JPH06154646A - Method for sorting magnetic powder - Google Patents

Abstract

PURPOSE:To attain the precise magnetic separation of magnetic powders by providing a line of magnetic poles where different poles are adjacent to each other on the rear side of a substrate so that the magnetic field of nearly the same intensity may be applied to each magnetic particle in a thin layer formed on the surface of the substrate and performing the magnetic separation by differences in magnetic susceptibility. CONSTITUTION:A cylindrical sleeve 21 is provided as a substrate and a cylindrical magnet 31 is provided as the line of magnetic poles inside the inner peripheral surface of the sleeve 21. The cylindrical magnet 31 is a surface multi-pole magnet where unlike poles form in line in the circumferential direction. Also, magnetic powder 10 is mounted on the top of the sleeve by an appropriate quantity and the cylindrical magnet 31 is turned relative to the sleeve 21, causing the magnetized magnet powder 19 to be turned and moved, allowing it to be made a thin layer. The magnetic powder 21 not magnetically stuck to the sleeve 10 falls from the surface of the sleeve 10 to be recovered in a tray 12. The intensity of the magnetic field on the surface of the sleeve 21 is properly set according to the kinds of magnetic powder to be sorted and its stage of sorting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selecting magnetic particles in magnetic powder according to their magnetic characteristics.

[0002]

2. Description of the Related Art As a rare earth magnet having high performance, an Sm-Co type magnet manufactured by powder metallurgy has an energy product of 32 MG.
Oe's are in mass production. However, this one is Sm,
It has a drawback that the raw material price of Co is high. Among rare earth elements, elements having a small atomic weight, such as cerium, praseodymium, and neodymium, are abundant and cheaper than samarium. Further, Fe is cheaper than Co. Therefore, in recent years, Rd-Fe-B based magnets such as Nd-Fe-B have been developed, and Japanese Patent Application Laid-Open No. 60-9852 discloses a high-speed quenching method.

The magnet manufactured by the rapid quenching method is applied to a bulk magnet such as a powder magnet and also used as a bonded magnet in which magnet particles are dispersed in a binder of resin or nonmagnetic metal. Bulk magnets generally have the drawback of being hard and brittle, but bonded magnets are light and elastic, have no cracks or cracks, are easy to mold into complicated shapes, and have excellent mass productivity, so their applications tend to expand. .

In the rapid quenching method, a single roll method or a twin roll method is usually used. In these methods, the molten alloy is brought into contact with the peripheral surface of the cooling roll and rapidly cooled to obtain a ribbon-shaped or flake-shaped quenched alloy.However, since the quenched alloy has a different cooling rate depending on the site, variations in crystal grain size occur. . For this reason,
The magnet powder obtained by crushing the quenched alloy is also composed of magnet particles having different magnetic properties. Therefore, in order to obtain a bonded magnet or a bulk magnet having good magnetic characteristics and small variations by using the rapid quenching method, it is necessary to select magnet particles according to the magnetic characteristics. Further, since the non-magnetic R-rich component forming the crystal grain boundaries is mixed in the powder, it is preferable to remove it in order to obtain high magnetic characteristics.

The selection of magnetic particles according to their magnetic properties is useful not only for R-Fe-B type magnets but also for other rare earth magnets and ferrite magnets, and also for magnetic particles for magnetic recording media. It can also be applied to soft magnetic particles.

Regarding magnetic selection of magnetic particles, for example, JP-A-64-15317 and JP-A-4-161258.
It is disclosed in Japanese Patent Publication.

Japanese Patent Laid-Open No. 64-15317 discloses a material having a relatively high magnetic energy product and a material having a relatively low magnetic energy product.
A method of magnetically separating is disclosed. In this method, a magnetic field is applied that is high enough to magnetize the low magnetic fraction (excess quenching material) during complete magnetization, but low enough to avoid substantial magnetization in the high magnetic fraction during complete magnetization. Therefore, a method of magnetically separating the two is disclosed. Specifically, a magnet pulley or the like is used as the magnetic separation means. In this method, the particle mixture is placed on a belt and conveyed to a magnetized rotating surface such as a magnetized pulley, idler or wheel. The belt runs around the rotating surface means. As the belt passes around the rotating surface means, the material with lower induced magnetism falls from the belt and the magnetized rotating surface means into the recovery means by its own weight. On the other hand, a material with high induction magnetism remains in contact with the belt due to the attraction force toward the magnetizing roller means, and when the belt moves the particles past the magnetic field of the magnetizing roller means, self-weight etc. Is forcibly removed from the belt by. In addition, a method is also disclosed in which an electromagnet is arranged in the vicinity of the flow of the granular material on the belt, a material having a low induction magnetism passes through, and a material having a high induction magnetism is collected on the surface of the electromagnet.

