JPH0361502A - Molding of slip casting - Google Patents

Abstract

PURPOSE:To obtain a ceramic molding having thin and thick intricately shaped wall parts in a simple process under such control as to prevent generation of cracking by forming and drying a coating film on the thin wall part of a slip molding. CONSTITUTION:A coating is applied to the thin wall parts of a separated slip molding to form a coating film-covered molding. The thin wall part of the slip molding is covered with coating material such as rubber or resin solution by immersion, spraying or coating. Preferably, the thickness of the thin wall part to be coated is at most about 1/4 that of the thick wall part. Even if differences in thickness between the thin and thick wall parts are smaller than the aforesaid value, the coating film on the thin wall part is made possible by proportionally coating the thin wall part, thereby preventing the occurrence of cracking. As organic coating material for forming the coating film, resins such as polyacrylic acid, polyvinyl alcohol and polyvinyl butyrale, styrene- butadiene rubber, diene rubber, silicone rubber and urethane rubber are used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a slip casting method for injecting a slip into a mold to form a ceramic molded body having a complicated shape having thick and thin parts. .

[Prior art] In the slip casting molding method, a slip obtained by mixing fine ceramic powder, a sintering aid, a deflocculant, a binder, water, etc. is poured into a water-absorbing casting mold, and the mold is absorbed by water. Form an ink layer along the mold surface. This ink layer grows to form a slip molded body. After demolding, the slip molded body is sufficiently dried in a drying step, and then sintered.

This method is widely used because ceramic molded bodies with complicated shapes can be easily obtained.

[Problem to be solved by the invention] However, in the case of a ceramic molded body with a complicated shape in which thick and thin parts coexist, cracks are likely to occur at the boundary where the thickness of the ceramic molded body changes during the drying process. . This tendency is particularly noticeable when the difference in wall thickness is large. It is thought that the cause of this cracking is that the drying rate is different between the thick and thin parts of the ceramic molded body.

In other words, the drying speed is significantly different between the thick and thin parts, which causes a difference in drying shrinkage of the slip molded product, and it is thought that shrinkage stress is concentrated in the area where the wall thickness changes, causing cracks to occur in that area. .

In order to prevent the occurrence of cracks, methods such as drying at low temperatures for a long time and drying under pressure are used. However, these methods are undesirable because they reduce productivity and increase costs.

As a method for preventing cracks that occur during drying of a slip molded body, Japanese Patent Laid-Open No. 62-92805 discloses that a part of the mold is formed of a meltable organic material with a thermosetting resin film provided on the inner surface. A molded body is formed by injecting the slip into a mold whose other portion is made of a material that absorbs the slip medium. A method is disclosed in which the obtained semi-solidified molded body is demolded, dried while covered with a thermosetting resin film, and then the thermosetting resin film is removed. However, in this method, the part covered with the thermosetting resin film does not absorb water in the mold, so if the molded product has thick and thin parts, drying will not necessarily be uniform during the drying process. There is a problem that drying takes a long time and productivity deteriorates.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to prevent the occurrence of cracks during the drying process using a method as easy as possible.

[Means for Solving the Problem] The slip casting molding method of the present invention injects and solidifies a slip whose main components are ceramic fine powder and a liquid medium into a casting mold to form a slip having a thick wall portion and a thin wall portion. a molding process of forming a molded body; a coating process of demolding the slip molded body and coating the surface of the thin part with an organic film to form a coating film to obtain a coated molded body; and a coating process of forming a coated molded body by removing the liquid from the coated molded body. It consists of a drying step to remove most of the medium, a removal step to remove the coating film from the coated molded body after drying, and a sintering step to sinter the molded body from which the coating film has been removed. It is characterized by

In this molding process, Karitsune's slip casting molding method can be applied. For example, a slip is formed by mixing known ceramic fine powder, a deflocculant, and a medium such as water, and the slip is cast into a predetermined casting mold. In this casting mold, the slip absorbs the liquid medium and solidifies to form a slip molded body having a predetermined complex shape, which is removed from the mold and isolated.

In the coating step, a coating film is formed on the thin wall portion of the isolated slip molded body to obtain a coated molded body. This coating film is applied to the thin-walled portion of the slip molded body by dipping, spraying, coating, or the like with a solution containing dissolved rubber or resin.

At this time, it is preferable that the thin-walled portion covered is approximately 1/4 or less of the thick-walled portion. However, even if the difference in wall thickness is smaller than this, cracking can be prevented by covering the relatively thin wall portion.

