Recent investments have made Boliden’s Garpenberg mine one of the most modern and productive in the world. This is a great feat for Sweden’s oldest, still active mine, which can trace its history back to the 13th century.
“I get about the same penetration rate with Powerbit, but a lot longer service life.”
Production at this complex ore mine will be 2.5 million tons per year when full capacity is reached in 2016. The ore contains zinc, lead, copper, silver and gold. Approximately half of the tailings sand is pumped back to fill the mine. The remaining part, about 1 million tons annually, is filled into the tailings pond. Most of the water from the pond is recirculated and used again in the metal concentration process. Excess water is filtered through a water treatment plant, and the clean water is let out to neighbouring streams. Every year, the dam needs to be raised a meter. To achieve this, tophammer drilling and blasting is done nearby to get material to raise the top of the dam.
The medium hard and very abrasive rock in Garpenberg is a real challenge for drill bits. Normal service life is approximately 250 meters drilled per bit. Powerbit testing was performed with retrac Powerbits, with 12.0 or 12.7 mm Trubbnos buttons. These Powerbits were compared with the driller’s normal 12.0 mm semi-ballistic button bits. The test results were excellent, and above expectations. Comparing the 12.0 mm button Powerbits with the reference bits indicated that the Powerbits have a slightly better penetration rate, and much better service life. Even more impressive is the fact that the Powerbits with 12.7 mm HD (heavy duty) buttons increased service life by 75 % with little or no loss in penetration rate.
At the end of the day, Powerbit delivered more meters drilled before the first regrind, more meters drilled between regrinds, and many more meters drilled at bit discard. “I get about the same penetration rate with Powerbit, but a lot longer service life”, states Mikael Waldén, driller at Berg- och Byggteknik. A key success factor when drilling in the hard, abrasive rock of Garpenberg, Sweden, was the use of Trubbnos grinding wheels. Re-creating the Trubbnos button shape at each regrind resulted in less frequent grinding and greatly increased overall service life of the bit.