JPH08100204A - Production of sintered part - Google Patents

Abstract

PURPOSE: To easily produce high-density, large-sized sintered parts. CONSTITUTION: A fine sintering powder of metal or ceramic or mixture of both, etc., is formed into a water-soluble slurry with which a binder is blended. A mold, into which the water-soluble slurry is poured, is defoamed under vibration, and cooling is done with pressurizing by means of compressed air to form a frozen and solidified formed part. This frozen and solidified formed part is vacuum-dried and then subjected to binder removal and sintering. The amount of the binder to be blended with the sintering powder can be remarkably decreased as compared with that in the MIM process, and as a result, the time for binder removal can be shortened, and simultaneously, even large-sized parts can be easily produced as sintered parts without causing cracks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered part using a sinterable powder such as a single powder of metal or ceramic or a mixed powder of metal and ceramic, and particularly a complicated and large product. The present invention relates to a method for producing a ceramic by sintering.

[0002]

2. Description of the Related Art Conventionally, a sinterable powder such as a single powder of metal or ceramic or a mixed powder of metal and ceramic is used as a raw material powder, and this raw material powder is molded using a mold to form a powder compact first. Then, the powder compact is sintered in a sintering furnace to obtain a product, which is widely used to manufacture parts by a so-called powder sintering method.

[0003] The powder sintering method that has been widely used in the past is that the raw material powder filled in the mold is first compacted by using a press machine, and then compacted by this compaction molding. This is a so-called powder compacting method in which a powder compact is sintered in a heating furnace.

However, in the case of the powder compacting method, since the molding is performed by press molding in which the molding directions are two directions, the shape of the product that can be molded is restricted, and only an extremely simple part can be manufactured.

Further, in the powder compacting method, if the particle size of the powder is small, even if pressure is applied, it will be plastically deformed and the powders will not be pressed against each other. Particle size 1
Since only powder having a relatively coarse particle size of about 00 microns can be used, a product having a high density cannot be produced, and there is also a drawback in that powder having a fine particle size must be granulated and then molded.

For this reason, in recent years, a metal powder injection molding method, a so-called MIM method, has been developed as a technique for producing a sintered part that solves the above-mentioned drawbacks of the powder compacting method.

In the MIM method, a sinterable powder having a particle size of 10 μm or less and an appropriate amount of a thermoplastic binder such as a thermoplastic synthetic resin or wax is used as a raw material powder, and this raw material powder is subjected to an ordinary thermoplastic synthesis. This is a method for producing a sintered component, in which, like a resin, first, injection molding is performed, and then the injection molded body is heated to melt and decompose the binder to remove the binder, and then sintered to obtain a product.

According to this MIM method, since the raw material powder is molded by injection molding, products of any shape can be molded,
Therefore, even a product having a complicated shape can be easily manufactured by the sintering method.

Further, in the case of the MIM method, since an extremely fine sinterable powder having a particle size of 10 μm or less is used, the obtained sintered product has an extremely high density and excellent dimensional accuracy.

[0010]

However, the MIM method has a drawback that it is difficult to make a large-sized product as in the case of the powder compacting method, and the cost is very high in the case of high-mix low-volume production. .

That is, since the MIM method is pressure molding as in the case of the powder compacting method, a molding machine and a mold are required for molding, and when molding a large-sized product having a complicated shape. First, a large molding machine must be prepared, but this is difficult, and then a large and complicated mold is very expensive.

It goes without saying that molding using a large-sized molding machine and a mold in this way requires a very high molding cost, but further, if this is a high-mix low-volume production, the cost will be very high.

Next, in the case of the MIM method, a thermoplastic binder is blended in the raw material for molding as described above, but this blending amount is in a weight ratio with respect to 100 of the metal powder in order to smoothly perform the injection molding. It is extremely high at around 10 and the binder occupies 40 to 50% of the capacity of the molded product.

In the case of the MIM method, the thermoplastic binder, which is blended in such a large amount in the injection-molded product, must be completely removed before sintering, so that thermal expansion and thermal decomposition of the binder due to heating at high temperature will occur. This causes cracks in the sintered product.

For this reason, the injection-molded article must be so-called binder removed before sintering by heating for a long time at a low temperature to gradually melt or thermally decompose the binder to remove it.

However, when the product is large, the amount of binder that must be removed by the binder removal process is so large that it is difficult to completely remove the binder for any amount of time, which results in cracking of the product. Since the number of defective products increases and the yield is low, not only manufacturing takes a very long time, but also the cost becomes very high.

The present invention solves the above-mentioned drawbacks of the prior art, and provides a method for producing a sintered part which can be produced in a short time and at low cost even when producing a large number of large-sized products in small quantities. That is the purpose.

