JPH10180492A - Method and device for packing powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To pack powder into a forming mold quickly, highly densely and also uniformly by throwing in a prescribed amount of powder in a forming mold, forming an airtight space of a prescribed capacity, and repeatedly imparting decompression and release of inner pressure to this airtight space in a high speed cycle. SOLUTION: With a forming mold 3 set in a die 2, the guide cylinder 12 of a cover body 5 and a seal reinforcing frame 8 are combined on top of the die so set. The forming mold 3 is formed along the inner shape of the die 2 by actuating a mold straightening means 9. A prescribed amount of a scaled powder is thrown in from above the guide cylinder 12 to the forming mold 3. The powder fills the molded recess 3a of the forming mold 3, and also is laminated into the guide cylinder 12. A cover part 13 is placed and fixed on the guide cylinder 12 to form an airtight space 6 facing the forming mold 3. Using a pressure tapping means 7, decompression and release of the internal pressure are repeated to the airtight space 6 in a high speed cycle. A high density packing is performed by tapping at a low decompression degree initially and at a higher degree successively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for obtaining a molded product using a powder having poor fluidity such as a metal powder and a ceramic powder, and quickly transferring the powder to a molding die such as a mold or a rubber mold. The present invention also relates to a powder filling method and a powder filling apparatus capable of performing a uniform filling density.

[0002]

2. Description of the Related Art In powder molding, it is preferable to fill a molding die with powder at high density and uniform density.
Isotropic molding using a rubber mold exerts its features on long products and the like, but has a problem with a filling device. By the way, as a method of filling powder into a molding die, the method most commonly called a grinding method is the most common when the molding die is a mold. In this method, the powder is put into a powdery box with a frame shape that is open at the top and bottom, and the powder is reciprocated on a molding die. It is to fill with density.

[0003] However, since the filling cannot be performed at a high density, the displacement of the compression molding is increased, which causes cracks in the molded product and a decrease in dimensional accuracy. When the molding die is a rubber die, there are problems in that the rubber die is worn in a relatively short time due to passing contact with the powder supply box and that the sliding resistance between the powder and the rubber die is large. The adoption of the cutting method is not suitable.

Therefore, in such a case, it has been studied to employ various powder filling methods such as a pusher pushing method, a mechanical tapping method, a division filling method, and a vacuum breaking method instead of the grinding method. All of these powder filling methods are the same up to the point where a guide cylinder is provided on the molding die and the powder is dropped from the upper part of the guide cylinder, and the subsequent processes are individually different as follows. ing.

In the pusher pushing method, after the powder is dropped and charged, the pusher is lowered into a guide cylinder, and the powder filling surface is pressed flat by the pusher. In the mechanical tapping method, mechanical vibration is propagated to a mold after dropping of a powder. In the case of the divided filling method, a pusher pushing method, that is, a combination of powder drop-in and pusher pressing is repeatedly performed several times for a certain filling depth.

In the vacuum breaking method, after the powder is dropped in, the inside of the guide cylinder is depressurized, and then the upper part of the cylinder is opened to return the inside of the guide cylinder to atmospheric pressure at a stretch.

[0007]

The pusher push-in method has a drawback that it is difficult to exhaust gas contained in the powder quickly and reliably when the pusher is pressed, so that the exhaust filter provided on the apparatus side is difficult. In addition, the dimensional accuracy of the molded product is reduced due to the uneven packing density generated when the gas in the powder is discharged.

[0008] The mechanical tapping method has a disadvantage that the apparatus is complicated and large. Further, there is also a problem that the mechanical vibration transmitted to the mold die holding the molding die is attenuated by the rubber mold, and the effectiveness is reduced. Although the split filling method has an advantage that each of the drawbacks seen in the pusher pushing method can be improved to some extent, it has a new drawback that it takes a long time to fill the powder and it is difficult to control the splitting operation.

[0009] In the vacuum breaking method, it is important whether or not the release to the atmospheric pressure can be performed instantaneously.
The more the conditions are satisfied, the more the powder spills due to outgassing at unspecified positions of the filling powder, and there is a problem that defects such as cracks and chips are more likely to occur in the molded body. The present invention
In view of the above circumstances, powder filling has been made so that the filling of the powder into the mold can be performed quickly, with high density and uniform filling density, regardless of whether or not a rubber mold is used as the mold. It is an object to provide a method and a powder filling device.

