JPS62247512A - Manufacture of multipolar anisotropy cylindrical magnet and device therefor - Google Patents

Abstract

PURPOSE:To form a very strong multipolar magnetostatic field on the surface of a molding cavity by a method wherein permanent magnets magnetized in the circumferential direction of the molding cavity are provided on the circumference of the molding cavity and magnetically soft material yokes are adjacently provided in such a way that the N poles and S poles of the magnets appear alternately on the surface of the molding cavity. CONSTITUTION:Permanent magnets 44a, 44b,... magnetized in the circumferential direction of an annular molding space 10 are disposed on the circumference of the molding space in large numbers. Moreover, these permanent magnets 44 are disposed in such a way that the magnetic poles of the same polarity are adjoined in the mutually adjoining permanent magnets. Moreover, yoke materials 45a, 45b,... consisting of a magnetically soft material are arranged between the permanent magnets. Accordingly, if one of the permanent magnets 44 is taken up as an example, the line of magnetic flux flowed out of this N pole passes through another yoke material 41 via the molding space 10 from the yoke mateiral 45 and is flowed in the S pole. By such a way, the N poles and the S poles can be alternately formed on the surface of the molding space.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method and apparatus for manufacturing a multipolar anisotropic cylindrical magnet by molding a kneaded material mainly composed of ferromagnetic powder in a magnetic field.

[Prior Art] In recent years, there has been a demand for magnet rolls of copying machines and motors having an increasing number of magnetic poles.

In particular, the rotor of a stepping motor is required to have an extremely large number of magnetic poles in order to accurately control the step angle.

Such multipolar anisotropic cylindrical magnets can be produced either by (a) press-molding a wet slurry of ferromagnetic powder, a binder, and a solvent in a magnetic field, and magnetizing it after sintering; It is produced by injecting a kneaded mixture of and into a mold cavity, applying a magnetic field during melting to make it anisotropic, and then magnetizing it. The latter method is attracting increasing attention because it does not require sintering and rarely requires machining after forming.

Various proposals have been made regarding methods of manufacturing cylindrical magnets having anisotropy. For example, JP-A-57-170501
No. 1 is a magnetic powder/resin mixed wire composition that is extruded into a mold consisting of a non-magnetic region and a magnetic region and formed into a roll or pipe shape. It discloses that a magnetic field is applied from the outside using an electromagnet or the like to generate lines of magnetic flux, and the axis of easy magnetization of magnetic particles blended in a molten resin is aligned in the direction of the lines of magnetic flux. In this case, the structure is such that the electromagnet is installed radially outward of the magnetic body (yoke) that comes into contact with the magnetized location of the magnet roll, so as the number of magnetized poles increases, the number of electromagnets also increases, and the structure of the mold changes. becomes extremely complex. Therefore, the number of magnetized poles cannot actually be increased too much.

JP-A-56-69805 discloses a method for manufacturing anisotropic plastic magnets by injecting a mixture of a polymer compound and ferromagnetic powder into a mold cavity in which a plurality of permanent magnets are embedded. There is. However, as the number of magnetic poles increases, the spacing between the permanent magnets for magnetic field alignment becomes narrower, and the alignment force rapidly weakens due to leakage of magnetic flux.

Japanese Patent Publication No. 54-80 discloses a magnetizing device in which an excitation coil is wound around a large number of magnetic yokes, and a permanent magnet is provided between each magnetic yoke to prevent leakage of magnetic flux from the excitation coils. . This structure increased the magnetizing magnetic field inside the cavity, but since an excitation coil is wound around each magnetic yoke, the structure is complicated, and in practice it is not possible to increase the number of yokes too much. .

JP-A-56-114309 discloses a mold in which a pair of electromagnets are provided on both sides of the axis of a cylindrical cavity.A mixture of ferromagnetic powder and synthetic resin is injected into the cavity. Opposite magnetic fluxes of the same polarity are generated by the electromagnets and collide at the center of the cavity to become magnetic fluxes in the radial direction of the cavity. This makes the ferromagnetic powder mixture radially anisotropic.

The compact is then magnetized to have a large number of magnetic poles.

However, in this method, multipolar anisotropy is not performed during molding.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to provide a method and apparatus for manufacturing multipolar anisotropic cylindrical magnets having predetermined magnetic properties using relatively simple equipment.

