JPH0739089B2 - Molding method for ceramics - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding a ceramic body, and particularly to pressurizing ceramic particles into a predetermined shape, and sintering and solidifying the molded body. To a method of forming the ceramic body according to claim 1.

[Outline of Invention]

The present invention is one in which the void portion of the pressure-molded body of ceramic particles is filled with chromium oxide and then sintered, and thereby shrinkage during sintering is reduced. is there.

[Conventional technology]

Ceramic bodies have come to be used as parts or components of various machines. In the case of molding such a ceramic body, conventionally, particles of a ceramic material have been pressed by press molding and thereby molded into a predetermined shape. Then, the formed body of the ceramic particles is sintered at a high temperature, whereby the formed body is solidified. Then, after this, it was ground and finished.

[Problems to be solved by the invention]

According to such a conventional method for molding a ceramic body, there is a drawback in that when the sintering is carried out at a high temperature, the molded body largely contracts, and thus the dimensional change becomes severe. Therefore, it was necessary to press-form into a large shape in advance in consideration of such a dimensional change, but the shrinkage at the time of sintering was not always uniform, and it was necessary to finish by grinding later. However, since the sintered ceramic body has high hardness, it was not easy to grind it. Further, in a compact having a complicated shape, there is a problem that stress is concentrated due to a large dimensional change during sintering and the compact is cracked.

The present invention has been made in view of the above problems, and provides a method for molding a ceramic body that reduces the dimensional change due to shrinkage during sintering and solidification of the ceramic body. The purpose is.

[Means for solving problems]

The present invention relates to a method in which ceramic particles are pressed to be molded into a predetermined shape, and the molded body is sintered and solidified, in which voids of the ceramic particle pressure molded body are filled with chromium oxide. After that, the above-mentioned sintering is performed.

[Action]

Therefore, according to the present invention, the void portion of the pressure-molded body of ceramic particles is filled with chromium oxide prior to sintering, whereby shrinkage during sintering can be reduced and dimensional change can be prevented. It becomes possible to hold down low.

〔Example〕

The present invention will be described below with reference to an embodiment shown in the drawings. This example relates to a method for forming a ceramic body from alumina (Al ₂ O ₃ ) which is relatively widely used among ceramics. 600 kg / cm of high-purity alumina powder
^It was molded into a predetermined shape with a pressing pressure of ² to form a molded body. As shown in FIG. 1, this molded body has innumerable voids formed therein continuously or discontinuously.

In order to fill the voids of the ceramic molded body with chromium oxide, the molded body was immersed in a chromic acid solution containing 60 parts by weight of chromic acid and 40 parts by weight of water. As a result, as shown in FIG. 2, the voids of the molded body were filled with the chromic acid solution. And about the molded body containing the chromic acid solution in the void
Baking at 700 ℃ removes water in the chromic acid solution and oxidizes chromic acid (CrO ₃ ) to produce chromium oxide (CrO3).
₂ O ₃ ). As a result, as shown in FIG. 3, chromium oxide is formed so as to cover the ceramic particles, and at the same time, a part of the void portion of the molded body is filled with chromium oxide.

If the filling with the above chromium oxide is performed only once,
As shown in the figure, the voids of the molded body are not completely filled with chromium oxide, and considerable voids remain.
Therefore, the above-mentioned dipping with the chromic acid solution and firing are repeated a plurality of times so that the voids of the ceramic molded body are almost completely filled with chromium oxide. Then, after this, the ceramic molded body was sintered at a temperature of 1600 ° C., which is the same temperature as the conventional one. As a result, the ceramic compact was solidified to obtain a ceramic body. This ceramic body was finished by grinding if necessary.

In this way, while pressing the alumina powder,
The process of filling the voids with a chromic acid solution and firing at 700 ° C is repeated multiple times to fill the voids of the compact almost completely with chromium oxide, and then linear shrinkage of the compact sintered at 1600 ° C. As a result, the results shown in FIG. 4 were obtained. At the same time, changes in the bulk specific gravity with respect to the number of times chromium oxide was filled and fired were examined, and the results are also shown in FIG.

With the ceramic body according to this example, the linear shrinkage rate due to sintering is reduced to a value of about 5%. This is because the voids of the alumina powder compact were filled with chromium oxide before sintering. And about the number of times of filling of chromium oxide, I repeated up to 14 times, but it was almost 10
The bulk specific gravity becomes saturated after about ten times, and the linear shrinkage ratio tends to be constant. Therefore, by repeating the filling of chromium oxide approximately 10 times, the low linear shrinkage ratio as described above can be obtained. By the way, in the conventional ceramic body of alumina particles, which is not filled with chromium oxide before sintering, the linear shrinkage ratio at the time of sintering is about
It was 17%.

[Application example]

Although the present invention has been described with reference to the embodiments of the ceramic body of alumina, the present invention is not limited to the above embodiments, and various modifications can be made based on the technical idea of the present invention. For example, as a raw material for the ceramic body,
In addition to alumina, zirconia (ZrO ₂ ) and silicon carbide (Si
C), magnesia (MgO), silicon nitride (Si ₃ N ₄ ) or the like may be used, and the present invention is also applicable to a ceramic body made of these materials.

〔The invention's effect〕

As described above, according to the present invention, chromium oxide is filled in the voids of the pressure-molded body of ceramic particles, and then the sintering is performed. Therefore, according to the present invention, it is possible to significantly reduce the shrinkage of the ceramic molded body at the time of high-temperature sintering as compared with the prior art, and thereby possible to suppress the dimensional change of the molded body after sintering as much as possible. Become. Therefore, it is possible to reduce the finishing work such as grinding after that, and it is possible to prevent the molded body from cracking due to shrinkage during sintering.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a main part of a press-molded ceramic molded body, FIG. 2 is an enlarged cross-sectional view of a ceramic molded body filled with a chromic acid solution, and FIG. 3 is a ceramic molded body filled with chromium oxide. FIG. 4 is an enlarged cross-sectional view of the main part of FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C04B 35/64 L

Claims (1)

[Claims] 1. A method in which ceramic particles are pressed to be molded into a predetermined shape, and the molded body is sintered and solidified, and chromium oxide is filled in the voids of the pressed molded body of ceramic particles. And then performing the above-mentioned sintering.