However, in the magnetic powder placed on the belt, the low magnetized particles may be mechanically held so as to be sandwiched between the high magnetized particle groups, so that it is difficult to perform accurate selection. is there. It is also difficult to separate particles having slightly different magnetizations in a low magnetic field strength, that is, particles having slightly different initial magnetization curves. This is because the magnetic powder placed on the belt is thick and the thickness is not uniform, and the magnetic field strength applied to each particle is not equal at the bottom and the top of the powder.

Japanese Unexamined Patent Publication No. 4-161258 discloses a magnetic separator in which a permanent magnet is arranged in the inner half of a rotating cylindrical body and a raw material falling from above is separated into a magnetic component and a non-magnetic component. Has been disclosed in which the magnetic poles are arranged so as to be parallel to the axial direction and the N poles and the S poles alternate in the circumferential direction, and the surface magnetic flux density of the cylindrical body is 3500 gauss or more.
In this magnetic separator, the non-magnetized component drops as it is, and the magnetically attracted component is attracted by the permanent magnet and moves downward while being attached to the cylindrical body. In this publication, it is an object to select even those which cannot be selected by a conventional magnetic separator, such as an anode button having glass attached to the periphery of the crushed material of a cathode ray tube. That is, this magnetic separator is used for selecting a magnetic material and a non-magnetic material, and not for selecting a magnetic material according to its magnetic characteristics.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of accurately magnetically selecting magnetic powder.

[0011]

The above objects are achieved by the present invention described in (1) to (3) below. (1) A method of selecting magnetic particles from magnetic powder according to a magnetic susceptibility, wherein a magnetic pole array is provided on the back surface side of a base so that different poles are adjacent to each other, and the magnetic powder is placed on the front surface side of the base. , The magnetic particles are incompletely magnetized by moving the magnetic pole row relative to the base in a direction in which different poles are adjacent to each other, and the magnetic particles are rotationally moved on the surface of the base. A thin layer of magnetic powder is formed to have a substantially uniform thickness so that a magnetic field of approximately equal strength is applied to each magnetic particle in the thin layer, and the difference in magnetic susceptibility of each magnetic particle is used. A method for sorting magnetic powder, characterized by performing magnetic sorting. (2) The base body has a cylindrical shape, the magnetic pole array is provided inside the inner peripheral surface of the base body in a cylindrical shape, and the direction in which different poles are adjacent is the circumferential direction, and the magnetic pole array is The method for selecting magnetic powder according to (1), wherein the magnetic powder is rotated relative to the substrate. (3) The method for selecting magnetic powder according to (1) or (2) above, wherein the magnetic powder is magnet powder.

[0012]

[Operation and effect] The magnetic particles in the magnetic powder placed on the front surface of the base are
It is magnetized according to the initial magnetization curve unique to each particle. The magnetization at this time is incomplete, and almost disappears when the magnetic field is removed. The magnetic particles magnetized to the extent that they can be magnetically attached to the surface of the base body rotate along with a change in the direction of the flow of magnetic flux when the magnetic pole array moves relative to the base body.
The axis of rotation at this time is substantially parallel to the surface of the substrate. By this rotation, the magnetic particles move to the side opposite to the moving direction of the magnetic pole array. By such rotational movement of the magnetic particles, the magnetic powder is thinned on the surface of the substrate. If the magnetic powder on the surface of the substrate is thick and the thickness is not uniform, the magnetic field strength applied to each magnetic particle will be greatly different, but by making it thin as described above, it is almost equal to each magnetic particle. A strong magnetic field is applied. Therefore, since each magnetic particle can be magnetized in a magnetic field having substantially the same intensity, each magnetic particle having a slightly different initial magnetization curve can be given a slightly different magnetization corresponding to each initial magnetization curve. . At this time, if the substrate surface is tilted with respect to the direction of gravity, the magnetic particles that are magnetized to the extent that they can be magnetically attached remain on the substrate surface, and magnetic particles with a lower magnetic susceptibility are Since it falls from above, it becomes possible to perform accurate magnetic separation according to each magnetic characteristic.

