JPH0740092A - Press molding method using flastic material mold - Google Patents

Abstract

PURPOSE:To prevent distorted deformation and to improve surface roughness by packing powder into a mold composed of a soft elastic material, setting the molded article pressurized in a low pressure region into a mold composed of a soft elastic material and subjecting the powder and molded article to press molding under a high pressure. CONSTITUTION:The powder 6 is packed into the first mold 1 and after its aperture is closed, a pressure medium is introduced between pressurizing rubber 5 and a high-pressure vessel 2 from an introducing hole 7. The pressurizing pressure is set at a low pressure to yield the molded articles 21 which can be handled. The first molded article 21 is taken out after the pressurization treatment and is set into the second mold 11, by which the molded article is subjected to the pressurization treatment under the high pressure and the second molded article 22 is obtd. A hard material is used for the elastic material 5 of the second mold 11 to prevent remaining of the shape of the powder 6 on the surface of the second molded article 22. The soft elastic material 5 capable of following up the shrinkage of the powder 6 is used for the first mold 1 which is large in change of apparent density and, therefore, the distorted deformation, such as elephant leg phenomenon, is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elastic molding die for pressing powder of powder metallurgy, ceramics or the like using an elastic molding die under isotropic pressure or pseudo isotropic pressure. The present invention relates to a pressure molding method, and more particularly to a pressure molding method having excellent molding accuracy.

[0002]

2. Description of the Related Art As a method for pressure-molding powder such as powder metallurgy or ceramics, a container or a mold made of an elastic material such as rubber is filled with the powder and compressed by fluid pressure from the outside of the container or the mold. Direction pressing method or a pressing method using an elastic molding die that is pseudo-isotropically pressed using a pressing device (JP-A-59-224308 and JP-A-4-36).
3010 publication). In all of these methods, the molding die is less expensive than the die molding in which a metal die is used for pressurization, and it is easy to apply to a product having a complicated shape.

However, in general, the relationship between the molding pressure and the density of the powder is shown in FIGS. 6 (alumina granulated powder) and 7 (silicon nitride granulated powder (KSN-10M-7 manufactured by Shin-Etsu Chemical Co., Ltd.).
As shown in (X)), the increase in the apparent density of the molded body, in other words, the dimensional shrinkage is remarkable at a pressure of 500 kgf / cm ² or less, and this tendency is the same for other ceramic powders. Generally, since the bulk density of the powder in the initial state filled in the mold is low, it changes to the closest packed state in the initial stage of pressurization, and the apparent volume of the entire powder shrinks greatly. On the other hand, in the low pressure region where the whole powder largely contracts, due to the rigidity of the elastic mold, the powder cannot contract following the powder, and even if the fluid pressure is isotropically applied by the cold isostatic pressing method. However, there is a tendency that a molded product deviated from the similar shrinkage is obtained. The tendency of this deviation becomes more remarkable as the elastic modulus (practically, hardness) of the rubber increases and the wall thickness of the molding die increases.

For example, when a thick elastic mold having a JIS hardness of 70 to 90 ° is used, in the initial stage of pressing,
Since it cannot follow the contraction of the powder, bending deformation occurs at the initial stage of pressing, and a cylindrical shaped body may be formed even if an attempt is made to obtain a cylindrical shaped body. Generally, when molding using a mold made of hard rubber with high rigidity, the outer diameter of the drum-shaped molded body or the upper and lower ends is larger than that of the center even if it is a simple cylindrical molding. The molded body is deformed more or less distorted, such as a molded body exhibiting a so-called elephant foot phenomenon is obtained, and it is necessary to perform processing such as cutting after molding.

On the other hand, when an elastic mold having a low rigidity and a small thickness is used, the elastic mold can shrink following the powder, and the molded body may deform to some extent. Although it can be reduced, it is difficult to manufacture the rubber mold itself with high accuracy and sufficient dimensional accuracy cannot be obtained. Further, there is a problem that the surface roughness is inferior such that the particle shape of the granulated powder (particle size is several 10 to 100 μm) remains on the surface of the molded body.

