Radial anisotropic cylinder type ferrite magnets and their manuf

Details Radial anisotropic cylinder type ferrite magnets and their manuf Radial anisotropic cylinder type ferrite magnets and their manuf

1994-01-18

1996-04-09

Picard, Leo P.

Electricity: magnetically operated switches, magnets, and electr

Magnets and electromagnets

Magnet structure or material

335296, 310156, H01F 100, H02K 2112

Patent

active

055065570

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to Sr ferrite and Ba ferrite compositions that are used in motors, etc., and in radial anisotropic cylinder type ferrite magnets compositions. This invention further concerns high performance radial anisotropic cylinder type ferrite magnets and their manufacturing methods to motors which do not require use of the usual segment magnets.


BACKGROUND ART

Conventional constructions of motors in which ferrite magnets are positioned in stators and rotors are shown in FIGS. 8, 9 and 10.
That is to say, the construction in FIG. 8 is an example of a motor utilizing a cylindrical ferrite magnet 1 on the stator side. The magnet is fastened to the inner circumference of the cylindrical yoke 2, and a rotor (not shown here) is placed in space 3 in the inner circumference side of the magnet. Usually, for a motor with such construction using a strong magnetic radial anisotropic ferrite magnet is difficult for the reasons explained later, and an isotropic cylinder type ferrite magnet 1 is utilized. As such, the motor has a relatively low output.
The construction shown in FIG. 9 is an example of a motor using a pair of segment magnets, 1a and 1b on the stator side. Each magnet is fastened to the inner circumference of the yoke 2, and a rotor (not shown) is positioned in the opposing space 3 on the inner circumference side where the magnetic pole system. Other motors use multiple segment magnets according to the number of magnetic poles. In such segment magnets, since it is possible to use a strong magnetic radial anisotropic ferrite magnet, they are used in relatively high output motors.
The construction shown in FIG. 10 is an example of a motor wherein a pair of segment magnets 1c and 1d are used on the rotor side. Each magnet is fastened to the outer circumference of the magnet support 5 and positioned within a stator (not shown) of the specified shape to configure a motor. Segment magnets 1c and 1d are ferrite magnets as shown in FIG. 9, and since they are strong magnetic radial anisotropic ferrite magnets, the motor produced has a relatively high output.
However, recently even for high output motors, from the point of view of simplification assembly (making the assembly operation more efficient) and preventing cogging, it has been sought to find a motor construction which positions radial anisotropic cylinder type ferrite magnets which have equivalent or better magnetic properties than the above stated radial anisotropic ferrite magnets.
As a method of manufacturing such radial anisotropic cylinder type ferrite magnets, raw material powder such as Sr ferrite pulverized powder and Ba ferrite pulverized powder with an average particle size of less than 2 micro meter are molded into a cylindrical form using the dry method under a magnetic field and sintered. Due to the shrinkage factors for the circumferential and radial direction differs in sintering, internal stress accumulates to cause easy cracking, preventing the implementation of this method.
To prevent cracking in the sintering process, it has been proposed to use a mixture of 50.about.80 wt % Sr ferrite pulverized powder with an average particle size less than 2 micro meter and 50.about.20 wt % Ba ferrite isotropic granulated powder with a particle size of 14.about.200 mesh in the presence of a magnetic field end to mold it using the dry method (Patent Bulletin Heisei 1-48643).
However, the magnetic characteristic of radial anisotropic cylinder shape ferrite magnets industrially sintered utilizing this method have upper limits of Br=3.4 kG, .sub.B H.sub.C =2.9 kG, and (BH)max=2.6 MGOe, and these are not enough to satisfy recent high performance demands.
That is to say, without the availability of radial anisotropic cylinder shape ferrite magnets with strong magnetic properties, which are indispensable to realization of sought after high power out-put motors, it is difficult to satisfy this demand.
As explained shove, for example, one body high performance radial anisotropic cylinder shape ferrite magnets consisting of Sr fe

REFERENCES:
patent: 4211195 (1980-07-01), Zechlin
patent: 4827173 (1989-05-01), Corbach
patent: 4877986 (1989-10-01), Shimizu
patent: 4992768 (1991-02-01), Mozis
patent: 5093595 (1992-03-01), Korbel

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