After selecting in this way, the magnetic field strength on the surface of the substrate is changed, and the above steps are repeated for each selected magnetic powder, whereby finer magnetic selection can be performed. As the base, various shapes such as a cylindrical shape as shown in FIG. 1 and a flat plate shape as shown in FIG. 2 can be used.

[0014]

Specific Structure The specific structure of the present invention will be described in detail below.

A structural example of the magnetic sorting apparatus used in the present invention is as follows:
This is shown in FIGS. 1 and 2.

The apparatus shown in FIG. 1 has a cylindrical sleeve 21 as a base body, and inside the inner peripheral surface of the sleeve 21,
It has a cylindrical magnet 31 as a magnetic pole array. The cylindrical magnet 31 is a surface multi-pole magnet and has different poles arranged in the circumferential direction.

The sleeve 21 and the cylindrical magnet 31 are connected to a driving device (not shown), respectively.
1 rotates clockwise, and the cylindrical magnet 31 rotates counterclockwise.

In order to cause the rotation of the magnetic particles suitable for thinning the magnetic powder, it is necessary to appropriately set the distance between the adjacent magnetic poles according to the diameter of the magnetic particles. Since the polarity reversal interval and the diameter of the magnetic particles on the outer peripheral surface of the sleeve 21 actually affect the rotation of the magnetic particles, the polarity reversal interval (the interval between the projected images of the magnetic poles on the surface of the sleeve 21) and the diameter of the magnetic particles are calculated. Set to an appropriate value. In order to smoothly perform the rotational movement, the polarity reversal interval is preferably twice or more the average diameter of the magnetic particles. In practice, the polarity reversal interval is preferably 1 mm or more, more preferably 5 mm or more. This is because if the polarity reversal interval is too short, it will be difficult to obtain a magnetic field of desired strength due to restrictions of the magnetic circuit. The average diameter of the magnetic particles is not particularly limited, but is usually 0.5 to 1000 μm, and particularly 2 to 500 μm.
It is preferable that In such a case, the polarity reversal interval is preferably 30 mm or less, more preferably 15 mm or less. If the polarity reversal interval is too long, the curve representing the magnetic field strength distribution on the sleeve deviates significantly from the sine curve shape, and the peak portion of the curve tends to have a depression. The magnetic particles stop rotating at the position of this recess and move together with the magnetic poles, so that the rotational movement efficiency decreases.

It is possible to perform better magnetic sorting by using a magnetic sorting device having a polarity reversal interval according to the grain size after classifying the magnetic powder.

In order to cause efficient rotational movement by moving the magnetic pole array, the magnetic particles preferably have shape anisotropy, for example, scale-like or needle-like.

The number of poles in the magnetic pole array may be determined according to the dimensions of the sleeve 21 and the cylindrical magnet 31 so as to obtain the above-mentioned distance between magnetic poles, but it is usually selected from the range of 4 to 32 poles. It is preferable. Further, the size of the sleeve 21 is not particularly limited, but usually the axial length is 50 to 100.
It is preferable to select from the range of 0 mm and the diameter of 7 to 80 mm.

In the illustrated magnetic sorting apparatus, batch processing is performed as described in the section of the operation. That is, by placing an appropriate amount of the magnetic powder 10 on the top of the sleeve 21 and rotating the cylindrical magnet 31 relative to the sleeve 21, the magnetized magnetic particles are rotationally moved to form a thin layer of magnetic powder. The magnetic particles that have not been magnetically adhered to the sleeve 21 are dropped from the sleeve surface and collected in the tray 12. In such batch processing, the amount of the magnetic powder supplied per time may be appropriately determined according to the length and diameter of the sleeve 21, but is preferably about 0.5 to 200 g, more preferably 2 to 50 g. It is a degree. The whole amount of the magnetic powder for one time may be supplied to the top of the sleeve, but it is preferable to continuously or intermittently supply a small amount in order to facilitate thinning.

After placing the magnetic powder 10 on the top of the sleeve 21, it is preferable to regulate the thickness of the magnetic powder by a scraper 11 or the like. By controlling the thickness of the magnetic powder when the magnetic powder is placed on the top of the sleeve 21, the magnetic powder can be quickly thinned.

