JP2551545B2 - Arc-shaped ferrite magnet, method of manufacturing the same, and wet molding apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arcuate ferrite magnet having anisotropy in the radial direction, a method of manufacturing the magnet and a wet molding apparatus used in the method.

[0002]

2. Description of the Related Art Electric motors for automobiles such as wiper drive motors are required to have high torque, small size and light weight. Such a motor is a DC two-pole motor, and as the magnet, an anisotropic arc-shaped ferrite magnet formed by dry molding or an anisotropic ring magnet formed by dry molding is used. However, it is difficult to obtain high anisotropy by dry molding, and sufficient magnetic properties cannot be obtained. Under such circumstances, there is a demand for an anisotropic magnet formed by wet molding that can increase the degree of orientation.

However, the production of the arc-shaped magnet by wet molding has the following problems.

There are two methods for wet-molding arc-shaped ferrite magnets, which have different pressing directions. The first method is the so-called right-angled magnetic field pressing method (horizontal magnetic field pressing) in which pressure is applied by the upper and lower punches in the direction perpendicular to the radial direction, that is, in the direction perpendicular to the magnetic field direction. In addition to the problem that a sufficient density of the molded body cannot be obtained, the height of the molded body becomes high, making it difficult to drain water during wet molding, which is not suitable for mass production. Further, there is a problem that the magnetic circuit of the die becomes complicated and the die cost becomes high.

A second method is a method of compression-molding the outer peripheral surface side with an upper punch having a concave surface and the inner peripheral surface side with a lower punch having a convex surface, but this method solves the above problems. However, there is a problem in that both ends of the arc-shaped ferrite magnet are cracked or chipped.

In order to prevent cracking and chipping of both ends of the arc-shaped magnet manufactured by such a wet molding method, for example, in Japanese Patent Publication No. 59-8047, a wet molding metal of a ferrite magnet material suspension is disclosed. In the mold, in addition to providing a dehydration filter hole on almost the entire surface of the upper punch, it has been proposed to provide a dehydration filter hole on a part of the lower punch (regions corresponding to the lower surfaces of both ends of the arc magnet). ing. This proposal is
By controlling the dehydration of the suspension, it is possible to prevent uneven density in the thick and thin portions of the molded product in the vertical direction. However, the mold of this proposal is not suitable for mass production because it is difficult to manufacture the lower punch, and since the filter holes of the lower punch are easily clogged with fine particles and are difficult to dehydrate, cleaning is required. Further, when an arc-shaped magnet having a large angle θ between both ends is manufactured using this mold, it becomes difficult to make the compact density uniform, and particularly when θ is 160 ° or more, the compact density becomes uneven. It cannot prevent the occurrence of cracks.

By the way, in a DC two-pole motor, two arc-shaped magnets are arranged so that their inner peripheral surfaces are opposed to each other. Since the magnetic flux changes abruptly, a large torque fluctuation occurs, which causes noise. Therefore, it is desired that the angle θ be as close to 180 ° as possible. For example, in Japanese Examined Patent Publication No. 3-32893, the central angle θ = 155 °
It is described that an arc-shaped molded body having 175 ° is sintered to produce a semicircular anisotropic ferrite magnet having a central angle of 165 ° to 182 °. The central angle θ has the same meaning as the angle θ between the both ends described above.

However, in the method of wet compression molding using the upper punch on the outer peripheral surface side and the lower punch on the inner peripheral surface side, when the central angle θ is 150 ° or more, particularly 160 ° or more, both end portions of the arc-shaped ferrite magnet are formed. It cannot be put to practical use because it will be significantly cracked or chipped. In fact, the molded body described in Japanese Patent Publication No. 3-32893 mentioned above compresses slurry magnet raw material powder or dry magnet raw material powder in the die in the direction perpendicular to the magnetic field direction by the upper and lower punches of the non-magnetic material. It is obtained by molding, and is obtained by the above-mentioned right angle magnetic field pressing method.

