What Makes Overland Conveyors Different
Overland conveyors β?typically defined as conveyors longer than 1km β?present engineering challenges that do not arise in plant conveyors. The combination of high tension, long belt travel, complex routing through terrain, and the economic consequences of unplanned downtime demand careful belt selection and system design.
Why Steel Cord Belts Are Standard for Overland Conveyors
For overland conveyors beyond 1,500m, steel cord (ST) belts are the standard choice for three fundamental reasons:
- Elongation: EP belts elongate 1.2β?.0% at operating tension. On a 5km conveyor, this means 60β?00m of belt elongation β?far beyond any practical take-up system. ST belts elongate only 0.15β?.25% β?6β?2.5m on the same conveyor.
- Tension capacity: Very long conveyors develop very high belt tensions. ST belts are available in ratings up to ST5400 N/mm, far exceeding the EP range.
- Fatigue life: ST belts have excellent fatigue characteristics under the cyclic tension fluctuations of overland conveying.
Horizontal Curves on Overland Conveyors
Unlike plant conveyors that run in straight lines, overland conveyors often follow terrain contours with horizontal curves. Belt selection must account for horizontal curve requirements:
- Minimum horizontal curve radius depends on belt width and tension: typically 300β?,000m radius for 1,200β?,000mm wide belts
- Standard troughing idler configuration is modified at horizontal curves β?special transition idlers required
- Belt must have adequate lateral flexibility to conform to curve radius without edge lifting
Regenerative (Downhill) Conveyors
When an overland conveyor descends significant elevation, the loaded belt may generate more braking force than driving force β?the motor operates as a generator, returning power to the grid. Belt selection for regenerative conveyors requires:
- Analysis of all operating modes (loaded downhill, empty return, start-up, emergency stop)
- Highest tension occurs during braking on loaded downhill β?this often governs belt rating, not steady running tension
- ST cord provides the stability needed for controlled regenerative braking
Cover Grade Selection for Overland Conveyors
| Material | AI (g/t) | Recommended Top Cover | Thickness |
|---|---|---|---|
| Iron ore (lump) | 400β?00 | Grade W | 8β?2mm |
| Crushed copper ore | 300β?00 | Grade W | 8β?0mm |
| Coal | 30β?0 | Grade M | 6β?mm |
| Copper concentrate | 50β?50 | Grade M or W | 5β?mm |
| Limestone | 80β?50 | Grade M | 6β?mm |
β?Splice Design for Overland Conveyors
ST cord belt splices on overland conveyors are under cyclic high tension for years. Splice fatigue is a primary failure mode. Key requirements: use only manufacturer-specified splice table for cord arrangement; never short-cut splice length; use only approved vulcanizing materials and equipment; document all splices with photo records; inspect quarterly. A single poor splice on a 10km overland conveyor can force a full belt replacement β?splice quality is a capital maintenance issue, not a routine task.
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