JP2016049502A - Airflow type classifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an airflow type classifier capable of separating raw material powder in high accuracy classification into fine powder and coarse powder.SOLUTION: A ceiling wall 3 of a classification chamber 6 comprises: an outer ceiling face 20; a step part 21 formed to have a height increased discontinuously toward an inner diameter side from the outer ceiling face 20; and an inner ceiling face 22 formed through the step part 21 on the inner diameter side of the outer ceiling face 20. In the portion which is positioned on the outer diameter side than the diameter of a fine powder exhaust port 9 at the center of a classification plate 2 of the inner ceiling face 22, there is opened an exit 7a of a material powder feed passage 7.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an airflow classifier that centrifuges raw powder into coarse powder and fine powder using a swirling airflow.

  Generally, when manufacturing fine powder such as nickel particles used as raw materials for electronic parts such as multilayer ceramic capacitors and toner particles used in image forming apparatuses such as copying machines, the raw powder is coarsened using a swirling airflow. An air classifier that centrifuges into powder and fine powder is used.

  This airflow classifier is required to have a small classification point and high classification accuracy. As an airflow classifier that meets such requirements, for example, the one described in Patent Document 1 has been proposed. As shown in FIGS. 1 to 3 of the same document, the airflow classifier of Patent Document 1 includes a casing, a classifying plate arranged to face the lower side of the ceiling wall of the casing, and the classifying plate and the ceiling of the casing. A classification chamber formed between walls, an air nozzle that forms a swirling airflow in the classification chamber by injecting air into the classification chamber, and a powder supply that injects a mixed fluid of raw material powder and air into the classification chamber It has a header, a fine powder outlet opening in the center of the classification plate, and a coarse powder outlet opening along the outer periphery of the classification plate. A suction blower is connected to the fine powder outlet through a solid-gas separator.

  The airflow classifier disclosed in Patent Document 1 forms a swirling airflow toward the center in the classification chamber by injecting air from the air nozzle into the classification chamber, and the raw material powder injected from the powder supply header into the swirling airflow. The raw material powder is separated into coarse powder and fine powder by the outward centrifugal force acting as the raw material powder swirls with air and the air flow moving toward the center . That is, the coarse powder moves radially outward in the classification chamber by an outward centrifugal force caused by swirling with air, and is discharged from the coarse powder discharge port on the outer periphery of the classification plate. It moves radially inward in the classification chamber by the air flow moving in the direction, and is discharged from the fine powder discharge port in the center of the classification plate.

Japanese Patent No. 4907655

  By the way, when the raw material powder is centrifuged into coarse powder and fine powder using the airflow classifier described in Patent Document 1, the coarse powder is mixed into the fine powder collected from the fine powder discharge port, and the necessary classification accuracy is obtained. It turned out that it may not be obtained. In particular, when classification of the ultrafine powder region is required, it is difficult to prevent the coarse powder having a particle diameter of about 0.5 μm or more from being mixed into the fine powder collected from the fine powder discharge port. Therefore, the inventors of the present application have examined the cause of the coarse powder mixed into the fine powder collected from the fine powder discharge port. As a result, the mixed fluid of the raw material powder and air injected from the powder supply header into the classification chamber is classified into the classification chamber. It was found that there is a possibility that coarse powder has jumped into the fine powder discharge port due to the disturbance of the swirling airflow.

  The problem to be solved by the present invention is to provide an airflow classifier capable of separating raw powder into fine powder and coarse powder with high classification accuracy.

