JP2007035786A - Radial orientation magnetic field forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radial orientation magnetic field forming apparatus capable of suppressing cogging torque during motor rotation while keeping high torque intact and of forming a highly reliable long annular bond magnet. <P>SOLUTION: The radial orientation magnetic field forming apparatus is configured such that a mixture 5 of magnetic powder and resin is filled between a central core rod 4B and annular dices 1 disposed around the core rod 4B, to form a magnetic field directed outward radially from the center of the dices 1 after passage through the core rod 4B, and in this state the mixture 5 is pressurized into a bond magnet. In the apparatus, the dices 1 are constructed by alternately arranging peripherally a dice piece 1A of a ferromagnetic material and a dice piece 1B of a non-magnetic material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radially oriented magnetic field forming apparatus for manufacturing a ring-shaped bonded magnet used in a spindle motor for information devices such as HDDs and DVDs and a vibration motor for mobile phones.

  The ring-shaped bonded magnet used for the above-described applications is required to have high magnetic performance, and an anisotropic bonded magnet is attracting attention as a high-performance magnet that can replace the conventional isotropic bonded magnet. An anisotropic bonded magnet is one in which the magnetic moments in the metal structure are uniformly aligned in a specific direction. In the case of a ring-shaped bonded magnet, a radially oriented magnetic field forming device is used around the mold. The magnetic moment of the magnetic powder is oriented in the radial direction by the magnetic field excited by the arranged electromagnet.

  FIG. 4 shows an example of a conventional radial orientation magnetic field forming apparatus. The molding die of the apparatus includes a ring-shaped die 1 made of a ferromagnetic material, an upper core rod 4A, a lower core rod 4B, and a cylindrical upper punch 2A and a lower punch 2B made of a nonmagnetic material. Above the dice 1, an air-core upper coil 3A is disposed surrounding the upper punch 2A, and an air-core lower coil 3B is also disposed surrounding the lower punch 2B. Until the upper coil 3A, the upper core rod 4A and the upper punch 2A are raised, the mixture 5 of the raw anisotropic magnetic powder and the thermosetting resin is filled in the die 1, and the upper core rod 4A is in contact with the lower core rod 4B. Lower. Thereafter, even if the upper punch 2A is lowered and the mixture 5 is kept at a slight pressure, the upper coil 3A is lowered directly above the die 1.

  Thereafter, a direct current is applied to the upper coil 3A and the lower coil 3B to form a magnetic field radially outward from the center of the die 1 through the core rod 4A as indicated by arrows in FIG. The anisotropic magnetic powder has its magnetic moment aligned with the radial magnetic field. Therefore, the pressurizing force of the upper and lower punches 2A and 2B is increased, and the mixture 5 is molded to a predetermined density to obtain a ring-shaped bond magnet. After direct current is applied for the required time, an AC decay current is supplied to the upper coil 3A and the lower coil 3B to demagnetize the molded body in the mold, and the upper core rod 4A, the upper punch 2A and the upper coil 3A are lifted and retracted, The molded body is detached from the mold.

  Here, FIG. 6 shows a plan view of the die 1, and the ring-shaped bonded magnet is radially oriented uniformly by 360 degrees by the DC magnetic flux (arrow in the figure) uniformly formed in the circumferential direction. The magnetic flux density pattern on the magnet surface after such a ring-shaped bonded magnet is multipolarized is a square wave as shown by line X in FIG.

In Patent Document 1, a radial orientation magnetic field in which nonmagnetic portions are formed at intervals in the circumferential direction by providing gaps that are recessed at a plurality of positions on the inner peripheral surface of a die that forms a ring-shaped forming space. A forming apparatus is shown.
JP 06-124822 A

  In the anisotropic ring-shaped bonded magnet manufactured by the conventional radial orientation magnetic field forming apparatus, since the magnetic powder is uniformly oriented around the entire circumference, the distribution of the magnetic flux density obtained after multi-pole magnetization is described above. As shown in FIG. For this reason, when used in a motor, a high torque can be obtained compared to an isotropic bonded magnet, but there is a problem that the cogging torque becomes excessive and causes abnormal noise and vibration of the motor. In the radial orientation, sufficient orientation is formed when the radial factor Fr = 2DH / d2 expressed by the outer diameter d of the core rods 4A and 4B, the inner diameter D of the die 1 and the molding height H is 1 or less. Therefore, the molding height H is limited so that Fr is 1 or less. For this reason, conventionally, when the required length of the bond magnet to be incorporated into the motor is increased, it is necessary to use a plurality of bond magnets in which the molding height H is lowered so that the Fr is 1 or less. There was a problem in reliability resulting from reliability, cost, and bonding accuracy.

