JPH05404A - Method and apparatus for molding fine pieces - Google Patents

Abstract

(57) [Summary] [Purpose] To reliably supply a predetermined amount of fine particles to the product cavity without excess or deficiency. [Structure] A mold 28 having a product cavity 36, an inlet 30 and a discharge passage 38 communicating with the product cavity 36, a mixing tank 10, and the mixing tank and the inlet are connected in communication with each other, and the on-off valve 2
2 and a passage means 26 having a molding device. While introducing the slurry consisting of the solvent and fine pieces stored in the mixing tank into the cavity through the inlet, the solvent in the slurry is discharged from the mold through the discharge passage, and the pressure between the cavity and the on-off valve. The on-off valve is closed when the value reaches the predetermined value. The molding apparatus has a pressure gauge 42 that detects the pressure between the cavity and the on-off valve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for molding fine particles such as powders, whiskers and fibers, and more particularly to the use of a high pressure solvent composed of a substance having a boiling point lower than room temperature. The present invention relates to a method for molding a resin and a molding apparatus used for carrying out the method.

[0002]

2. Description of the Related Art As one of methods for forming fine pieces, for example, Japanese Patent Application No. 3-8 filed by the same applicant as the present applicant.
3613 specification and drawings, a mold having a product cavity, an inlet communicating with the cavity and a discharge passage is prepared, and fine particles to be molded are mixed with a supercritical fluid to form a slurry, There has already been proposed a method for molding fine pieces in which a supercritical fluid in the slurry is discharged from the mold through a discharge passage while introducing the slurry into the cavity through the inlet.

According to this method, the fine pieces to be molded are mixed with a supercritical fluid to form a slurry, and the slurry is introduced into the product cavity through the introduction port of the molding die. Causes a steep pressure gradient in which the pressure gradually decreases from a pressure substantially higher than the critical pressure in the vicinity of the inlet to a pressure near the atmospheric pressure in the vicinity of the discharge passage. Since the supercritical fluid as a solvent is automatically removed from the molded body as a normal gas as well as when a molded body is formed, a liquid solvent is used and the step of molding the fine pieces and the step of removing the solvent are performed. Compared with the case of the conventional molding method performed as an independent process,
It is possible to manufacture a highly pure, high-density and homogeneous molded body much more efficiently and cheaply.

[0004]

However, the method according to the above-mentioned proposal has a mold having a product cavity, an inlet and a discharge passage communicating with the cavity, and a slurry having a volume larger than that of the cavity and storing the slurry therein. When a molding apparatus having a mixing tank (pressure vessel) and a conduit having the mixing tank and the inlet connected in communication and having an opening / closing valve in the middle is used to form a plurality of molded bodies continuously In the case where the on-off valve is not closed at an appropriate time after the on-off valve is opened and the supply of the slurry to the cavity is started,
The amount of fine particles supplied to the cavity becomes excessive or insufficient. In the former case, fine particles are also filled in the conduit, and in the worst case, the on-off valve cannot be opened and closed. In the latter case, the fine particles are insufficiently filled due to insufficient filling of fine particles. No molded body can be obtained.

Further, since the pressure of the slurry and the density of fine particles in the mixing tank gradually decrease each time molding is performed, the opening / closing valve is opened and the slurry is supplied to the cavity at a predetermined constant level. The problem described above cannot be solved by closing the on-off valve at the stage when the time has elapsed.

Further, in the case of forming a molded body in which the size and shape of the product cavity are different, formal molding is performed in order to obtain an appropriate time from the time when the supply of the slurry is started to the time when the on-off valve is closed. Prior to this, trial molding must be performed several times, so that it is not possible to easily and efficiently form a plurality of compacts having different sizes and shapes.

The above-mentioned problems are not limited to the case where a supercritical fluid is used as a solvent, and, for example, Japanese Patent Application No. 3-472 (reference number AT-4722) and application filed by the same applicant as the present applicant. As described in the specification and drawings of Japanese Patent Application No. 3-420 (Reference No. AT-4720), it consists of a substance whose boiling point is lower than room temperature and is substantially 1
Substantially 10 kg / c at a solvent in a liquid state pressurized to a pressure of 0 kg / cm ² or more and at a critical temperature and a critical pressure or less
It also occurs when a gaseous solvent pressurized to a pressure of m ² or higher is used.