[Means for Solving the Problems] The method for manufacturing a multipolar anisotropic cylindrical magnet of the present invention involves placing a permanent magnet having magnetic anisotropy in the circumferential direction around a cylindrical cavity of a mold. A large number of magnetic poles of the same polarity are arranged adjacent to each other, and a yoke material made of soft magnetic material is arranged between each permanent magnet, so that N and S poles are alternately arranged on the surface of the cylindrical cavity.
The method is characterized in that a multipolar static magnetic field having poles is formed, the kneaded material is injected into the cylindrical cavity, and anisotropic molding is performed for a predetermined period of time.

Moreover, the manufacturing apparatus of the multipolar anisotropic cylindrical magnet of the present invention comprises (a
) a cylindrical cavity for magnet molding; and (b) a large number of permanent magnets arranged around the cylindrical cavity, the surface of the cylindrical cavity being imparted with magnetic anisotropy in the circumferential direction. It is characterized by having a permanent magnet forming a multipolar static magnetic field having N poles and S poles alternately on the top thereof, and (c) a yoke material made of a soft magnetic material disposed between each of the permanent magnets. It is.

[Effect] In the present invention, around the annular molding space.

A large number of permanent magnets magnetized in the circumferential direction are arranged.

Furthermore, these permanent magnets are arranged such that magnetic poles of the same polarity are adjacent to each other in adjacent permanent magnets. Moreover, a yoke material made of a soft magnetic material is arranged between each permanent magnet. Therefore, when one of the permanent magnets is taken, the magnetic flux lines flowing out from the north pole flow from the yoke material, through the molding space, through the other yoke material, and into the south pole. In this way, north and south poles can be formed alternately on the surface of the molding space.

[Example] Embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an example of an apparatus for manufacturing a multipolar anisotropic cylindrical magnet according to the present invention. An apparatus 1 includes a fixed mold 2, a movable mold 4, and an annular body 6.

A core 8 having an axis coincident with the central axis of the annular body 6 is provided in the movable mold 4 . A cylindrical space formed by the fixed mold 2, the movable mold 4, the annular body 6, and the central core 8 is a magnet molding cavity 10. The outer periphery of the annular body 6 is surrounded by a backup member 7 made of non-magnetic material.

A fixed upper plate 12 and a lower plate 14 are provided on the fixed mold 2, and a nozzle opening 16 is formed in the upper fixed plate 12. The sprue 18 below the nozzle opening 16 is attached to the upper plate 1
2 and the lower plate 14, and is connected to a runner 20 formed on the lower surface of the fixed type fixed lower plate 14.

The runners 20 communicate with vertical runners 22 formed at corresponding positions on the fixed mold 2. Runner 22 is gate 2
4 to the cylindrical cavity 10.

The movable mold 4 is fixed on a movable mold fixing plate 26. Furthermore, the movable fixed plate 26 is fixed to a lower plate 32 via a spacer block 30.

The movable mold 4 has a vertical hole opening into the cylindrical cavity 10, through which a protruding pin 34 is vertically movable.

The ejector pin 34 is fixed to the ejector pin fixing upper plate member 36, and the rod 38 connected to the center of the lower surface of the lower plate member 37 fixed to the upper plate member 36 is inserted into the center hole 4 of the lower plate 32.
0 and is connected to the piston (not shown) of the cylinder.

2 and 3 show the structure of the annular body 6 in detail. The annular body 6 includes permanent magnets 44a, 44b magnetized in the circumferential direction,
44c... and between each permanent magnet are yoke materials 45a, 45 made of soft magnetic material whose tips face toward the cylindrical cavity.
b, 45c, . . . are formed side by side in the circumferential direction.

A non-magnetic sleeve 46 is provided on the inner circumferential surface of the ring 6.

The above permanent magnet group is arranged such that the magnetic poles of adjacent permanent magnets have the same polarity. For example, permanent magnet 44a
, 44b, 44c, the north pole of permanent magnet 44b is adjacent to the north pole of permanent magnet 44a, and permanent magnet 44b is adjacent to the north pole of permanent magnet 44b.
Since the S pole of is adjacent to the S pole of the permanent magnet 44c, and there are yoke materials 45a and 45b on both sides of the permanent magnet 44b,
The magnetic flux lines flow as shown by arrows, and the tip of the yoke material 45a becomes the north pole. By the same principle, the adjacent yoke material 45
The tip of b becomes the S pole. In this way, the yoke material 45
At the tips of a, 45b, 45c..., N, S, N...
・Magnetic poles of opposite polarity appear alternately. Due to the alternating magnetic poles of this permanent magnet.

