Background
A copper smelter in Jiangxi Province, China was experiencing rapid belt failure on its copper concentrate feed conveyor β the belt that carried blended copper concentrate from the concentrate storage building to the flash smelting furnace feed system.
The conveyor was 800mm wide EP250, 220 meters long, running at 1.5 m/s. The concentrate was a mixture of copper sulfide concentrates averaging 28% Cu content with significant iron sulfide content.
The belts were failing at 3β4 months with cover blistering and cracking β the same heat-damage signature seen in underpowered heat-resistant specifications.
Investigation
Temperature measurement at the concentrate loading point showed ambient temperature of 55β65Β°C from radiant heat from the smelting furnace building and the concentrate drying system nearby. The concentrate itself was pre-dried and warm β surface temperature at loading approximately 70β85Β°C.
The existing EP250 belt had standard SBR covers. SBR softens and degrades above 70Β°C sustained exposure. At 55β65Β°C ambient plus 70β85Β°C material contact, the cumulative thermal load exceeded what standard SBR could handle.
Additional factor: Copper concentrate contains sulfur. Sulfur compounds are aggressive to standard rubber compounds, accelerating degradation beyond the thermal effect alone.
Specification
The replacement specification needed to address both heat and sulfur compound exposure:
Cover compound: T1 grade EPDM with sulfur-resistant modification - T1 rated to 100Β°C material contact temperature - EPDM base compound resists both moderate heat and sulfur compounds better than SBR
Carcass: EP250 (unchanged β adequate for tension requirements) Width: 800mm (unchanged) Top cover: 8mm (increased from 6mm for additional thermal buffering) Bottom cover: 4mm
Additional measure: A partial enclosure was built around the loading zone to reduce radiant heat from the furnace building reaching the belt. This reduced ambient temperature at the belt surface from 65Β°C to approximately 48Β°C β below the point where even standard covers would be stressed.
Outcome
The T1 EPDM belt with the partial heat shield ran for 18 months before the first inspection showing significant wear. Cover degradation was from normal abrasion rather than heat damage β no blistering or cracking observed. Projected total life: 24β28 months.
This compared to 3β4 months for the previous standard SBR belt β approximately 6β7Γ improvement in belt life.
The partial heat enclosure cost relatively little to build and contributed meaningfully to the improvement. Reducing ambient temperature below the cover compound's stress threshold made the specification more robust with less margin dependence.
Key Points
Ambient temperature matters as much as material temperature. A belt in a hot smelter environment is stressed by both the material on top and the radiant heat from surrounding structures. Measuring only material temperature can underestimate total thermal exposure.
Sulfur compounds attack rubber. Standard SBR and NR rubber is attacked by elemental sulfur and sulfur compounds. Copper concentrate, zinc concentrate, and other sulfide mineral products contain sulfur. EPDM has better sulfur resistance than SBR β specify it for sulfide concentrate applications.
Enclosures reduce specification burden. Sometimes the cheapest solution is a heat shield or enclosure that reduces the environment the belt operates in, rather than a more expensive specialty belt compound to cope with the harsh environment. Both approaches work; the right answer depends on relative costs.
Elephant Rubber supplied the T1 EPDM belt for this project.