[0018]

That is, according to the present invention, a step of forming an aqueous slurry for sintering by mixing a sinterable powder such as metal or ceramic with water in which a water-soluble binder is dissolved, The process of injecting an aqueous slurry into the cavity, the process of evacuating the air mixed in the aqueous slurry in the cavity while applying vibration to the foam to defoam it, and cooling the defoamed mold while pressurizing the inside of the cavity with compressed air. The first claim comprises a step of freeze-solidifying and molding the slurry in the cavity, a step of drying the freeze-solidified article taken out of the mold, and a step of debinding the dried freeze-solidified article and then sintering. Furthermore, the method for producing a sintered component according to the second aspect is characterized in that the freeze-solidified molded article according to the first aspect is dried by vacuum drying.

[0019]

The present invention is constructed as described above. First, since the raw material for molding is an aqueous slurry, the molding is performed by so-called casting in which the slurry is poured into a mold. In this case, no pressure is applied during molding. Since there is no such mold, a simple mold such as a rubber mold, a resin mold containing metal powder, a non-ferrous metal casting mold, a gypsum mold, etc., which can be molded from a product master and can be made inexpensively in a short time, can be used.

Next, the slurry that has been injected into the simple mold is defoamed by vacuum exhaust to remove the mixed air, and is further cooled while being pressurized with compressed air to freeze the water and solidify into the product shape. At the same time as precisely replicating the shape of the cavity, a freeze-solidified molded product can be obtained in which air that could not be removed by vacuum evacuation is crushed and no bubbles are present.

Since the freeze-solidified molded product thus obtained is solidified by utilizing the effect of freezing of water, the shape can be sufficiently maintained even if the blending amount of the binder is small, and as a result, the blending of the binder is carried out. The amount is only required to maintain the shape when the water is removed by vacuum drying.

Therefore, since the amount of the binder to be blended can be made much smaller than that in the case of the MIM method, the binder can be completely removed in a relatively short time even if the product is large, and cracks hardly occur in the sintered product. Yield improves.

[0023]

EXAMPLES Next, the manufacturing process of the present invention will be explained based on the manufacturing process table of FIG.

First, the first step is the adjustment of the aqueous slurry.

The aqueous slurry is prepared by separately preparing the sinterable powder and the aqueous solution of the binder and thoroughly mixing them.

In this case, the sinterable powder includes various metal powders such as SUS, copper alloys, Ti alloys, W alloys, etc. having an average particle size of 30 μm or less, preferably about 10 μm or alumina,
Various ceramic powders such as zirconia and silicon nitride are appropriately selected according to the characteristics of the product to be manufactured and used alone or as a mixture.

The aqueous solution of the binder is CMC, starch, PVA,
It is formed by dissolving a natural or synthetic water-soluble polymer compound such as sodium alginate in water, or diluting a vinyl acetate-based or acrylic-based synthetic resin emulsion with water.

In this case, the concentration of the aqueous solution of the binder is such that the slurry has fluidity suitable for casting, and the shrinkage and density of the sintered product are appropriate, and at the same time, the amount of the binder is sinterable powder. The volume is adjusted to 20% or less, preferably 10% or less, but the solvent is not limited to water, but may be a mixed solvent with a hydrophilic solvent such as lower alcohol or cellosolve. .

A formulation example of the aqueous slurry satisfying the above conditions is as follows. Sinterable powder SUS powder having an average particle size of 10 microns 100 parts by weight Binder aqueous solution PVA 5% by weight aqueous solution 10 〃

Next, as a second step, an aqueous slurry as in the above-mentioned formulation example is injected into a mold. In this case, the mold used is a liquid mastering material obtained by casting by a casting method. A simple type with cavities is sufficient.

That is, when a liquid mastering material such as silicon rubber, epoxy resin containing metal powder, low melting point alloy, gypsum, etc. is poured into a mold in which the product master is provided and solidified, the product master is taken out. It is possible to form a simple mold having a shape as a cavity, and since the mold is not pressed by high pressure in the present invention, there is no problem even if such a simple mold is used.

Next, in the third step, a mold in which the aqueous slurry was injected into the cavity was placed in a closed box and vibrated while being vibrated.
The so-called defoaming is carried out for about 1 minute by evacuating at a vacuum degree of about 0 to 100 torr to remove air mixed in the aqueous slurry injected into the mold cavity.

Next, as the fourth step, the defoamed mold is put in a closed box as in the case of defoaming, and the inside of the cavity is pressurized with compressed air of a pressure of about 5 kg / cm ^{2 at} -30 ° C.
After about 10 minutes of cooling, the slurry in the cavity is freeze-solidified.

