| 摘要 |
PURPOSE:To reduce remarkably noises by cutting out required portions of a protective plate opposed to a fan built in an apparatus to form a plurality of concentric protective members and form a connecting member for these protective members at a predetermined angle to the direction perpendicular to the fan. CONSTITUTION:In a protective plate 5 are disposed in equal intervals connecting members 8 for interconnecting a plurality of thin concentric protective members 7, 7 circumferentially of the concentric member 7. And an angle theta made by radial lines l1, l2 connecting center O of an inscribed circle 9 and a circumscribed circle 10 of these connecting members 8 and points T1, T2 on the connecting members 8 is set to 120 deg.. Further, the angle theta is an angle (radian) made with the reference line passing the center O. Thus, when a fan is rotated and advances to any phase, it always cross the connecting member 8 at a certain distance from the center without crossing the member 8 at a time over the whole radius so that a shock force is small and thus a specified frequency sound produced by mutual action between the fan 3 and the protective plate 5 is reduced to attenuate noises.
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