JPH0450176A - Method for defatting ceramic molding - Google Patents

Abstract

PURPOSE:To reduce the deformation of a molding in a defatting process and efficiently perform the embedding and taking-out works of the molded product by employing hollow particles as an embedding material when the molded product is embedded in the embedding material to defat the molding. CONSTITUTION:A ceramic molding containing at least molding ceramic particles and an organic binder is embedded in a embedding material comprising a embedding ceramic and subsequently heated to defat the molding. In the defatting method, hollow ceramic particles not reacting with the embedding ceramic particles in the defatting process, such as alumina aluminasilica-balloon or shirus balloon are employed as the embedding ceramic particles. Because of its small bulk density and good flow ability, the embedding material minimizes the deformation of the molding during the defatting process and efficiently performs an embedding and taking-out works.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for degreasing a ceramic molded body, and particularly to a method for degreasing an injection ceramic molded body. INDUSTRIAL APPLICATION This invention is utilized for the manufacture of ceramic products, such as a turbine rotor.

[Conventional technology]

In recent years, the applications of ceramic materials have been rapidly expanding, including automobile parts, heat-resistant materials, electronic materials, and mechanical tools.
Along with this, product shapes are also becoming more complex. For this reason, injection molding has been adopted as a method for efficiently and accurately molding ceramic materials into complex-shaped molded bodies.

However, in this injection molding method, organic binders, plasticizers, which account for approximately 50% by volume (approximately 30% by weight),
A degreasing process is required to add a lubricant and the like for molding.

This degreasing is usually carried out for a long time (for example, for a wall thickness of about 10 mm, about 1
If a non-oxide ceramic material is used, the heating is performed in a non-oxidizing atmosphere such as nitrogen or argon to suppress oxidation.

Furthermore, in order to heat uniformly or to prevent sagging due to its own weight during degreasing, a method is known in which a ceramic molded body is embedded in an embedding material made of alumina powder and degreased (Japanese Unexamined Patent Application Publication No. 1983-1991). -100973 publication, etc.)
.

[Problem to be solved by the invention]

In the former method, a large temperature difference occurs between the surface layer and the inside, and the surface layer is rapidly degreased, causing cracks in the surface layer.

When the latter molded body is embedded in an embedding material and degreased, the deformation (sagging) of the thin walled part of the molded body is supported from below by the powder of the embedding material, so deformation is prevented;
Not enough. That is, for example, as shown in FIGS. 1 to 3, a rotor shape (T/
In the molded body 2 (C, G/T, etc.), the thin portion 21 often deforms due to the weight of the embedding material 3 in the temperature range where the binder softens. This is because (1) the weight of the embedding material itself is considerable, and (2) the embedding material is affected by the vibration of the furnace during degreasing and the surface tension of the binder seeped from the molded body 2 onto the embedding material 3. This is because 3 moves, the volume decreases, and the filling bulk density increases.

The present invention has been made in view of the above-mentioned points of view, and is capable of deforming a ceramic molded body after degreasing while maintaining degreasing performance.
The purpose of the present invention is to provide a degreasing method that can prevent cracks and chipping and is excellent in embedding and removing molded objects.

[Means to solve the problem]

The ceramic particles for embedding used in the degreasing method of the first invention are characterized in that they do not react with the ceramic particles for molded bodies during degreasing and are hollow.

The molding method for this molded body is not particularly limited as long as it requires degreasing afterwards, but injection molded bodies are preferred. This is because this injection molded product usually requires a large amount of organic binder and has a complex shape and thin wall portions.

The ceramic particles for embedding may be hollow bodies. That is, it has a lower density than a solid material, has a spherical outer shape, and has excellent fluidity. Although the particle size distribution of the particles is not particularly limited, it is preferable to have a somewhat wide distribution rather than to sharpen the distribution by classification. this is,
This is because when the binder in the molded article oozes out, the narrower the gap between the filler particles, the less movement of the particles during degreasing, which prevents the filling bulk density from increasing. This distribution is 10 to 400 μm, especially 50 to 200 μm, as shown in the second invention.
is preferred. This is because it is easy to handle and has good leaching efficiency. If the particle size is less than 10 μm, it will easily scatter as dust during work, and if it exceeds 400 μm, traces of particles will remain on the surface of the molded product.

Further, the smaller the filling bulk density is, the more preferable it is from the viewpoint of preventing sagging due to its own weight, but if it is too small, the strength of the hollow body will decrease, which is not preferable. Therefore, in terms of the balance between the two, as shown in the second invention, it is preferably about 0.3 to 0.6, particularly about 0.4 to 0.5.

[Effect]

Commonly used alumina sand (filling bulk density: 1)
Compared to the case where silicon nitride powder (filling bulk density: 1) is used, the bulk density of the hollow body is smaller, so when filling this around the molded body, the filling bulk density is 0.3 to 0.6. The degree becomes smaller. Therefore, when this hollow body is used as an embedding material, the weight of the molded body eliminates or reduces the sag of the molded body, especially the sag of the thin wall portion, during degreasing.

Furthermore, since the hollow body is spherical and has good fluidity, the work efficiency is improved in the work of embedding and taking out the molded body.

Furthermore, when degreasing a complex molded body with thin walled parts, such as a radial rotor, the green strength after degreasing is low. Therefore, when conventional alumina grain sand is used, its packed bulk density is high and its fluidity is low, so if it is forcibly pulled out during removal, the blades will break. However, when a hollow body is used as in the present invention, the bulk density is small and the fluidity is good, so even if the same work is performed, there will be no or very few chips in weak parts such as wing parts. .

