JPH04278306A - Pressing method of powdered formed body - Google Patents

Abstract

PURPOSE:To obtain highly dense formed body having little ununiformity in density at the isostatic pressing of a powdered forming body having a hollow. CONSTITUTION:Under the condition that stock powder is filled between an outer frame mold 1 and a rubber mold 2, which is arranged in the interior of the mold 1, pressing force is applied outwards against powder-filled layer 2 from the inside of the rubber mold.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for press-molding powder compacts such as ceramic compacts having hollow holes.

0002

2. Description of the Related Art Hydrostatic pressing is known as a typical method for forming ceramic molded bodies. FIG. 3 schematically shows isostatic pressing of a ceramic molded body having hollow holes. In the figure, (5) is a core metal for molding a hollow hole, (6) is a rubber mold, (2) is a ceramic powder filling layer, and the ceramic powder is filled around the core metal (5). The outside is covered with a rubber mold (6).

[0003] The powder-filled bed (2) is heated toward the surface of the inner core metal (5) under the action of hydrostatic pressure using gas or liquid as a pressure medium, which is applied from the outside through the rubber mold (6). The material is compressed and densified as shown in FIG. After applying pressure for a predetermined time, remove the rubber mold (6),
By removing the core metal (5), a ceramic molded body having a cylindrical shape is obtained.

[0004] The quality of the ceramic molded body has a great influence on the quality, yield, etc. of the ceramic product obtained through the subsequent firing process. In order to improve product yield and quality, it is necessary to increase the density of the ceramic molded body, minimize unevenness in density, and make it highly homogeneous.

[0005]

[Problems to be Solved by the Invention] In isostatic pressure molding, pressure can be applied uniformly over the entire circumference of the powder-filled bed (2) via the rubber mold (6); During the compression process of the powder-filled bed (2) due to the pressure, crosslinks are likely to be formed between the particles, and the formation of crosslinks hinders sufficient densification of the powder-filled bed.

[0006] The limit of densification due to crosslinking formation depends on the particle shape and particle size structure of the ceramic powder used, but generally the densification effect is almost saturated at a pressing force of about 3000 kgf/cm2, and then Even if a pressure exceeding 100% is applied, densification hardly progresses, and therefore the density of the obtained molded product remains at about 60 to 75%, and there is considerable unevenness in density between the outer surface layer and the inner surface layer. accompanied by. In addition to the pressure molding of ceramic powders, similar problems occur in the pressure molding of metal powders in powder metallurgy.

[0007] The present invention makes it possible to obtain a highly densified molded body with little unevenness in density due to the effective action of the pressing force on the powder filling layer, which is less likely to cause crosslinking of particles during the compression densification process. To provide a hydrostatic pressing method that can be used.

[0008]

[Means for Solving the Problems and Effects] The method for pressure molding a powder compact of the present invention includes an outer frame mold and a molded body disposed inside the molded body in an isostatic pressure molding method for a powder compact having hollow holes. The method is characterized in that a raw material powder is filled between the rubber mold and the rubber mold, and a pressing force is applied to the powder-filled layer from the inside of the rubber mold outward.

The present invention will be explained below with reference to the drawings. FIG. 1 shows an example of pressure forming of a cylindrical ceramic molded body. In the figure, (1) is the outer frame mold, (3) is the rubber mold, the rubber mold (3) is placed inside the outer frame mold (1), and the ceramic powder filling layer (2) is the outer frame mold. Mold (1)
and the rubber mold (3). Comparing this with the conventional isostatic pressing shown in Fig. 3, in the present invention, the outside of the ceramic powder filled layer (2) is
) instead of the core metal (5) shown in Fig. 3.
3), and a pressure medium is introduced into the rubber mold (3).

[0010] In the present invention, the powder packed bed (2) comprises:
Under the action of hydrostatic pressure applied from the inside through the rubber mold (3) in a radially outward direction (arrow), the rubber mold (3) moves toward the surface of the outer frame mold (1) as shown in Fig. 2. Compressed. As in the conventional method shown in Figs. 3 and 4, the powder-filled bed (2
) In pressure molding, in which pressure is applied from the outside to the inside, particles adjacent on the left and right are compressed inward while changing their positions so that they approach each other. In the pressure molding of the present invention in which a pressure force is applied, the particles are pushed toward the outer frame mold (1) while being spread out.

[0011] For this reason, the powder-filled bed (2
) In the compression process, crosslinking between particles is less likely to occur, and the pressing force is effectively transmitted to the particles. the result,
Compared to conventional pressure molding, higher densification is possible with the same pressure load, and unevenness in the density of the powder-filled layer in the layer thickness direction is alleviated. In addition, the pressure at which the compression densification effect is saturated increases, so by increasing the pressure,
It is also possible to further increase the density.

