JPH0578392B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an air classifier that generates a high-speed swirling vortex in a powder material supplied to a classification chamber to centrifugally separate it into fine powder and coarse powder.

[Background technology]

Conventionally, air classifiers include the Clacyclone (Nagoya Institute of Technology Report 8 [4] 235 (Showa 34)) and the Iitani classifier (Japanese Society of Mechanical Engineers 59 [3] 215 (Showa 34)).
31) have been proposed, but with these, the separated particle size is determined by the mechanical shape, making it difficult to adjust the classification point. In addition, since the powder material is introduced into the classification chamber from a single point, the dispersion of the powder is poor, and if the raw material input speed is increased, the classification accuracy will drop significantly and the separated particle size will shift to coarser particles. It has the following problems. As a solution to this problem, Japanese Patent Application Laid-Open No. 54-48378
A method has been proposed in which the height of the classification chamber can be controlled, as in Japanese Patent Application Laid-open No. 54-79870, in which a cyclone-shaped guide tube is attached above the classification chamber. In reality, a combination of these proposals has been put into practical use.

Figure 5 shows a schematic diagram of a classification device that has been put into practical use.

However, this type of air classifier as shown in Fig.
The part for supplying powder material to the classification chamber (combining the technology described in the above publication) has a cyclone-like shape, and a guide cylinder 50 is provided in the center of the upper surface of the upper cover 60 in an upright manner. A supply cylinder 80 is connected to the upper outer peripheral surface of the guide cylinder 50. Supply cylinder 80
are connected to the outer periphery of the guide cylinder 50 so that the powder material supplied via the supply cylinder 80 is introduced into the guide cylinder in a circumferential tangential direction. When the powder material is supplied into the guide tube 50 from the supply tube 80, the powder material turns and descends along the inner peripheral surface of the guide tube 50. In this case, the powder material descends in a band shape from the supply cylinder 80 along the inner circumferential surface of the guide cylinder 50, so the powder material falls into the classification chamber 80.
The distribution and concentration of the powder material flowing into the classification chamber become non-uniform (the powder material flows into the classification chamber only from a part of the inner peripheral surface of the guide cylinder), resulting in poor dispersion. Furthermore, if the throughput is large, agglomeration of the powder material is likely to occur, and furthermore, there is a problem that sufficient dispersion is not achieved, making it impossible to perform highly accurate classification. In addition, when the amount of air that conveys the powder material is large, there is a problem that the amount of air flowing into the classification chamber is large, so that the speed toward the center of the particles swirling in the classification chamber increases and the separated particle diameter becomes large. Therefore, when reducing the separated particle size, air is normally extracted from the upper part of the guide cylinder 140 by controlling it with a damper, but in practice, if a large amount of air is extracted, some of the powder material will also be discharged and lost. Problems may arise.

In addition, as proposed in Japanese Utility Model Application Publication No. 54-81172, as shown in Figs. 6 and 7, the passage area gradually decreases from the starting end on the inlet side to the terminal end on the outer periphery of the peripheral wall of the classification chamber. A spiral supply cylinder is provided, and a large number of louvers are provided tangentially to the circumferential direction of the annular communication portion provided between the supply cylinder and the classification chamber.
There is also an air flow classifier characterized in that an annular high-pressure air supply chamber is provided around the outer periphery of the supply cylinder, and a plurality of nozzle holes facing in the same direction as the louvers are formed in the circumferential direction of the inner peripheral wall of the supply chamber. Proposed. This classifier is improved so that the dispersed powder material flows into the classification chamber at a uniform speed from between the louvers. However, since the high pressure air A is injected into the supply tube 150 from the nozzle hole 220, turbulence occurs due to the high pressure air.
There is a problem that the classification accuracy decreases.

Therefore, a supply method in which high-pressure air is omitted as shown in Figs.
50, it does not flow uniformly into the classification chamber from between each louver, but flows in a large amount from the end, so it is possible to obtain the effect as shown in the device shown in FIGS. 6 and 7. Have difficulty.

Furthermore, in the apparatus shown in FIGS. 6 and 7, the swirling flow that contributes to classification in the classification chamber is only the air flowing in from between the louvers 70, so the powder material is Since the centrifugal force caused by the airflow causes the particles to move along the outer periphery of the classification chamber, similar to the effect of a cyclone, there is a problem in that the collection element is strong and fine particles tend to mix into the coarse particles.

[Purpose of the invention]

An object of the present invention is to provide an air classifier that solves the above problems.

An object of the present invention is to provide an air classifier that can uniformly introduce powder material into a classification chamber.

