| 摘要 |
A first carbon brush which comprises a graphite powder as a filler having a particle diameter distribution curve as determined by the laser diffraction method wherein an integrated value for the number of graphite particles having a particle diameter of 5 mum or less accounts for 10 % or less of the total particles, preferably 5 % or less; a second carbon brush which is the first carbon brush further wherein an integrated value for the number of graphite particles having a particle diameter of 100 mum or more accounts for 10 % or less; a third carbon brush which is the second carbon brush further wherein an integrated value for the number of graphite particles having a particle diameter of 10 to 40 mum accounts for 60 % or more; a forth carbon brush which is the third carbon brush further wherein an integrated value for the number of graphite particles having a particle diameter of 12 to 20 mum accounts for 40 % or more.
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