JP2608759B2 - Mold for magnetic field molding of plastic magnet - Google Patents

Description

The present invention relates to a magnetic field molding die for molding a plastic magnet.

[Contents and problems of conventional technology]

It is already known that in order to improve the magnetic properties of a ferrite magnet powder or a plastic magnet composed of a rare earth magnet powder and a resin, magnetic orientation is given during molding to give magnetic anisotropy.

Generally, as shown in FIG. 3, an anisotropic plastic magnet includes an axially anisotropic plastic magnet (a) and a radially anisotropic plastic magnet (b). However, especially in the molding of radial anisotropic plastic magnets, it is necessary to create an orientation magnetic field from the inner diameter side to the outer diameter side, and from the outer diameter side to the inner diameter side, so the inner diameter dimension limits the strength of the orientation magnetic field. There is a problem.

FIG. 2 shows an example of a mold for molding a radially anisotropic plastic magnet. In the figure, 1 is a magnetic field generating coil, 6 is a die mounting plate (die plate) of a molding machine, and 7
Is a tie bar. Reference numeral 2 is a yoke portion that forms a passage of an orientation magnetic field composed of a magnetic material having a high saturation magnetic flux density, and 3 is an inner cylinder portion that molds a plastic magnet. Conventionally, a hardened tool steel material or a super hard material is used. Was used. Reference numeral 4 denotes a cylindrical outer cylindrical portion for forming a plastic magnet through which an orientation magnetic field passes, and reference numeral 5 denotes a non-magnetic material, which constitutes a forming die. The magnetic flux generated by the magnetic field generating coil 1 flows along the arrow, and flows radially from the inner diameter side to the outer diameter direction of the plastic magnet formed from the inner cylinder part 3 to the outer cylinder part 3. The amount of magnetic flux flowing from the inner tubular portion 3 toward the outer tubular portion 4 is determined by the saturation magnetic flux density of the magnetic material forming the inner tubular portion 3 and the cross-sectional area.

Therefore, the radial orientation magnetic field applied to the plastic magnet is small when the inner diameter is smaller than the outer diameter and height of the magnet to be molded, or when a material with a low magnetic saturation value is used for the inner cylinder. Become. When the orientation magnetic field is small, the magnetic properties of the obtained plastic magnet are low. Generally, in the case of a rare-earth plastic magnet, a magnetizing magnetic field of at least 10 kilogauss is required.However, when a sufficient magnetic field cannot be applied to the orientation magnetic field, only a plastic magnet having low characteristics can be obtained. there were.

In order to increase the orientation magnetic field, a material having a high saturation magnetic flux density is required for the inner cylindrical portion of the mold, but a material having a high saturation magnetic flux density generally has a low degree of hardening and is easily worn.

That is, the normal alloy tool steel has a high saturation magnetic flux density of 4πI of 16,000 gauss before the quenching treatment, but has a low hardness. 5 to 6 times, but the saturation magnetic flux density 4π
I was 13,000 gauss, the magnetic resistance at high magnetic flux density was large, and a high orientation magnetic field could not be obtained. or,
Pure iron has a high saturation magnetic flux density, but the surface hardness of the material is low, so it was not normally used as a mold material.

[Object of the invention]

The present invention has been made to eliminate these drawbacks, to increase the radial orientation magnetic field of the plastic magnet molding portion, and to improve the workability of molding,
An object of the present invention is to provide a magnetic field molding die having high wear resistance on the surface of the inner cylindrical portion and high saturation magnetic flux density.

[Configuration of the invention]

In the present invention, the inner cylindrical portion of the mold has a double structure, a soft magnetic material having a high saturation magnetic flux density is used inside the inner cylindrical portion, and the inner cylindrical portion has a high outer peripheral portion requiring wear resistance. By encapsulating a material having hardness, the mold has a high saturation magnetic flux density and high wear resistance.

That is, the inner cylindrical portion of the mold is constituted by a central portion made of pure iron or a material that is not subjected to hardening treatment of tool steel, and an outer peripheral portion made of a hardened material such as a hardened material of tool steel or a super hard material. In general, the outer wall thickness is preferably 1 to 3 mm, but as described above, the amount of magnetic flux is proportional to the product of the saturation magnetic flux density and the cross-sectional area of the magnetic material, so a constant orientation magnetic field is obtained. The thickness of the outer peripheral portion can be determined from the calculation with the ratio to the soft magnetic material to determine the limit thickness. But 1m
If it is less than m, the outer strength when shrinking the outer periphery can not be maintained,
The surface may be damaged during shrink fitting.

That is, the present invention is as follows: 1) In a magnetic field molding die of a plastic magnet for molding a cylindrical plastic magnet having radial magnetic anisotropy, the outer circumference of the inner cylindrical portion forming the inner diameter portion of the plastic magnet is concentrically formed. Using a magnetic material with high hardness,
A mold for forming a magnetic field of a plastic magnet, wherein a magnetic material having a high saturation magnetic flux density is formed in a central portion to form a magnetically double structure.

2) A carbide tool material having a thickness of at least 2 mm is used on the outer circumference of the inner cylinder portion, and a magnetic material having a high saturation magnetic flux density of iron alloy or iron-cobalt alloy is used for the central portion. A magnetic field molding die for a plastic magnet according to claim 1.

3) The mold for forming a magnetic field of a plastic magnet according to claim 1, wherein a hard layer having a thickness of at least 1 mm is formed on the outer periphery of the inner cylindrical portion by quenching with an iron alloy tool steel. .

