JPH0997730A - Manufacture of sintered permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a conventional longitudinal magnetic field molding method to contrive to enhance the degree of orientation of a sintered permanent magnet and to make it possible to perform a compacting of the magnet of an arbitrary shape. SOLUTION: In a method of manufacturing a permanent magnet by a powder sintering method, permanent magnet powder is filled in a die mold, a pulsed magnetic field, whose peak magnetic field is 20kOe or higher and whose peak magnetic field's half-value width is 1msec or wider and 500msec or narrower, is applied to the powder in a state that the powder filling apparent density is 30% or higher and 50% or lower and after the powder is orientated in the direction of the magnetic field, a compacting of the magnet is performed at one axial pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered permanent magnet, and more particularly to the production of a high-performance rare earth sintered magnet.

[0002]

2. Description of the Related Art The magnetic characteristics of a permanent magnet produced by powder metallurgy are primarily influenced by the material and composition of the magnet, but are influenced by various factors in the manufacturing process. For example, crushed particle size and powder particle size distribution, powder orientation degree, sintering temperature and pattern,
The heat treatment conditions, the sintering heat treatment atmosphere, the processing accuracy, and the like.
Among them, the degree of orientation of the magnet powder due to the powder compaction of the magnet powder in the magnetic field is particularly important.

It is well known that, in the magnetic field compaction of permanent magnet powder, there are a longitudinal magnetic field compaction method and a transverse magnetic field compaction method depending on the orientation magnetic field direction and the compaction compaction direction. In the transverse magnetic field molding, the orientation magnetic field direction and the powder compacting direction are orthogonal to each other, and the magnet powder oriented in the magnetic field is less likely to be disturbed in the powder compacting process. On the other hand, in the vertical magnetic field molding, the orientation magnetic field direction and the powder compacting direction are parallel, and the orientation of the magnet powder oriented in the magnetic field is considerably disturbed in the powder compacting process. Depending on the type of magnet powder, the degree of property deterioration due to orientation disorder will differ.
Even if the same magnet powder is used for NdFeB magnets, the characteristics deteriorate by 10% or more in longitudinal magnetic field molding as compared with transverse magnetic field molding.

Longitudinal magnetic field molding is indispensable for producing a ring-shaped magnet for a motor whose magnetization is oriented in the axial direction, and improvement of orientation disorder in the powder compacting process is desired. In order to improve this alignment disorder, various magnetic field molding methods have been proposed. The present inventors have previously proposed a pulse molding method in which a powder magnetic field is applied within a time period of applying a pulse magnetic field by using a peak magnetic field having a high pulse magnetic field by employing a pulse magnetic field and a pulse pressure. According to this, molding is completed in a short time, and since it is possible to mold in a magnetic field much higher than the magnetic field of an ordinary electromagnet (however, at a peak magnetic field of 20 kOe or more), disturbance of the magnet orientation is suppressed, and a transverse magnetic field equivalent to A degree of orientation can be realized.

However, since this method uses pulse pressure, it is difficult to finely adjust the pressing conditions for powder compacting, and there is a problem with the soundness of the compact. That is, cracks and cracks are likely to occur, and the shape that can be molded is also limited.

On the other hand, a method has been proposed in which the magnet powder is oriented by a pulsed magnetic field, but the powder compaction is performed by ordinary hydraulic pressure or mechanical pressure. However, in this method, since the powder compacting takes time, it is impossible to perform the pulse magnetic field and the powder compacting in synchronization. Therefore, since no magnetic field was applied during the powder compaction process, the orientation of the magnet powder was significantly disturbed, and the degree of orientation could not be improved. In order to improve this, it has been proposed to apply a pulsed magnetic field and then a static magnetic field to perform powder compaction. However, in this powder compacting process, only the same magnetic field strength as in the past can be applied, so that the degree of orientation has not been improved so much.

Recently, a rubber-type hydrostatic molding method has been proposed by Sagawa et al. In this method, a rubber die is inserted into a die die, magnet powder is filled, a lid is placed, a pulse magnetic field is applied to orient the magnet powder, and then powder compacting is performed with an upper punch. The rubber mold is isotropically compressed in the die mold, and the magnet powder is isotropically pressed. Therefore, even if a magnetic field is not applied in the powder compacting process, the orientation of the magnet powder is compacted without being disturbed. With this method, an orientation degree equal to or higher than that of transverse magnetic field shaping can be realized, and almost any magnet shape including a ring shape can be realized.

However, since the process is considerably different from the conventional die mold molding, the conventional hydraulic molding machine or mechanical molding machine cannot be used as the press molding machine, and a new press molding machine must be prepared. Furthermore, the proposer of this method has announced a multi-stage magnetic field forming machine. Although this method is an excellent method for improving the degree of orientation, it is not as versatile as the current die mold molding because there is a limitation on the shape that can be molded and it is not possible to mold many pieces at once.

