JPH08243431A - Selective separation of magnetic material and device therefor - Google Patents

Abstract

PURPOSE: To provide a method and a device in which powder of magnetic material is separated selectively and efficiently in a wet process in accordance with magnetic characteristics. CONSTITUTION: An external magnetic field is acted on powder 2 of magnetic material mixed with a dispersion medium such as water in a vessel 1. Orientation chaining particle groups 3 constrained by the magnetic field are formed and fluid flowing in the direction parallel to the magnetic field is acted on the particle groups 3 while leaving this state. Herein, only particles having weak connecting force are selectively separated and removed regardlessly of particle diameter. In a permanent magnet produced by magnetic material separated and purified by this method, the characteristic of the magnet especially residual magnetic characteristic is largely enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for selectively separating wet magnetic material powder, which is a raw material for ferrite magnets and rare earth magnets, in accordance with its magnetic characteristics, and efficiently separating it. An external magnetic field is applied to the mixed magnetic material powder to form a group of oriented chain particles that are bound by the magnetic field, and a required fluid is applied to this to selectively separate and remove only particles with weak coupling force. Thus, the present invention relates to a magnetic material selective separation method and apparatus for improving the magnetic characteristics of a permanent magnet manufactured from the obtained magnetic material.

[0002]

2. Description of the Related Art Improvement of magnet characteristics is still an important development factor even in the most popular permanent sintered ferrite magnet among permanent magnets. At present, there is still room for development, with the actual magnetic properties of the ferrite material itself being less than 80% of the theoretical magnetic properties of the ferrite material itself.

The difference with respect to the theoretical characteristic value is caused more by the manufacturing method rather than by the material itself, and the biggest problem is that it is difficult to control the particle size of the raw material powder. The main reasons why it is difficult to control the particle size of such magnetic materials are that the materials themselves are magnetic and aggregate with each other, and that their particle sizes are extremely small and they cannot be efficiently separated into the required particle sizes.

Further, in recent research, it is not sufficient to improve the characteristics of the magnet by simply classifying the particles by the particle size to make the average particle size uniform, and it is important to selectively remove particles having small magnetic characteristics. I have come to understand that. That is, even if the magnetic material has a powder particle size of about 1 μm and is suitable for improving the magnetic properties, it is necessary to remove particles having magnetic properties smaller than those of the magnetic powder, and the particle size is 0.2 μm.
That is, even if it is relatively small, one with high magnetic properties should not be removed.

Combining the conventional techniques for the purpose of improving the magnet characteristics, a trial was conducted to classify the magnetic material powder in the above-mentioned difficulties due to magnetic aggregation.
As a method for carrying out such classification, there are a dry method and a wet method.
As a typical dry method, there is a method in which a magnetic material is scattered in an alternating magnetic field and classified by a known method, as a typical example of Japanese Patent Publication No. 32-382. However, in a normal ferrite sintered magnet, it is general that the magnetic material is pulverized by a wet method and then is molded by a wet method, and in order to carry out the classification by the dry method in the steps of these wet methods, the raw material is It becomes necessary to dry and mix again with water before molding, which complicates the process.

On the other hand, in the wet method, as shown in Japanese Patent Publication No. 52-275, the same hard magnetic material powder is suspended in a fluid and an alternating magnetic field is applied to disconnect the magnetic particles by mutual adsorption. , There is a method of performing classification using Stokes' law based on the balance between gravity and drag force of fluid from particles.

[0007]

The classification of hard magnetic materials, which could not be classified due to strong magnetic agglomeration in the past, seems to have some effect by applying an alternating magnetic field, but as shown below. There is a problem.

