JPS61106464A - Process for dewaxing ceramic injection molded body - 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 Field of Industrial Application This invention relates to a degreasing method for injection molding a kneaded product consisting of ceramic powder and an organic binder and removing the organic binder from the obtained injection molded product.

Conventional technology Various methods such as compression molding have been known as molding methods using ceramic powder as a raw material, but injection molding is effective when mass production and automation are desired. . This method is a molding technology derived from polymer molding technology, in which ceramic powder and an organic binder whose main component is a thermoplastic resin are kneaded.
This is a method in which the organic binder kneaded material is heated to give it fluidity and then injected into a predetermined mold, where it is cooled and solidified or hardened to form a molded product. This method not only automates the molding process and is suitable for mass production, but also allows complex-shaped parts to be molded easily. It also opens up ways to use materials.

By the way, since the above-mentioned injection molded article contains an organic component, it is necessary to remove the organic component before firing, and therefore, degreasing is performed after injection molding, and then firing is performed. Degreasing is an operation that decomposes and removes organic components contained in injection molded products by heating the injection molded product in a heating furnace to raise its temperature.It is an important process because the degreasing conditions have a large effect on quality. . In other words, the thermally decomposed organic components turn into gas and scatter from the ceramic molded body, but if the heating rate is too fast, the gas generated inside the molded body cannot escape completely, and the pressure causes internal cracks. Defects such as cracks, surface cracks, and even peeling occur. Therefore, conventionally, in order to gradually progress the thermal decomposition of the specific components from the surface to the inside of the molded article, it has been recommended to
Heating is performed at a fairly slow temperature increase rate of about 10° C./hr.

Problems to be Solved by the Invention If the temperature increase rate in the degreasing step is as slow as described above, the thermal decomposition of the organic component can be gradually progressed from the surface of the molded article to the inside. The time required to complete degreasing differs depending on the amount of organic components contained in the molded article, so thin parts are quickly degreased, whereas thick parts are difficult to degrease and take a long time. Therefore, when degreasing the entire complex-shaped injection molded article with thin and thick parts by heating it at a uniform temperature increase rate, even after the thin part has been completely degreased, the thick part will still be degreased. As degreasing continues, cracks may form at the interface between the thin wall and the thick interior. In order to resolve this inconvenience, it may be possible to delay the degreasing in thin-walled areas so that degreasing progresses evenly throughout the entire product, but it is extremely difficult to vary the heating rate for each part of a single product, and in reality Due to the difference in degreasing speed, cracks often occur in the boundary area between the thin wall part and the thick interior part. This tendency becomes more pronounced as the difference in wall thickness increases, and for example, when injection molding complex-shaped parts such as engine parts, the yield decreases.
In addition, problems such as loss of reliability regarding quality have arisen.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a degreasing method that can quickly degrease an injection molded article having a large difference in wall thickness without causing defects such as cracks. This is the purpose.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a method for degreasing an injection molded article having a complex shape having a thick inside and a thin wall part, by removing the material around the thin wall part. This method is characterized by filling a ceramic powder-organic binder kneaded material having the same composition as the kneaded material, and then heating and raising the temperature in a state in which the ceramic powder is further filled around the entire product.

In the method of the present invention, the thickness ratio between the thick part and the thin part is 10.
It is suitable to apply this method to injection molded articles of about 0 or less.

In addition, the ceramic powder-organic binder mixture to be filled around the thin-walled part is in the form of a powder (one flat particle size is 50 to 10
00μ) or pellet shape (aspect ratio 1-10)
Although any of these may be used, a powder state with an average particle size of 100 to 200 μm is particularly preferable. Further, the heating atmosphere may be in diluted air by reducing the pressure, in the air, or in an inert atmosphere, but an inert atmosphere is preferable. Furthermore, the ceramic powder in this invention includes silicon nitride (Si3N4), silicon carbide (SiC),
Zirconia (ZrO2), alumina (A1203)
, boron nitride (BN>, ittria (Y20s),
It may be one of magnesia (M2O) and spinel, or a mixture of several types thereof. These ceramic powders may be used in either powder or granule form, but preferably granule form. The resin used as the main component of the organic binder is preferably polyethylene, polystyrene, polypropylene, wax, paraffin and other thermoplastic resins.

Function: In the method of the present invention, the kneaded material filled around the thin-walled portion is also degreased, and furthermore, the decomposition of organic components gradually progresses from the entire surface including the kneaded material toward the inside. Therefore, in terms of degreasing in which organic components are thermally decomposed, filling the kneaded material around the thin walled portion is equivalent to making the thin walled portion thicker. That is, according to the method of the present invention, differences in degreasing speed due to differences in wall thickness are alleviated.

