JPH071742B2 - Anisotropic ferrite magnet molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molded body for producing a ferrite sintered magnet having radial anisotropy, and more specifically, it has a cylindrical shape and an inner peripheral surface thereof. The present invention relates to an anisotropic ferrite magnet molding for sintering in which a plurality of shallow notches having an approximately V-shaped cross section extending in the axial direction are dispersed in the circumferential direction.

[Prior Art] In various small motors, a cylindrical ferrite sintered magnet exhibiting anisotropy in the radial direction (radial direction) is often used as a rotor.

Such a cylindrical ferrite magnet is molded by a dry / wet magnetic field molding method, an extrusion molding method, a sheet winding integration method, or the like. In any case, in the prior art, a sintered magnet is manufactured by forming a cylindrical molded body having a perfect circular shape on both the inner peripheral surface and the outer peripheral surface and firing the molded body under a predetermined temperature condition.

[Problems to be Solved by the Invention] However, in the anisotropic ferrite magnet oriented in the radial direction, the shrinkage ratio during firing is different in the radial direction and the circumferential direction, and therefore is different from the isotropic magnet. A complex problem arises. In other words, simply molding into a cylindrical shape and firing, in the firing process, a strong internal stress is generated especially when cooled from a high temperature state to room temperature, which causes microcracks in various directions in the sintered body, which causes unspecified Will be decomposed,
In an extreme case, a phenomenon of breaking apart occurs.
Such a phenomenon is more serious as the orientation is higher.

In addition, even if the sintered body is not decomposed into pieces, if many microcracks are generated or internal strain remains, not only the mechanical strength is greatly lowered but also the magnetic properties are lowered and it becomes impossible to actually use. .

As described above, when the conventional molded body is used, the higher the degree of orientation and the better the magnetic performance, the more the yield is deteriorated.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to prevent microcracks from entering various directions by concentrating internal stress generated at the time of temperature reduction after sintering only at a specific location. An object of the present invention is to provide a molded body which can release an internal stress by dividing at a specific position and manufacture an anisotropic ferrite magnet without defects such as residual internal strain.

[Means for Solving the Problems] The present invention that can achieve the above-mentioned object is that the axis of easy magnetization of the magnet powder inside is oriented in the radial direction and the whole has a cylindrical shape. This is an anisotropic ferrite magnet molding for sintering in which two to three shallow notches each having an approximately V-shaped cross section extending in the axial direction are dispersed on the circumferential surface in the circumferential direction.

This molding may be formed by extrusion molding, compression molding, or a sheet winding integration method.

[Operation] When a cylindrically shaped body oriented in the radial direction is fired, a large difference occurs between the radial shrinkage and the circumferential shrinkage in the baking process, particularly in the process of cooling from a high temperature state to room temperature. Internal stress occurs. This internal stress concentrates in the groove formed in the axial direction of the inner peripheral surface of the molded body. Then, due to the internal stress, the groove is divided and the excessive internal stress is released. Therefore, microcracks are prevented from entering in various directions inside the sintered body, no internal strain remains, and a magnet having high mechanical strength and good magnetic properties can be obtained.

In the present invention, since there are 2-3 stress-concentrated portions, there is no possibility of disassembling into a large number of fragments, and therefore it is extremely easy to combine sintered divided pieces and restore them again into a cylindrical shape. Is.

In the present invention, in particular, the notch is defined to be formed in the axial direction of the inner peripheral surface of the molded body.When the notch is formed on the outer peripheral surface side, the notch does not crack at the notched portion and often breaks at other portions. It happened and it turned out to be meaningless as a result of experiments.

[Example] FIG. 1 is a perspective view showing an example of an anisotropic ferrite magnet molding according to the present invention. The compact 10 has a cylindrical shape in which the axis of easy magnetization of the magnet powder is oriented in the radial direction, and has a structure in which a shallow notch 12 having a substantially V-shaped cross section extending in the axial direction is provided on the inner peripheral surface thereof. In this embodiment, the notches 12 are respectively formed at two places having an angle of about 180 ± 5 degrees with respect to the central axis.

