JPH01152201A - Method for removing additive in metal powder green compact - Google Patents

Abstract

PURPOSE:To complete degreasing for short time and to prevent the development of cracking and crazing by exposing the surface of metal powder green compact, coating the remaining part with resin film, heating the green compact under condition of hydrostatic-pressurizing the coated surface and scattering the additive from the exposed surface. CONSTITUTION:Porous body 8 made of alumina, etc., is piled at one side of end part of the metal powder green compact 3 and these surfaces are coated with the air-tight resin film 2 under joining condition with a hollow pressure tube 5 fixed to a heat resistant vessel. The pressure vessel is filled up with boric acid water, etc., the temp. of the metal powder green compact 3 is raised under pressurized condition of the boric acid water. The additive contained in the green compact is gasified with vaporization, decomposition or sublimation and scattered to the space 7 at outer part from the exposing surface part through the porous body 8 and the hollow pressure tube 5. The cracking and crazing in the degleased green compact 3 are not developed and the packing ratio of the power is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for removing additives from a metal powder compact. More specifically, it relates to a method of heating and scattering an additive used as a molding aid from a metal powder compact formed by injection molding in order to obtain a sintered alloy, a so-called degreasing method for a metal powder compact. .

[Background technology]

BACKGROUND OF THE INVENTION With technological innovations in the automobile industry, aircraft industry, etc., the need for alloy members with complex shapes and high performance has been increasing in recent years.

The so-called powder metallurgy method, which is a method of forming metal powder and then heating it to obtain a sintered alloy, has the excellent advantages of being able to obtain a shape close to the finished shape and of being easy to control the metal structure. There is.

Therefore, the powder metallurgy method is the most expected industrially as a method for obtaining the above-mentioned high-performance alloy members. That is, Fe, Ni, Cr, Ti, Co, S
Metal powders such as n, Cu, etc. are mixed in a predetermined ratio, additives are added to the metal powders, the mixture is molded into a desired shape by injection molding, degreased, and then the metal powder compacts are sintered. A high-performance alloy member can be obtained by igniting the material to the temperature required for the purpose.

The injection molding method used herein refers to materials such as polystyrene, polyethylene, diethylene phthalate, paraffin, fatty acid ester, polyvinyl, etc. that exhibit plasticity as a whole and become easy to mold when kneaded with the metal powders such as Fe and Ni mentioned above. 10 to 25 parts by weight of an additive such as alcohol is added to 100 parts by weight of the metal powder and kneaded,
This is a method of press-fitting this kneaded material into a mold of a desired shape. The obtained powder compact is taken out from the mold,
After the additive is scattered and removed by heating, for example, 800~
By igniting to 1200°C, a sintered alloy in the desired shape can be obtained.

Hereinafter, in the present invention, the thermoplastic agent, plasticizer, dispersant, solvent, etc. added to the metal powder during injection molding will be collectively referred to as additives. The operation of scattering the additives remaining in the molded body obtained by the injection molding method by heating is hereinafter referred to as "degreasing" according to the common terminology of those skilled in the art.

However, sintered alloys obtained by degreasing and igniting metal powder compacts obtained by injection molding have fewer defects (those that cannot be considered as products) with defects such as cracks and surface peeling. There is a problem that this happens without any problems.

Furthermore, if these defects occur inside the sintered alloy,
Since it is difficult to detect defects at the stage of commercialization, some products end up being produced as is, and there is a major problem in that they can break during use and cause accidents.

What should be particularly pointed out here is that most of the defects such as cracks and surface peeling occur during the degreasing process. That is, if additives remain in the metal powder compact, when the powder compact is ignited to form a sintered alloy, the remaining additives will rapidly vaporize, and the expansion force caused by this vaporization will cause the additives to evaporate rapidly. As a result, cracks and cracks occur in the sintered alloy.

In order to prevent this, the metal powder compact is subjected to a degreasing process to remove the additives prior to ignition.

Therefore, it is obvious that it is desirable to remove the additive as completely as possible in the degreasing step.

