JPH0656820B2 - Method for manufacturing anisotropic permanent magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for producing an anisotropic permanent magnet by a powder metallurgy method,
In particular, it relates to improvement of vertical pressing molding.

[Prior Art and Problems] In the manufacture of anisotropic magnets by the powder metallurgy method, it is generally practiced to orient the powder in a static magnetic field by an electromagnet and then press-mold it. Static magnetic field strength is usually a few kOe ~
It is 10 kOe. However, the degree of orientation decreases for various reasons. This is due to the strength of the magnetic field, parallelism, non-uniformity of pressure in press molding, non-uniformity of powder filling, etc.
In the magnetic field press, there are two kinds of methods depending on the directions of the magnetic field and the pressure.

One is "lateral pressing" in which the magnetic field and the pressure are perpendicular to each other, and the other is "longitudinal pressing" in which they are parallel to each other. Especially in the latter case, when the rare earth cobalt magnet or the like has a large disorder of orientation and is evaluated by the saturation magnetization (4πMz) which is one of the indexes of the orientation degree, the vertically pressed sample becomes nearly 10% lower than the horizontally pressed sample.

The reason why the vertical pressing with large orientation disorder is used is that a ring-shaped anisotropic permanent magnet having a magnetic field oriented in the axial direction cannot be produced by lateral pressing. Many such magnets are used for motors.

An anisotropic magnet having the same C-shaped magnet and oriented in a magnetic field in the thickness direction is also very difficult to manufacture by lateral pressing.

For this reason, vertical pressing molding is often performed even if the magnetic properties are deteriorated due to the deterioration of the orientation degree. Regarding the improvement of vertical pressing molding, the degree of orientation improves when uniform pressure is applied, but a hydrostatic pressure generator such as a rubber press is practical because it requires a long molding time and it is difficult to incorporate a magnetic field generator. Not. The degree of orientation can be improved by molding in a high static magnetic field of several tens of kOe. An electromagnet is generally used to generate a static magnetic field of several kOe to 10 kOe in a space of 10 to 100 mn, but a superconducting magnet is used to generate a static magnetic field of higher strength.
There is only a solenoid coil with normal conduction, which is not practical in view of the price of equipment, maintenance cost, and operability. Therefore, the present invention relates to a method for producing an anisotropic permanent magnet, which improves the orientation in vertical pressing and improves the magnetic properties.

[Structure of the Invention] As a result of extensive studies in view of the above-mentioned conventional problems, the present invention overcomes the deterioration of the magnetic properties in the step of orienting the powder in a magnetic field and then press-molding (hereinafter referred to as magnetic field press), The present invention has been accomplished by finding a method capable of significantly reducing the time required.

The main point is that in the production of an anisotropic permanent magnet composed of rare earth-transition metal or rare earth-transition metal-boron by the powder sintering method, the peak value of the pulse magnetic field is 5 kOe or more in the ferromagnetic fine powder, and A pulse magnetic field having a pulse magnetic field width of 5 msec or more and 1 sec or less is applied, and while the easy axis of magnetization is oriented in the pulse magnetic field direction, while the pulse magnetic field is being generated, it is parallel to the preceding application direction of the pulse magnetic field and A method for producing an anisotropic permanent magnet, characterized by pressurizing and molding a pulse pressure having a pulse pressure width of 1 μsec or more and 500 msec or less, which causes a peak 5 msec to 10 msec later than the peak occurrence. It is in.

This will be described in detail below.

Conventionally, in the production of anisotropic permanent magnets composed of rare earth-transition metal or rare earth-transition metal-boron by the powder sintering method, the magnetic field pressing step of ferromagnetic fine powder is performed by a static magnetic field by an electromagnet and a quasi-static by a hydraulic press. Although it has been performed by the action of dynamic pressure, the inventors of the present invention have performed “lateral press molding” in a static magnetic field.
As a result of investigating how the saturation magnetization (4πMz) of the orientation magnetic field (H) changes in the sintered sample after (H⊥P) and “longitudinal pressing forming” (H / P), as shown in FIG. As described above, it was found that the orientation degree in a high magnetic field is remarkably improved especially in the vertical pressing molding.

Based on this fact, the present invention was able to realize a high degree of orientation, which has not been obtained in the past, by press molding combining a pulsed magnetic field and a pulsed pressure that is generated in a short time by shock.

