JPS58200518A - Formation of magnetic field of powder - Google Patents

Abstract

PURPOSE:To realize magnetization of multiple poles at the external circumference, set a magnetic field molding speed to about 5sec, improve the optimum magnetic field orientation rate and enhance production efficiency by generating magnetic field oriented vertically to the pressing direction by a pulse current and by forming pulse magnetic field through the orientation of magnetic field. CONSTITUTION:A magnetic field perpendicular to the pressing direction is formed at the die portion of punch by winding a magnetic field generation coil at the circumference of die of punch so that magnetic flux is generated in vertical to the pressing direction or by winding a coil to the yoke oriented to the vertical direction to the pressing direction, the timing of generating magnetic field is interlocked with movement of punch, and disturbance of orientation is minimized at the time of pressing powder material. Here, if the height of molding is (b), distance between upper punch and lower punch at the time of molding is (a), height of powder charged to the die set is (c), the desirable timing of generating pulse magnetic field should be in the following relation; 1.3<=a/b<=c/b.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for magnetic field molding of powder, in which powder is molded by magnetic field orientation perpendicular to the pressing direction.

Generally, when manufacturing sintered magnets, magnetic raw material powder is press-molded in a magnetic field to impart magnetic anisotropy.
It is well known that permanent magnets with excellent magnetic properties can be manufactured, but conventionally, such magnetic field forming
A method is used in which a press machine is used to generate a magnetic field by passing a sustained current through an air-core coil using a DC power supply, and molding is performed in this magnetic field. In this case, the orientation of the magnetic field will usually coincide with the pressing direction, and once
For example, a ring-shaped magnet to which magnetic field shaping is applied has magnetic anisotropy in the direction of the center axis of the ring.

However, in recent years, efforts have been made to impart magnetic anisotropy in the direction perpendicular to the central axis and in the radial direction (hereinafter simply referred to as the "radial direction") to ring-shaped permanent magnets used in coreless motors and steno knob motors. It has been reported that the performance of these motors is further improved by the above methods, and for this reason, various attempts have been made to manufacture sintered permanent magnets having magnetic anisotropy in the radial direction.

As a typical manufacturing method for these conventional sintered permanent magnets with magnetic anisotropy in the radial direction, ordinary electromagnets are set on both sides of the mold, and a magnetic field is applied perpendicularly to the direction in which the powder is pressed. There is a method to orient the wires, but in this case, a normal electromagnet has a large number of windings and is bulky, so it is difficult to lower the entire electromagnet below the die table surface.
At most, a ring-shaped permanent magnet with two poles in the radial direction was manufactured. Another method is to wind coils around the upper and lower punches and press them up and down while generating bipolar magnetic fields on the end faces of the punches, so that the magnetic fields are oriented in the direction of leakage magnetic flux of the same polarity, that is, in the radial direction.

However, subsequent research has shown that the performance of these motors can be further improved by increasing the number of radial poles of the ring-shaped permanent magnets incorporated into the coreless motors and step monitors mentioned above to four or more if possible. It is clear that the latter method of the conventional method achieves a high orientation rate. Taking these into account,
At present, a satisfactory method for manufacturing sintered permanent magnets has not yet been found.

From the above-mentioned viewpoint, the present inventors conducted research to find a method that allows magnetic field orientation with a large number of poles in the pressing direction in magnetic field forming in the manufacturing process of permanent magnets using powder as a raw material. When generating a magnetic field with a pulsed current, a large current instantly flows through the coil, so the number of turns in the coil can be reduced to obtain the same magnetic flux density, making it possible to downsize the magnetic field generating coil and electromagnet. ■ Therefore, when generating a magnetic field oriented perpendicular to the press direction using a pulsed current, the electromagnet can be made smaller and fit below the die table surface, allowing it to be incorporated into the outer periphery of the mold. It is now possible to create a circuit that generates a magnetic field in a direction perpendicular to the pressing direction, and more electromagnets can be installed as the size of the electromagnets has been reduced.
It is possible to orient the magnetic field to the number of poles that the electromagnet can be placed in. ■ In contrast to the conventional DC magnetic field generated by DC current, if the magnetic field is generated by pulsed current, the press cycle can be made very fast, and the magnetic field We have come to the knowledge shown in (1) to (3) above that it is possible to employ a press that has a faster molding speed than the generally used hydraulic press for molding.