The present invention has been made based on the above technical background, and an object of the present invention is to provide a powder compact which can satisfy the requirements of shape and dimensional accuracy by using an elastic mold. It is to provide a pressure molding method that can be obtained.

[0007]

A method of pressure molding using an elastic body molding die of the present invention is a method in which a first molding die made of a soft elastic body is filled with powder and pressed in a low pressure range. A first step of obtaining a first molded body by pressing; the first molded body is set in a second molding die made of a hard elastic body, and pressure molding is performed at a higher pressure than in the first step. 2 steps and; are included.

[0008]

The first mold used in the first step is made of a soft elastic body. Therefore, in the first step, since the first mold can shrink following the shrinkage of the powder, a first compact having no distorted deformation can be obtained despite the large amount of shrinkage of the powder due to pressurization. Next, in the second step, pressure is applied at a higher pressure than in the first step, but the dimensional shrinkage of the first molded body is
Since it is not as large as the contraction of the powder in the first step, it can be followed even by the second molding die made of a hard elastic body. On the other hand, since pressure molding is performed with a hard second molding die, particles on the surface of the molded body are crushed, and thus the surface roughness of the molded body obtained in the second step is excellent.

[0009]

The method of the present invention will be described below with reference to FIG. FIG. 1 shows an embodiment in which the pressure molding method of the present invention is applied to a dry isotropic pressure molding method. Figure 1 (a)
Shows a dry cold isotropic pressurizing device 10 provided with a first molding die 1 used in the first step. This device is a cold isotropic pressurizer conventionally used in the dry bag method. That is, the cylindrical first molding die 1 is provided in the cylindrical high-pressure container 2 with the pressing rubber die 5 interposed therebetween. Lids 3 and 3 are attached to the upper and lower openings of the high-pressure container 2, and punches 4 and 4 for pressing the powder filled in the first mold 1 are attached to the lids 3 and 3. Has been. The size of the first mold 1, that is, the size of the portion filled with powder is represented by a diameter D ₁ and a height H ₁ .

Here, the constituent material of the first molding die 1 may be a soft elastic body having a large compression amount in a low pressure region, and specifically, a latex having a JIS hardness of 50 ° or less, particularly 20 ° or less. , Urethane rubber, silicone rubber and the like are preferably used. The size of the first molding die 1, that is, the diameter D ₁ and the height H ₁ is appropriately selected depending on the shape and size of the molded body to be obtained, the type of powder to be filled, the filling amount, and the like.

The first mold 1 is filled with the powder 6 to be molded, the opening of the first mold 1 is closed and sealed, and then a low pressure P ₁ is applied. The pressurizing process is performed through the pressurizing rubber 5 by introducing the pressurized pressure medium into the space formed by the pressurizing rubber 5 and the inner surface of the high-pressure container 2 through the introducing hole 7. The pressurizing pressure P _{1 in} the first step is appropriately selected depending on the type of the molding powder, so that a pressure can be obtained in which the molded body can be handled in a low pressure range where the apparent density of the molded body is largely changed. For example, in the case of the granulated powder of alumina having the characteristics shown in FIG. 6, the density increase due to pressurization is remarkably 300 to 400 kgf / cm ² or less, and 150 kgf / cm ² or more from the viewpoint of handling of the molded body. P ₁ may be selected from the pressure range.

After the pressure treatment at P ₁ , the first mold 1
Take out the molded body. The first compact obtained by the pressure treatment in the first step is indicated by 21 in FIG. 1 (b).
By the pressure treatment in the first step, the size (diameter d ₁ , height h ₁ ) of the first molded body 21 has a diameter d ₁ <D ₁ and a height h ₁ <.
It is H ₁ . Next, the first molded body 21 is set in the second cold isotropic pressurizing device 20 including the second molding die 11 (see FIG. 1C).

Here, the second cold isotropic pressurizing device 20 is the first one except that the size of the second mold 11 is reduced.
It has the same configuration as the cold isostatic pressing device 10. First
The parts equivalent to those of the cold isostatic pressing device 10 are designated by common reference numerals and the description thereof will be omitted. The size of the second molding die 11 is smaller than that of the first molding die 1 and is larger than that of the first molding body 21 so that the first molding body 21 can be accommodated therein. is there. That is, there is a relationship of diameter d ₁ <D ₂ <D ₁ and height h ₁ <H ₂ <H ₁ .

