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Hardness LEEB

Principle of hardness control according to Leeb's method



d = diameter of the impression
Epot = potential energy
Ekin = kinetic energy





Hardness is indirectly measured through the energy loss of an impact body. The figure illustrates the physical principle of measurement. A mass m is accelerated to the surface of the test object and hits it at a defined speed (measured before impact), ie. kinetic energy. The impact creates a plastic deformation of the surface, i.e. a footprint, deformation that absorbs some of the energy - or velocity - of the impact body. The softer the material, the larger the footprint, and the greater the energy absorbed - and the decreased speed - is important. Technically, this principle of measurement is implemented by means of a tungsten carbide spherical impact body which is projected onto the test surface by means of a spring.
The speeds before and after impact are measured without contact. This is done by a small permanent magnet in the impact body that produces an induction voltage during its passage in a coil, this voltage being proportional to the speed.
The Swiss inventor of this method, D. Leeb, has defined his own hardness value, Leeb hardness value. The hardness value of Leeb, HL, is calculated from the ratio of impact velocity and rebound according:  HL = VR/VI×1000

VI, VR = Speed before / after the impact.

However, few users indicate the Leeb HL hardness value in its characteristics or test reports. For this reason, the rebound hardness method becomes interesting if we can convert it to normalized hardness (HV, HB, HS, HRC, HRB, N / mm2). For this reason, conversion tables for the most common materials are stored in all instruments.

In order to obtain reproducible and precise results, it is necessary:
- to have a clean surface with a correct roughness.
- to have sufficient rigidity of the impact zone: if the part deforms elastically during the impact, part of the kinetic energy will be used for this elastic deformation and restored during the rebound instead of being used for plastic deformation => measurement error. For this reason, we ask for a weight and a minimum thickness of the part which are functions of the type of impact body used (see table of probes).


All LEEB hardness meters incorporate LEEB hardness conversion tables to other scales depending on the material. These tables are indicative.
Example of a conversion range for a HLD probe

Materials
HV
HB
HRC
HRB
HSD
Steel
81~955
81~654
20~68,4
38,4~99,5
32,5~99,5
Alloy tool steel
80~898
-
20,4~67,1
-
-
Stainless steel
85~802
85~655
19,6~62,4
46,5~101,7
-
Grey cast iron
-
63~336
-
-
-
Ductile iron
-
140~387
-
-
-
Cast aluminium
-
19~164
-
23,8~84,6
-
Brass
-
40~173
-
13,5~95,3
-
Bronze
-
60~290
-
-
-
Copper
-
45~315
-
-
-

Pen type hardnesstester LEEB HN-D

Pen type hardnesstester LEEB HN-D

Free Shipping B,L,F,NL,D

1290.00

€ 912.00Without VAT
Pen type hardnesstester LEEB TH-170/D

1360.00

€ 1299.00Without VAT
Pen type hardnesstester LEEB TH-172/C

1780.00

€ 1701.00Without VAT
Pen type hardnesstester LEEB TH-174/DL

1990.00

€ 1901.00Without VAT
Hardnesstester LEEB HMM

Hardnesstester LEEB HMM

Free Shipping B,L,F,NL,D

1090.00

€ 771.00Without VAT
Hardnesstester LEEB HMM-NP

Hardnesstester LEEB HMM-NP

like HMM, but without printer

850.00

€ 601.00Without VAT
Hardnesstester LEEB HMO

Hardnesstester LEEB HMO

Free Shipping B,L,F,NL,D

1770.00

€ 1251.00Without VAT
Hardnesstester LEEB HK-D

Hardnesstester LEEB HK-D

Free Shipping B,L,F,NL,D

1250.00

€ 884.00Without VAT
Hardnesstester LEEB HK-D & reference block D

1390.00

€ 983.00Without VAT
Hardnesstester LEEB ROCKY TH-110

1570.00

€ 1500.00Without VAT
Hardnesstester LEEB ROCKY TH-160

1780.00

€ 1701.00Without VAT