JPH0111314Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to a classification device for powder particles, and more specifically to silicide powder used in fine ceramics and magnetic powder used in magnetic storage devices. It is used in so-called advanced technology such as, and is industrially applicable for particle size classification of ultrafine particle materials that require a very high degree of homogeneity into single or multi-phase with very high precision. It concerns the improvement of new technology.

(Prior art) In the following description, "fine particles" refer to particles with a particle size of 1 μm.
m. “Ultrafine particles” refer to particles with a particle size of 1 μm.
m. Point to the following particles. Furthermore, the term "powder particle group" refers to a group composed of fine particles or ultrafine particles distributed over a certain particle size range. Furthermore, the term "powder particle small group" refers to a small group comprised of fine particles or ultrafine particles distributed over a narrower particle size range within such a powder particle group.

For example, a certain powder particle group has a diameter of 0.9 to 0.1 μm. If it is composed of ultrafine particles distributed over a particle size range of 0.7 to 0.5 μm. A small group composed of ultrafine particles distributed over a particle size range of is one of the powder particle groups.

Furthermore, the expression "higher (or lower) particle size range" is a comparative expression, and for example, in the case of the above powder particle group, 0.9 to 0.7 μm. The grain size range is "high"
, and on the other hand, 0.5 to 0.3 μm. The particle size range of is "low".

The ultrafine particle materials used in the advanced technology fields mentioned above are extremely highly homogeneous;
That is, it is strongly required that the particle size be uniform. This is because, in the case of ultra-thin transparent ceramics used for lenses, for example, the electrical insulation properties and resolving power of the resulting lens are greatly influenced by the homogeneity of the silicide powder used as the material. Furthermore, in the case of storage media used in computers, such as magnetic tape, the storage density of the resulting medium is greatly influenced by the homogeneity of the magnetic powder used in the material.

In order to advance the production technology of such ultrafine particles, it is essential to develop handling techniques such as pulverization, classification, and transportation, and this invention is directed to classification techniques.

As techniques for classifying powder particles, techniques using centrifugal force, techniques using jet jets, and techniques using fluid elements are already known. However, in all of these known classification techniques, the classification limit is at most microns.
It certainly does not reach the level of ultrafine particles with a particle size of submicron units. Although some of them have been successful at the theoretical stage, many problems remain in terms of actual production processing capacity and power consumption, and there are still no examples of those that have been implemented on an industrial scale. Do not look.

Further, as will be described later, this invention utilizes ultrafine particles or the electrostatic deposition phenomenon of ultrafine particles, but electrostatic precipitators are already known as devices that utilize the electrostatic charge of particles. That is, it has a vertically elongated structure, with a discharge electrode and a dust collecting electrode plate facing each other with a gap in between, and a dust-containing airflow is caused to rise within the gap during discharge, collecting charged dust particles. The dust particles are captured and deposited on the electrode plate, and the accumulated dust particles are removed by being brushed off downward into the gap at regular intervals.

If such an electrostatic precipitator is used, when fine particles of micron size or larger are present in the dust-containing airflow, it is easy to separate them from the dust-containing airflow and remove them. This is sufficient for the purpose of dust collection (that is, dust removal). However, the function of an electrostatic precipitator stops there; it collects ultrafine particles, including the fine particles that have been removed, and either collects and classifies them according to particle size, or escapes dust removal and enters the upper atmosphere. There is no hope for the function of classifying the emitted ultrafine particles.

Furthermore, since ultrafine particles are very easy to fly up into the air, even if several small groups of powder particles are collected by some method from a group of powder particles, it is difficult to remove them all at once. This mechanism has a purpose and structure completely different from that of classification operations. Also, if ultrafine particles fly up during dusting,
Not only does it contaminate the working environment, but its loss also reduces the classification yield.

In view of these circumstances, the present applicant previously proposed the invention "Method and Apparatus for Electrostatic Classification of Powder Particles" by filing a patent application.

In this invention, a group of powder particles consisting of fine particles or ultra-fine particles covering a wide particle size range is mixed in a conveying air stream to form a solid-gas mixed phase flow having a uniform velocity distribution, and the particles are placed facing each other in a closed classification chamber. This solid-gas mixed phase flow is guided into the gap between the installed DC high voltage applied discharge plate and two or more collection elements installed vertically in parallel, and is caused to advance upward. A small group of powder particles having a particle size range of 100 to 100 mm are sequentially separated from the ongoing solid-gas mixed phase flow, and individually captured and recovered by each collection element.

