JPH05234747A - Permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture in a high mass production automated line without inner peripheral burrs by bringing one annular end face into contact with a filter, wet molding, then sintering, allowing an inner periphery of a side end face of the filter to protrude from an outer periphery, and polishing at least the inner periphery of the side end face of the filter. CONSTITUTION:A molded form 100 is manufactured by using slurry in which powder of permanent magnet 1 material is dispersed. The form 100 is formed substantially in a cylindrical state in such a manner that the bottom surface and the upper surface are substantially parallel, and one side end face 11 of a filter in contact with the filter is formed uneven at the time of molding, and burrs 17 are generated at inner and outer peripheries of the side end face 11 of the filter. The obtained form 100 is annealed by an ordinary method. Prior to the annealing, the burrs of the outer periphery of the side end face 11 of the filter is removed. The obtained sintered material 10 is allowed at the inner periphery of the side end face of the filter to protrude from its outer periphery by molding in which its C axis is oriented by axially inclining. Then, the material 10 is polished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an annular permanent magnet used in a magnetic circuit such as a speaker or a magnetron, and a method for manufacturing the same.

[0002]

2. Description of the Related Art An anisotropic oxide permanent magnet of magnetoplumbite such as Sr ferrite or Ba ferrite is known. It is formed into an annular shape and both end surfaces thereof are magnetized to produce a speaker or a magnetron. It is used for applications. Such an oxide permanent magnet is manufactured by wet-molding into an annular shape in a magnetic field and then sintering.

To form an oxide permanent magnet by wet molding, a slurry prepared by suspending oxide magnetic powder in a dispersion medium such as water is pumped and filled into the cavity of a molding die and pressed in a magnetic field. Molding is performed while removing the dispersion medium from the inside of the cavity. When removing the dispersion medium, a filter body such as a filter cloth is usually placed on one of the punches forming the cavity.

However, the concavo-convex shape of the filter body is transferred to the annular end surface on the filter body side of the thus obtained annular molded body, and in particular, the inner circumference and the outer circumference thereof are respectively inward and outward. A protruding burr will occur. If a sintered body is obtained from a molded body in which this burr particularly occurs on the inner circumference, a great obstacle occurs when mounting the magnet.

By the way, in recent years, in order to improve the mass productivity of such a permanent magnet and reduce the manufacturing cost thereof, its manufacture has been carried out in an unmanned automated manufacturing line. The burr on the outer periphery of the end surface of the molded body on the filter body side can be easily removed before firing by, for example, bringing a roller or the like into contact with the outer periphery of the molded body during transportation of the molded body.
However, it is difficult to remove the burrs on the inner circumference before firing, and it is almost difficult to use the automated line. For this reason, if the inner peripheral burr is to be removed before firing only by manual work, it takes time to remove it, and the yield is poor, which is a major obstacle to improving mass productivity and reducing costs. Is.

On the other hand, when sintering is performed in the presence of such inner peripheral burrs, naturally, burrs also occur in the sintered body. Polishing may be performed to remove the inner peripheral burr of the sintered body. However, as a method capable of mass-producing polishing on an automated line, it is inevitable to employ polishing of the end face on the filter body side or both upper and lower end faces.

However, the upper and lower end surfaces of the sintered body obtained from the molded body wet-molded by the usual method are planes parallel to each other, and in order to remove the inner peripheral burr, one end surface on the filter body side or There is no choice but to polish both end faces, which increases the polishing load, slows the processing speed, and reduces mass productivity.
The cost is high. Moreover, since the amount of polishing is large, the weight yield is poor, and chipping and chipping occur due to polishing on both the inner and outer peripheral edges, especially the outer peripheral edge, and the quantity yield is deteriorated, further increasing the cost.

[0008]

SUMMARY OF THE INVENTION The main object of the present invention is to provide an annular permanent magnet which has no inner peripheral burr, has very few defects, and can be manufactured with high mass productivity in an automated line, and a manufacturing method thereof. It is to be.

[0009]

The above objects are achieved by the present invention described in (1) to (12) below.

