The past six years have seen a close cooperation between the rope manufacturer Casar and the Telfer gold mine in the Pilbara region in the state of Western Australia. The Telfer mine is wholly owned by Newcrest Mining. Gold and copper are extracted, above ground as well as underground. The copper and gold deposits were discovered in 1972, and mining began in 1977. In 2008 it was decided to increase the extraction capacities to over six million tons per year.
This provided the basis for initial talks between Telfer and Casar. As well as wanting to increase extraction capacities, the mine operator was not happy with the service life of the ropes from another manufacturer that were in use on the floor hoisting machine. The hoisting machine is a ground-mounted friction winder that transports a payload of 34.5t at a speed of 16.25m/s from a depth of 1,132m to the top.
The service life of the original ropes was maximally 95,000 cycles, corresponding to almost a year. The costs incurred by downtimes and the rope replacement after 95,000 cycles were immense and had to be drastically reduced to make extraction cost-effective. After a detailed study of the site and application, Casar decided to deploy a Starplast construction. This is a rotation-free rope construction made of compacted strands. A rope set consists of four hoist ropes, each with a length of 1,360m and a rope diameter of 45mm.
Casar succeeded in continuously increasing the lifetime, up to an impressive 210,000 cycles reached with the third version of Starplast. The lifetime was more than double the previous figure. Furthermore, the ropes were in perfect condition even after these 210,000 cycles and only had to be discarded as a result of mechanical damage due to rockfall, not because of wear and tear.
In addition, it was possible to virtually exclude undesired effects such as rope elongation and rope slipping on the drum, and wear on the inlays of the rope discs was reduced to less than a quarter of the previous value. In particular, the reduction of the elongation effect is highly valued by Telfer as the usually necessary shortening of the ropes after occurrence of the setting effect is no longer necessary. At present the value of elongation for the fourth version of Starplast is less than 800mm.
Casar and Telfer are confident that they are able to use the knowledge gained to further increase the service life to over 300,000 cycles. In this case the ropes would not have to be replaced for at least three years. This alone would represent major cost savings for the mine and also save a lot of time, which could be used for other maintenance and repair work. It is estimated that at least 10 working days that would normally be needed to replace the rope could already be saved during the service life of the rope currently being used.
The ropes currently in use already reached 170,000 cycles in March 2015 and are still in perfect condition. Casar is therefore confident of reaching the set goal.
Telfer reports that it particularly values the fact that the efforts started in 2008 aimed at increasing the service life were backed up throughout with advice and support. Not only were system measurements and destruction-free rope examinations carried out on site, but there were also intensive examinations of discarded rope pieces, always focused on improving the product.
Overall, this package of customised products coupled with outstanding expertise and technical support on-site has justified the higher purchase price of these ropes. As a result, Telfer has purchased its hoist ropes exclusively from Casar since 2009.?
Christian Schorr-Golsong is with Casar. www.casar.de