The problems are as follows: 1) Basically, the Stokes' law using gravity is used, so that the classification efficiency is extremely low. 2) The magnetic field is used by applying a magnetic field to overcome 1). It has been proposed to use Stokes' law, but in practice it is extremely difficult to obtain a magnetic field that is stable in an alternating magnetic field and has a constant magnetic flux density gradient, and stable classification cannot be expected 3) The biggest problem with the existing method is that classification is performed only by the particle size, and as a result, small particles with high magnetic properties that are effective in improving the magnetic properties are removed, and conversely, the particle size is low but the magnetic properties are low. It is to leave the particles.

The present invention is directed to a method and apparatus for selectively and efficiently separating magnetic material powders according to their magnetic characteristics, while applying an external magnetic field to the magnetic material powders mixed in a dispersion medium. , A selective separation method of magnetic material capable of improving the magnetic characteristics of a permanent magnet manufactured by a separated and purified magnetic material by selectively separating and removing only particles having weak magnetic characteristics, and an apparatus therefor It is intended to be provided.

[0010]

As a result of various investigations by the inventor for the purpose of selectively and efficiently separating magnetic material powders according to their magnetic characteristics by a wet method, as a result, magnetic materials mixed in a dispersion medium have been obtained. When an external magnetic field is applied to the powder to form a group of oriented chain particles that are constrained by the magnetic field and a fluid flowing in a direction parallel to the magnetic field is applied to the particle group in this state, regardless of the particle diameter. It was found that it is possible to selectively separate and remove only particles having a weak coupling force, and that the permanent magnet manufactured by the magnetic material separated and purified by this method has greatly improved magnetic properties, and the present invention completed.

That is, according to the present invention, an external magnetic field is applied to a magnetic material powder mixed in a dispersion medium of a fluid so that magnetic particles in the material are connected in a chain form and restrained and fixed. At this point, a fluid having a flow velocity relative to the oriented chain particle group constrained by the magnetic field is caused to flow to selectively separate and remove particles having a weak coupling force from the magnetic material powder containing the oriented chain particle group. It is a method of selectively separating a magnetic material having a feature.

Further, according to the present invention, in the above structure,
A container capable of containing the magnetic material powder mixed in the dispersion medium,
A selective separation device for a magnetic material, characterized by having a piping means capable of allowing a dispersion medium fluid in a container to flow down in a required direction and a magnetic circuit capable of applying a magnetic field parallel to the dispersion medium fluid flow in the container. We also propose.

[0013]

The operation of the separation method according to the present invention will be described in detail with reference to the drawings. FIG. 1A is an explanatory view showing a state in which magnetic particles are column-shaped and chain-bonded by an external magnetic field, and FIG. 1B is a separation method of the present invention in which the bonded state is enlarged and a fluid flow is given to the chain. It is explanatory drawing which shows a basic principle.
FIG. 2 is a longitudinal sectional view showing an example of the separation apparatus according to the present invention, and FIG. 3 is an explanatory view showing the concept of the separation apparatus for continuously performing the separation method according to the present invention.

First, as shown in FIG. 1A, a magnetic material powder 2 mixed with a liquid such as water is put in a processing container 1,
When magnetic fields a and b are applied from the outside, the two particles of the magnetic material powder inside the container 1 are arranged in parallel with the magnetic field by this magnetic field. Two magnetic material powder particles have a tensile force acting in the magnetic flux direction, and a repulsive force acts in a perpendicular direction to the magnetic material powder particles. Therefore, as shown in FIG. The arrangement is such that it is fixed by being constrained by the magnetic field. This is called a group of oriented chain particles.

FIG. 1B is an enlarged view showing a chained arrangement state of two particles of columnar magnetic material powder arranged and constrained by the magnetic field of FIG. 1A, that is, an oriented chained particle group 3. In the present invention, a fluid flow as shown by an arrow in the figure is applied to the constrained columnar aligned particle group 3 so that only particles having a small mutual coupling force are caused to flow out by the fluid. It is based on the principle.