In order to solve the above problems, the present invention provides an airflow classifier having the following configuration.
A casing having a ceiling wall and a peripheral wall extending downward from the outer periphery of the ceiling wall;
A classification plate arranged to face the lower side of the ceiling wall;
A classification room formed between the classification plate and the ceiling wall;
A gas injection port for injecting gas from the peripheral wall into the classification chamber so as to form a swirling airflow in the classification chamber;
A raw material powder supply path for supplying the raw material powder into the classification chamber;
A fine powder outlet opening in the center of the classification plate;
In the airflow classifier having a coarse powder outlet opening along the outer periphery of the classification plate,
The ceiling wall of the classification room is
An annular outer ceiling surface located above the outer diameter side portion of the swirling airflow formed in the classification chamber with the gas injected from the gas injection port;
A stepped portion formed so as to discontinuously increase in height from the outer ceiling surface toward the inner diameter side,
An inner ceiling surface formed on the inner diameter side of the outer ceiling surface through the stepped portion,
An airflow classifier characterized in that an outlet of the raw material powder supply path is opened at a portion located on the outer diameter side of the diameter of the fine powder discharge port at the center of the classification plate on the inner ceiling surface.

  In this way, a corner area is formed by the inner ceiling surface and the inner peripheral surface of the stepped portion. In this corner area, even if the turbulence occurs, the influence of the turbulence on the swirling airflow in the classification chamber is small. And since the outlet of the raw material powder supply path is open on the inner ceiling surface forming this corner region, when the raw material powder is supplied from the raw material powder supply path into the classification chamber, the swirling airflow in the classification chamber Is not disturbed. Therefore, it is possible to prevent the coarse powder from jumping into the fine powder discharge port and to separate the raw material powder into the fine powder and the coarse powder with high classification accuracy.

  As the raw material powder supply path, it is possible to adopt a configuration in which the compressed gas and the raw material powder are mixed and injected into the classification chamber. However, the raw material powder is supplied to the classification chamber without using the compressed gas. It is preferable to employ a configuration in which the product is supplied to be dropped.

  In this way, turbulence of the swirling airflow in the classification chamber can be prevented more effectively than when a raw material powder supply path configured to inject the compressed gas and the raw material powder into the classification chamber is used. It becomes possible.

  The step portion is preferably formed such that the height of the step portion is 5 to 25% of the inner diameter of the step portion.

  When the height of the stepped portion is 5% or more of the inner diameter of the stepped portion, the fine powder recovery rate can be increased, and when the height of the stepped portion is 25% or less of the inner diameter of the stepped portion, the coarse powder becomes fine powder. Can be effectively prevented.

  In the airflow classifier of the present invention, a corner region is formed by the inner ceiling surface and the inner peripheral surface of the step portion. In this corner area, even if the turbulence occurs, the influence of the turbulence on the swirling airflow in the classification chamber is small. And since the outlet of the raw material powder supply path is open on the inner ceiling surface forming this corner region, when the raw material powder is supplied from the raw material powder supply path into the classification chamber, the swirling airflow in the classification chamber Is not disturbed. Therefore, it is possible to prevent the coarse powder from jumping into the fine powder discharge port and to separate the raw material powder into the fine powder and the coarse powder with high classification accuracy.

Sectional drawing which shows the airflow classifier of embodiment of this invention Fig. 1 is an enlarged cross-sectional view near the classification chamber of the classifier Sectional drawing which shows the comparative example of the classifier shown in FIG. It is a figure which shows the test result when the test which classifies the raw material particle | grains of nickel whose maximum particle diameter is about 1.5 micrometers is performed, (a) is collect | recovered classified by the airflow classifier of embodiment of this invention. (B) is a micrograph of recovered fine powder classified by a conventional airflow classifier. The figure which shows the particle size distribution of the fine powder when the test which classifies the raw material particle | grains of silicon whose maximum particle diameter is 10 micrometers or more was done

  FIG. 1 shows an airflow classifier according to an embodiment of the present invention. This airflow classifier includes a casing 1 and a classification plate 2 accommodated in the casing 1.

  The casing 1 includes a ceiling wall 3, a peripheral wall 4 that extends downward from the outer periphery of the ceiling wall 3, and a coarse powder collection unit 5 that is provided at the lower end of the peripheral wall 4. The classification plate 2 is disposed to face the lower side of the ceiling wall 3. A classification chamber 6 is formed between the classification plate 2 and the ceiling wall 3. The ceiling wall 3 is provided with a raw material powder supply path 7 for supplying the raw material powder into the classification chamber 6 from the outside of the casing 1.

