JP2620603B2 - Permanent magnet and manufacturing method thereof - Google Patents

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 for a magnetic circuit such as a speaker and a magnetron, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Magnet plumbite anisotropic oxide permanent magnets such as Sr ferrite and Ba ferrite are known. They are formed in an annular shape, and both end surfaces thereof are magnetized to provide a speaker or a magnetron. It is used for applications. Such an oxide permanent magnet is manufactured by sintering after being wet-formed in an annular shape in a magnetic field.

In order to form an oxide permanent magnet by wet molding, a slurry in which an oxide magnetic powder is suspended in a dispersion medium such as water is pressure-filled into a cavity of a mold, and is pressurized in a magnetic field. The molding is performed while removing the dispersion medium from the cavity. When the dispersion medium is removed, a filter such as a filter cloth is usually disposed on one of the punches constituting the cavity.

[0004] However, the concavo-convex shape of the filter is transferred to the annular end face on the filter side of the annular molded body obtained in this way, and particularly on the inner and outer circumferences thereof, respectively, inwardly and outwardly. Protruding burrs occur. When a sintered body is obtained from a molded body in which the burrs are formed particularly on the inner periphery, a great obstacle occurs in mounting the magnet.

[0005] In recent years, in order to increase the mass productivity of such permanent magnets and reduce their manufacturing costs, their production has been carried out on unmanned automated production lines. Burrs on the outer periphery of the filter-side end surface of the molded body can be easily removed before firing by, for example, contacting a roller or the like with the outer periphery of the molded body during transportation of the molded body even in an automated line.
However, burrs on the inner periphery are difficult to remove before firing, and are almost difficult in an automated line. For this reason, removing the inner peripheral burrs before firing has to be done only by hand, which requires time for removal work, the yield is poor, and it is a major obstacle to improving mass productivity and reducing costs. It is.

On the other hand, when sintering is performed in a state where such inner peripheral burrs are present, burrs are naturally generated in the sintered body. Polishing may be performed to remove the inner peripheral burr of the sintered body. However, as a method that can be polished with high productivity in an automated line, polishing of the end face on the filter body side or the upper and lower end faces must be employed.

However, the upper and lower end surfaces of the sintered body obtained from the wet-formed body 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 Both end faces must be polished completely, polishing load increases, processing speed is slow, mass productivity is reduced,
Cost is high. In addition, since the amount of polishing is large, the weight yield is poor, and in addition, chipping and chipping due to polishing occur on the inner and outer peripheral edges, particularly on the outer peripheral edge, the quantity yield is reduced, and the cost is further increased.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ring-shaped permanent magnet which can be manufactured with high productivity in an automated line, in particular, having no inner peripheral burrs and having very few defects, and a method of manufacturing the same. It is to be.

[0009]

This and other objects are achieved by the present invention which is defined below as (1) to (12).

(1) One end face is in contact with a filter and wet-molded, and then sintered to make an inner peripheral portion of the filter-side end face protrude from an outer peripheral portion. Permanent magnet with polished inner circumference.

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

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

(4) Assuming an annular shape, where the outer radius is Ro and the inner radius is Ri, 0.2 (Ro-R)
i) The permanent magnet according to any one of the above (1) to (3), wherein the above region is polished.

(5) A filter is placed on one of the punches, and an oxide permanent magnet material is wet-molded in a magnetic field using the punch, die, core rod, and the other punch to obtain an annular molded body.
The molded body is sintered to obtain a sintered body in which an inner peripheral portion of the filter-side end surface protrudes from an outer peripheral portion, and at least an inner peripheral portion of the filter-side end surface of the sintered body is polished to obtain an inner peripheral portion. Manufacturing method of permanent magnet for removing burrs.

(6) The method for manufacturing a permanent magnet according to (5), wherein the outer peripheral surface of the sintered body is transported while being supported, and both end surfaces are polished between opposing grinders.

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

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

(9) In the wet molding, 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 filter-side end face toward the inner peripheral direction of the opposite end face. Of manufacturing permanent magnets.

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

(11) The sintered body is annular, and 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. 5)
To (10).

(12) Assuming that the thickness of the permanent magnet is T, the method for manufacturing a permanent magnet according to any one of the above (5) to (11), wherein a thickness of 0.01 T or more in the inner periphery is polished. .

