Five minutes, a roll of kitchen foil, and you know whether your ultrasonic tank is telling the truth. The foil test is the industry's oldest field diagnostic — crude, cheap, and still the fastest way to see a sound field with your own eyes. Here is how to run it properly, read it honestly, and know when to escalate.
Standard household foil, a piece roughly the size of your tank's working cross-section, held vertically on a wire frame or weighted so it hangs in the middle of the working zone — not touching walls or floor.
Normal working bath — your chemistry, at working temperature, degassed. Testing in cold fresh water fails the test before the tank gets a vote.
Sixty seconds at full power (thin 40 kHz+ tanks may want less; heavy 25 kHz tanks will make their point quickly). Withdraw, rinse, hold it up to the light.
Uniform dense perforation and dimpling across the sheet: healthy field, argue with your chemistry instead (№5). Even but weak dimpling: energy is low everywhere — suspect dissolved air, cold bath, foaming chemistry, or genuine power loss. Clear dead zones: geography is information — a dead stripe over one transducer bank names its suspect; a dead top half in a deep tank is the depth-fade story from №8. Repeat monthly and keep the foils: a dated foil archive is the cheapest condition monitoring in industry.
It maps intensity, not adequacy — a foil-shredding tank can still fail your parts if chemistry or process is wrong, and delicate-duty tanks are not supposed to shred foil at all. It is a screen, not a certificate. For process-grade proof, cleaning trials on real parts with defined endpoints are the standard.
Where a quality system wants numbers instead of souvenirs, handheld cavitation meters — NIST-traceable probes that read cavitation intensity directly — turn the foil's picture into a logged value, repeatable at fixed positions and depths. The pairing works best together: foil maps the geography cheaply, the meter trends the intensity over months, and the two agree on when a transducer bank is genuinely fading. Published erosion work confirms the foil's honesty: perforation patterns track cavitation hot-spots faithfully, including the standing-wave stripes that betray a sweep left off.
A dated foil + meter audit across a customer's tank fleet — degradation caught before parts showed it.
To be created — add to case-study production listOn VarioSonic-driven machines the generator already knows what the foil approximates: live frequency, power delivery and fault states on the HMI, per generator. A drifting resonance or a sagging output channel shows up on the panel months before it shows up on parts — which turns the foil test into a pleasant confirmation instead of a discovery. If your current machine cannot tell you its own output, that is itself diagnostic information about the machine.
The classic upgrade from eyeball to evidence costs one kitchen scale: weigh the foil before and after, and the mass lost to perforation becomes a number you can trend month over month. Same foil brand, same immersion time, same position — and your archive turns from photographs into a graph. When the trend line bends, you book service before the parts ever notice.
A standard foil exposure at working temperature — long enough to map the field, short enough to run monthly without ceremony.Field diagnostic practice; pair with the archive-board method above.
Standard household aluminium foil, standard conditions, or the comparison is worthless — that is the whole discipline. Cut strips long enough to span the working depth, mount them on a wire frame or rigid holder so they hang flat without touching walls or basket, and place them at fixed grid positions you record on a tank sketch: centre, corners, and any position where parts have disappointed. Bath at operating temperature, freshly degassed, normal chemistry at normal concentration — test the machine as it actually runs, not a sanitised version. Expose every strip for the same fixed time; 60 seconds suits most industrial tanks (a violent low-frequency tank may want 30, a gentle high-frequency unit 2–3 minutes — pick once, then never vary it). Then read: even stipple and perforation across all positions is health; smooth untouched regions are dead zones worth naming; horizontal stripes are the standing-wave signature that says sweep is off or unserviceable; and one position dramatically weaker than its mirror image points at a transducer bank or generator channel.
Date every foil, note position, time, temperature and concentration on the sleeve, and file the set. The first audit is a baseline; the value compounds from the second onward, because the comparison is what converts "seems weaker" into "bank two's corner has lost attack since March." Quarterly suits most single-shift operations; monthly earns its keep on production-critical or multi-shift tanks.
Send the foil photo and your machine details — we diagnose remotely first, and quote repair or replacement honestly.