However, as mentioned above, metal powder compacts contain 10 parts by weight or more of additives per 100 parts by weight of metal powder, so metal powder compacts containing such a large amount of additives can cause cracks and It is essentially extremely difficult to remove the additive by scattering it by heating without causing cracks, because the large expansion force of the additive that accompanies heating scattering acts strongly on the metal powder compact, which has extremely low mechanical strength. This is a difficult problem.

Therefore, conventionally this process was carried out at atmospheric pressure or 5 kg/
Metal powder compacts can be produced up to 600% under pressure of about CD or less.
This is done by heating the metal powder compact to around °C and scattering and removing the additive through vaporization, decomposition, etc. However, due to the need to keep the expansion force of the additive low, the heating rate of the metal powder compact is slow. It is carried out under extremely slow conditions of 1 to 3°C/h. Since the degreasing process has to adopt such a slow temperature increase rate, it usually takes a long time of 5 to 7 days.
There was a problem in that productivity was significantly hindered.

In addition, when the amount of additives is increased, the voids that are formed when the additives are removed during the degreasing process increase, so the amount of additives must be as small as possible, and the performance that is easy to mold is required. The property of being easy to use is also required.

However, there is a problem in that it is essentially extremely difficult to satisfy all of these properties, even if expensive materials such as the aforementioned polystyrene and polyethylene are used.

Furthermore, since the mechanical strength of a degreased metal powder compact is almost zero, cracks or cracks can easily occur due to slight vibrations or shakes during the process of transferring or transporting the compact to the next sintering process. To prevent this, vibration at this time,
It was necessary to prevent shaking as much as possible.

As described above, productivity is extremely low (despite being produced using extremely careful operations, there are quite a few defective products in the obtained sintered alloys, and this is mainly due to the degreasing process. The actual situation was that this was caused by defects in the metal powder compacts that occurred in the process.

[Summary of the invention]

The purpose of the present invention is to solve these drawbacks of the prior art with a completely new method. According to the method of the present invention, the degreasing process can be carried out in an extremely short time, and at the same time, the degreasing process can be performed in an extremely short time. A novel degreasing method is provided that can significantly suppress the occurrence of defects in metal powder compacts.

[Disclosure of the invention]

The inventors of the present invention have conducted intensive studies with the aim of fundamentally eliminating the drawbacks of the conventional technology, and have found that even if the additive is removed at a lower temperature and in a shorter time than in the conventional method, the metal The present invention has been completed by discovering a method that can significantly suppress the occurrence of defects such as cracks and cracks in powder compacts compared to conventional methods.

That is, the above-mentioned object of the present invention is to provide a method for removing additives from a metal powder molded body formed by adding an additive to metal powder by heating and scattering the additive. (Other than leaving a part of the exposed surface, cover the rest with an airtight resin thin film, heat the powder compact while applying hydrostatic pressure to the coated surface, and remove the additive from the exposed surface.) This is achieved by scattering it through a surface.

(Detailed disclosure of the invention) The present invention will be explained in detail below.

In the present invention, when degreasing a metal powder compact that still contains additives obtained by injection molding, a part of the surface of the metal powder compact is left exposed in advance, and the rest is made of airtight resin. Cover with a thin film.

Coating with such a thin resin film is achieved by applying a liquid resin that solidifies by evaporation of the solvent or by a chemical reaction directly onto the surface of the metal powder molding, by spraying it, or by dipping and pulling it up, and then drying or heating if necessary. This can be carried out by forming a resin coating on the surface by applying treatments such as the following. Examples of liquid resins that can be used in this method include industrially produced resins such as vinyl acetate emulsion, styrene-butadiene latex, acrylic emuldigon, and natural rubber latex. Further, polyurethane resins, silicone resins, epoxy resins, acrylic resins, polyester resins, chlorbrene resins, phenol resins, etc. can also be used. Furthermore, among acrylic resins, epoxy resins, polyester resins, etc., there are resins that are processed so that when they are applied in a powder state and heated, the powders fuse to form a coating film. Other resins can also be used.