[0009]

DISCLOSURE OF THE INVENTION The present invention considers the cause of the decrease in the degree of orientation during the powder compaction process of magnet powder, and improves the conventional longitudinal magnetic field compaction by fundamentally considering the prior art. It aims to realize powder compacting in an arbitrary magnet shape by improving the degree.

The present invention solves the problems in the conventional longitudinal magnetic field molding, improves the degree of orientation, and follows the conventional method as a mechanical element to realize powder compacting in an arbitrary magnet shape. Is what you are trying to do.

[0011]

DISCLOSURE OF THE INVENTION The present invention uses a pulsed magnetic field and a conventional die mold molding machine in the longitudinal magnetic field molding, and the gist thereof is the production of a permanent magnet by a powder sintering method. In the method, the die magnet is filled with permanent magnet powder, and the powder filling apparent density is 30% or more and 50% or less,
The peak magnetic field is 20 kOe or more, and the half width of the peak magnetic field is 1
This is a method for producing a sintered permanent magnet, in which a pulsed magnetic field of at least msec and no more than 500 msec is applied, the permanent magnet powder is oriented in the magnetic field direction, and then powder compacting is performed with uniaxial pressure.

The decrease in the degree of orientation in the vertical magnetic powder compaction process occurs when powder compaction is performed while the magnet powder row oriented in a beaded shape is collapsed, whereas in the transverse magnetic field press, it is oriented in a beaded shape. It is considered that the degree of orientation is not significantly reduced because the powder compaction is performed in such a manner as to move in parallel without breaking the magnet powder row. When a high peak magnetic field with a pulsed magnetic field is applied, even if the magnet powder moves during the powder compaction process, the magnetic field is aligned in the direction of the magnetic field application due to the high magnetic field strength, so the degree of orientation does not decrease, and the degree of orientation is similar to that of transverse magnetic field shaping. It is thought that can be realized.

Therefore, in order to improve the degree of orientation in the vertical magnetic field molding, it is essential to apply a high magnetic field in the powder compacting process. On the other hand, in the rubber-type hydrostatic molding, before applying the pulse magnetic field, the magnetic powder in the rubber mold is lightly pressed to increase the apparent density in the mold, and then the pulse magnetic field is applied. This is because it is necessary to reduce the amount of deformation of the rubber mold as much as possible in order to eliminate the "elephant's foot" phenomenon that occurs in compaction molding using a rubber mold. Further, in the powder compacting method, the orientation of the magnet powder is not disturbed even though no magnetic field is applied in the powder compacting process, which is considered to be due to isotropic powder compacting. ing.

However, as a result of various studies and experiments on the rubber type hydrostatic molding, the present inventor has found that the cause of the less disorder of the orientation degree in the powder compacting process is not necessarily due to the hydrostatic molding, but the pulse magnetic field. Since the apparent density was made high before the application, it was found that it was caused by the small movement amount of the magnet powder in the powder compaction process.
In the magnetic field molding using an ordinary electromagnet, the magnetic field strength that can be applied is at most 10 kOe to 15 kO even in the case of a rare earth magnet.
It is e. Therefore, the apparent density of the magnet powder packed in the die mold had to be about 30% or less of the true density.

When the apparent density was higher than the above value, the magnet powder was not sufficiently oriented in the magnetic field application direction, resulting in deterioration of magnetic properties. In compaction molding in a filling state of 30% or less of the true density, the magnet powder moves a large distance in the compaction process, and the longer the movement distance, the greater the decrease in orientation degree.

According to the present invention, pre-compacting is performed before applying a magnetic field, and a pulse magnetic field sufficient to rotationally orient the magnet powder in the magnetic field application direction is applied in a state where the apparent density is improved as much as possible. It is compacted in a mold.
The higher the apparent density after the pre-compaction is, the more preferable, but a higher pulse magnetic field is required for orienting the magnet powder, and therefore the apparent density of filling the die is 50% or less. Further, if the apparent density of filling is 30% or less, the degree of orientation reduction in the powder compacting process becomes large, and therefore it is necessary to be more than that.

The pulse magnetic field strength sufficient to orient the pre-compacted magnet powder depends on the apparent density of the packing, but a peak strength of 20 kOe or more is required.
30 kOe or more is good. The pulsed magnetic field is generated by installing an air core coil or the like outside the die die.

Therefore, in a pulse magnetic field having a short rise time to the peak value, an eddy current is generated in the mold, and the pulse magnetic flux does not sufficiently penetrate into the mold cavity. Therefore, the full width at half maximum of the pulsed magnetic field needs to be 1 msec or more. It is desirable that the full width at half maximum of the pulse magnetic field is as long as possible, but if it is too long, the capacitor capacity of the pulse power supply must be increased and the number of air core coil windings must be increased, so the power supply becomes very large and expensive, and the coil Since the number of turns is large, the coil temperature rises after the magnetic field is applied, and the temperature inside the coil does not easily fall. Therefore, the full width at half maximum of the pulsed magnetic field is 500 ms.
It is desirable to be ec or less. The most desirable half-value width of the pulse magnetic field is 5 msec to 50 msec.

