JPH02282404A - Method and device for packing permanent magnet powder - Google Patents

Abstract

PURPOSE:To uniformly pack permanent magnet powder into molding space at the fixed quantity in a short time by setting a solenoid coil at the specific position near opening part of the cylindrical molding space in a metallic mold, arranging a truncated cone shape magnetic pole along the center axis of the above coil and impressing Ac magnetic field. CONSTITUTION:The solenoid coil 20 is set in direction of the center axis thereof almost corresponding to the depth direction of the molding space 18 near the opening part of the molding space 18 in the metallic mold. The truncated cone shape magnetic pole 22, in which the upper face diameter has >=1/6 of the lower face diameter and the lower face diameter has the same or a little smaller than a diameter of a lower rod 12 on the center axis of the solenoid coil 20. The permanent magnetic powder 24 is piled on the upper part of the molding space 18, and by supplying AC current to the solenoid coil 20, the AC magnetic field is formed in the permanent magnet powder 24 and the molding space 18. The AC magnetic field can be concentrated in the molding space 18 with the magnetic pole 22, and even if the current is low, the permanent magnet powder 24 can be effectively attracted into the molding space 18.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention installs a solenoid coil and a magnetic pole near the opening of a cylindrical molding space of a mold, and applies an alternating magnetic field to generate permanent magnet powder. This relates to a technique for uniformly filling a molding space in a short time. The magnetic pole is shaped like a truncated cone, and the diameter of the upper surface is 1/6 or more of the diameter of the lower surface, and the diameter of the lower surface is the same as or slightly smaller than the diameter of the lower rod of the mold forming the cylindrical molding space.

This technology can be used to mold rare earth magnets, ferrite magnets, metal magnets, etc., or to manufacture bonded magnets using them.

[Prior art] In order to develop good magnetic properties, the molding of permanent magnet powder usually involves filling the molding space of a mold with permanent magnet powder and compression molding it with a press molding machine. ing.

In compression molding, permanent magnet powder is filled into the molding space using natural falling due to gravity. In other words, a bottomless powder supply mechanism that slides on the top surface of the die that makes up the mold fills the molding space by letting it fall naturally from the opening, and the powder supply mechanism is slid to remove excess powder. A common method is to fill the molding space of a mold with a certain amount of powder using a sliding method.

If the opening area of the molding space is quite large, it is possible to fill it using this method, but if the width of the opening is small, such as a thin cylindrical shape, simply move the powder supply mechanism to the upper surface of the mold. It is difficult to fill the container sufficiently by simply sliding it along.

For this reason, methods such as applying vibration to the mold to fill the powder, or providing forced filling vanes (pushing members) above the molding space to forcibly push the powder, etc., are sometimes adopted.

[Problems to be Solved by the Invention] The method of filling a mold by applying vibrations has the disadvantage that the filling rate tends to change depending on the state and shape of the powder, and that the vibrations may loosen the tightening of bolts, etc. of the device. There were disadvantages such as the fact that the filling efficiency was not improved much, and the reproducibility of the filling amount was poor.

In addition, with the method of force filling using blades, not only does it take a very long time to fill the powder, but it is difficult to automate the powder filling in the pressing process, resulting in extremely poor manufacturing efficiency. There are local areas where the shape of the filled powder differs from the previous shape (before filling), which makes it difficult to fill uniformly and quantitatively, leading to disadvantages such as uneven weight and uneven density distribution during molding. Ta.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to fill a thin cylindrical molding space with a constant amount of permanent magnet powder uniformly in a very short time, and thereby to provide good magnetic properties. An object of the present invention is to provide a filling technique for permanent magnet powder that can manufacture permanent magnets and can be immediately applied to existing press molding machines.

[Means for Solving the Problems] The present invention, which can achieve the above objects, includes a solenoid coil near the opening of the cylindrical molding space of the mold.
The solenoid coil is installed so that its central axis direction substantially coincides with the depth direction of the molding space, and on the central axis of the solenoid coil,
A truncated conical magnetic pole is provided whose upper surface diameter is 1/6 or more of the lower surface diameter and whose lower surface diameter is the same as or slightly smaller than the diameter of the lower rod of the mold forming the cylindrical molding space, and an alternating current is supplied. This is a method of filling permanent magnet powder by magnetically attracting and filling the permanent magnet powder above the opening into the molding space. Here, the term "cylindrical" is used in a broad sense, including not only a long axial length but also a ring shape with a short axial length.

