JPH05195009A - Production of kneaded body for powder molding - Google Patents

Abstract

PURPOSE:To produce a uniform kneaded body for powder molding free from air and moisture by heating and kneading metal or ceramic powder and an org. binder in a vacuum while applying a specified pressure. CONSTITUTION:Metal powder and/or ceramic powder and an org. binder are heated and kneaded in a vacuum while applying >=4.0kgf/cm<2> pressure About 5-15wt.% thermoplastic resin is suitable for use as the org. binder. The vacuum is preferably a reduced pressure of about <=50Torr but a high vacuum of about 5X10<-3>Torr is used if necessary so as to perfectly remove air and moisture. The kneading temp. depends on the org. binder and is usually regulated to about 110-180 deg.C. The wettability of the powder with the binder is improved, high disper-sibility is ensured and a kneaded body free from mixed air and absorbed moisture is obtd. A molded body of this kneaded body hardly contains bubbles and moisture, does not cause swelling, cracking, etc., at the time of removing the binder and can give a high density and high quality sintered product.

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 kneaded material for powder molding. More specifically, the present invention has a high density and a high quality which are useful in a method of forming a kneaded product of a metal powder and / or a ceramic powder and an organic binder, debinding and sintering to produce a required sintered product. The present invention relates to a new method for producing a kneaded material for powder molding, which enables production of a sintered product.

[0002]

2. Description of the Related Art In recent years, a powder molding / sintering method has been attracting attention, which is capable of producing a molded and sintered product with high productivity with high accuracy even for a product having a three-dimensional complex shape. Metal powder injection molding method (Metal Inj.) In which powder, etc. are mixed with an organic binder, kneaded, injection molded, and then sintered.
Section Molding Process (MIM) is expected to innovate future molding technology.

Such a metal powder injection molding method (MIM)
In the past, conventionally, powder of metal or alloy was mixed with a thermoplastic organic binder and kneaded in the atmosphere,
The kneaded material thus obtained is injection molded. However, in the case of such a conventional method, after the above kneaded product is injection molded, this molded product is debindered and then sintered. Fatal defects such as blisters and cracks are likely to occur, and the dimensional changes have to be large.

Such a drawback is that moisture in the air inhibits the adsorption of the organic binder on the metal powder, and it is difficult to uniformly disperse the metal powder and the organic binder during kneading. This is due to moisture absorption and the mixture of air. Therefore, attempts have been made to achieve uniform dispersion during kneading and to slow the heating / heating rate during debinding. However, even with such processing, the above-mentioned drawbacks cannot be eliminated.

Further, as a conventional method, it has been attempted to knead in a vacuum condition instead of in the atmosphere, but in the methods hitherto, since the method is under vacuum, the pressure kneading is hardly performed. Therefore, the metal powder and the organic binder could not be uniformly kneaded, and the dispersibility thereof was not sufficient. For this reason, it was difficult to ensure quality uniformity.
This invention has been made in view of the above circumstances, eliminates the drawbacks of the conventional method, improves the dispersibility of the metal powder and the organic binder, defects such as blisters and cracks at the time of debinding It is an object of the present invention to provide a new method that suppresses the occurrence of slag and enables the production of high-density and high-quality molded and sintered products.

[0006]

In order to solve the above problems, the present invention provides a metal powder and / or a ceramic in the production of a kneaded product for powder molding, which comprises a metal powder and / or a ceramic powder and an organic binder. 4.0 kg of powder and organic binder in vacuum
Provided is a method for producing a kneaded product for powder molding, which comprises heating and kneading while pressurizing to f / cm ² or more.

The present invention also provides a method for producing a powder-sintered product, characterized in that the kneaded product produced by the above method is powder-molded, debindered and then sintered.

[0008]

In the method of the present invention, unlike the conventional method, since heating and pressurization are performed in a vacuum rather than in the air, water molecules on the surface of the metal powder or ceramic powder are removed, and Dispersion with the organic binder is made uniform, resulting in a better condition. Further, since the vacuum condition is used, it is possible to suppress the mixing of air into the kneaded product and the absorption of moisture in the air, and it is possible to suppress defects such as blisters and cracks during debinding.

