JP2580193B2 - Cyclone type dry classifier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder classifier, and more particularly to a classifier capable of classifying powder in a dry manner using a cyclone. .

BACKGROUND OF THE INVENTION Classification of powders has been increasingly demanded in recent years, particularly with the development of the ceramic industry and the development of high precision and high technology in this field, and at the same time, classification in the submicron range. There is an increasing demand for improving the performance of the apparatus, such as performance improvement, mass processing, reduction of the classification cost, simplification of the structure of the classification apparatus and easy maintenance and inspection, especially prevention of contamination at the time of classification.

In general, apart from a device for classifying powders by a wet method, a device for classifying powders by a dry method is known as a device for classifying powders by a forced vortex method utilizing centrifugal force. This applies a centrifugal force to the powder by passing the powder over the rotating rotor, and also applies a gas conveying force in a direction against the centrifugal force, that is, in a radial direction of the rotor, to act on both powders. According to the balance of the conveying force, a powder having a large particle diameter is conveyed to the outside of the rotor, and a powder having a small particle diameter is conveyed to the inside of the rotor.

By the way, such a forced vortex classifier utilizing a centrifugal force has a mechanical operation part called rotor rotation, and therefore has an excellent classification performance, but has a complicated structure and tends to be an expensive device.

On the other hand, for classifying powders of several microns or sub-microns, a classifier that has a simpler structure and is less expensive than the above-mentioned forced vortex classifier, and has less burden of maintenance and inspection. Although development is desired, an industrial apparatus capable of accurately classifying powder of several microns or less in a dry manner has not been provided yet.

For example, it is possible to use a cyclone generally used as a dust collector for a dry classification device based on the above-described viewpoint, but in a normal classification using such a cyclone, 10 μm or less is used. In the case of the powder of the above, the classification accuracy index (κ) obtained from the particle size distribution measured by a laser diffraction type particle size analyzer (Microtrack: manufactured by Nikkiso Co., Ltd.) becomes small, and it can be used industrially sufficiently. It is said that it is not possible to classify with sufficient classification characteristics. The problem of such a classification accuracy index is that, for example, when classification is performed at a classification point of 1 μm, a difference in the classification accuracy index results in the incorporation of coarse particles of 1 μm or more into fine powder on the one hand and 1 μm or less into coarse powder on the other hand. This leads to the problem of mixing fines.

(Object of the Invention) The present invention has been made from the above viewpoints, and an object of the present invention is to perform dry classification of powder having a particle size of 10 μm or less, which has a classifying performance sufficient for industrial use. To provide a dry classification device that can

Another object of the present invention is to enable continuous and large-scale processing of powder classification, and to use a free-vortex type cyclone to have a simple structure, easy maintenance and inspection, and reduce classification costs. It is an object of the present invention to provide a dry classification device having a structure suitable for reduction.

Another object of the present invention is to provide an excellent performance which has substantially no mechanically operating part and therefore does not need to substantially consider the occurrence of contamination due to abrasion of the mechanically operating part during classification. To provide a dry classifier.

(Summary of the Invention) For the purpose as described above, the present inventors have proposed that a cyclone having no mechanical working part and having one side excellent suitability as a classifier is made of a ceramic such as 10 μm or less. Various investigations have been made on a device for ensuring a sufficiently useful classifying property for a powder, preferably a powder having a size of 5 μm or less.

As a result, the classification performance when using cyclones is
First, the state when powder is introduced into the cyclone,
It has been found that the influence of the mode of introduction leads to the fact that, in general, the powder that is easily agglomerated as it becomes finer is sufficiently dispersed in the state of the primary particles at the preceding stage of the cyclone, and is immediately added to the cyclone before reagglomeration occurs. This led to the development of a cyclone-type dry classification device that introduced the introduced powder smoothly and appropriately to the body of the cyclone tower, which classifies coarse and fine powder. .