Further, in JP-B-63-29504, two end faces of the arc-shaped magnet are provided with two planes (horizontal direction and vertical direction) orthogonal to the inner peripheral surface and the outer peripheral surface, respectively, and the magnet end portions are provided. It has been proposed to prevent the
The publication does not describe a molding method. In addition, in the publication,
Since there is a description that the angle θ between both ends of the inner peripheral surface is preferably in the range of 120 to 140 °, it is not intended to prevent the wide angle magnet having θ of 150 ° or more from fraying.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an angle between both end portions of the inner peripheral surface is 150 ° or more, particularly 1 by using a wet molding method suitable for mass production.
It is an object of the present invention to obtain a radial anisotropic arc-shaped ferrite magnet having an angle of 60 ° or more without cracking or chipping at both the outer peripheral surface end portion and the inner peripheral surface end portion.

[0011]

The above objects are achieved by the present invention described in (1) to (10) below. (1) An arc-shaped ferrite magnet manufactured by a wet molding method, which has anisotropy in a radial direction and has a radial direction at a center in a circumferential direction as a height direction, and the above-mentioned height direction during molding. When pressure is applied to the inner peripheral surface, and the angle formed by both ends of the inner peripheral surface is θ _a , 150 ° ≦ θ _a ≦ 180 °, and near the outer peripheral surface both end portions and substantially parallel to the height direction. An arc-shaped ferrite magnet having a flat outer peripheral surface area.

[0012] (2) When the height of the measured height direction the peripheral flat region and h _a, the radial thickness of the circumferential center was t _a, (-0.5 × 10 ^-2 _{) θ a + 0.95 ≦ h a} / t a ≦
The arc-shaped ferrite magnet according to (1) above, wherein (-10 ⁻² ) θ _a +2.5.

[0013] (3) When the radius of curvature Ro _a of the outer peripheral surface, the radius of curvature of the inner peripheral surface was _{Ri a, 1.10 ≦ Ro a /} Ri a ≦ 1.45 in the above (1) or (2 ) The arc-shaped ferrite magnet according to [1].

(4) The arc-shaped ferrite magnet according to any one of (1) to (3) above, wherein 160 ° ≦ θ _a ≦ 180 °.

[0015] (5) the radius of curvature of the outer peripheral surface Ro _a, when the curvature radius of the inner peripheral surface was _{Ri a, {Ri a - (} Ro a -t a)} / t a in represented by eccentricity 0 The arc-shaped ferrite magnet according to any one of (1) to (4) above, wherein

(6) Using a wet molding apparatus having an upper punch having a concave surface and a lower punch having a convex surface, the raw material powder slurry is placed in an arc-shaped cavity sandwiched between the upper punch and the lower punch. And a radial direction at the circumferential center of the arc-shaped cavity is defined as a depth direction. At this time, molding is performed so that the direction of pressure applied to the raw material powder slurry is the depth direction of the arc-shaped cavity and the direction of the magnetic field applied to the raw material powder slurry is the radial direction of the arc-shaped cavity. Then, when the angle formed by both ends of the inner peripheral surface is θ _b , 130 ° ≦ θ _b ≦ 165 °, and when the radial direction at the center in the circumferential direction is the height direction, near both ends of the outer peripheral surface. Has an outer peripheral plane area substantially parallel to the height direction, the height of the outer peripheral plane area measured in the height direction is h _b, and the radial thickness at the center in the circumferential direction is t _b . Then, (−0.5 × 10 ⁻² ) θ _b + 0.88 ≦ h _b / t _b ≦
A method of manufacturing an arc-shaped ferrite magnet, which comprises forming an arc-shaped molded body having a shape of (-10 ^-2 ) θ _b +2.35.

(7) When the radius of curvature of the outer peripheral surface is Ro _b and the radius of curvature of the inner peripheral surface is Ri _b in the molded body, 1.10≤Ro _b / Ri _b ≤1.45. The method for producing an arc-shaped ferrite magnet according to 6).

(8) The method for producing an arc-shaped ferrite magnet according to the above (6) or (7), wherein 139 ° ≦ θ _b ≦ 165 °.

(9) When the radius of curvature of the outer peripheral surface is Ro _b and the radius of curvature of the inner peripheral surface is Ri _b in the molded body, it is expressed by {Ri _b- (Ro _b -t _b )} / t _b . The method for producing an arc-shaped ferrite magnet according to any one of (6) to (8), wherein the eccentricity is 0 to 0.5.

(10) A wet molding apparatus used in the manufacturing method according to any one of (6) to (9), wherein the upper punch having a concave surface contacts the outer peripheral surface of the arc-shaped molded body, A wet forming apparatus, wherein a lower punch having a convex surface is configured to come into contact with an inner peripheral surface of an arc-shaped formed body.

