JPH07201558A - Dry-molded ferrite magnet, its manufacture, and dry-molding device - Google Patents

Abstract

PURPOSE:To prevent a ferrite magnet from being disturbed in orientation at its both ends by a method wherein an angle which a straight line connected between two optional points located on a Bd distribution curve makes with an X axis is specified, and a relation between the maximum and the minimum of Bd in an evaluation region and an area surrounded by a Bd distribution curve and an X axis are specified. CONSTITUTION:The length of a measurement region is indicated on an X-axis, Bd is indicated on a Y-axis, and a pattern of Bd distribution is plotted so as to draw a Bd distribution curve graph. The maximum value Bdm of Bd on a Y-axis on its inner peripheral surface is set to 60% of a length AB of a measurement region on an X axis. Provided that a center part of the measurement region that amounts to 60% of it is defined as an evaluation region, an angle of theta which a straight line connected between two optional points located on a Bd distribution curve makes with an X axis is set smaller than 45 deg.. A relation between the maximum and minimum value, alpha and beta, of Bd in the evaluation region of a Bd distribution curve graph, an area Bdi surrounded by the inner peripheral face of a Bd distribution curve and an X axis and an area Bdo surrounded with the outer peripheral face of a Bd distribution curve and an X axis are so as to satisfy formulas, I and II.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc-shaped ferrite magnet manufactured by a dry molding method and having radial anisotropy, a manufacturing method thereof, and a molding apparatus used in the dry molding method.

[0002]

2. Description of the Related Art Motors used for home appliances and electric components of automobiles are required to have high performance, small size and light weight. Such a motor is a DC motor, and an anisotropic arc-shaped ferrite magnet formed by dry molding or an anisotropic ring magnet formed by dry molding is used as the magnet. These motor magnets are anisotropy so that the easy axis is in the radial direction. These magnets are required to have a strong surface magnetic flux density on the inner peripheral surface side and have a uniform surface magnetic flux density on the inner peripheral surface side in the circumferential direction.
If the fluctuation of the surface magnetic flux density is large in the circumferential direction of the inner peripheral surface, cogging will occur and good motor characteristics cannot be obtained.

Anisotropic arc-shaped ferrite magnets are manufactured using dry molding or wet molding. Wet molding has good orientation, but increases manufacturing costs. On the other hand, in dry molding, the orientation tends to be disturbed at both ends of the arcuate magnet, and it is difficult to obtain good motor characteristics.

Japanese Examined Patent Publication No. 12726/1990 discloses an apparatus for compression molding with an upper punch having a concave curved surface and a lower punch having a convex curved surface, and a non-magnetic material having an arcuate cross section on the molding space side surface of the upper punch. It is described that the body is fitted and provided, and the thickness of the non-magnetic body portion is made eccentric between the center point of the outer circumferential surface arc and the center point of the inner circumferential surface arc of the non-magnetic material to thicken the central portion. According to the publication, the magnetic characteristics of the inner peripheral surface of the magnet can be significantly improved by using this molding device. This molding apparatus is for wet molding. Further, Japanese Patent Publication No. 2-13452 describes a molding device provided with a non-magnetic material having a bow-shaped cross section, but this molding device is also for wet molding.

[0005]

SUMMARY OF THE INVENTION The present invention has been made under the circumstances as described above, and when an arc-shaped ferrite magnet having radial anisotropy is manufactured by dry molding,
The purpose is to prevent orientation disorder at both ends of the magnet.

[0006]

