Background
A coal washing plant in the South Gobi Desert, Mongolia was experiencing belt failures during winter months. The conveyor fed crushed coal from a stockpile reclaim to the washing plant feed bin — 280 meters long, 800mm wide, running at 2.0 m/s. Operating hours were continuous during the winter production season.
The failure mode was consistent: in temperatures below -25°C (common at night and in the early morning hours), the belt cover developed transverse surface cracks that propagated into the carcass within days. By the time the belt was identified as damaged, cracks extended 3–4mm into the carcass in multiple locations. Three belts had failed in this way over two winter seasons.
Root Cause
The belt in use was a standard EP200 with SBR compound covers. SBR rubber has a glass transition temperature (Tg) around -50°C at which it becomes truly rigid, but it begins to lose meaningful flexibility well above that — typically becoming noticeably stiff below -15°C and prone to cracking under cyclic bending stress below -25°C.
At -30°C, an SBR belt bending around a 400mm tail pulley at the return end was experiencing stress concentrations that exceeded the rubber's brittle-temperature flexural capacity. Each passage around the tail pulley added micro-cracks that accumulated into visible cracking within days of cold-weather operation.
Correct Specification
The correct specification for South Gobi operating conditions required:
Cold-flex cover compound maintaining rubber flexibility to at least -45°C. This uses a modified NR or EPDM compound with low-temperature plasticizers that maintain the elastomeric properties needed to flex around pulleys without cracking.
The replacement belt specification: - EP200 carcass (adequate for this conveyor's tension requirements) - 800mm width - Top cover: 6mm cold-flex compound (rated -45°C) - Bottom cover: 4mm cold-flex compound - Minimum pulley diameter check: existing 400mm tail pulley was confirmed adequate for EP200 construction
Additional recommendation: Insulate the conveyor structure around the tail and drive pulley areas during winter months to reduce the temperature differential between the belt surface and the pulley. Thermal shock (belt warming rapidly at the drive pulley after running cold in the open air) contributes to cracking. Even basic wind shielding reduces the temperature variation.
Outcome
The cold-flex belt was installed at the start of the following winter season. Over two complete winter seasons (including temperatures reaching -38°C), no cold-related cracking occurred. The belt showed normal abrasion wear in the coal handling zone and was still in service at the 20-month mark.
The wind shielding recommendation was implemented partially — the tail pulley area was enclosed with sheet metal panels. The maintenance team reported that morning start-up was smoother with less belt stiffness noticeable on the first run of the day.
Key Points
Cold climate belt failure is not random. Transverse cracking on a cold-climate belt at consistent locations (tail pulley, return idlers) is a clear signature of cold-brittleness. The failure mode identifies the solution.
The cover compound matters more than the EP rating in cold climates. Upgrading from EP200 to EP315 would not have helped — the failure was in the rubber compound, not the carcass tension capacity.
Cold-flex specification should be standard for Mongolia, Siberia, northern Canada, and high-altitude Andean operations. It is not a premium option for unusual conditions — it is the correct baseline specification for these environments.
Elephant Rubber supplied the cold-flex EP200 belt for this application.