The second molding die 11 used in the second step is
It is made of an elastic material that is harder than the constituent material of the first mold 1. In particular, when the first molded body 21 is composed of granulated powder, the molded body obtained in the second step (hereinafter,
(Referred to as "second molded body") 22 so that the powder shape of the granulated particles does not remain on the surface, JIS hardness is 50 ° or more, especially 70 °
It is preferably composed of the above rubber material. As the elastic material made of the second mold 11, urethane rubber,
In addition to a high hardness rubber material such as nitrile rubber or natural rubber, a rubber material in which fine ceramic particles or the like are dispersed to increase rigidity is used. In addition, it is also possible to use a molding die having a double structure in which only a contact portion of the second molding die 11 with the first molding body 21 is made of a hard elastic body.

After setting the first molded body 21 in the second molding die 11, the opening is closed and sealed, and the cold isostatic pressing process which is the second step is carried out. The pressurizing pressure P ₂ in the second step is higher than the pressure P _{1 in} the first step and is a pressure necessary for obtaining a dense second molded body, and is appropriately selected. The second molded body 22 obtained in the second step is shown in FIG. Second molded body 2
The size of ₂ is represented by a diameter d ₂ and a height h ₂ .

According to the above-mentioned molding method, the first molding die 1 can shrink following the shrinkage of the powder 6 in the first step, so that the first molding can be performed without causing an elephant foot phenomenon. Body 2
1 can be obtained. Next, in the second step, since the density change of the molded body 21 is small, the second body made of a hard elastic body is used.
Even the molding die 11 can sufficiently follow and shrink. Moreover, since the contact portion with the first molded body 21 is made of a hard material, even if the granulated particles are used as the molding powder 6, the particle shape of the granulated particles appearing on the surface of the second molded body 22 is crushed. can do. That is, it is possible to improve the surface roughness.

Therefore, according to the pressure molding method of the present invention,
It is possible to obtain a second molded body that is free from distorted deformation such as an elephant foot phenomenon and has an excellent surface roughness. In the above examples, the dry cold isostatic pressing treatment was performed in both the first step and the second step, but the present invention may be performed by a method of pressing using an elastic mold. Alternatively, for example, a method using a wet cold isotropic pressurizing device as shown in FIG. 2 may be used. In FIG. 2, the elastic mold is indicated by 31. Further, not only the pressurization by the fluid but also the pressing method using the elastic body forming die in which the elastic body forming die 32 is pressed by the punch 33 or the like as shown in FIG. For details of the pressing method using the elastic mold, see JP-A-59-2.
It is disclosed in Japanese Patent No. 24308.

The method and effect of the present invention will be described below based on concrete examples. [Specific Example] Example 1 A prototype was produced with the goal of producing an alumina molded body having a diameter of 22 mm and a length of 50 mm.

As the first mold, an elastic mold made of urethane rubber having a JIS hardness of 20 ° and having a powder-filled portion having a diameter of 30 mm, a length of 60 mm and a wall thickness of 5 mm was used. This first molding die was filled with 50 g of alumina granulated powder (US3061C manufactured by Showa Denko KK), the opening was closed and sealed, and then placed in a cold isostatic press for 200
The pressure treatment was performed at kgf / cm ² . The dimensions of the first molded product taken out from the first molding die are 23.4 mm in diameter and 5 in length.
The outer diameter was 1.1 mm, and the outer diameter was constant over the entire longitudinal direction, but the shape of granulated particles remained on the surface.

Next, the first molded body was set in a second molding die made of urethane rubber having a hardness of 70 °. The size of the filling portion of the second mold is 24 mm in diameter, 52 mm in length, and 2 in wall thickness.
It is 0 mm. After closing the opening of this second mold and sealing it, it was placed in a cold isostatic pressing device to obtain 1000 kgf /
Pressure treatment was performed at a pressure of cm ² . The dimensions of the second molded body taken out from the second molding die are an outer diameter of 22.5 mm and a length of 50.
It was 8 mm. The surface of the obtained second molded body is magnified 10 times.
When observed under a microscope at a magnification of 0, the granulated particles were crushed and the unevenness was reduced. In FIG. 4, 60 of the second molded body surface
A double photomicrograph is shown.

