JP6011350B2 - Sintered magnet and preform before firing - Google Patents

Description

  The present invention relates to a sintered magnet used for an electrical component or an electronic component, and a pre-fired preform for producing the magnet.

  As a shape of a magnet used for an electric component such as a motor, there are many C-shaped shapes obtained by dividing a cylinder in a circumferential direction. The C-shaped magnet has an arcuate outer surface and an inner surface which is an arc surface having different radii of curvature with respect to a central axis common to the outer surface.

  The C-shaped magnet is provided with a C surface (tapered surface) at the intersection of the outer surface and the end surface to prevent the end surface from being chipped and to make it easier to put the magnet into the case when incorporated in a motor. (For example, Patent Document 1 below).

  In such a conventional sintered magnet, only a single C-plane is formed. In a sintered magnet obtained by a conventional manufacturing method, even a sintered magnet having a single C-plane has been processed in order to obtain dimensional accuracy, so there is almost no problem.

  However, the ferrite magnet product obtained by the CIM molding (magnetic field injection molding) proposed recently by the applicant of the present application is required not to be processed after molding. Thus, the present inventors have newly found that there is a problem of forming a convex portion. The convex portion may affect the gap size required between the rotor and the magnet when the magnet is incorporated into a motor or the like.

JP 2008-246526 A

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a sintered magnet and a pre-fired preform with desired dimensional accuracy without performing secondary processing.

In order to achieve the above object, the pre-fired preform according to the present invention is:
A pre-fired preform for producing a sintered magnet having an outer surface and an end surface intersecting the outer surface,
The pre-fired preform is obtained by melting a raw material containing magnetic powder and a binder resin, and injection-molding in a mold cavity to which a magnetic field is applied,
A first tapered surface formed adjacent to the end surface and a second tapered surface formed between the first tapered surface and the outer surface are formed at a portion where the outer surface and the end surface intersect. It is.

  In the pre-fired preform according to the present invention, at least two stages of tapered surfaces are formed in the C surface portion of the end portion (intersection portion between the outer surface and the end surface). Therefore, in the present invention, even if CIM molding is performed in which a raw material containing magnetic powder and a binder resin is melted and injection molding is performed in a cavity of a mold to which a magnetic field is applied, firing is performed on the C surface portion at the end. The convex portion formed later on the outside can be reduced, and desired dimensional accuracy can be maintained without performing secondary processing. The desired dimensional accuracy means that the maximum unevenness difference on the outer surface is less than 0.05 mm, preferably 0.025 mm or less.

  In addition, in the conventional preform with a single tapered surface, the following points can be considered as the reason why the convex portion is deformed outwardly after firing at the C surface portion of the end portion. Ferrite magnet materials have nearly double the reduction ratio in the C-axis direction and the direction perpendicular to the C-axis. In CIM molding, because of the fluidity of the material at the time of injection into the mold and injection molding while applying a magnetic field, the orientation direction of the magnet particles is changed from the outer surface to the C surface. It changes suddenly along. Therefore, it is considered that when the preform is fired, it is greatly deformed to the outside under the influence of the shrinkage difference, and a convex portion that protrudes larger than the outer surface is formed.

  In the present invention, since at least two stages of tapered surfaces are formed, even if CIM molding is performed, the orientation direction of the magnet particles gradually changes in at least two stages. For this reason, in the C surface portion at the end portion, a convex portion is hardly formed even after firing, or even if it is formed, it is considerably small. According to the experiments by the present inventors, it was confirmed that the maximum unevenness difference on the outer surface can be made 0.05 mm or less when firing a preform with at least two stages of tapered surfaces. On the other hand, in the conventional preform with a single tapered surface formed, a convex portion protruding from the outer surface is detected, and the maximum unevenness difference on the outer surface is 0.075 mm or more, and the convex portion is processed. It has been confirmed that there is a need for removal.