In view of the above-mentioned problems in the method according to the above-mentioned proposal, the present invention ensures a predetermined amount of fine particles regardless of the size and shape of the fine piece molded body to be formed. It is an object of the present invention to provide an improved method and a mold for forming fine pieces so that the pieces can be supplied to a product cavity.

[0009]

According to the present invention, the above-mentioned object is to provide a mold having a product cavity, an inlet and a discharge passage communicating with the cavity, a mixing tank, the mixing tank, and the mixing tank. Prepare a molding device having a passage means having an on-off valve in communication with the inlet, and mixing the slurry in which a solvent made of a substance having a boiling point lower than room temperature and fine particles to be molded are mixed. The slurry is stored in a tank, and while detecting the pressure in the inlet or the passage means between the cavity and the opening / closing valve, the slurry is passed through the inlet at a pressure of substantially 10 kg / cm ² or more. The solvent in the slurry is discharged to the outside of the mold through the discharge passage while being introduced into the cavity, and when the detected pressure reaches a predetermined value, molding of a fine piece is performed to close the on-off valve. Method, And a mold having a product cavity, an inlet and a discharge passage communicating with the cavity, a mixing tank, a passage means for connecting the mixing tank and the inlet to each other and having an opening / closing valve in the middle, and the inside of the inlet. Or a pressure detecting means for detecting the pressure in the passage means between the inlet and the opening / closing valve.

[0010]

According to the method of the present invention, a mold having a product cavity, an inlet and a discharge passage communicating with the cavity, a mixing tank, and the mixing tank and the inlet are connected in communication, and an on-off valve is provided on the way. A molding apparatus having a passage means having is prepared, and a slurry in which a solvent composed of a substance having a boiling point lower than room temperature and fine particles to be molded are mixed is stored in a mixing tank, and the pressure in the inlet or the inlet When the pressure in the passage means between the switch and the on-off valve is detected, the slurry is substantially 1
The solvent is discharged from the mold through the discharge passage while being introduced into the product cavity through the inlet at a pressure of 0 kg / cm ² or more, and the open / close valve is closed when the detected pressure reaches a predetermined value. Be spoken.

When the fine pieces are filled up to the upstream side of the site where the pressure is detected in the inlet or the passage means, the pressure drops due to the pressure of the fine pieces filled up to the upstream side of the site where the pressure is detected. Is substantially atmospheric pressure. Therefore, by closing the opening / closing valve when the detected pressure reaches a predetermined value, for example, substantially atmospheric pressure or close thereto, it is possible to reliably supply the predetermined amount of fine particles to the product cavity without excess or deficiency. Will be possible.

Further, according to the molding die of the present invention, since the pressure detecting means for detecting the pressure in the inlet or the pressure in the passage means between the inlet and the on-off valve is provided, the inlet or passage means is provided. It is possible to reliably detect that the fine pieces are filled up to the upstream side of the site where the pressure is detected, and thus the above method can be easily and surely performed.

The solvent used is a supercritical fluid, a solvent whose boiling point is lower than room temperature, and which is a liquid solvent pressurized to a pressure of 10 kg / cm ² or more. Regardless of whether the solvent is a gaseous solvent pressurized to a pressure of 10 kg / cm ² or more, the cavity is closer to the discharge passage than a pressure of 10 kg / cm ² or more in the vicinity of the inlet. There is a steep pressure gradient where the pressure gradually decreases to a pressure close to the atmospheric pressure, and this pressure gradient causes fine particles to be pressed against the wall surface of the part near the discharge passage of the product cavity, and finally to the inlet port. Since this phenomenon progresses rapidly after being molded, a high-density and homogeneous molded body of fine pieces can be efficiently and inexpensively formed.

Further, the high-pressure solvent constituting the slurry rapidly lowers its pressure in the process of passing through the product cavity and the discharge passage, and due to the pressure gradient, it efficiently flows through the discharge passage from the inside of the product cavity. Outflow into the atmosphere. Therefore, in the process of forming the molded product of the fine pieces in the product cavity as described above, the solvent is efficiently removed from the molded product in the process of being formed, whereby the molding of the minute pieces and the removal of the solvent are simultaneously performed. Since this is also performed, the molded body of fine pieces can be formed efficiently and at low cost.

[0015]

[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 can be pressurized to a pressure of substantially 10 kg / cm ² or more. Although it may be present, CO ₂ , air, N _2, etc. are preferable from the viewpoints of price, safety, easiness of handling and the like.