In order to obtain this knowledge, the present inventors wound a magnetic field generating coil around the die periphery of the mold so that the magnetic flux was generated perpendicular to the pressing direction, and created a yoke oriented perpendicular to the pressing direction. A magnetic field perpendicular to the pressing direction is created in the die part of the mold, and the timing of the magnetic field generation is linked to the movement of the punch, and when the powder raw material is press-molded, the orientation Needless to say, we have carefully considered the magnetization timing that can minimize the disturbance of the magnetic field.

Figure 1 shows a cam diagram of conventional magnetic field forming [Figure 1 (a)]
and cam diagram of magnetic field shaping using pulsed magnetic field [1st
Figure (b)] is illustrated together with the timing of the magnetizing magnetic field and the demagnetizing magnetic field. As is clear from FIG. 1, the press cycle using a pulsed magnetic field is much faster than the conventional press.

Therefore, this invention was made based on the above-mentioned knowledge found from various studies, and in a magnetic field compaction method of powder using a press machine, a magnetic field oriented perpendicular to the pressing direction is generated by a pulsed current. The present invention is characterized in that a molded article having radial magnetic anisotropy can be manufactured at high speed by magnetically oriented and molded using this pulsed magnetic field.

Note that the press machine in this invention is not only a hydraulic press, but also a mechanical press, a rotary press, etc., and the pulse current can be used, for example, by storing charge in a capacitor and releasing it, or by a rotary press. It goes without saying that this can also occur by shortening the contact time of the electrodes, and various other known methods can also be adopted.

And the magnetic field? The electromagnet for generation is, as mentioned above,
Either a coil wrapped around a mold or a coil wrapped around a yoke can be used.

Figure 2 shows the height of the molded body as b, and the distance from the upper punch to the lower punch during molding as a.
The crystal orientation ratio relative to the ratio of b is determined from X-ray diffraction.

In order to obtain properties for the molded body to be used as a magnet, it is desirable that the orientation rate is 80% or more.
As is clear from the figure, when a/b is smaller than 1.3, the powder raw material is molded before being oriented by the magnetic field, and the orientation is less than 80% and the magnetic properties are significantly degraded. In addition, when a/b exceeds c/b (where C is the height of the powder charged in the die set), the orientation wheel will not change much, but when a pulsed magnetic field is applied, the amount from the die will change. This is not practical as powder leakage, etc. increases, resulting in loss of raw materials. That is, if the magnetic field is applied before the upper punch enters the die, the powder will overflow from the die.

For this reason8, in the magnetic field shaping method of the present invention, the timing of pulse magnetic field generation is set to 13≦a/b.
It is desirable that ≦c/b, or furthermore, 1.3≦a
/b≦3.0 is more preferable. Because a/b is 3,
When the value exceeds 0, the distance the punch moves from when the pulsed magnetic field is applied to when the powder is formed is long. Therefore, once oriented, the powder is broken and formed, and the orientation ratio drops below 80%. This is because there is fear.

Furthermore, in the method of the present invention, good results can be achieved even when a pulsed magnetic field is used with nine superimposed pulsed magnetic fields on a DC magnetic field.

Next, the method of the present invention will be explained by comparing examples and comparative examples.

Example 1 A raw material having a composition of BaO.6Fe203 was pulverized to an average particle size of 1μ, and a yoke was attached to four poles on the outer periphery of a mold. Hollow copper pipe in yoke (outer diameter: 3 dragons, inner diameter: 1mm)
A magnetic field of 5 KOe was generated by winding it with 5 turns. Under the magnetic field condition of generating for 171000 seconds with magnetic field timing of a/b = 1.3, this was made into a diameter of 13 mm and an inner diameter of 9 m.
m+ It was molded into a shape with a thickness of 4u.

The molding speed at this time was 5 sec/cycle. The resulting molded body had an orientation ratio of 82.

This molded body was sintered at 1150°C for 1 hour, the outer 4 poles were magnetized with an 8KG pulsed magnetic field, and each direction was cut out and the magnetic properties were measured. Br: 3200 (),
)lc: 18000e, BHmax: 2.6MG
It showed Oe.