  Preferably, it further has an inner surface corresponding to the outer surface, and the outer surface and the inner surface are circular arc surfaces having different radii of curvature with respect to a common central axis. A sintered magnet obtained by firing a preform having such a shape is housed in a cylindrical casing and can be suitably used as a magnet for a motor.

  Preferably, a second angle of the second tapered surface with respect to the reference line of the outer surface is smaller than a first angle of the first tapered surface with respect to the reference line of the outer surface. By configuring in this way, the orientation direction of the magnet particles can be changed more gradually in at least two stages from the outer surface to the end surface. In the magnet after firing, the desired direction can be obtained without performing secondary processing. It becomes easy to have dimensional accuracy.

  Preferably, the first angle is 30 to 60 degrees, and the second angle is 20 degrees or more smaller than the first angle. By configuring in this way, the orientation direction of the magnet particles can be changed more gradually in at least two stages from the outer surface to the end surface. In the magnet after firing, the desired direction can be obtained without performing secondary processing. It becomes easier to have dimensional accuracy.

  Preferably, the length of the first tapered surface along the reference line is 1/2 times to 1/10 times longer than the length of the second tapered surface along the reference line. That's it. By configuring in this way, the orientation direction of the magnet particles can be changed more gradually in at least two stages from the outer surface to the end surface. In the magnet after firing, the desired direction can be obtained without performing secondary processing. It becomes easier to have dimensional accuracy.

  The sintered magnet according to the present invention is a sintered magnet obtained by firing the pre-fired preform described above. The sintered magnet of the present invention can be suitably attached, for example, in a motor casing.

FIG. 1 is a perspective view of a pre-fired preform according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a main part of the preform shown in FIG. FIG. 3 is a schematic view showing magnetic field injection molding. FIG. 4 is a cross-sectional view showing an example of using a sintered magnet obtained by firing the preform shown in FIG. FIG. 5 is a perspective view of a pre-fired preform according to another embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view of a main part of a conventional sintered magnet.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
As shown in FIG. 1, a pre-sintered preform 20 for manufacturing a sintered magnet according to an embodiment of the present invention is manufactured by a magnetic field injection molding apparatus 2 shown in FIG. First, the magnetic field injection molding apparatus 2 for performing magnetic field injection molding will be described.

  The magnetic field injection molding apparatus 2 includes an extruder 6 having a hopper 4 into which pellets 10 are charged, and a mold apparatus 8 for molding a melt of the pellets 10 extruded from the extruder 6 in a cavity 12. . This magnetic field injection molding apparatus is a molding apparatus using CIM (ceramic injection molding) molding.

  Although not shown in the figure, the mold apparatus 8 is provided with an electromagnetic coil or a magnet as a magnetic field applying means, and magnetic lines of force are generated in the cavity 12 in the thickness direction of the cavity 12 (in the radial direction of the arc). It is supposed to be.

  In the method for manufacturing a sintered magnet according to this embodiment, first, a raw material powder of magnetic powder is prepared. The raw material powder of the magnetic powder is not particularly limited, but preferably ferrite is used, and in particular hexagonal ferrite such as magnetoplumbite type M phase and W phase is preferably used.

Such ferrite is particularly preferably MO.nFe ₂ O ₃ (M is preferably one or more of Sr and Ba, n = 4.5 to 6.5). Such ferrite further contains rare earth elements, Ca, Pb, Si, Al, Ga, Sn, Zn, In, Co, Ni, Ti, Cr, Mn, Cu, Ge, Nb, Zr, and the like. May be.

In particular, ferrite having hexagonal magnetoplumbite type (M type) ferrite containing A, R, Fe and M as constituent elements shown below as a main phase is preferable. However, A is at least one element selected from Sr, Ba, Ca and Pb, R is at least one element selected from rare earth elements (including Y) and Bi, and M is , Co and / or Zn. The total composition ratio of these metal elements of A, R, Fe, and M is based on the total amount of metal elements.
A: 1 to 13 atomic%,
R: 0.05 to 10 atomic%,
Fe: 80 to 95 atomic%,
M: 0.1 to 5 atomic%.