Further, when the pressure of the slurry when being supplied to the forming die is 10 kg / cm ² or less, a steep pressure gradient required for forming fine pieces can be formed in the product cavity of the forming die. Therefore, it is impossible to efficiently form a high-density molded body. Therefore, in the method of the present invention, the pressure of the slurry when it is supplied to the mold is 1
It is set to 0 kg / cm ² or more.

The present invention will be described in detail below with reference to the accompanying drawings.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram showing one embodiment of a molding apparatus according to the present invention.

In FIG. 1, 10 indicates a mixing tank,
Although not shown in the figure, the mixing chamber 12 of the mixing tank is connected by a conduit 14 to a cylinder for storing CO ₂ therein. Further, the mixing chamber 12 is heated to a predetermined temperature by a heater 16, and an agitator 20 is provided in the mixing chamber 12 for agitating the fine pieces 18 to be molded which are loaded in the mixing chamber 12. Has been.

The mixing chamber 12 is connected to a slurry inlet 30 of a molding die 28 by a conduit 26 having an opening / closing valve 22 and a pump 24 on the way. In the illustrated embodiment,
The molding die 28 is composed of an upper die 32 and a lower die 34, and when fitted together, defines a slurry inlet 30 and a product cavity 36 communicating with the inlet. The product cavity 36 communicates with the atmosphere through a minute gas discharge passage 38 formed as a minute gap between the parting surfaces of the upper mold 32 and the lower mold 34. Further, in the illustrated embodiment, the forming die 28 is provided with an inlet 30 through a passage 40.
A pressure gauge 42 for detecting the internal pressure is provided.

Next, one embodiment of the molding method of the present invention performed by using the molding apparatus formed as described above will be described.

According to the present invention, a powder compact mainly composed of silicon nitride powder was formed by using CO ₂ in a supercritical state as a solvent and using the molding apparatus formed as described above.

First, a raw material powder consisting of 9.6 kg of silicon nitride powder (average particle size 0.5 μm), 200 g of yttrium oxide (average particle size 0.1 μm) and 200 g of alumina powder (average particle size 0.1 μm). 18 was loaded into the mixing chamber 12 of the mixing tank 10. Then, with the on-off valve 22 closed, CO ₂ 15 is supplied into the mixing chamber 12 from the cylinder (not shown) via the conduit 14 while pressurizing by a pump (not shown). 16 temperature 80 ° C. the CO ₂ by heating the CO ₂ by, brought to a supercritical state of the pressure 120 kg / cm ^2.

Next, the stirrer 20 is rotated for 3 hours to stir and mix the raw material powder and CO _{2 in a} supercritical state,
This formed a slurry of raw material powder using CO ₂ in a supercritical state as a solvent. Next, by opening the on-off valve 22 and operating the pump 24, a part of the slurry in the mixing chamber 20 was pressurized to 300 kg / cm ² and injected into the product cavity 36 of the molding die 28. The indication value of the pressure gauge 42 was about 300 kg / cm ² at the start of the injection of the slurry, but at the stage when the indication value of the pressure gauge became substantially atmospheric pressure, the on-off valve 22 was closed and the pump 24 And stirrer 20 was stopped.

Although not visually observable in this case, the supercritical CO ₂ in the slurry introduced into the product cavity 36 is communicated with the atmosphere by the gas discharge passage 38. Therefore, it is presumed that the pressure was gradually decreased in the cavity, and the gas became substantially atmospheric pressure from the supercritical state and was released into the atmosphere. Further, in the product cavity 36, a pressure gradient occurs in which the pressure gradually decreases from the vicinity of the slurry introduction port 30 toward the gas discharge passage, and this pressure gradient causes the raw material powder to be in a portion near the gas discharge passage of the molding die. It is speculated that it was gradually pressed while being pressed against the inner wall surface.

Next, the molding die 28 is disassembled, and the powder compact 44 molded in the product cavity 36 is taken out and its size, shape and density are investigated. It was confirmed that it had a corresponding exact size and shape, had a uniform density throughout, and had no defects such as shrinkage or cracking.
It was also confirmed that the raw material powder was filled up to the connection between the inlet 30 of the molding die 28 and the conduit 26.