The thickness of the resin thin film to be coated can be selected appropriately depending on the shape of the metal powder compact, the particle size of the metal powder, the pressure of hydrostatic pressing, the type of resin thin film, etc. It is sufficient if the thickness is greater than the thickness.

According to the experimental findings of the present inventors, the thickness of the resin thin film is usually 1
It is desirable that the thickness is 0 μm or more. Further, although the upper limit of the thickness of the resin thin film is not particularly defined, it is preferably up to about 5 mI++ for convenience of handling.

Of course, depending on the type of resin thin film, it is possible to use a thin film with a thickness smaller than or greater than this.

Further, it is more preferable that the oil spray thin film has some degree of elasticity. By coating the surface of the metal powder formed body with such a resin thin film and heating and degreasing the coated thin film under hydrostatic pressure as described later, the resin thin film forms a metal powder formed body under the hydrostatic pressure. The hydrostatic pressure is effectively transmitted to the metal powder compact through the resin thin film,
The voids in the metal powder compact caused by scattering of the additive can be eliminated very effectively by isotropic shrinkage of the compact due to isostatic pressure. Note that for this purpose, as described above, it is preferable that the resin forming the thin film has some degree of elasticity. This can be based on the fact that the glass transition point of the resin is below the proposed temperature at the temperature during the degreasing operation.

In the present invention, it is necessary to leave at least a portion of the surface of the metal powder compact uncovered and exposed. During degreasing, additives are scattered from the exposed surface. n The position of the exit surface should be selected taking into account the shape of the powder compact and the local mechanical load when it is made into a sintered alloy.0 For example, if the shape of the metal powder compact is axially symmetrical, If there is, it is preferable to set it at the end in the axial direction because the pressurizing operation is easy.Also, if the shape of the metal powder compact is, for example, cylindrical as shown in Fig. 1, the exposed surface is set at one end. The cross section, as shown in Figure 2 (if it is propeller-shaped, the cross section of one end of the rotating shaft is preferable. The reason is that it is difficult for the metal powder to be evenly pressed near the exposed surface, so this part is made of sintered alloy. This is because the mechanical load is not large when this happens.The exposed surface 1 as shown in FIGS. 1 and 2 satisfies the above-mentioned conditions.

The area of the exposed surface is required to prevent additives from scattering from this surface, so if the area is too small, the time required for degreasing will be longer, and conversely, if the exposed area is too large, the additive will be spread evenly on the metal powder compact. The number of areas that are difficult to compress increases.

An appropriate exposed area is selected by considering these trends together with the size and shape of the metal powder compact. According to the experimental findings of the present inventors, the exposed area is approximately 0.5 to 20% of the total surface area, preferably approximately 1 to 10%.

The metal powder molded body, in which at least a portion of the metal powder molded body is coated with the resin thin film, is then heated while the coated surface is pressurized with hydrostatic pressure.

In the hydrostatic pressurization method, the coated surface is immersed in liquid,
This liquid is pressurized using a pump, etc. (The preferred pressurizing liquid is boric acid water or hydraulic oil with a concentration of about 30% by weight.The pressure applied to the liquid here is The pressure should be such that the expansion force generated by heating does not cause defects such as cracks in the metal powder compact, and should be selected depending on the type of additive, heating temperature, shape of the metal powder compact, etc. In order to achieve this objective, the pressure is preferably 5 kg/cJ or more.

Furthermore, it is desirable that the pressure of the hydrostatic pressurization is such that the voids caused by the scattering of the additive can be eliminated by the isotropic contraction of the metal powder compact due to the hydrostatic pressurization. The pressure is preferably 500 kg/c+a or more and 50 T/cd or less.

As a method of pressurizing only the coated surface, there is a method as shown in FIG. 3, for example. That is, the metal powder compact 3 shown in FIG. 3 and the hollow pressure tube 5 are connected, and the surface of the metal powder compact and the outer surface of the pressure tube are coated with an integral thin film.

