Overview - ISO 21509:2006 (Plastics and ebonite - Verification of Shore durometers)
ISO 21509:2006 defines how to verify Shore durometers (Type A and Type D) used for hardness testing of plastics and ebonite (as performed to ISO 868). The standard sets out required checks, measurement conditions, verification methods and reporting elements to ensure durometers give reliable Shore A / Shore D hardness readings for quality control and material testing.
Key topics and technical requirements
- Scope and environment
- Verification applies to Type A and Type D Shore durometers.
- Ambient verification temperature: 21 °C–25 °C (or 25 °C–29 °C for tropical conditions if agreed), per ISO 291.
- Elements to be verified
- Geometry and dimensions of the indenter (diameter, tip radius/angle, full protrusion).
- Maximum protrusion of the indenter beyond the presser foot base.
- Geometry and hole diameter/centering of the presser foot.
- Scale of the indicating device (verify 0 and 100 points; check maximum-reading indicators).
- Force exerted by the measurement spring on the indenter.
- Force verification methods
- Method 1: Dynamometric device (measure applied forces corresponding to Shore readings; repeat increasing/decreasing loads).
- Force equations: F = 550 + 75·HA (mN) for Shore A; F = 445·HD (mN) for Shore D.
- Tolerances: ±75 mN (A) and ±445 mN (D).
- Measurement device resolution recommendations: ~10 mN (0.13 Shore A) for A, ~50 mN (0.11 Shore D) for D.
- Method 2: Purpose-built verification devices that indicate directly in Shore units and apply calibrated loads.
- Frequency
- Verify and certify: after production, after repair, after damage (especially indenter), and annually.
- Verification devices themselves: checked after production/repair/damage and every two years.
- Reporting
- Verification report must include traceability of equipment, detailed measurements (see Annex A tables), adjustments/repairs, and a compliance statement.
Applications and users
- Calibration and accreditation laboratories performing durometer calibration and certification.
- Materials testing and quality assurance teams in plastics and rubber manufacturing.
- R&D and product development labs requiring reliable Shore hardness data.
- Equipment manufacturers and service providers offering durometer repair/calibration services.
Related standards
- ISO 868:2003 - Determination of indentation hardness by means of a durometer (Shore hardness).
- ISO 291 - Standard atmospheres for conditioning and testing.
Keywords: ISO 21509:2006, Shore durometer verification, Shore A, Shore D, hardness testing, ISO 868, calibration report, plast‑ics testing, measurement spring, dynamometric device.