A multipolar static magnetic field is formed on the surface of the cavity 10.

In a preferred embodiment of the invention, a magnetic field strength of 300,000 or more is required to achieve sufficient orientation. For this reason, the above-mentioned permanent magnet for generating magnetomotive force must have a high residual magnetic flux density in order to form an extremely large number of magnetic poles at small intervals on the magnet surface. For this reason samarium
Rare earth magnets such as cobalt magnets and neodymium/iron/boron magnets are preferred. These rare earth magnets are 8,500
It has a residual magnetic flux density Br of G or more, preferably 10,0 OOG or more (see, for example, JP-A-55-50100 and JP-A-58-142507). From the viewpoint of magnetic field strength, a multipolar static magnetic field of 30 or less poles is preferable.

The shape and dimensions of the permanent magnet yoke that constitutes the magnetic circuit of the mold can be set as appropriate using analytical methods such as the finite element method, depending on the number of poles and required magnetic properties of the anisotropic cylindrical magnet to be manufactured. can.

The apparatus of FIG. 1 is particularly suitable for injection molding of composite magnets. Such injection molding can be performed as follows.

First, mix the magnetic powder and resin at about 50°C to about 350°C.
temperature and about 600 kg/cm” to about 1,000
It is injected from the nozzle port 16 at a pressure of 100 kg/Cm'', and is injected into the cylindrical cavity via the sprue 18 and runners 20 and 22.

After being cooled, the anisotropic composite magnet is moved downward through the movable mold 4, and is moved onto the rod 3 by a piston (not shown) of the cylinder.
By pushing up the protruding pin 34, it can be removed from the core 8 and recovered. Subsequently, the ejecting pin 34 is returned to its original position and the movable mold 4 is raised until it comes into contact with the annular body 6, thereby restoring the cylindrical cavity 10 and carrying out the next molding cycle. The obtained composite magnet molded body is processed to have a predetermined outer diameter as required, and magnetized in the same direction as the anisotropic direction.

In the case of forming the above composite magnet, ferrite powder such as Ba ferrite or Sr ferrite, alnico magnet powder, Fe-CrCo magnet powder, Nd-Fe magnet powder, rare earth cobalt magnet powder, etc. can be used as the magnetic powder. can. As a resin, styrene-butadiene copolymer,
Thermoplastic resins such as ethylene-vinyl acetate copolymers, polyethylene, polyamides, etc. can be used.

The blending ratio of magnetic powder and resin needs to be 60% by weight or more from the viewpoint of magnetic properties, but if it exceeds 90%, molding becomes difficult. In order to improve moldability, a small amount (several percent by weight) of a lubricant such as polyethylene or calcium stearate may be added. Further, in order to improve the wettability between the magnetic powder and the resin, the magnetic powder can be coated with an organic silicon compound, an organic titanate compound, or the like.

In addition to the injection molding of the composite magnet described above, the present invention is also applicable to extrusion molding thereof and wet molding of ferrite and the like.

Wet molding uses powder of magnetic material such as ferrite, approximately 50 to 70
About 0.01% to about 0.2% by weight of a binder such as polyvinyl alcohol or methylcellulose and about 30% to about 50% by weight of a solvent such as water are kneaded to form a slurry, and the slurry is poured into the mold of the present invention. In this case, multipolar anisotropy is performed in the static magnetic field described above.

The present invention will be explained in more detail using the following specific examples.

[Specific example] Ferrite particles (Sr0.6Fe) with an average particle size of 1.2 μm
20. ) and 1.35 kg of nylon 12 (Ube Industries 3
014U) was added, premixed using a Henschel mixer, premixed using a twin screw extruder at a temperature of 235°C, and hot cut to produce pellets.

The pellets were put into an injection molding machine equipped with the mold shown in Figs.
Cavity 10 in a mold heated to 80 °C with a pressure of m2
It was injected and then cooled and solidified. The dimensions inside the cavity were an inner diameter of 35 mm, an outer diameter of 40 mm, and a length of 9.6 mm. The permanent magnet for generating magnetomotive force is a samarium cobalt magnet (H-30 manufactured by Hitachi Metals, Ltd.), and has a B r 10
,800G,a He 8,0000e,IHC9
,0000e. The magnetic field strength on each pole at the surface of the cavity 10 is approximately 3.5000e. Since 30 permanent magnets were used in this example, the multipolar static magnetic field had 15 north poles and 15 south poles alternately on the surface of the cavity 10.