Thus, the cyclone-type dry classification device according to the present invention, which is provided for realizing such a purpose, is characterized in that the powder in a dry state is dispersed into primary particles and is continuously discharged. And a cyclone connected immediately after the outlet of the dispersed powder of the dispersing machine, wherein the cyclone comprises:
The body as the main body of the cyclone tower, which has a substantially upright cylindrical shape, and the inner peripheral wall for the powder guide whose diameter gradually decreases in the circumferential direction around the upper part of the body, may be extended over half of its circumference. The dispersed powder that is provided and blown in and introduced in the horizontal direction from the disperser is gradually rotated radially inward by the inner peripheral wall surface for the powder guide as a rotational flow along the lower inner peripheral wall surface of the lower body. Circumferential spiral structure type powder introduction part to guide, and primary air extraction for removing fine powder, which is suspended downward from the ceiling of the cyclone tower along the radial center of the body for a certain length and whose lower end is open The structure has a cylinder and a storage tank connected to the lower end opening of the cyclone tower and storing coarse powder falling from the lower end opening.

In the above, the disperser constituting a part of the classifier is a method of supplying powder to a narrow path while passing a high-speed air flow through the narrow path, for example, as shown in FIG. An air jet type dispersing machine is preferably used in which the powder is supplied from 21 and the powder is dispersed by the ejector effect of a high-speed air flow and discharged from 22. In addition to such a dispersing machine, as shown in FIG. 18, a spatula-shaped blade 26 is provided at the bottom of the cylindrical container 24, powder is supplied from the container upper portion 25 while rotating the blade, and the rotating blade is rotated. The shear flow, vortex, or blade generated by 26
Alternatively, a mechanical type disperser that disperses powder by collision with and discharges the powder from 27 may be used.

In the classifier having the above configuration, the powder introduction portion formed as the introduction powder guide portion of the cyclone tower has an inner peripheral wall surface for powder guide (hereinafter, referred to as a guide wall surface) whose diameter gradually decreases along the circumferential direction. It must be provided as a circular spiral structure type having at least a half-week or more. If the guide surface is less than half a circumference or a tangential entrance type having no guide, sufficient classification performance cannot be obtained.

In addition, the classifying performance of coarse powder and fine powder in the main body of the cyclone is also affected by the gas transport state after the classification, and particularly, coarse powder falling from the lower end opening of the body of the cyclone main body is smoothly discharged. It has been experimentally confirmed that this has a favorable effect on the improvement of the classification performance, and the following configuration is preferably adopted in order to smoothly discharge the falling powder from the lower opening of the body portion of the main body. ing.

That is, in the above configuration, the storage tank that is connected to face the lower end opening of the body and stores the falling coarse powder has a conical shape with an inclination angle of approximately 45 °, with a tapered tip facing the lower end opening of the body. It is preferred to provide a block for falling coarse powder guide. This falling coarse powder guide block
By promptly guiding the coarse powder falling from the trunk to the outside in the radial direction of the block, there is an effect that the discharge of the coarse powder from the lower end opening of the trunk is favorably maintained and the classification performance is improved.

It is also preferable to connect a secondary air outlet cylinder to the coarse powder storage tank. The degree of extraction of air from the secondary air outlet cylinder is preferably set at 10 to 15% of the amount of powder blown into the cyclone tower. There is an effect that the discharge of the coarse powder falling into the tank becomes smoother, and the classification performance with the fine powder discharged to the outside from the primary air outlet cylinder is improved.

Embodiments of the Invention Hereinafter, the present invention will be described based on embodiments shown in the drawings.

Embodiment 1 FIGS. 1 to 3 are diagrams for explaining a first embodiment of the present invention, and FIG. 1 illustrates an entire system of a classification facility configured by applying a classifier according to the present invention. FIG.

In this figure, reference numeral 1 denotes a powder feeder, which stores powder to be classified, discharges the powder from a lower discharge port as appropriate continuously by a feeder screw 1a, and supplies the powder to a disperser 2.

The dispersing machine 2 in this example is configured as a high-speed air flow type that supplies powder to a narrow path while passing a high-speed air stream through the narrow path, and disperses the powder by an ejector effect of the high-speed air stream. I have.

The dispersed powder that has passed through the disperser 2 is conveyed to the powder introduction unit 6 of the cyclone tower 5 from the outlet of the dispersed powder of the disperser through the powder conveying pipe 3.

The structure of the cyclone tower 5 is shown in detail in FIG. 2, and the main body 5a of the upright cylindrical cyclone tower has:
The upper half has a straight cylindrical shape, the lower half is provided in a tapered shape whose diameter is slightly reduced downward, and the lower end is opened to face the closed type coarse powder storage tank 8. I have.

