Spotlight Feature Articles ME Elecmetal Comminution Mar17 | Page 6

COMMINUTION AND CRUSHING
advantage of cost-effective short haul truck and shovel operations . High throughputs and short relocation times enable mines to achieve their efficiency and productivity goals whilst delivering a greener approach to mining .
Introducing the Joy MVT-II
Joy Global has supplied customers with more than 2,500 feeder-breakers to date , both underground and in surface mining . Thanks to its decades of experience in the industry , Joy Global is able to provide machines with high capacities that work in difficult applications . “ Joy has supplied feeder-breakers with capacities over 6,000 t / h and can crush materials with a compressive strength of over 200 MPa . A feederbreaker is unique in that the mineral moves horizontally through the machine . This allows the installation height of a feeder-breaker to be lower than most other types of crushing equipment with comparable capacity . A low installation height reduces the civil works cost of a typical primary crushing installation by reducing the height of the retaining wall . The lower centre of gravity allows the machine to be more easily relocated . Combining low installation cost and ease of relocation make feeder-breakers a good fit for customers looking for a semi-mobile crushing station .”
Recent surface mining applications for Joy feeder-breakers include limestone , phosphate , coal , bauxite , overburden , nickel and gold ores . “ If you compare an 8,000 t / h gyratory crusher to two 4,000 t / h feeder breakers in a hard abrasive application like copper ore , the gyratory has a 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
The new Joy Global MVT-II
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
International Mining | MARCH 2017