The magnetic particles that are rotationally moved but are not magnetically adhered to the sleeve 21 at a position where gravity exceeds the force of the magnetic field.
The non-magnetic particles fall from the surface, and the non-magnetic particles also fall due to the rotation of the sleeve. However, if the thinning of the magnetic powder is insufficient, magnetic particles that should be magnetically adhered may fall. Therefore, the yield may be increased by repeatedly supplying the magnetic powder dropped and collected to the sleeve top.

If the layer is not sufficiently thinned, low-magnetization particles or non-magnetic particles, which should have fallen, are mechanically held so as to be sandwiched between high-magnetization particle groups and may not fall. Therefore, until the thinning progresses sufficiently, the sleeve 2
It is preferable to continue relative rotation between 1 and the cylindrical magnet 31.

In order to remove the non-magnetic particles from the powder that has fallen and is collected in the tray 12, after such magnetic sorting, magnetic sorting with a magnetic field of relatively high strength is performed if necessary. Is preferred.

The thickness of the magnetic powder thin layer formed on the surface of the sleeve 21 is preferably about 2 to 1000 μm. In this thin layer, the magnetic particles are preferably 10
The number of layers is preferably at most 5, more preferably at most 5, and most preferably at most 1. That is, it is most preferable that the magnetic particles are not laminated. When magnetic particles are laminated in a thin layer, the magnetic particles usually rotate and move as aggregated secondary particles.

In the illustrated example, the sleeve 21 and the cylindrical magnet 3
1 is rotated in the opposite direction, but in order to move the magnetized particles while rotating them and to efficiently drop the non-magnetized particles, the cylindrical magnet 31 is opposed to the sleeve 21. Since it suffices that the sleeve 21 rotate in a uniform manner and at least the sleeve 21 rotates, in addition to the example shown in the figure, it may have a configuration in which both rotate in the same direction or a configuration in which only the sleeve 21 rotates. However, when both rotate in the same direction, the magnetic particles that rotate and move on the sleeve surface may not apparently move. In that case, it is preferable to change at least one of the rotation speeds. Further, the sleeve 21 may not rotate, but in this case, the number of times the particles pass through the lower surface of the sleeve is reduced, so that the efficiency of dropping the non-magnetic particles or the low-magnetization particles is lowered.

Among these, the most preferable embodiment is the case where the sleeve and the cylindrical magnet rotate in mutually opposite directions, and the rotational speed of the sleeve is lower than the rotational speed of the cylindrical magnet. In this mode, the influence of centrifugal force due to the rotation of the sleeve is small, and the efficiency of thinning the magnetic powder is improved.

In order to smoothly rotate the magnetic particles, the moving speed of the polarity reversal point on the surface of the sleeve 21 is preferably 0.2 to 100 cm / sec, more preferably 2 cm.
~ 50 cm / sec. The moving speed of the magnetic particles on the sleeve surface varies depending on the moving speed of the polarity reversal point, the size and shape of the magnetic particles, and the like, but is preferably 5 to 50.
It is 0 mm / min, more preferably 25 to 250 mm / min.

The rotation speed of the sleeve 21 and the rotation speed of the cylindrical magnet 31 may be appropriately determined so that the moving speed of the polarity reversal point described above falls within a preferable range. 120 rpm, especially 20 ~
It is preferably about 60 rpm. If the rotation speed of the sleeve 21 is too low, the non-magnetized particles tend not to slide off smoothly, and if the rotation speed is too high, the magnetized particles may fall due to the influence of centrifugal force. .
The rotation speed of the cylindrical magnet 31 is preferably about 10 to 1000 rpm when the sleeve and the cylindrical magnet rotate in opposite directions.

The magnetic field strength on the surface of the sleeve 21 may be appropriately set according to the type of magnetic powder to be selected and the stage of selection. In the present invention, the magnetic field strength needs to be such that the magnetic particles are magnetically rotatably attached to the surface of the sleeve 21.
5 to 5000 G, preferably 50 to
Select from the range of 700G. If the magnetic field strength is too strong,
The magnetic particles are strongly magnetically attached to the surface of the sleeve 21 and the rotational movement as described above becomes impossible, and the magnetic particles are irreversibly magnetized and aggregated, which makes subsequent processing difficult.

The magnetic particles magnetically attached to the sleeve 21 are
The magnetic field strength on the surface of the sleeve 21 can be reduced to zero or recovered by a means such as pulling out the cylindrical magnet 31 from the sleeve 21.