(1) An annular shape, one end surface of which is brought into contact with a filter body to be wet-molded, and thereafter sintered to cause an inner peripheral portion of the filter body side end surface to protrude from an outer peripheral portion, and at least the filter body side end surface. A permanent magnet whose inner circumference is polished.

(2) From the outer peripheral direction of the end face on the filter body side,
The permanent magnet according to (1) above, in which the easy axis of magnetization is inclined toward the inner peripheral direction of the opposite end face.

(3) The permanent magnet according to the above (1) or (2), which has an unpolished portion on the outer peripheral portion of the end surface on the filter body side.

(4) When the outer circumference radius is Ro and the inner circumference radius is Ri, 0.2 is formed from the inner circumference (Ro-R).
i) The permanent magnet according to any one of the above (1) to (3), wherein the above regions are polished.

(5) A filter body is arranged in one punch, and the oxide permanent magnet material is wet-molded in a magnetic field by this punch, a die, a core rod, and the other punch to obtain an annular molded body,
The molded body is sintered to obtain a sintered body in which the inner peripheral portion of the end surface on the filter body side projects from the outer peripheral portion, and at least the inner peripheral portion of the end surface on the filter body side of the sintered body is ground to form an inner periphery. Method for manufacturing a permanent magnet for removing burr of.

(6) The method for producing a permanent magnet according to the above (5), in which the sintered body is conveyed while being supported, and both end surfaces are polished between the grinders facing each other.

(7) The method for producing a permanent magnet according to the above (5) or (6), wherein the outer peripheral burr of the compact is removed before the sintering.

(8) The filter body is arranged on the side of the upper punch having the drainage hole, and is brought into contact with the die and the core rod, and the lower punch or the upper punch is pressed to form a slurry of the oxide permanent magnet material. The method for producing a permanent magnet according to any one of the above (5) to (7), which comprises molding in a magnetic field.

(9) Any one of the above (5) to (8) wherein a magnetic field is applied to the molded body from the outer peripheral direction of the end surface on the filter body side to the inner peripheral direction of the end surface on the opposite side during the wet molding. Manufacturing method of permanent magnet of.

(10) In the above polishing, an unpolished portion is provided on the outer peripheral portion of the end face on the filter body side (5) to (9).
1. A method for manufacturing a permanent magnet according to any one of 1.

(11) The sintered body has an annular shape, and when the outer circumference radius is Ro and the inner circumference radius is Ri, a region of 0.2 (Ro-Ri) or more from the inner circumference is polished. 5)
(10) The method for manufacturing a permanent magnet according to any one of (10) to (10).

(12) The method for producing a permanent magnet according to any one of the above (5) to (11), wherein the thickness of the permanent magnet is T and the thickness of the inner periphery is 0.01 T or more. ..

[0022]

In the present invention, a sintered body is obtained in which the end surface on the filter body side is convexly warped, and the inner peripheral portion is polished to remove the inner peripheral burr. Since this polishing may be carried out, for example, by carrying the sintered body between opposed grinders, mass productivity is extremely high. Moreover, since it suffices to polish a predetermined region of the inner peripheral portion, the polishing load is remarkably reduced, the processing speed is increased, and the cost is reduced as compared with the case of polishing the entire surface. Further, since the polishing amount is reduced, the quantity yield and the weight yield due to chipping and chipping are remarkably improved, and the cost can be reduced in this respect as well.

[0023] Incidentally, Japanese Patent Laid-Open No. 61-54601 proposes to obtain a molded body having a chamfered edge portion of the end surface on the filter body side, and to prevent chipping and peeling during polishing due to this. However, in this proposal, attention is not paid to the removal of the inner peripheral burr on the automated line, and even if it is a chamfered shape, the burr is still generated,
There is no choice but to solve the above-mentioned increase in cost because the entire surface must be polished to remove the inner peripheral burr.

Further, conventionally, it has been known that when a magnetic field that is inclined with respect to the axial direction of the annular body is applied for molding, the surface (weak magnetic surface) of the sintered body on the magnetic field divergent side is convexly warped. However, by controlling the alignment of the molding device and the arrangement of the filter body that cause such warpage, the molding is performed, the sintered body is partially polished, and the inner peripheral burr based on the surface shape of the filter body is removed. There has been no proposal to that effect.

