JPH06170821A - High speed slip cast molding method using porous ceramics mold - Google Patents

Abstract

PURPOSE:To increase the cast molding speed of ceramics. CONSTITUTION:A mold to be used with a void size of 0.6mum or less and voids of 30vol.% or more is composed of the sintered matter of a molded object molded from a ceramics compd. powder raw material with a particle size of 2.0mum or less containing 10wt.% or less of a vitreous binder and well arranged in shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slurry casting molding method characterized by using a specific molding die. More specifically, the present invention relates to a method for high-speed slurry casting by using a porous ceramics molding die having a controlled pore size and porosity.

[0002]

2. Description of the Related Art Among ceramics molding methods, the casting molding method has a long history as a molding method for ceramics along with the lathe molding method. That is, a slurry in which clay, which is a raw material for ceramics, is dispersed in water is poured into a plaster mold, which is a porous material,
At the gypsum mold-slurry interface, water is absorbed inside the gypsum mold, and solid-liquid separation is performed to cause clay to adhere to the surface of the gypsum mold, whereby the molding is performed. In recent years, isotropic pressure molding (CIP) and injection molding methods have been developed as molding methods for fine ceramics, but this casting molding method can mold complex and large-sized products, and obtain high-density molded products. Therefore, researches on forming methods of alumina, zirconia, silicon nitride, etc. have been actively conducted.

[0003]

[Problems of the prior art] The problems of the conventional casting method are:
The molding speed is low, Ca contamination of the molded body due to wear and dissolution of the gypsum mold and deterioration of dimensional accuracy. For the friction and dissolution of the gypsum mold, it has been considered to use a deplaster mold such as a resin mold, but it is necessary to apply pressure because the mold material is hydrophobic. Further, although a molding die made of a sintered ceramic compound sintered body and having a pore diameter of 1 μm or less has been developed, only a study for making a gypsum mold that can be used semipermanently has been made. (Kaisho 62-244603). The molding speed in cast molding is an important factor for obtaining a molded product having a uniform structure. That is, since the ceramic raw material dispersed in the slurry aggregates with the passage of time, the compact density decreases with the passage of the shaping time. This agglomeration phenomenon becomes stronger as the ceramic raw material becomes finer particles. Since the casting speed is governed by the water absorption pressure and water absorption speed of the gypsum mold, it has been attempted to increase the molding speed by applying external pressure to the slurry.

[0004]

SUMMARY OF THE INVENTION According to the present invention, in pouring and molding of ceramics, the problem of the conventional technique that the molding speed is slow is not the means of applying external pressure to the slurry, but the porosity and the pore diameter of the ceramics molding die. It is something that is tried to solve by controlling. That is,
In cast molding of ceramics, the purpose is to dramatically improve the molding speed by using porous ceramics whose porosity and pore diameter are controlled instead of the gypsum mold.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a casting method with a high molding speed. The high-speed slurry casting method of this invention is
Particle size containing less than 10% by weight of vitreous binder is 2.0
A sintered compact of a ceramic compound powder raw material having a particle size of less than or equal to μ and a pore size of 0.6 μ or less and a porosity of 30 vol% or more, preferably a pore size of 0.6 μ or more. It is characterized by using a molding die which is small and has a porosity of 30% by volume or more. Examples of the ceramic compound powder raw material used in the present invention include powders of alumina, silicon carbide, silicon nitride, zirconia, and the like. As the glassy binder, known alkali metal compounds and alkaline earth metal compounds are used. Then, the powdery raw material molded body is obtained by a known molding method such as press molding, plastic molding, and slurry casting.

Control of Porosity and Pore Diameter of Porous Ceramic Molds Porous ceramics are manufactured by various methods. The simplest method is to mold a ceramic raw material and lower the temperature by 100 to 400 ° C. lower than the sintering temperature. It is obtained by sintering at. The porosity, which is the most important factor of the porous ceramics, is determined by the molding density and the sintering temperature. The lower the molding density and the sintering temperature, the higher the porosity. Regarding the control of the pore diameter, if a well-sized ceramic raw material is used, the pore diameter can be controlled to about 1/3 of the average particle diameter. The porous ceramics used as a mold material in the present invention is, for example, one in which a vitreous binder is added to sized alumina in an amount of 0 to 10 wt% and the pore diameter and porosity are controlled by the above method. The well-sized ceramic compound powder is a powder having a narrow particle size distribution, and the standard deviation σ of the lognormal distribution formula is in the range of 1.0 to 2.0.