[0021]

Specific Structure The specific structure of the present invention will be described in detail below. An example of the arc-shaped ferrite magnet of the present invention is shown in FIG. The arc-shaped ferrite magnet 1 shown in the figure has anisotropy in the radial direction. When applied to a DC two-pole motor, when the angle formed by both ends of the inner peripheral surface is θ _a , the noise and high magnetic characteristics are obtained as θ _a approaches 180 °, and in particular 150 ° ≦ In the range of θ _a ≦ 180 °, preferably 160 ° ≦ θ _a ≦ 180 °, noise is remarkably reduced, and the total amount of magnetic flux is improved. Therefore, in the present invention, θ _{a is set} to the above range.
When θ _a is set close to 180 ° in this way, in the conventional arc-shaped ferrite magnet, pressure is applied in the height direction (the radial direction at the center of the inner peripheral surface in the circumferential direction), that is, in the vertical direction in FIG. However, in the present invention, when the magnet is produced, cracks and chips frequently occur at both ends of the magnet after sintering.
_{Even when a} is in the above range, it is possible to prevent cracking and chipping.

The center O, which is the reference for the measurement of θ _a , is the center of the circle including the inner peripheral surface of the arc-shaped ferrite magnet. By the way, the compaction anisotropy by the molding in a magnetic field has different shrinkage rates at the time of sintering in the anisotropic direction (the easy axis of magnetization) and the direction perpendicular thereto. Therefore, the arc-shaped ferrite magnet 1
The inner peripheral surface of may be distorted. In such a case, five or more measurement points are set on the inner peripheral surface, and a virtual circle whose part is the inner peripheral surface is assumed by the least square method, and θ _a is obtained with the center O of the virtual circle as the center O. . Also, the arc-shaped ferrite magnet 1
The end of the inner peripheral surface may be designed to have a shape deviating from the arc shape. In this case, the arc shape portion is virtually extended to both ends to obtain θ _a .

The arc-shaped ferrite magnet 1 of the present invention has outer peripheral flat surface regions near both ends of the outer peripheral surface. It is preferable that the outer peripheral flat surface region is provided so as to be substantially parallel to the height direction, and preferably the angle between them is 5 ° or less. The inclination direction of the outer peripheral flat area may be any direction.

When the height of the outer peripheral flat surface area measured in the height direction is h _a and the radial thickness at the center of the inner peripheral surface in the circumferential direction is t _a , preferably (−0. _{^{5 × 10 -2) θ a +}} 0.95 ≦ h a / t a ≦
(-10 ^-2) θ _a +2.5, more preferably _{^{(-0.5 × 10 -2) θ a}} + 0.95 ≦ h a / t a ≦
(−10 ⁻² ) θ _a +2.35. The outer peripheral flat area is for equalizing the pressure applied to the slurry of the raw material powder during molding. h _a / t
_{When a} is less than the above range, that is, when the height of the outer peripheral flat surface area is relatively insufficient with respect to the radial thickness, the pressure in the vicinity of the outer peripheral surface end portion becomes excessive during molding. Defects such as cracks and chips occur near the part. Also, h _a
When / t _a exceeds the above range, that is, when the height of the outer peripheral flat surface region is relatively large with respect to the radial thickness, the pressure applied to the end portion of the inner peripheral surface during molding is insufficient, Defects such as cracks and chips occur near the edges of the inner surface.

In the arc-shaped ferrite magnet 1 of the present invention, the radius of curvature of the outer peripheral surface is Ro _a and the radius of curvature of the inner peripheral surface is R a.
when a i _a, typically, are _{1.10 ≦ Ro a / Ri a ≦} 1.45. If Ro _a / Ri _a is within this range, h _a /
the effect of limiting the range of t _a becomes higher. When determining Ro _a and Ri _a , a virtual circle is used as necessary, as in the case of determining θ _a .

The arc-shaped ferrite magnet of the present invention is shown in FIG.
It may be eccentric as shown in (b). If it is eccentric, molding becomes easy, but the total amount of magnetic flux decreases. In the present invention, even if the eccentricity is as small as 0 to 0.5, molding can be performed without cracking or chipping, so the degree of freedom in molding is improved, and a magnet with high magnetic characteristics can be obtained. Eccentricity in this _{case, {Ri a - (Ro a} -
t _a )} / t _a .