[0025]

[Specific Structure] The specific structure of the present invention will be described in detail below.

The permanent magnet 1 of the present invention is a magnetoplumbite type ferrite magnet and has an annular shape as shown in FIG. One annular end surface of the permanent magnet 1 of the annular body is the filter body side end surface 12, and a part of this surface, that is, the outer peripheral portion is usually the unpolished portion 14, so that the transfer pattern of the uneven shape of the filter body remains. On the other hand, the inner peripheral portion is a polishing portion 15 which is polished flat.

To obtain such a permanent magnet 1, a slurry in which a powder of a permanent magnet material is dispersed is used to produce a molded body 100 as shown in FIG. In the illustrated example, the molded body 1 has a substantially cylindrical shape with a bottom surface and an upper surface being substantially parallel to each other, and one end surface 1 on the filter body side that contacts the filter body during molding.
In Fig. 1, the uneven shape of the filter body is transferred to form unevenness. And, on the inner and outer circumferences of the end face on the filter body side,
A burr 17 (only the inner peripheral portion is shown) is generated.

Such burrs are generated as follows. That is, the molded body 100 is wet-molded in a cavity formed by the upper punch 21, the lower punch 25, the die 31, and the core rod 35, as shown in FIG. In the case, it is provided on the end face side of the upper punch 21). However, when arranging the filter body 7, the filter body is apt to bend or the like, and the upper punch 2
1 and the core rod 35 and the die 31 are likely to form a minute gap, and the slurry entering this portion causes burr. In particular, when molding is performed on an automated line, the contact position between the die 31 and the upper punch 21 can be assembled with high precision, but the core rod 35 has an elongated shape.
The vertical assembling accuracy is inevitable, and the assembling accuracy is deteriorated by the material adhered to the filter and the material adhered on the rod even by continuous molding. For this reason, especially in an automated line, the inner peripheral burr is often generated. On the other hand, the filter body 7 is arranged on the side of the upper punch 21 and is pressed by pressing the lower punch 25 or the upper punch 25. Therefore, the end surface 12 on the side opposite to the filter body 7 is pressed by, for example, the lower punch 25 to form a flat surface having no unevenness. The end surface 11 side on the filter body 7 side and the end surface on the opposite side are substantially parallel to each other as before.

From the molded body 100 thus obtained, a sintered body is obtained, in which the end face on the side of the filter body is convexly warped so that the inner peripheral side is projected,
According to the present invention, in order to perform polishing for removing the inner peripheral burr at a more effective and fast speed, the easy axis of magnetization (axial direction in ferrite) is not made parallel to the axial direction of the annular body,
As illustrated, the C-axis direction is oriented from the outer peripheral direction of the filter body side end surface 11 toward the inner peripheral direction of the opposite end surface 12 thereof,
It is preferable to perform magnetic field orientation so that the end surface 12 on the filter body side is a weak magnetic surface on which the magnetic field diverges, and the end surface on the opposite side is a ferromagnetic surface on which the magnetic flux converges.

FIG. 4 shows an example of the molding apparatus. More specifically, referring to FIG. 4, the die 31 is supported by the support column 5, and the upper punch 21, the lower punch 25, and the rod core 35 are arranged on the die 31. A coil 8 is attached to the outer peripheral portion of the die 11, and both punches 21 and 25 are made magnetic so that a magnetic field can be oriented during molding. Now, the core rod 35 is fixedly arranged in the die 31. Also, the upper punch 21,
The lower punch 25 can be moved up and down by cylinders 41 and 45, respectively. The upper punch 21 descends to come into contact with the upper surface of the die 31, and the lower punch 14 moves inside the penetrating portion provided in the die 11. It is designed to rise and perform pressure molding. That is, the slurry of oxide magnet powder is filled and molded in the cavity formed by the upper punch 21, the lower punch 25, the die 31, and the core rod 35. Therefore, the die 31 is
A supply path (not shown) communicating with the cavity is formed.