In addition, the disadvantage of the conventional debinding process which takes a long time can be solved. Therefore, a high-density product can be obtained by the sintering performed after the debinding process.
In particular, the excellent effect of the present invention is that Ni-T
It is effective in kneading active metals such as i, Ti, Ti-Al, Fe-Al, and Fe-Cu or alloys thereof. Even in the case of such an active metal or its alloy, it is possible to prevent the agglomeration of the powder, and to ensure the uniform dispersion by improving the wettability and the suppression of the defect generation due to the reduction of the residual pores.

In order to realize such an action, in the present invention, powders of various metals and alloys, for example, powders having a particle size of about 2 to 25 μm are mixed with an organic binder and, as described above, under vacuum conditions. 4.0 kgf / cm ²
The mixture is heated and kneaded while applying pressure. First, at the time of mixing, as an organic binder, a binder made of a thermoplastic resin can be mixed in an amount of about 5 to 15% by weight. Polyolefins, polystyrenes, ethylene / vinyl acetate copolymers, polyacrylics, waxes, DBPs, DOs
P and others are used.

Commercially available products are also used as these binders. Then, in the present invention, the mixture of the metal powder and the organic binder is kneaded under pressure / heat under a vacuum condition. Regarding the vacuum condition, the pressure is evacuated by a rotary pump or the like, the pressure is reduced to 50 Torr or less, and this condition is secured during kneading. When it is necessary to further increase the degree of vacuum, the degree of vacuum can be further increased by using a vacuum pumping device such as a mechanical booster in addition to the rotary pump. For example, by setting a high vacuum of about 5 × 10 ⁻³ Torr, the kneading can be extremely effectively performed even with highly active metal or alloy powder.

The kneading under vacuum is usually carried out by heating to about 110 to 180 ° C. and applying a pressure of 4 kgf / cm ² or more. Four
If it is less than kgf / cm ^{2, the} dispersion due to kneading will inevitably be non-uniform, resulting in a high-quality kneaded product, and molding /
The manufacture of sintered products becomes difficult. In any case, vacuum conditions and heating and pressurization of 4 kgf / cm ² or more are essential to the present invention.

The apparatus used for kneading is not particularly limited, but since heating / pressurizing kneading itself under vacuum has not been considered in the past, it is desirable to devise its implementation. Therefore, for example, 4 kgf /
In order to enable the pressurization of not less than cm ^2, it is preferable to employ a forced pressurizing means such as a biaxial blade method in order to bring the kneading into a pressurizing state while maintaining the atmosphere in the tank at a vacuum.

By the heating and pressure kneading under the above vacuum,
The wettability between the metal powder and the binder is improved, and high dispersibility and reduction of residual pores are realized. The obtained kneaded product is molded by injection molding, extrusion molding or the like, and is sintered after debinding. For example, injection molding can be performed as follows. (1) Molding For example, in injection molding, a temperature of 110 to 200 ° C.
Conditions of a pressure of about 300 to 1500 kgf / cm ² can be adopted. (2) Degreasing The molded body is degreased.

For example, room temperature to 450 ° C., average heating rate 5
~ 30 ° C / hr, pressure 500-800 Torr, and
Use of nitrogen, argon, etc. as carrier gas
It is exemplified as a condition for. Also, even in the atmosphere
Yes. (3) Sintering Sintering is preferably performed in a vacuum atmosphere, for example,
1100 to 1450 ° C temperature, average heating rate 80 to 13
0 ° C / hr, pressure 1.0 x 10^-Four~ 1.0 x 10 ^-NTor
It can be carried out under conditions of about r.

The present invention will be described in more detail below with reference to examples.

