JP4582342B2 - Processing method of ceramic molded body - Google Patents

Description

  The present invention relates to a method for treating a ceramic molded body. Examples of the ceramic molded body include a ferrite molded body used as a core of a coil device.

  As disclosed in Patent Document 1, the ferrite molded body is generally manufactured by the following process. First, a ferrite powder is kneaded with a binder such as PVA (polyvinyl alcohol) to produce granules having a structure in which ferrite powder is aggregated with the binder. Next, these granules are put into a predetermined mold and subjected to pressure molding to obtain a ferrite molded body. And after drying a ferrite molded object, a required characteristic, for example, a magnetic characteristic, is ensured by baking.

  By the way, in order to use the ferrite molded body as the core of the coil device, it is necessary to process the ferrite molded body into a desired shape. For example, when trying to obtain a drum-shaped core, it is necessary to scrape a cylindrical ferrite molded body with a disk-shaped grindstone to form a winding core portion around which a conducting wire is wound. Since the ferrite molded body is extremely hard at the stage after firing and becomes difficult to process, it is desirable to process at the stage before firing.

  However, since the ferrite molded body before firing is in a state where the granules are simply pressed together, it is extremely brittle and has low strength. For this reason, when processing a ferrite molded object, there exists a possibility of producing breakage, such as a chip and a crack. In addition, there is a risk of breakage when an impact is accidentally applied during handling at a stage before firing, such as when the ferrite compact is transported to a firing furnace.

Particularly, in recent years, with the downsizing and thinning of the coil device, the size of the ferrite molded body used as the core of the coil device has been reduced. For example, the ferrite molded body is thin. For this reason, the ferrite compact tends to be damaged at the stage before firing, and there is an increasing need to increase the strength in order to prevent the damage.
JP 2003-282343 A

  The subject of this invention is providing the processing method of the ceramic molded object which can improve the intensity | strength of a ceramic molded object in the step before baking.

  In order to solve the above-described problems, in the method for treating a ceramic molded body according to the present invention, an unfired ceramic molded body containing a water-soluble binder is formed by pressure molding. Then, water vapor is applied to the ceramic molded body. Thereafter, the ceramic molded body is dried.

  As a result of diligent research to find out the cause of the low strength of the ceramic molded body formed by pressure molding, the inventors have found that the defect of the binder film inside the ceramic molded body is a major factor. I found out. That is, even if the ceramic molded body is pressure-molded, the binder films are only pressed against each other inside the ceramic molded body and are not sufficiently bonded. For this reason, the strength of the ceramic molded body is low.

  Therefore, in the present invention, water vapor is applied to the ceramic molded body formed by pressure molding. Thereby, water vapor | steam is osmose | permeated inside from the surface of a ceramic molded object, the film | membrane of a water-soluble binder is moistened, and a film | membrane of a binder can be joined.

  Thereafter, the ceramic molded body is dried. Thereby, unnecessary moisture can be removed from the bonded binder film and solidified. Therefore, the strength of the ceramic molded body is improved as a whole.

  Suitably, the ceramic molded body is subjected to water vapor having a temperature in the range of 60C to 90C.

  Further, suitably, the ceramic molded body is preheated before water vapor is applied to the ceramic molded body. More suitably, the ceramic molded body is preheated so that the temperature of the ceramic molded body is in the range of 60 ° C to 100 ° C.

  As described above, according to the present invention, it is possible to provide a method for treating a ceramic molded body that can improve the strength of the ceramic molded body at a stage before firing.

  FIG. 1 is a flowchart showing an embodiment of a method for treating a ceramic molded body according to the present invention. In the present embodiment, as an example of a ceramic molded body, a ferrite molded body used for a core of a coil device is processed.

First, as shown in step S1, a ceramic powder is prepared. In the case of the present embodiment, since the ferrite compact is to be processed, ferrite powder is used as the ceramic powder. The ferrite powder is obtained by the following method, for example. First, a raw material powder mainly composed of Fe ₂ O ₃ , NiO, CuO, and ZnO is prepared. Next, after sufficiently mixing the raw material powder, it is pre-sintered by calcining to obtain a pre-sintered body. Then, the temporary sintered body is pulverized with a ball mill or the like to obtain ferrite powder made of pulverized powder. The particle size of the ferrite powder is 2 μm, for example.

  Next, as shown in step S2, granules are produced from the ceramic powder and a water-soluble binder. Specifically, after adding a binder to the ceramic powder and kneading sufficiently, granulation is performed by a spray dryer to obtain granules having a structure in which the ceramic powder is aggregated with the binder. Furthermore, the particle size of the granules is made uniform by a wire mesh. As an example of a water-soluble binder, PVA (polyvinyl alcohol), a polyacrylic acid polymer, etc. can be mentioned, for example. The particle size of the granules is, for example, 100 μm.