Since the cavity is pressed by the compressed air during the freeze-solidification molding, the slurry adheres well to the wall surface of the cavity, and at the same time, the air that could not be removed by the above-mentioned defoaming is also crushed and removed. It is possible to obtain a good molded product that faithfully reproduces the shape.

After the freeze-solidified molded product is obtained, as a fifth step, drying is performed to remove water from the freeze-solidified molded product, but water is rapidly removed without losing the shape of the freeze-solidified molded product. Then, vacuum drying is performed in a vacuum heating drying oven.

The vacuum drying conditions vary depending on the shape of the freeze-solidified molded product and the water content, but are, for example, 10 ^-1 t.
After drying at room temperature for 1 hour at a vacuum degree of orr, 100 ℃
And further dry for 1 hour.

The freeze-solidified molded product retains its shape by the binding force of the binder even if the water content is removed by vacuum drying. Finally, as the sixth step, the vacuum-dried molded product is placed in a vacuum drying furnace. According to the method, it is heated in a vacuum state to remove the binder and sinter.

The conditions of this binder removal and sintering differ depending on the type of sinterable powder and the compounding amount of the binder. For example, when the slurry shown in the compounding example is used, 10 ^-1 to
After removing the binder at a vacuum degree of rr at 300 ° C. for 1 hour, sintering at 1300 ° C. for 1.5 hours at a vacuum degree of 10 ⁻² torr and cooling in an inert gas atmosphere such as nitrogen and argon. A high-density sintered part having a density of 95% or more is obtained.

A specific method for carrying out the method for manufacturing a sintered part of the present invention, which is basically constructed as described above, will be described below with reference to the drawings.

FIG. 2 shows a freeze-solidification molding apparatus for carrying out the present invention. Reference numeral 1 denotes a closed box having a lid 2 having an open top surface and closing the opening. A vacuum exhaust pipe 3 connected to a vacuum pump and a compressed air supply pipe 4 connected to a compressor (not shown) are connected.

A vibrating device 5 is provided in the closed box 1. The vibrating device 5 supports the vibrating plate 6 by a spring 7 standing on the bottom surface of the closed box 1, and the vibrating plate 5 is provided on the back surface of the vibrating plate 6. A vibration generator 8 for vibrating the diaphragm 6 is attached and formed.

Further, on the vibration plate 6, a cooling frame 9 having an opened upper surface in which a cooling pipe 10 is embedded is placed.

In order to freeze-solidify and sinter the sinterable powder using the apparatus constructed as described above, first of all, the simple mold 11 such as a silicone rubber mold as described above is placed in the cooling frame 9. The lid 2 is placed in the closed box 1 with the lid 2 opened.

Next, a slurry injecting cylinder 14 is provided so that the slurry injecting cylinder 14 is aligned with the slurry injecting opening 13 connected to the cavity 12 on the upper surface of the simplified mold 11, and the aqueous slurry 16 is removed from the slurry injecting cylinder 14. 12
Inject into.

Slurry 1 for cavities 12 of simplified type 11
When the injection of 6 is completed, the slurry injection cylinder 14 is removed, the lid 2 of the closed box 1 is closed, the valve of the vacuum exhaust pipe 3 is first opened to make the inside of the box a vacuum degree of about 50 to 100 torr, and the vibration device 5 The vibration generator 8 is operated to evacuate the simplified mold 11 for about 1 minute to evacuate the aqueous slurry 16 injected into the cavity 12 of the mold 11.

When the defoaming is completed, as shown in FIG.
The operation of the vibration device 5 is stopped, the valve of the vacuum exhaust pipe 3 is closed, the valve of the compressed air supply pipe 4 is opened, and the pressure in the closed box 1 is 5k.
Pressurized with compressed air of about g / cm ² , and at the same time, a coolant such as liquid nitrogen is caused to flow through the cooling pipe 10 embedded in the cooling frame 9 to cool the simplified mold 11 at around -30 ° C for about 10 minutes. Aqueous slurry 1 injected into 11 cavities 12
6 is freeze-solidified and molded to obtain a freeze-solidified molded product 17.

As described above, the freeze-solidification molding apparatus is used to freeze-solidify the aqueous slurry 16 for freeze-solidification molding 1.
7 is obtained, the closed box 1 of the freeze-solidification molding apparatus stops the supply of compressed air to return to atmospheric pressure, and at the same time stops the supply of refrigerant to the cooling pipe 10 to stop the cooling of the mold and open the lid 2. Then, the simplified mold 11 is taken out of the cooling frame 9.