In this way, a 30-pole anisotropic cylindrical composite magnet was obtained. This composite magnet was placed in a magnetizing device having a known coil type structure having 30 magnetic poles, and magnetized with a magnetic field of 8,000 e. When the surface magnetic flux density distribution of the obtained magnet was measured, the waveform shown in FIG. 4 was obtained. The average surface magnetic flux density was 1400G.

On the other hand, in the case of a composite magnet obtained by radial anisotropy and magnetization as disclosed in JP-A-56-114309, the average surface magnetic flux density was only about 1000G.

Although the present invention has been described based on examples, various changes can be made to the present invention without departing from the embodiments. For example, although the cavity 10 is completely cylindrical in the embodiment, it can also be an incomplete cylinder, such as a semi-cylindrical shape, depending on the use of the magnet. Therefore, the term "cylindrical" used in this specification is defined to include not only a complete cylinder but also an incomplete cylinder such as a semi-cylindrical shape. Further, in the embodiment, the multipolar static magnetic field is formed on the outer diameter surface of the cavity, but it can also be formed on the inner diameter surface of the cavity depending on the use of the magnet. Therefore, the term "cavity surface" should be understood to include both the outer diameter surface and the inner diameter surface of the cavity. Permanent magnets and soft magnetic yokes magnetized in the circumferential direction are placed adjacent to each other on the surface of the molding cavity so that north and south poles appear alternately, so an extremely strong multi-pole static magnetic field is applied to the cavity. Can be formed on the surface. In addition, by using such a device, it has become possible to manufacture multi-polar anisotropic cylindrical magnets with as many as 30 poles, which was previously unachievable.6 Furthermore, by forming a magnetic circuit using only permanent magnets and yokes, , the structure of the entire device can be made extremely simple.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an apparatus according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1, and FIG.
FIG. 4 is a partially enlarged view of the figure, and FIG. 4 is a graph showing the surface magnetic flux density distribution of a multipolar anisotropic cylindrical magnet obtained in an example of the present invention. 2... Fixed type 4... Movable type 6... Annular body 8... Core 10... Cavity 44... Permanent magnet No. 1 Figure 36゛ σ4mJσ σ4 σ7 Jt:
2nd 3rd drawing procedure amendment, 1. Indication of the case 1985 Original Patent No. 268785 2. Name of the invention Method and apparatus for manufacturing multipolar anisotropic cylindrical magnet 3. Person making the amendment Relationship to the incident Patent Applicant Address: 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name (508) Hitachi Metals, Ltd. Methods and Apparatus"

Claims (1)

[Claims] 1. In a method for manufacturing a multipolar anisotropic cylindrical magnet by molding a kneaded material mainly composed of ferromagnetic powder in the presence of a magnetic field, A large number of permanent magnets having magnetic anisotropy in the circumferential direction are arranged so that the magnetic poles of the same polarity are adjacent to each other, and yoke materials made of soft magnetic material are arranged between each permanent magnet to alternately cover the surface of the cylindrical cavity. niN
A method characterized in that a multipolar static magnetic field having a pole and a south pole is formed, the kneaded material is injected into the cylindrical cavity, and anisotropic molding is performed for a predetermined period of time. 2. The method according to claim 1, wherein the permanent magnet is a rare earth magnet having a Br of 8,500 G or more. 3. The method according to claim 1 or 2, wherein the kneaded material mainly contains ferromagnetic powder and resin. 4. An apparatus for manufacturing a multipolar anisotropic cylindrical magnet, which includes (a) a cylindrical cavity for forming the magnet, and (b) a large number of permanent magnets arranged around the cylindrical cavity, a permanent magnet that is given magnetic anisotropy in the circumferential direction and forms a multipolar static magnetic field having alternating N and S poles on the surface of the cylindrical cavity; (c) disposed between the permanent magnets; and a yoke material made of a soft magnetic material. 5. The method according to claim 4, wherein the permanent magnet is a rare earth magnet having a Br of 8,500 G or more.