[Explanation by Examples]

FIG. 2 shows a cross-sectional structure of a mold for molding a radial anisotropic plastic magnet. In the figure, reference numeral 11 denotes a plastic magnet, which can be molded at a time on a surface perpendicular to the plane of the drawing. is there. 1 is a coil for magnetic field generation, which creates a magnetic field of about 15 kilogauss, but the magnetic flux is 7 tie bars made of ferromagnetic material, a mold mounting plate 6 for mounting the mold to the injection molding machine, and a yoke of the mold Part 2, inner cylinder part 3,
From the inner cylinder part, the plastic magnet molded body passes through the yoke of the outer cylinder part from the inner diameter to the outer diameter direction, and the yoke part 2, the mold mounting plate 6,
One magnetic circuit is formed through the tie bar 7.

When molding a plastic magnet, a heated and viscous plastic magnet is injected into the mold from the spool 8 on the left side, and the magnetic field applied from the magnetic field generating coil 1 passes through the above-described path and the plastic in the mold is formed. A magnetic field is applied to the magnet for molding. When the molding is completed, the mold is divided into left and right on the EE side, and the ejector plate 9
And the plastic magnet 11 is extruded from the mold by a rod provided with one to four plastic magnets per plastic magnet, thereby completing the molding.

In the molding die for a plastic magnet shown in FIG. 2, the inner cylindrical portion connected to the inner diameter of the plastic magnet is a mold for molding the plastic magnet, and has a role of a yoke for forming a magnetic path. As shown in the figure, since the periphery is made of a non-magnetic material, all magnetic fluxes passing through the mold mounting plate pass through the inner cylindrical portion and give an orientation magnetic field to the plastic magnet.

FIG. 1 shows the structure of the present invention of the inner cylinder portion of the plastic magnet. The inner cylinder portion of the mold for molding the ring-shaped rare earth magnet having an outer diameter of 30 mm, an inner diameter of 25 mm and a height of 10 mm is SKD-11.
The non-quenched material of SKD-11, the material of which the entire inner cylinder of SKD-11 has been quenched, and the central part is
Non-quenched material of D-11, SKD-11 with a peripheral thickness of 2.0 mm
When the double structure is made of quenched material, the outer circumference 22 is thick
This is an example when it is wrapped with 2mm normal tungsten carbide carbide material and the inside is made of pure iron.

Table 1 shows the orientation magnetic field of the plastic magnet molded portion obtained by the above four types of molds, the magnetic specialty of the obtained plastic magnet, and the surface hardness of the mold cylinder.

The plastic magnets shown in Table 1 were prepared by kneading 2-17 type samarium balt magnet powder with nylon 12 at a molding temperature of 270 ° C. to 290 ° C. and a molding pressure of 1 ton / cm ² .

In general, magnet properties are evaluated by the value of BHmax,
Since the residual magnetic flux density can be more accurately evaluated for the degree of the characteristics of the magnet orientation, the residual magnetic flux density was evaluated.

In the examples shown in Table 1, the cemented carbide used for the outer circumference of the inner cylindrical portion 3 of Example 4 requires a minimum thickness of about 2 mm in terms of strength. Mold material SKD-11
The surface hardness of the inner cylinder using the surface hardening method
The thickness with HRC value of 60 is possible up to about 1 mm.

Further, it is preferable to use an iron alloy having a high saturation magnetic flux density or an iron cobalt alloy in the central portion of Example 4,
In particular, when molding a plastic magnet having a small inner diameter, a cobalt-iron alloy having a cobalt content of 20 to 60% is effective.

〔The invention's effect〕

Mold a plastic magnet with a magnetic field oriented in the radial direction.Inject a thin cemented carbide material into the outer circumference of the inner cylinder of the mold to form pure iron inside, or to heat only the surface layer of ordinary hardened steel. By putting it in, it is almost 20% compared to the case of molding using the mold of the inner cylinder part by the conventional method.
The magnetic properties of were improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the structure of an inner cylindrical portion of a plastic magnet molding die according to the present invention. FIG. 2 is a cross-sectional view showing an embodiment of a mold for molding a radial direction anisotropic plastic magnet. FIG. 3 is a perspective view showing a magnetization direction of the anisotropic ring-shaped plastic magnet. (A) is an axially anisotropic plastic magnet, and (b) is a radially anisotropic plastic magnet. A: Magnetic material (yoke iron part). B: Non-magnetic material (non-magnetic stainless steel). C: Plastic magnet part. 1 ... Coil for magnetic field generation. 2 ... Yoke Department. 3, 3 ...... within the cylindrical portion. 4 ... Outer cylinder part. 5 ... non-magnetic part. 6 ... Mold mounting plate. 7 ... Tie bar. 8 ... Spool. 9 ... Ejector plate. 10 …… Rod. 11 …… Plastic magnet. 21 ... High saturation magnetic flux density material. 22 Carbide or hardened material. Arrow: Direction of magnetic flux.

Claims (3)

(57) [Claims] In a metal mold for molding a magnetic field of a plastic magnet for molding a cylindrical plastic magnet having radial magnetic anisotropy, the outer circumference of an inner cylinder portion for molding the inner diameter portion of the plastic magnet is concentrically formed with a hardness equal to or smaller than the hardness. A magnetic field forming mold for a plastic magnet, wherein a high magnetic material is used, and a magnetic material having a high saturation magnetic flux density is used in a central portion to form a magnetically double structure. 2. A cemented carbide tool material having a thickness of at least 2 mm is used for the outer circumference of the inner cylindrical portion, and a magnetic material having a high saturation magnetic flux density of an iron alloy or an iron-cobalt alloy is used for the central portion. The mold for forming a magnetic field of a plastic magnet according to claim 1, characterized in that: 3. A magnetic field forming metal for a plastic magnet according to claim 1, wherein a hard layer having a thickness of at least 1 mm is formed on the outer periphery of the inner cylindrical portion by quenching treatment with an iron alloy tool steel. Type.