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Hardness and Tactile Probing Methods

Working group 5.11

IRHD normal, IRHD low, IRHD micro, IRHD very low (DIN ISO 48)


The hardness test is based on the measurement of the difference in the indentation depths of a hardened steel ball in the elastomer which arises for a small preliminary test force and a large total test force.
The ball indentation hardness IRHD (International Rubber Hardness Degree) is a numerical value taken from a table, which is depends on the respective indentation depth under the acting test force.

Forces and dimensions of the test device

Hardness scale Diameter Preliminary force Additional force Total force Force acting from the pressure foot onto the sample surface
mm N N N N
IRHD N Ball: 2,50
Foot: 20
Hole: 6
0,30 5,40 5,70 8,3
IRHD L Ball: 5
Foot: 22
Hole: 10
0,30 5,40 5,70 8,3
mm mN mN mN mN
IRHD M Ball: 0,395
Foot: 3,35
Hole: 1
8,3 145 153,3 235
VLRH Ball: 2,5
Foot: 6,0
Hole: 3,0
8,3 91,7 100,0 235

Fields of application:

Hardness scale Fields of application
IRHD N Soft to medium-hard rubber, very soft thermoplast
IRHD L Soft to medium-hard rubber, very soft thermoplast
IRHD M Soft to medium-hard rubber, very soft plastics, plane and lightly curved samples, small semi-finished parts or finished parts or rubber coatings, also relatively thin samples
VLRH Silicones