There is no particular limitation on the length of the magnet measured in the direction perpendicular to the radial thickness (direction perpendicular to the drawing).
It may be appropriately determined according to the application.

The composition of the arc-shaped ferrite magnet of the present invention is not particularly limited, and the effects of the present invention are realized regardless of the composition of the ferrite.

Next, the manufacturing method of the present invention will be described. The arcuate ferrite magnet is manufactured by sintering an arcuate shaped body. FIG. 2 shows an example of the wet molding apparatus used in the present invention. In this wet molding device,
Is a die supported on the floor by the columns 12, 13 is an upper punch, and 14 is a lower punch. Reference numeral 15 denotes a magnetic field coil attached to the outer peripheral portion of the die 11, which is used for imparting anisotropy to the molded body by performing magnetic field orientation during molding. Upper punch 13 and lower punch 14
Can be moved up and down by cylinders 16 and 17, the upper punch 13 descends and abuts the upper surface of the die 11, and the lower punch 14 rises in the through-hole provided in the die 11 to perform pressure molding. Is configured to do. In the cavity formed by the upper punch 13, the lower punch 14 and the die 11, a supply path 111 for supplying the slurry of the raw material powder is opened. The upper punch 13 is provided with a plurality of drainage holes 18 for discharging the liquid pushed out from the slurry to the outside of the cavity during pressurization, and the drainage holes 18 communicate with a drainage passage 19. further,
A filter body 20 made of cloth, paper, or the like is provided on the cavity-side inner surface of the upper punch 13, and functions to push only the liquid into the drain hole 18 and press the raw material powder into the cavity at the time of pressurization. Is doing. Filter body 20 is roll 2
It is wound around 1 and 22, and by appropriately rotating these rolls, continuous molding is possible without replacing the filter body 20.

In the wet molding apparatus configured as described above,
Molding is performed as follows. First, cylinder 1
When the upper punch 13 comes into contact with the upper surface of the die 11 and the lower punch 14 descends by the operation of 6, the upper punch 13, the die 11 and the lower punch 14 form a cavity for molding. Of the slurry is pressure-fed and filled by the supply path 111. After the filling, the lower punch 14 moves up to pressurize the slurry. By this pressurization, the liquid in the slurry is filtered by the filter body 20, pushed out into the drainage hole 18, and discharged to the outside through the drainage passage 19. On the other hand, the raw material powder in the slurry is the upper punch 13
And it is compressed by the lower punch 14 to form an arc-shaped molded body.

In this forming apparatus, the upper punch 13 forms the outer peripheral surface of the arc-shaped formed body, and the lower punch 14 forms the inner peripheral surface of the arc-shaped formed body. That is, when the radial direction at the center of the arc-shaped cavity in the circumferential direction is the depth direction, the direction of the pressure applied to the raw material powder slurry is the depth direction of the arc-shaped cavity. Moreover, the direction of the magnetic field applied to the raw material powder slurry is the radial direction of the arc-shaped cavity.

In the present invention, when the angle formed by both ends of the inner peripheral surface is θ _b by such a wet molding method, 130 ° ≦ θ _b ≦ 165 °, preferably 139 ° ≦ θ _b ≦ 165 ° In the vicinity of both end portions of the outer peripheral surface, there is an outer peripheral flat surface area that is substantially parallel to the height direction, and the height of the outer peripheral flat surface area measured in the height direction is h _b, and at the center in the circumferential direction. When the radial thickness is t _b , (−0.5 × 10 ⁻² ) θ _b + 0.88 ≦ h _b / t _b ≦
(−10 ⁻² ) θ _b +2.35, preferably (−0.5 × 10 ⁻² ) θ _b + 0.88 ≦ h _b / t _b ≦
An arcuate shaped body of (-10 ⁻² ) θ _b +2.20 is manufactured.

In the molded product, the height direction and the outer peripheral flat surface region may be substantially parallel to each other, but the angle between them is preferably 0.3 to 5 °. Generally, the outer peripheral flat surface region is preferably inclined so that the lower end thereof approaches the center O.

Further, it this arcuate shaped body, and a radius of curvature of the outer peripheral surface and Ro _b, the radius of curvature of the inner peripheral surface and Ri _b, is _{1.10 ≦ Ro b / Ri b ≦} 1.45 Is preferred.