[0017]

Examples 1 to 3 Stellite powder having an average particle size of 13 μm was used in a weight ratio of 62% polybutene-based thermoplastic resin and 35 olefin wax.
%, Plasticizer DOP 3%. The amount of binder added at this time is 6.0% by weight.
And

This is 1 at a vacuum degree of 20 Torr.
The mixture was heated to a temperature of 35 ° C. and kneaded under pressure at 4 to 9 kgf / cm ² . The resulting kneaded product was evaluated for its flow characteristics and residual pores after debinding. Table 1 shows the result. It had excellent properties as a kneaded product.

Injection molding, debinding and 1300
Even if a sintered product was manufactured by sintering at 1 ° C. for 1 hour, a homogeneous high-density (99% or more relative density) sintered product was obtained without defects during debinding.

[0020]

[Table 1]

Comparative Examples 1 to 2 In Examples 1 to 3, kneading was performed by setting the pressure degree to 1 to 3 kgf / cm ² . The obtained kneaded product had remarkably inferior flow characteristics, and it was actually quite difficult to mold. Example 4 Vacuum degree 5 × 10 ⁻³ Tor at a binder addition amount of 6%
kneading was carried out in the same manner as in the above-mentioned example under the condition of a pressure of 9 kgf / cm ² at a temperature of 135 ° C.

This was injection molded, debindered and sintered. The relative density (%) at this time was about 99.6% as shown in FIG. Further, the flow characteristics of the kneaded product were evaluated at a temperature of 130 to 190 ° C. FIG. 2 shows the result. Excellent characteristics are obtained. Also,
The density (Archimedes method) was also evaluated for the kneaded product and the molded product.

FIG. 3 shows the result. Comparative Examples 3 to 5 Kneading was performed under the following conditions, and the density of the sintered product was evaluated. The results are shown in Fig. 1. The density did not reach that of Example 4.

Comparative Example 3 9 kgf / cm ² pressure, 135 ° C. heating in air ・ Comparative Example 4 20 Torr vacuum, 3 kgf / cm ² pressure, 135 ° C.
Heating-Comparative Example 5 9 kgf / cm ² pressure, 135 ° C. heating and 2 in air
In a vacuum of 0 Torr, pressure of 3 kgf / cm ² and heating at 135 ° C. The flow characteristics and true specific gravity were evaluated in the same manner as in Example 4. None of them fell short of those of the present invention, as shown in FIGS. Example 5 The kneaded product obtained in Example 4 was extruded at a temperature of 120 ° C. from a nozzle having a diameter of 2.5 mm, and the length at which it was broken under vertical conditions was measured. As a result, a large green strength was obtained as shown in Table 2. Comparative Examples 6 to 8 For each of Comparative Examples 3 to 5, the green strength was evaluated in the same manner as in Example 5. As is clear from Table 2, this invention was far behind.

[0025]

[Table 2]

The above examples are examples in which metal powder is used as the powder, but in the present invention, the same effect can be obtained by applying ceramic powder of alumina, zirconia or the like or a mixed powder of metal powder and ceramic powder. Obtainable.

[0027]

As described in detail above, according to the present invention, metal powder and ceramic powder having fresh water are hydrophobized, the water resistance of the metal powder or ceramic powder and the binder is improved, and high dispersibility and residual porosity are obtained. Achieve a reduction and enable high quality products.

[Brief description of drawings]

FIG. 1 is a measurement diagram showing relative density.

FIG. 2 is a diagram showing a flow characteristic (MFR).

FIG. 3 is a measurement diagram of a density of a molded body.

Claims (2)

[Claims] 1. In the production of a kneaded product for powder molding, which comprises a metal powder and / or a ceramic powder and an organic binder, the metal powder and / or the ceramic powder and the organic binder are 4.0 kgf / c in a vacuum.
A method for producing a kneaded product for powder molding, which comprises heating and kneading while applying a pressure of m ² or more. 2. A method for producing a powder-sintered product, which comprises subjecting the kneaded product produced by the method of claim 1 to powder molding, subjecting it to binder removal treatment, and then sintering.