An object of the present invention is to provide an air classifier with improved classification density by reducing the velocity of powder particles swirling in the classification chamber toward the center of the classification chamber.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air classifier capable of classifying powder materials having a fine particle size more precisely than conventional devices.

[Summary of the invention]

The present invention provides an annular guide chamber communicating with a powder supply tube in the upper part of the classification chamber, and the powder material supplied from the powder supply tube through the guide chamber together with conveying air is rotated and descended. so as to be introduced in a distributed manner toward the center of the classification chamber.
A plurality of introduction louvers are provided between the guide chamber and the classification chamber, the tips of which are oriented tangentially to the inner circumferential direction of the guide chamber, and the bottom of the classification chamber is formed such that the center portion is higher. A slanted classification plate is arranged, and classified air is sucked and introduced from the outside around the classification chamber so as to further accelerate the rotation speed of the powder material introduced into the classification chamber from between the introduction louvers. A plurality of classification louvers are arranged for the classification plate, and a coarse powder discharge port is provided for discharging the coarse powder classified from the powder material by centrifugation using classification air on the classification plate to the outer periphery of the classification plate. and a fine powder discharge chute connected to a fine powder discharge port for discharging fine powder classified from the powder material from the center of the classification plate.

[Specific description of the invention]

Hereinafter, the present invention will be explained based on the accompanying drawings.
1 and 2 are diagrams schematically showing an embodiment of the air classifier of the present invention.

In FIG. 1, 1 indicates a cylindrical main body casing, and 2 indicates a lower casing, to which a hopper 3 for discharging coarse powder is connected. The inside of the main casing 1 is formed with a classification chamber 4, and the upper part of the classification chamber 4 includes an annular guide chamber 5 attached to the upper part of the main casing 1 and a conical (umbrella-shaped) upper part with a high central part. It is closed by a cover 6.

A plurality of introduction louvers 7 arranged in the circumferential direction are provided on the partition wall between the classification chamber 4 and the guide chamber 5.
The powder material and air sent into the chamber are swirled and flowed into the classification chamber 4 from between the respective introduction louvers 7.
Note that it is necessary for the air and powder material flowing through the guide chamber 5 through the supply cylinder 8 to be uniformly distributed to each introduction louver 7 for accurate classification. The flow path leading to the introduction louver 7 must be shaped to prevent concentration due to centrifugal force, and as shown in Fig. 2, the supply tube is connected perpendicularly to the direction of the surface of the outer periphery of the guide chamber. It communicates with the guide room which has sufficient space above the louver. As shown in FIG. 3, a plurality of supply tubes 8 are attached, or
As shown in FIG. 4, the supply cylinder 8 may be connected from above perpendicular to the horizontal plane of the classification chamber 4.

In this way, air and powder material are supplied to the classification chamber 4 through the introduction louver 7, and when supplied to the classification chamber 4 through the introduction louver 7, a marked improvement in dispersion is obtained compared to the conventional method. It will be done. Further, the introduction louver 7 is movable, and the louver interval can be adjusted.

Classifying louvers 9 arranged in the circumferential direction are provided in the lower part of the main body casing 1, and classified air that causes a swirling flow is introduced into the classification chamber 4 from the outside through the classifying louvers 9.

A conical (umbrella-shaped) classification plate 10 with a high central portion is provided at the bottom of the classification chamber 4, and a coarse powder discharge port 11 is formed around the outer periphery of the classification plate 10. Further, a fine powder discharge chute 12 is connected to the center of the classification plate 10, and the lower end of the chute 12 is bent into an L shape.
This bent end portion is located outside the side wall of the lower casing 2. Further, the chute is connected to a suction fan via a fine powder collection means such as a cyclone or a dust collector, and the suction fan applies suction force to the classification chamber 4, causing the air to flow into the classification chamber 4 from between the classification louvers 9. The suction air creates the swirling flow required for classification.

The air classifier shown in the embodiment has the above-mentioned configuration, and when powder material is supplied together with air from the supply cylinder 8 into the guide cylinder 5, the air containing the powder material flows from the guide chamber 5 between each classification louver 7. The liquid flows into the classification chamber 4 while being swirled and dispersed at a uniform concentration.

The powder material introduced into the classification chamber descends while swirling, and the swirling speed is increased by the suction fan connected to the fine powder discharge chute 12 as the suction air flows in from between the classification louvers 9 at the bottom of the classification chamber. The centrifugal force acting on each particle centrifugally separates coarse powder and fine powder on the classification plate, and the coarse powder swirling around the outer periphery of the classification chamber 4 is discharged from the coarse powder discharge port 11, and is discharged from the hopper 3 at the bottom. more excreted. Further, the fine powder moving toward the center along the upper inclined surface of the classification plate 10 is discharged by the fine powder discharge chute 12 to the fine powder collecting means.

