Background
A copper porphyry mine in Kazakhstan was replacing the belt on its primary gyratory crusher discharge conveyor every 9β10 months. The conveyor was 1,200mm wide EP400, 380 meters long, receiving ROM ore from the crusher at a drop height of approximately 1.5 meters. Top size of crushed ore was 250mm.
The failure mode was consistent: impact damage in the first 15 meters of the conveyor from the loading point. Transverse cuts and punctures through the belt cover and into the carcass. These developed into carcass tears that required patching or accelerated the need for full belt replacement.
Loading Zone Assessment
The loading zone inspection found: - No impact cradle or impact bars in place β the belt was supported only by standard 35Β° trough idlers at 1.2m spacing in the loading zone - The gap between idlers at the impact zone was 1.2 meters β when 250mm ore lumps landed between idlers, the belt deflected significantly into the space between idler rolls, stretching the cover and carcass - Sharp-edged ore pieces at this size were cutting through the cover on impact
Standard trough idlers in a primary crusher discharge zone of this severity are inadequate. The belt deflects between idler rolls under impact, concentrating stress at the idler contact edges rather than distributing it across the belt.
Solution: Impact Cradle with UHMWPE Bars
An impact cradle was designed for the first 6 meters of the loading zone (the area receiving the primary impact load from ore falling from the crusher discharge chute):
- UHMWPE impact bars mounted on a rubber cushion base
- Bar spacing: 100mm (eliminating the large gaps of the idler arrangement)
- Continuous support across the full 1,200mm belt width
- Rubber cushion layer (60 Shore A NR): 50mm thick beneath the UHMWPE bars
- UHMWPE bar dimensions: 80mm wide, 40mm thick, 1,200mm length
The transition from the impact cradle to standard trough idlers was designed with gradual spacing increase (200mm, 400mm, 800mm, 1,200mm) to avoid a sudden support gap change.
Rubber impact liners were also installed in the transfer chute above the belt to reduce material velocity at landing β the chute was re-profiled to direct ore onto the belt at a lower angle, reducing the vertical component of impact velocity.
Outcome
After installation of the impact cradle and chute modification:
- No transverse impact cuts were observed in the first 6 months of operation
- The UHMWPE bars showed approximately 20% wear at 6 months β estimated life of 24β30 months
- Belt cover in the impact zone showed normal, gradual abrasion wear rather than punctures and cuts
At the 12-month belt inspection, the belt was in good condition with no impact damage. The previously 9β10 month replacement cycle was extended β the belt was still serviceable at 18 months when the mine conducted its next planned maintenance review.
Key Points
Standard idlers are not adequate for primary crusher discharge. The gap between idlers at 1.2m spacing allows significant belt deflection under large-lump high-energy impact. An impact cradle with continuous support is the correct solution for this loading condition.
Chute design affects belt life. Reducing material velocity at the loading point by re-profiling the chute is often as important as the belt support system underneath. Both together produced the improvement; neither alone would have been as effective.
UHMWPE bars are a consumable. The impact cradle bars will wear and need replacement β at 24β30 months in this application. Plan for this as routine maintenance. The bars are much cheaper to replace than the belt.
Elephant Rubber supplied the impact cradle system and the replacement EP400 belt for this project.