Further, in the arc-shaped molded body, {Ri _b -
The eccentricity represented by (Ro _b −t _b )} / t _b is 0 to
It is preferably 0.5.

Θ _b , h _b , t in this arcuate shaped body
_b, Ro _b and Ri _b are, theta _a in arcuate magnet described above, h _a, t _a, and correspond respectively to the Ro _a and _{Ri a, θ b, h b} / t b, Ro b / Ri _b
And _{{Ri b - (Ro b -t} b)} / reasons for limiting the t _b is, _a theta in arcuate _{magnet, h a / t a, Ro} a / R
i _a and _{{Ri a - (Ro a -t} a)} / reasons for limiting the t _a and respectively similar. Since the arcuate shaped body shrinks during sintering, and the shrinkage rate differs between the direction of the easy axis of magnetization and the direction perpendicular thereto, the ranges of θ _b and h _b / t _b are θ _a and h _a / t _a . Although slightly different from the ranges, the effect of preventing cracks and chips at both ends is the same.

In the production method of the present invention, the ratio of the raw material powder in the slurry is not particularly limited, but is preferably 60.
-80% by weight. Also, the molding pressure is not particularly limited. The strength of the magnetic field applied during molding may be set to a level at which the raw material powder is saturated.

In the above description, the wet molding apparatus having the structure shown in FIG. 2 is taken as an example, but the present invention is not limited to this, and the upper punch and the die may be lowered to compress the slurry. Good. That is, in the case of a wet forming apparatus having a configuration in which the upper punch having a concave surface contacts the outer peripheral surface of the arcuate molded body and the lower punch having a convex surface contacts the inner peripheral surface of the arcuate molded body, The effect of the present invention is realized regardless of the movement of the die, the movement of the die, the slurry supply position, the slurry supply method, or the like.

[0039]

In the present invention, an arcuate shaped magnet having radial anisotropy is sintered to manufacture an arcuate ferrite magnet. The arc-shaped molded body is formed in the arc-shaped cavity formed by the upper punch 13 having a concave surface, the die 11 and the lower punch 14 having a convex surface by using the wet molding apparatus having the configuration shown in FIG. It is manufactured by filling the raw material powder slurry into and compression molding.

As a result of research on a wet molding method using such an apparatus, the present inventors have obtained the following findings.

FIG. 3 shows the cavity shape at the time of completion of molding, that is, the shape of the arcuate molded body, and the distribution of the compressibility calculated from the shape. The compressibility in this case is a value obtained by dividing the pressurization distance by the cavity depth when the slurry filling is completed. The pressurization distance is a value obtained by subtracting the cavity depth after completion of molding from the cavity depth after completion of slurry filling. The pressurization distance is constant at all positions in the cavity, but the cavity depth differs depending on the position, so the compression rate distribution is as shown in the figure.

If the fluidity of the raw material powder in the slurry is extremely good, even if the calculated compressibility varies depending on the position as shown in FIG. Pressure will be applied.
However, since the raw material powder of ferrite has poor fluidity, the pressure distribution during molding shows the same tendency as the compressibility distribution shown in FIG. That is, since the molding pressure is small at the inner peripheral surface end of the cavity and extremely large at the outer peripheral surface end, cracks and chips occur near the outer peripheral surface end of the arc-shaped magnet.

Therefore, in the present invention, an outer peripheral flat surface region (corresponding to h _a and h _b ) is provided near the outer peripheral surface end portion of the cavity to prevent the molding pressure at the outer peripheral surface end portion from becoming excessive.

On the other hand, the compression ratios in the vicinity of the center of the arc-shaped cavity in the circumferential direction and in the vicinity of the end of the outer peripheral surface are larger than those in the vicinity of the end of the inner peripheral surface. The raw material powder is moved to the vicinity of the end portion of the inner peripheral surface by the pressure, whereby the compact density near the end portion of the inner peripheral surface is improved. However, if the outer peripheral flat surface area is made too large in order to reduce the excessive pressure in the vicinity of the end of the outer peripheral surface, the molding pressure near the end of the outer peripheral surface becomes insufficient and the supply of the raw material powder to the vicinity of the end of the inner peripheral surface becomes insufficient. This is sufficient, and the density of the molded body near the end of the inner peripheral surface is insufficient, causing cracks and chips. Therefore,
It is necessary to set the upper limit of the size of the outer peripheral flat area.