[0010]

According to the present invention, the following technical measures have been taken in order to achieve the above object. That is, in the powder filling method according to the present invention, after a predetermined amount of powder is charged into a molding die, an airtight space having a predetermined capacity is formed in the molding die so as to include the powder filling portion. Then, the pressure reduction and the internal pressure release are repeated in this airtight space at a high speed cycle.

If the depressurization and the internal pressure release are repeated in a high-speed cycle as described above, unlike the pusher pushing method, the gas can be exhausted from the powder without difficulty and without fail. No problem arises. In addition, unlike the divided filling method, it does not take too much time to fill the powder. In the vacuum breaking method in which the pressure is released to the atmospheric pressure at a stretch and instantaneously, the pressure difference at the time of releasing the internal pressure is small, so that there is no occurrence of a defect due to outgassing in the molded product.

[0012] Furthermore, if the method of tapping the powder by utilizing such pressure fluctuations is used, unlike the case where vibration is transmitted to the powder in the rubber mold by the mechanical tapping method, the powder is reliably applied to the powder. Vibration can be transmitted. In addition, the degree of decompression during decompression in each tapping operation in one cycle, the decompression speed, the internal pressure release speed, the number of tappings (the number of alternations between decompression and internal pressure release), and the like are determined by the flow characteristics of the powder and the size of the molding recess in the mold. Various changes can be made according to the shape and the like.

[0013] After performing a process of alternating between decompression and internal pressure release for a predetermined time, the pusher is advanced toward the molding die so that the powder filling surface is leveled flat so as to match the upper surface of the molding die. It is preferable because the surface roughness of the upper surface of the body can be improved, and the powder can be surely spread to every corner of the formed concave portion to prevent chipping of the edge of the formed body.

The present invention is not limited to the case where the mold is a rubber mold, but only when the rubber mold is used, at least during the replacement process between the pressure reduction and the internal pressure release, It is more preferable to reduce the pressure between the circumference of the surrounding die and the mold to correct the mold to a predetermined shape in order to increase the dimensional accuracy of the molded product. On the other hand, in the powder filling apparatus according to the present invention, in order to form an airtight space above the molding die held in the die,
A cover body is provided on the mold as needed.
In addition, the cover body is provided with a pressure tapping unit that repeats pressure reduction and internal pressure release in a high-speed cycle.

With this configuration, unlike the mechanical tapping method, there is no need to actively transmit mechanical vibration to the die, lower punch, and molding die, and peripheral equipment for these components is not required. On the other hand, since there is no need to employ a vibration blocking structure, there is an advantage that the structure is simple and small. If the cover body has a guide cylinder portion for guiding the dropping of the powder and a lid body portion for covering the upper portion of the guide cylinder portion, when the powder is charged, the molding die or the die is It is possible to attach and detach only the lid. Therefore, the structure can be further simplified. In this case, the pusher may be provided on the lid.

When the mold is a rubber mold and the pressure between the inner peripheral surface of the mold die and the outer peripheral surface of the mold is reduced to correct the mold to a predetermined shape, the cover is joined to the upper part of the mold. so,
A seal reinforcing frame is provided around the cover body, and a mold correcting means capable of reducing the pressure between the inner peripheral surface of the die and the outer peripheral surface of the molding die is provided for the seal reinforcing frame. Compared to providing a passage structure for decompression in the mold die itself, it is preferable for enhancing the decompression effect and simplifying the structure.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a powder filling apparatus 1 according to the present invention. The powder filling apparatus 1 includes a mold die 2 having a virtual cylinder-shaped mold insertion space 2a therein, and a mold insert of the mold die 2. Mold 3 held in space 2a
A lower punch 4 provided in the mold die 2 to support the molding die 3; and a lower punch 4 provided to cover the upper portion of the molding die 3 when the molding die 3 is held in the mold die 2. And an inverted cup-shaped cover body 5.

By providing the cover body 5 above the molding die 3, an airtight space 6 is formed above the molding die 3. The cover body 5 is provided with a pressure tapping means 7. In addition, in the powder filling apparatus 1, when the cover body 5 is coupled to the upper part of the molding die 3, a seal reinforcing frame 8 is provided around the cover body 5. The seal reinforcing frame 8 is provided with a mold correcting means 9.

The molding die 3 is a rubber die. In this molding die 3, the outer shape is a molding space 2 a of the die 2.
However, the molded concave portion 3a formed therein has a shape corresponding to a desired outer shape, such as molded products A and B as shown in FIGS. 3 and 4, for example. ing. The cover body 5 has a lower guide cylinder 12 and a lid 13 that covers the upper part of the guide cylinder 12. A pusher 14 is provided on the back side of the cover 13 (inside the guide tube 12) of the cover 5.