FIG. 1 shows an outline of an impact-type magnet molding apparatus that performs press molding with a pulse magnetic field and pulse pressure. The apparatus is roughly classified into 1) a pulse pressure generating mechanism, 2) a pulse magnetic field generating mechanism, and 3) a molding press. It is composed of a mechanism. The configuration and function of each mechanism will be described below.

The pulse pressure generating mechanism of 1) has a built-in upper hammer 5 which is controlled by the solenoid valve 4 for controlling the discharge time of the high pressure air, and a lower hammer 6 which is hit with the high pressure air at a high speed. Both the upper hammer 5 and the lower hammer 6 are initially located at the lower part, but by opening the solenoid valve 17 to blow air between the upper hammer 5 and the lower hammer 6, and at the same time opening the upper solenoid valve 18, ,
The upper hammer 5 is pushed upward. When the upper hammer 5 reaches the upper part, the solenoid valves 17 and 18 are closed. Once the upper hammer 5 is pushed up, the space between the upper hammer 5 and the lower hammer 6 is sealed, so that air does not escape and the upper hammer 5 is held at the upper portion.

The high-pressure air generated by the compressor 1 (1-8 kgf / cm ² in this mechanism, but a higher molding pressure can generate a higher forming pressure) is stored in the tank 2 while adjusting it to a desired pressure with the pressure reducing valve 3. In addition, the solenoid valve 4 is rapidly opened, and at the same time, the air escape solenoid valve 19 is opened to open the upper hammer 5
The air between the lower hammer 6 and the lower hammer 6 is discharged. The upper hammer 5 accelerated by high-pressure air and its own weight hits the lower hammer 6, and the lower hammer hits the upper punch 11, whereby the magnetic powder 10 in the die 14 is molded. That is, molding is performed by converting the kinetic energy of the hammer into molding energy.

The pulse magnetic field generation mechanism of 2) is composed of a photoelectric switch 7, a delay pulser 8 and a discharge pulse power source 9, and a magnetic field for orienting the ferromagnetic powder is generated when the upper hammer 5 crosses the light beam of the photoelectric switch 7. , The pulse signal generated in the delay pulsar 8 is input to the discharge pulse power source 9 with a little delay in order to adjust the timing of the pulse pressure and the pulse magnetic field, whereby a pulse current is passed through the coil 13 and the ferromagnetic fine powder 10 is supplied. A pulse magnetic field is applied, and at the same time, a pulse current waveform is input to the transient converter 16.

The forming press mechanism of 3) is composed of a die 14 wound with a pulse magnetic field coil 13, an upper punch 11, which is hit by a lower hammer 6, a load cell 12, a dynamic strain measuring device 15, and a transient converter 16. Ferromagnetic fine powder
The pulse pressure received by 10 is converted into a pulse voltage by the load cell 12, sent to the dynamic strain measuring device 15, amplified, and input to the transient converter 16. The transient converter 16 displays a transient phenomenon, and after the input pulse current and pulse voltage are stored in the memory once, each waveform is repeatedly drawn on the cathode ray tube or drawn on the pen recorder. The waveforms of the pulse magnetic field and the pulse pressure as shown in Fig. 2 are displayed.

The forming press mechanism is composed of a set of two hammers, an upper hammer and a lower hammer, but of course, only the upper hammer may be used. The relationship between the pulse magnetic field and the pulse pressure at this time is obtained by subtracting the time T ₂ delayed by the delay pulser 8 from the time T ₁ until the lower hammer 6 collides with the upper punch 11 (T ₁ −T ₂ ). Therefore, for example, as shown in FIG. 2, the delay time between each peak time can be adjusted by the delay pulser 8. The pulsed magnetic field may be applied once or more, but usually once is sufficient. Also, it is needless to say that the magnetic field pulse must precede the pressure pulse because the magnetic powder does not orient even if a pulsed magnetic field is applied after molding, but since the degree of orientation changes depending on the timing of the magnetic field and pressure, there is a delay. Optimal conditions can be found by changing the time. However, the optimum delay time varies greatly depending on the pulse magnetic field waveform and pulse pressure waveform, but it is 2 msec to 20 m
Second, preferably 5 msec to 10 msec, and the magnetic field applying direction and the pulse pressure pressurizing direction are parallel. The higher the peak of the pulse magnetic field, the better. The peak magnetic field of 5 kOe or less is not preferable because the orientation sharply decreases. "Rise time", "Pulse half width", "Magnetic field pulse width"
The "pressure pulse width" is shown in FIG.