In this way, the surface of the powder molded body in contact with the inside of the hollow pressure-resistant tube becomes an exposed surface not covered with a resin thin film, and the coated surface can be pressurized in this state.

In the present invention, in order to prevent distortion from occurring in the vicinity of the exposed surface, it is preferable to press the exposed surface by some method. For example, as shown in FIG. An effective method is to place the body 8 in contact with the exposed surface in a hollow pressure-resistant tube.The pore diameter of the porous body is preferably at least 5IIllI or less, preferably 1mm or less, and more preferably 0.1mm or less. .01
μ− or more.

In this way, while the coated surface of the non-metal powder-formed body is subjected to isostatic pressure, the molded body is heated from the outside to vaporize the additive once by decomposition or sublimation, and thus the vaporized additive is heated. The agent passes through the exposed surface of the metal powder molded body that is not covered with the resin thin film, flies out of the molded body, and is removed. Heating a metal powder compact to disperse additives can be done by heating a liquid such as pressurized boric acid water or hydraulic oil, and the heating rate, temperature reached, and holding time depend on the type of additive. be selected as appropriate.

In addition, in the present invention, the following industrial advantages can be realized by selecting the type of additive. That is, since the present invention is a method of scattering additives while applying hydrostatic pressure to a metal powder compact, even if voids are created inside the metal powder compact due to this scattering, these voids can be removed by hydrostatic pressure. It can be easily eliminated by isotropic shrinkage of the compact. Therefore, when adopting the injection molding method in the present invention,
It is not necessarily necessary to use expensive additives such as conventionally used polystyrene and polyethylene; for example, adding water-soluble polymers such as polyvinyl alcohol, carboxymethyl cellulose, and polyethylene glycol to water in an amount of about 0.1 to 5%. Inexpensive liquids such as viscous liquids dissolved in alcohol and liquids in which about 1 to 20% of fats and oils such as lauric acid, palmitic acid, stearic acid, and glycerin are dissolved can be used.

In the present invention, since it is possible to use as an additive a substance having a boiling point lower than that of the conventional polystyrene or polyethylene as described above, it is also possible to carry out the heating temperature during degreasing at a much lower temperature.

In the present invention, the method of heating the metal powder compact during degreasing is of course arbitrary, but the following method is listed as one of the preferable methods based on the experimental findings of the present inventors. That is, from normal temperature to the boiling point of the volatile components in the additive,
The temperature may be raised at any rate until it reaches a temperature as low as °C, but once this temperature is reached, it must be 2° below the boiling point of the continuous component.
The temperature is kept at a temperature as low as C for 3 to 10 hours, during which time about 40 to 60% of the volatile components are scattered and removed.
This completes the degreasing process.

In addition, when heating as described above, it is also a preferred embodiment to suction through the exposed surface with an exhaust device such as a fan or blower in order to quickly scatter volatile components out of the molded article.

Since the present invention is such a degreasing method, for example, if the volume of the metal powder compact is about 11, the total heating time is 24.
Degreasing can be completed within hours, which is much shorter than the conventional method, which takes 5 to 7 days.

〔Effect of the invention〕

In the present invention, a part of the surface of a metal powder molded body is exposed, and the rest is covered with an airtight resin thin film, and then
Since this is a method of scattering the additive through the exposed surface while applying hydrostatic pressure at a pressure of g/cd or more, according to the present invention, the expansion force generated when the additive is heated and vaporized is effectively absorbed by the hydrostatic pressure. Therefore, degreasing can be carried out in an extremely short period of time, and at the same time, the occurrence of defects such as cracks and cracks accompanying degreasing can be significantly suppressed compared to conventional methods.

In addition, the voids inside the metal powder molded body that occur in the area where the additive has been removed can be easily eliminated by isotropic compression of the molded body, so even if the amount added is small, the plasticity will be reduced when kneaded with the metal powder. Another advantage is that it is not necessarily necessary to use expensive polystyrene, which has been developed as an additive that is easy to display and easily dispersed by heating.

