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2.4 Leeb Hardness Testing Principle
The basic principle is to use an impact body of certain weight impacts against the testing surface under
certain test force, then measure the impacting velocity and the rebounding velocity of the impact body
respectively when the spherically test tip is located 1mm above the testing surface.
The calculation formula is as follows:
HL=1000×VB/ VA
Where, HL—— Leeb hardness value
VB—— Rebounding velocity of the impact body
VA—— Impacting velocity of the impact body
3 Preparation
3.1 Instrument Preparation and Inspection
Verification of the instrument is by using standard test block. The error and repeatability of displayed
value should be within the regulation of Appendix table 2. The instrument and impact device must be
calibrated using a standard hardness block before use as the first time, or having not been used for a
long time, or having reset the instrument system.
Press
key, meanwhile pressing down the
key to power on the system. Then the user calibration
screen shows as left below.
Test for 5 points on the standard hardness block.
It would display the average measured value
after measuring 5 times. Press
key to
change to its nominal value.
Press key to confirm the calibration finally. Or
press the
key to cancel the calibration.
Range of adjustment: ±30HL.
3.2 Impact Device Selection
Refer to Appendix Table 1 and Table 3 for selection of impact device.
3.3 Preparation of the Sample Surface
Preparation for sample surface should conform to the relative requirement in Appendix Table 3.
In the preparation processing for sample surface, the hardness effect of being heated or cold
processing on the surface of sample should be avoided.
Too big roughness of the being measured surface could cause error. So, the surface of the sample
to be measured must appear metallic luster, smoothing and polish, without oil stain.
Support of test sample. Support is no necessary for heavy sample. Medium-weight parts must be
set on the smoothing and stable plane. The sample must set absolutely equability and without any
wobble.
Curved surface: The best testing surface of sample is flat. When the curvature radius R of the
surface to be tested is smaller than 30mm (D, DC, D+15,C, E and DL type of impact device) and
smaller than 50mm (G type of impact device), the small support ring or the shaped support rings
should be chosen.
The sample should have enough thickness, minimum thickness of sample should conform to Table
3.
For the sample with hardened layer on surface, the depth of hardened layer should conform to Table
3.