  Therefore, the present invention solves such a problem, and maintains a high torque, suppresses cogging torque during motor rotation, and can form a long ring-shaped bonded magnet with high reliability. The purpose is to provide.

  As described above, the inventors have passed the magnetic lines of force radially from the center of the die over 360 ° in the present radial orientation magnetic field forming apparatus. However, when a ring-shaped bonded magnet is used for a motor, If the isotropic state can be maintained without orienting the boundary region between the pole and the pole, it is thought that the cogging torque can be prevented from being excessively suppressed by suppressing the square wave-like steep magnetic flux change of the magnetic flux density. At the same time, the magnetic lines of force passing in the radial direction of the die can be saved, and accordingly, the magnetic lines of force passing in the radial direction in the length direction of the bonded magnet can be increased, and the molding height H of the bonded magnet can be increased. I thought.

  Therefore, in the present invention, a mixture (5) of magnetic powder and resin is filled between the central core rod (4A, 4B) and the annular die (1) disposed around the central core rod (4A, 4B). The die (1) is shown in FIG. 1 in a radially oriented magnetic field molding apparatus that presses the mixture (5) and forms a bond magnet in a state where a magnetic field radially outward from the center of the die (1) is formed. Thus, the die pieces (1A) of the ferromagnetic material and the die pieces (1B) of the nonmagnetic material are alternately arranged in the circumferential direction.

  In the present invention, a ferromagnetic dice piece (1A) is provided at a position corresponding to the magnetic pole in accordance with the desired number of poles, and a non-magnetic dice piece (1B) is provided at a position corresponding to between the magnetic poles. 2), the magnetic field lines selectively flow only in the ferromagnetic die piece (1A) as shown in FIG. In this case, since the magnetic lines focused on the center of the die (1) from the upper and lower core rods (4A, 4B) do not pass through the non-magnetic die piece (1B), the magnetic lines passing through the die piece (1A) increase. . For this reason, the strength of the magnetic field of the magnetic pole part can be increased as compared with the conventional apparatus, and as a result, the molding height can be increased.

  Here, when the number of magnetic poles of the bonded magnet is n, the die piece (1A) of the ferromagnetic material is matched with the position of each magnetic pole of the bonded magnet, and 50% to 80% of the magnetic pole angle 360 / n °. It is good to provide in the angle range. A non-magnetic die piece (1B) is provided in the remaining angle range. In this case, the radial factor Fr is expressed by P · 2DH / d2. Here, the value of P is 0.5 to 0.8 because the ferromagnetic dice piece (1A) is provided at 50% to 80% of the angle between the magnetic poles as described above. When P <0.5, the molding height H of the bonded magnet can be increased, but the distribution of the surface magnetic flux density after magnetization becomes a narrow distribution at the pole center as shown by the line Y in FIG. Although it is low, the driving torque of the motor is also reduced. On the other hand, if P> 0.8, the molding height H cannot be increased so much that the effects of the present invention cannot be obtained. The ferromagnetic material is preferably a highly saturated magnetization ferromagnetic material such as pure iron or permendur, but is not limited thereto as long as it is a ferromagnetic material. The nonmagnetic material may be a normal nonmagnetic steel or nonmagnetic super steel.

  As described above, according to the radially oriented magnetic field forming apparatus of the present invention, it is possible to form a long ring-shaped bonded magnet with high reliability while suppressing cogging torque during motor rotation and maintaining high torque. .

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples shown in Table 1. In each Example and Comparative Example, anisotropic NdFeB-based magnetic powder and epoxy resin were mixed to produce a dry mixed powder having a magnetic powder weight ratio of 92 wt%. After drying, the particle size of the mixed powder was 32 mesh or less. The molding die was the same as that described in the prior art except for the dies described below. The die has four poles, the inner diameter is 23 mm, and the outer diameter of the core rod is 21 mm. In each embodiment, as shown in FIG. 1, the annular die 1 is formed by alternately arranging fan-shaped ferromagnetic die pieces 1A and non-magnetic die pieces 1B in the circumferential direction and joining them together. did. The angle range θ where the die pieces are provided is 50% to 80% (P value 0.5 to 0.8) of the 90 ° angle between the magnetic poles corresponding to the position of each magnetic pole. On the other hand, in each comparative example, the dies are all made of a ferromagnetic material, and therefore the P value is 1.

