JPH0419684B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a mold for molding a cylindrical ferrite magnet with radial anisotropy used for rotors of various motors, and more specifically, Two or three blade-like protrusions are attached to the rod or mandrel part of the rod or mandrel from which the molded body slides in the axial direction to release the mold, and are distributed in the circumferential direction to form an approximately V-shaped cross section extending in the axial direction on the circumferential surface of the molded body. The present invention relates to a mold for forming an anisotropic ferrite magnet that is capable of forming two to three incisions.

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

Such cylindrical ferrite magnets are manufactured by dry/wet magnetic field molding methods, extrusion molding methods, sheet winding integration methods, and the like. In any case, in the prior art, the rod or mandrel for forming the inner diameter portion of a cylindrical molded body has a perfectly circular cross section, and the resulting molded body also has a perfectly circular inner and outer circumferential surface.

A sintered magnet is manufactured by firing such a cylindrical molded body 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, the firing process
In particular, when cooling from a high temperature state to room temperature, a strong internal stress is generated, which causes microcracks to occur in various directions, unspecified decomposition, and in extreme cases, to break into pieces. . 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 drawbacks of the prior art as described above, and to concentrate the internal stress generated during cooling after sintering in a specific location to prevent microcracks from occurring in other locations. , provides a mold for forming an anisotropic ferrite magnet that is always divided at a certain point to release internal stress and prevent internal strain from remaining, and also to obtain a sintered body that is easy to assemble. It's about doing.

[Means for Solving the Problems] The present invention, which can achieve the above-mentioned objects, is a mold for forming a sintered cylindrical ferrite magnet having anisotropy in the radial direction. This is a modified rod or mandrel that forms the inner diameter of the body. In other words, in the present invention, two or three axially elongated blade-like protrusions are attached to the part of the rod or mandrel from which the cylindrical molded body slides in the axial direction and is released from the mold, and are distributed in the circumferential direction. This is a molding die for a sintered anisotropic ferrite magnet characterized in that the height of the blade-like protrusions is much smaller than the wall thickness of the molded body.

Examples of the molding die used in the present invention include a rod for extrusion molding, a mandrel used in the sheet winding and integration method, and the like.

[Function] A molded body of a cylindrical ferrite magnet having anisotropy in the radial direction is produced by the molding die. This molded body is taken out by sliding along a rod or mandrel, but since two or three blade-like protrusions are attached to it and distributed in the circumferential direction, the axis of the inner circumferential surface of the cylindrical molded body 2~ almost V-shaped cross section in the direction
Three cuts are formed. The internal stress generated during the firing process, especially during the cooling process from a high temperature state to room temperature, is concentrated in this notch, preventing microcracks from forming in other parts. Furthermore, the internal stress causes the film to be divided at the notch, and the excessive internal stress is released and disappears, so that no defects such as internal distortion remain.

Therefore, the obtained sintered magnet does not disintegrate into a large number of pieces, and therefore, it is extremely easy to restore it to a cylindrical shape. Furthermore, these sintered magnets have no internal microcracks and no residual internal strain, so they have high mechanical strength and sufficiently good magnetic properties.

In the present invention, in particular, the blade-like protrusion is attached to the rod or mandrel that forms the inner diameter part of the molded body to form a notch on the inner surface of the molded body. This is because experiments have shown that it often happens that the material does not break at that point but breaks at other parts, which is of little significance.

[Example] FIGS. 1 and 2 show an example of the present invention, and are a sectional view and a front view showing an example in which the invention is applied to an extrusion mold.

The molding die attached to the tip of the extruder consists of a rod 10 located at the center and a die 1 surrounding it.
2, and a gap having an annular cross section therebetween constitutes a flow path 14 for the kneaded material. A kneaded mixture of ferrite powder and binder is extruded by an extruder, and is oriented in the radial direction through the narrow annular passage 14 to be formed into a cylindrical shape.

Here, the feature of the present invention is that, as is clear from FIGS. 1 and 2, there are two or three slender axially extending parts in the part where the extruded molded product slides in the axial direction and is released from the mold. The blade-like protrusions 16 are attached in a distributed manner in the circumferential direction, and the height of the blade-like protrusions 16 is set to be much smaller than the wall thickness of the molded body.

In this embodiment, the blade-like protrusions 16 are attached to the tip of the rod 10 at two locations approximately symmetrically.

