JPH0324204A - Method for cast-forming powder body - Google Patents

Abstract

PURPOSE:To obtain a cast-formed body of powder in which strain and deformation are difficult-to-be-developed in the inner part thereof, by dispersing metal powder or ceramic powder into dispersion medium, casting the obtd. slurry into a porous mold, heating the slurry together with the mold, vaporizing or heat-decomposing the dispersion medium and removing this. CONSTITUTION:Mixed powder of 2% Ni and 98% Fe, metal powder of SUS316 powder, etc., or ceramic powder of Al2O3 powder, ZrO2 powder, etc., is dispersed in the dispersion medium of alcohol kind, ketone kind, etc., to make the slurry. In this case, particle diameter of the above powder is about 0.2 - 100mum and concn. of the powder in the slurry is desirable to be 45 - 85vol.%. Successively, this slurry is cast into the porous mold composed or porous sintered ceramic, etc., of alumina, etc. Then, this porous mold containing the slurry is charged into a heating device and heated to the necessary temp. to vaporization and heat decomposition of the dispersion medium to remove the dispersion medium. In this result, from the obtd. formed body a sintered body having extremely high dimensional accuracy is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of dispersing metal powder or ceramic powder in a liquid dispersion medium to form a slurry, and casting the slurry into a mold.

[Conventional technology]

Metal powder, ceramic powder, cera [casting method is a method for forming mixed powder of tsukusu and metal.

The present inventors previously disclosed in Japanese Patent Application Laid-Open No. 62-192502 that metal powders or ceramic powders can be extracted with liquid or supercritical carbon dioxide, and that the main material is a substance with a melting point of 0 to 100°C. A method for forming metal powder or ceramic powder is disclosed in which the powder is dispersed in a suitable dispersion medium to form a slurry, and the slurry is cast into a non-liquid-absorbing mold. In this method, the cast slurry is cooled and freeze-solidified to form a molded body, which is then demolded, and then the main portion of the dispersion medium in the molded body is extracted and removed using liquid or supercritical carbon dioxide. . The shaped body thus obtained is heated to remove the residual dispersion medium by thermal decomposition. Then, in the sintering process, the sintered body is densified to form a sintered body. An outline of the above process is shown in FIG.

Such sintered bodies are used as cutting tools, mechanical structural parts, etc. after being subjected to machining if necessary.

The present inventors have also proposed an improved method in which a slurry in which metal powder or ceramic powder is dispersed in a dispersion medium containing at least 10% by weight of a liquid extractable by a supercritical fluid or liquefied gas is placed in a porous mold. Casting, the slurry is kept in a porous mold at a temperature higher than the melting point of the dispersion medium, and at least 10% of the dispersion medium is extracted with a supercritical fluid or liquefied gas to give the object shape retention. We have also developed a method for imparting (Japanese Patent Application No. 1983-218300).

[Problem to be solved by the invention]

The conventional method of casting metal powder and ceramic powder has the following problems. That is, after the slurry is poured, it is cooled and solidified, but the solidification causes a volume change in the dispersion medium. For example, when paraffin wax is used as a dispersion medium, a volume shrinkage of about 25% occurs. Solidification begins at the part in contact with the mold, and as the solidified part contracts, distortion occurs inside the object. As a result, the object to be treated, which has been solidified and has achieved shape retention, is inevitably deformed to varying degrees. For this reason, it becomes difficult to form the mold, and the kai-form body may even be damaged due to difficulty in separating from the mold when removing the mold. The degree of deformation depends significantly on the temperature of the prepared slurry, the casting pressure, the temperature of the coolant in the mold, and the holding time. Therefore, it is necessary to find appropriate casting conditions, but this requires a long period of trial and error. In addition, internal strain during molding can be reduced by extraction with supercritical fluid or liquefied gas in the post-process, thermal decomposition,
It is released during sintering and deformation progresses. And when it comes to large irregularly shaped products that make the dimensional accuracy of the sintered body insufficient,
This problem becomes even more obvious.

[Means to solve the problem]

The present invention was made to solve this problem, and by casting a slurry in which metal powder or ceramic powder is dispersed in a dispersion medium into a porous mold, and heating the slurry while it is in the porous mold. This was achieved by discovering that by removing the dispersion medium by evaporation or thermal decomposition, it can be converted into a shape-retaining body.

The powder formed by the method of the present invention is 2%Ni-98%re.
Mixed powder, metal powder such as SUS316 powder, high speed steel powder, ceramic powder such as alumina powder, zirconia powder, silicon nitride powder, silicon carbide powder, tungsten carbide-cobalt mixed powder,
It is a mixed powder of metal such as titanium carbide-nickel mixed powder and ceramics. The particle size of these powders is 0.2-100n
That's about it.