The guide tube portion 12 is attached to and detached from the mold die 2 and the mold 3 when the mold 3 is attached to and detached from the mold die 2 or when the molded product is taken out from the mold 3. . Further, the lid 13 is used for the guide cylinder 1 when the powder is dropped into the molding die 3 via the guide cylinder 12.
Attach and detach from 2. The inner surface of the guide tube portion 12 is provided with a downwardly tapered taper for smoothly dropping and feeding the powder. The outer diameter of the guide cylinder 12 is
Are set to be smaller than the outer diameter and outside the inner peripheral surface of the molding concave portion 3a, and the inner diameter of the guide cylindrical portion 12 is set to enter inside the inner peripheral surface of the molding concave portion 3a. . The contact between the lower surface of the guide cylinder 12 and the upper surface of the molding die 3 is performed such that the guide cylinder 12
A sealing material such as a sponge is attached to the lower surface of.

The pusher 14 is provided at the lower end of the plunger 16 provided through the cover 13. Since the plunger 16 can be moved up and down by an appropriate lifting drive mechanism (not shown), the pusher 14 can pass through the inside of the guide cylinder 12 and move back and forth between the upper surface of the mold 3. Has become.

The lid 13 is provided with an air passage 18 communicating with the inside and outside through the upper surface thereof. This ventilation path 1
The pressure tapping means 7 described above is connected to the air piping 8 by air. The air passages 18 are provided at several locations on the same circumference on the upper surface of the lid 13 so that the pressure reduction and the internal pressure release to the airtight space 6 can be performed uniformly and instantaneously. The pressure tapping means 7 is constituted by a decompressor, a vacuum generator, and the like. The pressure tapping means 7 is capable of depressurizing the airtight space 6 formed in the cover body 5. A switching valve (not shown) capable of alternately switching between depressurization and internal pressure release of the hermetic space 6 at a high speed is provided at an appropriate position.

The seal reinforcing frame 8 has a ring shape capable of airtightly surrounding the guide tube portion 12 of the cover body 5, and the lower surface near the outer periphery can be airtightly coupled to the upper peripheral surface of the die 2. It has become. Accordingly, the seal reinforcing frame 8 covers the circumferential gap between the upper inner peripheral surface of the die 2 and the upper outer peripheral surface of the molding die 3. The seal reinforcing frame 8 is formed on the lower surface thereof with a concave portion having a diameter larger than that of the guide tube portion 12 of the cover body 5, and this concave portion forms an annular shape with the outer peripheral surface of the guide tube portion 12. The reduced pressure path 20 is formed. The decompression path 20 has a communication relationship with a peripheral gap between the upper inner peripheral surface of the die 2 and the upper outer peripheral surface of the molding die 3.

The seal reinforcing frame 8 is provided with a ventilation path 21 for guiding the pressure reduction path 20 to the outer peripheral side. The mold correcting means 9 described above is connected to the ventilation path 21 with an air pipe. The mold correction means 9 is constituted by a decompressor, a vacuum generator, and the like. Therefore, the pressure between the inner peripheral surface of the mold die 2 and the outer peripheral surface of the molding die 3 can be reduced through the ventilation path 21 and the decompression path 20.

In order to obtain a molded article having a hollow shape as shown in FIG. 4, a powder filling apparatus 1 as shown in FIG. 2 is used. In this powder filling apparatus 1, a mandrel 23 that rises through the inside of the molding die 3 protrudes from the lower punch 4 provided in the mold die 2, whereas a pusher 14 provided on the cover body 5 has A downward concave portion 24 for escaping interference with the mandrel 23 is formed.

Next, a method for filling the molding die 3 with the powder using the powder filling apparatus 1 having the above-described configuration will be described. First, the molding die 3 is set on the die 2, and the upper part of the guide cylinder 12 of the cover body 5 and the seal reinforcing frame 8 are coupled thereto. Then, the mold correcting means 9 is operated to form the molding die 3 along the inner shape of the die 2. At this time, the degree of decompression by the mold correcting means 9 is set to be higher than the maximum decompression degree of the depressurization tapping operation, though it depends on the rubber hardness and the thickness of the molding die 3.