In the illustrated example, the surface multi-pole cylindrical magnet 31 is used.
Although the magnetic pole array is configured by, any magnet may be used as long as different poles are alternately arranged. For example, a magnet having an arc-shaped cross section obtained by cutting out a part of the cylindrical magnet as shown in the drawing may be used. However, when such a magnet is used, the efficiency of thinning the magnetic powder decreases, and the thinning tends to be insufficient.

The sleeve 21 is usually made of a non-magnetic material, for example, various non-magnetic metals such as Al, Cu and brass, various non-magnetic ceramics, plastics, etc. so that the magnetic particles can be rotationally moved as described above. Consists of
In addition to these, weak magnetic materials can also be used. The weak magnetic material is one that can be easily saturated by the magnetic field from the magnetic pole array to generate sufficient leakage magnetic flux on the sleeve surface, and examples thereof include weak magnetic stainless steel.

The distance between the sleeve 21 and the cylindrical magnet 31 is not particularly limited, and may be set appropriately according to the magnetic field strength required on the sleeve surface.

The substrate used in the present invention is not limited to the cylindrical shape shown in FIG. 1, but may be, for example, a flat plate shape as shown in FIG.

The magnetic sorting apparatus shown in FIG. 2 has a flat plate-shaped substrate 22 as a base body, and a belt-shaped rubber magnet 32 as a magnetic pole array on the back surface side of the substrate 22. The surface of the substrate 22 is inclined by an angle θ with respect to the direction of gravity, and the rubber magnet 32 is arranged so that its surface is substantially parallel to the surface of the substrate 22. The rubber magnet 32 is configured to move in a direction in which different poles are arranged (from the right side to the left side in the figure) by a driving device (not shown), and the moving direction is substantially perpendicular to the gravity direction.

In this magnetic sorting apparatus, the magnetic powder to be sorted is placed or supplied at the upper left corner of the surface of the substrate 22 in the figure. Since the rubber magnet 32 is moving in the direction in which different poles are arranged (from the right side to the left side in the figure), the rubber magnet 32 causes the substrate 2 to move.
The magnetic particles magnetized to the extent that they can be magnetically attached to
The powder is thinned by moving while rotating the surface from the left side to the right side in the figure, and the movement stops when it reaches the right corner of the substrate 22, but when the powder collected here becomes thick, Since the strength of the magnetic field applied to the magnetic particles is reduced, the magnetic particles slide off from the collected powder. Therefore, it is preferable to control the supply amount of the powder to be appropriate and to re-sort the slid particles.

On the other hand, non-magnetic particles and low-magnetization particles in the powder slide down in the tilt direction or have a velocity component in the right direction in the figure because the substrate 22 is tilted with respect to the direction of gravity. To do. In the powder, non-magnetic particles and low-magnetization particles may be mechanically retained in the highly magnetized particle group magnetically adhered to the surface of the substrate 22, but the powder becomes thinner as the powder becomes thinner. Non-magnetic particles and low-magnetization particles held in the body also slide off, and only high-magnetization particles substantially accumulate in the right corner of the substrate 22.

Various conditions such as the material of the substrate 22, the polarity reversal interval on the substrate surface, the moving speed of the polarity reversal point, etc. may be considered according to the configuration example of FIG. The inclination angle θ of the substrate 22 may be appropriately determined according to the size and shape of the magnetic particles, the supply amount, and the like.

The present invention is suitable for the selection of various magnet material particles such as rare earth magnets such as R-Fe-B magnets and ferrite magnets, and the selection of metal magnetic particles and oxide magnetic particles for magnetic recording media. It is also suitable for It can also be applied to the selection of soft magnetic particles.

In R-Fe-B magnets and the like, in general, a magnetic material having a lower magnetic susceptibility at a low magnetic field strength has a higher coercive force and a higher maximum energy product. That is, the lower the rising of the initial magnetization curve, the higher the magnet characteristics. Therefore, usually, magnetic selection is performed in order to improve the purity of the low-magnetization particles in the powder, but in the present invention, both the low-magnetization particles and the high-magnetization particles can be sharply selected, and the low-magnetization particles also have the high magnetization. Since the particles can also be collected with a high yield, it is suitable not only for magnetic powders having characteristics such as R-Fe-B magnets but also for magnetic powders having various characteristics such as soft magnetic powders.

