EN - 19
B
A
4 Background information
4.1 Method of measurement
An impact body with a ball-shaped measuring tip made of tungsten carbide is propelled against the test surface
by a spring force and rebounds. The impact and rebound velocities are measured when the distance of the impact
body from the test surface is 1 mm. The measurement is made as follows: a permanent magnet in the impact body
induces an electrical voltage into the coil when passing through the coil in its holder. This voltage is proportional to
the velocities of the magnet. Leeb hardness values can be obtained using the following formula:
HL = 1000 x (V / V )
B A
HL: Hardness according to Leeb
V : Rebound velocity
V : Impact velocity
The voltage curve of the output signal when the impact body passes through the induction coil is illustrated in the
following figure:
If you measure the hardness of a material with the traditional static test method, the applied pressure will affect the
measurement value, e. g. 760 HLD
≠ 760 HLC ≠ 760 HLG. Since different types of impact devices require different
conversion curves when converting Leeb hardness values into different hardness values, not only the converted
value should be stated but also the impact device used.
V
A
REBOUND
TIME
IMPACT
V
B
E
n
g
lish
V
E
L
O
C
IT
IE
S
