Dizzy, et. al. -
Ultrasonic cleaning is used in many applications, including medical sterilization pre-cleaning, metal fabrication, jewelry, and optical/lens cleaning. My father was a dentist, and used one to prep. implants, partials, and crowns as well as for pre-cleaning his instruments (before putting them in the autoclave).
It might work on a bowling ball if you could get a unit big enough. I wouldn't be too worried about the core or cover cracking, as a bowling ball is subject to tremendous amounts of vibration and stress upon impact with the pins. I think it would be tough to get such a cleaning unit to a resonance frequency at a high enough amplitude so as to cause damage to the ball.
My $0.02 worth.
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Dan
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Engineering * Bowling = a fun and practical application of rotational kinematics.
Bowling Nerd Herd (TM) Member