JPH058215A - Manufacture of hollow fine piece molded body - Google Patents

Abstract

PURPOSE:To manufacture efficiently and inexpensively a hollow fine piece molded body. CONSTITUTION:To prepare a mold 28 where it possesses a product cavity 30 corresponding to a form of a hollow fine piece molded body, which is to be formed, and a wall surface part of the product cavity is formed of a porous body 32. Slurry 44 is formed by being mixed up a necessary quantity of fine pieces to form a fine piece molded body having a desired thickness and a solvent comprised of a substance having the boiling point lower than the normal temperature and pressure of at least 10kg/cm<2> with each other, the slurry is introduced into the product cavity and the solvent in the product cavity is discharged outside of a molding tool through the porous body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hollow molded article composed of fine particles such as powder, whiskers and fibers.
More specifically, it relates to a method for producing a hollow fine piece molded body using a high-pressure solvent made of a substance having a boiling point lower than room temperature.

[0002]

2. Description of the Related Art As one of the methods for producing a hollow molded body made of powder such as a sintered material, a slip casting method is applied to form a slurry made of powder and water as a solvent, and the slurry is used as a gypsum mold. A method of discharging the residual slurry in the cavity when the powder is introduced into the product cavity and the thickness of the powder on the wall surface of the product cavity reaches a predetermined thickness is conventionally known.

Further, in the above method, since it is difficult to control the thickness of the wall thickness to a predetermined value, the thickness of the wall thickness can be adjusted as described in, for example, Japanese Patent Application Laid-Open No. 1-99804. A method of introducing a slurry containing a predetermined amount of powder and water necessary for obtaining a predetermined thickness into a product cavity and depositing all the powder on the wall surface of the product cavity has been conventionally known.

[0004]

However, the above-mentioned Japanese Patent Laid-Open No.
In the method described in Japanese Patent Publication No. 99804, since molding is performed by allowing water in the slurry to absorb water in a gypsum mold, it takes a long time to form a hollow powder molded body, and a liquid solvent is used. Since it is used, it is necessary to remove the solvent from the molded product by heating the molded product to a high temperature for a long time after completion of the molding, and such a solvent removal step requires a long time such as ten and several hours, and If this step is not performed under appropriate conditions, there is a problem that defects such as cracks and abnormal shrinkage are likely to occur in the molded body.

In view of the above problems in the conventional method for producing a hollow fine piece molded article, the present invention provides a method capable of efficiently and inexpensively producing a hollow fine piece shaped article. It is an object.

[0006]

According to the present invention, the object as described above has a product cavity corresponding to the shape of the hollow fine piece molding to be formed, and the wall surface of the product cavity is porous. Prepare a mold formed of a body, and substantially 10 k consisting of a quantity of fine pieces necessary for forming a hollow fine piece molded body of a desired wall thickness and a substance having a boiling point lower than room temperature
A slurry mixed with a solvent having a pressure of g / cm ² or more is formed, the slurry is introduced into the product cavity, and the solvent in the product cavity is discharged to the outside of the mold through the porous body. This is achieved by the method for producing a hollow fine piece molded body.

[0007]

According to the method of the present invention, a molding die having a product cavity corresponding to the shape of a hollow fine piece molded product to be formed and having a wall surface of the product cavity formed of a porous body is used. To form a slurry in which an amount of fine particles required to form a hollow fine particle molded body having a desired thickness and a solvent having a boiling point lower than room temperature and having a pressure of 10 kg / cm ² or more are mixed. Then, the slurry is introduced into the product cavity, and the solvent in the product cavity is discharged to the outside of the molding die through the porous body.

Therefore, the solvent to be used is a supercritical fluid maintained above the critical pressure and critical temperature of the substance constituting it, a solvent in a liquid state pressurized to a pressure of substantially above 10 kg / cm ² , and a critical Substantially 10 kg / below pressure
The high-pressure solvent in the slurry introduced into the product cavity rapidly flows out of the mold through the porous material regardless of whether it is a gaseous solvent pressurized to a pressure of cm ² or more. Since the fine pieces are attached to the wall surface of the cavity and stacked by being conveyed by the solvent, a hollow fine piece molded body having a desired thickness is efficiently formed along the wall surface of the product cavity.

Further, due to the flow resistance when the high-pressure solvent passes through the layer of the fine pieces formed on the wall surface of the cavity, the pressure of the fine pieces is substantially higher than the pressure of 10 kg / cm ² or more inside the layer of the fine pieces. A steep pressure gradient occurs where the pressure gradually decreases to the outside of the layer, and this pressure gradient presses the fine pieces against the wall of the porous body that bounds the product cavity, so that the fine pieces are densely and uniformly hollow molded. The body is formed efficiently and inexpensively.

