JP2013146748A - Method for producing compact by using cold isostatic pressing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of obtaining easily and stably a large-sized compact.SOLUTION: The method for producing a compact is used to produce the compact by using a cold isostatic pressing, and is characterized in that the compact is obtained by preparing a molding die made from a soft material, which has at least one or more partition dies for dividing an inner space of the molded molding die, by filling a powder for molding in the inner space separated with the partition die, by putting this into a pressure vessel of the cold isostatic pressing device, and by pressurizing the powder for molding with isotropic pressure.

Description

  The present invention relates to a molding method for obtaining a compact by isostatically pressing a powder such as ceramics using hydrostatic pressure.

In recent years, industrial members made of ceramic materials have shifted to large-sized and complicated shapes. When manufacturing structural members using ceramics, etc., press the raw material powder at a pressure of 1000 kgf / cm ² or more to form a near net shape (solidify into a shape that is as close as possible to the final product) and then sinter to obtain the desired product shape. Attempts have been made to produce in a reduced number of processes, and first of all, it is necessary to obtain a large, uniform, high-density molded body.

  In general, as a molding method for obtaining a high-density molded body, there are a die press molding method and a cold isostatic pressing method (Patent Documents 1 and 2).

  In the die press molding method, the desired product shape is, for example, a simple cylindrical shape, and the pressure applied to the pressing surface when molding an aspect ratio (ratio of the length of the cylinder to the diameter) of 1 or more. In order to produce a powder compact by propagating the inside of the compact, it was necessary to rely on a multi-stage action method in which the raw material powder was put into a metallic mold in several batches and pressed sequentially. In this case, there is a problem that the work becomes complicated and the amount of the raw material powder entering the mold may be different between the early stage and the later stage, and the density of the molded body tends to be uneven. Furthermore, for example, when a molded body having a diameter of 300 mm is obtained, a press machine of 700 tons or more and a dedicated metal mold having sufficient strength and structure to withstand the applied pressure are necessary, and there is a problem that such costs are expensive.

  On the other hand, in the cold isostatic pressing method, a soft mold is used so that water, which is a propagation medium of molding pressure, does not penetrate into the raw material powder. The soft mold is compressed together with the raw material powder filled therein by being pressurized from all directions in the pressure transmission medium, and the approximate shape of the inner wall of the soft mold is imparted to the molded body. Because it is isostatically pressed with hydrostatic pressure, it is easy to obtain a large and uniform powder compact with a uniform density distribution compared to the mold press molding method. The size depends on the size of the soft mold and is within the dimensions of the pressure vessel. It is generally used because it can be obtained freely and inexpensively.

JP 2006-193797 A JP 2003-266198 A

  However, in the conventional cold isostatic pressing method (Patent Document 1), the molding powder filling portion of one molding die is composed of a single chamber, and only one molded body is obtained. Therefore, when a plurality of molded bodies are required, it is necessary to prepare either the required number of molds and perform the molding process at the same time or perform the molding process multiple times with one mold. There was a problem that the cost would be high.

  Here, Patent Document 2 describes a method of simultaneously obtaining a plurality of molded bodies by sandwiching plate bodies made of rigid bodies therebetween. However, in this method, since the other molding die forming the internal space filled with the molding powder itself is also a rigid body, the compression molding direction is limited to a uniaxial direction, and the aforementioned aspect ratio is 1 or more. There has been a problem that it is difficult to obtain a large-sized molded product.

  An object of the present invention is to solve these problems and to provide a method capable of easily and stably obtaining a large-sized molded product.

  In order to achieve the above object, a method for producing a molded body according to the present invention is a method for producing a molded body using a cold isostatic pressing method, in a mold made of a soft material. Dividing the space, having at least one partition mold, filling the molding powder into the internal space partitioned by the roughly partition mold, and placing it in the pressure vessel of the cold isostatic press, It is characterized in that a compact is obtained by isostatically pressing a roughly molding powder.

  Moreover, as a preferable aspect of the manufacturing method of the molded object of this invention, the Shore A hardness of the shaping | molding die for partitions is 40 or less in the said shaping | molding die.

  Moreover, as a preferable aspect of the manufacturing method of the molded object of this invention, in the said shaping | molding die, the thickness of the shaping | molding die for partitions is 2-10 mm or less.

  According to the production method of the present invention, a large molded article can be obtained easily and stably.

Schematic cross-sectional view of a mold provided for explanation of the cold isostatic pressing method of the present invention Schematic cross-sectional view of a pressure vessel provided for explanation of the cold isostatic pressing method of the present invention

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a mold used for explaining a cold isostatic pressing method according to an embodiment of the present invention.

