Background
A potash mining operation in the Caspian Depression region of Kazakhstan was commissioning a new overland conveyor to move potash ore from the mine head to the processing plant — a distance of 3.2 kilometers across flat steppe terrain. The conveyor was designed for 2,200 tonnes per hour of potassium chloride (sylvinite ore) at a belt speed of 3.5 m/s.
The environment combined multiple challenges: - Steppe winter temperatures reaching -40°C - Summer temperatures reaching +42°C - Highly abrasive halite (rock salt) gangue in the ore - Potassium chloride is hygroscopic and mildly corrosive to standard rubber
Belt Selection
Tension calculation: For 3.2km flat at 2,200 t/h at 3.5 m/s, calculated maximum belt tension was approximately 285 kN/m. With safety factor of 7: minimum break strength = 1,995 N/mm. Selected: ST2000, 1,400mm wide.
EP belt was not viable at this tension — EP630 (maximum standard EP) provides only 630 kN/m, far below the 1,995 N/mm requirement. Steel cord was the only practical option.
Cover compound: Four requirements had to be satisfied simultaneously: 1. Cold-flex to -45°C (Kazakhstan steppe winter) 2. Heat-stabilized to +50°C surface temperature (summer) 3. Chemical resistance to KCl brine (potash is hygroscopic — the belt surface is often wet with KCl solution) 4. Abrasion resistance for halite gangue (rock salt at Mohs 2.5, but in angular crystalline form)
Standard cold-flex SBR compound handles cold but has limited KCl resistance. EPDM handles chemicals but standard EPDM is stiffer at low temperature than the -45°C requirement needed.
The solution was a custom cold-flex EPDM compound — EPDM formulated with a low-temperature plasticizer package to achieve flexibility at -45°C while retaining EPDM's chemical resistance to KCl. This is not a standard off-the-shelf compound; it required formulation work and testing before production.
Cover specification: - Top: 10mm cold-flex EPDM, M24 equivalent abrasion - Bottom: 6mm cold-flex EPDM
Compound Verification
Before committing to the full belt order, a compound sample was tested: - Brittleness temperature test (ASTM D746): passed at -48°C - Low-temperature flexibility test (ISO 4661): acceptable flexibility at -45°C - KCl immersion test: minimal swelling after 30 days in saturated KCl solution - Abrasion test (DIN 53516): abrasion loss 82mm³ (within M24 requirement of 90mm³)
All four tests passed. The compound was approved for production.
Installation and Commissioning
The 3.2km belt was shipped in 12 rolls of approximately 267m each. Splicing was done on-site during commissioning — 11 vulcanized splices total, each requiring the trained splicing crew approximately 4 hours per splice.
The commissioning was during summer (July) when the ambient temperature was +38°C — favorable for vulcanizing but a reminder of the thermal range the belt would experience over its service life.
Winter Operation Verification
The first winter operation (November through March, temperatures -30°C to -40°C) was monitored carefully:
- Belt start-up at -38°C: no unusual stiffness observed, drive motor current within normal range
- Cover flexibility on return run: no cracking observed at tail pulley (-40°C recorded during inspection)
- Carryback: slightly increased in deep winter (KCl adheres more at low temperature) — managed by adjusting scraper tension monthly
The belt performed within specification through the first winter. The cold-flex EPDM compound behaved as the low-temperature flexibility tests predicted.
Key Points
Long flat overland conveyors almost always require steel cord. The tension calculation determines this — EP belt capacity tops out well below what a 3km+ high-tonnage conveyor requires.
Multi-requirement environments need custom compound solutions. Cold AND chemical resistant AND UV stable is sometimes achievable with a standard compound, but not always. When standard options don't cover all requirements, custom formulation is the answer — but it requires verification testing before production.
Don't skip compound verification testing. A compound that fails in service on a 3.2km ST2000 belt is a very expensive failure. The cost of pre-production testing is trivial relative to the risk.
Elephant Rubber developed the custom cold-flex EPDM compound and supplied the ST2000 belt for this project.