What is cavitation?
Cavitation is the formation and violent collapse of vapour bubbles in a liquid under rapid pressure change. In an ultrasonic cleaning bath it is the actual cleaning mechanism: each collapsing bubble produces a microscopic jet that removes soil from the surface it strikes.
In an ultrasonic tank the sound wave alternately pulls the liquid apart and pushes it together. During the low-pressure half-cycle the liquid cannot hold together and cavities form; during the high-pressure half they implode, briefly generating extreme local temperature and pressure in a volume smaller than a grain of dust.
Cavitation intensity is destroyed by three things: dissolved gas, foam, and cold liquid. Fresh water carries dissolved air that cushions the collapse, which is why a new bath must be degassed by running it empty for 10–20 minutes. Foam does the same thing permanently, which is why foaming cleaners are useless in ultrasonics.
Cavitation is also destructive if unmanaged. Left too long, it erodes soft aluminium, removes plating and dulls polished faces. Cycle time should be validated on scrap parts rather than assumed.