  The cold isostatic pressing method is, for example, injecting a liquid such as water into a cylindrical pressure vessel, and molding powder into a molding die made of a soft material such as bag-like rubber. This is a method of obtaining a molded body by isotropically pressing a molding powder by enclosing and immersing and applying hydraulic pressure to the outside of the molding die.

In the present invention, raw powder such as zirconia ceramic powder is placed in the inner space surrounded by the lower lid mold 2 and the cylindrical mold 3 which are separable molds made of soft materials such as natural rubber and nitrile rubber. A predetermined amount of the molding powder 5 is filled, the partition mold 4 is inserted, the remaining molding powder 5 is filled, the upper lid mold 1 is sealed, and each joint is sealed. This is placed in a water tank as a pressure vessel 8 shown in FIG. 2, and water pressure is applied and isotropically pressurized by applying a water pressure of 1000 kgf / cm ² from the outside of the mold, thereby forming powder. 5 is compressed to obtain a molded body 6.

  By this method, it is possible to obtain a plurality of molded bodies at a time as compared with the conventional cold isostatic pressing method for obtaining a molded body without a partition mold.

  That is, in the molded body 6 according to the embodiment of the present invention, the partition mold 4 that is at least one plate body is provided between the upper lid mold 1 and the lower lid mold 2, and the molding powder is provided between the partition molds. By filling 5 and isotropically pressing, a plurality of molds can be obtained simultaneously from one mold by a single molding process. Furthermore, it is possible to form molded bodies having different thicknesses at once by changing the filling amount of the molding powder in each layer.

  Here, in the case where the material of the partition mold is a rigid body made of metal or the like, the soft material is applied at the contact portion with the cylinder 3 that is the molding mold when water pressure is applied and the pressure propagates from the outside of the molding mold. Since the partition 3 is buckled and deformed while the cylinder 3 made of the material is compressively deformed, anisotropy occurs in the compressive deformation of the filled molding powder 5 and cracks occur in the resulting molded body 6. There is a case. Furthermore, the partition mold 4 may bite into the tubular mold 3 itself, which is a forming mold, and be damaged. Therefore, the material of the partition mold is a soft material as in other molds.

  The soft material is a material that undergoes compression deformation at the time of pressurization in the cold water pressure molding method. Moreover, it is preferable that it shrinks at the time of pressurization, easily returns to its original shape at the time of pressure release, has high deformability and shape memory property, and is not easily damaged even if deformation is repeated. Examples include natural rubber, silicon rubber, butadiene rubber and the like.

  The partition type will be described in more detail.

  The partition mold is not particularly limited as long as it is the above-mentioned soft material. However, the smaller the hardness, the better the compressive deformability when pressure is propagated from the outside of the molding mold, and the resulting molded body 6 has less density change. A homogeneous and high strength product is obtained. If the Shore A hardness of the partition mold is greater than 40, the mold may have low compressive deformability and may not be able to follow, and partial bending may appear in the partition mold. Since the shape of the partition mold is transferred to the surface of the obtained molded body, similar partial unevenness may occur, and further, it may break from the same location. Therefore, the partition type Shore A hardness is preferably 40 or less. Furthermore, 30 or less is preferable and 20 or less is more preferable.

  The partition mold has the same thickness, and the smaller the thickness, the better the compressibility of the partition mold 4. However, since the partition mold is easily tilted or distorted when the partition mold is inserted into the mold, there is a case where unevenness occurs when the mold is positioned on the filled molding powder, and the uniform shaped molded body 6 cannot be obtained. is there. Therefore, a thickness range having a certain amount of shape retention is preferable. When the thickness of the partition mold is smaller than 2 mm, the compressive deformability increases, but the shape retainability decreases, and thus the above-described problem may occur, and the surface of the resulting molded body may be swelled. On the other hand, when it is larger than 10 mm, the shape retaining property is improved, but the compressive deformability is lowered, so that the outer peripheral corner portion of the molded body located on the outer peripheral portion of the partition mold may be broken. Therefore, the thickness of the partition mold is preferably in the range of 2 to 10 mm.

  The powder for the molded body is not particularly limited as long as it can be molded by a cold isostatic pressing method, and ceramic powders such as tetragonal zirconia, alumina, silicon nitride, silicon carbide, or composite ceramics containing two or more of these. Examples are powders.

  Hereinafter, the present invention will be described in detail by way of examples. The measurement and evaluation of the examples were performed as follows.

