Overview
EN ISO 21509:2015 (equivalent to ISO 21509:2006) specifies procedures for the verification of Shore durometers used to measure indentation hardness of plastics and ebonite (as tested by ISO 868). The standard covers verification methods for type A and type D Shore durometers, environmental conditions for verification, required instruments, pass/fail criteria and the contents of the verification report.
Key topics and technical requirements
- Scope and environment
- Verification is for Shore A and D durometers used in hardness testing of plastics and ebonite.
- Ambient verification temperature: 21 °C to 25 °C, or 25 °C to 29 °C for tropical conditions per ISO 291.
- Instruments and uncertainty
- Requires dimensional measuring tools and dynamometric (force-measuring) instruments.
- Recommended measurement uncertainty: ~1/5 of the tolerance on the value being verified.
- Elements to be verified
- Indenter geometry and maximum protrusion (e.g., full protrusion specified as 2.5 mm ± 0.04 mm in the standard figures).
- Presser foot geometry (hole diameter 2.5–3.5 mm and centring).
- Indicating device scale: verify points 0 and 100 and, if present, the maximum‑reading indicator.
- Measurement spring force: verified using either a dynamometric device or a purpose-built verification device.
- Force/stiffness checks
- Stiffness relations (as given in the standard): F (mN) = 550 + 75·HA (Shore A) and F = 445·HD (Shore D).
- Dynamometric readings Fi must match calculated F within specified tolerances (as stated in the standard).
- Verification-device check tolerances: ±10 mN for Shore A and ±50 mN for Shore D.
- Frequency
- Verification required: after production, after repair, after damage (especially indenter), and annually.
- Reporting
- Verification report must identify the verifier, client, durometer details (manufacturer, model, serial), date, equipment traceability, measured data and statement of compliance.
Applications and who uses this standard
- Calibration and metrology laboratories performing durometer verification and issuing calibration certificates.
- Plastics and rubber manufacturers ensuring incoming/outgoing inspection and process control rely on correct Shore hardness readings.
- Quality control and R&D teams that validate hardness-testing instruments for product development and compliance.
- Third‑party testing bodies and accreditation organizations needing consistent verification procedures for Shore A/D instruments.
Related standards
- ISO 868 - Determination of indentation hardness by means of a durometer (Shore hardness).
- ISO 291 - Standard atmospheres for conditioning and testing (temperature/humidity references).
Keywords: EN ISO 21509:2015, Shore durometer verification, durometer calibration, Shore A, Shore D, plastics hardness testing, ISO 868.