  On the upper surface of the classification plate 2, a conical surface 8 is formed which gradually increases toward the center. The conical surface 8 has a shape that is inclined at 40 ° or less with respect to the horizontal plane. A fine powder discharge port 9 is opened at the center of the classification plate 2, and a fine powder discharge cylinder 10 that passes through the peripheral wall 4 of the casing 1 and communicates with the outside is connected to the fine powder discharge port 9. A suction blower (not shown) is connected to the fine powder discharge cylinder 10 via a solid-gas separator (not shown). The solid-gas separation device is a device that collects fine powder by separating a solid-gas mixed fluid (a mixture of fine powder and air) discharged from the fine powder discharge cylinder 10 into fine powder and air. The suction blower sucks air in the classification chamber 6 and maintains the pressure in the classification chamber 6 at a negative pressure. Between the outer periphery of the classification plate 2 and the inner periphery of the peripheral wall 4, an annular coarse powder outlet 11 that opens along the outer periphery of the classification plate 2 is provided. The coarse powder discharge port 11 communicates with the coarse powder collection unit 5 at the lower end of the casing 1.

  As shown in FIG. 2, the peripheral wall 4 is provided with a plurality of air injection ports 12 at equal intervals in the circumferential direction. Each air injection port 12 communicates with an annular compressed air supply passage 13 provided on the peripheral wall 4 so as to surround the classification chamber 6, and the air supplied from the compressed air supply passage 13 is passed into the classification chamber 6. Spray. Each air injection port 12 is formed to inject air in a direction inclined with respect to the radial direction so as to form a swirling airflow in the classification chamber 6. Each air injection port 12 is arranged at a position higher than the highest portion in the center of the classification plate 2 (that is, the peripheral edge portion of the fine powder discharge port 9).

  A plurality of guide vanes 14 are provided at intervals in the circumferential direction at a portion of the peripheral wall 4 below the air injection port 12. An air inflow passage 15 is formed between adjacent guide vanes 14, and the outside of the casing 1 is caused by a pressure difference between the classification chamber 6, which is made negative by a suction blower via the fine powder discharge cylinder 10, and the outside of the casing 1. The air is introduced into the classification chamber 6 through the air inflow passage 15. The air inflow path 15 between the adjacent guide vanes 14 is inclined in the same direction as the air injection port 12 with respect to the radial direction. Each guide vane 14 is disposed at a position lower than the highest portion in the center of the classification plate 2 (that is, the peripheral edge portion of the fine powder discharge port 9). By providing this guide vane 14, the fine powder contained in the coarse powder centrifuged by the swirling airflow in the classification chamber 6 can be returned again to the swirling airflow in the classification chamber 6, thereby improving the recovery rate of the fine powder. be able to.

  The ceiling wall 3 of the classification room 6 has an outer ceiling surface 20, a stepped portion 21, and an inner ceiling surface 22. The outer ceiling surface 20 is a lower surface of an annular portion projecting radially inward from the upper end of the peripheral wall 4, and swirling airflow is generated in the classification chamber 6 by the air injected from the air injection port 12 on the inner periphery of the peripheral wall 4. When formed, it is a ceiling surface located above the outer diameter side portion of the whirling airflow. The outer ceiling surface 20 is formed in a conical shape that gradually increases from the outer diameter side toward the inner diameter side. Here, the outer ceiling surface 20 has a conical shape having an inclination in a range of 10 to 35 ° with respect to the horizontal direction. Moreover, the air injection port 12 is arrange | positioned at the upper part of the surrounding wall 4, Specifically, the difference of the height direction between the position of the outer-diameter end of the outer side ceiling surface 20 and the center position of the air injection port 12 is the following. The air injection port 12 is disposed so as to have a size in the range of 1 to 10% of the inner diameter of the stepped portion 21.

