JP2006320796A - Cylindrical screen classifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylindrical screen classifier which enables a direct arrangement and use to a high concentration and high vacuum transporting apparatus. <P>SOLUTION: In the cylindrical screen classifier (102), a rotor (9) rotating at high velocities and a plurality of blades (16) attached to an outer periphery of the rotor radially and with a slight twist angle, and provided with a small clearance between the outer peripheral edge and an inner surface of a cylindrical screen are fitted on the center line (11c) inside the cylinder of the synthetic resin cylindrical screen (11) to which a tension is applied in a cylindrical axial direction. Thus, the cylindrical screen classifier (102) supplies powder raw materials from an end of the cylindrical screen (11) to the inside, and sieves them into more coarse grains and finer grains compared to a screen net. In the cylindrical screen classifier connected to a transport means (L) transporting the powder raw materials in high concentrations and high vacuum, a coarse grain-discharge preventing disc (15) is provided openably on a discharge end discharging the coarse grains of the cylindrical screen (11). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to inorganic powders such as metal powder, nickel powder, calcium carbonate, alumina and silica, powders such as pharmaceuticals, active pharmaceutical ingredients, food processing powders, cosmetics such as foundations, toners for developing electrostatic images, powder coatings, etc. The present invention relates to a cylindrical screen classifier for sieving raw materials.

  This type of cylindrical screen classifier has a plurality of flat blades attached to the outer periphery of a support disk on a rotor that rotates at high speed, with a slight twist angle, and an interval that does not contact the blades. The powder raw material is introduced from one end of the outer periphery of the rotor that rotates at high speed, and is swirled while uniformly dispersing the raw material along the circumferential inner surface of the cylindrical screen by the action of a blade. As a result, centrifugal force of several tens of times gravity is applied to the raw material particles, and finer particles than the mesh of the cylindrical screen pass through this mesh, and the powder particles remaining on the inner surface of the screen are conveyed by the effect of the twist angle of the blade. And discharged from the other end.

The cylindrical screen is made of a synthetic resin woven net such as polyester, nylon, polypropylene, and fluororesin. By applying an appropriate tension in parallel with the central axis of the cylinder, the cylindrical screen has an amplitude with reference to one end and the other end of the cylindrical surface. Small high-frequency micro vibrations occur, preventing screen clogging.
Based on such a principle, the cylindrical screen classifier has a larger passing amount per unit area of the screen than other vibrating sieves and can finely classify those having a size of 1 mm or less and 10 microns or more. (See Patent Document 1.2.)

JP-A-60-220173 JP-A-01-262972

In conventional cylindrical screen classifiers (Patent Documents 1 and 2), the powder raw material is supplied at a high speed by supplying the raw material quantitatively at or near normal atmospheric pressure. By using a plurality of blades attached to the inner surface of the cylindrical screen, the raw material was uniformly dispersed and swirled, and the performance could be demonstrated.
As feeders for feeding raw materials to the cylindrical screen classifier, fixed feeders such as screw feeders, vibratory feeders, and rotary valves are used, and a storage hopper that temporarily accumulates the raw materials above the feeders. It has been done.
The fine powder and coarse powder that have been sieved may be transferred directly to the product tank using gravity, or may be transported together with air using the power of the blower and then transported to the product tank.

In recent years, in the pharmaceutical industry, the food industry, and other industries that handle powder raw materials using various chemical equipment, a method using high concentration and high vacuum has been adopted as a means for supplying and transporting the powder raw materials. .
The high concentration high vacuum mentioned here refers to a state where the concentration in the mixing ratio is 10 kg or more of powder with respect to 1 kg of air and the degree of vacuum in the transport piping is -10 to -50 kPa.

  This method has the following advantages: (1) Compared to low-concentration and low-vacuum using conventional blowers, etc., powder is transported with a small amount of air, so the capacity of equipment such as pipe dust collectors and cyclones can be reduced, and space can be reduced. (2) The powder can be transported at a slower speed and the pressure fluctuation is reduced, so that there is less wear on the piping and equipment caused by the powder material, and the powder particles are damaged during transportation ( (3) The amount of air required for transportation is reduced, the compressor and the electric motor are reduced, and the energy cost is reduced.

