JPH01108002A - Molding of ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the molding of ceramics, and particularly to a solid casting method suitable for molding long objects.

[Conventional technology]

In conventional solid casting, slurry is injected into the mold.

Furthermore, a slurry reservoir is placed in the upper part, and it is filled with excess slurry, and the solid part is solidified while being cast without removing the slurry, and then the mold is removed, and assimilation is performed from the lower part and the sides. For long objects, solidification progresses from the sides without being affected by the lower part. Therefore, in the case of long objects, the center solidifies last, causing nest-like defects and bubbles to occur in the center. P.L., 11).

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not give any consideration to the assimilation of the ceramic, especially the solidification of the upper and lower parts, and has the problems described above.

The purpose of the present invention is to reduce the thickness of the assimilated layer during the assimilation process from the bottom to the top by changing each cross-sectional area of the mold, that is, the shape of the pool is changed from a cylindrical shape in the conventional method to an inverted conical shape, The tension generated in the center is intended to prevent nest-like defects and air bubbles from forming, thereby obtaining a sound molded product.

[Means for solving problems]

The above object is achieved by reducing the cross-sectional area of the mold from the bottom to the top. That is, gypsum is generally used as a mold for solid casting of ceramics, and solidification progresses as water in the slurry is absorbed by the gypsum mold. Therefore, if the cross-sectional area of the upper and lower molds is the same, assimilation proceeds at the same speed from the sides except near the bottom. In the present invention, the problem was solved by making the cross-sectional area of the mold larger at the lower part and smaller at the upper part to achieve directional solidification.

[Effect]

That is, the water absorption capacity is proportional to the thickness of the plaster, and the water absorption capacity is greater in the lower part. Therefore, the solidified layer from the bottom surface becomes thicker, and on the contrary, the liquid phase part is very small at the bottom, and the shape of the pool becomes an inverted cone. As a result, the final solidification of each cross section is directional from the bottom to the top, and a healthy ceramic molded body without nest-like defects or bubbles can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 3.

FIG. 1 shows a longitudinal section of the molded body and mold. Figure 2 shows the state of a conventional mold after several hours of casting. That is, the slurry was poured and then drained, and the thickened portion was defined as solid phase 2, and the drained portion was defined as liquid phase 1. A sleeve that does not absorb moisture is attached to the upper part of the mold 3 to replenish the slurry that has shrunk as the slurry is assimilated, but this sleeve has been omitted for the sake of simplicity.

The molds 3 are all made of plaster, and the dimensions of the molded bodies are 30 m in diameter, 300 m in length, and the height of the mold is 330 mm.
In the case of the figure, the lower part was 100 mm and the upper part was 40 nm.

The slurry was prepared by adding a small amount of deflocculant to Sialon powder with an average particle size of 0.6 μm, and further adding 28% water, stirring and mixing well, and then performing icing for 48 hours to vacuum defoaming.

After pouring the slurry into a mold and solidifying it sufficiently, the molded body was demolded. After pre-sintering the molded body, 1
Cut at 30mm and 170mm positions, φ30XQ4
A 0 m test piece was taken. A through hole was drilled in the center of the test piece, and the hole diameter was gradually enlarged, and changes in hole diameter and weight were measured to determine the density distribution in the cross section. The results are shown in FIG. In the density distribution of products molded using conventional molds, there is a large difference between the surface and the center, and in particular, the density decreases rapidly near the center. In contrast, in the method of the present invention, the mold becomes thinner as it progresses from the bottom to the top.

Since the water absorption capacity decreases as the mold becomes thinner, the solidification rate in the upper part becomes slower. As a result, the density of the molded body is lower at the surface than when using a conventional mold, but the density decreases less from the surface to the center. When observing the cross section of the molded body using a magnifying glass, there are many minute defects in the center of the molded body formed using the conventional method, which correspond to the cavities found in castings, and this causes a decrease in density near the center. It seems to be big. In contrast, in the case of the present invention, there is no defect in the center. In other words, in the present invention, as directional assimilation progresses, the area of the liquid phase with good fluidity becomes larger in the upper part, and the supply of slurry is facilitated, making it difficult for minute nest-like defects to appear in the center. it is conceivable that.

Next, as a result of sintering the molded body, cracks occurred in the center of the molded body produced using the conventional method, indicating that it is difficult to mold a long body by solid casting. On the other hand, when the mold of the present invention was used, a crack-free sintered body was obtained, although the amount of shrinkage was large in the upper part.

According to this example, it was confirmed that even long objects such as rolling rolls can be solid cast by using the method of the present invention.

Furthermore, the effects of the present invention will be enhanced if directional assimilation is facilitated by changing the shape of the mold. As one method, we produced a mold whose outer surface changed in a quadratic curve and compared it with a case in which the outer surface changed in a straight line.As a result, we found that the mold had greater directivity, confirming the effects of the present invention.

Further, the method of the present invention is effective not only for cylindrical objects but also for prismatic objects.

〔Effect of the invention〕

According to the present invention, it is possible to prevent nest-like defects and bubbles from occurring in the center.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a mold and a molded body according to an embodiment of the present invention, Fig. 2 is a longitudinal cross-sectional view of a conventional mold and a molded body, and Fig. 3 is a density distribution diagram of a cross-sectional view of the molded body. be. Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. A method for molding ceramics, characterized in that the cross-sectional area of the upper part of the mold is smaller than that of the lower part, in a solid casting method of ceramic long cylinders and square pillars.