In short, particles having a small connecting force, that is, magnetism is weak and magnet characteristics are improved by utilizing the magnitude relation between the connecting force of the particles of the oriented chain particle group 3 connected in a columnar chain and the drag force received from the fluid. The particles that do not contribute are removed. Further, since the columnar oriented chain particle group 3 itself is constrained by the external magnetic field, the columnar oriented chain particle group 3 itself maintains a substantially oriented chain state due to the resistance from the fluid, and only particles having weak magnetism are removed. Restraining the magnetic material powder particles by such an external magnetic field is the main constitution of the present invention, and is a constitution completely different from the conventional method.

Further, in the present invention, since the balance between the coupling force between the magnetic material powder particles and the drag force received from the fluid is the basic principle of separation, the Stokes caused by gravity and fluid force or a gradient external magnetic field and fluid force The structure is completely different from the conventional method using the law, and it is decided whether or not to remove the particles based on the magnitude of the connecting force between the particles, which has the advantage that particles with weak magnetism are selectively removed. is there. For example, when classification is performed by the balance between gravity and fluid force, particles with a small particle size are uniformly removed, but with the method of the present invention, even if particles with strong magnetism and large coupling force are fine particles, they remain. However, particles having weak magnetism and small coupling force will be removed even if they are coarse particles.

It is considered that this principle has a similar tendency in classification using a balance between an external magnetic field having a gradient and a fluid force. However, as a practical problem, the magnetic field is greatly influenced by the magnetic fluid therein, so that it is uniform. It is extremely difficult to form a stable gradient magnetic field in the above, and as shown in the prior patent publication, it is almost impossible to form a gradient magnetic field by using an alternating magnetic field together.

The reason why the magnetic material powder particles are connected in a columnar shape by applying an external magnetic field is as follows. That is, when the magnetic material powder particles are not constrained by the external magnetic field, the particles are about several tens of μm even if they are aggregated,
The fluid flow causes the particles to flow or rotate and flow into the flow, and as a result, the relative velocity with the fluid cannot be maintained. Therefore, unless the magnetic particles are restrained by the magnetic field, the particles having a small coupling force cannot be separated.
In order to release the particles in this way, it is necessary to fix the particles with a magnetic field and to give a fluid flow with a large relative velocity to the particles, and the restriction of magnetic particles by an external magnetic field is an essential element. . Further, in the method of the present invention, since a fluid force that causes the particles to be disconnected from each other is applied, a high flow velocity can be applied as compared with the conventional method, and it is a great advantage that the separation efficiency can be sufficiently large. .

In the present invention, the flow of the fluid is shown in parallel with the parallel magnetic field and the columnar oriented chain particle group 3 in FIG. 1B, but it is not always required to be parallel and is required for the columnar oriented chain particle group 3. It is also possible to flow the fluid at an angle of, and the same effect can be expected. However, when the fluid flows in parallel with the columnar chain, there is an advantage that the flow resistance is minimized. The external magnetic field does not necessarily have to be a parallel magnetic field, and may have any orientation as long as the magnetic material powder particles can be aggregated to form a columnar oriented chain particle group. The flow direction of the dispersed fluid does not necessarily have to be constant as shown in FIG. 1B, and inflow and outflow may be alternately repeated.

An example of the configuration of the separating device will be described below.
The magnetic material powder 2 is stored in the storage space of the processing container 1, and a large number of flow path holes 4 and 5 are arranged on the bottom surface and the upper surface of the processing container 1, respectively. 5
Filter media 6 and 7 for preventing the magnetic particles from entering the flow path holes 4 and 5 due to an external magnetic field described later are arranged at the locations facing the. The processing container 1 is arranged at the center of a box-shaped yoke 10 that constitutes a magnetic circuit. Here, the processing container 1 is fitted and arranged between a lower pipe 11 and an upper pipe 12 which penetrate through the center of the yoke 10. The flow path holes 4 and 5 communicate with the lower pipe 11 and the upper pipe 12, respectively. Also,
In the box-shaped yoke 10, a pair of electromagnetic coils 13 and 14 are arranged above and below the processing container 1 so that a predetermined magnetic field can be applied inside the container 1. Any known magnetic circuit such as an electromagnet type or a permanent magnet type can be applied to the magnetic circuit.

