JPH0191999A - Forming of powder body - Google Patents

Abstract

PURPOSE:To manufacture a powder formed body of a metal, ceramic, etc., without using an expensive rubber mold by forming the mold having one opening part from a synthetic resin film (n) sheet, making a preform by filling a raw material powder body and making it dense by a press treatment. CONSTITUTION:A pinhole 2 is passed through by actuating a vacuum pump, first, to start a suction from the inside of a permeable mold supporting body 1. When the synthetic resin film 3 heated in this state is placed on the upper face of the porous mold 1, the film is closely fitted by its expansion to the permeable mold supporting body 1. A raw material powder body 12 is then filled up from an opening part 6 in the mold completing the preparation. A felt like filter 13 is placed on the raw material powder body 12, the rubber plug 14 conformed to the shape of the opening part and a suction port 15 are fitted and the inside of the mold is evacuated by a vacuum pump 16. The preforming body thereof is immediately inputted into a CIP device, subjected to a pressure rise to a fixed atm. and a green compact can be obtd. by holding the pressure for several minutes.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for molding powder that can be molded using powder such as metal powder or ceramics to obtain a molded body with high dimensional accuracy. It is related to.

[Prior art] In the cold isostatic pressing (hereinafter referred to as CIP) method, powder such as metal or ceramics is filled into a bag made of rubber-like elastic material, the bag is sealed, and a liquid such as water or oil is added from the outside. It is well known as a method of pressure molding using it as a pressure medium.

When carrying out such a molding method, a rubber-like mold (hereinafter referred to as "rubber mold for cars") made of rubber, synthetic resin latex, PVC, polyurethane, etc. is usually used.

It goes without saying that this rubber mold must have such strength and thickness that it will not be deformed by the weight of the powder filled during molding.

By the way, when carrying out the method described above, since the deformation behavior of the rubber mold and the powder filling are different, the hydrostatic pressure applied from the outside of the rubber mold is
It is unlikely that the powder will be transmitted as it is to the powder filled inside, and in particular, the powder located at the corners of the rubber mold may be restrained by the rubber mold and difficult to shrink.

For this reason, the molded body not only has a shape different from the cavity shape of the rubber mold when no load is applied, but also a density difference may occur between the inside and the surface layer, and stress may remain, causing cracks.

Therefore, when using the normal CIP method, there has always been a problem that it is difficult to obtain a molded product with high dimensional accuracy and uniformity.

In order to solve this problem, in Japanese Patent Publication No. 47-37383, a rubber bag is placed in a mold of a predetermined shape, powder is filled into the rubber bag, and the pressure inside the bag is then reduced to maintain the shape of the mold. A method is described in which the rubber bag filled with powder and granules is taken out of the mold and subjected to CIP molding as it is.

In addition, in Japanese Patent Publication No. 60-56499 and Japanese Patent Application Laid-open No. 59-183780, an air permeable mold made of porous material is used as an outer supporting mold with further improvements, and a thin-walled mold is used on the inner side. After attaching the elastic cover to the outer support mold while subjecting it to low pressure and filling it with powdered molding material, the low pressure to the outer support mold is released, and after further low pressure is created in the thin-walled cover, the outer breathable support is attached. A method of removing the mold and CIPing the powder-filled and sealed thin elastic sheath is disclosed.

Further, Japanese Patent Application No. 139158/1983 describes how to obtain a molded body with high dimensional accuracy by improving the above-mentioned method and making a thin elastic cover similar in shape to the outer supporting mold.

[Problems to be Solved by the Invention] However, such conventional techniques have the following problems.

In other words, ■ There are restrictions on the rubber bag that can be placed in the mold. Specifically, expanding a commercially available rubber balloon (about 7 cm in diameter) into a mold (for example, a cube of about 20 cm) and making it fit tightly is difficult to do. There is a risk that the elastic limit of the rubber balloon will be exceeded and the balloon will break. When a spherical rubber mold is expanded and brought into close contact with an angular shape such as a cube or rectangular parallelepiped, the thickness of the expanded rubber bag becomes uneven, and the corners of the bag are not tightly adhered to the mold. This has the disadvantage that the corners become rounded as a result.These problems can be avoided to some extent by forming the rubber bag in a similar shape to the mold in advance. However, even if the shape of the rubber bag and the shape of the mold are made to be similar, there is another problem in that the rubber bag must be set securely so that it fits well inside the mold when it is expanded and brought into close contact.