Example 2 As a granulated powder, silicon nitride (KSN-10M-7X manufactured by Shin-Etsu Chemical Co., Ltd.) powder was added with yttria (7%) and alumina (3%) as sintering aids. Using this, a circular shaped body was formed.
The first mold is made of silicone rubber with a hardness of 20 °, and the size of the filling part is 22 mm in diameter and 50 mm in height.
Then, using a mold with a wall thickness of 5 mm, 200 kgf / cm
Cold isostatic pressing was performed at a pressure of ² . Diameter 16.8 mm,
A cylindrical first molded body having a length of 44 mm and a relative density of 51.8% was obtained.

Next, the first molded body is filled with a second molded die made of urethane rubber having a hardness of 90 ° and having a filling portion size of 17 mm in diameter, 45 mm in height and 3 mm in wall thickness. Then, the cold isostatic pressing process was performed again at a pressure of 2000 kgf / cm ² . The dimensions of the second molded product taken out from the second molding die are 16 mm in diameter and 42 mm in length, and the relative density is 5
It was 9.5%. When the surface of the second molded body was observed under a microscope at a magnification of 100, it was confirmed that the granulated particles were crushed and the unevenness was reduced.

Example 3; hardness of 20 ° as the first molding die
Made of silicone rubber, the filling part is 50mm x 50mm x
A mold having a thickness of 10 mm and a thickness of 10 mm was filled with the same alumina powder as in Example 1, and the pressure was 200 kgf / cm.
It was treated cold isostatic pressing at ^2. The obtained first compact is 1
The side length is 41.6 mm, the thickness is 8 mm, and the relative density is about 52.
%Met.

Next, this first molded body is filled in a second molding die made of urethane rubber having a filling portion size of 42 mm × 42 mm × 8 mm, a hardness of 90 ° and a wall thickness of 10 mm.
Cold isostatic pressing was performed again at a pressure of 000 kgf / cm ² . The obtained molded body has a size of 41 mm x 41 mm x 7.6 m.
m, the relative density was 56.6%, and no large distortion was observed in the overall shape. The surface roughness by observation with a microscope was also good.

Comparative Example 1 The first molding die used in Example 1 was filled with the same powder as that used in Example 1, the opening was closed and sealed, and then cold isostatic pressing was performed. It was put in the apparatus and pressurized at a stroke with a pressure of 1000 kgf / cm ² .
The molded body taken out exhibited a so-called elephant foot phenomenon in which the end portion in the longitudinal direction was swollen. In addition, the size of the molded body was such that the central portion had a diameter of 23.1 mm and a length of 49.3 mm. When the surface of the molded body was observed under a microscope at a magnification of 100, it was observed that the shape of the granulated particles remained as it was. FIG. 5 shows a 60 × photograph of the surface of the molded body.

Comparative Example 2 The same powder as that used in Example 1 was filled in a molding die made of urethane rubber having a hardness of 70 ° and having a size of a filling portion having a diameter of 30 mm, a length of 60 mm and a wall thickness of 20 mm. After closing the opening and sealing it, put it in a cold isotropic pressurizing device and blow it to 1000 kgf / cm ^{2 at} a stretch.
Was pressure-treated. The molded body taken out of the molding die exhibited a remarkable elephant-foot phenomenon, and was in a state in which the end portions were almost chipped. The diameter of the central part of the molded body is 2
It was 1.8 mm.

Comparative Example 3; The first molding die used in Example 2 was filled with the same powder as that used in Example 2 and subjected to cold isostatic pressing at a pressure of 2000 kgf / cm ² . . The relative density of the obtained first molded body was 59.8%, and the size was such that the diameter of the central portion was 15.8 mm and the length was 42.5 mm.
However, the diameter of the end was slightly less than 17 mm, and some elephant foot phenomenon was observed. Further, the surface of the obtained molded body is magnified 10 times.
When observed under a microscope at a magnification of 0, it was confirmed that the original spherical shape of the granulated particles remained as it was, and that the surface roughness was inferior to that of the molded body obtained in Example 2 by visual observation. Admitted.

