioned ceramic molded body having a shape of 100 × 100 × 80 mm, the difference in moisture concentration between the inside and the surface of the molded body can be set to about 3% by mass in the entire drying process.

  The wet ceramic molded body used in the present invention is formed from a ceramic raw material obtained by adding various additives such as water and a binder to ceramics. Examples of ceramics include oxide ceramics such as alumina, mullite, zirconia, and cordierite; non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. A silicon carbide / metal silicon composite material, a silicon carbide / graphite composite material, or the like can also be used.

  Examples of the binder include polyvinyl alcohol, polyethylene glycol, starch, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, polyethylene oxide, sodium polyacrylate, polyacrylamide, polyvinyl butyral, ethyl cellulose, cellulose acetate, polyethylene, and ethylene-acetic acid. Examples include vinyl copolymers, polypropylene, polystyrene, acrylic resins, polyamide resins, glycerin, polyethylene glycol, and dibutyl phthalate.

  The ceramic molded body is for manufacturing ceramic products for use in various applications, and can be used in various shapes, such as insulators for high voltage transmission lines, automobile exhaust gas purification, etc. And a molded body having a shape such as a catalyst carrier for automobiles, a ceramic member for automobiles, and a kiln tool for firing.

  The hermetic container used in the present invention is capable of accommodating a ceramic molded body to have a hermetic structure, and is made of a material that is heat resistant to a heating temperature of about 150 ° C. There is no particular limitation. In general, a metal material is preferable, and a metal or stainless steel plate is preferable. It is also possible to use a heat-resistant resin material. The sealed container is in a sealed state after the ceramic molded body is accommodated, but a steam discharge port is provided in the lower part thereof, and excess water vapor is discharged from the steam discharge port during heating and drying.

  Next, a drying apparatus for carrying out the method of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a drying apparatus having a sealed container inside a hot air dryer. In FIG. 1, reference numeral 2 denotes a hot air dryer, and a sealed container 3 is provided inside the hot air dryer 2. The sealed container 3 has a sealed structure except for the water vapor outlet 4. In the present invention, the ceramic molded body 1 in a wet state before firing is placed inside the sealed container 3 and heated from the outside of the sealed container 3. By heating the ceramic molded body 1 in this way, the water held by the ceramic molded body 1 itself is evaporated, and an overheated steam atmosphere is formed in the internal space of the sealed container 3. Then, the ceramic molded body 1 is dried while maintaining this superheated steam atmosphere. A thermocouple 5 for measuring ambient temperature is installed in the space inside the sealed container 3.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

Example 1
A preliminary test of drying of the ceramic molded body was performed using a drying apparatus having a sealed container inside the hot air dryer as shown in FIG.

  First, a 100 × 100 × 80 mm rectangular parallelepiped wet ceramic molded body was prepared as a sample. The ceramic molded body of this sample was placed in a sealed container, and a thermocouple for temperature measurement was attached to the center and surface of the ceramic molded body and the space in the sealed container. In this state, heating was started from the outside of the sealed container through hot air by a hot air dryer, and drying was performed while controlling the space temperature inside the sealed container to be 110 ° C. By drying at a space temperature (atmosphere temperature) of 110 ° C., the inside of the sealed container became a superheated steam atmosphere at a temperature of 110 ° C., and drying of the molded body proceeded.

  During the drying, the temperature change at the three parts of the center and surface of the molded body and the superheated steam atmosphere was measured, and when 17 hours, 22 hours, 29 hours, and 47 hours passed after the start of drying ((1 ) To (4)), the moisture distribution of the sample was measured. As shown in FIG. 3, the moisture distribution of the sample was obtained by dividing the molded body into 25 equal parts in the vertical and horizontal directions, collecting samples at 5 locations in each of the vertical and horizontal directions, and measuring the water content. The results of this temperature measurement are shown in FIG. 2, and the change in moisture distribution is shown in FIG.

  As can be seen from FIG. 2, the temperature of the superheated steam atmosphere became 110 ° C. about 5 hours after the start of heating, and was controlled to be substantially constant at this temperature until the end of heating. The ceramic molded body had a temperature of 101 ° C. at about 5 hours after the start of heating, and was maintained at this temperature until about 30 hours. This period is a constant rate drying period under a superheated steam atmosphere. After about 30 hours, the temperature of the molded body was increased, and it was found that the constant rate drying was completed and the reduced rate drying was started.

  In the middle of this drying period, a sample was taken at the time indicated by (1) to (4) in FIG. 2, and its moisture distribution was determined. The result is shown in FIG. From this result, it was found that in the constant rate drying under the superheated steam atmosphere, the moisture content decreased from (1) to (4) and the drying progressed. Further, in any of the stages (1) to (4), the difference between the moisture content on the surface of the molded body and the moisture content in the central portion is about 3%, and the moisture difference between the surface and the interior is very small. all right.

