Continuous mining systems have been established in coal and soft rock mining for about a century now and the technology to cut through hard rock has been successfully used in civil engineering projects since the late 1950s. One would think that by now, continuous hard rock mining would also be a reality but it is not. The possibility of the technology being applied to hard rock mining has in fact remained stuck between a rock and a hard place for a very long time – until now. Drilling and blasting finally has an emerging competitor.
Last September at MINExpo 2016, Caterpillar commercially launched the Cat Rock Straight System, a fully-mechanized longwall system for continuous hard rock mining that features the cutting- edge HRM220 hard rock miner. While Caterpillar is the first to reach commercialization, it is not the only one striving to develop the technology. Atlas Copco, for example, began working on its new generation Mobile Miner continuous hard rock mining technology with Rio Tinto in 2009. It has been working with Anglo American on the development of a continuous hard rock mining system, in a project named Rapid Mine Development System (RMDS), since 2012. Testing of the RMDS at an Anglo American mine began in 2016. Those tests are close to completion and Atlas Copco is planning a formal commercial launch later this year, said Mikael Ramström, Atlas Copco’s director for mechanical rock excavation. As well, Joy Global, now Komatsu Mining, has been testing the prototype for its DynaMiner, which features DynaCut hard-rock cutting technology, since September 2016 with very promising results, according to the company. Sandvik is also developing a continuous hard rock miner called the MX650, but declined the opportunity to discuss its work with CIM Magazine.
Different approaches
The biggest problem with mining hard rock is that it is difficult to break mechanically and that poses challenges in advance rates and energy use, not to mention how quickly it wears down cutting parts. Each manufacturer is using a different approach to increase the wear life of components and reduce the time and energy it takes to break the rock. Caterpillar’s HRM220 has numerous picks mounted on two cutting heads to hit the rock from an angle designed to exploit the rock’s tensile strength, which is 10 to 20 per cent of its compressive strength. “The movement, or activation, of the cutting tool enables each pick to hit the rock with momentum like a hammer,” said Jens Steinberg, commercial manager of hard rock cutting for Caterpillar Global Mining. “The contact is very short and it limits pick heating and wear. The movement is achieved by superimposing rotational movements.”
Komatsu Mining’s DynaMiner, on the other hand, employs a DynaCut disc mounted to a smart boom that oscillates. Using an undercutting method, the system chisels the rock with action reminiscent of a heavy, high-speed hammer that exploits the weaker tensile properties of the rock as well.
Like the DynaMiner, Atlas Copco’s Mobile Miner uses disc cutters, a technology based on what is used in conventional tunnel boring machines. The company continues to refine the technology. “You have to tune your machine to excavate rock at a certain speed and that speed is very much dependant on the hardness of the rock,” said Ramström. “You can have discs working at a very high speed but that increases the wear on the parts, so you try to tune the machine for that specific rock hardness.”
To do this, the Mobile Miner uses sensors in its hydraulic system that monitor how the rock is responding to the pressures and adapts the force accordingly. In fact, modern computer and sensor technologies are being used in all the new hard rock miners for more intelligent and efficient cutting in machines more compact than those used in conventional tunnel boring.