From a practical standpoint, rubber molds and molds are often made of non-transparent materials, making it impossible to visually recognize and prevent accidents such as rubber molds and molds becoming misaligned. At present, problems often occur after the molding operation is completed.

Even if this problem is solved, the rubber mold must be made in a similar shape to the mold, which not only makes the rubber mold very expensive, but also makes it difficult to manufacture rubber molds. , there are restrictions on the shape of the rubber mold.

The purpose of this invention is to change the conventional idea and produce a molded body of powder such as metal ceramics without using such a rubber mold.

[Means for Solving the Problems] The present invention was achieved through various studies in order to achieve the above-mentioned object. After each synthetic resin film is expanded and brought into close contact with each other, a breathable mold support is assembled, a mold with one opening is formed using n sheets of synthetic resin film, the raw material powder is filled into this mold, and the opening is closed. After the inside of the mold is vacuum degassed, the air-permeable mold support is dismantled to take out the preform housed in the synthetic resin film, and this is subjected to cold isostatic pressing treatment to densify it. This is a powder molding method in which the special i number is .

[Function] The divided breathable mold support used in this invention refers to a member that forms a mold having one opening when assembled.

This divided air-permeable mold support requires expanding and adhering the synthetic resin film to the surface (inside) that will be assembled to form a mold. can be brought into close contact.

Therefore, 41. There are so-called porous materials such as plaster and breathable resin, but there are also materials that are not inherently breathable, such as wood, metal, and acrylic resin, but they can be ventilated by making vent holes or pinholes in them. It is also possible to use something with a gender.

On the other hand, in this invention, the synthetic resin film is expanded and adhered by utilizing air permeability, so that the expanded synthetic resin film has tear resistance, appropriate elongation, high tensile strength, and has an appropriate thickness. It is necessary to have one.

Specific examples of films with such characteristics include polyethylene film, polypropylene film, flexible polyvinyl chloride film, polyvinyl alcohol-based synthetic resin film, chloride comb film, and polybutylene film, and their thickness is The symmetrical breathable molding [- Although it cannot be determined uniformly because it varies depending on the unevenness and shape of the support, it is appropriately selected and used from among those of about 20 to 500 μm as necessary.

In addition, if it is not possible to completely adhere the film using only the suction force from the breathable mold support, heat it as necessary, or spray water or a solvent to make the film plastic. can give.

After the film with such plasticity is completely adhered, n pieces of breathable mold support are assembled and
A breathable mold with one opening made of a sheet of synthetic resin film is completed.This breathable mold is filled with raw material powder, and then the inside of the breathable mold is vacuum degassed through the opening. Seal this breathable mold.

Therefore, a breathable mold made of n sheets of synthetic resin films is naturally prone to vacuum overflow from the gaps formed between the films.

For this purpose, vacuum overflow is created by assembling a breathable mold support, sometimes filling this gap with adhesive, or heating a heater built into the breathable mold support to heat and press the film. No opening 1
This completes the air permeable mold.

The reason is that it is easier to fill the air permeable mold formed in this way evenly and in fine detail if the powder is processed as a raw material to have a particle size and shape with good fluidity. , it is desirable to use powder in such a shape.

Specifically, for example, in the case of stainless steel, tool steel, superalloys, etc., spherical powder produced by the argon gas atomization method, the vacuum injection method, or the rotating electrode method is suitable, and the rotating electrode method is also suitable for titanium and titanium alloys. The spherical powder is good.

In addition, metal fine powder such as carbon iron and carbon nickel,
Dispersion strengthened alloy powder such as cemented carbide, alumina, zirconia, silicon nitride, silicon carbide, Sialon 12 and usually 1μ
It is preferable to use spherical powder processed into granules because there are many fine powders with a size of less than m and the fluidity is not good.

[Function] Hereinafter, the function of the present invention will be explained in more detail with reference to specific examples.

