Rockwell Hardness (Scales L, M, E, K)

For polymers the scales R, L, M, E and K in the Rockwell hardness testing method were developed, whereby steel balls with various diameters are used (scale R: 12.7 mm, scales L and M: 6.35 mm, scales E and K: 3.175 mm). These methods recorded exclusively the part of the remaining deformation and are standardised by DIN EN ISO 2039-2 and ASTM D 785. A conversion of the results between the individual scales is not possible.

Specimen Preparation

  • Specimen requirements: smooth, flat, plan-parallel, minimum thickness 6 mm
  • Extraction from component parts

Testing Conditions

  • Registered macrohardness testing system ZWICK ZHU 2.5 with temperature control
  • Temperature range from -100 °C to +100 °C
  • 5 individual measurements
  • Steel ball-indenter 6.35 mm in diameter (scales L and M) and 3.175 mm in diameter (scales E and K)
  • Preload (exposure time 10 s): 98.07 N
  • Testing load (exposure time 15 s): 588.4 N (scale L) and 980.7 N (scale M)
  • Determination of the Rockwell hardness after unload and under effect of the preload based on the remaining penetration depth

Accredited Standards

  • DIN EN ISO 2039:
    Plastics – Determination of hardness
    • Part 2: Rockwell hardness

Other Standards

  • ASTM D 785:
    Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials


Dipl.-Wirtsch.-Ing. Stephan Arndt
Telefon: +49 (0)3461 30889-68



  • Rockwell hardness
  • Scales L, M
  • Spherical indenter
  • Steel ball indenter


  • Rockwell hardness HRL
  • Rockwell hardness HRM
  • Rockwell hardness HRE
  • Rockwell hardness HRK


  • DIN EN ISO 2039-2
  • ASTM D 785

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