It is better to travel hopefully than to arrive,” the proverb says. But in mining this couldn’t be farther from the truth. When you develop a gateroad in a coal seam it should go as fast as possible, because securing the path to the coal just represents money spent and little gained. At the same time you must make sure the gateroad is safe by securing the roof and sometimes the walls with bolts. All this was once done in separate steps, forcing a drill rig to take turns with a machine cutting the gateroad.

“Doing one step after the other took time, and coal mines were looking for a way to speed up the process by doing them in parallel,” says Hanno Bertignoll, marketing communications manager at Sandvik Mining.

An answer to that demand is the Sandvik MB600 series of bolter miners, which have changed the whole scenario. A bolter miner is a continuous mining machine that drills and bolts at the same time as it cuts, loads and conveys the material that is removed for the gateroad.

“The biggest challenge was to build what is basically two machines within the size of one,” Bertignoll says. “We had to find space for the sliding frame arrangement with all its components and still provide enough space to give the operators a safe and ergonomic workplace.”

Sandvik MB600 bolter miners move on crawlers and have a hydraulic sliding frame with a cutter drum up front. Integrated on the frame are up to six bolting rigs, four roof bolters and two rib bolters for the walls. An operating cycle begins by tramming the bolter miner into cutting position in front of the face. Two stab jacks located at the rear are set and the canopy in front is raised to stabilize the machine between roof and floor.

Bolter miners in the MB600 series cope easily with sandstone intrusions and similar materials that are hard to cut. They also offer an advantage when the mine floor is soft and would be destroyed by continuous mining machines on crawlers. Bolter miners don’t do that because the whole unit is locked in position by the stab jacks and canopy, while the hydraulic boom pushes the cutter drum forward. No crawlers are needed to sump in.

A bonus from this concept is that MB600 bolter miners are sometimes used for production mining under soft floor conditions. In that case you just stabilize and sump in without any drilling and bolting.

The operating cycle continues with the bolting mode engaged, and the cutter boom is raised to sump in and start drilling for the bolts. As drilling and bolting begins, the rotating cutter drum is moved forward via the slide frame. An apron with a loading device and a conveyer is also moved forward for best possible material clearance. Starting in top position the cutter repeatedly shears down to floor level until the required advance has been reached, up to a maximum of one metre. When cutting and bolting have been completed, the cutter drum and canopy are retracted. Then the stab jacks are raised and the cutter bolter can move forward in position for the next cycle.

“The main benefit from combining cutting and bolting is the time it saves through increased speed, but it also makes the job safer for the operators,” Bertignoll says. “On the machine they are well protected by a support canopy behind the cutter drum, and the risk of accidents is reduced.”

Based on an analysis of mine accident statistics and operator experiences, the MB600 series of bolter miners have large platforms with ergonomically positioned controls. The platforms can be lifted and lowered hydraulically, giving operators comfortable reach to all bolting positions. The drill rigs are manoeuvred with push-button controls that allow electronic mapping of drilling data. Intensive lighting around the platforms reduces the risk of accidents considerably, and the hydraulic power pack that propels the bolter miner has been soundproofed to reduce the noise.

Other important features that improve the working environment are high-pressure water sprays and ventilation at the face to remove dust and gas. The generation of dust is also kept down by a low pick tip speed.

It is important that the resulting gateroad is big enough to allow access for all machinery to the longwall where coal is mined. The gateroad must also allow enough fresh air to flow through so that the mine is properly ventilated. The MB600 series includes three basic models with different operating heights, covering a range from 2.9 to 4.5 metres.
“They should be as small as possible but as large as needed,” Bertignoll says.