Overview
ISO 1535:1975 specifies belt widths and belt edge clearances for troughed belt conveyors (other than portable conveyors) used in continuous mechanical handling of loose bulk materials. The standard defines dimensional tolerances for conveyor belts and the minimum gap - the edge clearance - between each belt edge (on both carrying and return runs) and the nearest fixed obstacle. It applies primarily to non‑portable troughed belt conveyors and gives guidance relevant to typical conveyor speeds up to 3 m/s.
Key topics and technical requirements
- Scope: Dimensions and clearances for troughed belt conveyors handling bulk materials; non‑portable equipment.
- Belt widths and tolerances: Nominal widths follow ISO/R 251 (Widths and lengths of conveyor belts). Tolerance allowances are specified in the annex:
- +5 mm for 400 mm and 500 mm belt widths
- +3/16 in for 16 in and 20 in widths
- +1% of nominal value for widths greater than 500 mm (20 in)
- Edge clearance (definition): The gap between each edge of the carrying and return belts (in their correct positions) and the nearest obstacle liable to be approached by the belt edge.
- Minimum clearances: A table in the standard lists minimum edge clearances per side; these minimums apply to individual and repeated obstacles. (Do not place obstacles inside the vertical projection lines from the outer ends of inclined idlers.)
- Special conditions:
- For conveyors with concave curves, manufacturers must account for potential belt lifting and flattening that affects clearances.
- For belt speeds above 3 m/s, additional clearance may be required and should be accounted for by the manufacturer.
Applications and who uses it
ISO 1535:1975 is intended for:
- Conveyor belt manufacturers and suppliers specifying belt widths and tolerances
- Mechanical and conveyor system designers and OEMs creating troughed belt conveyor installations
- Bulk handling operators in mining, ports, cement, aggregates, power plants and agriculture ensuring safe clearances
- Maintenance, inspection and safety personnel checking compliance with dimensional and clearance requirements
- Procurement and quality assurance teams requiring standard conformity in belt selection and acceptance
Using this standard helps reduce belt damage, avoid edge snagging on nearby structures, and ensure reliable operation of continuous bulk handling systems.
Related standards
- ISO/R 251 - Widths and lengths of conveyor belts (referenced for nominal widths)
- ISO Recommendation R 1535-1970 - predecessor to ISO 1535:1975 (ISO 1535 replaces it)