Overview
ISO 8398:1989 specifies a laboratory method for measuring the static angle of repose of solid fertilizers. The method produces a cone by allowing a sample to fall through a defined funnel onto a horizontal baseplate and uses physical measurements of that cone to determine the angle. It is intended for free‑flowing fertilizers and for static angles greater than 20°. The procedure is not suitable for materials with a large proportion of particles exceeding 5 mm in diameter.
Key topics and requirements
- Scope and limitations
- Applicable to free‑flowing solid fertilizers; not suitable for coarse materials (particles > 5 mm) or for angles ≤ 20°.
- Apparatus
- Funnel with slide, spout internal diameter 25 mm (rigid plastic or stainless steel).
- Funnel support so the tip of the spout is 120 mm above the center of the baseplate.
- Square baseplate 750 mm x 750 mm, matt, undamageable and damp‑proof; four lines drawn at 45° intervals crossing at the centre.
- Sample and test conditions
- Test sample of appropriate size (note: typically ~10 kg is sufficient).
- Determination at ambient temperature; ensure baseplate is level and funnel is fixed.
- Procedure
- Fill funnel with sample, open slide to form a steady stream until the cone top approaches the funnel tip; add more if necessary.
- Mark the cone base on designated radii, measure four diameters and the cone height.
- The static angle is calculated from the measured height (h) and the arithmetic mean of the four diameters (d) using the equation provided in the standard.
- Precision and reporting
- Precision established by interlaboratory tests (ISO 5725). The test report must cite ISO 8398, results and expression method, any unusual observations and any departures from the standard procedure.
Applications and who uses it
- Fertilizer manufacturers and quality control laboratories - to characterise powder/granulate flowability.
- Bulk storage and handling engineers - to inform hopper, silo and stack geometry and to estimate storage capacities.
- Equipment suppliers and process designers - to select appropriate feeders, chutes and conveyors and to reduce bridging/rat‑holing risks.
- Useful when comparing materials, monitoring batch consistency, or validating handling and storage designs.
Related standards
- ISO 3944 - referenced for funnel design compatibility.
- ISO 5725 - used for determining precision (repeatability and reproducibility).
- Alternative methods (for dynamic angle or angle of slide) such as tilting‑box tests are noted in the standard.
Keywords: ISO 8398, static angle of repose, angle of repose measurement, fertilizers, flowability, bulk handling, storage design.