The shorter the magnetic field pulse width, the shorter the energy required to generate it and the less the coil heat is generated when viewed from the side of the pulse current, but the shorter it is, the larger the eddy current generated in the mold inserted into the coil. Is not desirable.

On the other hand, the longer the pulse width of the magnetic field, the easier it is to set the timing, but on the other hand, in order to obtain a pulse magnetic field with a high peak value, the capacity and voltage of the pulse power supply must be increased, which is inevitably large. A pulse value of 1 second or more is not preferable because it becomes large in scale and expensive, and the heat generation of the coil also becomes large.

In order to make the pulse pressure width shorter than 1 microsecond, it is necessary to increase the upper hammer speed, but the upper punch will be damaged by hitting between the metals, and the generated pressure will be too high and the orientation will be disturbed. If it is longer than 500 msec, the molding time will not be completed within the pulse magnetic field generation time, which is not preferable. The range of 0.5 msec to 0.1 sec is more preferable.

[Effect of the Invention] According to the present invention, the degree of orientation of the permanent magnet powder can be improved and 4π.
Evaluated by Mz, several percent or more, nearly 10% higher. The maximum energy product (BM) max, which is one of the guidelines for magnetic properties,
It brings about 20% improvement in properties.

In addition, since the press forming is instantaneously completed in both magnetic field and pressure in pulse form, the press forming time is greatly shortened. That is, in the conventional magnetic field pressing mechanism, it takes 10 to 20 seconds from completion of depressurization of a molded body after applying a magnetic field and press molding, but according to the method of the present invention, it is completed within 1 second. As this time is shortened, the pulse pressure generation mechanism has an excellent effect such as a simpler structure than the hydraulic press mechanism.

Example 1 Sm, Co, Fe, Cu, and Zr in atomic ratio Sm (Co
_0.725 Fe _0.200 Cu _0.055 Zr _0.020 ) Weighed to _7.5 and then melted in a high frequency melting furnace. The molten ingot was finely pulverized with a jet mill to have an average particle size of 3 to 5 μm. The fine powder was fed to a die, and powder orientation and press molding were performed at the position shown in FIG. 1 while timing the pulse magnetic field and the pulse pressure.

The pulse current was obtained by instantly discharging the charging voltage of the capacitor, and the capacitor used was 800 μF, max.
It has a withstand voltage of 5 kV. Peak value of pulsed magnetic field is 10kOe ~ 45kO
At e, the rise time to the peak value is 1.5 msec and the peak value of pulse pressure is about 1 t / cm ² . The obtained molded body was sintered in an inert gas atmosphere at a temperature of 1,100 to 1,200 ° C. for 1 hour and then rapidly cooled. The result of measuring the saturation magnetization 4πMz of the sintered body is shown in FIG. Fig. 4 shows the magnetic properties of this sintered body after it was held in a heat treatment furnace for 800 × 2 hours and gradually cooled to 400 ° C at 0.5 ° C / min. It can be seen that as the peak value of the magnetic field pulse increases, the saturation magnetization 4πMz of the sintered body increases, and the magnetic characteristics improve.

Example 2 Nd, Fe, and B were weighed so that the atomic ratio was Nd ₁₅ Fe ₇₈ B _7, and then press-molded under the same conditions and processes as in Example 1. This molded body is placed in an inert gas 1,000 to 1,1
After sintering at a temperature of 00 ° C for 1 hour, the mixture was rapidly cooled to room temperature, and then kept at 500 ° C for 1 hour in a heat treatment furnace and then rapidly cooled. Table 1 and Table 2 show the saturation magnetization of 4πMz after sintering and the magnetic properties after aging. However, this value is a value when the delay time is optimum. For comparison, Table 2 also shows the characteristics of the sample oriented by a static magnetic field of 10 k Oe and molded by a hydraulic press.

