Process and parameters · 4 min read · Updated 2026-09-25
Rinsing and drying after ultrasonic cleaning
The wash lifts the soil; the rinse takes the wash off the part; the dryer takes the rinse off. Skip either and the part carries a film of detergent, or water in every blind hole. How each stage is done, from a bucket to a DT dryer tank.
Technical guide. Figures are taken from our own spec tables; for your process we confirm the settings with a cleaning trial.
A part lifted out of a cleaning bath is wet with cleaning solution, and that solution has the soil in it. Left to dry, it leaves a residue: a haze of detergent, a ring of redeposited oil, spots of dissolved minerals. For some jobs nobody minds. For anything that is painted, coated, bonded, welded, measured or assembled with seals, the residue is a defect. Rinsing and drying are the two stages that prevent it.
Rinsing
The rinse replaces the film of cleaning solution with a film of clean water. The physics is dilution: each rinse reduces the residue by the ratio of the film volume to the rinse volume, so a part carrying 5 ml of solution into 50 litres of water leaves the rinse with a film that is ten thousand times weaker. Two rinses in series do that twice.
How it is done, in order of effort:
- Dip rinse. A tank of clean water, warm, next to the wash. The part goes in for a minute, ideally with a little agitation. Adequate for parts that go on to machining or handling.
- Ultrasonic rinse. The same, with ultrasound. Cavitation flushes the film out of blind holes and threads, which a still dip does not. The second tank of an MT multi-tank line usually has transducers for this reason.
- Demineralised final rinse. Tap water leaves its minerals behind when it dries, the white spots on a black part. A last rinse in deionised or reverse-osmosis water, conductivity below about 20 µS/cm, leaves nothing. Required before painting, coating and optical or electronic assembly.
- Spray rinse. A hand lance or a spray station over the tank, for large parts or when a dip tank would be contaminated by carry-over too fast.
Rinse water warms to 40 to 60 °C; warm water drains faster and takes less energy to dry. A rust inhibitor in the last rinse protects bare steel between cleaning and the next process.
Drying
Water sits where the sound used to be: in blind holes, threads, bores and pockets. Drying is about moving air through those places at a temperature that evaporates the water without heating the part more than it can take.
- Drip and air. Tilt the basket, wait. Fine for open parts in a warm shop; useless for blind holes.
- Compressed air blow-off. Fast for a few parts, slow and noisy for a basket, and it moves water rather than removing it.
- Hot-air drying tank. The DT series: a stainless tank the size of the wash tank, a heating turbine that circulates air at 30 to 100 °C through the basket, a diamond lid that drains condensate out rather than back onto the parts. The DT-96 matches the ST-96 tank (600 × 400 × 400 mm), the DT-206 the ST-206 (750 × 550 × 500 mm), so one basket of those two sizes passes through wash, rinse and dry without repacking. A basket of steel parts dries in 5 to 15 minutes at 80 °C.
- Vacuum drying. For deep bores and parts that must not exceed 60 °C. A special, quoted per case.
What to specify
| Result required | Rinse | Dry |
|---|---|---|
| Handled or machined again | dip | drip |
| Clean and dry for storage | dip or ultrasonic | hot air |
| Before painting, powder coating, plating | ultrasonic plus demineralised | hot air |
| Before bonding, welding, optical assembly | ultrasonic plus demineralised | hot air, clean-room filtered where needed |
| Bare steel stored for days | as above plus inhibitor | hot air, promptly |
In a single-tank setup, the rinse is a second ST tank or a sink next to it and the dryer a DT of the same size, moved between by hoist. In an MT multi-tank line all three are stations under one carriage; the multi-tank article covers the layout. The MT-75 puts wash, rinse and dry for small parts in one frame.
Common faults
- White spots after drying: tap-water minerals. Demineralised final rinse.
- Streaks or a dull film: detergent carried over; the rinse tank is spent. Change it, and change it on a schedule tied to the wash.
- Flash rust on steel within an hour: wet steel in warm air. Inhibitor in the rinse, dry immediately, or both.
- Water in blind holes after the dryer: holes facing up in the basket. Turn the parts; see loading.