Meaning of Pore Diameter Control as Cast Mold When casting slurry of ceramics, when the slurry is pressurized, the higher the pressure, the faster the molding speed. The osmotic pressure ΔP of the liquid in the hydrophilic porous body can be represented by the formula I because it is due to the wetting effect of the liquid in the casting at normal pressure. Here, γ _L cos θ is the free energy of wetting, and r is the pore radius. It can be seen from the formula I that the material having a larger free energy of wetting with water and the porous ceramics having a smaller pore diameter have a higher osmotic pressure and a higher molding speed in casting. Further, since the ceramic raw material is further finely divided, and the ceramic powder dispersed in the slurry enters the pores when the porosity of the casting mold is large and causes clogging, it is significant that the pore diameter can be controlled. That is.

[0008]

[Reference Example] Performance Comparison of Porous Alumina and Gypsum as Mold Material As a gypsum mold, 45 parts of water is added to 100 parts of α-gypsum generally used for cast molding of fine ceramics and stirred for 5 minutes, After standing for 5 minutes, it was made into a plaster mold (referred to as mold 1). On the other hand, with respect to porous alumina, the average particle diameters of 20, 3, and 1.3 μm are 30
Press molded at a pressure of Mpa, 1650 ° C. for 20 μm alumina, 140 for 3 and 1.3 μm.
It was sintered at 0 ° C. to obtain a porous body (referred to as mold 2 to mold 4). Further, for the average particle diameter of 1.3 μm, three test bodies were press-molded at a pressure of 60 MPa and the sintering temperature was changed (1400 ° C., 1500 ° C., 1550 ° C.) to obtain a porous body (mold 5 to mold 5). 7). Table 1 shows the average pore diameter (mercury porosimeter method), porosity (weight method in water), and free energy of wetting with water (penetration rate method) of gypsum and porous alumina. In Table 1, the average pore diameter of the plaster of type 1 is 4.4 μm, while the average pore diameter of the porous alumina is 2 to 2.
The average particle size of the mold 4 and the raw material used decreased as it decreased, and was approximately 1/3 of the average particle size of the raw material used.
Has become. It is proved that the mold 4 and the mold 5 are different from each other only in the molding density, and the molds 5 and 6 are different from each other only in the sintering temperature, and the porosity is determined by the molding density and the sintering temperature. . The free energy of wetting of porous alumina increases as the average pore diameter decreases, and does not show a constant value. It is considered that this depends on the shape of the pores and the state of the surface of the pores, but in any case, the free energy of wetting of the porous alumina is 8 to 14 times as large as that of gypsum. Therefore,
From the formula I, it can be said that, as compared with gypsum, the smaller the average pore diameter, the larger the osmotic pressure due to the wetting effect of the porous alumina.

[0009]

EXAMPLES Alumina cast molding tests were carried out on the seven types of porous bodies, types 1 to 7, shown in Table 1. Mold 4-6
Is the example of the present invention, and the others are comparative examples. For an alumina slurry prepared by adding 30 parts of water, 0.4 parts of a polycarboxylic acid ammonium salt as a dispersant, and 1.5 parts of an acrylic binder to 100 parts of alumina having an average particle diameter of 0.6 μm, a casting time t
The thickness L of the inking was measured, and the rate constant (L ² /
t) was calculated. FIG. 1 shows the relationship between the water penetration pressure ΔP and the inking rate constant. In FIG. 1, the inking rate constant of gypsum shows a value slightly larger than 20 μm of alumina,
As the average pore diameter of porous alumina decreased, the rate of inking rate increased, and 1.3 μm of alumina compared to gypsum.
Has a maximum value of about 12 times. This fact is that if porous ceramics, which is a material with high free energy of wetting against water and has an average pore size as small as possible, is used as a casting mold for ceramics, the molding speed is dramatically faster than that of a plaster mold. It teaches that

[0010]

INDUSTRIAL APPLICABILITY The present invention has the effect that the molding speed can be dramatically increased by controlling the porosity and the pore diameter of the molding die in the slurry casting molding method using the porous ceramics molding die. It plays.

[Brief description of drawings]

FIG. 1 shows the relationship between the osmotic pressure of molds 1 to 7 and the infiltration rate constant.

Claims (2)

[Claims] 1. A sintered body of a ceramic compound powder raw material compact having a particle size of 2.0 μm or less and containing 10% by weight or less of a glassy binder and having a pore size of 0.6.
A high-speed slurry casting molding method, which comprises using a mold having a porosity of not more than μ and a porosity of not less than 30% by volume. 2. The high-speed slurry casting method according to claim 1, wherein the ceramic compound is alumina.