1 to 9 show examples of operations that can be adopted in carrying out the method of the present invention, and in this case, for the sake of simplicity, the air permeable mold support is A case where the number of divisions n=2 will be explained.

The breathable mold support 1 shown in FIG. 1 is made of wood and has many pinholes 2 in some of its corners.
It's placed on top.

This suction box 5 is connected to a vacuum pump 4 and sucks the air inside the synthetic resin film 3 through the pinhole 2 of the breathable mold support 1 to bring it into close contact with the breathable mold support 1. It is a container that is formed to allow for.

Now, when the vacuum pump 4 is activated, suction is started from the inside (in the case of FIG. 1, the top surface) of the breathable mold support 1 through the pinhole 2.

When the heated synthetic resin film 3 is placed on the upper surface of the air-permeable mold support 1 in this state, the film is expanded and brought into close contact with the air-permeable mold support 1 as shown in FIG.

Using exactly the same method as in FIG. 1, the synthetic resin film is expanded and brought into close contact with the second breathable mold support 1.

Figure 2 shows a state in which two mold supports 1 in which the synthetic resin films prepared as described above are expanded and brought into close contact are put together. The part 8 is the remaining part of the film.

As mentioned above, when creating a vacuum inside the mold,
Since there is a high risk of leakage through the part 7 where the films are glued together, the mold is closed to one opening 6 by using an adhesive or by heat-pressing this part.
It can be produced in a form in close contact with the inside of the mold support 1, except for.

The mold produced as shown in FIG. 2 is rotated 90 degrees and supported so that the opening 6 is on the top surface as shown in FIG.

In this case, as is clear from FIG. 3, it is preferable to set it on a vibrating table 10, for example, in order to improve the powder filling.

The mold prepared as described above is filled with raw material powder 12 through the opening 6 as shown in FIG. A compact and uniform molded body can be obtained.

Next, as shown in FIG. 5, a felt filter 13 is placed on top of the raw material powder 12, a rubber plug 14 that matches the shape of the opening and a suction port 15 are attached, and the vacuum pump 16 is activated. Then, the inside of the mold is evacuated through the suction port 15 and filter 13 (Fig. 6).

When suction is performed by the vacuum pump 4.9, it is sufficient that the degree of vacuum is at least sufficient to expand and adhere the synthetic resin film 3 to the breathable mold support 1, and the value is generally -400 mm. It suffices if it is about Hg.

However, the higher the vacuum in the mold, the better, preferably higher than the vacuum achieved by the vacuum pump 4.9.

Next, the vacuum pumps 4 and 9 are stopped until the self-conformity can be maintained as shown in FIG.

At this time, observe the vacuum gauge 17, and if the degree of vacuum decreases after the vacuum pump 4.9 is stopped, there may be a leak from the part 7 where the films are bonded together or a pinhole 2 in Fig. 1. There is a possibility that the leak is due to the film biting into the film, so repair the leak with gas-impermeable adhesive tape.

Furthermore, if the location of the leak is unknown, it is desirable to wrap the mold in a vacuum packaging bag.

When the process is completed in this manner, as shown in FIG. 8, a preform 18 is obtained in which the opening 6 of the synthetic resin film is sealed and the mold is housed in the film.

Since this preformed body 18 has a vacuum inside, atmospheric pressure is hydrostatically applied thereto, so that it can continue to maintain its shape even without the breathable mold support 1.

This preform 18 is immediately subjected to CIP treatment as shown in FIG.
It is better to obtain a powder compact than to put it in a device, bring it to a pressure of, for example, 1,000 to 7000 atmospheres without any pressure, and hold this pressure for several minutes.

In an actual industrial apparatus, from the viewpoint of improving productivity, the above-mentioned preforms 18 can be accommodated in the CIP in groups of several or several tens.

In this case, it is better to leave the figure 7 as is than leave it as it is in figure 8.
It is preferable to leave it as it is as shown in the figure, as the vacuum will be maintained.

[Example] Hereinafter, the structure and effects of the present invention will be explained in more detail by specifically showing examples.

Example 1: Green compacts were produced using two types of powder: 1081 steel spherical powder (particle size: 80 to 200 mesh) and alumina granules (particle size: 20 to 100 μm).

