PURPOSE: To prevent the crack of a bonded magnet portion from occurring by providing a taper structure starting from the end of the magnet of a magnet roll in which a length-outer diameter ratio is at least 4 and in which a shaft portion of at least 1/4 of magnet length becomes gradually small toward the center.
CONSTITUTION: A taper processing which gradually becomes small toward the center 7 at the part of at least 1/4 from both ends of a magnet 2' is made in a shaft 3 of the magnet 2' of a magnet roll in which a length-outer diameter ratio is at least 4. A bonded magnet 2' is formed with a solid injection molding by a shaft inset using a compound of strong magnetic powder and high polymer resin. Therefore, the crack of the bonded magnet 2' is prevented from occurring.
HAGI CHITOSHI
KOIZUMI SATORU
SHIINA SHUICHI
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