Cavitation erosion is rare, but it can occur in certain materials when they are placed in ultrasonic cleaners. Short cleaning cycles prevent this type of damage.
Ultrasonic cleaners work on the basis of cavitation. Gas bubbles form in the cleaning liquid due to alternating high and low pressure cycles, and as the bubbles on the low-pressure side of the cycle get too big to stay intact, they implode, releasing a microscopic but intense burst of high temperature and pressure gas at a very high velocity.
Typically these gas bubbles tend to form where surfaces are uneven—like at the inface between the part and a contaminant, and at cracks, crevices, and surface discontinuities. It’s one of the true benefits of ultrasonic cleaners; they effectively clean the tight spaces that other types of cleaning systems can’t reach.
Most ultrasonic cleaning cycle times are way too short to have a detrimental effect on the parts being cleaned. However, if certain types of parts are placed in ultrasonic cleaners and left there for too long, cavitation erosion will begin to occur.
Cavitation erosion is the displacement and removal of the base material. The process leaves behind pits in the surface of the part, caused by repeated explosions of the cavitation bubbles against the surface long after the cleaning process has been completed. Materials most rapidly affected by cavitation erosion are usually soft and not very resilient, like lead, aluminum, brass, and some plastics.
Cavitation erosion tends to show up in those very same places where cavitation bubbles form most frequently on a part during ultrasonic cleaning—sharp corners, cracks, crevices, and other surface discontinuities. Minute particles of the base material are literally ripped away due to the explosions. When cavitation erosion continues for a very long time, the pits created can eventually be seen by the naked eye.
Parts are perfectly safe in ultrasonic cleaners if we follow common cleaning practices and are mindful of the types of materials we place in them and how long they are left in. Cleaning tanks should occasionally be inspected on the interior surfaces at the transducers. If we find any pitting, we simply buff out the pitted area and restore it to a smooth surface.
By routinely inspecting our ultrasonic cleaners for cavitation erosion and repairing the tank surface at the first sign of attack, our units will last for a very long time.