Background
A potash mining operation in Central Asia was experiencing unusually rapid cover degradation on the conveyor belts transporting potassium chloride (KCl) product from the crystallization plant to the product storage building. The conveyors were 600mm wide EP200, approximately 180 meters long. Standard M24 cover grade belts were being replaced every 5β6 months β well short of the 18β24 months expected for this relatively light-duty application.
Investigation
The failure mode was cover swelling, softening, and surface tackiness β not abrasion wear. Potassium chloride itself is a mild abrasive, but not aggressive enough to cause the observed degradation rate. The symptoms pointed to chemical attack rather than mechanical wear.
Investigation of the process environment identified two factors:
1. High humidity and hygroscopic salt. KCl is highly hygroscopic β it absorbs moisture from the air and forms a brine (concentrated KCl solution) on the belt surface. Standard SBR compound is attacked by concentrated potassium chloride brine over time, causing the observed swelling and softening.
2. Residual process chemicals. The crystallization plant process involved trace amounts of ammonium compounds that occasionally reached the belt surface with the product. Even at low concentrations, these accelerated SBR degradation.
Specification Change
The replacement belt was specified with EPDM compound covers β ethylene propylene diene monomer rubber, which has substantially better resistance to salt solutions, mild acids, and alkalis compared to SBR.
EPDM is the standard recommendation for: - Potash and salt handling - Fertilizer (especially ammonium-based) handling - Areas with exposure to mild process chemicals - Outdoor applications where ozone resistance is also needed (EPDM has excellent ozone resistance)
The belt specification: - EP200, 600mm wide - Top cover: 6mm EPDM compound, M24 equivalent abrasion - Bottom cover: 4mm EPDM
Outcome
The EPDM belt was installed. At 14-month inspection, no chemical degradation symptoms were observed β no swelling, no softening, no surface tackiness. Cover wear was minimal (approximately 15% of top cover thickness lost), consistent with the light-duty mechanical loading of the application.
Projected belt life: 5β7 years based on the wear rate observed at 14 months. This compares to 5β6 months for standard SBR covers.
Process Change Consideration
In parallel with the belt specification change, the plant maintenance team reviewed how ammonium compound residues were reaching the conveyor. A minor process adjustment at the crystallization plant (improved wash-down before product transfer) reduced the ammonium contamination of product, which further improved the belt environment. This was not the main solution β the EPDM compound handled the chemical exposure regardless β but it improved conditions generally.
Key Points
Chemical failure looks different from abrasion failure. Swelling, softening, and tackiness are chemical degradation symptoms. Abrasion failure produces a steadily thinning cover with normal texture. Recognizing the difference leads to the correct solution.
Potash and salt handling requires chemical-resistant covers. This is not an unusual application β potash mines and fertilizer plants worldwide use EPDM or other chemically resistant compounds for belt covers exposed to salt brines and ammonium compounds. SBR is the wrong material for this environment.
The correct compound costs little more than standard SBR. EPDM compound costs modestly more per meter than standard SBR. The cost difference is trivial compared to the labor and downtime cost of a belt replacement every 5 months.
Elephant Rubber supplied the EPDM compound belt for this application.