The above-mentioned invention proposes that (a) in a solid-gas mixed phase flow, ultrafine particles with similar particle sizes agglomerate with each other to form a kind of agglomerate, and (b) in this case, ultrafine particles with a smaller particle size are easier to agglomerate; Large nodules are formed (c) The nodules in the solid-gas multiphase flow rising in the gap under discharge are acted upon by the upward force of the carrier airflow, and this is combined with the ion flow according to the charge amount of the particles. This is based on the mechanism that the nodules are deflected by the lateral force and electrostatic attraction caused by the particles, and (2) the nodules are made up of large-diameter particles with a large amount of charge, and the nodules are deflected earlier and more greatly. . In other words, the basis of classification is based on the agglomeration phenomenon of ultrafine particles.

The above proposed invention is highly praised in that it has made it possible to classify ultrafine particles in submicron units with high precision and on an industrial scale. However, as mentioned above, the basis of classification is based on the agglomeration phenomenon of ultrafine particles, and this aggregation phenomenon is not artificially controlled in any way, so the most unsatisfactory aspect is the accuracy of classification. , and the flexibility of responding to subtle changes in process conditions was unsatisfactory.

(Purpose of the invention) The purpose of this invention is to improve the accuracy of the electrostatic classification technology that has already been proposed for the industrial scale production of ultrafine particles with higher homogeneity suitable as materials for advanced technology. The aim is to further improve this process, and also to give it the ability to respond flexibly to subtle changes in process conditions.

(Basic structure of the invention) According to this invention, powder particles consisting of fine particles or ultrafine particles over a wide range of particle sizes are mixed in a conveying air stream to form a solid-gas multiphase flow with a uniform velocity distribution. Two or more DC high-voltage discharge plates arranged vertically in parallel in a classification chamber and collection elements preferably having collection holes grouped in the vertical direction are placed facing each other with a gap in between, and the upper discharge plate Increase the applied voltage. The solid-gas mixed-phase flow is introduced into the gap and progressed upward, and the small groups of powder particles having a lower particle size range are sequentially separated from the ongoing solid-gas mixed-phase flow under the discharge, and each collection hole of the collection element is separated from the solid-gas mixed phase flow. Each group is individually suctioned and collected.

(Embodiment of the invention) As described above, ultrafine particles in a solid-gas multiphase flow form agglomerates by aggregation, and this aggregation is further promoted when the solid-gas multiphase flow is exposed to electrostatic discharge. The effect of the applied DC voltage for electrostatic discharge on agglomeration is determined by the concentration of ultrafine particles (g/
If m ³ ) is kept constant, there will be a tendency approximately as shown in FIG. That is, the applied DC voltage is 50~
In the range of 100 KV, as the voltage increases, aggregation is promoted and the nodules become larger in approximately linear proportion. This invention utilizes the relationship between the applied DC voltage for electrostatic discharge and the nodules fostered and formed as a result of electrostatic discharge, as seen in FIG.

Figure 2 shows an example of the electrostatic classification device of this invention, which has a vertically elongated structure, the main part of which is a substantially hermetic shape defined appropriately by a frame and a wall. Classification room (this is omitted in the diagram)
It is arranged to accommodate.

This electrostatic classification device includes a solid-gas multiphase flow supply section 1 that sends out a solid-gas multiphase flow in which a group of powder particles to be classified is mixed with a conveying airflow in a rectified state so as to have a uniform velocity distribution. , a powder particle classifying section 2 is provided above and separates small groups of powder particles according to a predetermined particle size range from the supplied mixed flow; It consists of a transport airflow storage section 3 that actively takes over.

Of these, at least the classification section 2 is arranged in the above-mentioned closed classification chamber. Further, the supply section 1 and the storage section 3 form a rectified airflow by a so-called push-pull method by actively sending out and actively taking back the airflow.

The solid-gas multiphase flow supply section 1 includes a blowing mechanism 1 for conveying airflow.
1 and the rectifying discharge mechanism 1 that opens at the bottom of the classification chamber.
2 and a duct 13 connecting the two,
Opening at the ceiling of the duct is the bottom of a hopper 14 which accommodates powder particles over a wide range of particle sizes. The powder particles in the hopper 14 have a particle size of 1μ
m. It is composed of fine particles or ultrafine particles of various particle sizes, and is fed in a predetermined amount per unit time into the duct 13 by the action of, for example, a known rotary feeder.

As the rectifying discharge mechanism 12, for example, Patent No.
No. 1027787 (Special Publication No. 55-14981) or Patent No.
1175637 (Japanese Patent Publication No. 57-40413), etc., "Flow velocity equalization device at duct discharge port" may be used. The powder particles falling and being supplied from the hopper 14 are mixed with the conveying air stream, and are discharged upwardly to the rectifying discharge mechanism 12 in the form of a solid-air mixed phase flow having a uniform velocity distribution.