The upper punch 21 has a drain hole 6 for discharging the dispersion medium (water) pushed out from the slurry by pressurization.
1 is provided in plural numbers, and the drainage holes 61 are used as drainage paths 65.
Is in communication with. Further, the filter body 7 is provided on the upper punch 21 side.
Is installed, and only the dispersion medium is drained when pressurizing.
It has the function of pushing out into the cavity and stopping the magnet powder in the cavity. The filter body 7 is wound around rolls 71 and 75, and can be appropriately wound by rotating the rolls 71 and 75. Continuous molding is possible without changing the sheet each time. ing.

In order to obtain a molded body of a permanent magnet by the apparatus having such a structure, the upper punch 21 is operated by operating the cylinder 41.
Abutting the upper surface of the die 31 and lower punch 25
Is lowered to form a cavity for molding by the upper punch 21, the die 31, the core rod 35, and the lower punch 25, and the slurry of the magnet powder is pressure-fed and filled into the cavity. This pumping is performed from a supply path communicating with the cavity, and after this supply, the lower punch 25 moves up to pressurize the slurry. By this pressurization, the dispersion medium in the slurry is filtered by the filter body 7 and pushed out into the drainage hole 61 and discharged from the drainage port 65 to the outside, and the magnet powder is discharged by the upper punch 21 and the lower punch 25. It is squeezed to form a molded body 100 of a permanent magnet having a predetermined shape. Then, at the time of this molding, the surface uneven shape of the filter body 7 is transferred. Note that unlike the above, the upper punch 21 may be pressed.

As described above, the upper punch 21 and the end surface on the filter body 7 side form the weak magnetic surface of the permanent magnet 1, and the lower punch 25.
The side end surface preferably forms a ferromagnetic surface. For this purpose, for example, the magnetic pole area of the lower punch 25 is smaller than that of the upper punch 21, or a non-magnetic member is provided on the pressing surfaces of the lower punch 25 and the upper punch 21 so as to be inclined with respect to the axis. The orientation magnetic field may be inclined by providing a non-magnetic member on the outer peripheral side of the pressing surface. The filter 7 may be of various types such as filter cloth and filter paper.

The molded body 100 thus obtained is then sintered according to a conventional method. Prior to sintering, it is preferable to remove burrs on the outer peripheral portion of the end surface 11 on the filter body side. That is, after the molding is completed, the upper punch 21 is raised to open the cavity, and then the lower punch 25 is raised to take out the compact 100 from the apparatus and convey it. During this conveyance, the outer peripheral burr can be easily removed by preferably supporting the outer peripheral surface of the molded body 100 and rotating it to bring the support roller or the guide roller into contact with the outer peripheral surface.

Sintered body 10 obtained by the subsequent sintering
3, due to the effect of molding by orienting the C axis with being inclined with respect to the axial direction, the inner circumference of the filter body side end surface 12 is warped so as to project from the outer circumference thereof, as shown in FIG. The amount of warpage varies depending on the outer circumference radius Ro, the inner circumference radius Ri, the thickness T, etc. of the permanent magnet 1, but the usual permanent magnet size Ro = 10 to 110 mm, Ri = 5 to 55 mm, T = 5 to 2
When obtaining 5 mm, the amount of warp represented by the difference in height between the outer peripheral edge and the inner peripheral edge of one end surface of the sintered body 10 is 0.1.
.About.4 mm, particularly about 0.2 to 2 mm, and the maximum height T'when the lower surface of the sintered body 10 is placed on a flat plate is T '/
It is preferable that T ≦ 1.2, particularly 1.02 ≦ T ′ / T ≦ 1.10. It should be noted that, as shown in the figure, the end face opposite to the filter body 7 is also usually curved toward the filter body.

On the other hand, the surface shape of the filter body 7 is transferred to the end surface 11 of the sintered body 10 on the filter body side. This transfer shape differs depending on the filter body 7, but when the filter body 7 more preferable in terms of the ability to remove the dispersion medium is used, the recess depth is about 0.05 to 0.2 mm. Then, as shown in FIG. 2, on the inner peripheral edge of the filter body side end surface 11,
There are burrs 17 that could not be removed by the automated line. The inner peripheral direction growth length of the burr 17 is generally 0.2 to 5
mm, the height of the burr 17 protruding upward is 0.05 to
It is about 0.3 mm.