  Next, as shown in step S3, a ceramic compact is produced from the granules by pressure molding. Specifically, after putting the granule in a mold having a predetermined shape, the mold is closed and pressure is applied to obtain a ceramic molded body. Examples of the shape of the ceramic molded body include a columnar shape and a prismatic shape.

  Next, as shown in step S4, the ceramic molded body is preheated and the temperature of the ceramic molded body is raised. As a method for preheating the ceramic molded body, a method of putting the ceramic molded body in a preheating chamber maintained at a constant temperature, a method of directly heating the ceramic molded body, or the like can be employed.

  Next, as shown in step S5, water vapor is applied to the ceramic molded body. As a method for applying water vapor to the ceramic molded body, a method of spraying water vapor onto the surface of the ceramic molded body with a nozzle, a method of placing the ceramic molded body in an atmosphere filled with water vapor, or the like can be employed. The temperature of the water vapor is preferably set in the range of 60 ° C to 90 ° C, more preferably in the range of 70 ° C to 80 ° C. Moreover, although it depends on the dimension or shape of the ceramic molded body, the time for which water vapor is applied is set, for example, in the range of 15 minutes to 480 minutes.

  Next, as shown in step S6, the ceramic molded body is dried. As a method for drying the ceramic molded body, a method using a batch oven, a method of directly heating, or the like can be employed. The drying temperature and drying time are set to 120 ° C. and 1 hour, for example, although depending on the size or shape of the ceramic molded body.

  As described above, in the ceramic molded body produced by pressure molding, the defect of the binder film inside the ceramic molded body is a major factor for reducing the strength. FIG. 2 (a) schematically shows the state of the binder at the stage of pressure molding. Referring to FIG. 2A, a binder 2 film is formed around the ceramic powder 1. However, even by pressure molding, the films of the binder 2 are merely pressed against each other and are not sufficiently bonded. For this reason, the intensity | strength seen as the whole ceramic molded object will become low.

  As a technique for joining the films of the binder 2 during the pressure molding, a technique in which the binder is softened by adjusting the water content of the binder in advance is considered. However, if pressure molding is performed in a state where the moisture content of the binder is increased, the granules adhere to the mold, and the pressure molding cannot be performed smoothly.

  Therefore, in this embodiment, after pressure forming, as shown in step S5, water vapor is applied to the ceramic formed body obtained by pressure forming. Thereby, water vapor is penetrated from the surface of the ceramic molded body to soften the binder film, whereby the binder 2 films can be joined to each other as shown in FIG.

  Thereafter, as shown in step S6, the ceramic molded body is dried. Thus, by removing unnecessary moisture from the binder inside the ceramic molded body, as shown in FIG. 2C, the film of the binder 2 can be contracted and solidified in a joined state. Therefore, the strength of the ceramic molded body as a whole is improved.

  As a result of investigations by the inventors, instead of applying steam to the ceramic molded body in step S5, if the ceramic molded body is immersed in water (dipped in jab), the surface of the ceramic molded body collapses, and the ceramic molded body The body shape cannot be maintained.

  Furthermore, the mechanism of strength improvement will be described from the viewpoint of the entire structure of the ceramic molded body. First, as shown in FIG. 3A, at the stage of pressure forming (step S3), the ceramic powder 1 is in contact with the binder 1 by pressure inside the ceramic molded body 3.

  Next, when water vapor is applied to the ceramic molded body in step S5, the binder 2 contained in the ceramic molded body 3 takes in the water vapor and expands as shown in FIG. 3B. At that time, although the ceramic powder 1 is subjected to compressive stress due to the expansion of the binder 2, the ceramic molded body 3 is not broken because the structure of the ceramic molded body 3 is loosened.

  Thereafter, when the ceramic molded body is dried in step S6, the binder 2 is dried and contracted as shown in FIG. 3C, and a tensile stress A2 is generated in the entire ceramic molded body 3. The strength of the ceramic molded body 3 can also be improved by this tensile stress A2.

  Furthermore, as a result of investigations by the inventor, if water vapor is applied to the ceramic molded body to cause condensation on the surface of the ceramic molded body, the surface of the ceramic molded body may collapse and the shape of the ceramic molded body cannot be maintained. There is sex.

  Therefore, in the present embodiment, when the present method is applied to a ceramic molded body having a shape in which condensation is likely to occur, the ceramic molded body is preheated as shown in step S4 before applying water vapor. By preheating the ceramic molded body, it is possible to suppress the occurrence of condensation when water vapor is applied thereafter.