  When a conventional cylindrical screen classifier is placed in such a high-concentration, high-vacuum transport pipe and sieved, a high-concentration powder material is supplied to one end of the cylindrical screen, and the powder is applied to the inner surface of the cylindrical screen. It is difficult to disperse and swivel the body material uniformly and with a thin powder layer thickness, and when the powder layer thickness on the inner surface of the cylindrical screen is increased, most of the powder material that must originally pass through the cylindrical screen is the screen. A large amount remains without passing through, and what is supposed to be an under-sieving product is discharged as an over-sieving product, and the classification efficiency is significantly deteriorated.

  Therefore, when using a cylindrical screen classifier for high-concentration, high-vacuum transport powder, until now, the powder raw material is temporarily stored in a storage hopper separated from the vacuum line after transport, and from that hopper, It was necessary to take a method of supplying the raw material to the cylindrical screen classifier with a quantitative feeder such as a feeder, a vibratory feeder, or a rotary valve. As a result, a storage hopper and a supply machine space are required, the cost of equipment increases, and the advantages of high-concentration and high-vacuum transportation are hindered.

  In view of the above circumstances, an object of the present invention is to directly put a cylindrical screen classifier into a high-concentration and high-vacuum transport line so that efficient classification performance can be maintained.

  According to a first aspect of the present invention, there is provided a rotor that rotates at high speed on a center line in a cylinder of a synthetic resin cylindrical screen that is tensioned in the cylinder axis direction, and is attached to the outer periphery of the rotor with a radial and slightly twisted angle. A plurality of blades provided with a small gap between the outer peripheral edge and the inner surface of the cylindrical screen, and the powder raw material is supplied into the inside from one end of the cylindrical screen, and is larger than the mesh of the screen. A cylindrical screen classifier for sieving into fine particles and small fine particles, wherein the coarse powder of the cylindrical screen is discharged; At the end of the discharge opening, a coarse grain discharge prevention disk is installed, which is in close contact with the screen mounting frame on the coarse grain discharge end side and closed, and the screen is attached at a fixed time. It was released from the coarse to discharge the sieved product chamber, and wherein the opening and closing freely operate.

When a high-concentration powder raw material is directly fed into a cylindrical screen classifier from a high-concentration high-vacuum transport line (means), a cylinder is provided with quantitativeness in a screw feeder in the raw material supply chamber and is attached to the classification chamber. It is put into one end of the screen.
At this time, the high-concentration powder raw material is swirled while being dispersed on the inner surface of the cylindrical screen by a support disk of the rotor in the rotating part of the cylindrical screen classifier and a plurality of blades radially attached to the outer periphery of the support disk. . However, since it is a high-concentration powder, the dispersion layer thickness is increased, and many of the powder particles that should pass through the screen are conveyed to the coarse particle discharge end of the cylindrical screen without contacting the cylindrical screen. .

At this time, the coarse particle discharge prevention disk of the cylindrical screen is brought into contact with the cylindrical screen mounting frame on the coarse particle discharge end side and attached with sufficient sealing, and the powder particles that should pass through the screen stay in the cylindrical screen. , So that it is not discharged into the product chamber on the sieve.
As a result, the powder raw material is blocked by the coarse particle discharge prevention disk and is not discharged into the product chamber on the sieve, but continues to swivel on the inner surface of the cylindrical screen by the action of the rotating blade.

As the high-concentration powder continues to swirl within the cylindrical screen, the powder particles have an opportunity to contact the screen sequentially and pass through the screen.
During this time, high-concentration powder is sequentially supplied to the cylindrical screen classifier and is prevented from being discharged into the product chamber on the sieve. When the raw material layer thickness increases, the centrifugal force increases further, and the amplitude generated on the resin cylindrical screen increases. Since the vibration acceleration is increased and the amount of powder passing through the cylindrical screen is increased, the classification is continuously performed even when the high-concentration powder is successively supplied.

  If the raw material is continuously supplied into the cylindrical screen for a certain period of time, the coarse particles cannot be passed through the screen, and the coarse particles stay inside the screen. . Therefore, after a certain period of time, the coarse particle discharge prevention disk is connected to an air cylinder, etc., and released from the coarse particle discharge side cylindrical screen mounting frame, thereby discharging coarse particles on the cylindrical screen to the sieve product chamber. To do.

