Chilean copper group Codelco has awarded a large scale conveyor system for its El Teniente mine expansion to Takraf. The system connects a new ore body to the existing processing facilities. In its final stage it will transport primary crushed copper ore at more than 12,000 t/h. Running at 6 m/sec, the 2 m wide belt conveyor system will carry the ore over almost 12 km. The three principal conveyors, one 9 km long tunnel conveyor and two 1 km steep uphill conveyors (slope of 15°) to feed the existing stockpile and in the future a new stockpile. The contract also involves the extension of an existing conveyor line. For this it will be necessary to carry out the final tie-in within just a four day shutdown. Constructability is therefore of fundamental importance to the success of the project and is incorporated in all design aspects.

With ever increasing energy cost, drive efficiency and conveyor running resistance is becoming more and more important. Codelco has therefore selected direct or gearless drives. The higher efficiency of the direct drive, combined with the variable speed will provide long term benefits to the project. It will also allow the El Teniente operations to run the conveyor system initially at lower speeds to suit the lower conveying capacities in the earlier years of production thus saving power and reducing wear, which will further save maintenance cost. Reduced maintenance combined with its high efficiency and reliability are strong points in favour of gearless conveyor drives.  Takraf in partnership with ABB has integrated features within gearless drives which have already been standard features for conveyor drive systems for a long time – for example ease of alignment and ease of drive change. The aim has been to reduce the amount of work in the field to an absolute minimum so that a faulty drive can be simply replaced and repaired in the shop.

In order to accomplish this the motor is mounted on a special base frame. This also allows the use of standard pulleys – another important feature. The configuration of the direct drive unit can induce very significant forces into the pulleys which have caused considerable problems with pulleys in the past but with the Takraf, design this has been eliminated. Takraf says its innovative approach has produced “a reliable and easy to maintain drive concept combining proven technology with state of the art direct drives. Particularly the long tunnel conveyor has been designed to minimise its running resistance by ensuring accurate alignment through special conveyor frames and the use of low running resistance rubber compound for the belt.” The two steep inclined conveyors, which in their final stage will be both equipped with four 2,500 kW drives, presented some challenges particularly regarding the service of the idler rolls along the conveyor run, which is mainly in tunnels. With idler rolls weighing 45 kg respectively, 65 kg manual handling is not only difficult but carries a high risk of injury for the maintenance personnel.

For this reason Takraf has developed a unique system to service these steep conveyors. A special maintenance cart straddling the conveyor has been designed to minimise the tunnel cross section. It is equipped with a small service crane and runs on rails along the entire conveyor length. The crane is fitted with special lifting frames which pick up the rolls and help to place them in position. The maintenance personnel only need to “manipulate” the rolls, the weight is taken by the crane. The cart can carry spare rolls, all required tools and up to four people. This makes idler roll changes a safe and easy task. The group adds: “Special attention has been played to safety with independent and fail-safe braking and clamping systems. Takraf`s focus on safety, maintainability and long term reliability of the system and the combination of proven technology with the latest advances in conveyor design have contributed to Takraf`s success in the market place in general and to this project in particular.”