On the other hand, using a press machine that generates opposing magnetic poles by winding coils around the upper and lower punches using the conventional magnetic field forming method using a DC power source, the raw material powder of the above composition was
It was molded in 0 seconds. Note that the orientation rate of the molded body obtained as a result was 65%.

The sintered body obtained by sintering this compact was magnetized with four poles on the outer periphery, and various pieces were cut out and their magnetic properties were measured.
: 2700. Hc: 1500. BH+aax: 1
．． It showed 8 M()Oe.

From these results, the method of the present invention not only makes it possible to generate two or more outer polarities while generating a magnetic field in the direction perpendicular to the pressing direction, but also achieves much better productivity. It can be seen that the produced magnet has better properties than those produced by the conventional method.

Example 2 Sm (C0o6y cuo, l Feo, 21'5
zro, o15) A raw material having a composition of 7.25 was ground to an average particle size of 4μ to obtain a raw material powder.

Using a mold that can mold this raw material powder into a shape with a diameter of 13 m and a thickness of 25 m, magnetic field timing a / b = 2
.

Magnetization time: 17,100 seconds, magnetic field applied to the mold to generate a magnetic field with four outer circumferential poles (magnetic field generated perpendicular to the pressing direction): 8 K
Molding was performed under the conditions of Oe and molding speed of 10 sec/cycle. This compact, which had an orientation rate of 91%, was sintered in vacuum at 1230° C. for 1 hour and then rapidly cooled in an inert gas. This sintered body is heated at 24°C to 800-400℃
Heat treatment was performed with continuous cooling for hours.

When the magnetic properties of the sintered body thus obtained were measured, the Br was 99,000. Hc is 40000e.

Bl-imax is 24. '5 M()Oe value is shown.

Example 3 A raw material having a Sm of 36.5% by weight in a 5mCo5 composition was pulverized in an inert gas to an average particle size of 4μ to obtain a raw material powder. This raw material powder was molded using a normal rotary press having a molding speed of 500 pieces/min. For molding, a mold that can be molded to a diameter of 13 mm and a thickness of 21111 mm is set, the contact positions are adjusted to the rotary to meet the conditions of a/b-2, 5, and a current of 200 OA is applied for 171,000 seconds through the contacts of the mold. A magnetic field was generated at six poles on the outer periphery, and a magnetic field of 1 OKOe was applied. The resulting molded product had an orientation rate of 88%.

Next, this powder compact was sintered in an inert atmosphere for 9 days, and the magnetic properties of the obtained sintered body were measured, and it was found that Br was 8300C), Ha was 'i' 5000e, and BHm.
ax showed an excellent value of 1'7.2 MGOe.

As described above, according to the present invention, it is possible to generate a magnetic field perpendicular to the pressing direction, making it possible to magnetize multiple poles on the outer periphery, which not only increases productivity but also reduces the conventional magnetic field forming speed to 1. The cycle time, which used to be about 40 seconds, can be reduced to about 5 seconds, and the optimum magnetic field orientation rate at that time is 8, which yields better results and greatly improves the production efficiency of powder molded magnets. This brings about industrially useful effects such as the ability to

[Brief explanation of the drawing]

Figure 1 is a cam diagram of magnetic field compaction of powder, and Figure 1 (a
) shows the conventional method, FIG. 1(b) shows the method of the present invention, and FIG. 2 is a diagram showing the crystal orientation rate with respect to the value of a/b. Applicant Mitsubishi Metals Co., Ltd. Agent Tomi 1) Kazuo Article 8 1 (a) 05ec (b) sec

Claims (1)

[Claims] (1) In the magnetic field compaction method of powder, a magnetic field oriented perpendicularly to the pressing direction is generated by a pulsed current, and the powder is shaped by being oriented by the pulsed magnetic field. Magnetic field forming method. (2. In the method described in claim 1, the distance from the lower punch to the upper punch (a), the height of the molded body b), and the height of the powder charged in the die set C)
A method for magnetic field compaction of powder, characterized in that a magnetic field is generated under conditions where the relationship 13≦a/b≦c/b is satisfied. (3) In the method according to claim 2, 13
A method for magnetic field compaction of powder, characterized in that a magnetic field is generated under conditions satisfying ≦a/b≦3.0.