However, the molding pressure near the end of the inner peripheral surface is affected by not only the pressure near the end of the outer peripheral surface but also the pressure near the center in the circumferential direction, as described above. That is, the smaller radial thickness of the cavity (corresponding to t _a and t _b) is, the difference between the compression ratio and the inner peripheral surface end portion vicinity of the compression ratio in the circumferential direction near the center increases. Therefore, if the compression rate near the center in the circumferential direction is set to an appropriate value, the molding pressure near the end of the inner peripheral surface becomes too low.If the pressure near the end of the outer peripheral surface is not increased to flow the raw material powder, Sufficient pressure cannot be obtained at the peripheral edge. Therefore, when t _a and t _b are small, the upper limits of h _a and h _b are small. In the present invention, therefore, it has a configuration to limit the scope of h _a / t _a and h _b / t _b.

Further, the difference between the compression rate near the center in the circumferential direction and the compression rate near the end portions of the inner peripheral surface is the angle (θ _a
And θ _b )), and the larger this angle, the greater the difference between them. Therefore, in the present invention, h _a / θ that is optimal for wide-angle magnets in which θ _a and θ _b are equal to or greater than a certain value
It sets the range of t _a and h _b / t _b.

Due to such a limitation, there is no cracking or chipping near both the outer peripheral surface end portion and the inner peripheral surface end portion, and the density is uniform and a wide-angle circle with little positional variation in magnetic characteristics. An arc-shaped ferrite magnet has been realized.

The pressurizing distance is appropriately determined according to various conditions such as the solid-liquid ratio of the slurry, and the absolute value of the compressibility may differ from that shown in FIG. Even if the values are different, the shape of the compression ratio distribution curve shows almost the same tendency.

[0049]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention. A slurry of ferrite raw material powder was supplied into the cavity of a wet molding apparatus as shown in FIG. 2 and was dehydrated and pressure-molded in a magnetic field to obtain an arc-shaped compact having radial anisotropy. . The ratio of the raw material powder in the slurry was 70% by weight. Then, the molded body was sintered to obtain an arc-shaped anisotropic ferrite magnet. A plurality of magnet samples were prepared by changing the shape of the cavity. The length of the magnet was 45 mm.

Table 1, Table 2 and Table 3 below show the values of variables representing the shape and dimensions of each sample and the molded body used for its production. 100 magnets were produced for each sample, and the occurrence rates of cracks and chips near both ends of the outer peripheral surface and both ends of the inner peripheral surface were examined. The results are shown in each table.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

In sample No. 5, the density of the molded body was extremely low at both ends, so that both ends of the magnet spread and the roundness was remarkably reduced, making it impossible to measure θ _a .

The effects of the present invention are clear from the results shown in the above tables. That is, when a molded body having h _b / t _b within the range of the present invention is used, there is almost no cracking or chipping at both ends of the magnet.

Further, as compared with the magnet No. 12 shown in Table 3, the magnet Nos. 7 to 9 shown in Table 2 and the magnet Nos. 2 to 4 shown in Table 1 significantly reduced noise, and the total amount of magnetic flux. Also increased.

[0057]

According to the present invention, a wet-molding method having high productivity in which an upper punch having a concave surface and a lower punch having a convex surface are used to form an arc shape having a wide angle between both ends of the inner peripheral surface. When manufacturing an anisotropic ferrite magnet, it is possible to prevent cracks and chips at both ends.

The wide-angle magnet realized by the present invention reduces noise and becomes equivalent to a dry ring magnet, and cracks and chips are generated by the conventional method using the upper punch and the lower punch as described above. The total amount of magnetic flux is increased by about 3 to 4% or more as compared with the arc-shaped magnet (the angle between both end portions of the inner peripheral surface is about 140 °) that could be manufactured without the above.

Therefore, according to the present invention, an arc-shaped ferrite magnet which can be miniaturized with high torque and has low noise can be obtained with an extremely high yield.

[Brief description of drawings]

1A and 1B are front views showing an arcuate ferrite magnet of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of a wet molding apparatus used in the manufacturing method of the present invention.