As the organic film forming this coating film, resins such as polyacrylic acid, polyvinyl alcohol (PVA), and polyvinyl butyral, styrene-butadiene rubber, diene rubber, silicone rubber, urethane rubber, and the like can be used.

The coating film may be any film that can prevent the liquid medium from escaping directly from the surface of the coated molded body. Moreover, the size of the film thickness does not particularly matter. In particular, it is preferable that it be in close contact with the surface of the slip molded body.

In the drying step, the formed coated molded body is placed in, for example, a dryer and dried. Drying is carried out under normal conditions and does not require special conditions.

In the removal step, the coating film of the coated molded body that has been dried is removed. This removal may be carried out by thermal decomposition or incineration by heating, or by mechanical peeling. Furthermore, it can also be performed at the same time as the later sintering.

A conventional sintering method can be applied to the sintering process, and a ceramic molded body can be obtained.

Thin-walled areas covered with a coating film cannot be removed unless the liquid medium of the slip can directly emanate from the surface and migrate to the uncoated areas. Therefore, the drying of the thin-walled portion is delayed, and as a result, the difference in drying shrinkage in the molded product is reduced, and stress concentration is suppressed. This can prevent cracks from forming.

[Function] In the slip casting molding method of the present invention, the surface of the thinner portion of a slip molded body formed by solidifying a slip and having different wall thicknesses is coated with a coating film and dried. In this drying process, drying of thin-walled parts is suppressed,
Drying takes place in the thick section. The liquid medium in the thin wall portion is diffused according to the concentration gradient of the liquid medium, eliminating the difference in drying shrinkage of the molded article as a whole, thereby preventing the occurrence of cracks due to concentration of shrinkage stress.

[Example] This will be explained in detail below using Examples.

FIG. 1 shows a cross-sectional view of a rotor formed by slip casting, and FIG. 2 shows a front and back view of the rotor.

This rotor has a shape in which 12 thin (about 3 m) 11 parts 2 are joined to a hub part 1 (about 50 m1) with a large wall thickness at the center in a spiral shape.

A slip is formed by mixing silicon nitride fine powder with an average particle size of 0.9 μm, sintering aid Ittria powder, and alumina powder, and then adding water and a deflocculant (ammonium polyacrylate salt). The mixture was poured into the rotor casting mold described above to form a ceramic rotor slip molded body having the shape shown in FIGS. 1 and 2.

A thin wall portion of the demolded slip molded body, which corresponds to two parts of the rotor wing portion, was immersed in a toluene solution of polyacrylic acid resin (wL degree: 45%) to form a coating film 3. This coated molded body 4 is
Place it in the drying container 5 shown in the figure and fix it with the fall prevention stand 6 for 80 minutes.
It was kept at ℃ for 1 week.

Thereafter, the coating film 3 was thermally decomposed and removed at 450° C. for 2 hours. No defects such as cracks were observed at the joint between the blade portion 2 and the hub portion 1 of the obtained rotor.

As a comparison, a slip molded body formed using the same slip and the same casting mold as in the example was kept in the drying container 5 at 80° C. under the same drying conditions for one week without forming a coating film, and the wing part Cracks were observed at the joint between No. 2 and hub portion 1. Therefore, by forming the coating film 3 on the thin-walled portion of the slip molded body and drying it in this way, it is possible to prevent the occurrence of cracks.

The obtained molded body was sintered by a conventional method, but it was a good sintered body without any cracks or the like.

[Effects] According to the method of the present invention, a ceramic molded body with a complex shape in which thick and thin parts coexist can be produced by a simple process of forming a coating film on the thin walled part of the slip molded body and drying it. It can be easily obtained by suppressing the occurrence of cracks.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the rotor of the example, FIG. 2 is a front and rear view of FIG. 1, and FIG. 3 is a cross-sectional view showing a dry state in a drying container. 1... Hub part 2... Wing part 3... Coating film

Claims (1)

[Claims] (1) A molding process in which a slip mainly composed of fine ceramic powder and a liquid medium is injected and solidified into a casting mold to form a slip molded body having thick and thin parts, and the slip molded body is removed. A coating step of forming a mold and coating the surface of the thin-walled part with an organic film to form a coating film to form a coated molded product; a drying step of removing most of the liquid medium from the coated molded product; and a drying step of removing most of the liquid medium from the coated molded product, and after drying. A slip casting molding method comprising: a removing step of removing the coating film from the coated molded body; and a sintering step of sintering the molded body from which the coating film has been removed.