Background
A cement plant in northern India was experiencing premature failure of the belt on its clinker conveyor. The conveyor carried hot clinker from the grate cooler outlet to the clinker storage silo — a conveyor approximately 120 meters long with a 15-meter lift.
The plant had been running standard M24 grade EP315 belt. Belts were lasting 4–6 months before cover blistering and cracking required replacement. The plant manager described the belt surface as "melting" in areas.
Investigation
The plant's maintenance team had assumed the belt was failing due to abrasion — clinker is highly abrasive — and had been specifying M24 cover grade (good abrasion resistance) accordingly. However, the failure mode described (blistering, cracking, surface softening) is not consistent with abrasion. These are heat damage symptoms.
Temperature measurements were taken at the loading point using an infrared thermometer:
- Clinker temperature at cooler discharge: 145–175°C (varying with kiln output)
- Clinker temperature at belt loading point (after short chute travel): 135–160°C
Standard SBR and NR rubber compounds begin to soften at 70°C and degrade significantly above 90°C. The M24 cover (standard SBR compound) was completely unsuited to this application. The 4–6 month belt life was not a quality problem — it was a specification problem.
Correct Specification
The correct specification for this application was a T2 heat-resistant belt (rated to 150°C material contact temperature per DIN 22102), using an EPDM compound cover.
Given that clinker temperatures occasionally reached 175°C at the cooler discharge, the loading point temperature of 135–160°C was within T2 range but with limited margin. The recommendation was:
- Primary specification: T2 EP315, EPDM cover, M24 equivalent abrasion resistance
- Cover thickness: Top cover 8mm (thicker than standard to provide more heat-buffering mass)
- Additional measure: Improve cooler performance to reduce clinker exit temperature — this was a process issue beyond the belt specification
The plant was also advised to install a thermal shield over the first 10 meters of the conveyor at the loading zone, reducing radiant heat from the nearby cooler structure onto the belt's return run.
Outcome
The T2 belt was installed. Over the following 14 months of operation, no heat-related cover damage was observed. The cover showed normal abrasion wear (clinker is abrasive) but no blistering, cracking, or softening. The belt was still in service at the 14-month inspection, compared to 4–6 months for the previous specification.
The thermal shield was installed during a planned shutdown. This had the additional benefit of reducing the ambient temperature in the drive motor area, which was previously running hot.
Key Lessons
Failure mode analysis before re-ordering. If a belt fails in 4–6 months and the failure looks like blistering or cracking rather than gradual surface wear, suspect heat damage before assuming the belt quality is poor. The same belt that fails in 4 months due to heat would last years in a room-temperature application.
Measure material temperature, not process temperature. The kiln itself operates at 1400°C — that's irrelevant to the belt. What matters is the temperature of the material when it contacts the belt. In this case, the cooler reduces temperature significantly, but not to a safe level for standard belt.
Cover thickness provides thermal buffering. A thicker cover takes longer for heat to penetrate to the carcass. This is not a substitute for the correct compound, but it adds margin in applications where temperature is at the edge of a grade boundary.
Elephant Rubber supplied the T2 EPDM heat-resistant belt for this application.
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