(Example 2)
Using a drying apparatus provided with a sealed container inside a hot air dryer as shown in FIG. 1, a drying test using heated steam was performed on a ceramic body having a shaded coconut body shape.

  First, as a sample, a molded body in a wet state of a 4-shade shade-shaped insulator having a shade diameter (large) of 250 mm, a shade diameter (small) of 200 mm, and a trunk diameter of 100 mm was prepared. Place the ceramic molded body of this sample in a sealed container, and attach thermocouples for temperature measurement to the center and surface of the body of the ceramic molded body, the surface of the shade, and the space inside the sealed container (superheated steam atmosphere). It was. In this state, heating was started from the outside of the hermetic container through hot air by a hot air dryer, and the shade-shaped cocoon body-shaped ceramic molded body was dried. By drying the space temperature (superheated steam atmosphere temperature) at 111 ° C., the inside of the sealed container became a superheated steam atmosphere at a temperature of 111 ° C., and drying of the molded body proceeded. Heating was completed after about 90 hours from the start of drying, and drying of the ceramic molded body was completed.

  As a result of this drying test, no cracks or cracks were found in the shade, and a good dry product could be obtained. Further, during this drying operation, temperature changes were measured at four locations on the middle of the ceramic molded body of the above-mentioned shade-shaped insulator, the barrel surface, the shade surface, and the superheated steam atmosphere. The result is shown in FIG.

  As can be seen from FIG. 4, drying proceeds at a temperature of about 104 ° C. at the insulator body, and drying proceeds quickly at the tip of the shade, and the temperature at the tip of the shade begins to rise quickly. The temperature difference was small.

(Example 3)
Using the same shade shaped ceramic molded body as in Example 2 as a sample, the shade shaped palm body shaped ceramic was formed by the same drying operation as in Example 2 except that the space temperature (superheated steam atmosphere temperature) was 103 ° C. The body was dried. In this case, the heating was finished about 180 hours after the start of drying, and the drying of the ceramic molded product was finished.

  As a result of this drying test, no cracks or cracks were found in the shade, and a good dry product could be obtained. Further, during this drying operation, temperature changes were measured at four locations on the middle of the ceramic molded body of the above-mentioned shade-shaped insulator, the barrel surface, the shade surface, and the superheated steam atmosphere. The result is shown in FIG.

  As can be seen from FIG. 5, the temperature at the tip of the shade as well as the body of the insulator is almost the same as 102 ° C., and the temperature difference is very small. Therefore, the moving speed of moisture inside the molded body is slow, and it takes a long time for drying.

Example 4
In the same manner as in Example 2, using a drying apparatus having a sealed container inside a hot air dryer as shown in FIG. 1, the following two types of shaded body-shaped ceramic molded body heated steam A drying test was performed. The results are shown in Table 1.

  As can be seen from this result, in the case of the drying method using the superheated steam atmosphere of the present invention, the drying can be performed in a short time of 1/2 to 1/3 compared with the drying by the conventional humidity conditioning drying method, In addition, it was possible to obtain a dry product of good quality without occurrence of cracks or cracks in the obtained dry product.

  The method for producing a ceramic molded body of the present invention can dry a ceramic molded body in a shorter time than the conventional method without using a special superheated steam heating device or the like compared to the conventional method, and A good dry product can be obtained, which is useful in the production of various ceramic products using insulators for power transmission lines and other ceramic molded bodies.

1. Ceramic compact 1. 2. Hot air dryer Airtight container 4. 4. Water vapor outlet thermocouple

Claims (7)

  The wet ceramic molded body is placed inside a sealed sealed container except for the water vapor outlet, and superheated steam is generated by moisture generated from the ceramic molded body that has moistened the internal space of the sealed container by heating from the outside of the sealed container. A method for producing a dried ceramic molded body, which is dried while maintaining this state in an atmosphere.   The method for producing a dried ceramic molded body according to claim 1, wherein the temperature of the internal space of the sealed container is maintained at 100C to 130C and is dried.   The method for producing a dried ceramic molded article according to claim 1, wherein the temperature of the internal space of the sealed container is maintained at 101C to 120C to be dried.   The method for producing a dry ceramic molded body according to any one of claims 1 to 3, wherein the sealed container is a metal container or a heat-resistant resin container.   The method for producing a dried ceramic molded body according to any one of claims 1 to 4, wherein the sealed container is provided with a water vapor outlet at a lower portion thereof.   The method for producing a dried ceramic molded body according to any one of claims 1 to 5, wherein the heating means from the outside of the sealed container is hot air.   The method for producing a dried ceramic molded body according to any one of claims 1 to 6, wherein the thickness of the ceramic molded body before drying is 10 mm or more.

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