As a device for carrying out this method, there is one in which a solenoid coil and a magnetic pole are coupled and integrated with a non-magnetic connecting member.

The magnetic pole is shaped like a truncated cone so that the permanent magnet powder can smoothly enter the cylindrical molding space. Here, setting the diameter of the top surface to 1/6 or more of the diameter of the bottom surface means 1
This is because if it is less than 76, magnetic saturation tends to occur near the top surface, the magnetic field applied to the mold becomes small, and the force for moving the powder into the molding space becomes weak. In addition, the reason why the diameter of the lower surface is the same as or slightly smaller than the diameter of the lower rod of the mold is because if it is too small, the magnetic pole will become thinner and magnetic saturation will easily occur. Ideally, the diameter should be the same as that of the mold, but it is preferably slightly smaller because it will be moved on the mold die when supplying powder and molding.

In the method of the present invention, any permanent magnet powder such as rare earth type, ferrite type, alnico type, neodymium-iron-boron type, etc. can be used, and powder of any particle size or state can also be applied. Therefore, it may be a powder for sintered magnets or a powder for bonded magnets kneaded with resin.

[Operation] As is well known, permanent magnet powder having a certain coercive force reacts sensitively to magnetic fields. These permanent magnet powders naturally have the property of being attracted in the direction of a strong magnetic field, so a solenoid is installed near the opening of the molding space of the mold in an orientation such that its central axis almost coincides with the depth direction of the molding space. When the coil is installed and an alternating current is supplied, an alternating magnetic field is applied, which gives a moving force to the permanent magnet powder. Since a magnetic pole is provided in the center of the solenoid coil, the magnetic field is concentrated by this magnetic pole, and even a small current can impart a sufficiently large moving force to the permanent magnet powder.

This moving force acts in the direction of attracting the permanent magnet powder into the molding space, and the permanent magnet powder is sequentially filled into the space. Since the process is carried out using targeted suction force, the process can be carried out smoothly in a very short time even if the width of the opening of the molding space of the mold is extremely narrow. However, unlike conventional forced filling using blades or the like, the permanent magnet powder is filled almost uniformly without being broken.

The magnetic pole has a truncated conical shape with the diameters of the upper and lower surfaces at a predetermined ratio and the lower surface corresponds to the lower rod of the mold. Fills smoothly.

〔Example〕

FIG. 1 is an explanatory diagram showing an example of an apparatus suitable for carrying out the method of the present invention. This shows part of a mold for obtaining a cylindrical molded body.

A die 10 having a circular hole in the center, a lower rod 12 arranged with a gap in the center thereof, and a cylindrical die that can freely slide vertically within the cylindrical gap between the die 10 and the lower rod 12. It is equipped with a lower punch 14. The cylindrical void formed by these holders becomes the molding space 18.

The molding space 18 is filled with permanent magnet powder, and a cylindrical upper punch (not shown) is inserted from above and pressurized to perform compression molding. The mold structure of such a press molding machine is basically the same as that of the conventional case.

In the present invention, the solenoid coil 20 is arranged near the opening of the molding space 18 of the mold. This solenoid coil 20 is oriented so that its central axis direction substantially coincides with the depth direction of the molding space 18, and its inner diameter is slightly larger than the outer diameter of the molding space 18.

A magnetic pole 22 made of pure iron is installed on the lower rod 12 along the central axis of the solenoid coil 2o.

This magnetic pole 22 has a lower surface diameter D1 than the lower rod 12.
It has a truncated conical shape that is the same as or slightly smaller than the diameter of (
That is, DI /6≦D) Here, solenoid coil 2
0 and the magnetic pole 22 are non-magnetic connecting members (not shown).
It is connected and integrated so that it can move when feeding powder.

