ST or SF: when the bath needs its own filtration

Two of our series overlap between 200 and 400 litres and answer different questions. The ST series answers "how do I clean this part?"; the SF series answers "how do I clean this part all day, every day, without changing the bath every week?".

Side by side

	ST-206	SF-225	ST-300	SF-310	ST-400	SF-360
Tank volume	206 L	225 L	300 L	310 L	400 L	360 L
Tank inside (L × W × D)	750 × 550 × 500 mm	900 × 500 × 700 mm	900 × 600 × 560 mm	750 × 600 × 870 mm	1100 × 600 × 600 mm	1000 × 600 × 800 mm
Useful depth	260 mm (basket)	560 mm	260 mm (basket)	730 mm	260 mm (basket)	660 mm
Ultrasonic	2520 W, 42 transducers	2880 W, 48	3720 W, 62	3600 W, 60	5760 W, 96	4320 W, 72
Heating	6 kW, to 110 °C	6 kW, to 110 °C	8 kW	9 kW	10 kW	9 kW
Transducers	bonded to the tank	in a stainless box	bonded	box	bonded	box
Filtration	add-on loop	built in: pump, filter, buffer tank, skimmer, laminar flow	add-on	built in	add-on	built in
Basket load	100 kg	200 kg	125 kg	200 kg	150 kg	200 kg
Outside (L × W × H)	945 × 710 × 870 mm	1535 × 1215 × 1070 mm	1210 × 880 × 990 mm	1385 × 1385 × 1215 mm	1410 × 880 × 1030 mm	1635 × 1415 × 1170 mm

On the ST the useful depth is that of the standard basket, 260 mm on all three sizes, although the tank itself is 500 to 600 mm deep; a taller part needs a deeper basket or a deeper tank. The SF tanks are deeper for their volume and considerably bigger on the outside, because the buffer tank, the pump and the filter housing stand beside the cleaning tank in the same frame. The transducers sit in a sealed box rather than under the floor, which leaves the floor free for the circulation to sweep and lets the box be lifted out for service without draining.

What the SF loop does

Liquid is drawn from the surface overflow and from the floor.
It passes a bag or cartridge filter that takes out chips, grit and carbon flakes.
It rests in the buffer tank, where free oil separates and a skimmer takes it off.
It returns to the cleaning tank as a laminar sheet across the surface, pushing floating oil and foam to the overflow, so the part leaves the bath through clean liquid.

The loop runs between cycles and during them. The result is a bath that stays at working strength for weeks on oily, chip-laden work instead of days, and parts that do not pick up a film on the way out. The filtration article covers why that matters.

Choose the ST when

The parts are lightly soiled or the soil is dry: dust, polishing compound, light oil.
The tank runs a few batches a day, and a weekly bath change is acceptable.
The floor space is tight: the ST-206 takes about a third of the floor area of the SF-225.
The process is hot soaking and carbon, where the chemistry, not the particle load, ends the bath.
A loop might be wanted later. A stand-alone filtration unit can be added to any ST tank.

Choose the SF when

Machining swarf, coolant or grinding fines come in every batch.
Oily parts go through all day and the bath must not lay a film back on them.
The bath change is a cost: 300 litres of heated solution and its disposal, every week, is what the SF saves.
The parts must leave through a clean surface: before coating, before assembly, before inspection.
The transducers must be serviceable without draining, or side-mounted for a deep load.

In numbers

An unfiltered 300-litre bath on oily machined parts lasts three to five working days; the same bath in an SF-310 with the skimmer running lasts three to five weeks. At one change a week versus one a month, the SF saves around forty bath changes a year, each one 300 litres of water, the heat to warm it, the cleaner concentrate and the disposal of an oily alkaline waste. Whether that pays for the difference in price is a calculation for your shop; the running-costs article has the inputs.

And above that

Beyond 400 litres, or when a lift is needed, the choice moves to the AL series, where modular filtration and laminar flow are options on every size, and to the AU series for tanks up to 8000 litres. The lift systems article takes it from there.