Comparative Example 4; the size of the filling portion is 50 mm ×
A mold having a size of 50 mm × 10 mm and a wall thickness of 5 mm and a hardness of 90 ° was filled with the same alumina powder as in Example 3, and 20
Cold isostatic pressing was performed at a pressure of 00 kgf / cm ² . The molded body taken out from the molding die had a drum shape in which the elephant foot phenomenon was severe in the thickness direction, and it was cracked into four. The thickness of the central portion was about 6 mm, but the outer peripheral portion also had a thickness of about 8.5 mm. [Evaluation] Table 1 collectively shows the pressure treatment conditions and results of Examples 1 to 3 and Comparative Examples 1 to 4.

[0029]

[Table 1]

As can be seen from Table 1, each of the molded products obtained by the method of the present invention was superior in surface roughness and shape to the molded products obtained in Comparative Examples. That is, when the molding die made of soft rubber, that is, the first molding die was subjected to a high-pressure treatment at once, the granulated particle shape remained on the surface of the molded body, and the surface roughness was inferior. In addition, all of the moldings obtained by high-pressure treatment at once using a molding die made of hard rubber, that is, a second molding die, have a marked elephant foot phenomenon, and the end portions may be chipped or cracked. there were.

[0031]

EFFECT OF THE INVENTION The pressure molding method of the present invention comprises a soft elastic body capable of following compression of powder at low pressure, which causes distorted deformation of the molded body, with shrinkage of the powder. Since pressure is applied using a molding die, distorted deformation such as an elephant foot phenomenon can be prevented. Further, in the second step, since the pressure is applied using the second molding die made of a hard elastic body, it is possible to improve the surface roughness.

Therefore, according to the pressure molding method using the elastic body molding die of the present invention, it is possible to obtain a molded body excellent in dimensional accuracy, shape and surface roughness.

[Brief description of drawings]

FIG. 1 is a process drawing showing a pressure molding method according to an embodiment of the present invention.

FIG. 2 is a view showing a pressure device used in another embodiment of the present invention.

FIG. 3 is a view showing a pressure device used in another embodiment of the present invention.

FIG. 4 is a micrograph showing the surface texture of the second molded body obtained in Example 1.

5 is a micrograph showing the surface texture of the molded body obtained in Comparative Example 1. FIG.

FIG. 6 is a graph showing the relationship between the pressure of alumina powder and the density of a molded body.

FIG. 7 is a graph showing the relationship between the pressure of silicon nitride powder and the density of a molded body.

[Explanation of symbols]

 1 1st shaping | molding die 6 powder 11 2nd shaping | molding die 21 1st shaping | molding body 22 2nd shaping | molding body

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[Procedure amendment]

[Submission date] January 13, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a process drawing showing a pressure molding method according to an embodiment of the present invention.

FIG. 2 is a view showing a pressure device used in another embodiment of the present invention.

FIG. 3 is a view showing a pressure device used in another embodiment of the present invention.

FIG. 4 is a ceramic material of a second molded body obtained in Example 1.
It is a microscope picture which shows the surface of the texture of a material .

FIG. 5 shows the ceramic material of the molded body obtained in Comparative Example 1.
It is a microscope picture which shows the surface of a structure .

FIG. 6 is a graph showing the relationship between the pressure of alumina powder and the density of a molded body.

FIG. 7 is a graph showing the relationship between the pressure of silicon nitride powder and the density of a molded body.

[Explanation of Codes] 1 First Mold 6 Powder 11 Second Mold 21 First Molded Body 22 Second Molded Body

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

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[Figure 5]

Claims (1)

[Claims] 1. A first step of filling a first molding die made of a soft elastic body with powder and pressurizing it in a low pressure range to obtain a first molding body; And a second step of performing pressure molding at a pressure higher than that of the first step by setting the second molding die composed of the elastic body of 1. Molding method.