The operation will be described. When a predetermined current is applied to the magnetic coils 13 and 14 of the magnetic material powder 2 mixed in the dispersion medium fluid contained in the processing container 1 to cause an external magnetic field to act, FIG. As shown, the oriented chain particle group 3 constrained by the magnetic fields a and b is formed, and the particle group 3 remains in this state.
When a fluid flowing from the bottom to the top in the direction parallel to the magnetic field, that is, from the flow path hole 4 to the flow path hole 5 is applied, only particles having a weak coupling force are selectively separated regardless of the particle diameter. Can be removed. Therefore, by appropriately selecting the meshes of the upper and lower filter media 6 and 7, particles having a weak coupling force can be discharged from the flow path hole 5 to the upper pipe 12.

Further, in the separating apparatus having the structure shown in FIG. 2, in order to use it for continuous operation, the processing container 1 is made replaceable,
The method is such that the processing container 1 containing the unseparated magnetic material powder is replaced at a predetermined interval, or as shown in FIG. 3, a mixed fluid of the magnetic material powder and the fluid is flown through a pipe 20, and processing is performed in the middle thereof. A continuous separation process can be carried out by installing the container 1 and allowing the fluid to flow in or out from the lower pipe 11 and the upper pipe 12. At this time, the mixed fluid may be allowed to flow continuously, but it is possible to realize an effective separation process by making it flow intermittently to prolong the residence time in the processing container 1 and stabilize the separation.

By the method of the present invention described above, it is possible to selectively separate the magnetic material powder to the extent that there is no problem in practical use, but in order to improve the efficiency, the external magnetic field is changed temporally or spatially. Therefore, it is effective to change the chain state of the oriented chain particle group, that is, the columnar magnetic particles. For example, repeatedly giving strength to the strength of the external magnetic field, repeatedly changing the direction of the external magnetic field, repeatedly moving the external magnetic field, etc. changes the chain of magnetic particles, and particles with weak magnetism to be selectively removed. Can be exposed to the flow of fluid more efficiently,
This improves the efficiency of separation. However, in any case, it goes without saying that the particles to be removed are allowed to flow out while the magnetic particles are bound by the external magnetic field.

Further, in the present invention, the strength of the external magnetic field and the flow velocity of the fluid serve as control variables when selectively separating the magnetic particles of the magnetic material, and the characteristics of the fluid, such as fluid type, temperature, viscosity and density. The processing time and the like also affect the separation conditions, and it is necessary to set these conditions in accordance with the desired characteristics after separation. In addition, the filter material and piping means of the separation device are appropriately selected according to the fluid type, the set flow rate, the temperature and the viscosity, and commercially available woven cloth, felt, etc. can be used as the filter material. Target. The dispersion fluid is appropriately selected according to the material of the magnetic material, but in the case of the magnetic material for the ferrite magnet, water, ethylene glycol aqueous solution, ethyl alcohol aqueous solution, methyl cellulose aqueous solution, etc. are preferable.

[0026]

【Example】

Example 1 A cylindrical processing container having a diameter of 50 mm and a depth of 15 mm was filled with 42% by weight of Sr ferrite mixed water in a weight percentage, and FIG.
A magnetic field substantially parallel to the central axis direction of the container was applied by using the same device as the structure shown in FIG. The magnetic field strength at this time was about 4000 Oe at the center. As a result, ferrite particles were arranged in the depth direction to form a group of oriented chain particles. 2 mm in diameter for the 50 mm diameter lid on the top and bottom of the processing container
The inflow and outflow holes of No. 2 were perforated at 2 mm intervals, and a filter cloth for passing particles of 5 μm or less was placed on the surface in contact with the ferrite mixture.

