Spindle motor and method for manufacturing the integrated rotary magnet yoke

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PROBLEM TO BE SOLVED : To improve dimensional accuracy markedly by fitting a driving magnet constituted of a cylindrical rare earth bonded magnet into the inside of a cylindrical yoke, and applying compressive stress to the inside of the driving magnet. SOLUTION : A cylindrical driving magnet 4 is disposed inside a cylindrical yoke 2 for heating. The driving magnet 4 expands to such a degree that its outer surface reaches the inner wall of the yoke 2 and, finally, is then attached to the inner wall of the yoke 2 by pressure. The driving magnet 4 and the yoke 2 forms a fitting interface S and are fitted into each other integrally. At this time, the driving magnet 4 is prevented from further expansion by restrain of the yoke 2, and compressive stress is applied to the inside of the driving magnet 4. The yoke 2 is formed out of steel, stainless steel, or the like, and the driving magnet 4 is constituted of a bonded magnet formed out of the mixture of rare earth magnet powder and resin. It is thus possible to significantly improve the dimensional accuracy of the driving magnet 4 and attain high-speed rotation of a spindle motor.