Developments in continuous hard rock cutting are being accelerated by Mining3 in partnership with industry, promising greater productivity, lower costs and energy efficiency. DAVID SIMPSON reports

Article from resourceful: Issue 10

RESEARCH PERSPECTIVE

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Like many other areas of the Australian economy, the hard rock mining industry is faced with the challenges of change.

Short-term factors such as global commodity prices and exchange rates are combining with longer term issues including productivity decreases, owing to lower grade ores, longer haul distances and decreasing ore accessibility.

The result is that the industry is under pressure to improve the efficiency of mining processes to maintain and maximise Australia’s competitive advantage as a leading producer of both energy and minerals.

The efficiency goal in hard rock mining is to change from batch to continuous production. The batch process is the familiar drill and blast fragmentation system in which rock is fractured by explosive blasts and mechanically removed before the process is repeated.

Continuous production on the other hand, is typified by the shearer and conveyors used in coal mining.

This leads to a continuous flow of material for processing and increases efficiency and safety, while lowering the overall costs of production.

Another important factor is that as easy-to- reach, high-value surface deposits are depleted, hard rock mining operations are migrating underground, which is capital intensive and requires developing complex infrastructure.

This changing production model, together with the need to maximise the safety of the work environment, are adding to the impetus towards continuous and autonomous production.

Hard rock cutting is generally energy-intensive, and the existing technologies, such as tunnel boring machines extensively used in civil industry, are inflexible and cumbersome, making them unsuitable for mining operations.

Mining3 is developing solutions for continuous production in hard rock mining. The main objective is to achieve competitive excavation and cutting rates. This requires long-life cutters with low-energy requirements, minimal machine footprints and suitable material handling – especially in confined underground areas.

Building on a successful track record in developing cutter/rock interaction models, sensing for characterisation, and smart control systems for automation, the Mining3 team is currently working to bridge the knowledge gap on the mechanics of hard rock failure under the action of static and actuated undercutting discs.

According to Mining3 researcher, Dr Sevda Dehkhoda, the process of undercutting could revolutionise hard rock mining operations. Breaking the rock under tension while rolling around its axis, these cutters are theoretically more effective and efficient than their conventional equivalents: drag picks and roller discs.

“The energy requirement of the cutting method determines the excavation rate,” Dr Dehkhoda says.

“While the cost of energy usually is not a problem, the amount of energy transfer through the tool to the rock – which is in turn controlled by the strength of the cutter material – is the real constraint.

“This means we can’t improve the rates just by increasing machine power – we have to look for methods like undercutting disc that require less energy for breaking the rock.”

Dr Dehkhoda has expertise in rock mechanics and rock fracture mechanics and says she is looking for processes that take advantage of rock weaknesses to break the rock with minimal energy requirements.

“I look into a rock’s failure mechanisms taking into account the kinematics of the cutter, cutter/rock interaction and properties of the rock, answering questions like: What happens at the boundary of the cutter and the rock? What factors influence how rock breaks? How does the strength / toughness of the rock affect the whole rock failure mechanism?”

By using fully-instrumented, kinematic controlled and highly stabilised test rigs, Mining3 researchers are able to isolate their objectives and measure the stresses and forces at the cutter / rock interface, which are solely the result of the cutting process.

Of particular interest are two types of rock failure, known as ductile and brittle. Ductile failure involves breaking rock grain by grain, creating a powdery material. Whereas, brittle failure produces larger chips – shards of material that literally chip off the rock.

Since it fails the rock in finer particles, for a unit volume of rock, ductile failure generally requires more energy than brittle failure and will consequently be less efficient for excavation.

“Our primary objective is to contribute to the development of a successful hard rock mining machine – a machine that is robust and strong enough to re-disband the high reaction forces from cutting in hard and abrasive material, but at the same time, be small enough to manoeuvre in a confined underground environment,” Dr Dehkhoda says.

Mining3 is also working on applications of novel rock cutting technology.

Mining3 (initially when operating as CRCMining) has licensed their oscillating disc cutter technology (ODC) to a leading mining equipment and services provider Joy Global since 2006.

The company has rebranded the technology as DynaCut, and since then, equipment development has been carried out by Joy Global, who has made substantial improvements to the operating performance and mechanical reliability of DynaCut technology.

Brad Neilson, President of Hard Rock Mining at Joy Global, said that DynaCut will revolutionise hard rock cutting for mining.

“The gains for mining are significant. A continuous mining process in hard rock tunneling can yield a 20 per cent improvement in advance rates, and up to 20 per cent reduction in costs,” Mr Neilson says.

“Another benefit is less disturbance of the surrounding rock mass when compared with drill and blast methods.”

According to Mining3 Principal Research Engineer, Dihon Tadic, continuing collaboration with Joy Global will further develop the DynaCut system to improve cutter performance and service life, while developing predictive performance models for the cutting tools.

“The future is very promising – I believe we’ll develop highly flexible and mobile hard rock cutting machines that can cut varying excavation geometries, negotiate tight bends and ultimately become fully-autonomous systems for mine development and orebody extraction.” Mr Tadic says.

Reaching this goal will be a significant contribution to achieving, maintaining and maximising Australia’s competitive advantage as a leading producer of both energy and minerals.

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