Process and parameters · 2 min read · Updated 2026-09-25
28 kHz or 40 kHz: which frequency cleans your part?
Lower frequency hits harder, higher frequency reaches further. The part, the soil and the surface decide.
Technical guide. Figures are taken from our own spec tables; for your process we confirm the settings with a cleaning trial.
What the frequency does
Ultrasonic cleaning works by cavitation: the sound field tears microscopic vacuum bubbles into the liquid and collapses them against the part, thousands of times a second. The frequency sets the bubble size. At 28 kHz the bubbles are larger and each collapse releases more energy; at 40 kHz they are smaller, there are more of them, and they form in narrower gaps.
When 28 kHz is right
Heavy, adherent soil on robust parts: baked-on carbon on engine parts, grease on castings and gearbox housings, polishing paste on steel. Larger parts with simple geometry get the fastest result at 28 kHz. It is also more audible, so the tank should stand where the noise does not matter or a lid stays closed.
When 40 kHz is right
Fine features and delicate surfaces: threads, small bores, cooling channels, machined faces, polished or anodised aluminium, electronics and optics. The smaller bubbles reach where the larger ones cannot, and the gentler collapse keeps erosion on soft metals low. Most Sonixtek industrial tanks are built for either frequency at order; benchtop STS units run at 40 kHz.
Power density matters as much
Frequency alone does not clean. Our industrial tanks run around 15 W of ultrasonic power per litre: the ST-96 has 1440 W in 96 litres, the AL-75 has 1200 W in 75. Too little and the bath is slow; much more and delicate surfaces erode. Sweep, standard on every industrial tank, keeps the field moving so no zone in the basket is starved.
If you need both
A shop that cleans castings in the morning and injectors in the afternoon has two honest options: a dual-frequency machine such as the UMX Pro, which switches between 28 and 40 kHz, or two tanks in a line, which is also how a multi-tank installation is usually laid out. Send us a sample and we will run it at both.