The above objects are achieved by the present invention described in (1) to (6) below. (1) A bow-shaped dry-molded ferrite magnet having an arc-shaped cross section and having anisotropy in its radial direction, in which the horizontal axis represents the measurement region length (circumferential length of the peripheral surface) and the vertical axis represents Bd ( In the Bd distribution graph of (surface magnetic flux density), the maximum value of Bd on the vertical axis is 60% of the measurement area length (circumferential length of the inner peripheral surface) on the horizontal axis.
When the Bd distribution curve of the inner peripheral surface is plotted so that 60% of the central portion of the measurement area is used as the evaluation area, a straight line passing through any two points on the Bd distribution curve and the horizontal axis in the evaluation area. Is less than or equal to 45 °, and the relationship between the maximum value α of Bd and the minimum value β of Bd is (α−β) /α≦0.2 in the evaluation region, and the Bd distribution graph In B, the area enclosed by the Bd distribution curve on the inner peripheral surface and the horizontal axis is defined as Bdi, and Bd on the outer peripheral surface is
When the area surrounded by the distribution curve and the horizontal axis is Bdo, Bdi / Bdo = 1.4 to 1.9. (2) The dry-molded ferrite magnet according to (1) above, wherein the angle θ is 42 ° or less, (α−β) /α≦0.18, and Bdi / Bdo = 1.5 to 1.9. (3) A molding device for forming a bow-shaped body by filling raw material powder of a ferrite magnet into a molding space having an arcuate cross section and performing dry molding in a magnetic field. An upper mold and a lower mold made of a magnetic material, a mold made of a non-magnetic material, and two orientation ferromagnetic materials, so that the convex surface of the molding space is on the lower side, The molding space is formed by an upper mold, a lower mold, and a mold, and has magnetic field applying means for applying a magnetic field in the radial direction of the molding space, and two orientation ferromagnetic bodies are provided in the molding space. A dry molding apparatus, which is provided on both sides in the circumferential direction of the mold through a mold, and the upper end of the lower mold at the start of pressurization and the upper end of each of the orientation ferromagnetic bodies are substantially aligned with each other. (4) The lower mold has a lower non-magnetic body facing the molding space,
The dry molding apparatus according to the above (3), which is provided on the upper side of the lower punch made of a ferromagnetic material. (5) The upper mold has an upper non-magnetic body facing the molding space,
The dry molding apparatus according to (4) above, which is provided below the upper punch made of a ferromagnetic material. (6) A method for manufacturing a dry-molded ferrite magnet, comprising manufacturing the dry-molded ferrite magnet according to (1) or (2) using the dry-molding apparatus according to any one of (3) to (5).

[0007]

FUNCTION AND EFFECT According to the present invention, by using the dry molding apparatus provided with the above-mentioned ferromagnetic material for orientation, a molded article in which the anisotropic directions are aligned in the radial direction can be obtained. For this reason,
As can be seen from the surface magnetic flux density distribution curve, an arc-shaped ferrite magnet having a large surface magnetic flux density on the inner peripheral surface side and a uniform distribution can be obtained. Therefore, the motor using the magnet of the present invention is powerful and has a small cogging torque. Further, conventionally, cracks frequently occurred near both ends of the inner peripheral surface during sintering due to the disorder of the orientation at both ends of the magnet, but in the present invention, the disorder of the orientation at both ends of the magnet is significantly reduced. Therefore, such cracks are drastically reduced.

By the way, in Japanese Patent Publication No. 3-32892, there is a difference in that the arcuate cross-section has anisotropy in the radial direction of the arc surface, and the arc inner peripheral surface is a ferromagnetic surface and the outer peripheral surface is a weak magnetic surface. An isotropic ferrite magnet is described. FIG. 1 (A) of the publication discloses a surface magnetic flux distribution diagram of the inner peripheral surface and the outer peripheral surface measured in the circumferential direction. However, when the same measurement as the present invention is performed on this surface magnetic flux distribution diagram, the angle θ
Is about 58 °, (α-β) / α is about 0.16, Bdi / B
The do is about 1.73, and the angle θ is out of the range of the present invention. Moreover, only the description of wet molding is found in the publication, and there is no description of dry molding.

Further, Japanese Utility Model Laid-Open No. 57-10729 discloses a magnetic circuit for forming an anisotropic ferrite magnet having an arc-shaped cross section. In this magnetic circuit for molding, a ferromagnetic material is provided in a part of a die (form), but the positional relationship between the ferromagnetic material and the lower punch is different from that of the dry molding apparatus of the present invention. Actually, when the same measurement as in the present invention is performed on the surface magnetic flux distribution diagram shown in FIG. 1 (b) of the publication, the angle θ is about 47 °, (α−β) / α is about 0.22, and Bdi /
Bdo is about 1.48 and the angle θ and (α-β) /
α is outside the range of the present invention.

That is, a dry-molded ferrite magnet satisfying all of the angles θ, (α-β) / α and Bdi / Bdo has not been heretofore known.