The powder compacting machine may basically be a uniaxial molding machine using the same hydraulic pressure or mechanical pressure as in the conventional case. Instead of an electromagnet,
An air-core coil and a pulse power supply are required to generate a pulsed magnetic field. Insert the die mold inside the air core coil.
In the conventional powder compacting method, the upper punch descends to the upper surface position of the die die filled with magnet powder, and once stopped, a magnetic field is applied by an electromagnet to orient the magnet powder in the magnetic field direction, With the magnetic field applied, the upper punch was lowered to compact the magnet powder in the die mold. In the present invention,
The upper punch descends and is inserted halfway into a die die filled with magnet powder to perform pre-compaction. In that state, the upper punch is once stopped, a pulsed magnetic field is applied to orient the magnet powder, and then the upper punch is further inserted to perform final powder compaction.

Since conventional mechanical devices are used except for the pulsed magnetic field, no special development or modification of mechanical elements is required, and it is possible to stably produce a sound compact of any size. Basically, it is not necessary to apply a static magnetic field in the final powder compacting process, but if a static magnetic field is applied, the degree of orientation will decrease less. It is possible to apply a plurality of pulse magnetic fields in the final powder compacting process, but it is not effective because the pulse magnetic fields and the compacting pressure cannot be synchronized and the time widths are different.

The present invention is applicable to magnet powders in general, but is most suitable for the orientation of rare earth magnet powders which require high magnetic field strength for magnetic field orientation. Rare earth magnets include 1-5SmCo magnets,
There are 2-17SmCo magnets, NdFeB magnets, etc., but they are applicable to all of them.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to Examples and Comparative Examples.

[0023]

【Example】

Examples 1 to 4, Comparative example, Nd ₁₅ Fe metal and FeB alloy in atomic percentage of Nd ₁₅ Fe
_It was weighed to be ₇₈ B _7, and then an alloy was prepared in a vacuum melting furnace. The alloy was roughly pulverized to 20 mesh or less by mechanical pulverization, and then finely pulverized by a jet mill using high pressure N ₂ gas so that the average particle size was 4 μm. The fine powder was filled in a die press die, and the apparent density before applying a magnetic field was 20
Changed from 60% to 60%. After that, the peak magnetic field is 40 kOe
Then, after applying a pulse magnetic field having a pulse half-value width of 10 msec to orient the fine powder filled in the mold, the upper punch was pushed into the die to perform powder compaction.

The molded body taken out was treated with 1,100 in Ar gas.
Sintering was performed at 1 ° C for 1 hour, and then heat treatment was performed at 580 ° C for 1 hour to obtain a sintered body. Then, these sintered bodies are
Table 1 shows the results of measuring the magnetic properties with the H tracer.

Comparative Example For comparison, a mold was filled with the fine powder to an apparent density of 25%, a static magnetic field of 10 kOe was applied to orient the fine powder, and then the powder was compacted while the magnetic field was applied. The sintering and heat treatment were performed in the same manner as in the example to obtain a sintered body, and the magnetic characteristics were measured with a BH tracer. Table 1 shows the results.

[0026]

[Table 1]

[0027]

According to the method of the present invention, it is possible to manufacture a high-performance rare earth sintered magnet, and it is possible to obtain an optimum permanent magnet for use in a DC brushless motor, an AC servomotor, a stepping motor, or the like.

Claims (4)

[Claims] 1. A method for manufacturing a permanent magnet by a powder sintering method, wherein a permanent magnet powder is filled in a die and the apparent density of powder filling is 30% or more and 50% or less, and a peak magnetic field is 20%.
At kOe or more, the half-width of the peak magnetic field is 1 msec or more and 500 ms
A method for producing a sintered permanent magnet, which comprises applying a pulsed magnetic field of ec or less to orient the permanent magnet powder in a magnetic field direction, and then performing powder compacting with uniaxial pressure. 2. The powder compaction is carried out with a uniaxial pressure in a state where a static magnetic field is applied after a pulsed magnetic field is applied to the permanent magnet powder to orient it in the magnetic field direction. Method for manufacturing a sintered permanent magnet according to. 3. The method for producing a sintered permanent magnet according to claim 1, wherein the permanent magnet powder is formed by a vertical magnetic field in which a magnetic field applying direction and a powder compacting direction are parallel to each other. 4. The method for producing a sintered permanent magnet according to claim 1, wherein the permanent magnet powder is a rare earth permanent magnet.