Overview
ISO 2039-2:1987 - Plastics - Determination of hardness - Part 2: Rockwell hardness specifies a standardized method to measure the indentation hardness of plastics using a Rockwell hardness tester. It defines the use of the Rockwell M, L and R scales, the relationship between indentor penetration and the Rockwell hardness number, and essential controls such as loading times, calibration and specimen conditioning. The standard emphasizes that creep and recovery of plastic materials make timed load application and measurement critical to repeatable results.
Key topics and requirements
- Test principle: Rockwell hardness number (HR) is derived from the net increase in depth of impression when load is raised from a fixed minor load to a major load and returned to the minor load; HR = 130 − e (e measured in 0.002 mm units on the M/L/R scales).
- Scales, loads and indentors:
- Minor load: 98.07 N (all scales).
- R scale: 12.7 mm ball, major load ≈ 588.4 N.
- L scale: 6.35 mm ball, major load ≈ 588.4 N.
- M scale: 3.175 mm ball, major load ≈ 980.7 N.
- Timing and creep: The standard specifies limits for times of load application and measurement because high creep/recovery in plastics significantly affects results.
- Apparatus & calibration: Rockwell tester with a depth-measuring device accurate to 0.001 mm (0.002 mm per scale division). Periodic calibration using metal test blocks and procedures to determine the machine spring constant are required.
- Specimens & conditioning: Flat sheets (minimum thickness 6 mm), or stacked like-materials if thinner; condition specimens in the atmosphere specified by the relevant material standard or ISO 291.
- Procedure & reporting: Minimum five indentations per specimen (for isotropic materials), spacing and edge-distance rules, and a required test report including scale used (M/L/R), individual readings, mean and conditioning.
Applications and who uses it
- Quality control and acceptance testing in plastics manufacturing and product assembly.
- Materials characterization during R&D and comparative testing of thermoplastics and thermosets.
- Independent test laboratories and compliance verification for component suppliers.
- Useful for material selection where hardness correlates to wear, compressibility or service performance.
Related standards
- ISO 2039-1 - Ball indentation hardness of plastics (relationship/overlap with Rockwell-a measurement).
- ISO 291 - Standard atmospheres for conditioning and testing plastics.
- ISO 868 - Shore hardness (alternative when Rockwell scales are not suitable).
Keywords: ISO 2039-2:1987, Rockwell hardness, plastics hardness testing, Rockwell M L R scales, indentation hardness, conditioning, test procedure, calibration.