First, upper and lower breathable mold supports were made of wood to form a mold with a thickness of 50 mm and a negative side of 300 mm.

At this time, the diameter corresponding to the frontage was 25 mmφ, and the thickness was cut off at 25 mm, so the air permeable mold support was divided into upper and lower halves.

Place this breathable mold support on top of the suction box,
Commercially available ethylene-vinyl acetate resin (EVA) film (
(thickness: 100 μm) was heated to bring it into close contact with an air-permeable mold support.

The wooden support used here was approximately 2 cm.
Holes with a diameter of 0.3 mm were made at intervals of .

According to the method described above, a preform is made by adding raw material powder, and in the case of steel powder, it is 5000 Kg/cm2.
, CI P at 3000 g/cm' for alumina powder,
After performing % embedding and consolidation, the green compact plate was measured, and the following results were obtained.

Green compact size (mm) Steel spherical powder 256.8 x 256.6 x
43.2 Alumina powder 229.1 x 229
゜lX38. '1 The thus obtained flat plate showed no warping or bending as far as I could see.

Example 2 5 wt % MgO was added to Si3N powder and granulated to a size of 50 to 100 μm L7 using a PVA binder to produce a green compact.

On the other hand, a brass object with the shape shown in Figure 10 (
In the figure, a: 40 mmφ, b: 40 mmφ,
C9120mmφ, d: 30mm, e: 9On
+m, f: 30mm) was made, and this was used as a mold to make thick rubber using silicone rubber using the conventional method.

Note that the rubber thickness at this time was 10 mm.

Furthermore, a plaster mold was made using this mold to produce a three-part breathable mold support.

Using this plaster mold and a 200 μm thick EVA film, Si
When the 3N4 base granulated powder was molded, a.

31.4±0.2 mmφ, b: 94.3±0.4
A green compact having dimensions of mIr1φ, c: 31.5±0.2 mmφ could be produced.

On the other hand, when molding was performed using silicone rubber, which is the conventional method, only a CIP body divided into three parts as shown in FIG. 11 was obtained, and it was impossible to obtain an integral molded body.

[Effects of the Invention] The method of the invention can improve the dimensional accuracy of a molded article without using expensive tool steel such as an injection mold.

By replacing the comb bag that traditionally forms the mold with a film, we have solved the problem of rubber bags, which had been a bottleneck up until now, all at once.

[Brief explanation of the drawing]

Figure 1 is a partial sectional view showing the positional relationship between the breathable mold support and the suction box, and Figure 2 is a partial cross-sectional view showing the positional relationship between the breathable mold support and the suction box. Figure 3 is a partial cross-sectional view showing the mold in Figure 2 standing upright on a vibration table;
The figure is a partial cross-sectional view showing the scene in which raw material powder is supplied to the mold, Figure 5 is a partial cross-sectional view showing the scene in which the raw material powder in the mold is sealed, and Figure 6 is a partial cross-sectional view showing the scene in which the raw material powder in the mold is sealed. FIG. 7 is a partial cross-sectional view showing the scene of degassing, FIG. 7 is a partial cross-sectional view illustrating the situation of measuring the vacuum leak state. FIG. 9 is a sectional view showing the preformed body installed in a cIp device, FIG. 10 is a perspective view of the mold, and FIG. 11 is a perspective view of the molded body. 1.・Breathable mold support, 2... pinhole,
3... Synthetic resin film, 4, 9, 16... Vacuum pump, 5... Suction box, 6... Opening, 7...
- Portion where films are adhered to each other, 8... Surplus portion of film, 10... Vibration table, 11... Hopper, 12... Raw material powder, 13... Filter, 14
...Rubber stopper, 15 river suction port, 17...vacuum gauge,
18... Preformed body.

Claims (1)

[Claims] Inside the breathable mold support divided into n parts (n≧2),
After the synthetic resin films are brought into close contact with each other, a breathable mold support is assembled, a mold with one opening is formed using n sheets of synthetic resin films, the raw material powder is filled into this mold, and then this opening is After the inside of the mold is vacuum degassed, the air-permeable mold support is dismantled to take out the preform housed in the synthetic resin film, which is subjected to cold isostatic pressing treatment to densify it. A method for molding powder, characterized by: