Alpha ROCKWELL Hardness
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Alpha ROCKWELL hardness
General information
Although the ROCKWELL hardness test method was originally designed only for metallic materials (HRC, HRB, etc.), there are now scales and loads that make it suitable for plastics as well (HR15Y, HR30Y with 15 and 30 kg loads).
Alpha Rockwell hardness for plastics
In the case of the Rockwell α hardness test, a comparatively large steel ball with a diameter of 12.7 mm is used. Similar to the ball pressure method (see: ball indentation hardness), a preload of 98.1 N and a main load of 588.4 N are applied. To determine a clear condition for the hardness test, the relevant value is determined after a holding time of 15 seconds. Due to the large diameter of the indenter (see also: indenter) and the high force, the hardness can be determined in a relatively large hardness range. The relatively deep indentation created during the penetration process also helps to prevent the surface from influencing the characteristic value of the hardness.
The Rockwell hardness HRα is calculated using the following equation:
with h in mm.
Performing hardness measurements according to α-Rockwell (HRα)
The schematic design of such a measuring system and the measuring process are shown in the following Figure. The relationship between ball indentation hardness and Rockwell α hardness is non-linear due to the different test conditions and the measuring technology used.
| Figure: | Schematic diagram of the HRα method and relationship between α-ROCKWELL hardness and ball indentation hardness (D = ball diameter, F0 = preload, F = test load, h0 = indentation depth after application of preload, h = indentation depth) |
A comprehensive literature analysis of HRα values is contained in Landolt-Börnstein Volume VIII/6A3 (see references).
See also
References
- Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, p.184 (ISBN 978-1-56990-806-8; e-Book ISBN 978-1-56990-807-5; see AMK-Library under A 22
- Koch, T., Bierögel, C., Seidler, S.: Conventional Hardness Values. In: Grellmann, W., Seidler, S. (Eds.): Mechanical and Thermomechanical Properties of Polymers. Landolt-Börnstein. Volume VIII/6A3, Springer, Berlin (2014) 357–379, (ISBN 978-3-642-55165-9; see AMK-Library under A 16)
- ISO 2039-2 (1987-07): Plastics – Determination of Hardness – Part 2: Rockwell Hardness
- ASTM D 785 (2023): Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
- Fett, T.: Materialprüfung 14/5 (1972) 151–153; https://doi.org/10.1515/mt-1972-140503