Furthermore, since the resin thin film coated on the metal powder molded body also has the role of reinforcing the metal powder molded body, cracks and cracks that occur in the metal powder molded body after degreasing in the process of transitioning to the sintering process are particularly important. It also has the effect of preventing.

In addition, in the present invention, since it is possible to use a substance with a lower boiling point than polystyrene or polyethylene as an additive, it is not necessary to use a substance with a boiling point lower than that of polystyrene or polyethylene.
It is not necessary to degrease at a high temperature of about 00°C, and depending on the type of additive, it can be performed at a much lower temperature than this, for example, as shown in the example below, it can even be carried out at a temperature of <250°C or less. It is also extremely advantageous in terms of thermal energy. In addition, the implementation temperature is preferably 300 to 50
It is in the range of about °C.

Since the present invention has such advantageous effects, it can be used for sintered alloys with relatively complex shapes that require methods such as injection molding, and that also require reliability in mechanical strength. It can be applied particularly effectively in manufacturing.

[Examples and comparative examples]

The present invention will be specifically explained below using Examples and Comparative Examples. In addition, in the following, % and parts each indicate a weight basis.

Example 1 As metal powder, 100 parts of metal Ti powder with a purity of 99.5% or more and an average particle size of 12 μm and a purity of 99.8%
Using 10 parts of the metal CO powder with an average particle size of 1.4 μm above, 20 parts of a polyvinyl alcohol aqueous solution with a concentration of 5% was added as an additive, and the mixture obtained by kneading was injected at a pressure of 500 kg/c + II G. Five cylindrical metal powder compacts each having a diameter of 25 mm and a length of 100% were obtained. The apparent volume of the obtained metal powder compact is the volume occupied by the raw material powder relative to its volume (hereinafter referred to as "powder filling ratio").
) was 68% on average.

These metal powder compacts were degreased as follows. That is, as shown in FIG. 4, an alumina porous body 8 (diameter 25 mm, height 10 m
m, average pore diameter 10 tt m) were superimposed and joined to a hollow pressure-resistant tube 5 fixed to a pressure-resistant container, and their surfaces were covered with a resin thin film 2 having a thickness of 350 μm. The coating method used was to apply a liquid acrylic emulsion to the metal powder compact, and then dry the water in the emulsion to form a thin resin film on the surface.

Next, the pressure container was filled with boric acid water with a concentration of 30%, and this boric acid water was compressed by a pump to 1500 kg/cffl.
By heating the metal powder molded body under pressure with a heater, the temperature of the metal powder molded body was increased and degreasing was performed. The boric acid solution was heated in the following manner.

That is, the temperature was raised from room temperature to 80°C at a rate of 50°C/h, the temperature was raised from 80°C to 95°C at a rate of 30°C/h, the temperature was maintained at 95°C for 2 hours, and the temperature was raised to 95°C. 110° from
The temperature was raised to C at a rate of 30°C/h, held at 110″C for 2 hours, and then cooled to room temperature by natural cooling.The total time from the start of heating until cooling to room temperature was 9 hours.

During this time, the boric acid water was maintained at a pressure of 150 (1 Kg/c111).

The water contained in the metal powder molded body was scattered from the exposed surface portion not covered with the resin thin film through the alumina porous body 8 and the hollow pressure-resistant tube 5 into the space 7 outside the pressure-resistant container. This external pressure was maintained at an absolute pressure of 0.8 to 0.9 kg/c+fl by suction with a blower.

None of the five metal powder compacts 3 taken out from the pressure container showed any changes in appearance such as cracks or damage to the resin thin film, and more than 99% of the water had been scattered.

Furthermore, the powder filling rate was 73% on average, which was higher than before degreasing.

Next, these powder compacts were heated to 1200°C for 1 hour in a vacuum at a pressure of 10-' Torr to obtain a sintered alloy.

The density ratio (apparent density/theoretical density) of the obtained sintered alloy was 99.3% on average.