When such a blade-like protrusion 16 is attached, two cuts having a substantially V-shaped cross section are formed symmetrically in the axial direction of the inner peripheral surface of the extruded cylindrical molded body.

In the above embodiment, a blade-like protrusion 16 is attached to the tip of the rod 10. If the rod 10 is disposed at a position away from the die 12 at the tip of the rod 10, the extruded molded body is not constrained on the outside, so no complicated force is applied to it, and the blade-like protrusion 1
Since 6 has an elongated shape in the axial direction, the cut formed has a clean straight line shape.

Figures 3A and 3B show another embodiment of the invention, which is an example of a mandrel in a sheet wrapping and integration method.

Hexagonal ferrite powder has a hexagonal plate-like crystal structure, and is oriented so that its easy axis is oriented in the thickness direction of the sheet by kneading it with a binder, forming it into a sheet, and rolling it. By winding such anisotropic sheets around a mandrel and bonding them together, a cylindrical molded body having radial anisotropy can be obtained.

In this embodiment, a blade-shaped protrusion 22 is attached to one end of the mandrel 20, that is, the end from which the molded body 24 is slid in the axial direction (indicated by arrow F) and released from the mold.

By attaching such a blade-like protrusion 22, a cut 26 having a substantially V-shaped cross section is formed in the axial direction of the inner circumferential surface of the cylindrical molded body 24 when the molded body 24 is released from the mold.

In the above embodiment, the blade-like protrusion 22 is attached at a position away from the part where the sheets are rolled up.
This is because if the sheet is wrapped around the blade-like protrusion, the sheet will break and the winding operation will become difficult.

In any case, a cylindrical molded body 24 as shown in FIG. 4 can be obtained using the various molding dies described above. This cylindrical molded body 24 has a cut 26 in the axial direction of its inner circumferential surface depending on the shape and position of the blade-like protrusion to be attached to the mandrel of the mold used.
is formed.

When a molded body with such notches is fired, large stress is applied internally 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 during the cooling process from a high temperature state to room temperature. but,
The large internal stress is concentrated at the notch 26, and no microcracks or the like occur anywhere other than the notch 26. Be sure to divide at the notch 26. Therefore, the obtained sintered body can be easily bonded to its original cylindrical shape using an adhesive or the like, making it suitable for motor rotors and the like.

Although preferred embodiments of the present invention have been described in detail above, it goes without saying that the present invention is not limited to only such a configuration. Although the blade-like protrusions are attached at two locations in this embodiment, they may be attached at three locations. At one location, the division position cannot be determined uniquely, and at four or more locations, there is a risk of complicated cracking, which is disadvantageous for subsequent assembly.

[Effects of the Invention] As described above, the present invention provides a mold for a sintered radial anisotropic ferrite magnet in which two to three blade-like protrusions are attached to the rod or mandrel portion in a manner distributed in the circumferential direction. Therefore, the parts where internal stress is concentrated during the firing process, especially when the temperature is lowered, are defined and the splitting positions are determined, so complicated fractures do not occur, the cylindrical shape is easily restored, and no internal strain remains.

Since the internal stress generated during the firing process is concentrated in the cut portion, microcracks do not occur in other locations, and a magnet with high mechanical strength and good magnetic properties can be obtained. 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 drawings]

Fig. 1 is a sectional view showing one embodiment of an extrusion mold according to the present invention, Fig. 2 is a front view thereof, and Figs. 3 A and B are examples of a mold for the sheet-wrapping and integrated method of the present invention. FIG. 4 is a perspective view showing an example of a cylindrical molded body obtained by the present invention. 10...rod, 12...dice, 16,22
...blade-like projection, 20 ... mandrel, 24 ... cylindrical molded body, 26 ... notch.

Claims (1)

[Claims] 1. In a mold for a sintered cylindrical ferrite magnet having anisotropy in the radial direction, the molded body slides in the axial direction of a rod or mandrel that molds the inner diameter part of the cylindrical molded body and is released from the mold. 2 to 3 blade-like protrusions elongated in the axial direction are attached to the part where the molded body is attached, distributed in the circumferential direction, and the height of the blade-like protrusions is made much smaller than the wall thickness dimension of the molded body. Molding mold for anisotropic ferrite magnet.