Overview
ISO 9856:2016 specifies a standardized method for determining the elastic and permanent elongation of conveyor belts and for calculating the elastic modulus. The procedure is intended for full‑thickness conveyor belts and is not applicable to light conveyor belts described in ISO 21183‑1. The test supports quality control, acceptance testing and provides data for belt selection and installation planning.
Key Topics
- Scope and applicability: Test method for elastic and permanent elongation; excludes light conveyor belts (ISO 21183‑1).
- Principle: A longitudinal test piece is cyclically loaded (sinusoidal force) and changes in length are recorded. After 200 cycles the permanent and elastic elongations are determined from the force–elongation graph.
- Sample and test-piece preparation:
- Sampling per ISO 282.
- Cut three rectangular test pieces in the longitudinal direction, each 50 mm wide and at least 300 mm long (plus clamping allowance).
- Remove covers so remaining cover thickness is between 0.5 mm and 1 mm.
- Condition test pieces in accordance with ISO 18573 before testing.
- Apparatus requirements:
- Dynamic tensile testing machine capable of applying up to a substantial portion of the nominal tensile breaking load, with force measurement compliant with ISO 7500‑1 (machine class 3 or better).
- Extensometer with measuring length of at least 100 mm and accuracy of 0.1 mm or better.
- Graphical recorder to capture force vs. actual elongation.
- Test procedure highlights:
- Apply initial force of 0.5 % of the nominal tensile strength (T) multiplied by specimen width.
- Cycle force approximately sinusoidally at 0.1 Hz between the defined upper and lower reference forces (10 % and 2 % of T, respectively).
- Record at least the first and the 200th cycles to read Δl_e (elastic) and Δl_p (permanent) and the applied ΔF.
- Calculations:
- Percentage permanent elongation ε_perm = (Δl_p / l_0) × 100.
- Percentage elastic elongation ε_elast = (Δl_e / l_0) × 100.
- Elastic modulus M = ΔF / ε_elast (expressed in N/mm width) or alternative formulae given in the standard.
Applications
- Quality control and acceptance testing of conveyor belts.
- Providing consistent data for belt selection, splicing decisions and take-up adjustment (relevant to ISO 3870 and ISO 5293 applications).
- Supplier–customer agreements where permanent elongation affects service performance; results can guide specification and commissioning.
Related Standards
- ISO 282 - Sampling of conveyor belts.
- ISO 7500‑1 - Calibration and verification of force measuring systems for tensile machines.
- ISO 18573 - Test atmospheres and conditioning periods.
- ISO 21183‑1 - Light conveyor belts (not covered by ISO 9856).
- ISO 3870, ISO 5293 - Practical applications where elongation data are used.
Practical value: ISO 9856:2016 provides repeatable, comparable test results (Δl_e, Δl_p, M) that help manufacturers, specifiers and users assess belt behavior under cyclic loading and make informed decisions about installation and maintenance.