JPS60171272A - Manufacture of ceramic product - 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] [Technical field] The present invention relates to a method for manufacturing ceramic products.

[Prior Art 1] Conventionally, ceramic products have been manufactured by molding a mixture mainly consisting of ceramic powder and a bonded material into a predetermined shape by injection molding to form a molded body, followed by degreasing and sintering. However, in this case, during injection molding, the flow of the mixture tends to cause non-uniformity in the degree of filling of the mixture, non-uniformity in the orientation of the binder, etc. That is, internal defects are likely to occur in the molded product after injection molding.

If such internal defects occur, minute cracks, cracks, etc. may occur when the molded body is heated during the degreasing or sintering process.
Otherwise, distortion etc. are likely to occur.

Since the occurrence of internal defects in molded bodies poses a problem, improvements are being made in industry to reduce the number of internal defects as much as possible.

[Object of the Invention] The present invention has been devised in view of the above circumstances. The present invention reduces the internal defects of a molded body having internal defects obtained by injection molding or the like in a subsequent process, thereby preventing the occurrence of defects such as distortions and cracks during the degreasing or sintering process.1. The purpose is to obtain good ceramic products.

[Summary of the Invention] The method for manufacturing a ceramic product of the present invention includes a first step of forming a molded body from a mixture mainly composed of ceramic powder and a binder, and a step of forming a molded body from a mixture mainly composed of ceramic powder and a binder, and a step of forming a molded body by immersing the molded body in the powder and applying the binder to the molded body. a second step of preheating the compact until it softens; a third step of pressurizing the compact in the same direction while the compact is embedded in powder; and a third step of pressurizing the compact while it is embedded in powder; A fourth step of heating the compact to remove the binder, and a fifth step of heating and sintering the compact after removing the binder to form a ceramic sintered body. This is what happens.

In the first step, internal defects in the molded body are removed in the second and third steps.

(Detailed explanation of the structure of the invention) The first step +1 is a step of forming a molded body from a mixture mainly consisting of ceramic powder and a binder.This molding step can be performed using a conventional method. can.

Among them, injection molding is a typical method in which a mixture of ceramic powder and a binder is molded into a predetermined shape. Here, as the ceramic powder, silicon nitride (,5i3N
a), silicon carbide (SiC) is typical, and in some cases aluminum nitride (AIN), boron nitride (B
Ni'rides such as N), carbides such as titanium carbide (TiC>),
Titanium boride (Ti32), zirconium boride (ZrBz
), oxynitrides such as sialon, zirconia (
Oxides such as ZrOt), alumina (AI 203>), cordierite, barium titanate (BaTiOs), and titanium oxide (Tilt) can be used.

As the binder, it is desirable to use an organic material mainly consisting of a thermoplastic resin. In this case, it is preferable to add a sublimable substance. Thermoplastic resins include atactic polypropylene (APP), polyethylene (PE), polystyrene (PS), and ethylene-vinyl acetate copolymer (E
VA) etc. can be used. Sublimable substances include naphthalene, paraffin, anthracene, ulthrobin,
Aromatic compounds such as phenanthrene and ginger, oils such as mineral oil, dioctyl phthalate (DOP), diethyl phthalate (DEP), cyatul phthalate (DAP)
, a plasticizer such as dibutyl phthalate (DBP), etc. can be used.

The second step is a step of preheating the molded body while it is embedded in heat-resistant powder to a temperature at which the binder softens. This preheating causes the binder to move due to thermal motion and removes defects such as resin orientation. Furthermore, non-uniform density of the molded body can be reduced. In the second step,
It is preferable to place the molded body together with a heat-resistant powder in a bag, for example, a cotton bag, and heat it in that state. In this case, the heat-resistant powder plays the role of keeping the temperature of the compact in the third step due to its heat capacity, and the heat-resistant powder is not sintered or It means a powder that is heat resistant to the extent that it will not melt.

Therefore, typical heat-resistant powders are boron nitride powder and graphite powder, and other heat-resistant ceramic powders may also be used. The particle size of the heat-resistant powder is preferably about 5 to 50 microns.

This is because if the inside of the refrigerator is too fine, it will scatter and become difficult to handle, and if it is too coarse, the surface of the molded product will become rough. In particular, in the case of graphite powder, the thickness is preferably about 100 to 50μ. The preheating temperature in the second step is preferably higher than the softening temperature of the thermoplastic resin or the like constituting the binder. The temperature is usually about 100 to 180°C.

The third step is a step of isotropically pressing the molded object while it is embedded in heat-resistant powder.

In this case, it is preferable to use a container made of a flexible material that transmits pressure, such as heat-resistant plastic or heat-resistant rubber. For example, the bag may be placed in the container, and the container may be sealed and pressurized isotropically. Isodirectional pressurization can be achieved by submerging the container in a liquid and applying an even static pressure from the outer envelope with the liquid. Although water is generally used as the liquid, it is not limited to water, and in some cases, oil such as silicone oil can be used.

By performing isodirectional pressure in heat-resistant powder in this way, defects such as non-uniform density inside the molded body can be reduced, and it is possible to reduce defects such as non-uniformity of density inside the molded body. It is possible to make the density uniform, and it is also possible to apply uniform pressure even if the molded object has a complicated shape! It can be manufactured with high precision. A portion of the softened resin may be contained in a heat-resistant powder. When applying pressure, the pressure is 1000 to 300
0k (approximately 1/Cll12 is good.Also, when pressurizing, it is recommended to heat it to promote the elimination of defects inside the molded product, but the temperature depends on the resin added to the molded product,
A temperature of about 60°C is sufficient.

