1. How big is the indentation on the surface of the workpiece to be tested?
Corresponding relationship between hardness value (HV), test force F (N) and indentation depth h (μm)：
h=0.062*√F/HV (GB/T34205-2017)
|
10N |
20N |
50N |
|
|
300HV |
11.3 |
16 |
25.3 |
|
600HV |
8.0 |
11.3 |
17.9 |
|
800HV |
6.9 |
9.8 |
15.5 |
Corresponding relationship between hardness value (HV), test force F (N) and indentation diagonal arithmetic mean value d (μm)：
HV≈0.1891*F/d²
|
10N |
20N |
50N |
|
|
300HV |
79.4 |
112.3 |
177.5 |
|
600HV |
56.1 |
79.4 |
125.5 |
|
800HV |
48.6 |
68.8 |
108.7 |
2. What are the requirements for the roughness of the surface to be measured?
The ultrasonic hardness tester has requirements on the surface roughness of the workpiece, especially when the loading force is small, the impact is more obvious. If the workpiece is too rough, the measured value will be low, or even no value. In this case, an abrasive material can be selected to improve the surface roughness of the workpiece and re-measure. The surface of the workpiece should also be clean without oil and rust.
Maximum allowable surface roughness Ra of the workpiece：
|
Test Force |
Maximum surface roughness Ra（μm） |
|
10N |
0.5 |
|
50N |
0.8 |
3. What occasions are probes with different loading forces suitable for?
The loading force of the probe depends on the hardness of the sample, the surface roughness and the thickness of the coating (plating) layer and the surface hardening layer.
Typical usage scenarios for loading force
|
Loading Force |
Typical usage scenarios |
|
10N |
Lon nitride layer of stamping dies, forgings. |
|
20N |
Flanges, gears, stamping parts, dies, crankshafts, turbine rotors, etc. |
|
50N |
Induction hardened layer and carburized layer of machine tool parts, such as camshafts, turbines, welds and heat affected zones. |
4. What is the smallest size of the workpiece that can be measured?
The thickness of the workpiece is generally not less than 5mm and the mass is not less than 300g.
For samples with a thickness of 2mm to 5mm, it is recommended to use coupling or bonding.
The thickness t of the coating (plating) layer and the surface hardening layer should not be less than 10 times the depth of the indentation.
5. Compared with the Leeb hardness tester, what are the characteristics of the ultrasonic hardness tester?
1)Ultrasonic hardness tester has a small indentation size and is less destructive to the surface of the test piece.
Comparison of indentation size between ultrasonic hardness tester 10N probe and Leeb D head
|
Hardness |
Leeb indentation depth |
UCI indentation depth |
Leeb indentation diameter |
UCI indentation diagonal |
|
300HV |
24μm |
11μm |
540μm |
79μm |
|
600HV |
17μm |
8μm |
540μm |
56μm |
|
800HV |
10μm |
7μm |
350μm |
48μm |
2)The ultrasonic hardness tester is simple to operate, and the measurement is completed with one press, with fast measurement speed and high efficiency.
3)Ultrasonic hardness tester probes can penetrate into tight spaces to measure locally hardened parts.
4)Ultrasonic hardness tester is mainly for hardness measurement of hardened layers, thin parts and small parts, and the quality of the Leeb measured material should be large enough compared to the ball head. Therefore, Leeb is not suitable for measuring small workpieces, thin workpieces ( including thin-walled tubes)
6. What is the reason for the poor repeatability of the measured values?
1)The operation is unstable and the pressing process is shaking. It is best to hold the probe with both hands to ensure the stability of the probe pressing process;
2)The probe is not perpendicular to the surface to be measured. When measuring, ensure that the probe is perpendicular to the surface to be measured. Note that the maximum inclination angle should be less than 5°. When measuring cylindrical workpieces, V-shaped feet can be installed as auxiliary supports. It is good to measure with a bench;
3)The DUT is not fixed, and the DUT should avoid movement and vibration during measurement.
4)The surface roughness of the measured workpiece does not meet the requirements. If the surface of the workpiece is too rough, the measured value will be low.
7. What is the reason for no value during measurement?
1)The connection cable is not firmly connected, reinstall and restart;
2)When the measured value exceeds the tolerance limit, the screen will display the over-limit arrow and accompanied by over-limit alarm sound;
3)The operation is too fast. After the probe is lifted, the next measurement can be performed only when the measurement mark appears in the lower right corner of the host.
4)High-frequency magnetic fields are present in the surrounding environment, as electromagnetic interference may cause the instrument to temporarily fail.
8. Do I need to press the probe for a certain time during measurement?
No need.
When measuring, just press the probe lightly on the workpiece, and lift it up after hearing the "beep" sound to complete the measurement. In this process, the indenter only needs a very short compression distance (about 0.7mm) to achieve the required test force, that is to say, the indenter has completed the measurement before it is fully compressed to the bottom of the probe. Therefore, force Excessive and prolonged pressure on the probe is unnecessary.