In addition, the powder introduction section 6 is provided above the body 5a of the cyclone tower. The powder introduction section 6 is provided at a predetermined height above the body section 5a, and has a radial dimension over a semicircle at a position radially outside the body section 5a. Is provided so as to have a spiral inner peripheral wall surface 6b for powder guide. Reference numeral 6b denotes a powder introduction port, which extends from a portion having the largest spiral diameter in a substantially tangential direction and is connected to the powder conveying pipe 3.

Reference numeral 7 denotes a primary air take-out cylinder which is suspended from the ceiling of the cyclone tower 5 to a certain height in a radial center position of the body 5a, and a lower end thereof is opened at a position below the powder introduction unit 6. . The primary air outlet cylinder 7 is provided with the trunk 5a.
The fine powder classified by the primary air transfer force is passed through a fine powder transfer pipe 7a, and is connected to a blower 10 via a fine powder recovery filter 7b and a suction pipe 7c.

Reference numeral 8 denotes a coarse powder storage tank provided so as to face the lower end opening of the body portion, which is provided in a closed structure and has an opening / closing portion (not shown) for taking out the stored coarse powder when necessary. Z) is provided.

The classification operation performed using the classification device having the above-described configuration will be described. First, the blower 10 is operated at a predetermined air volume, and the air is passed through the primary air take-out cylinder 7 from the inside of the body 5a of the cyclone tower 5. Creates a turbulent airflow.

In this state, the powder is continuously supplied from the powder feeder 1 to the disperser 2, and the dispersed powder is introduced into the powder introduction unit 6 of the cyclone tower 5 at a predetermined air flow.

The air flow containing the powder introduced into the powder introduction unit becomes a rotational flow along the spiral inner wall surface 6b for the powder guide of the powder introduction unit 6 and rotates around the entire circumference. Descending and inner wall of the torso
6b, and the air in the body 5a is taken out and discharged to the outside through the primary air take-out cylinder 7, so that the airflow that rotates along the inner peripheral wall 5b of the body 5a gradually increases. While descending the conical trunk, an updraft occurs in the central part of the trunk.

Therefore, the powder contained in the airflow that descends while rotating the body of the cyclone tower 5 has a large diameter and is relatively large in accordance with the balance between the conveying action received from the airflow and the centrifugal force due to the mass of the powder. The heavy coarse powder settles downward and falls into the coarse powder storage tank 8 from the lower end opening of the body. On the other hand, with respect to fine powder having a small diameter and relatively small weight, the action of the conveying force of the airflow discharged to the outside from the primary air take-out cylinder 7 overcomes, and passes through the fine-powder carrying pipe 7a from the primary air take-out cylinder 7. It will be conveyed to the fine powder collection filter 7b.

This is a standard powder for a classification test for the apparatus having the above configuration. A classification test was performed on 11 types of JIS standard powder (Kanto Rohm). The particle size distribution of the target powder is shown in FIG. 15 (Kanto Rohm).

 The dimensions of the equipment used and the test conditions are as follows.

Structure of cyclone tower 5 Main body: 350 mm in height, straight cylinder height: 110 mm, inner diameter: 70 mm, tapered section, height: 200 mm, lower inner diameter: 40 mm, powder inlet: total height, 60 mm, spiral radius, 50 mm, powder inlet, 20 mm, primary air outlet: cyclone tower Height from the ceiling 60mm Inside diameter 30mm Test conditions: Air volume of blower 10 1.4 ³ / min Air velocity to blow into cyclone tower 30m / s Amount of powder in air volume 0.01g / Processing time 45min Environmental condition: Humidity 56 % RH Temperature 29 ℃ Powder used …… 11 Kanto loam disperser Air jet type (DN-154 (manufactured by Nisshin Engineering)) The test result is the separation efficiency as shown by line A in Fig. 3. Classification point D _p50 , classification accuracy index κ, Newton efficiency,
The measurement results of the collection efficiency were as shown in Table 1 below.

In addition, a semicircular spiral structure type cyclone tower (No. 1) with the same configuration except that the powder introduction section is semicircular (maximum radius 67 mm)
(See FIG. 19), a classification test was performed, and the results are shown in Table 1 below as well as the results are shown by the line B in FIG. 3 as Example 2.

