Background
A phosphate mining and processing operation was experiencing rapid cover wear on the belt feeding its beneficiation plant from the primary crusher. The belt β 800mm wide EP250, 1,200 meters long β was being replaced every 8β9 months. Given the plant ran continuously, each belt replacement required a planned 6-hour shutdown.
The maintenance engineer described the wear pattern: heavy center-track wear with the cover worn to within 2mm of the carcass in the center zone, while the belt edges retained nearly full cover thickness. This center-heavy wear pattern is diagnostic information.
Diagnosis
Center-heavy wear indicates two possible causes:
- Material loading concentrated in the center of the belt (off-center chute discharge hitting narrow stream)
- The idler trough angle is too flat for the material being carried, causing material to pile in the center and the belt to ride on the center idler roll only, concentrating all abrasion in the central zone
Inspection of the loading chute showed the discharge stream was reasonably well centered. However, the conveyor used 20Β° trough angle idlers throughout. Phosphate ore at this plant had a relatively low angle of repose and was fine-grained β it spread across the belt easily. But the 20Β° trough was too shallow, causing the material cross-section to be concentrated in the center and putting the central idler roll under significantly higher load than the wing rolls.
The belt was riding primarily on the center roll rather than distributing load across all three rolls.
Solution
Idler replacement: The 20Β° trough idlers were replaced with 35Β° trough idlers throughout the conveyor. This created a deeper trough that distributed the material cross-section more evenly, loading all three rolls more equally and spreading belt contact across a wider width.
Belt specification upgrade: The existing EP250 had been borderline for the application load. The replacement belt was specified as EP315 with 8mm top cover (increased from 6mm) in M24 grade. The thicker cover provides more wear material and extends replacement intervals independent of wear rate improvements.
Loading chute modification: The chute discharge lip was extended by 300mm to reduce material velocity at belt loading β high-velocity material at loading point accelerates cover wear in addition to causing impact.
Outcome
After the combined intervention, belt life extended to approximately 22 months before the first inspection showing significant wear. The center-heavy wear pattern disappeared β wear was now distributed evenly across the belt width.
Annual belt replacements reduced from approximately 1.4 per year to approximately 0.5 per year β effectively halving the replacement frequency.
Key Points
Wear pattern is diagnostic. Center-heavy wear is not just a belt problem β it's a system problem. Replacing the belt with the same specification in the same conditions produces the same result. Understanding why the center wears faster than the edges leads to the actual solution.
Trough angle affects wear distribution. This is an underappreciated design parameter. A 20Β° trough for a freely flowing fine material often results in the center carrying most of the load. 35Β° or 45Β° trough distributes load better for most mining materials.
Cover thickness buys time but doesn't fix the root cause. A thicker cover extends intervals between replacements but the underlying wear rate is unchanged. Fixing the system issue (idler trough angle, loading velocity) reduces the wear rate itself.
Elephant Rubber supplied the replacement EP315 belt for this application.