  In this ferrite, the composition formula of ferrite when R is present at the A site and M is present at the Fe site can be expressed as shown in the following formula 1. Note that x, y, and z are values calculated from the above amounts.

_{A 1-x R x (Fe} 12-y M y) z O 19 ... Formula 1

  In order to produce such an anisotropic ferrite raw material powder, an oxide of the raw material of the ferrite composition or a compound that becomes an oxide by firing is mixed before calcining, and then calcined. The calcination is performed in the atmosphere at, for example, 1000 to 1350 ° C. for 1 second to 10 hours, particularly when obtaining fine calcined powder of M-type Sr ferrite at 1000 to 1200 ° C. for about 1 second to 3 hours. Just do it.

  Such calcined powder is substantially composed of granular particles having a magnetoplumbite-type ferrite structure, and the average primary particle size is 0.1 to 1 μm, particularly 0.1 to 0.5 μm. Preferably there is. The average particle diameter may be measured by a scanning electron microscope (SEM), and the coefficient of variation CV is preferably 80% or less, and generally 10 to 70%. The saturation magnetization σs is preferably 65 to 80 emu / g, particularly 65 to 71.5 emu / g for M-type Sr ferrite, and the coercive force HcJ is 2000 to 8000 Oe, and particularly 4000 to 8000 Oe for M-type Sr ferrite.

  In this embodiment, the calcined powder produced in this way is subjected to dry coarse pulverization as necessary, and then wet pulverization is performed once or more.

  In the dry coarse pulverization step, pulverization is usually performed until the BET specific surface area is about 2 to 10 times. The average particle size after pulverization is preferably about 0.1 to 1 μm, the BET specific surface area is preferably about 4 to 10 m 2 / g, and the CV of the particle size can be maintained at 80% or less, particularly 10 to 70%. preferable. The pulverizing means is not particularly limited, and for example, a dry vibration mill, a dry attritor (medium stirring mill), a dry ball mill, and the like can be used, and it is particularly preferable to use a dry vibration mill. What is necessary is just to determine a grinding | pulverization time suitably according to a grinding | pulverization means.

  Dry coarse pulverization also has an effect of reducing the coercive force HcB by introducing crystal distortion into the calcined particles. The decrease in coercive force suppresses particle aggregation and improves dispersibility. Also, the degree of orientation is improved. The crystal strain introduced into the particles is released in a subsequent sintering step, and thereby returns to the original hard magnetism and becomes a permanent magnet.

  After dry coarse pulverization, a slurry for pulverization containing calcined particles and water is prepared, and wet pulverization is performed using the slurry. The content of the calcined particles in the pulverizing slurry is preferably about 10 to 70% by weight. The pulverizing means used for wet pulverization is not particularly limited, but it is usually preferable to use a ball mill, an attritor, a vibration mill or the like. What is necessary is just to determine a grinding | pulverization time suitably according to a grinding | pulverization means.

  In this embodiment, a surfactant is added during wet pulverization. Specifically, sorbitol and mannitol are preferable as the surfactant.

  The surfactant used in the present invention may change its structure due to a mechanochemical reaction caused by pulverization. Furthermore, for example, the object of the present invention may be achieved by adding a compound such as an ester that generates the same organic compound as the surfactant used in this embodiment, for example, by a hydrolysis reaction. Two or more surfactants may be used in combination.

  The addition timing of the surfactant is not particularly limited and may be added at the time of dry coarse pulverization, may be added at the time of preparing the slurry for pulverization at the time of wet pulverization, or a part of it may be added at the time of dry coarse pulverization. The remainder may be added during wet pulverization. Or you may add by stirring etc. after wet grinding.

  After the wet grinding, the magnetic powder is dried. The drying temperature is preferably 80 to 150 ° C, more preferably 100 to 120 ° C. The drying time is preferably 60 to 600 minutes, more preferably 300 to 600 minutes.

