Background
A limestone quarry in Malaysia was operating a 1.8km overland conveyor that followed the terrain contour with a horizontal curve of approximately 800-meter radius in the middle section. The conveyor was 800mm wide EP315, carrying crushed limestone at 600 t/h.
The conveyor had persistent tracking problems in and around the horizontal curve section. The belt consistently drifted to the outer edge of the curve, eventually contacting the conveyor structure and causing edge damage. Various idler adjustments had been tried without lasting success.
Why Horizontal Curves Cause Tracking Problems
On a straight conveyor, the belt tracks by gravity β if it shifts left, the weight distribution change tends to bring it back toward center. This self-correcting behavior breaks down on horizontal curves.
On a curved conveyor, the belt's tension generates a lateral force toward the inside of the curve (centripetal reaction). This force tends to push the belt toward the inner rail of the curve. At the same time, the belt on the outer side of the curve travels a slightly longer path than the inner side, creating differential tension that can cause the belt to wander.
The combination of these forces means that standard straight-conveyor tracking adjustments (angling idlers) don't work well in curve sections β angling an idler can correct tracking at one belt load but cause problems at different loads.
Investigation
The quarry's maintenance team had been adjusting idlers in the curve section, sometimes improving tracking for a few days before it drifted again. The problem was intermittent β worse at lower belt loads and during start-up when belt tension distribution was different from steady-state running.
Key findings: 1. The idler spacing in the curve was the same as the straight sections (1.2m). For horizontal curves, closer idler spacing is recommended to provide more support points for the curved belt geometry. 2. Several return idlers in the curve approach section were slightly misaligned from installation β not perfectly perpendicular to the belt travel direction. 3. The belt itself was slightly asymmetric in tension β the left edge had slightly higher tension than the right, likely from a previous repair splice that had not been step-cut perfectly symmetrically.
Corrective Actions
Idler spacing in curve: Spacing in the curve section was reduced from 1.2m to 0.9m by adding intermediate idlers. This provided more support points and reduced the unsupported belt length that was contributing to lateral instability.
Return idler realignment: All return idlers within 50 meters of the curve were inspected and realigned to be perpendicular to belt travel.
Self-aligning idlers at curve entrance and exit: Two self-aligning (training) idler sets were installed at the approach and exit from the curve β positions where the tracking tendency changes direction.
Belt splice: The asymmetric belt was re-spliced at the next planned maintenance stop with a carefully centered step splice. This eliminated the tension asymmetry.
Outcome
After all four interventions, the belt ran centered through the curve without further tracking events over the subsequent 8-month monitoring period. The self-aligning idlers at the curve transitions showed their function visually β the idler tilt angle indicated the corrective force they were applying, confirming that tracking forces existed but were being managed.
Key Points
Horizontal curve tracking is fundamentally different from straight conveyor tracking. The physics are different. Solutions that work on straight sections may not work in curves and vice versa.
Idler spacing matters in curves. Standard straight-section spacing is often too wide for curved sections. Reducing spacing in the curve provides better geometric support for the belt.
Belt tension asymmetry causes tracking problems everywhere. A poor splice or uneven carcass tension creates a tracking tendency that no amount of idler adjustment will permanently fix. The belt itself needs to be symmetric.
Elephant Rubber supplied the replacement EP315 belt and self-aligning idler sets for this project.