The particle size distribution was measured by an X-ray transmission type particle size analyzer (Sedigraph: manufactured by Shimadzu Corporation).

For comparison, the classification point D _p50 , the classification accuracy index κ, the Newton efficiency, and the collection efficiency in the case of using the tangential inlet type cyclone tower in FIG. 20 (Comparative Example 1) were measured, and the results were described above. Also shown in Table 1 and the C line in FIG. 3 (Comparative Example 1)
Shows the separation efficiency.

As is clear from these results, D
_p50 is as small as 0.61 μm and 0.62 μm in Examples 1 and 2. In addition, the classification accuracy index κ of Example 1 is 0.
63, which is significantly higher than κ of Comparative Example 1, indicating that the present invention has high performance as a classifier.

Third Embodiment FIGS. 4 to 6 show a third embodiment in which a conical falling coarse powder guide block (hereinafter, referred to as a conical block) 8a is provided inside a coarse powder storage tank 8 so as to face a lower end opening of a trunk portion. Since other configurations are completely the same as those of the first embodiment, the description of the common parts will be omitted.

The details of the conical block 8a in this example are shown in FIG. 5, and a cone having a generally 45 ° inclination angle has its apex located at the center of the lower end opening of the body portion 5a, and the diameter of the lower peripheral edge is the same as that of the body. It is provided so as to be larger in diameter than the lower end opening of the portion 5a.

In this example, the cone falling coarse powder guide block is provided as a conical block of the above shape, but this is used for the purpose of a coarse powder guide that quickly separates the falling coarse powder from the vicinity of the opening at the lower end of the body. The above conical block was experimentally good.

The classifier with the above configuration is combined with the above 11 Kanto ROHM
The test was conducted under the same conditions as in Example 1 above, except that JIS 17-type calcium carbonate having a particle size distribution shown in FIG.
(11 types of Kanto loam) and Table 3 (calcium carbonate), and the classification efficiency is shown in FIGS. 6 and 7. The line A in the figure shows the measurement result in the case of Example 3, and the line B shows the measurement result in the case of Example 1 for comparison.

The particle size distribution was measured with a laser diffraction particle size analyzer (Microtrack: manufactured by Nikkiso Co., Ltd.) (the same applies hereinafter).

As is clear from this result, by providing the cone falling coarse powder guide block, in the case of 11 types of Kanto loam, the classification point D _p50 is reduced from 0.58 μm to 0.41 μm, and the classification accuracy index κ is from 0.36 It improved remarkably to 0.60. In the case of calcium carbonate, the classification point _Dp50 did not decrease, but the classification accuracy κ improved from 0.28 to 0.37. From the above, it can be seen that the provision of the cone falling coarse guide block of the present invention makes it possible to improve the performance as a classifier.

Embodiment 4 FIGS. 8 to 14 show that a secondary air take-out cylinder 9 is connected to a coarse powder storage tank 8 and a blower 10 is inserted into the coarse powder storage tank 8 through a coarse powder recovery filter 9a and a suction pipe 9b. Example 4 in which a slight negative pressure is applied is described.
Other configurations are completely the same as those of the first and third embodiments, and the description of the common parts is omitted.

The connection of the secondary air take-out cylinder 9 of this embodiment is preferably provided in the vicinity of the lower end opening of the body of the storage tank 8. In particular, in a classifier of an industrial scale, it is customary to design the storage tank as a large one having a considerable capacity, and the effect in that case is great.

The classifier having the above configuration was tested under the same conditions as in Example 1 above, using the above 11 Kanto loams as test target powders.
Table 4 below shows the measurement results (without conical block)
The results are shown in Table 5 (with the conical block of Example 3), and the classification efficiency is shown in FIGS. 9 and 10. The line A in the figure shows the measurement results when the secondary air take-out cylinder 9 is connected to the upper surface of the storage tank 8 at a position approximately 30 mm from the center (near connection), and the line B is the secondary air take-out cylinder 9 Is connected to a position below the side surface of the storage tank 8 (distant connection), and the amount of air taken out from the secondary air outlet tube 9 is 15% of the amount of air blown.

 The size of the storage tank 8 is 100 mm in diameter and 100 mm in depth.

Here, κ ′ indicates D _p10 / D _p90 .