  The average particle size of the magnetic powder particles after drying is preferably in the range of 0.03 to 0.7 μm, more preferably in the range of 0.1 to 0.5 μm. A surfactant is attached to the magnetic powder after drying. It is confirmed by thermogravimetric / differential thermal simultaneous analysis (TG-DTA) that the surfactant adheres to the magnetic powder after drying.

  The dried magnetic powder is kneaded with a binder resin, waxes, a lubricant, a plasticizer, a sublimation compound, etc., and formed into pellets with a pelletizer or the like. The kneading is performed with, for example, a kneader. As the pelletizer, for example, a monoaxial or biaxial extruder is used.

  As the binder resin, a polymer compound such as a thermoplastic resin is used, and as the thermoplastic resin, for example, polyethylene, polypropylene, ethylene vinyl acetate copolymer, atactic polypropylene, acrylic polymer, polystyrene, polyacetal, or the like is used.

  As waxes, synthetic waxes such as paraffin wax, urethanized wax, and polyethylene glycol are used in addition to natural waxes such as carnauba wax, montan wax, and beeswax.

  As the lubricant, for example, a fatty acid ester is used, and as the plasticizer, a phthalic acid ester is used.

  The addition amount of the binder resin is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the magnetic powder, the addition amount of waxes is preferably 5 to 20 parts by weight, and the addition amount of the lubricant is preferably 0.00. 1 to 5 parts by weight. The addition amount of the plasticizer is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

  In the present embodiment, such a pellet 10 is injection molded into the mold apparatus 8 using the magnetic field injection molding apparatus 2 shown in FIG. Prior to injection into the mold apparatus 8, the mold apparatus 8 is closed, a cavity 12 is formed therein, and a magnetic field is applied to the mold apparatus 8. The pellet 10 is heated and melted to 160 to 230 ° C., for example, inside the extruder 6 and injected into the cavity 12 of the mold apparatus 8 by a screw. The temperature of the mold apparatus 8 is 20 to 80 ° C. The applied magnetic field to the mold apparatus 8 may be about 5 to 15 kOe.

  After completion of the injection molding, the mold apparatus 8 is opened, and the pre-fired preform corresponding to the shape of the cavity 12 is taken out. Thereafter, the preform having a shape corresponding to the cavity 12 is subjected to binder removal processing.

  The binder removal treatment is a heat treatment at a temperature of 130 to 600 ° C. in the air or nitrogen. Next, in the sintering step, the formed body is sintered, for example, in the atmosphere, preferably at a temperature of 1100 to 1250 ° C., more preferably at a temperature of 1160 to 1220 ° C. for about 0.2 to 3 hours to obtain an anisotropic ferrite magnet. .

  In the method of the present embodiment, the magnetic powder uniformly disperses and flows in the mold corresponding to the magnetic field, and the magnetic field orientation along the direction of the magnetic field lines is favorably performed. That is, in the method of the present embodiment, unlike the conventional wet molding method, pressure that disturbs magnetic field orientation does not act, so the degree of orientation is improved.

  Therefore, the degree of orientation of the finally obtained sintered magnet is improved. The degree of orientation of the magnet is a ratio (Ir / Is) of residual magnetization (Ir) to saturation magnetization (Is). The degree of orientation of the magnet is proportional to the degree of magnetic field orientation of the magnetic powder in the preform after the magnetic field injection molding.

  Further, in the method of this embodiment, since the preform is formed with the binder resin interposed between the magnetic powder particles, a preform with the magnetic powder uniformly dispersed can be obtained, and the preform is fired. The magnetic properties of the sintered magnet obtained in this way become uniform.

  Furthermore, in the method of the present embodiment, during injection molding, a molten binder resin is used as a conveyance medium, thereby preventing aggregation between magnetic powder particles and preventing adhesion of particles to the conveyance path contact surface. The powder can be conveyed into the mold.