Next, such a sintered body 10 is polished. The polishing may be preferably partial polishing of at least only the end surface 11 on the filter body side, but if the polishing is carried out while the sintered body 10 is continuously transported, a very preferable result in mass production can be obtained. It is preferable to simultaneously polish the end surface 11 on the filter body side and the end surface 12 on the opposite side.

FIG. 5 illustrates such a preferred polishing process. In FIG. 5, a pair of grinders 91 and 95, which rotate in opposite directions, are arranged opposite to each other with a gap corresponding to the final thickness T of the permanent magnet 1 interposed therebetween. And
In order to make the radial direction of the sintered body 10 vertical, b in the figure
It may be conveyed in the same direction and polished on both sides. In the case of the sintered body 10 as shown in FIG. 3, since both end surfaces are both curved in the same direction, it is sharpened by the grinders 91 and 95 as compared with the case of polishing an annular body having no warp. The amount of polishing is remarkably small, the weight yield is remarkably improved, and the processing speed is extremely high.

In such a case, when polishing, it is preferable to polish a region (polishing portion 15) of 0.2 (Ro-Ri) or more from the inner circumference on the end face on the filter body side. If the area of the polishing portion 15 is too small, the effect of removing burrs becomes ineffective. In addition, the contact area with the yoke of the speaker or magnetron becomes small, and the amount of surface effect magnetic flux decreases. However, if the area of the polishing portion 15 is too wide, the polishing load becomes large, and if the entire area is polished and the area of the polishing portion reaches the outer peripheral edge, chipping or chipping is likely to occur at the outer peripheral edge. Furthermore, the weight yield also decreases due to the increase in the polishing amount. Generally, for example, the size of the yoke of the speaker is set to an outer diameter smaller than the outer diameter of the magnet, and even if the area of the polishing portion 15 is larger than the outer diameter of the yoke, the change in the effective magnetic flux amount is small. Therefore, it is preferable that the area of the polishing portion 15 is set to the yoke outer diameter or less, more preferably 0.95 Ro or less, and particularly 0.9 Ro or less to eliminate these disadvantages.

On the other hand, the polishing thickness ΔT is the total thickness T of the permanent magnet.
On the other hand, it is preferable that ΔT / T ≧ 0.01. Thereby, the inner peripheral burr can be effectively removed. However, ΔT
If too large, the same inconvenience as described above will occur, so it is preferable to set ΔT / T ≦ 0.1. Since the permanent magnet 1 shown in FIG. 3 is subjected to the above-mentioned double-side polishing, the end face opposite to the filter body is polished from the outer peripheral side with the same polishing allowance as above.

Further, as described above, in order to cause the warp of the sintered body 10, the C axis is inclined from the axial direction in a preferred embodiment. This inclination angle of the permanent magnet 1 is preferably within 15 °, and particularly preferably 1 to 15 °.

[0042]

According to the present invention, the inner peripheral burr can be removed with high productivity in an automated line. At this time, the polishing load is remarkably reduced, and the processing speed is remarkably improved. In addition, chipping and chipping are prevented, the quantity and weight yield are improved, and the manufacturing cost is remarkably reduced.

The present inventors conducted various experiments in order to confirm such effects. One example is shown below.

Experimental Example Using the apparatus shown in FIG. 4, a non-magnetic material was placed around the lower punch 25, Sr ferrite was molded in a wet magnetic field at a pressure of 400 kg / cm ² , and then sintered at 1240 ° C. .. Sintered body 10
Has an outer diameter of 2Ro = 70 mm and an inner diameter of 2Ri = 32 mm,
The filter body side end surface 11 was formed with unevenness having a recess having a depth of 0.1 mm. Moreover, the C-axis direction of the sintered body 10 was inclined at an angle of 2 to 12 ° with respect to the axial direction.

With the apparatus shown in FIG. 5, the inner peripheral side of the end face 11 on the filter body side of both end faces of this sintered body 10 and the end face 12 on the opposite end face 12
The outer peripheral side of the was polished. The polishing allowance is ΔR = 8 mm, Δt = 0.2 mm on one side, and the total thickness T = 10 mm is a permanent magnet (A).
And

On the other hand, for comparison, except that orientation was not performed by a gradient magnetic field and molding was performed in a magnetic field parallel to the axis, molding and sintering were performed in the same manner as described above, and one surface of the filter body was transferred to the end surface. Ro = 70 mm, which has a shape but is substantially free from warpage,
A sintered body with Ri = 32 mm was obtained. Then, on both sides of this.
The entire surface was polished with a polishing allowance having a thickness of 4 mm to obtain a permanent magnet B.

