Hard rock mining advances

Jon Lawson

The Cat Rock Straight System is a fully mechanised longwall system designed for continuous mining of flat and tabular deposits and reefs of hard rock minerals.

The system combines the use of a hard rock shearer that uses Cat activated undercutting technology, which is specifically designed for the extraction of bedded hard rock deposits.

A low-profile hard rock chain conveyor and hard rock hydraulic roof supports complete the system, which delivers simultaneous cutting, loading and hauling- controlled by the proven Cat longwall automation system.

The Rock Straight System is the first commercial continuous mining and hauling system for underground hard rock applications, and it is now commercially available after extensive field-testing.

The efficient mining system is designed to replace conventional drill-and-blast operations in low heights, ranging from 1.3 to 2.0m (4.2 to 6.6ft) and in bedded deposits such as some types of platinum, copper and gold deposits.

The system can follow the seam and maximise ore mined while keeping dilution to a minimum.

Additional benefits include reduced health and safety risks. The electrically powered rock cutter and hard rock conveyor have no exhaust emissions, and there is no need for explosives use in the production cycle. Compared to conventional hard rock mining, fewer people are needed underground, and remote control places the operator in a climate controlled cabin.

Cat activated undercutting technology is the key to the success of the cutting machine, the HRM220. The design of the two cutting heads enables the picks to attack the rock from an optimum angle to exploit its tensile strength, which is only 10 to 20% of its compressive strength. The activation movement optimises velocity, momentum and impact of each pick- while moving the pick away quickly to minimise wear and heating. The result is reduced energy consumption and replacement cost of cutting tools.

Each of the cutting units is powered by a 132kW (177hp) motor and can cut rock exceeding 120 MPa (17,404 psi) uniaxial compressive strength. Cutting unit haulage speed can be as much as 6m per minute (19.7ft per minute), depending on the properties of the cut rock. High capacity haulage in combination with a maximum cutting depth of 100mm (3.9in) delivers high production rates. The independent cutting units can be positioned at different heights to maximise the productivity of a single cutting sequence.

The HRM220 incorporates electronic modules that enable control, monitoring and protection of the miner. Remote operation and diagnosis of major components can be done from the operator cabin via on-screen information. Of course data can be transferred to a surface location for analysis when needed.

The robust mainframe protects electrical equipment and hydraulics from cutting and haulage forces, resulting in superior reliability and longer life. The cutting system has a total weight of 41.0 tonnes (45.2 tons).

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