Boliden is a metals company operating mines and smelters in Sweden, Finland, Norway and Ireland. Production at the Garpenberg mine comprises complex ore containing zinc, copper, lead, gold and silver. Major expansion plans for the mine with SEK 3.9 billion investments over a period of three years also include investments in high-performance condition monitoring equipment for a number of critical applications such as the jaw crusher, main hoist and concentrator mill, all for the purpose of securing the planned production increase.

The mill drum rotates at 15.7 RPM, driven by two frequency-controlled motors on opposite sides. Via a two-stage gearbox, a pinion gear drives the drum itself. To monitor the mill, a total of twenty shock pulse and eight vibration transducers are used, covering the motor, gearbox and drive shafts. Two RPM probes are mounted on the drive shafts.

During the period from January, 2012 to October, 2013, two serious problems were detected well before any serious consequences. The first incident was a bearing damage found in one of the two gearboxes. The other was a loose gear (wobbling gear) in the same gearbox. Both of these problems could have caused serious malfunctions with severe economic consequences, had they gone undetected.

The combination of vibration and shock pulse measurement is ideal for this type of application. The shock pulse technology is very suitable for detection of bearing damages in “noisy” environments like the gearboxes in this case study. Vibration technology is optimal for low frequency-related fault conditions like unbalance, loose gears and misalignment.

After more than 21 months of measurements the system is performing very well. Thanks to the sensitivity of the system and the long forewarning times, maintenance actions can be planned well in advance, thus creating a sense of being in control of this mission critical application.