Cast iron nodularity without breaking the part.
The QSV DL measures the ultrasonic propagation velocity in the part; from that velocity, you classify the type of cast iron — grey or ductile — and estimate the percentage of nodularity, with no destructive test.
The QSV DL doesn't give a percentage of nodularity directly: it measures the ultrasonic propagation velocity in the part.
You're the one who classifies the type of cast iron and estimates nodularity, by comparing that velocity against your own reference sample of known nodularity — no universal, reliable table exists for this: the manufacturer's own manual warns that velocities published in generic tables can vary significantly from the real value.
Propagation velocity, not thickness.
The QSV DL emits an ultrasonic pulse that travels through the part and bounces off the opposite face, just like an ultrasonic thickness gauge — but it works the calculation backwards: from an already-known thickness (entered by hand or from a digital calliper) and the time the pulse takes to travel there and back, it calculates the sound's actual propagation velocity in that material.
That velocity varies with the material's microstructure: in cast iron, it relates to the type of graphite — flake graphite in grey iron, spheroidal graphite in ductile iron — and to the percentage of nodularity. The same principle lets you classify and separate materials by propagation velocity when their external appearance alone isn't enough to tell them apart.
With your own reference sample, not a table.
The manufacturer's manual is explicit on this point: "in every case, the best result is obtained by measuring a reference sample made of the material you want to measure." That sample must be flat, with a smooth surface, and a thickness equal to the largest value you'll measure on the real part — and its nodularity must already be known, typically through metallography.
Heat treatment changes the velocity
The manual warns that "heat treatments can significantly affect the propagation velocity." If the reference sample and the part under test haven't had the same heat treatment, the comparison is no longer valid.
So does the testing temperature
Temperature variations change a material's propagation velocity. The manual requires calibrating on site, with the reference sample at the same temperature as the real part, to avoid introducing that error.
As a starting reference, not an exact table.
Evident Scientific (formerly Olympus, a reference manufacturer in non-destructive testing) publishes these longitudinal velocity values as general guidance — and gives the same warning as the DEMEQ manual: "exact velocities for your application will vary based on alloy composition, grain structure, and other process variables," and recommends always verifying them against calibration standards made from the real material.
| Material | Indicative velocity |
|---|---|
| Grey iron | ≈ 4,800 m/s |
| Ductile (nodular) iron | ≈ 5,600 m/s |
| Pure iron (reference) | ≈ 5,900 m/s |
Source: Evident Scientific, "Measuring Nodularity in Cast Iron Using Ultrasonic Testing". Use these only as a starting point to sense-check a reading — calibrating with your own reference sample is still essential.
QSV DL measuring range.
| Parameter | Value |
|---|---|
| Measurable part thickness | 1 – 500 mm |
| Velocity range | 100 – 19,999 m/s |
| Instrument operating temperature | -10 °C to +50 °C |
| Reference standard | ASTM E797 |
What usually goes wrong, and why.
Trusting a generic table instead of calibrating
The manufacturer itself warns that velocities published in material tables can differ considerably from your part's real velocity. Without your own reference sample, the classification loses reliability.
The "doubling" effect
Below the transducer's minimum thickness — or at greater thicknesses if the transducer is worn — the instrument can display a velocity that is exactly half the real one. The manual recommends checking against samples of known thickness across the whole working range before trusting a new reading.
Not repeating zero calibration when changing transducers
The delay changes between transducers. Switching transducers without recalibrating zero introduces an error that carries through the entire series of measurements.
Comparing parts at different temperatures
Calibrating with the reference sample at one temperature and measuring the real part at another introduces an error the instrument can't correct on its own.
It's a tool for fast, non-destructive classification and screening. The manufacturer's own manual insists on calibrating with your own reference sample and on operator training as conditions for reliable results — it never presents this as a substitute for a certified metallographic test.
What do you need to classify?
Tell us which cast iron or materials you need to tell apart. We'll confirm the instrument and accessories that fit.