As is clear from these results, in both cases where the conical block is not provided and the conical block is provided, the case where the secondary air outlet cylinder position is near the upper surface of the storage tank is better than the storage tank. Compared to the case of being far away from the upper surface, it is superior in the classification point D _p50 , the classification accuracy index κ, and κ ′.

From the above, it is understood that by providing the secondary air take-out cylinder on the upper surface of the storage tank, it is possible to improve the performance as a classifier.

11 to 14 show the relationship between the amount of secondary air taken out from the secondary air take-out cylinder 9 and the amount of air blown into the cyclone tower in the fourth embodiment.
The figure shows the results obtained by measuring the changes in the yield η, the classification point D _p50 , the classification number index κ and κ ′ in the classifier without using a conical block for 11 types of Kanto loam.
FIG. 12 shows the same measurement results in the case where the conical block of the third embodiment is additionally provided for 11 types of Kanto loam.

Fig. 13 shows the yield η and classification point of the classification device for calcium carbonate without a conical block.
Changes in D _p50 and classification accuracy indices κ and κ ′ are shown, and FIG. 14 shows the same measurement results in the case where the conical block of Example 3 was additionally provided for calcium carbonate.

As evident from these results, in each case,
By extracting air from the secondary air outlet cylinder, the classification point
D _p50 and classification accuracy index κ improved. The classification point D _p50 and the classification accuracy index κ showed peaks when the amount of secondary air taken out was 10 to 15% of the amount of blown air.

By taking out the secondary air by the above,
It can be seen that the performance of the classifier can be improved, and the secondary air take-out airflow is most preferably 10 to 15% of the blown airflow.

(Effects of the Invention) As described above, according to the cyclone-type dry classification device according to the present invention, the classification performance of a powder having a particle size of 10 μm or less is secured to an extent that can be used industrially sufficiently.
The effect that dry classification can be performed is obtained.

Further, according to the dry classification apparatus of the present invention, continuous and mass processing of powder classification can be performed, and a free vortex type cyclone is used, so that the structure is simple and maintenance and inspection are easy. , The equipment can be provided at low cost,
There is an effect that it is possible to provide a dry classification apparatus having a structure suitable for reducing the classification cost when the apparatus is used.

Further, the dry classification device of the present invention has substantially no mechanically operating part, and therefore it is not necessary to substantially consider that contamination occurs due to wear of the mechanically operating part. In addition, there is an effect that not only the classification performance but also excellent classification without mixing of foreign matters can be performed, and its usefulness is extremely large.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing, as an overall flow, an outline of the configuration of a first embodiment of a cyclone type dry classification device according to the present invention;
2 (a) and 2 (b) are diagrams showing the configuration of the cyclone tower of Example 1, wherein FIG. 2 (a) is a front view, and FIG. 2 (b) is a cross-sectional view taken along line (a) AA. is there. FIG. 3 is a classification characteristic diagram showing the results of a classification test performed using the apparatus of Example 1 in comparison with Comparative Examples. FIG. 4 is a diagram showing the overall configuration of a cyclone type dry classification apparatus according to a third embodiment as an overall flow, FIG. 5 is a view showing the internal configuration of a coarse powder storage tank according to the third embodiment, and FIG. FIG. 7 is a classification characteristic diagram showing the results of a classification test performed using the apparatus of Example 3 in comparison with Comparative Examples. FIG. 8 is a diagram showing the overall configuration of a cyclone type dry classification apparatus according to a fourth embodiment as an overall flow, and FIGS.
FIG. 11 is a classification characteristic diagram showing the results of a classification test performed using the apparatus of Example 4 in comparison with Comparative Examples, and FIGS.
The figure shows the effect of secondary air extraction in relation to the first and third embodiments. FIG. 15 and FIG. 16 are diagrams showing the particle size distribution of the powder used in the classification test of each example. FIG. 17 and FIG. 18 show examples of a classifier. FIG. 19 shows the structure of a semicircular spiral structure type classifier used in Embodiment 2 of the present invention, where (a) is a front view thereof, (b) is (a) FIG. It is sectional drawing of a line. FIG. 20 is a view for explaining a classification apparatus for a comparative test in which powder introduction is performed in a tangential manner in order to explain the effect of the classification apparatus according to the present invention, and (a) is a front view thereof. (B) is a sectional view taken along the line CC in FIG. 1: Powder feeder, 1a: Feeder screw 2: Disperser, 3: Powder transport tube 4: Air intake section 5: Cyclone tower, 5a: Cyclone tower body 5b: Body inner peripheral wall 6: Powder introduction section, 6a: Powder inlet 6b: Inner peripheral wall for powder guide 7: Primary air outlet cylinder 7a: Fine powder transport pipe, 7b: Fine powder recovery filter 7c: Suction pipe 8: Coarse powder storage tank, 8a: Conical block 8b: Conical Block support frame 9: Secondary air outlet cylinder, 9a: Coarse powder recovery filter 9b: Suction pipe 10: Blower 105: Cyclone 105a: Cyclone tower body 105b: Inner wall 106: Powder introduction section, 106a: Powder Inlet 106b: Inner peripheral wall for powder guide 107: Primary air outlet cylinder

