JPH0536205B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for manufacturing complex-shaped parts such as turbine wheels and stators for gas turbine engines using ceramic powder as a raw material.

Conventional technology Ceramic parts are basically manufactured by molding raw material ceramic powder into a desired shape and sintering it under pressure and heat, but recently, injection molding has been used as a molding method. It has become possible to manufacture ceramic parts with complex shapes by applying methods such as the slip casting method and the slip casting method, and by applying the hydrostatic pressing method as the pressurizing method. In other words, according to the injection molding method and the slip casting method, since the material is given fluidity and then injected into the mold, it is possible to obtain a molded product with a fairly complex shape, and the hydrostatic pressing method is an isostatic method. Since the pressurization is applied, there are no particular restrictions on the shape of the pressurized body, and the pressurization can be uniformly applied, thereby making the internal density of the molded body uniform. Therefore, by applying these molding methods and pressurizing methods, it has become possible to make parts with complex shapes, such as turbine wheels and stators for gas turbine engines, from ceramic.

By the way, a method called rubber press is known as a hydrostatic pressing method that is carried out at a cold temperature of about room temperature, and this is a method in which the object to be processed, such as ceramic powder, is placed in a rubber bag and subjected to hydrostatic pressing. . However, in such a method, the shape of the pressurized body is restricted to a relatively simple shape, so it is not suitable when the above-mentioned complex-shaped molded body is to be targeted. Conventionally, in order to solve this problem, instead of using a rubber bag to prevent penetration of the pressurizing body, a coating made of rubber or plastic was formed on the surface of the molded body, and hydrostatic pressure was applied in that state. is being developed. Since such a coating can be easily formed by immersing a ceramic molded body in a raw material solution for the coating, there are no particular restrictions on the shape of the molded body.

Therefore, the hydrostatic pressing method, which is carried out by forming the above-mentioned film, is particularly effective for ceramic molded bodies with complex shapes, but on the other hand, it is difficult to remove the film by mechanical means. Therefore, conventionally, the coating is removed by heating the molded body in air after isostatic pressure application.

Problems to be Solved by the Invention However, the coating is generally formed of an organic material, and therefore, if it is heated in air, it will harden and change in quality due to an oxidation reaction, causing extreme damage. If it ignites and burns. As a result, dimensional changes occur in the coating, which may cause peeling on the surface of the ceramic molded body. In complex-shaped parts that are difficult to machine, such as turbine wheels, defects caused by surface peeling cannot be corrected. However, defects caused by film removal result in defective products.
The hydrostatic pressurization method, which is performed by forming a film on the entire surface of the molded object, is effective in applying pressure uniformly to objects with complex shapes. It could not be applied to the production of ceramic parts.

In view of the above-mentioned circumstances, it is an object of the present invention to provide a method capable of obtaining complex-shaped ceramic parts with uniform density and without defects such as surface peeling or cracking.

Means for Solving the Problems In order to achieve the above object, the present invention applies a coating made of styrene-butadiene rubber or polyacrylic acid resin, which decomposes and disappears without producing a residue when heated, to a ceramic molded body. The film is formed on the entire surface, and then the molded body is subjected to isostatic pressure, and after the pressurization is completed, the molded body is heated in a non-oxidizing atmosphere to decompose and disappear, and then sintered. This method is characterized by the following.

The method of _the present invention is suitable for manufacturing complex-shaped parts such as turbine wheels and stators _for gas turbine engines. (SiC), aluminum nitride (AlN), or sialon. In addition, injection molding method or slip casting method can be used to obtain the molded product. Therefore, the ceramic molded product in this invention is a degreased product after the organic binder is flowed out and scattered. In the case of the slip casting method, it is a dried product after removing the dispersion medium.
Furthermore, styrene butadiene rubber (SBR) or polyacrylic acid resin is used as the material for the coating in this invention, and this is decomposed and eliminated by heating in a non-oxidizing atmosphere.

Example Examples of the present invention will be described below together with comparative examples.

Example 1 First, a target ceramic molded body was created as follows. A mixture consisting of 90wt% silicon nitride powder, 5wt% Ittria powder, and 6wt% alumina powder and a thermoplastic resin as a binder are uniformly kneaded and injected into the cavity of a predetermined mold, resulting in injection molding. The body was heated from room temperature to 480°C at a heating rate of 6°C/H to degrease it, and a ceramic molded body similar in shape to a turbine wheel for a turbocharger was produced.

A coating that prevents the penetration of a pressurizing medium during hydrostatic pressurization was formed on the entire surface of the molded product by immersing the molded product twice in a styrene-butadiene rubber (SBR) liquid. The film thickness is preferably 0.2 to 0.4 mm; if it is thinner than this, breakage may occur at the corners, and if it is too thick, There is a risk that the tip of the blade in the molded body may break due to the expansion and contraction movement of the coating itself.