It is to be noted that CO _{2 in} a liquid state pressurized to 100 kg / cm ² is used as a solvent, and a part of the slurry is added to 200
Product cavity 3 of mold 28 by pressurizing to kg / cm ^2.
When injected into 6 and as solvent 15 kg / cm ²
The raw material powder can be similarly satisfactorily molded even when a part of the slurry is pressurized to 60 kg / cm ² and injected into the product cavity of the mold using CO _{2 in} a gaseous state pressurized to It was

As in the case of the above-mentioned embodiment, in the former case, the liquid state CO ₂ in the slurry introduced into the product cavity gradually lowers its pressure in the cavity and becomes a gas which is more normal than the liquid state. It is presumed that the gas is released into the atmosphere in the state of the state. In the latter case, the high-pressure gaseous CO ₂ in the slurry introduced into the product cavity gradually lowers its pressure in the cavity, It is presumed that the gas state was substantially atmospheric pressure and was released into the atmosphere.

In the above-described embodiment, the pressure gauge 42 is provided on the molding die 28. However, as shown in FIG. 2, the pressure gauge 42 is provided between the on-off valve 22 and the molding die by the conduit 26. In particular, when the pump 24 is provided as in the illustrated embodiment, the pressure gauge is provided in the conduit 26 between the pump 24 and the mold 28 and as close to the mold as possible. Preferably.

Further, the on-off valve 22 is automatically closed when the detection value of the pressure gauge reaches a predetermined value by a control device (not shown) which responds to the detection result of the pressure gauge 42. It may be configured.

Further, regardless of whether or not a plurality of molded bodies to be formed have the same size and shape, a molding die in which fine pieces are filled in the product cavity when the on-off valve 22 is closed. May be removed from the conduit 26, and the molds to be filled next may be connected to the conduit in sequence to produce a plurality of molded bodies even more efficiently.

Although the present invention has been described in detail above with reference to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art that it is possible. 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.

[0033]

As is apparent from the above description, according to the molding method of the present invention, when the fine pieces are filled up to the upstream side of the site where the pressure is detected in the inlet or the passage means, Since the pressure of the portion where the pressure is detected due to the pressure drop due to the fine pieces filled on the upstream side of the portion where is detected is substantially atmospheric pressure, the detected pressure is, for example, substantially atmospheric pressure or it. By closing the on-off valve at the stage when the value reaches a near predetermined value, it is possible to reliably supply a predetermined amount of fine particles to the product cavity without excess or deficiency, and thus it becomes impossible to open and close the on-off valve. It is possible to reliably avoid that the molded body does not have a predetermined shape.

Further, according to the molding apparatus of the present invention, since the pressure detecting means for detecting the pressure in the inlet or the pressure in the passage means between the inlet and the on-off valve is provided, the inlet or passage means is provided. It is possible to reliably detect that the fine pieces are filled up to the upstream side of the portion where the pressure inside is detected,
This makes it possible to carry out the above method easily and reliably.

Further, according to the molding method and the molding apparatus of the present invention, it is possible to surely supply a predetermined amount of fine pieces to the product cavity without excess or deficiency, so that the yield of the fine pieces and the solvent can be improved, Further, even when a plurality of molded products having different sizes and shapes of product cavities are formed one after another, the molding can be easily and efficiently performed without performing trial molding.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a molding apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram similar to FIG. 1, showing another embodiment of the molding apparatus according to the present invention.

[Explanation of symbols]

10 ... Mixing tank 15 ... CO ₂ 18 ... Raw powder 20 ... Stirrer 28 ... Mold 30 ... Slurry inlet 36 ... Product cavity 38 ... Gas discharge passage 42 ... Pressure gauge 44 ... Powder compact

Claims (2)

[Claims] 1. A molding die having a product cavity, an inlet and a discharge passage communicating with the cavity, a mixing tank, and a passage means having an opening / closing valve in communication between the mixing tank and the inlet. A molding apparatus having a boiling point is stored in the mixing tank, and a slurry in which a solvent made of a substance having a boiling point lower than room temperature and fine particles to be molded are mixed is stored between the cavity and the on-off valve. While detecting the pressure in the inlet or the passage means, while introducing the slurry into the cavity through the inlet at a pressure of 10 kg / cm ² or more, the solvent in the slurry is discharged through the discharge passage. A method for molding a fine piece, wherein the opening / closing valve is closed at a stage when the pressure detected is further discharged from the molding die and the detected pressure reaches a predetermined value. 2. A molding die having a product cavity, an inlet and a discharge passage communicating with the cavity, a mixing tank, and a passage means having an opening / closing valve in the middle of connecting the mixing tank and the inlet. A molding device having pressure detecting means for detecting the pressure in the inlet or the pressure in the passage means between the inlet and the on-off valve.