Dosing an ultrasonic bath correctly

An ultrasonic bath cleans by cavitation — millions of microscopic bubbles imploding against the surface. But the bubbles only loosen the dirt; it is the cleaning concentrate that dissolves grease, oxides and particles and keeps them in the liquid. Water alone gives half the effect.

Underdosing means poor cleaning, longer run times — and with the wrong preparation, undosed water can attack the metal. Overdosing does not clean better: it wastes concentrate, and residue can be left on the parts.

The right percentage is not a matter of taste: it is on the preparation's label or data sheet, and varies with the application. Never dose by guesswork.

The amount to calculate with is the bath's working capacity — the liquid volume up to the fill mark in the tank. It is always less than the tank's total volume, and is stated in the bath's manual. A bath labelled "3 litres" may have a working capacity of about 2.7 — use the total volume in the calculation and you overdose every time.

Two practical tips: fill water first, then concentrate — that gives the right mix without a foam head. And let the bath degas for a few minutes after filling (run it without a load), so the ultrasound works at full effect from the first part.

The working solution is a consumable. Change it when it is visibly dirty, when cleaning performance drops, or when a film of grease or particles sits on the surface — the bubbles must pass through the surface, and a grease film dampens the effect in the whole bath. In hard use that can mean daily; in light workshop use the liquid lasts longer.

Remember too that the preparation must match the job: a universal cleaner for general work, acidic preparations for oxides and scale, alkaline ones for heavy oil and soot. Never use flammable liquids in an ultrasonic bath, and check that the preparation is approved for the material — aluminium and light alloys do not tolerate everything.