Overview
ISO 7119:1981 defines a practical, standardized method for calculating the drive power of screw conveyors used in continuous handling of loose bulk materials. It applies to screw conveyors operating in a horizontal or inclined position (up to ~20°) with a regular, controlled and continuous feed. The standard excludes special-purpose screws such as extracting, calibrating, mixing, moistening, steeply inclined (>20°) and vertical screws. ISO 7119 is intended for designers, OEMs and engineers who need reliable power calculation and conveyor sizing guidance for bulk-material handling systems.
Key topics and requirements
- Scope and applicability: horizontal and moderately inclined screw conveyors for continuous flow of bulk materials; exclusions listed above.
- Power component model: total shaft power is the sum of three terms:
- PH – power required to progress (convey) the material,
- PN – power to run the screw at no-load,
- Pst – power due to inclination (lifting or lowering material).
- Total power: P = PH + PN + Pst
- Capacity and flow: the standard gives a method to calculate volumetric and mass flow based on screw geometry (diameter, pitch), rotational speed and a trough-filling coefficient (p) that reflects the degree of filling.
- Empirical parameters: introduces the progress resistance coefficient (A) and provides guidance on typical ranges (A generally in the order of 2–4) and how material properties affect A and filling coefficient p.
- Typical filling-coefficient guidance: examples for common operating cases (e.g., p ≈ 0.45 for free-flowing, non-abrasive materials; p ≈ 0.3 for typical bulk materials; p ≈ 0.15 for heavy, very abrasive materials).
- Practical formulae and variables: symbols and units are defined (screw diameter, pitch, length, speed, bulk density, mass flow, lifting height, gravity, etc.).
- Informative annex: example values for bulk density and progress resistance coefficients for a range of materials to support selections.
Applications and users
- Bulk-material handling design in industries such as mining, aggregates, cement, food processing, agriculture, coal and chemicals.
- Mechanical engineers, conveyor designers, plant layout engineers, procurement/specification teams, and maintenance planners who need to:
- size drives and gearboxes,
- select motor ratings,
- verify conveyor performance under expected loading and inclination,
- estimate energy consumption for material transport.
Related standards
- ISO 2148 (nomenclature for continuous mechanical handling equipment) is referenced for terminology.
- ISO 7119 was developed by ISO/TC 101 and is based on FEM (European Mechanical Handling Confederation) Section II work.
Keywords: ISO 7119, screw conveyors, drive power calculation, continuous mechanical handling equipment, bulk materials, conveyor design, progress resistance coefficient, trough filling coefficient.