The dispersion medium that disperses the metal or ceramic powder plays the role of imparting fluidity to the powder, but does not need to play the role of a binder for prescribing as in conventional methods. This is because, in the present invention, by heating and removing the dispersion medium, the fluidity of the slurry is lost and shape retention is produced, resulting in a shaped body.

There are many liquids suitable for this purpose, such as alcohols such as methyl alcohol, ethyl alcohol, probyl alcohol, and butyl alcohol, ketones such as acetone, hydrocarbons such as hexane and benzene, and liquid paraffin. Among these, those that can be made into a high vacuum state are preferable in that they can remove air mixed into the slurry by stirring or the like when shaping a slurry of metal powder or ceramic powder, such as liquid paraffin. can be suitably used.
It is also possible to use only such a liquid as a dispersion medium.

If proper fluidity cannot be obtained with a single agent, use a dispersant such as oleic acid, polyvinyl alcohol, polyvinyl butyral, methylcellulose, carboxymethylcellulose, ethylcellulose, paraffin wax,
Add a thickener such as phenolic resin to adjust fluidity.

It is preferable that the slurry has as high a concentration of metal powder or seradan ivy powder as possible within a range that can ensure the fluidity necessary for casting. The concentration is desirably 45% by volume or more and 85% by volume or less. If it is less than 45 volume%, it will be difficult to densify it during the sintering process, and if it exceeds 85 volume%, it will be difficult to obtain the fluidity necessary for casting even if the particle size distribution of the powder, dispersant, etc. are modified. be. A measure of proper fluidity is that the viscosity of the slurry is in the range of 50 to 104 voids.

The porous mold must have the strength to withstand the holding pressure during casting of the slurry and the permeability to allow the gas generated when the dispersion medium is heated and removed to move to the outside through the mold. Materials suitable for this purpose include gypsum, silica sand, alkaline powder, and sera-ivy powder, which is the same as the material to be treated.
For example, ethyl silicate hydrolyzate, polyvinyl alcohol, polyvinyl butyral, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, paraffin wax, phenol resin, epoxy resin, etc., with organic binders added, porous sintered ceramics such as alumina, stainless steel, etc. Examples include porous sintered metals, foamed organic materials such as foamed styrene, and foamed urethane.

An example of the structure of a porous mold is shown in FIG. This is a split type and can be used repeatedly.

A mold for a conventional method having this same cavity is shown in FIG. In this case, the mold needs to have a built-in refrigerant pipe 1 in order to cool the slurry. For efficient cooling, the mold needs to have as high a thermal conductivity as possible, and for this purpose it is necessary to use a metal such as aluminium. As a result, the use of expensive materials and complex structures are unavoidable.

Another example of a porous mold structure for the method of the invention is shown in FIG. This is a so-called shell mold. That is,
A pattern corresponding to the shape of the mold cavity is created using resin such as wax or urea resin, and the surface of this pattern is coated with ceramic powder using an organic binder to obtain a desired thickness, followed by steam treatment, thermal decomposition, and water washing. Remove internal wax, resin, etc. In this way, a porous shell mold is obtained. Although this mold is disposable each time, it has the advantage of being able to handle complex shapes. An organic binder that disappears through thermal decomposition is used in this shell mold, and the shell mold is heated with the object to be processed in it to thermally decompose and remove the organic binder along with the dispersion medium in the object. Reduce the strength of the mold to facilitate subsequent demolding, or
Alternatively, the demolding step can be omitted by causing self-disintegration.

For this purpose, polyvinyl alcohol, polyvinyl butyral, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, etc. can be used as an organic binder for the shell mold. In order to thermally decompose these binders, a temperature of 400'C to 1200'C is suitable.

A slurry made by mixing metal powder or ceramic powder with a dispersion medium and kneading it is cast into a porous mold.

The porous mold containing the slurry is placed in a heating device and heated to a temperature necessary for evaporation or thermal decomposition of the dispersion medium. At this time, the pressure can be reduced if necessary.

In the case of thermal decomposition, the heating temperature is preferably about 400 to 600°C. 1000-13 if necessary after removing the dispersion medium
By calcining to about 00°C, the shape-retaining strength of the precepts can be increased. Next, the object to be treated that has entered the porous mold is taken out and demolded to obtain a molded body. The process flow of the present invention is shown in FIG.

In the case of a disposable shell mold, the following steps may be used. That is, during the thermal decomposition process, the organic binder of the shell mold is removed by thermal decomposition together with the dispersion medium in the object to be treated, thereby reducing the strength of the shell mold or causing it to self-destruct. Next, a pre-shaped body is obtained through a demolding process.

The precept form is made into a dense sintered body through a sintering process.

[Effect]

In the powder casting method of the present invention, the fluidity of the slurry is lost by evaporating the dispersion medium by heating or removing it by thermal decomposition, instead of the conventional molding using the solidification phenomenon of the dispersion medium. It is molded using

〔Example〕

Example 1 A silicon nitride bolt was made. First, the average particle size is 0.75.
si, s492.0 heavy part of μ1 and 36.0 parts by weight of y2o with an average particle size of 0.54 as a sintering aid, an average particle size of 1.
20t! Add 27.6 parts by weight of liquid paraffin and 3.0 parts by weight of oleic acid to 2.0 parts by weight of Altos of m.
The mixture was kneaded for 4 hours.