[0011]

[Specific Configuration] The specific configuration of the present invention will be described below.

The magnet of the present invention is an arc-shaped dry-molded ferrite magnet having an arc-shaped cross section and having anisotropy in its radial direction, and is a so-called anisotropic segment magnet. The magnet of the present invention is manufactured using a dry molding method.

The magnet of the present invention is characterized by the Bd (surface magnetic flux density) distribution measured in the circumferential direction of the inner peripheral surface, and the Bd distribution of the inner peripheral surface and the circumferential direction of the outer peripheral surface. It also has a characteristic in relation to the Bd distribution. The circumferential Bd distributions of the outer peripheral surface and the inner peripheral surface are measured by the procedure shown in FIGS. 2 and 3. First, the magnet incorporated in the non-magnetic case is fully magnetized on the inner surface using the inner surface magnetizing yoke shown in FIG. When measuring Bd, a Hall element is arranged near the peripheral surface of the magnetized magnet. At this time, the Hall element is positioned at the center of the circumferential surface in the height direction (vertical direction in FIG. 3) and is brought into contact with the circumferential surface or as close as possible. Then, by rotating the magnet in the circumferential direction,
The Bd distribution can be measured from one end A to the other end B in the circumferential direction of the circumferential surface. The magnet is rotated so that the distance between the Hall element and the peripheral surface does not change.

The Bd distribution thus measured is plotted on a Bd distribution graph in which the horizontal axis is the measurement region length (circumferential length of the peripheral surface) and the vertical axis is Bd.
Use a distribution curve graph. In FIG. 1, the maximum value Bdm of Bd on the inner circumferential surface on the vertical axis is 60% of the measurement area length AB on the horizontal axis (the AB distance measured along the inner circumferential surface in FIG. 3). When the central portion of the measurement area is 60%, the angle θ formed by the straight line passing through any two points on the Bd distribution curve and the horizontal axis in the evaluation area (the maximum value is within the area) The maximum value of the tangent slope of the Bd distribution curve is 45 ° or less, preferably 42 ° or less, and more preferably 35 ° or less. If θ is too large, the cogging torque will increase when the magnet is applied to the motor.

In the present invention, the relation between the maximum value α of Bd and the minimum value β of Bd in the evaluation area of the Bd distribution graph of FIG. 1 is (α−β) /α≦0.2, preferably ( α-β) /α≦0.18, more preferably (α-β) /α≦0.15. If (α-β) / α is too large, the torque fluctuation will be large when the magnet is applied to the motor.

In the present invention, in the Bd distribution graph, the area surrounded by the Bd distribution curve on the inner peripheral surface and the horizontal axis is defined as Bdi,
When the area enclosed by the Bd distribution curve on the outer peripheral surface and the horizontal axis is Bdo, Bdi / Bdo = 1.4 to 1.9, preferably Bdi / Bdo = 1.5 to 1.9, and more preferably Bdi / Bdo = 1.7 to 1.9. A magnet having too small Bdi / Bdo has insufficient magnetic properties on the inner peripheral surface side. On the other hand, Bdi / B exceeding 1.9
In order to obtain do, the difference in density between the inner peripheral surface and the outer peripheral surface of the molded body must be significantly increased. For this reason, cracks frequently occur during firing, which may make molding impossible.

In order to manufacture the above-mentioned magnet having a characteristic of Bd distribution by the dry molding method, it is preferable to use the dry molding apparatus of the present invention described below.

The forming apparatus of the present invention is for forming an arc-formed body by filling a raw material powder of a ferrite magnet into a forming space having an arcuate section and performing dry forming in a magnetic field. The molding apparatus of the present invention has an upper mold and a lower mold each of which at least a part is made of a ferromagnetic material, a mold made of a nonmagnetic material, and two orienting ferromagnetic materials. A molding space is formed by the upper mold, the lower mold, and the mold, and the convex surface of the molding space exists on the lower side.