[0022]

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

Japanese Patent Application Laid-Open No. 61-54601 proposes a molded article having a shape obtained by chamfering the edge of the end face on the side of the filter body to prevent chipping and peeling during polishing. However, this proposal does not focus on the removal of inner peripheral burrs in the automation line, and even if it is a chamfered shape, burrs will occur,
The entire surface must be polished to remove the inner peripheral burrs, and this does not solve the above-mentioned cost increase.

Also, conventionally, there has been known a phenomenon in which, when a magnetic field inclined with respect to the axial direction of an annular body is applied and formed, a surface (a weak magnetic surface) on the magnetic field divergence side of the sintered body is warped convexly. However, by regulating the alignment of the molding apparatus and the arrangement of the filter body that cause such a warp, 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 Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

The permanent magnet 1 of the present invention is a ferrite magnet of magnetoplumbite type or the like, and has an annular shape as shown in FIG. One annular end face of the annular permanent magnet 1 is the filter-side end face 12, and a part of this face, that is, the outer peripheral portion is usually an unpolished portion 14, so that the transfer pattern of the concavo-convex shape of the filter body remains. On the other hand, an inner peripheral portion thereof is a polishing portion 15 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 example shown in the figure, the formed body 1 has a substantially cylindrical shape with a bottom surface and a top surface substantially parallel to each other.
In 1, the unevenness of the filter is transferred to form unevenness. And, on the inner circumference and the outer circumference of the filter body side end face,
Burrs 17 (only the inner peripheral portion is shown) are 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 this case, it is provided on the end face side of the upper punch 21). However, when the filter body 7 is disposed, the filter body is liable to bend, etc.
1, and a minute gap is easily generated between the core rod 35 and the die 31, and the slurry that has entered this portion causes burrs. In particular, when molding is performed on an automated line, assembly of the contact position between the die 31 and the upper punch 21 can be performed with high accuracy, but since the core rod 35 is elongated,
The upper and lower assembling accuracy is inevitably deteriorated, and the assembling accuracy is deteriorated by the material adhered to the filter body and the material adhered to the rod by the continuous molding. For this reason, especially in an automation line, the occurrence of inner peripheral burrs increases. On the other hand, the filter 7 is disposed on the upper punch 21 side, and presses the lower punch 25 or the upper punch 25 to form the filter. For this reason, the end surface 12 on the opposite side to the filter 7 is pressed by, for example, the lower punch 25 to form a flat surface without irregularities. The end face 11 on the filter body 7 side and the end face on the opposite side are almost parallel as before.

From such a molded body 100, a sintered body whose end face on the side of the filter body is convexly warped so that the inner peripheral side protrudes is obtained.
In order to carry out the polishing for removing the inner peripheral burr more effectively and at a higher speed according to the present invention, instead of making the easy axis of magnetization (axial direction of ferrite) parallel to the axial direction of the annular body,
As shown in the drawing, 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,
It is preferable to perform magnetic field orientation such that the filter-side end surface 12 is a weak magnetic surface on which a magnetic field diverges and the opposite end surface is a ferromagnetic surface on which magnetic flux converges.

FIG. 4 shows an example of a molding apparatus. 4, a die 31 is supported by the 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 an outer peripheral portion of the die 11, and both punches 21 and 25 are made magnetic so that a magnetic field can be oriented at the time of 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 and abuts on the upper surface of the die 31, and the lower punch 14 moves through a through portion provided in the die 11. It rises and performs pressure molding. That is, the slurry of the oxide magnet powder is filled into the cavity formed by the upper punch 21, the lower punch 25, the die 31, and the core rod 35 and molded.
A supply path (not shown) communicating with the cavity is formed.

The upper punch 21 has a drain hole 6 for discharging a dispersion medium (water) pushed out of the slurry by pressurization.
1 are drilled, and the drain holes 61
Is in communication with Further, the filter body 7 is provided on the upper punch 21 side.
Are attached, and only the dispersion medium is drained when pressurized.
1 to stop 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, so that continuous molding can be performed without requiring sheet replacement each time. ing.

In order to obtain a molded body of a permanent magnet by the apparatus having the above-described structure, the upper punch 21 is operated by operating the cylinder 41.
Is brought into contact with the upper surface of the die 31 and the lower punch 25
Is lowered, and a cavity for molding is formed by the upper punch 21, the die 31, the core rod 35, and the lower punch 25, and a slurry of magnet powder is pressure-fed and filled into the cavity. This pressure feeding is performed from a supply path communicating with the cavity, and after this supply, the lower punch 25 rises to pressurize the slurry. By this pressurization, the dispersion medium in the slurry is filtered by the filter 7 and pushed out into the drain hole 61, discharged to the outside from the drain port 65, and the magnetic powder is separated 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 irregularities of the filter 7 are transferred. Note that, unlike the above, a configuration in which pressing is performed by the upper punch 21 may be adopted.