The classification section 2 includes a plurality of (four in the illustrated example) discharge plates 21a to 21d arranged adjacent to each other vertically, and a collection plate 22 extending vertically and facing the discharge plates 21a to 21d with a gap S therebetween. ing. The gap S becomes a conduit for the solid-gas mixed phase flow supplied into the classification chamber.

The discharge plates 21a to 21d each have a conductive wire 23a.
~23d is electrically connected to a separate DC high voltage power supply (not shown). The DC high voltage power supply has a higher voltage as it is connected to an upper discharge plate. That is, the higher the discharge plate is, the higher the applied voltage is. Further, as shown in FIG. 3, each discharge plate 21a~
A large number of needle-shaped discharge electrodes are densely planted on the surface facing the recovery plate 22 of 21d, protruding into the gap S.

The recovery plate 22 is divided into groups in the vertical direction, and a large number of recovery holes are formed therethrough at a density corresponding to the density of the discharge electrodes, and duct ends 24a to 24d are provided for each group on the back surface thereof. has been done. Each of the duct ends 24a to 24d is separately connected by a not-shown duct to a known separation and recovery section for small powder particles, which is equipped with a suction fan and a high-performance filter.

The opening area of the recovery hole (usually a circular hole, so represented by its diameter) is the same within the same group, but may be set differently for different groups. For example, the collection hole belonging to the lower group (for example, the group facing the discharge plate 21a with a lower applied voltage) has a smaller opening area, and the collection hole belonging to the upper group (for example, the group facing the discharge plate 21d with a higher applied voltage) has a smaller opening area. The hole is designed so that its opening area becomes larger. The size of the opening area of the recovery hole in each group and the degree of change in the opening area of the recovery hole between groups depend on process conditions such as the particle size distribution of the powder particles to be supplied and the required classification accuracy. This shall be determined as appropriate.

Of course, what has been described above is just one example, and this invention is not necessarily limited to this. For example, the collection holes do not necessarily need to be grouped as described above, and may have the same opening area throughout, or the opening area may be smaller toward the bottom in the vertical direction of the collection plate 22, and the opening area may be smaller toward the top. The area may be increased. Also, in the above example,
The collection holes in the collection plate 22 are grouped into discharge plates 21a~
Although the number and range correspond to 21d, it is not necessarily limited to this. The recovery holes on the recovery plate 22 side may be grouped regardless of the discharge plate.

The conveyance airflow storage section 3 has a suction mechanism 31 for the conveyance airflow, a rectification suction mechanism 32 that opens at the top of the classification chamber, and a duct 33 that connects the two. As the rectification suction mechanism 32, one having the same function as the rectification discharge mechanism 12 used in the solid-gas multiphase flow supply section 1 may be used. It acts as an inhaler.

Next, the operation of the electrostatic classifier having the above-mentioned configuration will be explained.

The powder particles supplied from the hopper 14 over a wide particle size range are mixed with the conveying air flow to form a solid-gas multiphase flow with a uniform velocity distribution,
It enters the classification chamber via the rectifying discharge member 12, and is guided into the gap S between the discharge plates 21a to 21d and the collection plate 22 as a rectified flow without drift or eddy current by a push-pull method.

By the way, as described above, at the stage where the powder particles are mixed with the conveying air flow, the ultrafine particles in the powder particles with similar particle sizes aggregate to form agglomerates. Here, the smaller the particle size of the ultrafine particles, the easier it is to form a large agglomerate, but at this point, the aggregation is still incomplete, so that an incomplete agglomerate is formed. Therefore, the solid-gas mixed phase stream contains unfinished nodules of various sizes at the time it is fed into the classification chamber. These unfinished nodules are led into a classification chamber and exposed to electrostatic discharge, where they are further agglomerated and grow into finished nodules.

Here, for convenience of explanation, it is assumed that the powder particles in the hopper 14 are divided into groups 1 to 2 in descending order of particle size range. Then, since the ultrafine particles belonging to the group belong to the lowest particle size range in the powder particle group, the largest unfinished nodules (referred to as "unfinished nodules", hereinafter the same) are mixed into the conveying air stream. Form.

Now, these unfinished nodules grow further due to electrostatic discharge when a solid-gas multiphase flow is introduced into the gap S between the discharge plates 21a to 21d and the recovery plate 22.
In this gap S, the nodules in the solid-gas multiphase flow are subjected to an upward inertial force due to the carrier air current and electrostatic attraction, and a lateral pushing force due to the ion stream, and the nodules are deflected in the direction of the vector of the resultant force. Ru.