Furthermore, in the present invention, since an embedding material made of a predetermined ceramic material is used, the ceramic molded body can be uniformly heated and the degreasing performance is also excellent.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

First, 100 parts by weight (hereinafter simply referred to as parts) of silicon nitride powder with an average particle size of 1 μm, 5 parts of alumina (1 μm in average particle size) as a sintering agent, and 1 part by weight of ittria (1 μm in average particle size).
μm) was added to prepare a silicon nitride mixture for sintering. To this mixture were added 5 parts of ethylene-vinyl acetate copolymer resin as an organic binder, 15 parts of microcrystalline wax, and 4 parts of diethyl phthalate as a plasticizer, and the mixture was heated and kneaded to prepare a ceramic raw material for injection molding.

Then, using a predetermined mold, the ceramic raw material was injection molded to form 100 radial turbine rotor molded bodies 2 having the shape shown in FIG. In this molded body, the maximum diameter of the wing portion after firing is 50 mm, and the thickness of the thinnest inner part after firing is about 1 mm.

As Example 1, as shown in FIG.
The pieces are embedded in the embedding material 3 filled in the degreasing sagger 1, and then the sagger 1 is vibrated to increase the filling bulk density. The filling bulk density in this case is shown in the table. In addition, as this embedding material, alumina-'y Rica balloon (Showa Denko (Showa Denko)
"Show Balloon SG" manufactured by Co., Ltd., filling bulk density 0.45,
(particle size 10 to 350 μm) was used. As the embedding material in Example 2, alumina-silica balloons were used which were classified to have a particle size of 8.0 to 100 μm. As the embedding material in Example 3, Shirasu balloons (manufactured by Shinsanko Shoji ■, "Sankilight") having a particle size distribution of 80 to 150 μm were used.

Next, each of the molded bodies was placed in a hot air circulating electric furnace at 100°C.
to 500°C at a rate of 5°C/hour under a nitrogen atmosphere to degrease. For each of these degreased bodies, occurrence of cracking, deformation (drooping of wings), and chipping when taken out were observed, and the results are shown in the table.

It should be noted that "no cracking" refers to a case where no cracking was found in both the magnifying glass inspection of the surface of the degreased body and the ultrasonic inspection of the inside of the degreased body. "A break occurs" refers to a case where a break is found in any of the above cases. The presence or absence of deformation was determined by a visual inspection of the blade shape.

As Comparative Example 1, the other 20 pieces were made of alumina powder as an embedding material (particle size: 100 to 200 μm, filling bulk density: 1.
03) It was buried inside and degreased in the same way. Furthermore, as Comparative Example 2, the other 20 pieces were degreased under the same conditions without using any embedding material.

According to the results, when alumina-silica balloons (Example 1) or Hashiras balloons (Example 3) with a predetermined particle size distribution are used as the embedding material, there is no possibility of cracking, deformation, or chipping. A high-quality degreased body was obtained. In addition, the alumina-silica balloon did not break even after degreasing, indicating that it has excellent strength, but the shirasu balloon was partially broken and its strength was somewhat low. Further, Example 2, which had a classified particle size distribution, also showed very good results, but compared to Example 1, there was a change in the bulk density of the embedding particles before and after degreasing.

From the above, it is preferable that the particle size of the embedding material shows a certain degree of distribution, and for example, a particle size of 10 to 400 μm shows excellent results. Moreover, when the filling bulk density is about 0.4 to 0.5, very excellent results are shown.

On the other hand, when alumina particles were used as the embedding material, deformation and chipping occurred. Furthermore, when no embedding material is used,
The degreasing performance was not excellent due to frequent occurrence of sharpness, and the occurrence of deformation was also large.

It should be noted that the present invention is not limited to those shown in the above-mentioned specific embodiments, and may be modified in various ways within the scope of the present invention depending on the purpose and use. That is, the hollow body may be made of a material other than those mentioned above, and the organic binder may also be of a type, amount added, etc. other than those mentioned above. In addition, organic plasticizers, lubricants, and other various additives can also be used. Furthermore, various degreasing conditions (degreasing temperature, degreasing rate, type of atmosphere, etc.) are selected depending on the materials used and the like.

〔Effect of the invention〕

In the degreasing method of the present invention, as shown in the above action,
Since a hollow body with good fluidity and a low filling bulk density is used as the embedding material, there is little (or no) deformation of the molded object due to the weight of the embedding material during degreasing, and there is also no chance of chipping when taking it out. In addition, the work efficiency is improved in the work of embedding and removing the molded body, and the molded body can be heated more uniformly, resulting in excellent degreasing performance.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the state in which the molded body is embedded in the embedding material in the example, Figure 2 is an explanatory diagram showing the state in which the weight of the embedding material is applied to the molded body, and Figure 3 is after degreasing. FIG. 2 is an explanatory diagram showing a state in which the wing portions of the molded article are hanging down. 1; Degreasing sagger, 2; Turbine rotor molded body, 21; Thin wall portion, 3; Embedded material. Patent applicant: NGK Spark Plug Co., Ltd. Representative: Kiyoji Kojima, patent attorney

Claims (3)

[Claims] (1) A ceramic molded body containing at least ceramic particles for a molded body and an organic binder is embedded in a embedding material made of ceramic particles for embedding, and heated to degrease the ceramic molded body. A method for degreasing a ceramic molded body, wherein the ceramic particles for embedding do not react with the ceramic particles for molded body during degreasing, and are hollow bodies. (2) The particle size distribution of the ceramic particles for embedding is 10 to
400 μm, and its filling bulk density is 0.3 to 0.
6. The method for degreasing a ceramic molded body according to claim 1. (3) The method for degreasing a ceramic molded body according to claim 1 or 2, wherein the ceramic molded body is an injection molded body.