All of the air that flows into the classification chamber 4 together with the powder material flows into the classification chamber 4 as a swirling flow. Classification with a small separation particle size is performed, and fine powder with a very small particle size can be discharged to the fine powder discharge chute 12. Moreover, since the powder material flows into the classification chamber at a substantially uniform concentration, it is possible to obtain powder with a fine distribution.

In particular, as shown in Figure 10, an air classifier is used in a system in which it is directly connected to a jet mill and serves as a classifier for the jet mill, separating coarse particles from the particles crushed by the jet mill and returning them to the jet mill for crushing. In this case, the amount of air supplied to the classifier (the amount of air flowing in from the supply cylinder 8)
This effect becomes more pronounced as the number increases. Furthermore, in this case, when increasing the throughput of the jet mill or obtaining pulverized products with small particle sizes,
It is necessary to increase the amount of grinding air used in the jet mill, resulting in a more significant effect.

Example 1 Styrene-acrylic resin 100 parts by weight Magnetic material (0.3μ) 60 parts by weight Charge control agent 2 parts by weight Low molecular weight polypropylene resin 4 parts by weight A toner material consisting of the above formulation was heated and kneaded,
After cooling, the powder material obtained by coarsely pulverizing it with a hammer mill is transferred to the air classifier shown in Figure 4 at a rate of 100 per minute.
As shown in Figure 10, the separated coarse powder was introduced into a jet mill (supersonic jet mill manufactured by Nippon Neumatic Industries Co., Ltd.) connected to the classifier, and finely pulverized (jet air pressure for pulverization was 5 kg).
f/cm ² ), and the finely pulverized powder material is again
It was put into the classifier together with the coarsely pulverized powder material to obtain separated fine powder as a pulverized product. Average particle size
A finely ground product with a particle size of 4.7 μm and a frequency of 0.1% by weight of 10 μm or more was obtained at 100 g/min. The average particle size is the median particle size of the particle size-weight distribution, and was measured using a Coulter Counter manufactured by Coulter Electronics.

Example 2 The same material as in Example 1 was fed into the same classifier-jet mill as in Example 1 at the same feed rate (100 g/min) as in Example 1, and the jet air pressure for crushing was set to 6.
A finely pulverized product was obtained at Kgf/cm ² , with an average particle size of 3.7 μm, a frequency of 0% by weight of 10 μm or more, and a yield of 100 g/min.

At this time, the amount of air that entered the air classifier together with the powder material was about 1.2 times that in Example 1.

Comparative Example 1 The same crushed material as in Example 1 was fed into the air classifier shown in Fig. 5 at the same feed rate (100 g/min) as in Example 1, and the separated coarse powder was transferred to a jet mill connected to the classifier. (Supersonic jet mill manufactured by Nippon Neumatic Industries Co., Ltd.) for fine pulverization (jet air pressure for crushing 5Kgf/cm ² ), and the finely pulverized material is again fed into the classifier together with the coarsely crushed material, and the separated fine particles are finely pulverized. When obtained as a product, its particle size was
The average particle size was 7.5 μm, the frequency of particles of 10 μm or more was 15.0% by weight, and the yield was 98 g/min.

Comparative Example 2 The same material as in Example 1 was fed into the same classifier/jet mill as in Comparative Example 1 at the same feed rate (100 g/min) as in Example 1, and the jet air pressure for pulverization was set to 6 kgf/cm ² to produce a finely pulverized product. The particle size was found to be 6.3 μm on average, and 7.0% by weight of 10 μm or more.
The yield was 97 g/min.

As described above, in Examples 1 and 2, finely pulverized products (separated fine powders) having smaller particle sizes than Comparative Examples 1 and 2 were obtained, respectively.

In addition, in Example 2, the jet air pressure for crushing was 1Kgf/ ^cm2 higher than in Example 1, and the air volume was 1.2
By doubling the amount, the particle size of the finely pulverized product was 4.7μm.
It was reduced by about 20% from 3.7 μn. On the contrary,
In Comparative Example 2 and Comparative Example 1, by similarly increasing the jet air pressure for pulverization by 1 kgf/cm ² , the particle size of the finely pulverized products was reduced by only 15% from 7.5 μm to 6.3 μm.

Furthermore, in Comparative Examples 1 and 2, loss of granular material from the guide cylinder upper part 140 was observed.

Comparative Example 3 The same material as in Example 1 was used in the same classifier as in Comparative Example 1.
When the material was fed into a jet mill and the jet air pressure for crushing was set at 5 kgf/cm ² to obtain a finely pulverized product with an average particle size of 4.7 μm, the maximum material feed rate at that time was 25 g/min, and the yield was is 24g/
It was min. Further, the particle size of the finely pulverized product was an average particle size of 4.7 μm, and the frequency of 10 μm or more was 0.5% by weight.