  The step portion 21 is a portion formed so as to discontinuously increase in height from the outer ceiling surface 20 toward the inner diameter side. That is, the height of the outer ceiling surface 20 and the height of the inner ceiling surface 22 change discontinuously at the position of the step portion 21. The step portion 21 has a cylindrical inner peripheral surface concentric with the center of the classification plate 2. The height of the step portion 21 (the difference in the height direction between the position of the inner diameter end of the outer ceiling surface 20 and the position of the outer diameter end of the inner ceiling surface 22) is 10 to 25% of the inner diameter of the step portion 21. (Preferably 15 to 20%) is set. When the height of the stepped portion 21 is 10% or more (preferably 15% or more) of the inner diameter of the stepped portion 21, the fine powder recovery rate can be increased, and the height of the stepped portion 21 is set to 25 of the inner diameter of the stepped portion 21. When the content is less than or equal to% (preferably less than or equal to 20%), it is possible to effectively prevent the coarse powder from being mixed into the fine powder.

  The inner ceiling surface 22 is a portion formed on the inner diameter side of the outer ceiling surface 20 via the step portion 21. Here, the inner ceiling surface 22 is a horizontal plane. In the inner ceiling surface 22, an outlet 7 a of the raw material powder supply path 7 is opened. The outlet 7 a of the raw material powder supply path 7 is disposed at a portion located on the outer diameter side of the diameter of the fine powder discharge port 9 at the center of the classification plate 2.

  As shown in FIG. 1, the raw material powder supply path 7 includes a hopper 23 that receives the raw material powder from the outside, and a vertical passage 24 that extends downward from the hopper 23. The hopper 23 is formed in a funnel shape whose diameter is increased upward. Above the hopper 23, a fixed quantity supply device (not shown) is provided, and the raw material powder is continuously supplied in a fixed quantity from the fixed quantity supply device into the hopper 23. The raw material powder supplied to the hopper 23 from above is dropped and supplied into the classification chamber 6 through the vertical passage 24. At this time, the raw material powder in the vertical passage 24 is drawn into the classification chamber 6 due to the ejector effect caused by the swirling airflow in the classification chamber 6.

  Next, the usage example of said airflow type classifier is demonstrated.

  In a state where the suction blower connected to the fine powder discharge cylinder 10 is operated, air is injected into the classification chamber 6 from each air injection port 12. At this time, since the air injection direction of each air injection port 12 is inclined with respect to the radial direction, a swirling airflow rotating in a certain direction is formed in the classification chamber 6. Further, since the air injection port 12 is disposed in the vicinity of the outer diameter end of the outer ceiling surface 20, the swirling airflow formed by the air injected by the air injection port 12 gradually turns along the ceiling wall 3. A swirling airflow that moves toward the center (that is, the swirling diameter becomes smaller) is directed to the center, and a downward swirling airflow is generated near the center of the classification chamber 6, and is discharged from the fine powder discharge port 9. Here, in the corner region 25 formed by the inner ceiling surface 22 and the inner peripheral surface of the stepped portion 21, the cross-sectional area of the flow changes abruptly from the outer diameter side toward the inner diameter side. ing. Further, in the classifying chamber 6, in addition to the above-described swirling airflow turning toward the center while turning along the ceiling wall 3, the airflow descending while turning along the inner periphery of the peripheral wall 4 due to the centrifugal force received by the air itself. Also occurs.