In both cases, burrs having a width of 0.2 to 3 mm and a height of about 0.2 mm were formed on the inner peripheral edge of the end surface on the filter body side of the sintered body 10, but these were all removed by the above polishing. We were able to. However, in the permanent magnet A, as compared with the comparative permanent magnet B, the processing speed was increased by 15%, the occurrence rate of chipping and chipping was reduced by 5%, and the polishing amount was halved.

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

[Brief description of drawings]

FIG. 1 is a sectional view showing a permanent magnet of the present invention.

FIG. 2 is a cross-sectional view showing a molded body according to the present invention.

FIG. 3 is a cross-sectional view showing a sintered body according to the present invention.

FIG. 4 is a cross-sectional view showing an apparatus used for wet molding of the present invention.

FIG. 5 is a perspective view showing an apparatus used for polishing of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Permanent magnet 10 Sintered body 100 Formed body 11 End surface of filter body 14 Unpolished portion 15, 16 Polished portion 17 Burr 21 Upper punch 25 Lower punch 31 Die 35 Core rod 7 Filter body 8 Coil 91, 95 Grinder

Claims (12)

[Claims] 1. An annular shape, one end surface of which is brought into contact with a filter body to be wet-molded and then sintered to cause an inner peripheral portion of the filter body-side end surface to protrude from an outer peripheral portion, and at least an inner portion of the filter body-side end surface. Permanent magnet whose periphery is polished. 2. The permanent magnet according to claim 1, wherein the axis of easy magnetization is inclined from the outer peripheral direction of the end surface on the filter body side toward the inner peripheral direction of the end surface on the opposite side. 3. The permanent magnet according to claim 1, further comprising an unpolished portion on an outer peripheral portion of the end surface on the filter body side. 4. An annular region, wherein when the outer radius is Ro and the inner radius is Ri, a region of 0.2 (Ro-Ri) or more from the inner periphery is polished. That permanent magnet. 5. A filter body is arranged on one punch, and an oxide permanent magnet material is wet-molded in a magnetic field by this punch, a die, a core rod, and the other punch to obtain an annular molded body. By sintering, a sintered body is obtained in which the inner peripheral portion of the end surface on the filter body side projects from the outer peripheral portion, and at least the inner peripheral portion of the end surface on the filter body side of the sintered body is polished to remove burrs on the inner periphery. Method for manufacturing a permanent magnet. 6. The method for producing a permanent magnet according to claim 5, wherein the sintered body is conveyed while being supported on its outer peripheral surface, and both end surfaces are polished between the grinders facing each other. 7. The method for producing a permanent magnet according to claim 5, wherein peripheral burrs of the molded body are removed before the sintering. 8. The filter body is arranged on the side of the upper punch having a drainage hole, is brought into contact with a die and a core rod, and the lower punch or the upper punch is pressed to apply a slurry of an oxide permanent magnet material in a magnetic field. The method for manufacturing a permanent magnet according to claim 5, wherein the permanent magnet is molded. 9. The permanent magnet according to claim 5, wherein a magnetic field is applied to the molded body from the outer peripheral direction of the end surface on the filter body side to the inner peripheral direction of the end surface on the opposite side during the wet molding. Production method. 10. The method for producing a permanent magnet according to claim 5, wherein an unpolished portion is provided on the outer peripheral portion of the end surface on the filter body side during the polishing. 11. The sintered body has a circular ring shape, and when the outer circumference radius is Ro and the inner circumference radius is Ri, a value of 0.
The method for manufacturing a permanent magnet according to claim 5, wherein a region of 2 (Ro-Ri) or more is polished. 12. When the thickness of the permanent magnet is T,
The method for producing a permanent magnet according to claim 5, wherein a thickness of 0.01 T or more on the inner circumference is polished.