Last year, Cortez’s four conveyor belts, which cover 15 miles and move 1,000 tons of ore per hour, were down for several months due to cable breaks like the one that occurred in July.
This time was different. A new monitoring system installed in January detected the flapper immediately and halted the conveyor. Repairs were made within hours, and the conveyor restarted the same day. The new system is an early example of the operational improvements and cost savings that are possible as Cortez begins digitizing its operations. Without the early warning, thousands of feet of cable would have unraveled before the break was discovered.
The new system has already paid for itself by detecting several potentially catastrophic breakdowns
Repairs in such cases take months, as new cable needs to be sourced and shipped from overseas. Last year, Cortez spent $1 million to purchase 50,000 feet of steel cable belt. When conveyors are down for prolonged periods, haul trucks are diverted from their regular duties to move ore to mill stockpiles—an activity normally performed by conveyors. This slows production and impacts costs.
“It increases our costs per ton substantially,” says Dave Yazzie, General Supervisor of the Overland Conveyor.
Cortez began testing the new monitoring system last year. The system uses sensors that magnetize the steel cables embedded in the conveyors. When a cable breaks, the sensors detect the resulting the electromagnetic surrounding the break area. Based on the strength of the field, the sensors can determine the size of the break and number of broken cables. The sensors connect to software in computer control rooms near the conveyors. When an anomaly occurs, a red light appears on a computerized model of the conveyor in the approximate area of the break. If the break exceeds pre-programmed parameters, the system automatically stops the conveyor and generates an alert. The alert tells the technicians the location and size of the break so they can efficiently locate it and make repairs.
“It’s fairly new technology and we’re one of only a few companies using it on this scale,” says Matt Majors, Process Maintenance Superintendent at Cortez.
The new system, made by Phoenix Conveyor Belt Solutions, cost just $210,000 to install. It has already paid for itself by detecting several potentially catastrophic breakdowns, Yazzie says. “The power of this is that it catches damage early so we can fix it before the damage grows and destroys thousands of feet of belt,” he says.
The mine’s previous rip-detect system relied on small, loop-shaped sensors interspersed throughout the conveyors. The sensors were thin and broke easily. As a back-up, the mine conducted manual scans of the conveyors every six months, but that was far too infrequent to prevent failures. “We’d be running blind with no protection,” Yazzie says.
The new, more robust real-time monitoring system has been a big improvement. Through August of this year, the Cortez conveyors had moved more tons of ore than in all of 2015.
However, the new system is just a start and does not detect all failure scenarios. If a piece of metal, for example, damages a conveyor without breaking any sections of cable, the system will not detect it. This scenario played out recently at Cortez resulting in a prolonged shut down of a conveyor. “It doesn’t cover all failure modes, but it covers us way more than we used to be,” Yazzie says.
Ultimately, as the digitization of Cortez advances, Yazzie and Majors envision further improvements that facilitate predictive maintenance. For example, deploying RFID (radio-frequency identification) technology would allow conveyor operators to identify when spliced sections of a belt are at risk of pulling apart. Integrating the new monitoring system with other predictive tools such as vibration and belt-tension monitoring would help generate more robust data that could be used to perform preventative maintenance and avoid unscheduled shutdowns.
“That is where we want to go,” Majors says.