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Shear up

The Sandvik MC470high-cutting power is a key feature of Sandvik’s continuous miner MC470. This and a heavy frame allow the machine to shear up and increase productivity in coal and potash mines.

Strong and heavy – with a light footprint

Sandvik Mining was faced with the challenge of creating a flexible continuous miner with maximum productivity for board-and-pillar coal mines. It should also keep the floor in good condition for the shuttle cars to stay in shape and move as fast as possible. The solution was the MC470, a powerful machine on hydraulic track drives with low ground pressure.

Closest to the face is a cutting drum with a 35-millimetre pick system. It is mounted on a vertically movable boom and propelled by two 270-kilowatt electric motors. Below is a floating loading apron with spinners that brings the cut coal to a conveyor. At the heart of the machine, is a frame that is rigid and heavy enough to handle the cutting forces, including during shear up. It gets extra help from a set of rear stabilizers with an operating sequence that will minimize floor damage.

The machine is operated by radio remote control and built to protect hoses, cables and components against damage from roof and rib fall. A 3.3 kilovolt power supply makes handling easy as the voltage allows for a relatively small trailing cable diameter. There is a scrubber that removes dust from the cutting zone, and the levels are also kept down by low cutter speed. The onboard equipment also includes a health-monitoring visualization screen and load-sensing hydraulics with continuous fluid filtration and cooling.

Productive board-and-pillar coal mining demands a chain of machines that operate efficiently together. This includes shuttle cars and roof bolters, but first in line is a continuous miner that sets the pace.

“The mines wanted a machine with high productivity and flexibility,” says Gerhard Reiter, product manager at Sandvik Mining.

Having South African coal mines particularly in mind, Sandvik developed the MC470 continuous miner.

With a cutting power of 540 kilowatts and a weight of 127 tonnes, it shears both down and up to increase productivity.

Shearing up is an operation where other types of machines would typically become unstable. This happens if the picks on the cutting drum begin to “climb” on the face, but the MC470 is designed to prevent that.

“To use the cutting force properly, the cutting tools and machine frame need to be very strong,” Reiter says. “So we ended up with a heavy, robust and powerful machine.”

To tap the full capacity of the MC470, the standard operating cycles for this type of mining need to be revised.

One example is to begin by shearing up at a depth of half the drum diameter. This will produce around 15 tonnes of coal, almost enough to fill a 20-tonne shuttle car. The remaining five tonnes will come when the machine sumps in to full drum diameter, after which the first car can leave.

Shearing down will then fill a second car in one go. Finally, a third car stays behind the MC470 as it brushes the floor before it moves forward for another operating cycle. The large bunker capacity on the loading table allows the machine to continuously cut during shuttle car change-out.

While productivity is also affectedby other factors, such as overall availability, this continuous cutting process and the shear-up function potentially add 30 minutes of coal cutting per shift.

Like Sandvik’s successful MB600 series of bolter miners, the MC470 moves on crawlers. They help the continuous miner to avoid unnecessary damage to the floor, which could slow the shuttle cars or destroy their wheel hubs. The crawlers are also important to create the required flexibility.

“After around 15 metres of cutting, a continuous miner has to move out of one entry (a ‘tunnel’ in board-and-pillar mining) and go into another one to allow a bolting machine to install roof support,” Reiter says

A quick change will add to productivity by giving the machine more operating time in a shift. The MC470 has a maximum tramming speed of 25 metres per minute and an electronically controlled drive system that keeps a straight line. And since the roof where it cuts has not yet been secured, the miners operate it from a safe distance by radio remote control.

So when should you use a continuous miner, and when is a bolter miner the best option?

The latter is a single-pass machine that cuts one entry width and bolts the roof at the same time. A continuous miner, however, is designed for multiple passes and cuts many different entry widths. This makes it a more productive option when several entries are cut in parallel, but the bolting must then be done by a separate machine. In addition to coal mines, the MC470 is also used for potash mining.