  In addition, when the magnetic powder is oriented by a magnetic field in the mold apparatus 8 shown in FIG. Therefore, in the method of this embodiment, it is possible to uniformly fill the narrow cavities 12 with magnetic powder, and the time required for one shot is short and the productivity is excellent. Moreover, in the method of the present embodiment, the flow path for removing the transport medium is not clogged, and problems such as deaeration processing do not occur. As a result, a relatively thin sintered magnet can be manufactured with high productivity.

  Furthermore, in the method of this embodiment, the magnetic powder obtained as the final product of the pulverization step is dispersed in a solvent for wet pulverization, so that the aggregation of the powder particles is loosened and the solvent is interposed between the particles. In this state, by attaching the surfactant to the magnetic powder, even if the dried magnetic powder is re-aggregated, the surfactant is sandwiched between the magnetic powder particles. Therefore, the re-agglomerated granules (aggregate of magnetic powder particles) are easily decomposed into magnetic powder particles in a subsequent process (kneading / molding).

  The pre-fired preform obtained by the method of the present embodiment is obtained by defining the shape of the inner peripheral surface of the cavity 12 of the device 2 shown in FIG. 3, and as shown in FIG. It has an arc shape (C shape) divided in the circumferential direction, and has an arc-shaped outer peripheral surface 22 and an inner peripheral surface 24 corresponding to the outer peripheral surface 22. As shown in FIG. 2, the outer peripheral surface 22 and the inner peripheral surface 24 are circular arc surfaces having different radii of curvature R1 and R2 with respect to a common central axis O. A value obtained by subtracting the curvature radius R1 by the curvature radius R2 is the thickness of the molded body 20 in the main portion radial direction.

  In the present embodiment, shaft end surfaces 26 are respectively formed at both ends along the central axis O of the preform 20. Moreover, the circumferential direction edge part 28 is formed in the both ends along the circumferential direction of the preform 20.

  In the present embodiment, the intersecting portion 30 where the outer circumferential surface 22 and the shaft end surface 26 intersect each other includes the first tapered surface 32 adjacent to the shaft end surface 26 and the outer circumferential surface between the first tapered surface 32 and the outer circumferential surface 22. 22 and a second tapered surface 34 adjacent to each other.

  In the present embodiment, the second angle θ2 of the second tapered surface 34 with respect to the reference line 22a of the outer peripheral surface 22 is smaller than the first angle θ1 of the first tapered surface 32 with respect to the reference line 22a of the outer peripheral surface 22. The reference line of the outer peripheral surface is a line included in the design surface of the outer peripheral surface 22, and is a line parallel to the central axis O in the present embodiment, and is substantially orthogonal to the end surface 26.

  The first angle θ1 is preferably 30 to 60 degrees, and the second angle θ2 is preferably 20 degrees or more smaller than the first angle. Preferably, the length L1 of the first tapered surface 32 along the reference line 22a is 1/2 to 1/10 times the length L2 of the second tapered surface 34 along the reference line 22a. It is the length of (L1 / L2). The total length L3 of the tapered surfaces 32 and 34, that is, the length L3 along the reference line 22a of the intersection 30 is 1/16 to 1/5 of the total length L0 along the reference line 22a of the molded body 20. Is preferred.

  In the present embodiment, two tapered surfaces 32 and 34 are formed at the intersecting portion 30, but three or more tapers are formed by forming a third tapered surface between these tapered surfaces. A surface may be formed.

  In the pre-fired preform 20 according to the present embodiment, at least two stages of tapered surfaces are formed at the intersection 30 between the outer peripheral surface 22 and the shaft end surface 26. For this reason, even if CIM molding is performed by the apparatus shown in FIG. 3 and then fired, as shown by the dotted line in FIG. The desired dimensional accuracy can be maintained without secondary processing. The desired dimensional accuracy means that the maximum difference Δh of the unevenness on the outer peripheral surface 22 is 0.05 mm or less, preferably 0.025 mm or less.