(1) Waviness of the surface of the molded body Obtained when a molded body is obtained from a molding mold having a configuration in which a partition mold is interposed at an intermediate position in the height direction in a molding mold in which the powder filling portion for molding is cylindrical. The in-plane height of the surface in contact with the partition mold of the molded body was measured, and the average value obtained by the following formula was determined.
(Maximum height)-(minimum height)
(2) Cracking of molded body The number of cracks was confirmed by observing the surface of the molded body. The number of samples shall be 10, "excellent" if there is no sample that is cracked in 10, "good" if there are no cracks in 10 or more, "good" if there are 3 or more cracks in 10 ".

(3) Relative density of sintered body The measured density of the sintered body was divided by the theoretical density, and the value expressed as a percentage was taken as the relative density. Here, the measured density of the ceramic sintered body was measured by the Archimedes method. Moreover, the following values were used for the theoretical density of the ceramic sintered body. Zirconia ceramics: 6.09 g / cm ²
(4) Partition type hardness (Shore A hardness)
The hardness of the partition type was measured according to the durometer hardness test method defined in JIS K6253 (2006). The apparatus used was a type A durometer hardness tester. The measurement produced the test piece of 60 mm x 60 mm x 10 mm, measured 5 times by making contact time 3 seconds, and calculated | required the center value.

Example 1
A zirconia powder having an average particle diameter of 60 μm is filled into a cylindrical molding mold (made of natural rubber, thickness 10 mm, hardness A40) having a diameter of a molding powder filling portion of a diameter of 600 mm and a height of 500 mm. An isostatic press molding at a pressure of 1000 kgf / cm ² is performed by a cold isostatic pressing apparatus at a position 250 mm in the middle with a partition mold configured as shown in Example 1 in Table 1 using a cold isostatic pressing apparatus. And the presence or absence of the crack of the obtained molded object was confirmed. Thereafter, a cylinder having a diameter of 30 mm and a height of 30 mm was cut out from the molded body, heated to 600 ° C. at 25 ° C./hour in an electric furnace, further heated, and sintered at 1400 ° C. for 3 hours. Density was measured. As a result, as shown in Table 1, the amount of undulation was 3 mm, the molded body was not cracked and was “excellent”, and the relative density of the sintered body was 99.3%.

(Example 2)
A sample was prepared and evaluated in the same manner as in Example 1 except that the conditions shown in Example 2 of Table 1 were used. As a result, as shown in Table 1, the amount of undulation was 5 mm, 8 out of 10 molded bodies were not cracked, and “good”, and the relative density of the sintered body was 99.2%.

(Example 3)
A sample was prepared and evaluated in the same manner as in Example 1 except that the conditions shown in Example 3 of Table 1 were used. As a result, as shown in Table 1, the amount of undulation was 3 mm, the molded body was not cracked and was “excellent”, and the relative density of the sintered body was 99.2%.

Example 4
It was created and evaluated in the same manner as in Example 1 except that the conditions shown in Example 4 of Table 1 were used. As a result, as shown in Table 1, the amount of undulation was 4 mm, 9 out of 10 molded bodies were not cracked, and “good”, and the relative density of the sintered body was 99.3%.

(Example 5)
It was created and evaluated in the same manner as in Example 1 except that the conditions shown in Example 5 of Table 1 were used. As a result, as shown in Table 1, the amount of undulation was 4 mm, 9 out of 10 molded bodies were not cracked, and “good”, and the relative density of the sintered body was 99.3%.

(Example 6)
It was created and evaluated in the same manner as in Example 1 except that the conditions shown in Example 6 of Table 1 were used. As a result, as shown in Table 1, the amount of undulation was 5 mm, 8 out of 10 molded bodies were not cracked, and “good”, and the relative density of the sintered body was 99.2%.

(Comparative Example 1)
The partition mold was prepared and evaluated in the same manner as in Example 1 except that the partition mold was a rigid body made of SUS304 material. The results are as shown in Table 2. However, because the partition mold breaks the cylinder mold at the time of molding, water as the pressure propagation medium enters the mold, and a normal green compact was not obtained. I couldn't.

1 Upper lid mold 2 Lower lid mold 3 Cylindrical mold 4 Partition mold 5 Molding powder 6 Molded body 7 Water 8 Pressurized container

Claims (3)

A method for producing a molded body using a cold isostatic pressing method, wherein a molding die made of a soft material has at least one partition die that divides an inner space of the formed molding die, Filling the internal space partitioned by the partition mold with the molding powder, placing it in the pressure vessel of the cold isostatic press, and isotropically pressurizing the molding powder to obtain a compact. The manufacturing method of the molded object using the cold isostatic pressing method characterized. The method for producing a molded body using the cold isostatic pressing method according to claim 1, wherein the partition type has a Shore A hardness of 40 or less. The manufacturing method of the molded object using the cold isostatic pressing method of Claim 1 or 2 whose thickness of a partition type | mold is 2-10 mm.

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