In FIG. 3, in area A covered by the lowest discharge plate 21a, electrostatic discharge occurs at the lowest voltage. As a result, the unfinished baby boom~
The particles further agglomerate to some extent and grow, but as the inner particle size increases, the amount of charge increases, so the originally smallest unfinished nodule becomes a completed nodule, and the above-mentioned combination of inertial force and pushing force increases. It is deflected the most from the discharge plate 21a and is directed toward the collection plate 22, and is captured and collected by the collection holes of the group corresponding to the discharge plate 21a, and the duct end 2
It is inhaled into 4a. As a result, nodules grown from unfinished nodules in the solid-gas mixed phase flow, that is, fine particles or ultrafine particles belonging to the highest particle size range group, are classified and separated. Other unfinished nodules also grow to some extent and are deflected, but they do not reach the collection plate 22 because of the large diameter of their constituent particles and because the amount of charge is small.

In region B covered by the second discharge plate 21b from the bottom, electrostatic discharge is performed at the next lowest voltage. As a result, the unfinished nodules ~ further aggregate and grow to some extent, but as the rising residence time elapses, the next largest unfinished nodule becomes a completed nodule, and is deflected the most towards the collection plate 22. The particles are captured and recovered by the collection holes of the group corresponding to the discharge plate 21b, and are sucked into the duct end 24b. As a result, nodules grown from unfinished nodules in the solid-gas mixed phase flow, that is, ultrafine particles belonging to the next particle size range group, are classified and separated. Other unfinished baby boomers will also grow to some extent and be deflected,
Because of the size of the constituent particles, and also because the amount of charge is not so large, it does not reach the collection plate 22.

In the region C covered by the third discharge plate 21c from the bottom, electrostatic discharge is performed at the second highest voltage. As a result, the unfinished nodules further agglomerate and grow to some extent, but the larger unfinished nodules become completed nodules, are deflected the most and are directed toward the collection plate 22, forming a group corresponding to the discharge plate 21c. It is captured and collected by the collection hole and sucked into the duct end 24c. As a result, nodules grown from unfinished nodules in the solid-gas mixed phase flow, that is, ultrafine particles belonging to the next particle size range group, are classified.
separated. The remaining unfinished nodules also grow to some extent and are modified, but because of their size and because the amount of charge is not large enough, they do not reach the collection plate 22.

In the region D covered by the uppermost discharge plate 21d, electrostatic discharge occurs at the highest voltage. As a result, the unfinished nodules further agglomerate and grow to become completed nodules, which are deflected and directed toward the collection plate 22, captured and collected by the group of collection holes corresponding to the discharge plate 21d, and then inside the duct end 24d. is inhaled. As a result, nodules grown from unfinished nodules, that is, ultrafine particles belonging to the lowest particle size range group, are separated from the solid-gas mixed phase flow.

The powder particle groups consisting of fine particles or ultrafine particles sucked into the duct ends 24a to 24d are sent to the collection section and collected as described above, but after collection, they may be used as they are, or they may be further finely collected. It may also be subjected to electrostatic classification.

Since ultrafine particles are not substantially contained in the solid-gas multiphase flow after the final nodule separation is completed, only the carrier air flow is accommodated in the storage section 3.

(Effects of the invention) According to this invention, by adjusting the applied voltage for electrostatic discharge, it is possible to freely control the agglomeration of ultrafine particles and the strength of the ion stream and/or the amount of charge. The classification accuracy is much improved compared to the electrostatic classification method proposed earlier, and since the voltage is an analog quantity and can be changed continuously, it can flexibly respond to subtle changes in process conditions. .

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the applied voltage for discharge and the size of agglomerated agglomerates, Figure 2 is a perspective view showing an example of the main part of the electrostatic device of this invention, and Figure 3 is a side view showing its classification action. It is. DESCRIPTION OF SYMBOLS 1... Solid-gas multiphase flow supply section, 2... Powder particle classification section, 12... Rectification discharge mechanism, 14... Powder particle group hopper, 21a to 21d... Discharge plate, 22...
Recovery plate, 3... Carrier airflow storage section, 32... Rectification suction mechanism, S... Gap.

Claims (1)

[Claims for Utility Model Registration] A mechanism for forming a conveying air current is provided above and below a vertically long classification chamber that is substantially closed. Plates 21a to 21d are provided, and these discharge plates are connected to a DC high-voltage power source whose voltage is higher as the upper one is disposed. Elements 22 are provided extending in the vertical direction, and each collection element is connected to a respective individual powder particle small group collection section. A solid-gas multiphase flow supply section 1 is provided which mixes a group of powder particles into the conveying air flow to form a solid-gas multiphase flow having a uniform velocity distribution and discharges the mixture to the lower end of the gap S. Electrostatic classification device for powder particles.