FIG. 4 shows a preferred configuration example of the dry molding apparatus of the present invention. The dry molding apparatus shown in FIG. 4A has an upper punch 1, a lower punch 2, a mold 3, an upper non-magnetic body 4, a lower non-magnetic body 5 and two orienting ferromagnetic bodies 61, 62. Further, it has a coil 8 for applying a magnetic field in the radial direction of the molding space 7. In this molding machine, the upper punch 1
And the upper non-magnetic body 4 compose the upper die, and the lower punch 2 and the lower non-magnetic body 5 compose the lower die. The molding space 7 is surrounded by the upper non-magnetic body 4, the lower non-magnetic body 5 and the mold 3 such that the convex surface thereof faces downward. The orientation ferromagnetic bodies 61 and 62 are provided on both sides of the molding space 7 in the circumferential direction, with the mold 3 interposed therebetween. Note that FIG.
Is a sectional view showing an arcuate section of the molding space 7,
FIG. 4B is a top view of the molding apparatus when the upper punch 1 is removed.

In such a molding apparatus, molding is performed as follows. First, the raw material powder is filled in the mold while being lifted from the upper punch mold. The raw material powder is usually filled up to the upper surface of the mold. After filling the raw material powder, the upper punch is lowered to form a molding space and press-mold the raw material powder. That is, the lower punch does not move during pressurization. After the pressure molding is completed, the upper punch is raised and the lower punch is further raised to take out the compact from the mold. Then, the lower punch is lowered to prepare for filling the raw material powder. In such a molding apparatus, the filling depth of the raw material powder is the depth at the lowest position of the molding space measured from the upper surface of the mold.

The orientation ferromagnetic materials 61, 62 have their upper ends substantially aligned with the upper end of the lower die (the upper end of the lower non-magnetic member 4 in FIG. 4) at the start of pressing (when the raw material powder is filled). Preferably, it is arranged such that the amount of deviation between the upper end of the orientation ferromagnetic material and the upper end of the lower mold is 30% or less of the maximum height of the molding space. If the orientation ferromagnetic material is located above the range with respect to the molding space 7, it becomes difficult to fill the raw material powder. This is because the orientation magnetic field is applied even when the raw material powder is filled, and the raw material powder is attracted into the mold by the magnetic field to perform the filling, so that the orientation ferromagnetic material is above the range. Then, such a suction action becomes difficult. On the other hand, if it is located below this range, the effect of providing the orientation ferromagnetic material cannot be sufficiently realized.

The orienting ferromagnetic materials 61 and 62 are usually formed in the structure shown in FIG.
It has a rectangular parallelepiped shape as shown in. The dimension of the orientation ferromagnetic material is preferably in the following range. First, in the cross section shown in FIG. 4, rectangular parallelepiped orientation ferromagnetic bodies 61, 62 are formed.
Let h be the height, w be the width, and d be the depth.

It is preferable that h is equal to the filling depth. Specifically, when the filling depth is H, 0.5 ≦ h / H is preferable. If h / H is too small, the effect of providing the orientation ferromagnetic material cannot be sufficiently realized. Note that even if h / H is increased, there is almost no adverse effect if the position of the orientation ferromagnetic material is appropriate, but h / H is 1.5.
Even if the size exceeds, the effect does not increase.

Further, the molding space 7 in the cross section shown in FIG.
It is preferable that w / W ≧ 0.3 when the width of W is W. If w / W is too small, the effect of providing the orientation ferromagnetic material cannot be sufficiently realized. There is no particular upper limit on w / W, and the dimension may be such that the orientation ferromagnetic material fits in the mold, but usually w / W is 1.5 or less.

Further, when the depth of the molding space 7 shown in FIG. 4 is D, d is preferably equal to or slightly larger than D. Specifically, 0.7 ≦ d / D ≦ 1.3 Preferably there is. If d / D is too small, the effect of providing the orientation ferromagnetic material cannot be sufficiently realized. On the other hand, if d / D is too large, the orientation tends to be disturbed near the four corners of the molding space.

The distance between the orientation ferromagnetic material and the molding space, that is, the thickness of the mold interposed therebetween, is to prevent damage during molding and to suppress the influence on the effect of the orientation ferromagnetic material. The thickness is usually about 2 to 10 mm.

It is preferable that the lower non-magnetic member 5 has a central portion thicker than both end portions in the illustrated cross section. By setting the cross-sectional shape of the lower non-magnetic body 5 in this way, the orientation near the end of the molded body is more toward the center, the degree of radial orientation is improved, and the magnetic characteristics are improved. In addition, since a non-magnetic material having a low magnetic permeability exists between the lower punch 2 made of a magnetic material and the raw material powder, abrupt magnetic flux changes are avoided and cracking during firing is prevented. Yield is improved.