The period during which this coarse particle prevention disc is operated is the period during which the product container of the high concentration high vacuum transporter is full, the vacuum state is released, and the high concentration transport is suspended and discharged to the external product tank. To do.
If this disk is opened while high-concentration powder raw material continues to be supplied to one end of the cylindrical screen in the classification chamber, the unsieved product, which should pass through the screen, will flow to the on-sieve product chamber Therefore, the period for operating the coarse particle discharge prevention disk is controlled to be performed within the above period.
By repeating this operation, the cylindrical screen classifier can exhibit the same performance as that of the conventional method of quantitatively supplying and classifying raw materials in the open atmosphere, even in a high concentration transport pipe.

  According to a second aspect of the present invention, there is provided a rotor that rotates at a high speed on a center line in a cylinder of a synthetic resin cylindrical screen that is tensioned in a cylindrical axis direction, and is attached to the outer periphery of the rotor with a radial and slightly twisted angle. A plurality of blades provided with a small gap between the outer peripheral edge and the inner surface of the cylindrical screen, and the powder raw material is supplied into the inside from one end of the cylindrical screen, and is larger than the mesh of the screen. A cylindrical screen classifier for sieving into fine grains and small fine grains, wherein the powder raw material is connected to a transportation means for transporting the powder raw material in high concentration and high vacuum; the width (B) of the blade and the The ratio (B / D) of the diameter (D) of the cylindrical screen is 0.02 to 0.1.

In the cylindrical screen classifier of the present invention, the high concentration powder raw material is supplied to one end of the cylindrical screen in the classification chamber, and a plurality of blades are attached radially to the outer periphery of the support disk of the rotor in the rotating part and the support disk. To disperse and swirl the raw material.
At this time, it is well known in aerodynamics that an eddy current corresponding to the blade width (height) is generated downstream of the rotation side of the flat blade rotating at a high speed. Is not uniformly dispersed, fine particles to be passed through the screen are entrained in the vortex and are transported to the discharge end of the cylindrical screen without coming into contact with the inner surface of the screen, resulting in poor classification efficiency. In particular, this phenomenon tends to appear remarkably in the case of high concentration powder.

  Accordingly, the second aspect of the present invention is attached to the outer periphery of the rotor in a radial manner at a small interval without coming into contact with the inner periphery of the cylindrical screen attached with appropriate tension applied in parallel with the rotation axis direction. In a cylindrical screen classifier having a plurality of blades, the ratio of the inner diameter (D) of the screen to the width (B) of the blade (B / D) is in the range of 0.02 to 0.1, and is generated by the blade. Eddy currents are suppressed, and the classification efficiency is greatly improved.

  The material of this blade is a steel plate made of titanium, stainless steel, corrosion-resistant aluminum, etc. that has chemical resistance, but when the screen has a fine mesh (100 microns or less), it is more elastic than steel. Resin materials with a small surface friction coefficient have higher performance to disperse raw materials more uniformly on the inner surface of the screen, and materials with chemical and solvent resistance such as fluororesin (registered trademark Teflon), polyacetal, MC It is desirable to use nylon, glass fiber, ultra high molecular weight polyethylene (high moller), or the like.

In addition, the blade is attached to the rotor support disk with a slight twist angle with respect to the axial direction and rotated to effectively convey the raw material, thereby enabling effective classification over the entire screen. .
Further, the effect of further suppressing the generated eddy current can also be seen by making the cross-sectional shape of the blade triangular, and mounting the blade so that one of the ridge lines is positioned on the downstream side in the rotation direction.

Conventionally, powder classification for high-concentration and high-vacuum conveyance is stored in a storage hopper that is open to the atmosphere at one end, and a raw material is supplied from the hopper to a cylindrical screen classifier using a quantitative feeder such as a screw feeder or vibration feeder. Although the classifying performance could only be demonstrated by supplying, the cylindrical screen classifier can be arranged directly in the high-concentration and high-vacuum transport piping according to the present invention.
As a result, it is possible to eliminate raw material hoppers and fixed-quantity feeders, which not only greatly reduces the required space, but also reduces the piping for powder conveyance, and has been used for high-concentration, high-vacuum transportation. By using a high vacuum generator using a vacuum pump or ejector and a product container equipped with a dust collecting function as they are, it is efficient, low cost and energy saving with less damage to powder particles and wear of equipment. The classification of became possible.

  In addition, by setting the ratio of the width (height) of the rotating blade of this classifier to the diameter of the cylindrical screen to be mounted in the range of 0.02 to 0.1, the vortex generated by the rotating blade can be reduced. As a result, the raw material can be uniformly dispersed on the circumference of the cylindrical screen, and the classification efficiency can be greatly improved.