Further, the high-pressure solvent forming the slurry is efficiently and automatically introduced into the atmosphere from the inside of the product cavity through the porous body due to the differential pressure between the pressure inside the product cavity and the pressure outside the molding die. leak. Therefore, in the process in which the hollow molded body of fine pieces is formed in the product cavity as described above, the solvent is efficiently removed from the forming body in the process of forming, whereby molding of the fine pieces and removal of the solvent proceed simultaneously. Since the solvent removing step of heating the molded body to a high temperature for a long time after the completion of molding is unnecessary, the molded body of fine pieces can be formed efficiently and at low cost.

[0011]

[Supplementary Explanation of Means for Solving the Problems] The solvent in the method of the present invention is any substance which has a boiling point lower than room temperature and which can be pressurized to a pressure of substantially 10 kg / cm ² or more. However, CO ₂ , air, N _{2 and the} like are preferable in terms of price, safety, easiness of handling and the like.

Further, when the pressure of the slurry when it is supplied to the forming die is 10 kg / cm ² or less, a rapid slurry flow necessary for forming fine pieces is formed in the product cavity of the forming die. Therefore, it is impossible to form a steep pressure gradient across the layer of fine pieces formed on the wall surface of the cavity, so that a high-density molded body cannot be efficiently formed. Therefore, in the method of the present invention, the pressure of the slurry when it is supplied to the molding die is 10 kg.
/ Cm ² or more.

[0013]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram showing one embodiment of a molding apparatus suitable for use in carrying out the method according to the present invention,
FIG. 2 is an enlarged vertical sectional view showing the molding die shown in FIG. 1 in a state during molding.

In FIG. 1, reference numeral 10 indicates a pressure vessel for storing high-pressure CO ₂ . High pressure CO ₂ is selectively supplied to the pressure vessel 10 from a cylinder (not shown) via a pump, and the temperature of CO ₂ in the pressure vessel 10 is shown in the figure. It is designed to be maintained at a predetermined temperature by a heater that is not installed.

The pressure vessel 10 is connected to a mixing tank 16 by a conduit 14 having an opening / closing valve 12 in the middle thereof. The mixing tank 16 is connected to a fine piece supply device 22 by a conduit 20 having an opening / closing valve 18 in the middle thereof. The fine piece supply device 22 is adapted to supply a predetermined amount of measured fine pieces to the mixing tank 16 via the conduit 20. Although not shown in the figure, the mixing tank 16 has a heater for maintaining the inside thereof at a predetermined temperature, and a propeller for mixing the high-pressure CO ₂ and fine particles supplied to the mixing tank with stirring to form a slurry made of them. And a stirring device such as.

The mixing tank 16 is connected to a molding die 28 by a conduit 26 having an opening / closing valve 24 on the way. As shown in detail in FIG. 2, the molding die 28 has a product cavity 30 for forming a hollow fine piece molding, and the wall surface of the product cavity is, for example, a porous ceramic having an average pore diameter of 0.2 μm. It is formed of a hollow mold 32 of half. The hollow mold 32 is supported by a support member 34 made of, for example, a porous metal having an average pore diameter of 50 μm.

In the illustrated embodiment, the product cavity 3
0 has an inverted Y shape, an end plate 36 made of solid metal is arranged at the upper end thereof, and end blocks 38 and 40 made of solid metal are arranged at the lower end of the fork, and these end plates and blocks form a product cavity. The corresponding end inside is closed. End plate 36
Defines a slurry inlet 42 for supplying the slurry into the product cavity 30.

Also, in the illustrated embodiment, the hollow mold 32 is shown at 32A and 32B, respectively.
The hollow molded body to be formed is thinly set in the region where the wall thickness is to be increased and the regions where the hollow molds are adjacent to each other, and conversely, the hollow to be formed as indicated by reference numeral 32C. It is set to be thick at the portion where the wall thickness of the molded body should be reduced.

Next, a concrete example of the method of the present invention performed by using the molding apparatus configured as described above will be described.

First, 63 g of aluminum titanate powder (average particle size 2 μm) was weighed by the fine piece supply device 22,
By opening the on-off valve 18, aluminum titanate powder was supplied into the mixing tank 16 from the fine piece supply device. The supply pressure of the CO ₂ to the figure is shown the volume from a cylinder not 10-liter high-pressure chamber 10, respectively 50 ° C. The temperature and pressure of the high pressure vessel, CO ₂ by maintaining the 450 kg / cm ² Was maintained in a supercritical state.

Next, by opening the open / close valve 12 with the open / close valves 18 and 24 closed, CO ₂ in a supercritical state is supplied from the high-pressure container 10 to the mixing tank 16 via the conduit 14, and the open / close valve 12 is opened. I closed the valve. Then, while maintaining the temperature in the mixing tank 16 at 50 ° C., an agitator (not shown) is operated to agitate and mix the aluminum titanate powder and CO _{2 in} a supercritical state for about 2 hours. Thus, a slurry of aluminum titanate powder using supercritical CO ₂ as a solvent was formed.

Next, the on-off valve 12 was opened, and about 1 second later, the on-off valve 24 was opened, whereby the slurry in the mixing tank 16 was supplied to the product cavity 30 of the molding die 28 via the conduit 26. After maintaining this state for about 10 seconds, the on-off valves 12 and 24 were closed and the molding die 28 was left as it was.

