Background
A manganese mine in the Hotazel area of South Africa's Northern Cape Province was replacing the belt on its primary ore conveyor β 1,000mm wide, 380 meters long, carrying run-of-mine manganese ore from the underground ore pass to the surface primary crusher at 800 tonnes per hour.
The outgoing belt had lasted 14 months. The maintenance engineer felt this was shorter than it should be given the moderate conveyor length, and asked for input on whether the specification could be improved.
Analysis of Outgoing Belt
The outgoing belt was EP315 M24 cover, 6mm top cover. Failure mode was cover wear-through in the central loading zone β the center 400mm of the 1,000mm wide belt had worn to the carcass while the edges retained nearly half the original cover thickness.
This center-heavy wear pattern, as with the phosphate case discussed in another case study, indicated either off-center loading or idler geometry issues concentrating load in the center.
Inspection findings: - Loading chute discharge was off-center by approximately 60mm β material stream hit the belt slightly left of center - Manganese ore at this mine was dense (bulk density approximately 2.1 t/mΒ³) β heavier than typical coal or limestone, concentrating the load impact on the central idler roll at the impact zone - The 35Β° trough idlers used were appropriate for manganese - The belt speed was 2.8 m/s β moderate
Two-Part Solution
1. Chute adjustment: The discharge chute position was corrected to center the material stream on the belt. This addressed the loading asymmetry.
2. Belt specification upgrade β cover thickness and grade:
The replacement belt specification was upgraded: - EP315 carcass (same β adequate for tension) - Top cover: 10mm DIN W grade (increased from 6mm M24)
DIN W (super abrasion resistant) has abrasion loss β€50mmΒ³ versus M24 at β€90mmΒ³. Manganese ore has a high silica content in this deposit, making it more abrasive than the ore's soft appearance suggests. The upgrade from M24 to W grade compound significantly improves abrasion resistance.
The 10mm cover thickness (versus 6mm) provides more wear material before the carcass is reached β a direct extension of the replacement interval.
Outcome
The W-grade 10mm cover belt was installed and monitored. At 14 months β the previous belt's end-of-life point β the new belt's central top cover showed approximately 3mm wear (30% of 10mm). Estimated remaining life: approximately 30 months total.
Projected improvement: approximately 2Γ belt life from the combined effects of centered loading and improved cover grade.
The cost of the W-grade 10mm belt was approximately 35% more than the original M24 6mm specification. At 2Γ belt life, the cost per month of operation was approximately 32% lower despite the higher unit cost.
Note on Manganese Ore Abrasiveness
Manganese ore abrasiveness varies significantly by deposit. The manganese oxides themselves (pyrolusite, psilomelane) are moderately hard (Mohs 5β6). However, manganese ore bodies typically contain significant gangue minerals including quartz (Mohs 7). The silica content in the gangue is often the dominant abrasive factor, not the manganese mineral itself.
When specifying belts for manganese ore, check the silica content of the ore. High-silica manganese ores are treated similarly to high-silica iron ore in terms of abrasion resistance specification.
Elephant Rubber supplied the DIN W grade replacement belt for this project.