Embodiments of the present invention will be described with reference to FIGS.
A cylindrical screen classifier (102) is incorporated in the high concentration high vacuum transport line (means) (L). The cylindrical screen classifier (102) includes a rotor (9) that rotates at a high speed on a center line (11c) in a cylinder of a synthetic resin cylindrical screen (11) that is tensioned in a cylindrical axis direction, A plurality of blades (16) are attached to the outer periphery of the rotor in a radial manner with a slight twist angle, and a small gap is provided between the outer peripheral edge and the inner surface of the cylindrical screen (11). The powder raw material (G) is supplied into the inside from one end of (11), and sieved into coarse particles larger than the mesh of the cylindrical screen (11) and small fine particles.

  Next, the classifier (102) will be described in detail. The left and right guide rods (4) are attached to the bearing case (1), and the raw material supply chambers are sequentially attached to the guide rods (4). (2) The classification chamber (3) and the sieve top product chamber (5) are inserted, and each part has a structure that fits so that the center of rotation coincides accurately. The chambers (2), (3), and (5) are screwed by knob bolts (not shown), and an O-ring (6) is attached to the boundary wall to maintain the vacuum sealability.

  In order toward the free end of the shaft (7) mounted on the bearing in the bearing case (1), the screw feeder (8) is placed in the raw material supply chamber (2), and the rotor is placed in the classification chamber (3). (9) is attached and is securely mounted on the shaft with the shaft end disk (10) and screw.

  The raw material supply chamber (2) is connected to the raw material tank (110) through a high concentration high vacuum transport pipe (111). The powder raw material in the raw material tank (110) is transported to the raw material supply chamber (2) with high concentration and high vacuum. Here, as described above, “high concentration and high vacuum” refers to 1 kg of air. It means that the degree of vacuum in the transport pipe is in the range of -10 kPa to -50 kPa in a concentration state with a weight mixing ratio of 10 kg or more of the powder.

  In the classification chamber (3), a cylindrical screen (11) is attached to a screen mounting frame (12), and a coarse particle discharge prevention disk (13) is openable and closable with respect to the screen mounting frame (12). An air cylinder (14) is provided for operation. The air cylinder (14) is fixed to the sieve product chamber wall (15), and its piston is fixed to the coarse particle discharge prevention disk (13).

  When the high-concentration powder raw material is introduced into the raw material supply chamber (2) of the classifier (102) by the suction force of the high vacuum generator (101) using an ejector or a vacuum pump, the raw material supply chamber ( 2) By the screw feeder (8) in the inside, the raw material is conveyed in the horizontal axis direction, enters the cylindrical screen (11) in the classification chamber (3), and is attached to the circumferential portion of the rotor (9). By the action of the plurality of blades (16), the blades are uniformly distributed and swirled on the inner surface of the cylindrical screen (11).

At this time, the powder raw material is uniformly dispersed on the inner periphery of the cylindrical screen (11) by the blade (16), and at the same time receives centrifugal force, generates high-frequency vibration in the cylindrical screen (11), and the screen is clogged. Is prevented.
The dispersed high-concentration powder raw material is finer (fine particles) than the opening of the circular screen (11) passes through the cylindrical screen and reaches the fine powder outlet (17).

  In this blade (16), the raw material is uniformly dispersed on the inner surface of the cylindrical screen, and at the same time, a vortex is generated according to the width (height) (B) of the blade (16). , Disturbing the dispersion and swirling action of the powder raw material, degrading the classification performance.

  Therefore, in order not to disturb this uniform dispersion action, the ratio (B / D) of the blade width (height B) to the diameter (D) of the cylindrical screen (11) is 0.02 to 0.1. It is desirable to use sized blades (16).

  The cross-sectional shape of the blade is formed in a rectangular shape as shown in FIG. 3, but this shape is formed in a substantially triangular shape as shown in FIG. There may be one ridge line portion having a triangular cross-sectional shape at one location on the flat portion of the shape and on the downstream side in the rotation direction.

  During the time when the high-concentration powder raw material is supplied to the cylindrical screen, the coarse particle discharge prevention disk (13) is in close contact with one end of the screen mounting frame (12), and the cylindrical screen in the input raw material Powder (fine particles) finer than the classification opening of (11) passes through the cylindrical screen (11) and is discharged to the fine powder discharge port (17). The powder discharged to the fine powder discharge port (17) is sucked and stored in a product container (103) connected by piping. The powder (coarse particles) coarser than the classification openings stays while swirling inside the cylindrical screen (11).