The obtained slurry was exposed to a vacuum atmosphere to degas it.

On the other hand, a cavity-shaped shell mold corresponding to the bolt shown in FIGS. 5 and 6 was molded by adding 5 parts by weight of polyvinyl butyral as a binder to 100 parts by weight of the above silicon nitride powder. Add the above slurry to this shell mold for 22 hours.
℃, and a casting pressure of 3 Kg/cm. Although the casting pressure temporarily decreased by the start of casting, it remained at 3 Kg/cm.
After confirming that the slurry had recovered to c1, the mold was immediately removed with the slurry still being filled. Charge this into a degreasing furnace,
3°C for 1 hour to 500°C while flowing nitrogen gas
The temperature was increased at a rate of . After reaching 500°C, the temperature was maintained for 2 hours, then allowed to cool, and the pressure was returned to atmospheric pressure. As a result,
The mold is extremely brittle and can be easily removed.
A healthy precept form was obtained. Si,N. It was filled with packing powder of 50% by weight and Sing 50% by weight and charged into a sintering furnace, and the temperature was raised to 1200''C in vacuum and held for 30 minutes. Subsequently, nitrogen gas was introduced at a gas pressure of 9.5Kg/cm. The temperature was further raised to 1,800°C and held for 2 hours while circulating at a temperature of 1,800°C. Increase the gas pressure to 9. It was cooled to 1000°C while maintaining the pressure at 5Kg/cm'', and then returned to normal pressure and allowed to cool.

As a result, a sintered body with a theoretical density ratio of 98.1% was obtained. The shrinkage rate of each part A, B, C, and D of this bolt-shaped sintered body was measured. The results are shown in Table 1, and the variation is 0.
It was extremely small at 1%.

Table 1 Comparative Example 1 A silicon nitride bolt was made using a bolt mold having the same shape and dimensions as in Example 1. First, 27.6 parts by weight of paraffin having a melting point of 42°C and 3.0 parts by weight of oleic acid were added to 100 parts by weight of raw material powder having the same composition as in Example 1, and the mixture was kneaded at 90°C for 24 hours. The obtained slurry was exposed to a vacuum atmosphere to degas it. This slurry was heated to 90°C1
The slurry was poured into a mold through which cooling water at 10°C was passed at a casting pressure of 3 kg/cta, and after the casting pressure had recovered to 3 kg/cm2, the slurry was held for 5 minutes to complete solidification and then removed from the mold. The molded body is charged into the extraction device and weighs 200Kg.
/cs+" and 60°C supercritical carbon dioxide was passed through the mixture for 4 hours. The mixture of paraffin and oleic acid extracted during this period corresponded to 62% by weight of the dispersion medium in the shaped body.Subsequently, The material was charged into a pressure degreasing furnace. The atmosphere was nitrogen, and the temperature was raised at a rate of 100"C/Hr while circulating the gas at a gas pressure of 6kg/cn+". 500°C.
After reaching the temperature, the pressure was maintained for 1 hour, then allowed to cool, and the pressure was returned to atmospheric pressure. In this way, the dispersion medium could be completely removed by thermal decomposition. When sintering was carried out under the same conditions as in Example 1, a sintered body with a theoretical density ratio of 98.4% was obtained. The shrinkage rate of each part is shown in Table 1 above, and the variation is 0.6%.
It was clearly inferior to Example 1 in dimensional accuracy.

(Effects of the Invention) Although the method of the present invention takes more time than the conventional method, it does not cause phase transformation of the dispersion medium that normally accompanies a volume change as in the conventional method, so there is no strain inside the molded body. As a result, a sintered body with extremely high dimensional accuracy can be obtained.

In addition, in the conventional method, trial and error was required to find the appropriate cooling conditions for the mold, but in the method of the present invention,
This is completely unnecessary.

[Brief explanation of drawings]

FIG. 1 is a process flow diagram showing one embodiment of the method of the present invention. FIG. 2 is a sectional view of an example of a mold used in the method of the present invention, and FIG. 3 is a sectional view of an example of a mold used in the conventional method. FIG. 4 is a cross-sectional view of another example of a mold used in the method of the invention. FIG. 5 is a plan view of an example of a precept-shaped body, and FIG. 6 is a front view. FIG. 7 is a process flow diagram of a conventional method.

Claims (1)

[Claims] A slurry in which metal powder or ceramic powder is dispersed in a dispersion medium is cast into a porous mold, and the slurry is heated while in the porous mold to evaporate or thermally decompose the dispersion medium and remove it. Method for manufacturing a molded body of metal powder or ceramic powder