| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-cost, reliable and high-quality dummy disk for a hard disk drive, instead of the use of a recording medium defective product, supply amount of which is reduced by increasing its yield, or a costly recording medium middle product as a dummy medium. SOLUTION: Even when a dummy medium 7 and a spacer ring 6 are formed to be united, the differences of inertial moment and weight with a conventional product 8, and the difference of thermal expansion rate with a recording medium 15 are suppressed within a fixed range, a disk part 17 and the recording medium 15 are placed in parallel, the thickness of the disk part 17 is uniform, the plane of the disk part 17 is precisely smooth, a sufficient strength is provided, the outer diameter of the disk part 17 is equal to or shorter than that of the recording medium 15, a dummy disk 18 having a thickness equal or thicker for a hard disk drive is manufactured.
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