In this embodiment, among the members constituting the mold, die 1
0 and the lower rod 12 are made of magnetic material, and the lower punch 14 (also the upper punch) is made of non-magnetic material.

The filling of permanent magnet powder is carried out as shown in the figure.The solenoid coil 2o and the magnetic pole 22 are installed as described above near the opening of the molding space 18 of the mold, and the permanent magnet powder is filled above the molding space 18. Fill the body 24. Then, an alternating current is supplied to the solenoid coil 2°. The magnetic field applied here is 5
0e or more, and the frequency of the alternating current used is 10 kHz or more. By passing an alternating current through the solenoid coil 2o, lines of magnetic force are generated as shown by broken lines in the figure, and an alternating magnetic field is formed within the permanent magnet powder 24, the molding space 18, and the like. The alternating magnetic field can be concentrated in the molding space 18 by the magnetic poles 22, and the permanent magnet powder 24 can be effectively attracted into the molding space 18 even with a weak current.

The shape of the magnetic lines of force is a rough representation of the path for convenience.

The magnetic flux generated by the solenoid coil 20 is collected by the magnetic pole 22, passes through the lower rod 12, the die 10,
Remove the outside of the solenoid coil 20 and attach the magnetic pole 22 again.
Return to Permanent magnet powder 24 piled up in the upper part of the molding space 18
When an alternating magnetic field is applied to the cylindrical molding space 18, the magnetic flux density in the cylindrical molding space 18 becomes larger than that in the powder heap, and the powder is magnetically attracted to the inside of the cylindrical molding space 18 due to the difference.

The permanent magnet powder 24 remaining on the die 10 also repeats complex vibrations in response to the alternating magnetic field, and even a very narrow gap is completely filled in a short time (within a few seconds).

Therefore, if necessary thereafter, excess permanent magnet powder is removed by a sliding method or the like, and compression molding is performed by lowering the upper punch and applying pressure.

In the present invention, the reason why the magnetic pole 22 is formed into the above-described specific shape is based on the following experimental results. Height H is 50a+m, bottom diameter is 50a+m.

was fixed at 185 mφ, and using seven magnetic poles whose top surface diameter D2 was varied from Ossφ (conical) to 18 mmφ (cylindrical), the amount of permanent magnet powder filled into the cylindrical molding space of the mold was controlled. It was measured. The diameter of the lower rod is also 18-mmφ.
It is. The measurement results are shown in FIG.

From FIG. 2, it can be said that the optimum range of the upper surface diameter D2 is 3×1φ or more. When the magnetic flux generated by a constant current applied to the solenoid coil flows through the magnetic pole, if the cross-sectional area of the magnetic pole is small, all of the magnetic flux does not pass through the magnetic pole and some of it leaks out of the magnetic pole. Therefore, the magnetic flux flowing into the cylindrical molding space of the mold decreases, and the force that attracts the permanent magnet powder into the molding space becomes weaker, resulting in a decrease in the filling amount.

Also, if it exceeds 15+wa+φ, the gap between the solenoid coil and the magnetic pole at the top (near the inlet) becomes narrower, so some permanent magnet powder (particularly powder with poor fluidity) can easily become clogged, and the top of the magnetic pole The permanent magnet powder placed in the center becomes difficult to fall, and the amount of filling is reduced. Therefore, in the case of powder with poor fluidity, Dg ≦5D
It is preferable to set it to I/6.

Next, an experimental example in which permanent magnet powder was filled according to the method of the present invention will be explained. Samarium with an average particle size of 1000μm
A cobalt (SmtCo+t) based alloy was ground to an average particle size of 3 μm using a jet mill. 1.5g of this raw material powder
Weigh and use the device shown in Figure 1 to determine the outer diameter of 1811+1.
It was filled into a cylindrical molding space with a diameter of 16 mm and a height of 15 mm, and molded at a press molding pressure of 3 ton/am''.

The measurement results of the filling time and molding density are shown in Table 1. In Table 1, the conventional method is to place the powder in a slide-type filling jig and make it reciprocate on the die to drop it and fill it into the molding space. This is a case where a combination of natural falling and forced press-in using a push rod are used.

