Background
A coal mining operation in East Kalimantan, Indonesia was experiencing chronic belt mistracking on a 450-meter overland conveyor carrying run-of-mine coal from the primary crusher to the ROM stockpile. The operation ran two 10-hour shifts per day, and the belt was drifting off center on the return run approximately 2β3 times per week, requiring manual intervention to re-center it each time.
The conveyor used a 1000mm wide EP315 belt. Annual belt replacement had become necessary due to edge damage from the belt contacting the conveyor structure during tracking events.
Problem Diagnosis
The maintenance team had already adjusted the idlers multiple times and had replaced several return idlers that appeared seized. The problem kept recurring.
A systematic inspection identified three contributing factors:
1. Uneven loading at the transfer chute. The feed chute was positioned slightly off-center, causing material to consistently load heavier on the right side of the belt. An off-center load creates a turning moment that causes the belt to drift to the lighter-loaded side.
2. Accumulated material on return idlers. Fine coal was building up on the return idler rollers in the flat section under the loading zone. Uneven buildup on rollers creates different effective diameters across the roller width, which steers the belt laterally. Several rollers had substantial cone-shaped buildup on one end.
3. Structural frame misalignment in one section. A 30-meter section of the conveyor frame had settled slightly on one side due to soft ground conditions in the rainy season, creating a slight lateral lean that the belt responded to.
Solution
The mistracking problem required addressing all three causes rather than adjusting idlers repeatedly to compensate for them:
Chute modification: The discharge lip of the transfer chute was adjusted by 80mm toward the centerline, recentering the material stream on the belt. A simple steel plate deflector was welded in position β no major structural work.
Return idler cleaning and replacement: Twelve return idlers with significant material buildup were replaced. The replaced idlers were cleaned and stored as spares. Self-cleaning rubber disc return idlers were installed in the section under the loading zone β these don't accumulate material buildup because the rubber discs shed material as they rotate.
Frame releveling: The settled frame section was shimmed and releveled during a planned maintenance window. Ground conditions were addressed by installing concrete footings under the affected support posts.
Belt edge trimming: The existing belt had edge damage from previous tracking events. The damaged edges were trimmed on both sides (approximately 20mm each side) to restore a clean, straight edge that responds predictably to tracking adjustments.
Outcome
After the three-part intervention, the belt ran centered for the following six weeks of monitoring without a single mistracking event requiring intervention. The operation subsequently went 14 months before the next tracking intervention was needed β a normal maintenance adjustment rather than an emergency re-centering.
Annual belt replacement was extended to a 2.5-year replacement cycle once the underlying causes were resolved.
Key Lessons
Repeated belt mistracking is almost never caused by a single factor. Each tracking adjustment that doesn't address the root cause adds complexity to the system and delays identifying what's actually wrong. A systematic approach β checking loading symmetry, idler condition, and frame alignment β is more effective than repeated idler adjustments.
Self-cleaning return idlers in the loading zone area are worthwhile on any conveyor running fine or wet material. The cost difference versus standard steel tube rollers is modest, and the reduction in buildup-related tracking problems justifies the investment.
Elephant Rubber supplied the replacement EP315 belt and the self-cleaning rubber disc return idlers for this project.
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