When the simple mold 11 is taken out of the closed box 1, the simple mold 11 is opened, the freeze-solidified molded product 17 is demolded, and the next vacuum drying is performed.

First, by using the freeze-solidifying apparatus as described above, the aqueous slurry 16 can be freeze-molded very easily, and then by using a silicone rubber mold as a simple mold, even if the shape of the freeze-molded article 17 is complicated. It is convenient that the die can be easily demolded without damaging the molded product.

The freeze-solidified molded product 17 released from the simple mold 11 is then placed in a vacuum drying furnace, and vacuum drying of water, binder removal, sintering and cooling are continuously performed.

The conditions for controlling the atmosphere and temperature of the vacuum drying furnace in this case are as shown in the vacuum drying furnace control state diagram of FIG. 4. First, the vacuum degree of the vacuum drying furnace is set to 10 ⁻¹ torr and the temperature is kept at room temperature for 1 hour. Then, the temperature is raised to 100 ° C. and vacuum-dried for 1 hour to remove water in the freeze-solidified molded product 17.

Subsequently, the vacuum drying furnace is set to a vacuum degree of 10 ^-1 torr.
The temperature is raised to 300 ° C. with the temperature kept at r, the binder is removed for 1 hour, and the binder in the freeze-solidified molded product 17 from which water has been removed is melted and thermally decomposed and removed.

If the water content of the freeze-solidified molded product 17 is first removed by vacuum drying and then the binder is removed by debinding, the vacuum degree of the vacuum drying furnace is set to 10 ^-2.
Raised to torr, the temperature is also the sintering temperature of stainless steel 1
The temperature is raised to 300 ° C. and heated for 1.5 hours for sintering.

When the sintering is completed, the vacuum degree of the vacuum drying furnace is kept at 10 ^-2 torr, the heating is stopped and the sintered parts are cooled, and if the temperature inside the furnace is lowered to about 500 ° C,
For example, an inert gas such as nitrogen gas is introduced to further cool the sintered part to room temperature under an inert gas atmosphere.

[0055]

The present invention has the constitution and operation as described above, and of course, an existing decompression box or freezer may be used, but a simple freeze-solidification molding apparatus combining these functions into one is provided. If used, a freeze-solidified molded product of a sinterable powder can be obtained more easily by using an aqueous slurry and a simple mold.

When a freeze-solidified molded product is obtained, it is put in a vacuum drying furnace, vacuum-dried to remove water, and then subjected to binder removal and sintering according to a conventional method to obtain a large sintered part. Can be easily manufactured.

Furthermore, since the freeze-solidified molded product contains only about 10% by volume of the binder with respect to the sinterable powder, the binder is contained in an amount of 50% or more. Binder removal can be done in a much shorter time of about 1 hour compared to the MIM method.

Further, in the conventional MIM method, a large amount of binder is removed after thermal expansion during binder removal and a large volume change occurs, so that defects due to cracking of sintered parts are likely to occur, and this tendency is particularly strong in large parts. According to the present invention, since the binder content is extremely small as described above, such a defect hardly occurs even in a large-sized component.

Further, as in the case of the MIM method, a very fine sinterable powder having a particle size of about 10 microns or less can be used, so that a sintered part having a smooth surface and a high density can be manufactured.

[Brief description of drawings]

FIG. 1 is a manufacturing process chart,

FIG. 2 Freeze-solidification molding device (state of pouring slurry into mold),

FIG. 3 Freeze-solidification molding device (freeze-solidification molding state),

FIG. 4 is a vacuum drying furnace control state diagram.

[Brief description of reference numerals]

 1 Closed Box 3 Exhaust Pipe 4 Compressed Air Supply Pipe 5 Vibration Device 6 Vibration Plate 9 Cooling Frame 10 Cooling Pipe 11 Simple Type 14 Cylinder for Slurry Injection 16 Aqueous Slurry 17 Freeze-solidified Molded Product

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C04B 35/64 C04B 35/64 Z

Claims (2)

[Claims] 1. A step of mixing a sinterable powder such as metal or ceramic with water in which a water-soluble binder is dissolved to form an aqueous slurry for sintering, a step of injecting the aqueous slurry into a cavity of a molding die, A process of degassing by vacuum exhausting the air mixed in the aqueous slurry in the cavity while giving vibration to the mold, cooling the mold after defoaming while pressing the inside of the cavity with compressed air to freeze-solidify the slurry in the cavity Process,
A method of manufacturing a sintered part, comprising: a step of drying a freeze-solidified molded product taken out of a mold; and a step of debindering the dried freeze-solidified molded product and then sintering. 2. The method for producing a sintered part according to claim 1, wherein the freeze-solidified molded product is dried by vacuum drying.