When CO ₂ did not substantially flow out from the surface of the molding die 28, the molding die was disassembled and a hollow molded body made of aluminum titanate powder formed in the product cavity was taken out. ..

Although it could not be visually observed in this case, as shown in FIG. 2, CO in a supercritical state which constitutes the slurry 44 supplied into the product cavity 30 of the molding die 28. ₂ flows out into the atmosphere through the hollow mold 32 and the supporting member 34, and the aluminum powder of titanic acid in the slurry is pressed against the wall surface of the hollow mold 32 by the flow of CO ₂ to form the powder layer 46, and the powder layer Becomes super-dense due to the pressure drop due to the differential pressure between the inside and the outside of the powder layer as it gradually increases its thickness, and finally inside the hollow mold 32 as shown in FIG. It is presumed that the hollow molded body 48 was formed with a predetermined wall thickness.

The powder compact formed as described above is 155
It was heated at 0 ° C. for 4 hours to be fired at atmospheric pressure, thereby forming a fired hollow tube. When the hollow tube thus formed was cut along the plane shown in FIG. 3 and its cross section was observed, as shown in FIG. 4, the wall thickness and density of this hollow tube 50 were substantially The thickness of the portion 50A corresponding to the thin portion 32A of the hollow die 32 is uniform, and the thickness of the portion 50C corresponding to the thick portion 32C of the hollow die 32 is larger than that of other portions. It was found that they were small and each had a desired thickness.

In the above-mentioned embodiment, the solvent is a supercritical fluid, but the temperature of the solvent is 35 ° C. and the pressure is 50 kg / cm.
² , high-pressure gaseous CO ₂ , temperature 20 ° C, pressure 100
Even when high-pressure liquid CO ₂ of kg / cm ² was used, a molded product could be formed much more efficiently than in the comparative example.

Although the present invention has been described in detail with reference to specific embodiments, the present invention is not limited to these embodiments, and various other embodiments within the scope of the present invention. It will be apparent to those skilled in the art that
For example, the fine pieces to be molded are not limited to powder as in the above-mentioned embodiment, but may be in other forms such as whiskers and short fibers.

[0029]

As is apparent from the above description, according to the present invention, the high-pressure solvent in the slurry introduced into the product cavity rapidly flows out of the molding die through the porous body to form fine particles. Since the solvent is transported by the solvent and adhered and laminated on the wall surface of the cavity, a hollow fine piece molded body having a desired thickness is efficiently formed along the wall surface of the product cavity.

Further, due to the flow resistance when the high-pressure solvent passes through the layer of the fine pieces formed on the wall surface of the cavity, the pressure of the fine pieces is substantially higher than the pressure of 10 kg / cm ² or more inside the layer of the fine pieces. A steep pressure gradient occurs where the pressure gradually decreases to the outside of the layer, and this pressure gradient presses the fine pieces against the wall of the porous body that bounds the product cavity, so that the fine pieces are densely and uniformly hollow molded. The body can be formed efficiently and inexpensively.

Further, the high-pressure solvent forming the slurry is efficiently and automatically introduced into the atmosphere from the inside of the product cavity through the porous body due to the pressure difference between the pressure inside the product cavity and the pressure outside the molding die. In the process of flowing out and forming the hollow molded body of fine pieces in the product cavity as described above, the solvent is efficiently removed from the forming body in the process of forming, thereby forming the fine pieces and removing the solvent. Since it will be done simultaneously,
A solvent removing step of heating the molded body to a high temperature for a long time after the completion of molding is unnecessary, and this also enables the molded body of fine pieces to be formed efficiently and inexpensively.

[Brief description of drawings]

1 is a schematic block diagram showing one embodiment of a molding apparatus suitable for being used for carrying out the method according to the present invention.

FIG. 2 is an enlarged vertical cross-sectional view showing the molding die shown in FIG. 1 in a state during molding.

FIG. 3 is an enlarged vertical sectional view showing a molding die and a molded body after completion of molding.

FIG. 4 is a vertical sectional view showing a hollow tube formed by firing the molded body shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Pressure vessel 16 ... Mixing tank 22 ... Fine piece supply device 28 ... Mold 30 ... Product cavity 32 ... Hollow mold 42 ... Slurry inlet 44 ... Slurry 46 ... Powder layer 48 ... Hollow molded body 50 ... Hollow tube

Claims (1)

What is claimed is: 1. A molding die having a product cavity corresponding to the shape of a hollow fine piece molded product to be formed and having a wall surface of the product cavity formed of a porous body is prepared, and a desired meat is prepared. Forming a slurry in which a sufficient amount of fine particles for forming a thick hollow fine particle molded body and a solvent having a boiling point lower than room temperature and having a pressure of substantially 10 kg / cm ² or more are mixed, A method for producing a hollow fine piece molded body, wherein the slurry is introduced into the product cavity, and the solvent in the product cavity is discharged to the outside of the molding die through the porous body.