Short answer
- A real inspection mixes large and small parts, castings, forgings and welds. No single portable hardness method works for all of them.
- The most common mistakes: measuring by Leeb a part without enough mass, ignoring the impact direction, measuring on a surface the device can't handle and converting to a scale the material doesn't allow.
- They are avoided by choosing the method and device for each part, correcting the impact direction and checking on a reference block.
Leeb for large parts, UCI for small parts and welds, and the impact direction corrected automatically. A mixed inspection, with a single hardness tester.
Problem 1: the part is too small or thin for Leeb
The symptom: on small parts, sheet or welds, Leeb readings come out low and widely scattered.
Why it happens: Leeb measures the rebound of an impact body. If the part is light or thin, it moves or vibrates with the impact and absorbs part of the energy, and the rebound is lower than its hardness would give.
How it is solved: for the D device, the usual one, the manufacturer requires a part of at least 5 kg unsupported, 2 kg on a rigid support, or 0.1 kg and 3 mm thick if coupled with paste to a solid base. Below that, the right method is UCI, which depends far less on mass: around 0.3 kg and 5 mm of thickness are enough (detailed in the guide Leeb or UCI).
With the QH7 C: you switch from the Leeb device to the UCI probe on the same instrument and keep measuring, without carrying a second tester.
Problem 2: the reading changes with the firing direction
The symptom: the same part gives different values when measuring downwards, on a vertical wall or under a beam.
Why it happens: in Leeb, gravity speeds up or slows down the impact body depending on the firing direction. If the instrument doesn't know which direction it was fired in, it applies the wrong correction.
How it is solved: by telling the tester the impact direction every time the position changes. It is easy to forget on large parts or structures, where you measure in every direction.
With the QH7: its impact devices carry GyroTag, which detects their own orientation, and the instrument corrects the direction automatically on every shot. The error disappears and measuring is faster.
Problem 3: the surface isn't prepared
The symptom: low or erratic readings on cast, forged or scaled parts.
Why it happens: on a rough surface, the impact or tip sits on peaks and valleys, not on sound material. Each device accepts a maximum roughness:
| Device | Maximum roughness (Ra) | Use |
|---|---|---|
| C | 0.4 µm | Treated surfaces and small parts |
| D, DC, DL, E | 2 µm | General purpose |
| G | 7 µm | Rough, cast and forged parts |
How it is solved: by preparing the spot (local grinding) to the device's roughness, or using one that accepts more: the G is designed precisely for unmachined castings and forgings. With UCI, the limit depends on the probe load: up to Ra 5 µm with the 10 N probe and up to 15 µm with the 50 N one.
With the QH7: it accepts every impact device, from C to G, and every UCI probe, so you choose the right one for each surface without changing instrument.
Problem 4: the specification asks for a scale the material doesn't allow
The symptom: the drawing for a cast part asks for hardness in Rockwell C or Vickers, and the tester only gives Brinell for that material.
Why it happens: the Leeb value is converted with a different curve for each material, and not every scale is available for every material. For cast iron, conversion is usually only to Brinell.
How it is solved: by checking before the inspection which scales the material allows with the chosen device (the tables are in the hardness conversion guide), and agreeing the scale if it isn't available.
With the QH7: with the D device it also converts grey and ductile iron to Vickers and Rockwell C, and cast aluminium to Vickers. It is the only one in the line that does.
Problem 5: you need to deliver a traceable report
The symptom: readings written down by hand, with no date or position, that then have to be typed up.
How it is solved: by storing every reading on the instrument and transferring them to PC.
With the QH7: 32,000-reading memory, USB and also RS232 output —it is the only one in the line with RS232, useful for connecting to existing quality systems— and dmq DataCenter software, at no cost, to graph and generate the report.
How to plan a mixed inspection
- Classify the parts by mass, thickness and surface condition: that decides the method and device.
- Check the scale the specification requires for each material.
- Check the instrument on a reference block of known hardness, with each device or probe you will use.
- Measure at least three times at each point and use the mean, never on a previous indentation (see how to hold the device and probe).
- Store the readings with their identification for the report.
Which hardness tester solves each case
| Feature | QH7 | QH5 | QH5 U |
|---|---|---|---|
| Leeb | Yes (QH7 L and QH7 C) | Yes | No |
| UCI | Yes (QH7 U and QH7 C) | No | Yes |
| Both methods in one instrument | Yes (QH7 C) | No | No |
| Leeb impact devices | All: D, DC, DL, C, G and E | Depends on version | — |
| UCI probes | 10, 50 and 98 N | — | 10, 50 or 98 N |
| Automatic angle correction (GyroTag) | Yes | No | — |
| More scales for cast iron and aluminium | Yes | No | — |
| Data output | USB and RS232 | USB | USB |
If you only work with one type of part, the QH5 (Leeb) or QH5 U (UCI) is enough. If your inspection mixes parts, surfaces and scales, the QH7 solves every problem in this guide with a single instrument.
Sources: DEMEQ, QH5 and QH5 U hardness tester user manuals (mass, thickness and roughness by device and by probe), QH7 series brochure and QH family comparison table.