As described above, the upper punch 21 and the end face on the side of the filter 7 form the weak magnetic surface of the permanent magnet 1, and the lower punch 25
The end face on the side preferably forms a ferromagnetic surface. For this purpose, for example, the magnetic pole area of the lower punch 25 is made smaller than that of the upper punch 21, a non-magnetic member is provided on the pressing surface of the lower punch 25 or 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. It should be noted that the filter 7 may be of various types such as filter cloth and filter paper.

The compact 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 filter-side end surface 11. 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 molded body 100 from the apparatus and transport it. The transfer is preferably carried out while supporting the outer peripheral surface of the molded body 100, and by rotating the molded body 100, the outer peripheral burr can be easily removed by bringing the outer peripheral surface into contact with a support roller or a guide roller.

The sintered body 10 obtained by the subsequent sintering
As shown in FIG. 3, the inner periphery of the filter-side end surface 12 is warped so as to protrude from the outer periphery thereof, as shown in FIG. The amount of warpage varies depending on the outer radius Ro, the inner radius Ri, the thickness T, and the like of the permanent magnet 1, but normal permanent magnet sizes Ro = 10 to 110 mm, Ri = 5 to 55 mm, and T = 5 to 2
When 5 mm is obtained, the amount of warpage represented by the difference in height between the outer peripheral edge and the inner peripheral edge of one end face of the sintered body 10 is 0.1%.
About 4 mm, especially 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. Usually, as shown in the figure, the end face opposite to the filter 7 is also curved toward the filter.

On the other hand, the surface shape of the filter 7 is transferred to the filter-side end surface 11 of the sintered body 10. Although the transfer shape varies depending on the filter 7, when a filter 7 which is more preferable in terms of the dispersing medium removing ability is used, the concave portion has a depth of about 0.05 to 0.2 mm. And, 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 automation line. The growth length of the burr 17 in the inner circumferential direction is generally 0.2 to 5 mm.
mm, the height of the burr 17 projecting upward is 0.05 to
It is about 0.3 mm.

Next, such a sintered body 10 is polished. The polishing may be preferably a partial polishing of at least only the filter body side end face 11, but if the polishing is performed during the transportation while continuously transporting the sintered body 10, a very favorable result in mass production is obtained. Preferably, the filter body side end face 11 and the opposite end face 12 are simultaneously polished.

FIG. 5 illustrates such a preferred polishing step. In FIG. 5, a pair of grinders 91 and 95 that rotate in opposite directions are opposed to each other with a gap corresponding to the final thickness T of the permanent magnet 1 therebetween. And
In the figure, b is set so that the radial direction of the sintered body 10 is vertical.
It may be transported in the direction, and both sides may be polished. In the case of the sintered body 10 as shown in FIG. 3, both end faces are curved in the same direction, so that the sintered body 10 is sharpened by the grinders 91 and 95 as compared with a case where an annular body without warpage is polished. The polishing amount is significantly reduced, the weight yield is significantly 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 periphery on the filter body end face. If the area of the polishing section 15 is too small, the removal of burrs is not effective. Further, the contact area with a yoke such as a speaker or a magnetron is reduced, and the surface effective magnetic flux is reduced. However, if the area of the polishing section 15 is too wide, the polishing load increases, and if the entire area is polished and the area of the polishing section reaches the outer peripheral edge, chipping and chipping are 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 dimension of the yoke of the speaker is set to an outer diameter smaller than the outer diameter of the magnet, and the change in the effective magnetic flux amount is small even if the area of the polishing section 15 is larger than the outer diameter of the yoke. For this reason, it is preferable that the area of the polishing section 15 be equal to or less than the yoke outer diameter, 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 equal to 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. Where ΔT
Is too large, the same disadvantages as described above occur. Therefore, it is preferable to set ΔT / T ≦ 0.1. In the permanent magnet 1 shown in FIG. 3, since the above-mentioned double-side polishing is performed, the end face opposite to the filter is polished from the outer peripheral side with the same polishing allowance as described above.