The molded body can be manufactured by various known molding methods. For example, a dry / wet magnetic field molding method, an extrusion molding method, or a sheet winding integration method may be used. In the case of the magnetic field molding method, if a blade-shaped ridge is formed on the rod, the incision can be compression-molded at the same time, and in the case of the extrusion molding method, a blade-shaped projection may be formed on the tip of the rod or the like. .
In the case of the sheet winding integral method, a blade-shaped projection is formed on the end portion of the winding core, and a notch can be formed by the blade-shaped projection when the molded body formed into a cylindrical shape by winding and integrating is pulled out.

When such an anisotropic cylindrical molded body 10 is fired, a large stress is generated inside due to the difference between the radial shrinkage and the circumferential shrinkage, particularly in the process of cooling from a high temperature state to room temperature. However, since the large internal stress concentrates at the location of the cut 12 having a V-shaped cross section, microcracks are prevented from entering other locations, and the cut 12 is divided into two. As a result, the internal stress disappears and no internal strain remains.

The sintered body is shown in FIG. As shown in FIG. 1, when the incision 12 is made at a position symmetrical with respect to 180 degrees or a position close thereto, the fracture surface is very cleanly split at the shortest distance in the process of sintering, that is, in the radial direction. The divided pieces 14a, 14b of the sintered magnet thus obtained are again joined and integrated into the original cylindrical shape with an adhesive or the like.

The shape of the notch 12 formed in the molded body 10 is more effective as the cross section is V-shaped and the width is narrower from the viewpoint of stress concentration. The depth is preferably set to an appropriate value within the range of 0.1 to 1.0 mm depending on the wall thickness of the molded product or the inner / outer diameter ratio. If the depth of cut is extremely shallow, internal stress generated during the cooling process after sintering may not be concentrated in the depth of cut, which may result in a complicated fracture surface.If the depth of cut is too deep, the core will break before sintering. This is because accurate dimensions cannot be obtained.

The number of cuts formed is two to three. Providing four or more is effective in removing internal stress, but cannot be adopted because it is divided into many pieces and complicates the subsequent assembly process.

When making two cuts, as described above,
It is desirable to provide the position of about 0 ± 5 degrees, that is, substantially symmetrically with respect to the central axis. However, depending on the case, it may be provided further asymmetrically with respect to the central axis. However, even if the cuts are arranged asymmetrically, the cracks will be cracked in the same way as in the symmetrical case, so if the cut position is extremely unbalanced such that one side is 90 degrees or less, the cut will not crack, Even if it breaks, the fractured surface is not good and is not preferable.

In addition, in the case where the multi-pole magnetization is performed, the position of the cut is selected so that the division surface is located exactly at the boundary of the magnetic poles.

EFFECTS OF THE INVENTION Since the present invention has a structure in which two or three shallow notches having a substantially V-shaped cross section extending in the axial direction of the inner peripheral surface of the cylindrical shaped body are distributed in the circumferential direction as described above. Since the dividing position is determined, complicated fracture does not occur, and since the internal stress generated in the firing process concentrates on the cut portion, microcracks do not enter in other places, the internal stress is released and internal strain is released. Since it does not remain, a magnet having high mechanical strength and good magnetic properties can be obtained.

Further, even if there is a cut on the inner peripheral surface side, the outer peripheral surface side can be restored to a continuous and clean circumferential surface, so that it is extremely convenient without any trouble especially for equipment such as a rotor that uses the outer peripheral surface.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an anisotropic ferrite magnet molded body according to the present invention, and FIG. 2 is an explanatory view of a divided piece obtained when firing it. 10 …… Molded body, 12 …… Incision, 14a …… Large divided piece, 14b …… Small divided piece, 16 …… Divided surface.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisayuki Sano 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Inventor Akira Asakura 5-36-11 Shinbashi, Minato-ku, Tokyo Fuji Electrochemical Co., Ltd. (56) Reference JP 61-206208 (JP, A) JP 51-118095 (JP, A) Actual development 62-58004 (JP, U) Actual 58-11233 ( JP, U)

Claims (1)

[Claims] 1. A magnet powder has a cylindrical shape in which the easy axis of magnetization is oriented in the radial direction, and a few shallow cuts having an approximately V-shaped cross section extending in the axial direction are dispersed in the inner peripheral surface in the circumferential direction. Anisotropic ferrite magnet compact for sintering, which is provided.