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Challenges of mechanised fragmentation in hard rock mining

Application of mechanised cutting/fragmentation technologies in hard rock mining environment is impeded with the limitations of the existing technologies: being power, size, mobility, and cutter life. Cutting technologies of hard rock mining should be robust and powerful to endure high reaction forces from breaking through strong material, but at the same time be flexible and small in size to navigate through sharp turns and confined spaces of underground mines.

Three main classes of rock cutting tools
Fig 1: Three main classes of rock cutting tools

Tunnel Boring Machines (TBM), which use roller disc cutters (Fig 1) and are predominantly used for excavation in civil engineering projects, are powerful and effective in cutting through very strong rocks; however, are large, cumbersome and inflexible, making them unsuitable to manoeuvre in narrow mine spaces. The road headers, which use drag picks (Fig 1), on the other hand, have the required mobility but are limited in power and cutter life and cannot effectively break through strong rocks. Therefore, there is a need for alternative cutting method that allows reducing the size of the excavation machines, without compromising their effectiveness in breaking hard rocks.

At CSIRO Hard Rock Mining program, we investigate a new dynamic cutting technology, which uses disc-shape cutters attacking the rock in an undercutting mechanism (Fig 1), as a solution for mechanising the hard rock mining.

Advantages of Undercutting Disc Technology

Undercutting disc technology combines the robustness and wear resistance of roller discs (mainly used on TBMs) with the efficacy of drag cutters (used on road-headers) in one single technology to cut very hard rocks. Breaking the rock under direct tension, undercutting discs consume less energy than conventional roller discs. This means that the overall power, required to mechanically excavate the rock is significantly reduced, allowing to manufacture small, agile, potent and energy efficient hard rock excavation machines specific for hard rock mining environment, the capabilities that are essential to overcome the limitations imposed by a mine’s great depth, confined spaces or hard and abrasive materials. Low energy consumption also means that the rock removal rate can be enhanced as the power of the machine is increased without having implications on life of the mechanical components. Application of mechanised and autonomous rock fragmentation in hard rock mining ultimately facilitates selective and continuous production process, ideal for many mining applications, while reducing the operational cost and improving the safety and the productivity.

Fig 2: Diagram of Linear Undercutting