As described above, in Comparative Example 3, in order to obtain a finely pulverized product with the same average particle size as in Example 1, the processing capacity was reduced to 1/4.

Example 3 A toner material having the same composition as in Example 1 was heated and kneaded, and after cooling, it was coarsely ground with a hammer mill, and then fed to a jet mill (supersonic jet mill manufactured by Nippon Neumatic Industries Co., Ltd.) to obtain an average The toner powder, which has a particle size of 7.0 μm and has been finely pulverized to 4.0 μm or less at a frequency of 15% by weight, is classified using an air classifier shown in Figure 4 so that the average particle size of the separated fine powder is 4.0 μm. As a result, the average particle size of the separated fine powder was
The average particle size of the separated coarse powder was 7.5 μm, and the frequency of particles of 4.0 μm or less was 1.5% by weight. Further, the yield ratio of the separated fine powder and the separated coarse powder was 20:80.

Comparative Example 4 Toner powder with an average particle diameter of 7.0 μm and a frequency of 15% by weight of 4.0 μm or less as in Example 3 was separated using the air classifier shown in FIG. 5 to obtain an average particle diameter of 4.0 μm.
When the separated fine powder had an average particle size of 4.0 μm and a frequency of 2.5 μm or less was 15% by weight, the separated coarse powder had an average particle size of 7.4 μm and a frequency of 4.0 μm or less was 5% by weight. Compared to Example 3, powders with sharper particle size-weight frequency distributions were obtained for both fine and coarse powders.

Further, the yield ratio of the separated fine powder and the separated coarse powder at this time was 25:75.

As explained above, in the present invention, the powder material and the conveying air flowing into the classification chamber 4 from the supply tube 8 are swirled into the classification chamber 4 from between the introduction louvers 7 provided between the guide chamber 5 and the classification chamber 4. However, since the powder material is allowed to flow in from the entire circumference at a uniform concentration, it is possible to accurately and effectively classify the powder material. Furthermore, since the speed of particles rotating in the classification chamber 4 toward the center can be reduced, the diameter of the separated particles can be reduced. In particular, when there is a large amount of air flowing in with the powder material, such as in a system connected to a jet mill, the effect of reducing the separated particle size is significant, and it is effective to reduce the particle size of finely pulverized products using the jet mill. can be obtained.

[Brief explanation of the drawing]

FIG. 1 shows a longitudinal sectional side view of an air classifier embodying the present invention, and FIG. 2 shows a sectional view taken from the side of FIG. 1. FIG. 3 is a diagram showing a modification of FIG. 2,
FIG. 4 shows a longitudinal side view of another embodiment. Fifth
6 and 8 show longitudinal cross-sectional views of conventional classifiers, and FIGS. 7 and 9 show cross-sectional views taken along the line 6 and 8. FIG. 10 is a flowchart of a system in which an air classifier and a jet mill are connected in Examples and Comparative Examples. 4... Classification room, 5... Information room, 8... Supply tube,
7... Louver, 9... Classification louver, 10...
Classifying plate, 20...Powder inlet, A...High pressure air.

Claims (1)

[Claims] 1. An annular guide chamber communicating with a powder supply tube is provided in the upper part of the classification chamber, and the powder material supplied from the powder supply tube through the guide chamber together with conveying air is rotated. While descending, the particles are dispersedly introduced toward the center of the classification chamber.
A plurality of introduction louvers are provided between the guide chamber and the classification chamber, the tips of which are oriented tangentially to the inner circumferential direction of the guide chamber, and the bottom of the classification chamber is formed such that the center portion is higher. A slanted classification plate is arranged, and classified air is sucked and introduced from the outside around the classification chamber so as to further accelerate the rotation speed of the powder material introduced into the classification chamber from between the introduction louvers. A plurality of classification louvers are arranged for the classification plate, and a coarse powder discharge port is provided for discharging the coarse powder classified from the powder material by centrifugation using classification air on the classification plate to the outer periphery of the classification plate. An air flow classifier comprising: a fine powder discharge chute connected to a fine powder discharge port for discharging fine powder classified from the powder material from a central portion of the classification plate. 2. The air classifier according to claim 1, wherein the powder supply cylinder is arranged above the guide chamber. 3. Claim 1, wherein a popper for accommodating coarse powder discharged from the coarse powder discharge port is disposed at the bottom of the classification plate, and a fine powder discharge chute for discharging fine powder is disposed at the bottom of the classification plate. Or 2 air flow classifier.