The five sintered alloys obtained in this way were cut into JIS
No. 10 test pieces (marker length 1 m 50 mm, diameter 12.5 mm) according to JIS Z 2201 (1968) were processed and subjected to a tensile test according to JIS Z 2241 (1977). As a result, the average tensile strength was 62
Kgf/mm”, standard deviation is 3.2 Kgf/nm”
Met.

Comparative Example 1 A cylindrical metal powder compact obtained by injection molding in exactly the same manner as in Example 1 was subjected to an absolute pressure of 0.8 without being covered with a resin thin film.
Degreasing was carried out in exactly the same heating manner as in Example 1 in air at ~0.9 Kg/cj.

After degreasing, the powder compact had many cracks in the gaps between 3 and 51111, and about 40% of the surface had a thickness of 0.5
Peeling of ~1+*m had occurred.

Comparative Example 2 100 parts of the same metal Ti powder used in Example 1 and metal C
12 parts of polyethylene, 8 parts of polypropylene, and 1 part of stearic acid were added to 10 parts of o powder, and the mixture obtained by kneading these was injection molded in exactly the same manner as in Example 1 to form a cylindrical metal powder molded body. I got 5 pieces.

The average powder filling rate of the five metal powder compacts was 67%.

Next, this metal powder compact was degreased by the following conventional heating method at high temperature and for a long time. In other words, raise the temperature from room temperature to 100°C at a rate of 30°C/h, 100°C
Increase temperature at 2°C/h to 600″C, then increase temperature at 2°C/h to
Hold for a while and then cool to room temperature by natural cooling. The atmosphere was a nitrogen gas atmosphere, and the pressure was atmospheric pressure.

The total time from the start of temperature rise until cooling to room temperature is 260
It took a long time.

The metal powder compact taken out from the container has cracks,
No change in appearance such as surface peeling was observed, more than 99.0% of additives such as polyethylene were scattered, and the powder filling rate was 67% on average, the same as before degreasing.

Next, these powder compacts were processed in exactly the same manner as in Example 1.
A sintered alloy was obtained by heating at 1200° C. for 1 hour in a vacuum of O-5 Torr. The average density ratio of the obtained sintered alloy is 9
It was 6.2%.

Test pieces were prepared from these sintered alloys in exactly the same manner as in Example 1, and a tensile test was conducted. As a result, the average tensile strength was 44 kgf/mmz, and the standard deviation was 6.1 kgf/ml.
1! Met.

A comparison between Example 1 and Comparative Example 1 shows that coating a metal powder molded body with a resin thin film and degreasing the coated surface while applying hydrostatic pressure is effective in preventing cracks and surfaces. It can be seen that this method has a remarkable effect on preventing JI separation.

Furthermore, a comparison between Example 1 and Comparative Example 2, which is a conventional degreasing method, shows that although the metal powder molded body degreased by the present invention was degreased at a much lower temperature and in a shorter time, its powder filling rate was lower than that of the conventional degreasing method. It can be seen that the tensile strength of the sintered alloy of the present invention is higher than that of the conventional technology, and that the tensile strength of the sintered alloy of the present invention is large and its variation is much smaller.

Examples 2 to 5 The same metal Ti powder and metal Co powder as in Example 1 were used as raw metal powders, and the additives shown in Table 1 were added to 100 parts and 10 parts of these as shown in Table 1. The mixtures obtained by adding and kneading were injection-molded five pieces each in exactly the same manner as in Example 1 to obtain metal powder molded bodies having the powder filling ratio shown in Table 1.

Next, in the same manner as in Example 1, these metal powder compacts were joined to a hollow pressure tube via an alumina porous body as shown in Figure 4, and their surfaces were coated with a resin thin film. coated. As for the coating method, in Examples 2 and 3, an acrylic emulsion was applied and dried in the same manner as in Example 1, and in Examples 4 and 5, an epoxy resin was applied and cured by heating. The thickness of the resin thin film was 350 μl in Examples 2 and 3;
In Examples 4 and 5, the thickness was 420 μm.

