JPH0449244B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a cylindrical sintered ferrite magnet having radial anisotropy, which is used for rotors of various motors, etc. In the axial direction of the inner circumferential surface of the molded body, two incisions are formed asymmetrically with respect to the central axis, each having an approximately V-shaped cross section and much shallower than the thickness of the molded body. The present invention relates to a method of manufacturing an anisotropic ferrite magnet, in which two large and small pieces, which are divided and sintered, are combined and integrated into a cylindrical shape.

[Prior Art] In various small motors, cylindrical sintered ferrite magnets exhibiting anisotropy in the radial direction are often used as rotors.

Such an anisotropic cylindrical ferrite magnet is
It is molded by dry/wet magnetic field molding, extrusion molding, or sheet wrapping and integration methods. In any case, in the prior art, a sintered magnet is manufactured by creating a molded body having a completely circular inner and outer peripheral surface and firing it under predetermined temperature conditions.

[Problems to be solved by the invention] However, in anisotropic ferrite magnets oriented in the radial direction, the shrinkage rate during sintering is different in the radial direction and the circumferential direction, and therefore, unlike isotropic magnets, the shrinkage rate is different in the radial direction and the circumferential direction. A complex problem arises. In other words, if the sintered body is simply formed into a cylindrical shape and fired, a strong internal stress will occur during the firing process, especially when cooling from a high temperature state to room temperature. Decomposition occurs, and in extreme cases, the phenomenon of breaking into pieces occurs. Such a phenomenon is more severe as the orientation is higher.

Furthermore, even if the sintered body does not decompose into pieces, if a large number of microcracks occur, not only the mechanical strength will be significantly lowered but also the magnetic properties will be lowered, making the sintered body unusable.

As described above, the prior art had the disadvantage that the higher the degree of orientation and the better the magnetic performance, the worse the yield.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to concentrate the internal stress generated when the temperature cools down after sintering only in a specific part that is asymmetrical with respect to the central axis, and to reduce the To provide a method for manufacturing an anisotropic ferrite magnet that prevents the occurrence of cracks, releases internal stress by dividing at the locations, and facilitates alignment when recombining and integrating. It is in.

[Means for Solving the Problems] The present invention, which can achieve the above-mentioned objects, has a structure in which the inner circumferential surface of a cylindrical ferrite molded body oriented in the radial direction is aligned with respect to the central axis in the axial direction.
Cuts with an approximately V-shaped cross section and much shallower than the thickness of the molded body are formed at two locations with an angle of 175 to 90 degrees, and the internal stress generated in the subsequent firing process divides the molded body into two at the positions of the cuts. , is a method of manufacturing an anisotropic ferrite magnet in which two sintered pieces, large and small, are joined together again into a cylindrical shape.

More preferably, in the cylindrical ferrite molded body, the angle between the two cuts with respect to the central axis is about 135 degrees.

[Function] When a cylindrical molded product oriented in the radial direction is fired, a large internal shrinkage occurs due to the difference between the radial shrinkage rate and the circumferential shrinkage rate during the firing process, especially during the cooling process from a high temperature state to room temperature. Stress occurs. This internal stress is concentrated in the cut having the V-shaped cross section, thereby preventing microcracks from forming in other parts. Then, it is divided by two cut portions due to internal stress, and excessive internal stress is released. Therefore, no internal strain remains in the sintered body, and a magnet with high mechanical strength and good magnetic properties can be obtained.

In the present invention, the two notches are located asymmetrically with respect to the central axis, and the angle is set in the range of 175 to 90 degrees, so that they are accurately divided into two parts during the firing process, and then combined. This facilitates accurate positioning.

The reason for forming cuts on the inner surface of the molded body is that it has been found through experiments that it is not very meaningful because the outer surface often does not crack at the cut portion, but breaks elsewhere.

[Example] Figures 1 and 2 show an example of the present invention, and are an example of molding by a sheet wrapping integral molding method.

Hexagonal ferrite powder such as barium ferrite has a hexagonal plate-like crystal structure, and is oriented so that the easy axis is oriented in the thickness direction of the sheet by kneading it with a binder and rolling it into a sheet. When such an oriented sheet is wound and integrated around a mandrel 10, a cylindrical molded body 12 having radial anisotropy is obtained.

In the present invention, at one end of the mandrel 10, that is, at the end where the cylindrical molded body 12 is slid in the axial direction (direction indicated by arrow F) and released from the mold, there are two Mandrel 1 with two axially elongated blade-like protrusions 14 attached at locations
Use 0.