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

[0042]

According to the present invention, it is possible to remove inner burrs with extremely high productivity in an automated line. At this time, the polishing load is significantly reduced, and the processing speed is significantly improved. In addition, chipping and chipping are prevented, and the quantity and weight yield are improved, thereby significantly reducing the manufacturing cost.

The present inventors conducted various experiments to confirm such effects. An example is shown below.

Experimental Example Using the apparatus shown in FIG. 4, a non-magnetic material was placed around the outer periphery of the lower punch 25, and 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 2Ro = 70 mm, an inner diameter 2Ri = 32 mm,
Irregularities having a concave portion having a depth of 0.1 mm were formed on the filter body side end surface 11. The C-axis direction of the sintered body 10 was inclined at an angle of 2 to 12 ° with respect to the axial direction.

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

On the other hand, for comparison, molding and sintering were performed in the same manner as described above except that molding was performed in a magnetic field parallel to the axis without performing orientation by a gradient magnetic field. Ro = 70 mm with shape but substantially no warpage
A sintered body of Ri = 32 mm was obtained. Then, both sides are placed at 0.
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 about 0.2 to 3 mm and a height of about 0.2 mm were formed on the inner peripheral edge of the end face of the sintered body 10 on the side of the filter body. We were able to. However, the processing speed of the permanent magnet A was 15% faster than that of the comparative permanent magnet B, the occurrence of chipping and chipping was reduced by 5%, and the polishing amount was reduced by half.

From the above, the effects of the present invention are clear.

[Brief description of the 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 article according to the present invention.

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

FIG. 4 is a 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 Molded body 11 Filter body side end surface 14 Unpolished portion 15, 16 Polished portion 17 Burr 21 Upper punch 25 Lower punch 31 Dice 35 Core rod 7 Filter 8 Coil 91, 95 Grinder

Claims (12)

(57) [Claims] 1. An annular shape, one end face of which is in contact with a filter body, is wet-formed, then sintered, and an inner peripheral portion of the filter body side end surface is projected from an outer peripheral portion. Permanent magnet with polished periphery. 2. The permanent magnet according to claim 1, wherein the axis of easy magnetization is inclined from an outer peripheral direction of the filter body side end surface to an inner peripheral direction of the opposite end surface. 3. The permanent magnet according to claim 1, wherein an unpolished portion is provided on an outer peripheral portion of the filter body side end surface. 4. The polishing apparatus according to claim 1, wherein an area of 0.2 (Ro−Ri) or more from the inner circumference is polished when the outer circumference is Ro and the inner circumference is Ri, which has an annular shape. That permanent magnet. 5. A filter is disposed on one of the punches, and an oxide permanent magnet material is wet-molded in a magnetic field with the punch, die, core rod, and the other punch to obtain an annular molded body. Sintering is performed to obtain a sintered body in which an inner peripheral portion of the filter body side end surface protrudes from an outer peripheral portion, and at least an inner peripheral portion of the filter body side end surface of the sintered body is polished to remove an inner peripheral burr. Of manufacturing permanent magnets. 6. The method of manufacturing a permanent magnet according to claim 5, wherein the sintered body is transported while supporting an outer peripheral surface thereof, and both end surfaces are polished between opposed grinders. 7. The method of manufacturing a permanent magnet according to claim 5, wherein a burr on an outer periphery of the molded body is removed before the sintering. 8. The filter body is disposed on an upper punch side having a drain hole, is brought into contact with a die and a core rod, and a lower punch or the upper punch is pressed to apply a slurry of an oxide permanent magnet material in a magnetic field. 8. The method for manufacturing a permanent magnet according to claim 5, wherein the permanent magnet is formed. 9. The permanent magnet according to claim 5, wherein, during the wet molding, a magnetic field is applied to the molded body from the outer peripheral direction of the end face on the filter side toward the inner peripheral direction of the end face on the opposite side. Production method. 10. The method of manufacturing a permanent magnet according to claim 5, wherein an unpolished portion is provided on an outer peripheral portion of the filter body side end surface during the polishing. 11. The sintered body has an annular shape, and its outer radius is defined as Ro and its inner radius is defined as Ri.
The method for manufacturing a permanent magnet according to any one of claims 5 to 10, wherein a region of 2 (Ro-Ri) or more is polished. 12. When the thickness of the permanent magnet is T,
The method for manufacturing a permanent magnet according to any one of claims 5 to 11, wherein a thickness of 0.01 T or more in an inner periphery is polished.