[0044]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

12.5Nd-6B-5Co-76.5F
An alloy ingot having a composition of e (numerical value represents atomic percentage) was prepared by arc melting. The obtained alloy ingot was put into a quartz nozzle and was made into molten metal by high frequency induction heating. This molten metal was rapidly cooled by the one-roll method to produce a flake-shaped permanent magnet material. The rapid cooling was performed in an Ar gas atmosphere.

The permanent magnet material was crushed by a pin mill to obtain a magnet material powder having an average particle size of 170 μm. The magnetic particles forming the powder were scaly.

Next, the powder was magnetically sorted by the magnetic sorting apparatus having the structure shown in FIG. The dimensions and conditions of each part of the magnetic separator were as follows.

<Sleeve 21> Material: Al outer diameter: 30 mm Inner diameter: 28 mm Length: 300 mm Rotation speed: 20 rpm

<Cylindrical magnet 31> Material: Ferrite magnet Diameter: 26 mm Length: 300 mm Number of poles: 12 poles Rotation speed: 200 rpm (rotating in the opposite direction of the sleeve)

The polarity reversal interval on the sleeve surface is 7.
85 mm, the magnetic field strength on the sleeve surface is 400
It was G. The amount of powder supplied was 5 g per time, and the powder was supplied little by little to the top of the sleeve, and the thickness was regulated by a scraper.

During the magnetic selection, it was visually confirmed using a magnifying glass that the magnetic particles were moving while rotating on the surface of the sleeve. The rotation axis at this time was almost parallel to the sleeve surface.

By the time the sleeve was rotated 500 times after the powder was supplied, the powder was thinned to a thickness of about 200 μm on the surface of the sleeve. As a result of observation with a stereoscopic microscope, it was confirmed that the particles in the thin layer did not substantially overlap with each other and that the particles had a single layer structure.

Next, the cylindrical magnet was pulled out from the sleeve, the powder magnetically adhered to the sleeve surface was recovered, and its magnetic characteristics were measured. In addition, the magnetic properties of the powder collected from the tray after falling from the sleeve surface were also measured. As a result, the magnetically adhered powders were Br: 8700G, iHc: 9500 Oe, (BH) max: 14.8MGOe, while the fallen powders were Br: 7700G, iHc: 8300 Oe, (BH). It was confirmed that the max was 11.5 MGOe, and the magnetic particles having a small difference in characteristics were extremely accurately selected.

For comparison, when magnetic selection was attempted in the same manner as above except that the magnetic field strength on the sleeve surface was set to 6000 G, the particles magnetically adhered to the sleeve surface did not rotate and move as described above. Some of them were rotating in the plane of the sleeve surface (the axis of rotation was perpendicular to the sleeve surface), but almost no change in the position on the sleeve surface was observed. Further, some of the magnetically adhered particles formed secondary particles and moved on the sleeve surface as the magnetic pole moved. It is considered that this is because a closed magnetic circuit was formed in the secondary particles. The particles that fell from the sleeve surface were only a small amount of non-magnetic particles, and it was impossible to sort them according to their magnetic properties.

From the results of the above examples, the effect of the present invention is clear.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a magnetic sorting device used in the present invention.

FIG. 2 is a perspective view showing a configuration example of a magnetic sorting device used in the present invention.

[Explanation of symbols]

 10 Magnetic Powder 11 Scraper 12 Tray 21 Sleeve 22 Substrate 31 Cylindrical Magnet 32 Rubber Magnet

Claims (3)

[Claims] 1. A method for selecting magnetic particles from magnetic powder according to a magnetic susceptibility, wherein a magnetic pole array is provided on a back surface side of a base so that different poles are adjacent to each other, and the magnetic powder is provided on a front surface side of the base. And the magnetic pole array is moved relative to the base in a direction in which different poles are adjacent to each other, whereby the magnetic particles are incompletely magnetized and are rotationally moved on the surface of the base. A thin layer of the magnetic powder is formed to have a substantially uniform thickness so that a magnetic field of approximately equal strength is applied to each magnetic particle in the thin layer, and the difference in magnetic susceptibility of each magnetic particle is used. A method for selecting magnetic powder, characterized by performing magnetic selection. 2. The magnetic pole array, wherein the base body is cylindrical, the magnetic pole row is provided inside the inner peripheral surface of the base body in a cylindrical shape, and the direction in which different poles are adjacent is the circumferential direction. The method for selecting magnetic powder according to claim 1, wherein the magnetic powder is rotated relative to the base. 3. The magnetic powder is magnet powder.
Alternatively, the method 2 of selecting magnetic powder.