(Margin below) Table 1 Here, R indicates (maximum value - minimum value), and σ.

indicates the variation when n=5.

Table 1 shows that the method of the present invention has a higher compaction density and less variation, especially when looking at the powder filling time.
It can be seen that the method of the present invention achieves good filling in a very short time of less than 1/10 compared to the conventional method.

The above-mentioned remarkable effects of the present invention are mainly due to the magnetic properties of the powder, so in the case of permanent magnet powder, in addition to the samarium cobalt magnet powder, ferrite, alnico, or Similar results can be obtained with any neodymium-iron-boron system. Needless to say, the present invention can be applied not only to powder for sintered magnets but also to powder for bonded magnets (powder kneaded with resin).

[Effects of the Invention] As described above, the present invention provides a solenoid coil that is installed near the opening of the cylindrical molding space of the mold in a direction in which the central axis direction substantially coincides with the depth direction of the molding space, and that the solenoid coil is installed along the central axis of the solenoid coil. This is a filling technology for permanent magnet powder in which truncated cone-shaped magnetic poles with a specific ratio are installed in the magnet, and an alternating current magnetic field is applied. Therefore, a magnetic attraction force acts on the permanent magnet powder, and the permanent magnet powder flows down smoothly.Even if the opening of the molding space is extremely narrow, the magnetic attraction force quickly moves the permanent magnet powder into the molding space. It can be filled into a thin cylindrical permanent magnet very efficiently. The alternating 2IT magnetic field that acts as the force for filling the permanent magnet powder is concentrated in the center by the magnetic pole, and the magnetic flux passing through the cylindrical molding space of the mold increases, so even a weak current can effectively fill the permanent magnet powder into the molding space. Can be filled with suction.

Moreover, in the present invention, the permanent magnet powder is not forced mechanically (it is filled by magnetic attraction force), so the original shape of the powder is maintained, resulting in a uniform density distribution and a reduced molded weight. It becomes constant, and permanent magnets with uniform characteristics can be mass-produced.

Furthermore, since the present invention only requires installing a filling device equipped with a solenoid coil and a magnetic pole at the top of the mold, it can be applied to any type of existing press molding machine, and can be applied to any type of press molding machine, depending on the particle size and condition of the powder. It can be used in various fields of manufacturing permanent magnets, regardless of the type of magnet.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the molding die used in the method of the present invention, the filling solenoid coil, and AC magnetic lines of force, and Fig. 2 is a graph showing the relationship between the shape of the magnetic pole and the amount of filling into the molding space. . DESCRIPTION OF SYMBOLS 10... Dice, 12... Lower rod, 14... Lower punch, 18... Molding space, 20... Solenoid coil, 22... Magnetic pole, 24... Permanent magnet powder. Figure 1 Patent applicant Shigeru Miyoshi, representative of Fuji Electrochemical Co., Ltd.

Claims (4)

[Claims] 1. A solenoid coil is installed in the vicinity of the opening of the cylindrical molding space of the mold, with its central axis direction substantially matching the depth direction of the molding space, and the solenoid coil is placed on the central axis of the solenoid coil so that the upper surface diameter is equal to the lower surface diameter. A truncated conical magnetic pole having a diameter of 1/6 or more and whose lower surface diameter is the same as or slightly smaller than the diameter of the lower rod of the mold forming the cylindrical molding space is provided, and an alternating current is supplied to the upper part of the opening. A method for filling permanent magnet powder, comprising filling the molding space with permanent magnet powder. 2. 2. The filling method according to claim 1, wherein the permanent magnet powder is powder for sintered magnets. 3. 2. The filling method according to claim 1, wherein the permanent magnet powder is powder for bonded magnets kneaded with resin. 4. It has a structure in which a solenoid coil and a magnetic pole located along its central axis are connected and integrated by a non-magnetic connecting member, and the magnetic pole has an upper surface diameter of 1/6 of a lower surface diameter.
A permanent magnet powder filling device characterized in that it is made of a truncated conical soft magnetic material whose lower surface diameter is the same as or slightly smaller than the diameter of the lower rod of the mold forming the cylindrical molding space.