It is preferable that the central portion of the upper non-magnetic member 4 is thinner than both end portions in the illustrated cross section. By setting the cross-sectional shape of the upper non-magnetic body 4 in this way, the orientation near the end of the molded body is more toward the center, the degree of radial orientation is improved, and the magnetic characteristics are improved. Further, since a non-magnetic material having a low magnetic permeability exists between the upper punch 1 made of a magnetic material and the raw material powder, abrupt magnetic flux change is avoided and cracking during firing is prevented. Yield is improved.

When the central portion of the lower non-magnetic member 5 is thicker than both end portions thereof, it is preferable that a flat portion is provided in the vicinity of the central portion to prevent the central portion from becoming too thick as shown in the figure. However, the cross-sectional shape of the lower non-magnetic member 5 is such that the upper edge and the lower edge are arcuate and are eccentric.
Alternatively, the upper edge and the lower edge may have different radii of curvature. The same applies to the upper non-magnetic body 4.

Although the upper non-magnetic material 4 and the lower non-magnetic material 5 are not essential, it is preferable to provide at least the lower non-magnetic material 5 in order to obtain better orientation, and the upper non-magnetic material 4 is further provided. By providing, the orientation is further improved. Further, the life of the upper punch and the lower punch is extended by providing these non-magnetic materials.

The constituent material of the lower non-magnetic material and the upper non-magnetic material is not particularly limited, and is usually appropriately selected from non-magnetic stainless steel and non-magnetic stellite. Also, the upper punch,
The lower punch and the ferromagnetic material for orientation may be made of a magnetic material such as S45C. The mold may be made of non-magnetic cemented carbide or the like.

The molding conditions are not particularly limited, and various conditions such as pressure and magnetic field strength at the time of molding may be the same as those in the normal dry molding method.

The dry molding apparatus of the present invention is usually used for manufacturing an arc-shaped magnet having a thickness (a distance between the inner peripheral surface and the outer peripheral surface) of about 3 to 15 mm.

[0034]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 A ferrite magnet sample was produced using the dry molding apparatus having the structure shown in FIG.
With this molding apparatus, h / H = 0.93, w / W = 0.41, and d / D = 1.05, all of which were within the preferred range of the present invention. Further, the distance between each orientation ferromagnetic material and the molding space is 2
mm. The orientation-oriented ferromagnetic bodies were arranged so that the upper ends thereof were at the same height as the upper ends of the lower non-magnetic bodies 5 at the time of filling the raw material powder.

The raw material powder of the ferrite magnet is filled in the molding space of this dry molding apparatus and pressure-molded in a magnetic field,
An arcuate shaped body having anisotropy in the radial direction was obtained. Then, the molded body was sintered to obtain an arc-shaped anisotropic ferrite magnet. As for the size of the magnet, the radius of curvature of the outer peripheral surface is 11.8 mm,
The radius of curvature of the inner peripheral surface was 8.5 mm, the width in the cross section including the radial direction was 20.4 mm, and the length (depth) was 18 mm. This magnet is referred to as Sample No. 1-1 of the present invention.

For comparison, an arc-shaped ferrite magnet sample was prepared in the same manner as Sample No. 1-1 of the present invention, using a dry molding apparatus having the same structure as that shown in FIG. 4 except that the orientation ferromagnetic material was not provided. It was made. This sample is referred to as Comparative Sample No. 1-2.

After the inner surfaces of the samples were fully magnetized by the above-mentioned method, the above-mentioned method was performed.
Bd was measured. The number of measurements was 5 for each sample. FIG. 5 shows Bd distribution curves of the inner peripheral surface and the outer peripheral surface of Sample No. 1-1 of the present invention. However, in the graph of FIG. 5, the maximum value of Bd on the inner peripheral surface is 60 which is the circumferential length of the inner peripheral surface.
It is not%. From the Bd measurement results, the angles θ, (α-β) / α and Bdi / Bdo were obtained by the method described above. As a result, in the sample No. 1-1 of the present invention, θ = 32 °, (α-β) /α=0.14, and Bdi / Bdo = 1.8, which were all within the range of the present invention. In Comparative Sample No. 1-2, θ = 40 °, (α−β) /α=2.3, Bdi / Bdo = 1.2, and (α−β) / α and Bdi / Bdo are the present invention. It was out of range. That is, it can be seen that when the ferromagnetic material for orientation is not provided, the absolute magnetic characteristics of the inner peripheral surface deteriorate and the uniformity of the magnetic characteristics of the inner peripheral surface also deteriorates.