The fourth step is a step in which the molded body is heated while it is embedded in heat-resistant powder, thereby decomposing and removing the binder bonded to the molded body.

This process is usually called a degreasing process. The heating temperature is a temperature at which the binder is dissolved or thermally decomposed, and is usually up to about 500°C, and the heating rate is about 1 to 10°C per hour. Note that degreasing can also be performed by heating under vacuum.

If the binder is removed while the molded body is embedded in the heat-resistant powder as in the fourth step, the removed binder can be leached into the powder. The fifth step is a step of sintering the molded body after removing the binder to form a ceramic sintered body. In this step, a known method such as a normal sintering method or a reaction sintering method can be used. Heating can be performed while pressurizing the atmospheric gas. When sintering non-oxide ceramics, the atmosphere during sintering is preferably an inert gas or vacuum atmosphere to prevent oxidation reactions. Nitrogen gas, argon gas, etc. can be used as the inert gas.

Ceramic sintered bodies that can be formed by the method of manufacturing ceramic products of the present invention include automobile turbo rotors, screw heads, pistons, and the like.

[Effects of the Invention] According to the manufacturing method of the present invention, defects inside a molded product obtained by injection molding or the like can be reduced. Therefore,
It is possible to suppress the occurrence of distortions, cracks, etc. during degreasing or sintering processes.

This is presumed to be due to one or more of the following factors.

That is, in the second step, the molded body is preheated while it is embedded in the heat-resistant powder, so the binder moves due to thermal movement and non-uniformity in the orientation of the resin etc. is removed. Moreover, in the third step, since the molded body is isotropically pressed while being embedded in the heat-resistant powder, defects such as uneven density +1 of the molded body are reduced.

Therefore, in the present invention, the density of the molded body is made uniform, thereby suppressing the occurrence of distortions, cracks, etc. during the degreasing process and the sintering process.

Further, in the present invention, the binder in the molded body is removed while the molded body is embedded in powder. Therefore, the binder that has oozed out from the surface of the molded tile can be leached into the powder and absorbed. Therefore, the binder can be effectively removed and the density of the ceramic sintered body can be improved.

[Example] An example of the present invention will be described. In this example, 3i 3N4 powder with an average particle size of 1.2 μm was used as the ceramic powder. A mixture of Attack Deck polypropylene, polyethylene, naphthalene, and paraffin was used as a binder.

First, ceramic powder and a binder are mixed together in 18.
Blend at a ratio of 3% and 1% in a high temperature kneader.
After kneading at 60° C. for 3 hours, the mixture was kneaded again using a twin-screw high-temperature extruder. Next, using an injection molding machine, the
The mixture was injected into a mold under conditions of 0 k+1/cm2 to obtain a molded product. Then, the molded body was placed in a cotton bag together with boron nitride powder. The boron nitride powder has a particle size of 5 to 3
A 5 μm one was used.

Next, the molded body was buried in boron nitride powder for 140 minutes.
The molded body was preheated by heating to ℃.

Next, the cotton bag containing the molded body together with boron nitride was quickly placed into a silicone rubber container to prevent it from getting cold, and the container was sealed in that state. Then, in this state, the container was submerged in water, and pressure was applied in the same direction under water using hydrostatic pressure, thereby making the density of the molded product uniform. The pressure is 1500 k (+
/cm2.

Next, the molded body was taken out from the container and heated to 480°C for 1 hour in a nitrogen gas atmosphere with the powder attached to the surface of the molded body.
The binder was removed by heating for 0 days. In this case the binder could be sucked off with a powder. The temperature increase rate is 1 to b pressure depending on the temperature range.

Next, the molded body was heated at 1750° C. for 2 hours to obtain a ceramic sintered body.

The yield rate of conventional ceramic products was around 65% due to many internal defects. On the other hand, in this example, the internal defects of the molded body were reduced, so the improvement was achieved to 93%. or,
Tensile strength is also 16kCI/m1 to 21,5 kg/m
improved to at.

Patent applicant: Toyota Motor Corporation Agent: Patent Attorney Hiroshi Okawa Patent attorney Osamu Fujitani Same patent attorney Akio Maruyama

Claims (7)

[Claims] (1) A first step of forming a molded body from a mixture mainly consisting of ceramic powder □ and a binder, and forming the molded body into a heat-resistant powder until the temperature at which the binder softens. a second step of preheating the compact, a third step of pressurizing the compact in the same direction while the compact is embedded in the heat-resistant powder, and a third step of pressurizing the compact while the compact is embedded in the heat-resistant powder. A fourth step of heating the compact to decompose and remove the binder, and a fifth step of sintering the compact after removing the binder to form a ceramic sintered body. A method for manufacturing a ceramic product characterized by: (2) The method for manufacturing a ceramic product according to claim 1, wherein the heat-resistant powder is boron nitride powder or graphite powder. (3) The method for manufacturing a ceramic product according to claim 1, wherein the ceramic powder is silicon nitride or silicon carbide. (4) The method for manufacturing a ceramic product according to claim 1, wherein the first step is performed by injection molding. (5) The method for manufacturing a ceramic product according to claim 1, wherein the binder is an organic substance mainly composed of a thermoplastic resin. (6) The method for manufacturing a ceramic product according to claim 1, wherein the binder is an organic substance mainly consisting of atactic polypropylene, naphthalene, paraffin, and polyethylene. (7) Ceramic sintered bodies are used in automobile turbo rotors,
A method for manufacturing a ceramic product according to claim 1, which is used for a piston head and a piston.