Process and parameters · 4 min read · Updated 2026-09-26
Cleaning liquids for ultrasonic cleaning
Water with a detergent does most jobs. Which chemistry for oil, carbon, oxide and flux, what never goes in the tank, and why concentration and temperature matter as much as the product.
Technical guide. Figures are taken from our own spec tables; for your process we confirm the settings with a cleaning trial.
Plain water cavitates, and for dust on glass it is almost enough. For everything else the liquid does half the work. The ultrasound breaks the soil loose and carries fresh liquid to the surface; the chemistry dissolves, emulsifies or lifts what the bubbles have loosened, and keeps it from landing back on the part. A good liquid also lowers the surface tension, which makes cavitation start more easily and reach further into fine detail. Choosing it comes down to three questions: what is the soil, what is the part made of, and what happens to the part next.
Match the chemistry to the soil
| Soil | Chemistry | Typical concentration | Temperature |
|---|---|---|---|
| Light oil, coolant, fingerprints | mild alkaline or neutral detergent | 2 to 3 % | 45 to 55 °C |
| Heavy grease, sludge, waxes | alkaline degreaser | 3 to 5 % | 60 to 70 °C |
| Carbon, varnish, baked oil | heavy-duty alkaline carbon remover | 5 to 10 % | 65 to 75 °C |
| Rust, scale, oxide | acidic or chelating deruster | 5 to 15 % | 40 to 60 °C |
| Rosin and no-clean flux | flux remover or saponifier | 3 to 10 % | 45 to 55 °C |
| Protein and biological soil | enzymatic cleaner | per maker | 35 to 45 °C |
| Polishing paste, buffing compound | alkaline cleaner with emulsifier | 3 to 5 % | 55 to 65 °C |
The detailed articles are oil and grease, carbon, rust and scale and flux.
Match the chemistry to the material
- Steel, cast iron, stainless: tolerate the full alkaline range. Bare steel needs a corrosion inhibitor in the bath or the rinse.
- Aluminium and zinc die castings: strong alkali etches them grey within minutes. Use a cleaner the maker rates for light alloys, usually pH 9 to 11 with inhibitors, and keep the temperature and the time down.
- Brass and copper: tarnish in strong alkali and in ammonia. Neutral or mildly alkaline cleaners.
- Anodised, painted, plated parts: mild and short, at 40 kHz.
- Plastics and rubber: below their softening temperature; some swell in solvent-based cleaners.
- Glass and ceramics: almost anything, but thermal shock from a hot bath can crack thick glass.
The data sheet of any cleaner lists the materials it is rated for; if your material is not on it, test one part.
Match the chemistry to the tank
Our tanks are AISI 304 stainless steel. Alkaline, neutral and enzymatic aqueous cleaners at working temperatures are fine. Acids and anything containing chloride are not: they pit 304 stainless from under the deposits on the floor. Use them only in a beaker or an insert tank, or order the tank in AISI 316; see tank material and direct and indirect cleaning.
Never put flammable solvents such as petrol, thinners, acetone or white spirit into an open heated ultrasonic tank. The ultrasound turns the surface into mist and the heater is an ignition source. Solvent work is done cold, in a closed beaker, in a ventilated area, and only with a solvent whose data sheet permits ultrasonic use.
Concentration and temperature
More is not better. Above the maker's recommended concentration most cleaners gain little, leave more residue and cost more to rinse off. Below it, the bath is spent sooner and cleans slowly. Check the concentration weekly with the supplier's titration kit and top up with solution at working strength, not with water alone; the filtration and bath life article explains why.
Temperature drives the chemistry faster, but cavitation weakens above about 70 to 80 °C in water. Most cleaning runs between 45 and 65 °C; see choosing the temperature.
Water quality
Hard tap water leaves lime scale in the tank and white spots on the parts, and it consumes some of the cleaner. For the wash, ordinary tap water is usually fine. For the final rinse of parts that are painted, coated or assembled, use demineralised water; see rinsing and drying.
Environment and disposal
Water-based, biodegradable cleaners are the standard for good reason: they are safer to handle and easier to dispose of. The spent bath is another matter: once it carries oil, metal fines or dissolved metals it is an industrial waste stream in most of the EU and goes to a licensed collector, not to the drain. Filtration and an oil skimmer cut its volume sharply.
