Background
An aggregate quarrying and stockpiling operation near Dubai was experiencing surface cracking of conveyor belt covers on its outdoor stacker conveyors within 4β6 months of installation. The cracks appeared on the top cover surface as a network of fine transverse cracks, initially cosmetic but deepening over time until they penetrated to the carcass.
The belts were 800mm wide EP250 with standard M24 SBR covers, running on two stacker conveyors that operated in full outdoor exposure β no enclosure or shade structure over any part of the conveyor run.
Investigation
The UAE's outdoor environment is one of the most aggressive for rubber belt covers:
- Solar UV radiation: At 25Β° north latitude, solar UV intensity is high year-round. UV radiation attacks the double bonds in SBR rubber, causing surface hardening and cracking β a process called photooxidative degradation.
- Ozone: Ground-level ozone reacts with rubber surfaces, attacking the same molecular bonds. The UAE's combination of heat, sunlight, and vehicle traffic generates elevated ozone levels.
- Temperature cycling: Daily temperatures swing from approximately 20Β°C at night to 45Β°C+ in summer days. The repeated thermal expansion and contraction of the rubber, combined with UV and ozone attack, accelerates surface cracking.
- Dry conditions: Unlike coastal industrial environments where humidity keeps rubber slightly more flexible, the dry interior UAE environment allows rubber to dry out, accelerating surface brittleness.
Standard SBR compound has limited UV and ozone resistance. In temperate European climates where most belt compound formulations were originally developed, outdoor exposure is less severe and standard SBR performs acceptably. In the Gulf, it fails significantly faster.
Solution
The replacement belt specification used EPDM compound covers with UV stabilizers and ozone inhibitors specifically formulated for Middle East outdoor conditions.
EPDM (ethylene propylene diene monomer) rubber has substantially better UV and ozone resistance than SBR because its molecular backbone does not contain the double bonds that UV and ozone attack most aggressively.
Additional specification elements: - Carbon black loading increased (carbon black provides UV shielding) - Antiozonant additive package included - Top cover thickness increased from 6mm to 8mm to provide more material before cracks reach the carcass
Outcome
The EPDM belts ran for 22 months before the first surface inspection showed any cracking β and at that point the cracking was superficial surface crazing rather than the penetrating cracks seen on the previous SBR belts at 4β6 months. Estimated remaining life at inspection: 12+ months.
The operation moved from replacing stacker belts every 5 months to an estimated 3-year replacement cycle β a significant operational and cost improvement.
Key Points
Standard SBR covers are not appropriate for outdoor Gulf installations. This is not an edge case β it is predictable. Any conveyor running fully outdoors in the UAE, Saudi Arabia, Oman, or similar climates should be specified with UV-stabilized, ozone-resistant covers as standard practice.
Cover thickness buys time but doesn't fix compound incompatibility. Thicker SBR would have delayed the cracking problem without solving it. The compound change was the essential fix.
The same principle applies to other high-UV environments. High-altitude Andean operations, Australian outback, and Saharan Africa all present similar UV/ozone challenges requiring similar compound specification.
Elephant Rubber supplied the UV-stabilized EPDM cover belts for this project.