  In the state where the swirling airflow is formed in the classification chamber 6 as described above, the raw material powder is supplied from the raw material powder supply path 7 to the corner region 25 in the classification chamber 6. At this time, the raw material powder introduced into the classification chamber 6 from the raw material powder supply path 7 is dispersed by the air current in the corner region 25 and then swirls on the swirling air current in the classification chamber 6. The raw material powder is separated into coarse powder and fine powder by the outward centrifugal force acting by swirling with air and the flow of air moving toward the center. That is, the coarse powder is moved radially outward in the classification chamber 6 by the outward centrifugal force by swirling with air, and is discharged from the coarse powder discharge port 11 on the outer periphery of the classification plate 2, and the fine powder is The inside of the classification chamber 6 moves radially inward by the flow of air that moves toward the center while turning, and is discharged from the fine powder discharge port 9 at the center of the classification plate 2. At this time, in the classification chamber 6, there is an air flow descending while swirling along the inner periphery of the peripheral wall 4, so the coarse powder that has moved radially outward in the classification chamber 6 enters the classification chamber 6. Without staying, it is smoothly discharged to the coarse powder outlet 11.

  In this airflow classifier, a corner region 25 is formed by the inner ceiling surface 22 and the inner peripheral surface of the step portion 21. In this corner region 25, even if the turbulence of the airflow occurs, the influence of the turbulence of the airflow on the swirling airflow in the classification chamber 6 is small. And since the exit 7a of the raw material powder supply path 7 is opened in the inner ceiling surface 22 that forms this corner region 25, when the raw material powder is supplied into the classification chamber 6 from the raw material powder supply path 7 In addition, the swirling airflow in the classification chamber 6 is not easily disturbed. Therefore, it is possible to prevent the coarse powder from jumping into the fine powder discharge port 9 and to separate the raw material powder into the fine powder and the coarse powder with high classification accuracy. In particular, when classification of the ultrafine powder region is required, it is possible to prevent the coarse powder having a particle size of about 0.5 μm or more from being mixed into the fine powder collected from the fine powder discharge port 9. Classification accuracy can be obtained.

  Further, in this airflow classifier, since the air injection port 12 is disposed at the upper part of the peripheral wall 4, an airflow descending while turning along the inner periphery of the peripheral wall 4 is also generated in the classification chamber 6. For this reason, the raw material powder hardly adheres to the inner surface of the peripheral wall 4.

  As the raw material powder supply path 7, it is possible to adopt a configuration in which compressed air and raw material powder are mixed and injected into the classification chamber 6, but compressed air is used as in the above embodiment. It is preferable to employ a configuration in which the raw material powder is dropped and supplied into the classification chamber 6 without being used. In this case, the turbulence of the swirling airflow in the classification chamber 6 is further reduced as compared with the case where the raw material powder supply path 7 configured to inject the compressed air and the raw material powder into the classification chamber 6 is used. It can be effectively prevented.

In order to confirm that the classification accuracy is improved by providing the step portion 21 on the ceiling wall 3 of the classification chamber 6, as shown in FIG. 2, the product of the embodiment in which the step portion 21 is provided on the ceiling wall 3 of the classification chamber 6 is used. As shown in FIG. 3, a classifier and a comparative classifier that does not have a stepped portion 21 on the ceiling wall 3 of the classification chamber 6 are prototyped, and a test for classifying calcium carbonate raw material particles in each classifier is performed. I did it. The test results are shown below.
Here, the D50 diameter of the fine powder is a particle size (so-called median diameter) when the cumulative number from the small particle size side becomes 50% of the total particle size distribution of the particles discharged as fine powder from the fine powder outlet 9. .

  According to this test result, the recovery rate of the fine powder is higher in the product in which the stepped portion 21 is provided in the ceiling wall 3 of the classification chamber 6 than in the comparative product in which the stepped portion 21 is not provided in the ceiling wall 3 of the classification chamber 6. Is high and the D50 diameter of the fine powder is small. That is, by adopting a configuration in which the stepped portion 21 is provided on the ceiling wall 3 of the classification chamber 6, it can be confirmed that not only the classification point is reduced, but also the classification accuracy is improved at the same time.

  1 and 2 and the conventional classifier shown in FIG. 4 of Japanese Patent No. 4907655 classify nickel raw material particles having a maximum particle size of about 1.5 μm. A test was conducted. The test results are shown in FIGS. 4 (a) and 4 (b).