Next, the coated surface of these metal powder compacts was coated with boric acid solution having a concentration of 30% by weight at a rate of 1500 kg/cIa in the same manner as in Example 1.
Under isostatic pressure, the boric acid water was heated with a heater to raise its temperature and degreasing was performed.

Here, the heating method was performed in Examples 2 and 3 in exactly the same manner as in Example 1, and in Examples 4 and 5 as follows. That is, the temperature was raised from room temperature to 50 °C in 1 hour, the temperature was raised from 50 °C to 60 °C at a rate of 10 °C/h, the temperature was held at 60 °C for 3 hours, and the temperature was raised from 60 °C to 75 °C for 15 minutes. The temperature was raised at a rate of °C/h, held at 75 °C for 2 hours, and then cooled to room temperature by natural cooling. The total time from the start of temperature rise until cooling to room temperature was 10 hours. In Example 2.3, the pressure outside the space 7 is an absolute pressure of 0.8 as in Example 1.
~0.9 Kg/cd, and in Example 4.5, atmospheric pressure.

There were no visible changes in the metal powder compact taken out of the pressure container, such as cracks or damage to the resin thin film.
More than 99% of all additives were scattered. Furthermore, as shown in Table 1, the powder filling rate was higher than that before degreasing in all cases.

Next, these metal powder compacts were made into sintered alloys in exactly the same manner as in Example I, and further processed into test pieces and subjected to a tensile test, with the results shown in Table 1.

Table 1: Main Carboxymethyl Cellulose Zero Rate Polyethylene Glycol Examples 6 to 8 The following experiment was conducted for the purpose of examining the effect of hydrostatic pressurization. That is, as metal powder, 100 parts of metal Fe powder with a purity of 99.5% or more and an average particle size of 5 μm, and a purity of 99.
．． Example 1 Using 4 parts of metallic Cu powder having an average particle diameter of 3 μm at 5% or more, 20 parts of a 0.5% aqueous solution of methylcellulose was added as an additive, and the mixture obtained by kneading these was prepared in Example 1.
Injection molding was carried out in exactly the same manner as above to obtain a metal powder compact with a powder filling rate of 64%.

Each of these metal powder compacts was made in exactly the same manner as in Example 1, and then inserted into a hollow pressure-resistant tube 5 via an alumina porous body 8.
A phenol resin was applied to these surfaces in a state where they were bonded to each other, and the resin was cured by heating to cover a resin thin film with a thickness of 240 μm.

Next, each of these five pieces was maintained under hydrostatic pressure at the pressure shown in Table 2, and heated in the same heating manner as in Example 1 to degrease. The powder filling rates after degreasing were the values shown in Table 2. Next, these metal powder compacts were heated to 1150'C for 1 hour in a vacuum at a pressure of 10-'Torr to obtain a sintered alloy. The density of the obtained sintered alloy and the results of the tensile test conducted in the same manner as in Example 1 were the values shown in Table 2, respectively.

Table-2

[Brief explanation of the drawing]

FIGS. 1 and 2 are perspective views showing examples of shapes of powder compacts used in the present invention. FIGS. 3 and 4 are cross-sectional views showing the powder compact used in the present invention placed in a pressurized container. In the drawings, 1------exposed surface, 2------1 thin film, 3
----One powder compact. 4-- Pressure vessel wall, 5-- Hollow pressure tube, 6-- Pressurized liquid, 7-- Atmosphere, 8
-... Indicates a porous body made of alumina or the like.

Claims (3)

[Claims] (1) A method of removing additives from a metal powder molded body formed by adding an additive to metal powder by heating and scattering the additive, in which at least a part of the surface of the metal powder molded body is exposed in advance. The remaining material is covered with an airtight resin thin film, and the metal powder compact is heated while the coated surface is subjected to hydrostatic pressure to scatter the additive through the exposed surface. A method for removing additives from a metal powder compact. (2) The method according to claim 1, wherein the metal powder compact is molded by an injection molding method. (3) The method according to claim 1 or 2, in which the metal powder compact from which additives have been removed is subsequently ignited to produce a sintered alloy.