  Preferably, the ceramic molded body is preheated so that the temperature of the ceramic molded body is in the range of 60 ° C to 100 ° C. If the temperature of the ceramic molded body is lower than 60 ° C., condensation may occur when water vapor is applied. Moreover, when the temperature of the ceramic molded body is higher than 100 ° C., the ceramic molded body is dried too much, and even if water vapor is applied thereafter, there is a possibility that water vapor is not taken into the binder inside the ceramic molded body.

  After the above-described steps S1 to S6, as shown in step S7, the ceramic molded body is processed into a desired shape. For example, when it is going to obtain the drum-shaped core used for a coil apparatus, a cylindrical molded object is shaved with a disk-shaped grindstone, and the core part for winding conducting wire is formed.

  Finally, the ceramic compact is conveyed to a firing furnace, and the ceramic compact is fired as shown in step S8. Thereby, the ceramic powder contained in the ceramic molded body is sintered, and necessary characteristics such as electrical or magnetic characteristics are ensured.

  Regarding the breakage in processing the ceramic molded body in step S7 or the breakage in transporting the ceramic molded body to the firing furnace in step S8, the strength of the ceramic molded body is improved in the previous steps S5 and S6. So this can be prevented.

  Next, experimental data related to improving the strength of the ceramic molded body will be described. In the experiment, PVA was used as a water-soluble binder, and seven cylindrical ferrite compacts were produced by pressure molding. These are designated as Samples 1-7. About sample 1, water vapor was not applied and only the drying process (120 degreeC-1 hour) was performed.

  Samples 3, 4, 5, and 6 were preheated and then applied with water vapor at temperatures of 60 ° C., 70 ° C., 80 ° C., and 90 ° C. for 10 minutes, respectively. Thereafter, the same drying treatment as that of Sample 1 was performed.

  For the remaining samples 2 and 7, after preheating, water vapor at temperatures of 45 ° C. and 100 ° C. was applied for 15 minutes, respectively. Thereafter, the same drying treatment as that of Sample 1 was performed.

  Furthermore, about each sample 1-7, fracture strength was measured, without baking. The fracture strength was measured by placing a ferrite molded body on a flat plate in such a manner that its outer peripheral surface is in contact with the flat plate and applying force to the outer peripheral surface of the ferrite molded body from above. The experimental results are shown in Table 1 below.

  Referring to Table 1, when only the drying treatment was performed without applying water vapor to the ferrite molded body (Sample 1), the fracture strength was a low value of 3.7 kgf. On the other hand, when water vapor was applied to the ferrite compact and further subjected to a drying treatment (samples 3 to 6), the fracture strength was significantly improved and became a high value of 6.3 kgf to 7.8 kgf.

  If the temperature of the water vapor is too low, only a small amount of water vapor can be taken into the water-soluble binder inside the ferrite molded body, and as a result, the fracture strength may not be improved (Sample 2).

  On the other hand, if the temperature of the water vapor is too high, the ferrite molded body is dried, so that the water-soluble binder inside the ferrite molded body is also dried and the fracture strength may not be improved ( Sample 7).

  The inventors confirmed that when the temperature of the water vapor is in the range of 60 ° C. to 90 ° C., a sufficient amount of water vapor can be taken into the water-soluble binder inside the ferrite molded body, and the fracture strength can be greatly improved. (Samples 3-6).

  As an example of the ceramic molded body to which the present invention is applied, the ferrite molded body used for the core of the coil device has been described, but the present invention is not limited to this.

  The present invention is not limited to this embodiment, and it goes without saying that various modifications and changes can be made within the scope of the claims.

It is a flowchart which shows one Embodiment of the processing method of the ceramic molded body which concerns on this invention. It is a figure which shows typically the state of the binder in the inside of a ceramic molded body. It is a figure which shows the structure of a ceramic molded body typically.

Explanation of symbols

1 Ceramic powder 2 Binder 3 Ceramic molded body

Claims (3)

An unfired ceramic molded body containing a water-soluble binder is formed by pressure molding,
Preheating the ceramic compact,
Thereafter, water vapor is applied to the ceramic molded body,
Then, the ceramic molded body is dried.
A method for treating a ceramic molded body. A method for treating a ceramic molded body according to claim 1,
Preheating the ceramic molded body so that the temperature of the ceramic molded body is in the range of 60C to 100C;
A method for treating a ceramic molded body. A method for treating a ceramic molded body according to claim 1 or 2,
Applying water vapor in the range of 60 ° C. to 90 ° C. to the ceramic molded body,
A method for treating a ceramic molded body.

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