By attaching the blade-shaped protrusions 14 at two locations in this way, the released cylindrical molded body 12 has two cross sections V in the axial direction of the inner circumferential surface, as shown in FIG.
A shallow cut 16 in the mold will be formed.

The reason why the blade-shaped protrusion 14 is provided at a position away from the part where the sheets are rolled up in the above embodiment is because if the sheet is wrapped over the blade-shaped protrusion, the sheet will break and the winding operation will be difficult. be.

When such an anisotropic cylindrical molded body 12 is fired, a large stress is generated inside due to the difference between the shrinkage rate in the radial direction and the shrinkage rate in the circumferential direction during the firing process, especially in the process of cooling down from a high temperature state to room temperature. Occur. However, since the large internal stress is concentrated at the notch 16, microcracks do not occur in other locations, and the chip is always divided into two at the notch 16. This eliminates internal stress and no internal strain remains.

In the thus obtained sintered body, as shown in FIG. 4, the large divided pieces 18a have a fan shape of 185 to 270 degrees, and the small divided pieces 18b have a fan shape of 175 to 90 degrees. Because they are not 180 degrees symmetrical,
When superimposed in the direction of arrow A, the facing surfaces 20 are brought into close contact with each other, and accurate positioning can be easily performed without being easily displaced in a direction perpendicular to the facing surfaces 20. The divided pieces 18a and 18b of such a sintered magnet are combined and integrated again into the original cylindrical shape using an adhesive or the like.

In the present invention, the large divided piece 18a is 185 to 270
The small divided piece 18b has an angle of 175 to 90 degrees.
The large split piece 1 was made to have an angle of 1 degree.
This is because if the angle of 8a becomes larger than that, the deformation after the division will be large in the firing process, making adhesion difficult, and cracks will easily enter the middle part, resulting in the division into three parts. On the other hand, if the smaller divided pieces 18b have a larger angle and both are close to 180 degrees, a relative shift in the lateral direction in FIG. 4 is likely to occur, making alignment difficult.
Therefore, according to the results of various prototype experiments, one
It can be said that it is preferable to divide the pieces by making cuts at positions that form an angle of about 135 degrees.

Although a preferred embodiment of the present invention has been described in detail above, it goes without saying that the present invention is not limited to only such a configuration. In the above embodiment, the sheet wrapping and integration method is adopted as the molding method, but the molding can also be performed by extrusion molding, press molding, etc. In that case, the mold part for molding the inner diameter part is What is necessary is just to provide a blade-like protrusion and form a cut of a predetermined shape at a predetermined position.

In the case of applications where multi-pole magnetization is performed, the positions (angles) of the two cuts are selected so that the dividing plane is located exactly at the boundary of the magnetic poles.

[Effects of the Invention] As described above, the present invention asymmetrically forms two incisions with a substantially V-shaped cross section and much shallower than the thickness of the molded body on the inner peripheral surface of the cylindrical molded body, and performs the firing process,
In particular, it was configured to take advantage of the internal stress that occurs when the temperature drops to divide it into two parts and combine them.
Because the dividing position is determined, complicated destruction does not occur.
Moreover, since the generated internal stress is concentrated in the cut portion, no microcracks are generated in other locations and no internal strain remains, resulting in a magnet with high mechanical strength and good magnetic properties. In particular, since it is asymmetrically divided into two parts, it is possible to easily perform accurate positioning when combining and integrating the parts.

Furthermore, even if there is a notch on the inner circumferential side, the outer circumferential side can be restored to a continuous and clean circumferential surface, so this is extremely convenient, especially for equipment that uses the outer circumferential surface, such as a rotor, without any problems.

[Brief explanation of the drawing]

Fig. 1 is a side view when forming into a cylindrical shape by the sheet winding and integration method in the present invention, Fig. 2 is a front view thereof, Fig. 3 is a perspective view of the cylindrical molded product obtained by this method, and Fig. 4 FIG. 2 is an explanatory diagram showing a divided state in the firing process. 10... Mandrel, 12... Cylindrical molded body, 14
...Blade-shaped projection, 16...Notch, 18a...Large divided piece, 18b...Small divided piece.

Claims (1)

[Claims] 1 The inner peripheral surface of a cylindrical ferrite molded body oriented in the radial direction, mutually aligned with respect to the central axis in the axial direction.
Cuts with an approximately V-shaped cross section and much shallower than the thickness of the molded body are formed at two locations with an angle of 175 to 90 degrees, and the internal stress generated in the subsequent firing process divides the molded body into two at the positions of the cuts. A method for manufacturing an anisotropic ferrite magnet, which comprises combining two sintered pieces, large and small, into a cylindrical shape.