COMMINUTION AND CRUSHING
The new Joy Global MVT-II
lower operating cost but a much higher total installation cost. Although in general, gyratory crushers have good availability, the machine will have downtime at a high cost.” Joy Global says it has had large copper producers interested in using feeder-breakers as a backup to their existing gyratory crushers.“ Even with today’ s commodity prices, a backup feeder-breaker would not have to have very high utilisation to justify the expense.”
The MVT-II is Joy Global’ s secondary and tertiary sizer product. The term“ MVT” stands for Matched Velocity Technology. The machine is designed so the tooth speed is set to match the speed of the mineral falling through the machine.“ Testing has shown this significantly reduces fines generated in secondary / tertiary crushing. The machine uses hard cast alloy wear segments available with different tooth configurations, dependent on the application. Teeth are available in white iron or work hardening alloys. The segments are connected to the shafts with bolts and keys. The design allows users to quickly replace worn segments. Worn segments are not scrap; customers can renew them by replacing the teeth and applying chromium carbide weld overlay. Joy Global also offers a program where it exchanges worn segments for factory renewed parts. Changing the segment used allows easy reconfigurion to produce a different product size. On a recent project, Joy supplied two machines where the direction of shaft rotation is reversible. This allows the machine to centre-size to make a fine product and side size when the mine is selling a coarser product, all with a push of a button.”
Grinding media developments
Grinding media has always been the secondhighest operating expense, after energy consumption, for many mining customers. Reducing the consumption of grinding media while simultaneously improving grinding efficiency and reducing energy consumption are common issues in the mining industry.
Cobre Las Cruces( CLC), the copper mine
located near Seville in southern Spain and part of First Quantum Minerals Ltd, is an open-pit operation and process plant that produces high grade A copper cathodes, over 80 % of them destined for the domestic market.
An atmospheric leaching process is used to recover the copper from the very rich Las Cruces chalcocite ore. Three crushing stages and a single grinding stage feed the mine ore to the leaching reactors and then further into the hydrometallurgical process. With an average copper grade of around 5-6 %, the Cobre Las Cruces deposit is 7 to 12 times richer in copper than other similar mines. Processing 1.5 Mt of ore brings 72,000 t of 99.999 % pure copper every year. With an estimated mine life to 2022, Cobre Las Cruces is currently investigating further expansion possibilities.
Exploration of the mine started in 1992 and production started in 2009. Since then, Metso has provided Cobre Las Cruces with forged balls( 80 mm size) and linings for their 5 x 6.95 m primary ball mill.“ Since the start, we’ ve always been very satisfied with the quality of the products and service provided by Metso,” says Lucas Alcón, Minerals Process Manager at CLC.“ During the plant studies, their EPC partner, SNC Lavalin, selected Metso for its high-quality products and proximity to the CLC mine to be the supplier of the balls and mill linings. We’ ve never had these products from other suppliers, as Metso keeps giving us the desired satisfaction one expects from their products,” he continues.
CLC has had several successful programs with Metso in order to reduce ball consumption and grinding ball inventory, save energy or improve the end product from the grinding stage.“ Since the start of operations, one real change was implemented and another might be just around the corner. A couple of years ago, tests were done with feeding different ball sizes( 80 mm and 60 mm) into the mill, but it didn’ t lead to significant improvements. A decision was then made to continue producing with only the 80 mm size balls. A later test was carried out with harder grinding balls, and a significant increase in lifetime was detected. The balls have a higher wearresistance and keep their round shape a lot longer. Today CLC and Metso are planning a new pilot test with superior quality balls to determine whether the yearly ball consumption could be further reduced.”
Alcón clearly states that all of these challenges are positively impacted by many factors, among
which, is the quality of Metso’ s grinding balls.“ Since the start of the operations here, we haven’ t seen any broken balls and the shape of the balls produced by Metso are close to being perfect,” he says.“ These clearly influence the grinding efficiency and energy consumption in a positive way. Over the years, Metso has always partnered with us to find better solutions to these challenges. They bring us the best benefits when comparing grinding media and mill linings from other suppliers. Today our whole plant is running at over 95 % availability, which is above international standards, and we’ re sure that is partly the result of working together with Metso.”
Reducing grinding consumption while simultaneously improving grinding efficiency and reducing energy consumption are common issues in the mining industry.“ Our grinding balls can help improve each of these in a significant way,” says Santiago Fernandez, Manager of Metso’ s Forjas del Guadalquivir operations and manufacturing facilities.“ This, in combination with our proximity to Cobre Las Cruces, has benefited our valued customer. Thanks to lower inventory levels, lower ball consumption and more recovery, they are able to better use their financial resources.”
In addition to the grinding media, CLC is also using Metso’ s Poly-Met™ mill lining, which they are very satisfied with, according to Rafael Sánchez, Maintenance Supervisor at the CLC plant.“ We are able to change the plates and lifter bars inside the whole mill in only two days; and since we are using the Poly-Met lining, we only need to do this every 7 to 8 months. This previously was needed every 4 to 5 months. This reduces our plant downtime and, consequently, also the costs involved. Since we changed to the Poly-Met mill lining, our costs decreased by around 15 % due to the longer wear life and fewer liner changes. The Metso grinding balls also have a positive influence on the changing schedule, as the quality of the balls definitely increases the lifetime of the linings,” he stipulates.“ Together with the Metso crew we’ re now looking into increasing the lifetime of the mill linings even further by eventually switching to a thicker size. Many factors influence the time between changes( quality of the grinding media and mill lining, mill speed, mill lining design, etc) but we have no doubt that we’ ll find the right balance with Metso’ s help,” he concludes.
When it comes to grinding media; design, raw material and manufacturing rigidity are critical for maximum performance. ME Elecmetal states:“ The worldwide success of the ME Elecmetal Grinding Media division is built on these three factors, as well as world class logistics and robust application engineering support. Since the introduction of SuperSAG ® and Ultragrind ® media
60 International Mining | MARCH 2017