Example 3 Sm, Co, Fe, Cu and Zr were melted and finely pulverized under the same conditions as in Example 1. Using the apparatus shown in FIG. 1, coils having different rise times were used, and powder orientation and press molding were performed while changing the delay time. The rise time of each coil was 0.2, 1.5, and 3.2 msec, and the peak value of the pulsed magnetic field was 20 kOe. Each pulse magnetic field waveform is shown in FIG. The peak value of pulse pressure is 1 t / cm ² . This compact was sintered in an inert gas atmosphere at 1,100 to 1,200 ° C. for 11 hours and then rapidly cooled, and 4πMz of the resulting sintered body was measured. The result is shown in FIG. Pulse magnetic field rise time 0.2m
At the time of second, since the effect of the eddy current appears a little, the effective orientation magnetic field generated in the die decreases, and thus 4πMz decreases a little.

Example 4 Sm, Co, Fe, Cu and Zr were melted and finely pulverized under the same conditions as in Example 1. By changing the air pressure of the tank to 1.5 atm, 2 atm and 3 atm with the device shown in Fig. 1 and changing the speed of the hammer, the molding energy is 12 kg each.
・ The pulse width of m, 17 kg ・ m, 20 kg ・ m or the pulse pressure at that time was changed to 8 ms, 5 ms, and 2 ms. Magnetic field orientation and press molding were performed while changing the delay time under the conditions of a rise time of 3 msec and a pulse magnetic field peak value of 20 kOe under the above pressure conditions. This molded body was sintered under the same conditions as in Example 3 and then 4π.
Mz was measured. Results are shown in FIG.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a mechanism used for carrying out the method of the present invention, FIG. 2 is a curve diagram showing the timing of the pulse magnetic field and the pulse pressure, and FIG. 3 is saturation when the peak value of the pulse magnetic field and the delay time are changed. FIG. 4 is a curve diagram showing changes in magnetization, FIG. 4 is a curve diagram showing changes in magnetic properties when the properties of the sample of FIG. 2 are measured after aging, and FIG. 5 shows coils with different rise times of pulsed magnetic fields. FIG. 6 is a curve diagram showing a change in saturation magnetization with respect to a delay time of a sample molded and sintered using FIG. 6, FIG. 6 is a curve diagram showing a change in saturation magnetization when the peak value of pulse pressure is changed, and the sample is sintered. FIG. 7 is a curve diagram showing the pulse waveform of each coil used in the pulse magnetic field press. FIG. 8 is the strength of the orientation magnetic field of the sintered sample after “lateral pressing” and “longitudinal pressing”. FIG. 6 is a curve diagram showing a change in saturation magnetization due to. 1 ... Compressor, 2 ... Tank, 3 ... Pressure reducing valve, 4 ... Solenoid valve, 5 ... Upper hammer, 6 ... Lower hammer, 7 ... Photoelectric switch, 8 ... Delay pulser, 9 ... Discharge pulse power supply, 10 …… Magnetic powder 11 …… Upper punch, 12 …… Load cell, 13 …… Coil, 14 …… Die 15 …… Dynamic strain measuring instrument, 16 …… Transient converter 17,18,19 …… Solenoid valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 58-200517 (JP, A) JP 58-157901 (JP, A) JP 59-64199 (JP, A) JP 55- 88998 (JP, A) Actual development Sho 59-37724 (JP, U)

Claims (3)

[Claims] 1. In the production of an anisotropic permanent magnet composed of a rare earth-transition metal or a rare earth-transition metal-boron by a powder sintering method, a ferromagnetic fine powder has a peak value of a pulse magnetic field of 5
A pulse magnetic field having a pulse magnetic field width of 5 msec or more and 1 sec or less, which is kOe or more, is applied, and the preceding application direction of the pulse magnetic field is generated while the easy axis of magnetization is oriented in the pulse magnetic field direction. Anisotropy permanent characterized by pressurizing and molding a pulse pressure having a pulse pressure width of 1 μsec or more and 500 msec or less, which is parallel to Magnet manufacturing method. 2. A pulsed magnetic field is applied at least once,
The method for producing an anisotropic permanent magnet according to claim 1, wherein pulse molding is performed at least once during the last remaining magnetic field to perform press molding. 3. The rise time of the pulsed magnetic field is 1 μsec or more, 50
Claim 1 characterized in that it is 0 msec or less.
A method for producing an anisotropic permanent magnet according to item.