Examples Below, examples of the present invention will be described together with comparative examples.
As shown in FIG. 10 and FIG. 2, degreasing was performed using an injection molded body 3 having a shape in which a plurality of k openings 2 were provided on the outer periphery of a shaft 1. The injection molded article 3 was obtained by adding 5% n% of itria (Y2O2> and spinel each) to silicon nitride (Si3N4) powder, adding 21ffi% of thermoplastic iJ resin to the mixed powder, and uniformly mixing the mixture. The ceramic powder-organic binder kneaded product was molded by injecting and injecting it into a predetermined mold using normal injection molding.The diameter of the shaft 1 was 10 times the thickness of the shaft 2.

Between 112, which is the thin wall portion of the injection molded body 3, 11'! Ceramic powder-separate binder kneaded material 4 having the same composition as the sacrificial material was made into a powder with an average particle size of 200μ and filled as shown in the figure, and silicon nitride granules (average particle size 50μ) 5 were added around the whole as a degreasing agent. filled with. Note that these were stored in a stainless steel container 6 as shown in the figure. Next, put it in a normal heating furnace (oven) and fill it with N2.
Degreasing was carried out by heating from air temperature to 450° C. at a temperature increase rate of 10° C./hr while flowing gas at a rate of 10 1 /mo.

After cooling, the obtained degreased body was examined using a stereomicroscope and XS.
Although surface and internal defects were investigated by A.A., no defects were observed in any of the 10 degreased bodies.

In addition, the above degreased body was heated at 1750°C x 4 times in a N2 gas atmosphere.
After firing for several hours, a complete sintered body with no cracks could be obtained.

It's a thin part! ! Degreasing was carried out by changing the shape of the kneaded material filled between 12. That is, the kneaded material with the above-mentioned composition was made into a pellet shape with a diameter of 3 ms and a length of 5 irises, and this was
2, and degreasing was carried out under the same conditions as in the example process.

The 10 obtained degreased bodies were inspected for defects in the same manner as in the example, but no defects were found in any of them.

Supervision II The same injection molded product as that shown in Example (2) was used. Only silicon nitride granules were filled around the molded body, and degreasing was carried out under the same conditions as in Example (2).

Cracks were found at the bases of the blades in the ten degreased bodies obtained. This is thought to be because the stomach, which is a thin walled portion, is degreased earlier than the shaft, which is a thick walled portion, and as a result, stress is applied to the boundary area between the two.

In addition, degreasing was carried out by slowing the heating rate from 10°C/hr to 1°C/hr, but cracks were observed in 8 out of 10 degreased bodies, and the effect of slowing the heating rate was not expected. could not.

Comparative example ■ The charge between the doors! Degreasing was carried out in the same manner as in the example except that the powder was replaced with the powdered kneaded material having an average particle size of 200 μm as described above, and a powder containing only a synthetic resin was used.

When the boned 10al defatted bodies were investigated for defects, 8 fissures were found in 9 defatted bodies. This is considered to be because the resin was in an excessive state and became difficult to degrease. In addition, so-called rough skin occurred in the areas that had been in contact with the am powder, and this is thought to be due to excessive forum permeating into the degreased body during degreasing and having an adverse effect.

Effects of the Invention As is clear from the above explanation, according to the method of the present invention, the difference in degreasing speed caused by the difference in wall thickness can be alleviated. The molded body can be degreased without causing cracks, and as a result, the good product rate and yield in injection molding can be improved, and the reliability of the product after firing can be improved. Furthermore, in the method of this invention,
It is not necessary to control the temperature increase rate in a complicated manner, and it can even be made somewhat faster, so it is also possible to speed up the degreasing.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an injection molded body filled with a ceramic powder-organic binder kneaded material and ceramic powder, and FIG. 2 is a schematic vertical side view of the same. DESCRIPTION OF SYMBOLS 1... Shaft, 2... Tone, 3... Injection molded article, 4... Ceramic powder-organic binder kneaded material,
5...Silicon nitride n grains. Applicant Toyota Motor Corporation Representative Patent Attorney Yutaka 1) Hisashi Take (and 1 other person)

Claims (1)

[Claims] When injection molding is performed using a kneaded material consisting of ceramic powder and an organic binder as a raw material, and degreasing the obtained injection molded body having a thick wall part and a thin wall part by heating and raising the temperature, around the thin wall part, A method for degreasing a ceramic injection molded body, which comprises filling a ceramic powder-organic binder kneaded product having the same composition as the kneaded product, and further heating and raising the temperature in a state in which the entire periphery is filled with ceramic powder.