Background
An iron ore operation in Western Australia was designing a new overland conveyor to move crushed ore from a secondary crushing station to the concentrator plant — a distance of 4.2 kilometers with a net lift of approximately 35 meters. The conveyor was specified for 4,500 tonnes per hour at 4.0 m/s belt speed, 1,400mm belt width.
The project engineering team was evaluating belt options for the tender package.
Belt Selection Analysis
The design team performed belt tension calculations using standard CEMA and DIN 22101 methodology. Key results:
- Calculated maximum belt tension at drive pulley: 312 kN/m width
- Required break strength with safety factor of 7: 312 × 7 = 2,184 N/mm minimum
- Specified belt rating: ST2500 (next standard rating above the minimum)
EP belt was evaluated and rejected for this application. EP630 (maximum standard EP) provides only 630 kN/m break strength, substantially below the 2,184 N/mm requirement. Even if a custom high-strength EP were achievable, the elongation characteristics of EP fabric would require a take-up travel of approximately 28 meters — difficult to accommodate in the conveyor structure. Steel cord at ST2500 provides elongation of approximately 0.18% at working load, requiring take-up travel under 8 meters.
Selected specification: - ST2500, 1,400mm wide - Top cover: 10mm DIN W (extra abrasion resistance for sharp crushed iron ore) - Bottom cover: 6mm M24 - Drive pulleys: 1,400mm diameter (meeting minimum radius requirement for ST2500)
Cold-Flex Specification
The mine site experiences overnight temperatures of -2°C to -8°C in winter months. While not extreme by global standards, this is sufficient to cause standard SBR covers to stiffen and increase drive motor load at cold morning start-up. The specification included cold-flex cover compound rated to -20°C as a precaution.
Splice Design
Four vulcanized splices were planned — one per 1,050-meter roll of belt. ST2500 splicing requires: - Minimum splice step length: approximately 3.5 meters per step (8 steps total for this rating) - Minimum overlap: approximately 28 meters total splice length - Press temperature: 145°C, cure time: approximately 90 minutes per splice - A trained splicing crew with appropriate press equipment
The project included a training session for the mine's conveyor maintenance team on steel cord splice inspection — identifying early signs of splice cord pull-out or cover delamination.
Outcome
The conveyor ran successfully from commissioning. At the 12-month inspection, belt wear in the impact zone at the loading point showed normal cover wear. No splice anomalies were detected. The cold-flex covers performed as specified during winter months — no unusual stiffness or increased motor load recorded at start-up.
Projected belt life based on wear rate at 12 months: 6–8 years before cover replacement would be considered.
Key Points for Similar Projects
ST rating comes from calculation, not estimation. The difference between ST2000 and ST2500 is not large in cost terms but significant in safety margin. Run the tension calculation properly.
Take-up travel is a practical design constraint. EP belt's elongation on long conveyors creates structural challenges. For conveyors over 2km, steel cord's low elongation often makes it the practical choice regardless of cost.
Splice quality is the critical variable on steel cord belts. A poorly made ST2500 splice is weaker than a well-made ST1250 splice. Invest in proper training and equipment.
Elephant Rubber manufactured and supplied the ST2500 belt for this project.