Background
A gold mine in Tanzania was experiencing repeated belt splice failures on its main ore conveyor β 900mm wide EP315, 420 meters long, carrying crushed ore from the secondary crusher to the ball mill feed bin at 800 tonnes per hour.
Over 18 months, the splice had failed four times. Each failure required a 6-hour conveyor stop for re-splicing. The maintenance team was frustrated and had started questioning the belt quality.
Investigation
Before assuming belt quality was the problem, a systematic review of the splice failures was conducted.
Splice failure documentation review: The four failures were all at the same splice location β the same joint that had been re-made each time. This was the first diagnostic indicator. If the belt carcass were weak, failures would be distributed along the belt length. A repeated failure at the same location points to a splice-specific problem, not a belt material problem.
Splice crew interview: The splice crew who had made all four splices was questioned about their process. Key findings: - The crew had not received formal vulcanized splice training - The vulcanizing press they used was a portable unit that they acknowledged "sometimes had temperature variations" - Cure time had been reduced twice when production pressure demanded the conveyor be restarted before the standard cure cycle was complete
Press equipment inspection: The portable vulcanizing press was tested with a calibrated thermometer. Results showed temperature variation of Β±18Β°C across the platen surface β the standard recommendation is Β±5Β°C maximum. At the cooler edges of the platen, cure temperature was insufficient to achieve full vulcanization of the splice rubber.
Splice sample analysis: A section of the most recently failed splice was examined. The bond between the splice cover rubber and the belt cover showed incomplete vulcanization β the rubber had not fully cross-linked, resulting in a weaker bond than a properly cured splice.
Root Cause
The splice failures were caused by a combination of: 1. Inadequate splice crew training 2. A defective vulcanizing press with non-uniform temperature distribution 3. Insufficient cure time on two occasions
The belt quality was not a factor. The same belt on a different conveyor in the same mine, spliced by a contractor with proper equipment and training, had run for 26 months without splice issues.
Corrective Actions
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Press replacement: The defective portable press was replaced with a unit from a reputable manufacturer, verified to achieve Β±4Β°C temperature uniformity across the platen.
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Training: Two maintenance staff attended a formal vulcanized belt splicing course. The course covered step preparation, rubber application, press setup, temperature monitoring, and cure time requirements.
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Cure time policy: A written maintenance procedure was established specifying that cure time could not be reduced regardless of production pressure. The procedure required a supervisor sign-off before the press could be opened.
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Splice documentation: Each splice was logged with date, crew members, press temperature profile (recorded from the press's data logger), and cure time. This created accountability and a maintenance record.
Outcome
The splice made with the new press by the trained crew ran for 22 months without failure β the longest period the conveyor had run without a splice issue since commissioning. The splice was still in service at the 22-month inspection and showed no abnormalities.
Key Points
Repeated failure at the same location is a splice problem, not a belt problem. This distinction is important and avoids unnecessary belt replacement.
Press calibration is not optional. A vulcanizing press with poor temperature uniformity produces unreliable splices regardless of how skilled the crew is. Press equipment should be verified before use.
Production pressure on cure time is a false economy. Each splice failure cost 6 hours of downtime. A proper cure takes an additional 30β45 minutes. The math is straightforward.
Elephant Rubber provided technical consultation and splice training materials for this investigation. The replacement belt was also supplied by Elephant Rubber.