When the high-concentration powder is continuously put into the raw material supply chamber (2) while receiving such an action, raw materials coarser than the screen openings start to increase.
At this time, when the raw material in the product container (103) accumulates and the level meter (106) senses that it reaches a specified level, for example, a full level, a signal is output to a control panel (not shown). . Then, the control panel stops the vacuum generator (101), and immediately after that, the vacuum breaker solenoid valve (not shown) is operated to bring the inside of the high-concentration high-vacuum piping to atmospheric pressure. Simultaneously with the atmospheric state, the valve (104) under the product container (103) is opened, and the product powder is discharged to the external product tank (105).

  At the time of discharging the product, the high-concentration raw material powder is not sucked and conveyed, and the inside of the cylindrical screen is similarly changed from the vacuum state to the atmospheric pressure. Therefore, the coarse powder discharge preventing disk (13) is provided by means such as an air cylinder (14). When opening from the discharge end of the screen mounting frame (12), coarse particles staying inside the cylindrical screen are discharged into the sieve product chamber (5).

When the product powder is completely discharged from the product container (103), the lower valve (104) is closed, and at the same time, the coarse particle discharge prevention disk (13) is brought into close contact with the coarse particle discharge side of the screen mounting frame (12). Thereafter, the high vacuum generator (101) is operated, the high-concentration powder raw material is sucked and conveyed, and the raw material is supplied again to the cylindrical screen classifier (102).
By using such a cycle repeatedly, it became possible to install a cylindrical screen classifier directly connected to the high concentration vacuum transport line.

Examples of the present invention will be described.
First, the first experimental example will be described.
Conditions for the first experimental example:
Cylindrical screen dimensions: Internal diameter 250mm Effective length 215mm
Cylindrical screen: Material polyester 150 micron opening Rotor rotation speed: 700rpm
Blade: Width 12mm (B / D = 0.048)
Material Polyacetal resin

Lactose was used as a raw material using the cylindrical screen classifier having the above specifications.
The particle size of the lactose raw material is 0.4% when the weight is 150 microns or more, and 10 hairs are mixed therein.
Using the high-concentration powder transporter (Stellar ST-10-20E, manufactured by Matsui Seisakusho Co., Ltd.) under the above conditions, can this machine be placed in the piping of the raw material tank and high-concentration transporter to ensure that foreign matter can be removed reliably? confirmed.

At this time, the high-concentration powder transporter transported the powder continuously at 350 kg / h and verified after processing 100 kg of the raw material. As a result, among the recovered raw materials, it passed through the 150-micron mesh screen. The weight of the non-sieved product was 0.6% and all 10 hairs were collected on the sieve.
Under the sieve on the product side, 99.4% by weight was collected, and 100% of foreign matter could be removed.

Next, a second experimental example will be described.
Conditions of the second experimental example Cylindrical screen dimensions Material Opening rotor rotation speed is exactly the same as the first experimental example, blade width 30mm (B / D = 0.12), material polyacetal, using the raw material Using the same lactose, a cylindrical screen classifier having a structure incorporating only the “invention according to claim 1”, that is, a cylindrical screen classifier provided with a coarse particle discharge prevention disk, and the first experimental example, The same high concentration powder transporter was used.

  As a result, the weight percent of products with an opening of 150 microns or more collected in the sieving product chamber side in the lactose raw material is 4.0%, and that of products less than 150 microns collected in the sieving product is 96.0. % By weight. The processing capacity at this time was set to 350 kg / h by operating the transporting capacity of the high-concentration powder transporting apparatus in the same state as in the first experimental example.

Next, a comparative example (conventional example) will be described.
Conditions of the comparative example Cylindrical screen dimensions Material Opening The rotor rotation speed is exactly the same as in the previous experiment, and the blade width is 30 mm (B / D = 0.12), the material is polyacetal, and the raw materials are the same. Using lactose, a cylindrical screen classifier having a conventional structure described in “Patent Document 1” or “Patent Document 2” and the same high-concentration powder transport machine as in the above experimental example were used.