The hydrostatic pressurization was carried out by immersing the ceramic molded body on which the coating had been formed into water as a pressurizing medium and pressurizing it to 1400 Kg/cm ² .

To remove the film, place the molded body in a firing furnace after completing the pressurization, introduce nitrogen gas to create a non-oxidizing atmosphere, and heat the film from room temperature to 600°C in that state. This was done by decomposing it.

After the above operation, the gas generated by the decomposition of the film is exhausted to the outside of the furnace, and then nitrogen gas is introduced into the firing furnace again and sintered at 1750°C, 10 atm N ₂ and held for 2 hours. I did this.

When the obtained ceramic sintered body was examined, no defects such as surface peeling or internal/external cracks were observed.

Example 2 The production of a ceramic molded body, the formation of a coating, and the hydrostatic pressing were carried out in the same manner as in Example 1.

The coating was removed by placing the compact in a firing furnace, heating it from room temperature to 600°C, and thermally decomposing it in a vacuum while exhausting the inside of the furnace and reducing the pressure.

Further, the molded body was fired at 600°C or higher in the same manner as in Example 1.

No defects such as surface peeling or internal/external cracks were observed in the obtained ceramic sintered body.

Comparative Example 1 A ceramic molded body produced by the same method as described in Example 1 was fired under the same firing conditions as in Example 1 without applying hydrostatic pressure.

All of the obtained sintered bodies (60 pieces) had cracks. This is thought to be because the density of the ceramic molded body is non-uniform because it has not been subjected to a pressurizing process.

Example 3 A ceramic molded body having a shape similar to that of a stator for a gas turbine engine was produced by slip casting using a powder mixture consisting of 98 wt% silicon carbide, 1 wt% boron, and 1 wt% carbon as a raw material.

Formation of a film on the molded body and hydrostatic pressing were performed in the same manner as in Example 1.

The film was removed by placing the molded body in a firing furnace, introducing argon gas into the furnace, and heating it from room temperature to 600°C.

After the film is removed, the gas generated by the thermal decomposition of the film is exhausted out of the furnace using a rotary pump, and then argon gas (1 atm) is reintroduced into the furnace, heated to 200℃, and fired. I did it.

As a result, it was possible to obtain a stator for a gas turbine engine free of defects such as surface peeling and cracks.

Comparative Example 2 A ceramic molded body produced by the same method as described in Example 3 was fired under the same conditions as in Example 3 without applying hydrostatic pressure.

Cracks had occurred at the boundary between the blade portion and the ring portion of the obtained stator. This is thought to be because the density of the ceramic molded body is non-uniform because it has not been subjected to a pressurizing process.

Example 4 A sintered body was produced using the same method and conditions as in Example 3, except that the film was formed of polyacrylic acid resin.

In the obtained sintered body, as in the above example,
No defects such as surface peeling or internal or external cracks were observed. This is because polyacrylic acid resin, like styrene-butadiene rubber, decomposes and disappears without leaving any residue when heated in a non-oxidizing atmosphere, and is made to have a uniform density by applying hydrostatic pressure. This is thought to be due to this.

Comparative Example 3 A sintered body was produced in the same manner as in Example 3 except that a coating was formed from silicone rubber and the other conditions and methods were the same as in Example 3.

Silica generated by thermal decomposition of the film remained and adhered to the surface of the obtained sintered body. Removal of the silica was extremely difficult due to the complicated shape of the sintered body.

Effects of the Invention As is clear from the above explanation, according to the method of the present invention, by applying isostatic pressure to a ceramic molded body and heating a coating for preventing penetration of pressurized medium, no residue is generated. In order to perform the following operations, the film is made of styrene-butadiene rubber or polyacrylic acid resin, which decomposes and disappears, and heating is performed in a non-oxidizing atmosphere to remove the film.
The ceramic powder on the surface layer of the molded product does not peel off when the coating is removed, and the internal density of the molded product is made uniform by hydrostatic pressure, resulting in a complex shape with no defects such as surface peeling or internal cracks. Ceramic parts can be obtained. Further, in this invention, since the coating is formed of styrene-butadiene rubber or polyacrylic acid resin, this coating decomposes and disappears without producing a residue by heating in a non-oxidizing atmosphere. According to this method, after the film removal process, the molded body can be transferred to the sintering process without taking it out from the furnace, and workability is improved.

Claims (1)

[Claims] 1 Styrene-butadiene rubber or polyacrylic acid that decomposes and disappears without producing a residue when heated when producing complex-shaped ceramic parts by pressurizing and sintering a complex-shaped ceramic powder compact similar to the final product shape. A coating made of resin is formed on the entire surface of the molded body, and then the molded body is subjected to isostatic pressure, and after the pressurization is completed, the molded body is heated in a non-oxidizing atmosphere to remove the coating. A method for manufacturing complex-shaped ceramic parts, characterized by decomposition and disappearance, followed by sintering.