When water was flown through the above-mentioned inflow hole at a flow rate of 1000 cc per minute for 1 minute for separation treatment, the fluid that flowed out was slightly colored, indicating that fine powder was separated. . Although it was attempted to measure the particle size of the separated particles, it was impossible to measure the particle size due to magnetic agglomeration and fine particles themselves.

After removing the weakly magnetic particles in this way, the ferrite-mixed water was taken out from the container, and ordinary wet press molding was carried out at a molding load of 450 kgf / cm ² to obtain a density of 3.25 g / cm ³ . A green molded body having a diameter of 10 mm was obtained. After drying this, 1 at 1220 ℃
It was sintered by holding for a time and magnetized in a magnetic field of 15 kOe to obtain a magnet.

When the magnet characteristics of the present invention manufactured as described above and separated according to the present invention and the magnet formed and sintered directly in the same manner without the separation according to the present invention were compared. The separation method has a residual magnetic flux density of 4.6 kOe and a coercive force of 3.3 kOe,
The residual magnetic flux density is about 10 compared to the comparative example not based on this method.
%, The holding power was confirmed to be improved by about 3%.

Example 2 Further, in order to evaluate the influence of the treatment conditions, an experiment was conducted by changing the magnetic field strength by the external magnetic field, the flow rate of water, the treatment time and the fluid as the dispersion medium of ferrite in Example 1 to obtain the results. The obtained material was compacted and sintered in the same manner as in Example 1, and the effect was evaluated by the residual magnetic flux density. The results are shown in Table 1. The larger the magnetic field strength and the flow rate of water, and the longer the treatment time, the higher the residual magnetic flux density as a magnet characteristic increases. However, at a certain value or more, the residual magnetic flux density becomes the upper limit and does not change further. I understand. It was also confirmed that the higher the viscosity of the dispersion medium, the greater the effect of separation.

[0031]

[Table 1]

[0032]

As is apparent from the examples, by using the method of the present invention for separating magnetic materials, it becomes possible to selectively and efficiently remove particles having weak magnetic properties. In particular, the remanent magnetism characteristic of the magnet is greatly improved. The effect of the invention is practically unrealizable by the conventional method, and an external magnetic field is applied to the magnetic material powder mixed in the dispersion medium to form a group of oriented chain particles constrained by the magnetic field. It can be realized only by causing a desired fluid to act and selectively separating and removing only particles having a weak coupling force.

[Brief description of drawings]

FIG. 1A is an explanatory view showing a state in which magnetic particles are linked in a columnar shape by an external magnetic field, and FIG. 1B is an enlarged view of the binding state to give a fluid flow to the chain. It is explanatory drawing which shows the basic principle of the separation method by.

FIG. 2 is a vertical cross sectional view showing an example of a separation device according to the present invention.

FIG. 3 is an explanatory view showing the concept of a separation device for continuously performing the separation method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing container 2 Magnetic material powder 3 Oriented chain particle group 4,5 Flow path hole 6,7 Filter medium 10 Yoke 11 Lower pipe 12 Upper pipe 13,14 Electromagnetic coil A, Magnetic field 20 Pipe

Claims (2)

[Claims] 1. A magnetic field is applied to a magnetic material powder mixed with a dispersion medium of a fluid in a state where an external magnetic field is applied so that the magnetic particles in the material are linked and constrained and fixed in a chain form. A magnetism characterized by causing a fluid having a flow velocity relative to a constrained group of oriented chain particles to flow to selectively separate and remove particles having a weak coupling force from the magnetic material powder containing the group of oriented chain particles. Selective separation of materials. 2. The container according to claim 1, which can accommodate the magnetic material powder mixed with the dispersion medium, the piping means capable of flowing the dispersion medium fluid in the container in a desired direction, and the dispersion medium fluid in the container. A selective separation device for magnetic material, comprising a magnetic circuit capable of applying a magnetic field parallel to a flow.