The mixed powder 5 (see FIG. 4) is filled into a space formed by the die 1, the upper and lower core rods 4A and 4B, and the upper and lower punches 2A and 2B, and the upper and lower coils 3A and 3B are closed when the upper punch 2A closes the space. A DC current of 100 A was applied to the substrate for 6 seconds, and then pressure was applied at 10 ton / cm 2. Then, an alternating magnetic field was applied to demagnetize and demold. This was heat-cured at 150 ° C., and after curing, a 1.5 mm square cube was cut out from the ring-shaped bonded magnet formed and hardened to examine the degree of orientation, and residual magnetizations Mx, My, Mz in the x, y, z directions were cut out. Sought. Here, assuming that Mx corresponds to the radial alignment direction, the degree of alignment is given by the following equation.
Degree of orientation (%) = 100 × Mx / (√ (Mx2 + My2 + Mz2))

  After magnetizing such a bonded magnet, it was incorporated into a motor having a 6-pole comb-like winding yoke, and the driving torque was measured.

  In Example 1 and Example 2 of Table 1, the P value of the radial orientation magnetic field forming apparatus was set to 0.72. In Example 1 in which the molding height H of the bonded magnet is 7 mm, a sufficiently large motor driving torque of 176 mN-m can be obtained. Under this condition, even if the molding height H is 13 mm (Example 2), the motor driving torque is maintained at a sufficient magnitude of 160 mN-m. Furthermore, when the P value is 0.55 as shown in Example 3, the motor driving torque is sufficiently large as 158 mN-m even if the molding height H is 18 mm. On the other hand, in the conventional apparatus having a P value of 1, as shown in Comparative Example 1, if the molding height H is 7 mm, a sufficient motor driving torque of 163 mN-m can be obtained. As in Comparative Example 3, when the molding height H is set to 13 mm and 18 mm, respectively, the motor driving torque is reduced to 110 mN-m and 80 mN-m, and sufficient torque cannot be maintained.

  In Examples 2 and 3 and Comparative Example 1, the motor drive torque is almost the same. In Comparative Example 1, the molding height is as low as 7 mm as described above, and the distribution of magnetic flux density is already present. As indicated by the line X in FIG. 3 described above, the cogging torque becomes excessive because of a square wave shape in the circumferential direction. On the other hand, in Examples 2 and 3 using dies in which ferromagnetic material dice pieces and non-magnetic material dice pieces are alternately arranged in the same manner as in Example 1, the distribution of magnetic flux density is the line Z in FIG. As shown in FIG. 5, since the magnetic pole does not rise steeply in the boundary region between the magnetized poles and becomes gentle, the cogging torque is suppressed to be small, and the generation of noise and vibration of the motor is prevented.

1 is a schematic horizontal sectional view of a radial alignment magnetic field forming device showing an embodiment of the present invention. It is a general | schematic horizontal sectional view which shows magnetic flux distribution of a radial orientation magnetic field shaping | molding apparatus. It is a graph which shows distribution of the surface magnetic flux density of the magnetized ring-shaped bond magnet. It is a general | schematic vertical sectional view of the conventional radial orientation magnetic field shaping | molding apparatus. It is a general | schematic vertical sectional view which shows magnetic flux distribution in a radial orientation magnetic field shaping apparatus. It is a general | schematic horizontal sectional view which shows magnetic flux distribution in a radial orientation magnetic field shaping apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Dice, 1A, 1B ... Die piece, 4A, 4B ... Core rod, 5 ... Mixture.

Claims (2)

Fill the mixture of magnetic powder and resin between the core rod in the center and the annular dies arranged around it, and pressurize the mixture in a state where a magnetic field radially outward from the die center is formed through the core rod. A radial alignment magnetic field forming apparatus for forming a bonded magnet in a radial alignment magnetic field forming apparatus, wherein the die is formed by alternately arranging ferromagnetic die pieces and nonmagnetic die pieces in the circumferential direction. 2. The number of magnetic poles of the bond magnet is n, and the die pieces of the ferromagnetic material are provided in an angle range of 50% to 80% of the magnetic pole angle 360 / n ° corresponding to the position of each magnetic pole of the bond magnet. The radial orientation magnetic field shaping apparatus described in 1.

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