Next, the molding die 3 is placed from above the guide cylinder 12.
A predetermined amount of powder weighed in advance is dropped into the container. The powder is filled up to the inside of the guide cylinder 12 after filling the molding recess 3 a of the molding die 3. In addition, even if the lamination state of the powder at this time is a heaping shape,
In addition, the peak may be uneven or flat. The stacking height of the powder is governed by the desired packing density and powder characteristics, but it is necessary that the height does not exceed the intermediate height of the guide cylinder 12.

Next, a lid 13 is provided above the guide cylinder 12.
To form an airtight space 6 facing the mold 3. Then, the pressure tapping means 7 is operated, and the pressure reduction and the internal pressure release to the airtight space 6 are repeated at a high speed cycle. High-density filling is facilitated by lowering the pressure at the initial stage of tapping and tapping at a higher pressure in order.

In this way, the powder in the guide cylinder 12 falls to near the upper surface of the molding die 3, and the powder has a high density and a filling density up to every corner in the molding recess 3 a of the molding die 3. Are uniformly filled. At this time, the degree of decompression, the decompression speed, the internal pressure release speed, the number of tappings, and the like are determined by the flow characteristics of the powder and the size of the molding recess 3a in the molding die 3,
Various changes can be made according to the shape and the like. The flow characteristics of the powder depend on the particle shape, particle size, particle size distribution, the presence or absence of a flow aid and its addition amount, the true density of the particles, the surface adsorbability and the like.

There is a tendency that when a molded article having a height of about 70 mm is manufactured and the particle size of the powder is 10 μm or less, the degree of decompression is set to 30 to 45 cmHg and tapping during one cycle is performed. It is preferable to determine the number of times within a range of 3 to 20 times. The packing density can be increased as the degree of decompression is increased and the closer to the vacuum, the more the packing density can be increased.On the other hand, at the time of depressurization, layer cracks and gas vent holes are generated in the powder filling layer. There is an adverse effect that makes it easier. To prevent this, conditions such as sequentially increasing the degree of pressure reduction are adopted, but care must be taken since this leads to a wrinkle defect as a molded product, a decrease in surface roughness, and the like.

After performing the alternation process between the pressure reduction and the internal pressure release for a predetermined time, the pusher 14 is lowered so as to coincide with the upper surface of the molding die 3, and the powder filling surface is pressed and leveled.
It is selected whether the lowering of the pusher 14 is performed under reduced pressure or under internal pressure release according to conditions such as powder fluidity. afterwards,
Full-scale compression and pressurization to obtain molded products. After that, the guide tube portion 12 is removed from the mold 3 and the molded product is taken out, and the molded product may be sintered or the like.

[0032]

(Experiment 1) A fan-shaped molded product A shown in FIG. 3 was manufactured using the powder filling apparatus 1 shown in FIG. The inside cross-sectional area of the mold is 11.3 cm ² and the height is 70 mm. The powder is
A metal powder having a maximum particle size of 5 μm for a magnetic material was used.

After setting the filling density to 35%, filling was carried out by changing the degree of pressure reduction, cycle time and the number of tappings in one cycle variously as shown in Table 1. Then, compression molding was performed isotropically at a molding pressure of 600 kg / cm ² . Whether the filling result is good or bad
A method in which the maximum width dimension W of the molded product A is measured at three positions, that is, an upper position, a middle position, and a lower position, and is compared with the corresponding dimension of the molding recess 3a of the molding die 3 in a non-compressed state. I went in. The corresponding portion dimensions in the molding die 3 were the same in the upper part, the middle part, and the lower part, and were 54.3 mm.

[0034]

[Table 1]

In Experiment 1, when the degree of decompression was set to 40 cmHg, the decompression time was set to 0.4 seconds, and the number of tappings in one cycle was set to 10 (test number 3), the molded product A
Of the maximum width dimension W was within ± 0.3 mm, which was the best result. At this time, the pressure release time is
0.2 seconds, and the total time required for the reduced pressure tapping operation was 6 seconds.

(Experiment 2) A cylindrical molded product B shown in FIG. 4 was manufactured using the powder filling apparatus 1 shown in FIG. The inner cross-sectional area of the mold is 9.4 cm ² and the height is 70 mm. As the powder, a metal powder having a maximum particle size of 5 μm for a magnetic material was used.