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-167470 (JP, A) JP-A 61-91344 (JP, U) JP-A 61-130352 (JP, U) 6925 (JP, Y2)

Claims (3)

(57) [Claims] 1. A disperser for dispersing a powder in a dry state to be inputted into a state of primary particles and continuously discharging the same, and a cyclone connected immediately after an outlet of the dispersed powder of the disperser. The cyclone has a body part as a main body of a cyclone tower having a substantially upright cylindrical shape, and an inner peripheral wall surface for powder guide whose diameter gradually decreases along the circumferential direction around an upper part of the body part, and has a half circumference or more. The dispersion powder blown and introduced in the horizontal direction from the dispersing machine is gradually moved radially inward by the powder guiding inner peripheral wall while moving along the lower trunk inner peripheral wall. A circular spiral type powder introduction part that guides as a swirling flow, and a fine powder removal part that is suspended downward for a certain length from the ceiling of the cyclone tower along the radial center position of the body, and the lower end is open Of the primary air take-out cylinder and the bottom opening of the cyclone tower Has been cyclonic dry classification apparatus, characterized in that a structure having a reservoir for storing the coarse particles falling from the lower end opening. 2. A disperser for dispersing a powder in a dry state into primary particles and continuously discharging the powder, and a cyclone connected immediately after a discharge port of the dispersed powder of the disperser. The cyclone has a body part as a main body of a cyclone tower having a substantially upright cylindrical shape, and an inner peripheral wall surface for powder guide whose diameter gradually decreases along the circumferential direction around an upper part of the body part, and has a half circumference or more. The dispersion powder blown and introduced in the horizontal direction from the dispersing machine is gradually moved radially inward by the powder guiding inner peripheral wall while moving along the lower trunk inner peripheral wall. A circular spiral type powder introduction part that guides as a swirling flow, and a fine powder removal part that is suspended downward for a certain length from the ceiling of the cyclone tower along the radial center position of the body, and the lower end is open Of the primary air take-out cylinder and the bottom opening of the cyclone tower And a storage tank for storing coarse powder falling from the lower end opening, and a cone having an inclination angle of approximately 45 °, which is disposed in the storage tank and has a tapered tip facing the lower end opening of the body. And a block for guiding coarse powder falling. 3. A disperser for dispersing a powder in a dry state to be inputted into primary particles and continuously discharging the same, and a cyclone connected immediately after a discharge port of the dispersed powder of the disperser. The cyclone has a body part as a main body of a cyclone tower having a substantially upright cylindrical shape, and an inner peripheral wall surface for powder guide whose diameter gradually decreases along the circumferential direction around an upper part of the body part, and has a half circumference or more. The dispersion powder blown and introduced in the horizontal direction from the dispersing machine is gradually moved radially inward by the powder guiding inner peripheral wall while moving along the lower trunk inner peripheral wall. A circular spiral type powder introduction part that guides as a swirling flow, and a fine powder removal part that is suspended downward for a certain length from the ceiling of the cyclone tower along the radial center position of the body, and the lower end is open Of the primary air take-out cylinder and the bottom opening of the cyclone tower And a storage tank for storing coarse powder falling from the lower end opening, and a secondary air outlet connected to the storage tank for extracting air at an air flow rate of 10 to 15% of the air flow rate blown into the powder introduction section. A cyclone-type dry classification device having a structure having a tube.