Further, when a magnet was produced using a dry molding apparatus in which the shape and dimensions of the upper non-magnetic material were optimized without providing the orientation ferromagnetic material, Bdi / Bdo was 1.4 or more. Although the absolute magnetic characteristics of the peripheral surface were improved, the angle θ exceeded 50 °.

Next, the total flux Φ was measured for Sample Nos. 1-1 and 1-2. As a result,
In the sample No. 1-1 of the present invention, Φ = 7280MX,
A significant improvement of + 3.7% was observed with respect to Comparative Sample No. 1-2. The total flux of 3.7
The increase in% is comparable to the wet molding method.

Next, the sample No. 1-1 of the present invention was ground to reduce the thickness by 3% to make the total flux equal to that of the comparative sample No. 1-2. The magnet after grinding is referred to as Sample No. 1-3 of the present invention. The sample No. 1-3 of the present invention and the comparative sample No. 1-2 were each incorporated in a motor, and the torque generated by the attraction balance between the magnet and the rotor was measured with a torque meter to measure the respective cogging torques. As a result, sample No. 1 of the present invention
3 has a cogging torque of 22.14 gcm, comparative sample
In No. 1-2, it was 27.64 g · cm, and it was found that the present invention reduced cogging torque by 20%.

The reason why the cogging torque is compared with the total flux being the same is that the cogging torque is remarkably increased as the total flux is increased. However, in the present invention, since the Bd distribution curve becomes extremely smooth, the cogging torque when the sample No. 1-1 of the present invention is used is 29.10 despite the total flux increasing by 3.7%. It was 63 g · cm, which was only about 7% higher than that of Comparative Sample No. 1-2. From this result, it is clear that the present invention realizes a practical high torque motor.

Example 2 A ferrite magnet sample was prepared using the dry molding apparatus having the structure shown in FIG.
This molding apparatus had h / H = 1.00, w / W = 0.48, and d / D = 1.02, all of which were within the preferred range of the present invention. The distance between each orientation ferromagnetic material and the molding space was 2 mm. The orientation-oriented ferromagnetic bodies were arranged so that the upper ends thereof were at the same height as the upper ends of the lower non-magnetic bodies 5 at the time of filling the raw material powder.

Using this dry molding apparatus, an arc-shaped anisotropic ferrite magnet was produced in the same manner as in Example 1. The magnet has a radius of curvature of 11.5 mm on the outer peripheral surface, a radius of curvature of 7.9 mm on the inner peripheral surface, and a width of 1 in the cross section including the radial direction.
The length was 7.0 mm and the length (depth) was 16.6 mm. This magnet is referred to as Sample No. 2-1 of the present invention.

For comparison, an arc-shaped ferrite magnet sample was prepared in the same manner as in the sample No. 2-1 of the present invention using a dry molding apparatus having the same structure as that shown in FIG. 4 except that the orientation ferromagnetic material was not provided. It was made. This sample is referred to as Comparative Sample No. 2-2.

Bd of these samples was measured in the same manner as in Example 1. The number of measurements was 5 for each sample. FIG. 6 shows Bd distribution curves of the inner peripheral surface and the outer peripheral surface of Sample No. 2-1 of the present invention. However, FIG.
In the graph, the maximum value of Bd on the inner peripheral surface is not 60% of the circumferential length of the inner peripheral surface. From the Bd measurement result, the angles θ, (α-β) / α and Bdi /
Bdo was calculated. As a result, the present invention sample No. 2-1
Θ = 40 °, (α−β) /α=0.18, and Bdi / Bdo = 1.53, all of which were within the scope of the present invention, but in Comparative Sample No. 2-2, θ = 47. °, (α-β) /α=0.21, Bdi / Bdo = 0.85, all outside the range of the present invention.