After compression molding the powder filled layer (2) by applying a predetermined hydrostatic pressure to the powder filled layer (2) from inside the rubber mold (3) as described above, the rubber mold (3) The pressure is reduced and the outer frame mold (1) and rubber mold (3) are removed to obtain a highly densified ceramic molded body having hollow holes.

[0013] In the above pressure molding, an example of a circular cross section was shown, but it is of course not limited to this, and molding of various polygonal shapes is also possible, and the hollow holes in the molded product are not limited to through holes. Needless to say, the present invention can also be applied to the molding of a hollow shaped body with only one end open and the other end closed.

Furthermore, the present invention is not limited to ceramic molded bodies, but can be applied to pressure molding of molded bodies in powder metallurgy to obtain the same effects as described above.

[0015]

[Example] As shown in Fig. 1, the outer frame mold (1) and the rubber mold (
3) Alumina ceramic powder (particle size: approx. 0.5~
2 μm) and formed into a hollow cylindrical shape by isostatic pressure molding with a pressure of 3000 kgf/cm2.
(Outer diameter: 500 mm, length: 800 mm, wall thickness: 30 mm) was obtained. In addition, the pressing force was increased to 6300 kgf/
A test molded product B was obtained by pressure molding under the same conditions as those for the molded product A above, except that the pressure was increased to cm2.

As a comparative example, as shown in FIG.
) and the rubber mold (6) are filled with the same alumina ceramic powder as above (filling amount is the same as above), and 3000 kgf
/cm2 isostatic pressure molding to give a sample molded body a (inner diameter:
440mm, length: 800mm, wall thickness: approx. 30mm
mm) was obtained. In addition, the pressing force was 6300 kgf/cm2.
A test molded product b was obtained by pressure molding under the same conditions as the test molded product a, except that the pressure was increased.

A test piece was taken from the axially intermediate portion of each test molded body, and the apparent density was measured, and the results shown in Table 1 were obtained.

[0018]

[Table 1]

In Table 1, looking at the molded body A pressure-molded according to the present invention and the molded body A obtained by the conventional method (pressing force is 3000 kgf/cm2 in both cases), the density of the latter is 2.7 g/cm2. cm3, the former is 3.1g/
cm3 and highly dense. In addition, in the conventional method, a molded body a (density: 2
．． 7g/cm3) and molded body b (density: 2.8g/cm3) with an increased pressure of 6300kgf/cm2, the conventional method has a pressure of 3000kgf/cm2.
The densification effect is almost saturated at cm2, and even if the pressing force is increased beyond that, no improvement in density can be expected. On the other hand, the molded body B according to the present invention (pressing force: 6300 kgf/cm2
) has a density of 3.6g/cm3, and the true density (approximately 3.99g/cm3).
/cm3) high densification of 90% or more has been achieved.

[0020]

Effects of the Invention: According to the method of the present invention, crosslinking between particles during the pressure molding process is less likely to occur, and the pressurizing force effectively acts within the powder layer, resulting in a highly dense and homogeneous powder with little unevenness in density. A molded article can be formed. Due to the high density and homogeneity of the molded body, the strength and rigidity of the molded body are increased, and it is less prone to deformation, cracking, breakage, etc. during the handling process and subsequent firing process, and the yield of the product (fired product) is improved. This brings about effects such as a reduction in machining allowance for finishing to a predetermined size, a reduction in processing cost, and an improvement and stabilization of product quality.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram showing an example of the present invention before pressure molding.

FIG. 2 is an explanatory cross-sectional view after pressure molding, showing an example of the present invention.

FIG. 3 is an explanatory cross-sectional view before pressure forming, showing a conventional pressure forming method.

FIG. 4 is an explanatory cross-sectional view after pressure forming, showing a conventional pressure forming method.

[Explanation of symbols]

1 Outer frame mold, 2 Powder filling layer, 3, 6 Rubber mold, 5 Core bar

Claims (2)

[Claims] Claim 1: In the isostatic pressing method of a powder compact having hollow holes, raw material powder is filled between an outer frame mold and a rubber mold placed inside the mold, and a powder-filled layer is filled with raw material powder. A method for pressure molding a powder compact, characterized by applying pressure outward from the inside of a rubber mold. 2. The method for pressure forming a powder compact according to claim 1, wherein a cylindrical compact is formed using ceramic powder as a raw material powder.