  When classification is performed with the classifier of the product shown in FIG. 1 and FIG. 2, as shown in FIG. 4 (a), the recovered fine powder has almost no coarse powder of 0.5 μm or more, and the maximum An extremely small fine powder having a particle size of about 0.3 to 0.5 μm could be obtained. On the other hand, when the classification is performed by the conventional classifier shown in FIG. 4 of Japanese Patent No. 4907655, as shown in FIG. 4B, the recovered fine powder is coarse powder exceeding 0.5 μm. There are many. As described above, when the airflow classifier of the above embodiment is used, it is possible to prevent the coarse powder having a particle diameter of 0.5 μm or more from being mixed into the fine powder when the ultra fine powder region is classified. Can be confirmed.

  Moreover, the test which classifies the raw material particle | grains of the silicon | silicone whose maximum particle diameter is 10 micrometers or more with the classifier of the implementation goods shown in FIG. 1, FIG. 2 and the conventional classifier shown in FIG. 4 of patent 4907655 gazette. I did it. The test results are shown in FIG.

  When classification is performed with the classifier of the embodiment shown in FIGS. 1 and 2, the maximum particle size of the particles recovered as fine powder is as very small as 3 μm, as shown by the solid line in FIG. When classification is performed with the conventional classifier shown in FIG. 4 of the publication, the maximum particle diameter of the particles recovered as fine powder is as large as 10 μm or more as shown by the broken line in FIG. In addition, when comparing the particle size distribution shown by the solid line in FIG. 5 with the particle size distribution shown by the broken line, the particle size distribution shown by the solid line is less than 1 μm in the total particles recovered as fine powder than the particle size distribution shown by the broken line There are many ratios. As described above, when the airflow classifier of the above embodiment is used, it can be confirmed that classification having an extremely small classification point and a sharp particle size distribution is possible.

DESCRIPTION OF SYMBOLS 1 Casing 2 Classification board 3 Ceiling wall 4 Perimeter wall 6 Classification chamber 7 Raw material powder supply path 7a Outlet 9 Fine powder discharge port 11 Coarse powder discharge port 12 Air injection port 20 Outer ceiling surface 21 Step part 22 Inner ceiling surface

Claims (3)

A casing (1) having a ceiling wall (3) and a peripheral wall (4) extending downward from the outer periphery of the ceiling wall (3);
A classification plate (2) arranged to face the lower side of the ceiling wall (3);
A classification chamber (6) formed between the classification plate (2) and the ceiling wall (3);
A gas injection port (12) for injecting gas from the peripheral wall (4) into the classification chamber (6) so as to form a swirling airflow in the classification chamber (6);
A raw material powder supply path (7) for supplying the raw material powder into the classification chamber (6);
A fine powder outlet (9) opening in the center of the classification plate (2);
In the airflow classifier having a coarse powder outlet (11) opening along the outer periphery of the classification plate (2),
The ceiling wall (3) of the classification room (6)
An annular outer ceiling surface (20) located above the outer diameter side portion of the swirling airflow formed in the classification chamber (6) with the gas injected from the gas injection port (12);
A step portion (21) formed so as to discontinuously increase in height from the outer ceiling surface (20) toward the inner diameter side;
An inner ceiling surface (22) formed on the inner diameter side of the outer ceiling surface (20) via the stepped portion (21),
An outlet (7a) of the raw material powder supply path (7) is provided at a portion located on the outer diameter side of the diameter of the fine powder discharge port (9) at the center of the classification plate (2) on the inner ceiling surface (22). Airflow classifier characterized by opening.   The airflow classifier according to claim 1, wherein the raw material powder supply path (7) is configured to drop and supply the raw material powder into the classification chamber (6).   The airflow type according to claim 1 or 2, wherein the stepped portion (21) is formed such that the height of the stepped portion (21) is 5 to 25% of the inner diameter of the stepped portion (21). Classifier.