Next, each of these samples was incorporated into a motor, and the electromotive force Ec when the rotor was rotated by external driving was measured. The electromotive force Ec is a value that is an index of motor characteristics. As a result, the present invention sample No. 2-
In the case of No. 1, Ec = 3.816 V, and comparative sample No. 2
A significant improvement of + 3.1% was observed with respect to -2.
The increase of the electromotive force Ec by 3.1% is comparable to the wet molding method.

When a large amount of each sample produced in each of the above-mentioned examples was manufactured, the number of magnets with cracks was 40% or less in the sample of the present invention as compared with the comparative sample. As shown in FIG. 7, the cracks are generated near both ends of the inner peripheral surface of the magnet, and are mainly caused by disordered orientation near the ends of the molded body.

From the above results, the effect of the present invention is clear.

[Brief description of drawings]

FIG. 1 is a Bd distribution graph illustrating an angle θ and (α−β) / α.

FIG. 2 is an explanatory diagram of a magnetizing method.

FIG. 3 is an explanatory diagram of a Bd measuring method.

4A is a cross-sectional view of a configuration example of a dry molding apparatus of the present invention, and FIG. 4B is a top view of the molding apparatus when the upper punch 1 is removed.

FIG. 5 is a graph showing a Bd distribution curve of the magnet of the present invention in an example.

FIG. 6 is a graph showing a Bd distribution curve of the magnet of the present invention in an example.

FIG. 7 is a perspective view for explaining cracks in a magnet.

[Explanation of symbols]

 1 Upper Punch 2 Lower Punch 3 Form Frame 4 Upper Non-Magnetic Material 5 Lower Non-Magnetic Material 61, 62 Orientation Ferromagnetic Material 7 Molding Space

Claims (6)

[Claims] 1. An arc-shaped dry-molded ferrite magnet having an arc-shaped cross section and having anisotropy in its radial direction, wherein the horizontal axis is the measurement region length (circumferential length of the circumferential surface), and the vertical axis is Bd
In the Bd distribution graph with (surface magnetic flux density), the Bd distribution curve of the inner peripheral surface is set so that the maximum value of Bd on the vertical axis is 60% of the measurement area length (circumferential length of the inner peripheral surface) on the horizontal axis. Is plotted and, when the central portion of the measurement area is 60%, the angle θ between the straight line passing through any two points on the Bd distribution curve and the horizontal axis is 45 ° or less in the evaluation area, In the evaluation area, the relationship between the maximum value α of Bd and the minimum value β of Bd is (α−β) /α≦0.2, and in the Bd distribution graph, the Bd distribution curve of the inner peripheral surface and the lateral When the area surrounded by the axis is Bdi and the area surrounded by the Bd distribution curve of the outer peripheral surface and the horizontal axis is Bdo, Bdi / Bdo = 1.4 to 1.9. . 2. The dry-molded ferrite magnet according to claim 1, wherein the angle θ is 42 ° or less, (α−β) /α≦0.18, and Bdi / Bdo = 1.5 to 1.9. 3. A molding apparatus for forming a bow-shaped body by filling raw material powder of a ferrite magnet into a molding space having an arcuate cross section and performing dry molding in a magnetic field, each of which is at least a part. An upper die and a lower die made of a ferromagnetic material, a mold made of a non-magnetic material, and 2
Having the orienting ferromagnetic material, the molding space is formed by an upper mold, a lower mold, and a mold so that the convex surface of the molding space is on the lower side. It has a magnetic field applying means for applying a magnetic field, and two orientation ferromagnetic bodies are provided on both sides in the circumferential direction of the molding space via molds, respectively. And the upper ends of the ferromagnetic materials for orientation are substantially coincident with each other. 4. The dry molding apparatus according to claim 3, wherein the lower die is provided with a lower non-magnetic body facing the molding space, above the lower punch made of a ferromagnetic body. 5. The dry molding apparatus according to claim 4, wherein the upper die is provided with an upper non-magnetic body facing a molding space, below an upper punch made of a ferromagnetic body. 6. A method for producing a dry-molded ferrite magnet, characterized in that the dry-molded ferrite magnet according to claim 1 or 2 is manufactured using the dry-molding apparatus according to any one of claims 3 to 5.