After setting the filling density to be 33%, filling was carried out by changing the degree of pressure reduction, cycle time and the number of tappings in one cycle variously as shown in Table 2. Then, compression molding was performed isotropically at a molding pressure of 400 kg / cm ² . Whether the filling result is good or bad
The outer diameter D of the molded product B is measured at three positions: an upper position, a middle position, and a lower position.
The method was performed by a method of comparing with the corresponding portion dimensions in the molding concave portion 3a. The corresponding portion size in the molding die 3 was the same in the upper portion, the middle portion, and the lower portion, and was 40 mm. For reference, the outer diameter of the mandrel 23 is 20 m.
m.

[0038]

[Table 2]

In Experiment 2, when the degree of decompression was set to 35 cmHg, the decompression time was set to 0.4 seconds, and the number of tappings in one cycle was set to 10 (test number 3), the molded product B
The variation of the outer diameter dimension D is within ± 0.3 mm,
It was the most successful. In Experiment 2, since the number of tappings was fixed to 10, it was considered that the powder moved downward as the degree of decompression was increased and the decompression time was increased.

The present invention is not limited to the above embodiment. For example, the mold 3 is not limited to a rubber mold, but may be a mold. In the case of a mold, by enabling high-density powder filling, the amount of compression during molding can be reduced, leading to a reduction in density distribution, and the advantage of preventing cracking, warping, deformation, and the like during sintering can be obtained.

The outer shape of the molding die 3 is not limited to a cylindrical shape. Powder material,
The treatment after molding and the shape of the molded article are not limited at all.

[0042]

As is apparent from the above description, in the powder filling method and the powder filling apparatus according to the present invention, an airtight space is formed facing the mold into which the powder has been charged, and the airtight space is depressurized. And the internal pressure release are repeated in a high-speed cycle, so that the vibration can be transmitted to the powder with certainty and high efficiency, the gas in the powder can be easily vented, and there is no accompanying defect.

The time required for filling the powder is
While the most efficient method required 30 seconds, the present invention was able to reduce it to 15 seconds or less. Furthermore, the dimensional accuracy of the molded product obtained after filling has a variation of ±
In contrast to about 1.0 mm, in the present invention, ± 0.3 m
m or less.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a powder filling device according to the present invention.

FIG. 2 is a front sectional view showing a powder filling apparatus for obtaining a hollow molded article.

FIG. 3 is a perspective view showing a molded product obtained by the powder filling device of FIG.

FIG. 4 is a perspective view showing a molded product obtained by the powder filling device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Powder filling device 2 Die 3 Mold 4 Lower punch 5 Cover body 6 Airtight space 7 Pressure tapping means 8 Seal reinforcement frame 9 Die correction means 12 Guide cylinder part 13 Cover part 14 Pusher

Claims (6)

[Claims] 1. A predetermined amount of powder is poured into a molding die (3), and a hermetic space (6) having a predetermined volume is formed facing the molding die (3). A powder filling method characterized by repeating a high-speed cycle of reducing pressure and releasing internal pressure. 2. After a predetermined period of time between the pressure reduction and the internal pressure release, a pusher (14) is advanced toward the molding die (3) so that the powder filling surface coincides with the upper surface of the molding die (3). The powder filling method according to claim 1, wherein the powder is leveled. 3. A mold in which the molding die (3) is a rubber mold, wherein the molding die (3) and the molding die (3) are fitted and held at least during a replacement process between depressurization and internal pressure release. Die (2)
3. The powder filling method according to claim 1, wherein the circumference of the mold is reduced to correct the mold (3) into a predetermined shape. 4. A molding die (2), a molding die (3) fitted and held in the molding die (2), and a lower punch (4) supporting the molding die (3) in the molding die (2). ) And a cover body (6) which can be connected to or detached from the upper part of the mold (3) held in the mold die (2) and forms an airtight space (6) facing the mold (3) at the time of connection. 5), wherein the cover body (5) has a pressure tapping means (7) that repeats a pressure reduction and an internal pressure release in a high-speed cycle with respect to the airtight space (6).
A powder filling device, comprising: 5. The cover body (5) includes a guide cylinder (12) for guiding the falling and introduction of powder, and the guide cylinder (1).
And a lid (13) for covering the upper part of (2). The lid (13) can be advanced to and retracted from the mold (3) through the guide cylinder (12). 5. The powder filling device according to claim 4, wherein a pusher (14) is provided. 6. A seal reinforcing frame (8) is provided around the cover body (5) in a state where the cover body (5) is connected to the upper part of the molding die (3). The powder according to claim 4 or 5, characterized in that a mold straightening means (9) capable of reducing the pressure between the inner peripheral surface of the mold die (2) and the outer peripheral surface of the molding die (3) is provided. Filling device.