JPS62128511A - Method and apparatus for manufacturing multipolar anisotropic cylindrical magnet - Google Patents

Abstract

PURPOSE:To manufacture a multipolar anisotropic cylindrical magnet by a simple facility by adjacently fitting permanent magnets, circumferential surfaces thereof are multipolar-magnetized, around a molding cavity so that N poles and S poles alternately appear on the surface of the molding cavity, injecting a kneaded material into a cylindrical cavity and molding the kneaded material in an anisotropic manner. CONSTITUTION:Permanent magnets 44 are arranged so that n poles and S poles are oppositely faced alternately to a cylindrical cavity 10. The kneaded material of magnetic powder and a resin is injected from a nozzle opening 16 at a temperature of approximately 250-350 deg.C and at pressure of approximately 600-1,000kg/cm<2>, and injected into the cylindrical cavity through a sprue 18 and runners 20, 22. A composite magnet of special-shapes formed in an anisotropic manner is cooled, a movable mold 4 is shifted downward, and the composite magnet is detached from a core 8 and recovered. The permanent magnet 44 consists of a rare earth magnet such as a samarium-cobalt magnet and the magnet having residual magnetic flux density of 10,000G or more is preferable. Rare earth cobalt magnet powder, etc. are employed as magnetic powder and a thermoplastic resin such as polyamide as the rein. The compounding ratio of magnetic power and the resin must be 60wt% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial 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, magnet rolls for copying machines, rotors for motors, and the like have been required to have 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. . Although this structure increases the magnetizing magnetic field inside the cavity, the structure is complicated because an excitation coil is wound around each magnetic yoke, and in practice it is difficult to increase the number of yokes. Can not.

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 applying multipolar magnetization around one periphery of a cylindrical cavity of a mold to form a ring-shaped permanent magnet. and forming a multipolar static magnetic field having N and S poles alternately on the surface of the cylindrical cavity, and injecting the kneaded material into the cylindrical cavity to perform anisotropic molding for a predetermined period of time. It is characterized by this.

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 ring-shaped permanent magnet placed around the cylindrical cavity, the periphery of which is multipole magnetized, and a magnet formed on the surface of the cylindrical cavity. Ntf! and a permanent magnet that forms a multipolar static magnetic field having alternating S and S poles.

[Function] In the present invention, a ring-shaped permanent magnet whose periphery is subjected to multipolar magnetization is arranged around the annular molding space. Furthermore, the permanent magnets are arranged such that the north pole and the south pole alternately face the molding space. Therefore, when one north pole of a permanent magnet is taken, the magnetic flux lines flowing out from this north pole flow into the south poles on both sides of the permanent magnet. 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. The apparatus 1 includes a fixed type 2, a movable type 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 a 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 a cylindrical cavity 10, through which a projecting 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 is formed of a ring-shaped permanent magnet 44 whose inner circumferential surface is multipole magnetized. A non-magnetic sleeve 46 is provided on the inner peripheral surface of the annular body 6.

The above-mentioned permanent magnet is arranged so that the N and S poles of the permanent magnet alternately face the cylindrical cavity 10. For example, if we look at the N2 pole of a permanent magnet, the N2 pole is made of Si.
, S, are adjacent to the poles, so the magnetic flux lines flow as shown by the arrows, and the tip of N2 becomes the north pole. Based on the same principle, the tips of the 81st and 82nd poles on both sides become S poles. In this way, magnetic poles of opposite polarity alternately appear inside the permanent magnet, such as S, N, S, and so on. A multipolar static magnetic field is formed on the surface of the cavity 10 by the alternating magnetic poles of the permanent magnet.

In a preferred embodiment of the invention, a magnetic field strength of 300,008 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 magnets constituting 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 of the anisotropic cylindrical magnet to be manufactured and the required magnetic properties. 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 600kg/am” to about 1,000k
It is injected from the nozzle port 16 at a pressure of 1.5 g/cm'' and is injected into the cylindrical cavity via the sprue 18 and the runners 20 and 22.

After cooling, the anisotropically formed composite magnet is removed from the core 8 by moving the movable mold 4 downward, pushing up the rod 38 with the piston (not shown) of the cylinder, and raising the protruding pin 34, and is recovered once. can do. 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 performing the first 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, Fa-Cr-Go magnet powder, Nd-Fe magnet powder, rare earth cobalt magnet powder, etc. are used as magnetic powder. be able to. As resins, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyethylene,
Thermoplastic resins such as polyamide 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 methyl cellulose and about 30 to about 50% by weight of a solvent such as water are mixed 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
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 1 in the mold heated to 80℃ with ``++'' pressure
It was injected to 0 and then cooled and solidified. Dimensions inside the cavity are inner diameter 35m, outer diameter 40++, length 9.6m++
It was +. The permanent magnet for generating magnetomotive force is a samarium cobalt magnet (H-30 manufactured by Hitachi Metals, Ltd.), and B
rlO, 800G, a Hc 8,0000 e
, xHc 9,0000e. The magnetic field strength on each pole at the surface of the cavity IO is approximately 3,5000 e
It is. In this example, a 30-pole permanent magnet was used, so the multipole static magnetic field had 15 north poles and 15 south poles alternately on the surface of the cavity IO.

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 in a magnetic field for 80,000 seconds. 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 1200G.

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, the present invention is not limited thereto, and various changes can be made without departing from the spirit of the present invention.For example, the cavity 10 is completely Generally, it is cylindrical, but depending on the purpose of the magnet, an incomplete cylinder such as a semi-cylindrical shape is also possible. 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 is also possible to form it 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.

[Effects of the Invention] As described above, the device of the present invention uses permanent magnets that are magnetized with multiple poles on the circumferential surface around the molding cavity (tee) so that N and S poles appear alternately on the surface of the molding cavity. Since they are placed adjacent to each other, an extremely strong multipole static magnetic field can be formed on the cavity surface.In addition, by using such a device, a multipolar anisotropy of as many as 30 poles, which was previously unachievable, can be achieved. It has become possible to manufacture magnetic cylindrical magnets.Furthermore, by forming a magnetic circuit using only permanent magnets.

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 tei / Figure, 36 64 41) , 31! ,! 4
．． 37,! 2Figure 2

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 ring-shaped permanent magnet with multipolar magnetization is arranged on the circumferential surface to form a multipolar static magnetic field having N and S poles alternately on the surface of the cylindrical cavity. A method characterized by injecting a kneaded material and performing anisotropic molding for a predetermined period of time. 2. In the method according to claim 1. A method characterized in that 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, comprising (a) a cylindrical cavity for molding the magnet, and (b) a ring-shaped permanent magnet arranged around the cylindrical cavity, A device comprising: a permanent magnet whose peripheral surface is subjected to multipolar magnetization to form a multipolar static magnetic field having N poles and S poles alternately on the surface of the cylindrical cavity. 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.