  In the conventional preform having a single tapered surface, as shown in FIG. 6, as shown in FIG. The following points can be considered. Ferrite magnet materials have nearly double the reduction ratio in the C-axis direction and the direction perpendicular to the C-axis. In CIM molding, because of the fluidity of the material at the time of injection into a mold and injection molding while applying a magnetic field, the orientation direction of the magnet particles is along the tapered surface from the outer peripheral surface at the intersection 30. Change suddenly. For this reason, when the preform is fired, it is considered that the convex portion 30a is greatly deformed to the outside due to the influence of the difference in shrinkage ratio and protrudes more greatly than the outer surface.

  In this embodiment, as shown in FIG. 2, since at least two stages of tapered surfaces 32 and 34 are formed at the stage of the molded body 20 before firing, even if CIM molding is performed, the orientation of the magnet particles The direction changes slowly in at least two steps. Therefore, in the intersection part 30, the convex part 30a is hardly formed even after baking, or even if it is formed, it is quite small. According to experiments by the present inventors, it was confirmed that when the preform 20 having at least two stages of tapered surfaces is fired, the maximum unevenness difference on the outer surface can be made 0.01 mm or less. On the other hand, in the conventional preform with a single tapered surface formed, the protruding portion 30a protruding from the outer surface is detected, and the maximum Δh of the unevenness difference on the outer surface becomes larger than 0.075 mm, It has been confirmed that there is a need to process and remove the portion 30a.

  The sintered magnet according to the present embodiment is a sintered magnet obtained by firing the pre-fired preform 20 described above. Therefore, the sintered magnet obtained by firing the molded body 20 of the present embodiment can be suitably attached to the inside of the motor casing 70, for example, as shown in FIG.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, in the embodiment described above, a single tapered surface is formed at the intersection 40 between the inner peripheral surface 24 and the end surface 26, but a tapered surface having two or more stages similar to the intersection 30 is formed. May be. In the present invention, the two tapered surfaces 32 and 34 that are close to each other do not necessarily need to directly intersect with each other, and these tapered surfaces 32 and 34 may be connected by curved surfaces. Further, the circumferential end portion 28 may be formed with two or more tapered surfaces similar to the intersecting portion 30.

  Further, the pre-fired preform in the present invention is not limited to the shape shown in FIG. 1, and may be a leaf-shaped preform 20 a shown in FIG. 5 or other shapes. In a molded body formed by magnetic field injection molding, when a single tapered surface is formed at the intersection between the outer peripheral surface and the shaft end surface, a protruding portion that protrudes from the outer peripheral surface is likely to be formed. Therefore, in the present invention, it is particularly effective to form a tapered surface having two or more steps as described above at the intersection between the outer peripheral surface and the shaft end surface.

20, 20a ... Pre-fired preform 22 ... Outer peripheral surface 24 ... Inner peripheral surface 26 ... Shaft end surface 30 ... Intersection 30a ... Convex part 32 ... First tapered surface 34 ... Second tapered surface

Claims (6)

A pre-fired preform for producing a sintered magnet having an outer surface and an end surface intersecting the outer surface,
The pre-fired preform is obtained by melting a raw material containing magnetic powder and a binder resin, and injection-molding in a mold cavity to which a magnetic field is applied,
A first tapered surface formed adjacent to the end surface and a second tapered surface formed between the first tapered surface and the outer surface are formed at a portion where the outer surface and the end surface intersect. A pre-fired preform.   The pre-fired preform according to claim 1, further comprising an inner surface corresponding to the outer surface, wherein the outer surface and the inner surface are circular arc surfaces having different radii of curvature with respect to a common central axis.   3. The pre-fired preform according to claim 1, wherein a second angle of the second tapered surface with respect to the reference line of the outer surface is smaller than a first angle of the first tapered surface with respect to the reference line of the outer surface. body.   The pre-fired preform according to claim 3, wherein the first angle is 30 to 60 degrees, and the second angle is 20 degrees or more smaller than the first angle.   The length of the first tapered surface along the reference line is ½ times to 1/10 times the length of the second tapered surface along the reference line. The preform before baking of Claim 3 or 4.   The sintered compact magnet obtained by baking the preform before baking in any one of Claims 1-5.

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