  As a result, the weight percent of products with an opening of 150 microns or more recovered in the sieving product chamber side in the lactose raw material is 42%, and the product of 150 microns or less recovered in the sieving products is 58.0%. became. That is, in this comparative example, the classification efficiency is extremely poor compared to the experimental examples 1 and 2, and as a result, even if a conventional cylindrical screen classifier is directly connected during high-concentration powder transportation, it is actually used. Classifying performance that can withstand The processing capacity at this time was set to 350 kg / h by operating the transporting capacity of the high-concentration powder transporting apparatus in the same state as in the experimental example.

It is front sectional drawing of the cylindrical screen classifier of this invention. FIG. 2A is a left side view, and FIG. 2B is a front view of a cylindrical screen of the present invention. The XX sectional drawing of FIG. 1 is represented. FIG. 1 is a cross-sectional view taken along line XX in FIG. 1 and shows another embodiment. It is a figure which shows the Example of the classification process using the cylindrical screen classifier of this invention.

Explanation of symbols

1 Bearing case 2 Raw material supply chamber
3 Classification chamber 4 Guide rod 5 Sieve product chamber 6 O-ring 7 Shaft 8 Screw feeder 9 Rotor 10 Shaft end disk 11 Cylindrical screen 12 Screen mounting frame 13 Coarse grain prevention disc 14 Air cylinder 15 Sieve product wall 16 Blade 17 Fine powder Discharge port 101 High vacuum generator 102 Classifier 103 Product container 104 Valve 105 Product tank 106 Level meter

Claims (6)

A rotor rotating at high speed on the center line in the cylinder of the synthetic resin cylindrical screen that is tensioned in the cylinder axis direction, and the outer periphery of the rotor is attached to the outer periphery of the rotor in a radial and slightly twisted angle. A plurality of blades with small gaps are attached to the inner surface of the cylindrical screen, the powder raw material is supplied from one end of the cylindrical screen to the inside, and coarse particles and small fine particles larger than the mesh of the screen A cylindrical screen classifier connected to transport means for transporting the powder raw material in high concentration and high vacuum;
A coarse particle discharge prevention disk is provided at the discharge opening end portion where the coarse particles of the cylindrical screen are discharged, and is tightly closed with the screen mounting frame on the coarse particle discharge end side, and is separated from the screen mounting frame at a predetermined time interval. A cylindrical screen classifier which is opened and opened and opened so that coarse particles are discharged into the sieve product chamber. A rotor rotating at high speed on the center line in the cylinder of the synthetic resin cylindrical screen that is tensioned in the cylinder axis direction, and the outer periphery of the rotor is attached to the outer periphery of the rotor in a radial and slightly twisted angle. A plurality of blades with small gaps are attached to the inner surface of the cylindrical screen, the powder raw material is supplied from one end of the cylindrical screen to the inside, and coarse particles and small fine particles larger than the mesh of the screen A cylindrical screen classifier connected to transport means for transporting the powder raw material in high concentration and high vacuum;
A cylindrical screen classifier having a ratio (B / D) of a width (B) of the blade and a diameter (D) of the cylindrical screen of 0.02 to 0.1. A rotor rotating at high speed on the center line in the cylinder of the synthetic resin cylindrical screen that is tensioned in the cylinder axis direction, and the outer periphery of the rotor is attached to the outer periphery of the rotor in a radial and slightly twisted angle. A plurality of blades with small gaps are attached to the inner surface of the cylindrical screen, the powder raw material is supplied from one end of the cylindrical screen to the inside, and coarse particles and small fine particles larger than the mesh of the screen A cylindrical screen classifier connected to transport means for transporting the powder raw material in high concentration and high vacuum;
A coarse particle discharge prevention disk for opening and closing the discharge opening end where the coarse particles of the cylindrical screen are discharged is provided,
A cylindrical screen classifier having a ratio (B / D) of a width (B) of the blade and a diameter (D) of the cylindrical screen of 0.02 to 0.1.   The blade has a substantially triangular cross-section, and has one triangular cross-section plane portion on the upstream side in the rotation direction and one triangular cross-section ridge line portion on the downstream side in the rotation direction. The cylindrical screen classifier according to claim 1, 2, or 3.   The transportation means transports the powder raw material in a state where the vacuum in the transportation pipe is in the range of -10 to -50 kPa in a state where the weight mixing ratio is 10 kg or more of the powder with respect to 1 kg of air. Item 4. The cylindrical screen classifier according to item 1, 2 or 3.   6. The cylindrical screen classifier according to claim 1, 2, 3, 4, or 5, wherein the blade is made of a synthetic resin having elasticity and having a slippery surface.

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