FIG. 3 is a graph showing the relationship between the cavity shape of the wet molding apparatus and the compressibility.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc-shaped ferrite magnet 11 Dice 111 Supply path 12 Support 13 Upper punch 14 Lower punch 15 Magnetic field coil 16 Cylinder 17 Cylinder 18 Drainage hole 19 Drainage path 20 Filter 21 Roll 22 Roll

Claims (10)

(57) [Claims] 1. An arc-shaped ferrite magnet manufactured by a wet forming method, which has anisotropy in a radial direction, and has a height in a radial direction at a center in a circumferential direction, and the height of the high When pressure is applied in the depth direction, and the angle formed by both ends of the inner peripheral surface is θ _a , 150 ° ≦ θ _a ≦ 180 °, and near the both end portions of the outer peripheral surface, the height direction is almost the same. An arc-shaped ferrite magnet having parallel outer peripheral plane regions. Wherein the height of the measured the height direction outer peripheral flat region and h _a, the radial thickness of the circumferential center when a ^{_{t a, (-0.5 × 10 -2}} ) _{θ a + 0.95 ≦ h a /} t a ≦
The arc-shaped ferrite magnet according to claim 1, wherein (-10 ⁻² ) θ _a +2.5. Wherein the radius of curvature of the outer peripheral surface Ro _a, when the curvature radius of the inner peripheral surface was Ri _a, according to claim 1 or 2 which is _{1.10 ≦ Ro a / Ri a ≦} 1.45 Arc-shaped ferrite magnet. 4. The arc-shaped ferrite magnet according to claim 1, wherein 160 ° ≦ θ _a ≦ 180 °. 5. The radius of curvature of the outer peripheral surface Ro _a, when the curvature radius of the inner peripheral surface was _{Ri a, {Ri a - (} Ro a -t a)} / t eccentricity represented by _a is 0 The arc-shaped ferrite magnet according to any one of claims 1 to 4, which has a value of 0.5. 6. A wet forming apparatus having an upper punch having a concave surface and a lower punch having a convex surface is used, and the raw material powder slurry is placed in an arc-shaped cavity sandwiched between the upper punch and the lower punch. A method for manufacturing an arc-shaped ferrite magnet, comprising the steps of filling and wet-molding in a magnetic field to form an arc-shaped molded body, wherein a radial direction at a circumferential center of the arc-shaped cavity is defined as a depth direction. At this time, the direction of the pressure applied to the raw material powder slurry is the depth direction of the arc-shaped cavity,
When molding is performed so that the direction of the magnetic field applied to the raw material powder slurry is the radial direction of the arc-shaped cavity, and the angle formed by both ends of the inner peripheral surface is θ _b , 130 ° ≦ θ _b ≦ 165 °, and when the radial direction at the center in the circumferential direction is taken as the height direction, there are outer peripheral flat surface regions that are substantially parallel to the height direction near both ends of the outer peripheral surface, and were measured in the height direction. The height of the outer peripheral flat area is h
_b, and the radial thickness at the center in the circumferential direction is t _b , (−0.5 × 10 ⁻² ) θ _b + 0.88 ≦ h _b / t _b ≦
A method of manufacturing an arc-shaped ferrite magnet, which comprises forming an arc-shaped molded body having a shape of (-10 ^-2 ) θ _b +2.35. 7. The molded body according to claim 6, wherein when the radius of curvature of the outer peripheral surface is Ro _b and the radius of curvature of the inner peripheral surface is Ri _b , 1.10 ≦ Ro _b / Ri _b ≦ 1.45. A method for manufacturing an arc-shaped ferrite magnet according to item 1. 8. The method for manufacturing an arc-shaped ferrite magnet according to claim 6, wherein 139 ° ≦ θ _b ≦ 165 °. 9. In the molded body, when the radius of curvature of the outer peripheral surface is Ro _b and the radius of curvature of the inner peripheral surface is Ri _b , it is represented by {Ri _b − (Ro _b −t _b )} / t _b. The method for manufacturing an arc-shaped ferrite magnet according to claim 6, wherein the eccentricity is 0 to 0.5. 10. The wet forming apparatus used in the manufacturing method according to claim 6, wherein the upper punch having a concave surface is in contact with the outer peripheral surface of the arc-shaped formed body, and the surface has a convex shape. A wet forming apparatus, wherein the lower punch is configured to contact the inner peripheral surface of the arc-shaped formed body.