Automatic balancing device and manufacturing method therefor

摘要

An automatic balancing device includes a hollow housing case body rotated with a rotary body and having an annular space formed inside of the hollow housing case body. A plurality of balance balls are accommodated in the annular space of the hollow housing case body in a freely movable manner so as to cancel an imbalance of the rotary body. A film of a volatile rust preventing agent is formed on a surface of the plurality of balance balls.