They know the drill

The performance of two of its state-of-the-art drilling machines on separate major new West Coast projects has got staff at Atlas Copco’s New Zealand subsidiary buzzing.   BY HUGH DE LACY

Two of the Atlas Copco’s ROC L8 down-the-hole crawler rigs are making mince-meat of the rock they’re drilling at Oceana Gold’s Globe-Progress opencast mine at Reefton, while a twin-boom Rocket Boomer M2D hydraulic tunnelling and mining machine is accelerating the driving of the main access tunnel at the Pike River Coal Company’s underground mine near Greymouth.

The 20-tonne ROC L8s are working round the clock at Globe-Progress, and the machines are unique in New Zealand, according to Atlas Copco NZ’s construction and mining techniques business line manager, Dave Barnes, in that they operate in reverse circulation (RC) mode for daytime sampling and conventional mode for night-time production drilling.

In RC mode, compressed air is forced down the gap between the outer and inner drill-tubes, with the several small holes in the drill-bit acting like a vacuum-cleaner nozzle, sucking the rock fragments and dust up through the inner drill-tube. At the top the material is collected into a system that is able to take samples every 1.5 metres or 1.7 metres to find out whether the drill has struck gold-bearing ore, or is still working its way through the overburden.

During the 12-hour night-time shift, the machines revert to the conventional air-circulation system.

“The L8 is the most advanced RC drill in the country – it’s state of the art,” Barnes says.

“The performance is so good it’s a struggle to keep up with the amount of material coming out of the hole, mainly because the rock’s a lot softer than these machines are used to encountering overseas. New Zealand rock is just a bit younger than everywhere else so the L8s are blasting through it.”

In production mode the machine drills a pattern of holes in an area of roughly three by four metres in preparation for the placing of explosives. With the ability to make passes of seven metres per rod, the L8 is the longest production drill in country.

It can drill holes ranging in size from 110mm to 165mm to a maximum depth of 54 metres. It’s powered by a water-cooled Caterpillar C13 engine rated at 328kW at 2000rpm.

The crawler tracks can take the machine, which is 11.25 metres long by 2.49 metres wide, up a 20 degree incline with a ground clearance of 405mm.

A fuel-saving device, eight-tube handling capacity, two-speed traction motors, retractable suction hood and heavy-duty tracks are all standard features, while optional extras include air-conditioning and heating in the cab, a central lubrication system, electronic hole inclination and depth control instrumentation, and hydraulic support leg and track chains with triple grouser pads.

After a cautious start prompted by the fragmented nature of the rock, the Atlas Copco Rocket Boomer M2D hydraulic tunnelling and mining rig is on target to reach Pike River’s  rich coal-seam in the Paparoa Range, 46 kilometres from Greymouth, by the end of the year.

When the uphill 2300 metre drive began in September last year, progress was relatively slow – by early January the hole was only 172 metres long.

“Anywhere round the southern divide whenever anybody digs a batter or drives a hole it all tends to fall down,” Barnes told Q&M. “But they’re well on top of that now, and the caution has paid off because there have been no cave-ins or anything like that.”

The M2D comprises a direct-controlled drilling system incorporating Atlas Copco’s anti-jamming rotation pressure-controlled feed force (RPCF) function, with separate pumps for percussion, dampening/positioning and rotation.

The twin BUT 32 heavy-duty booms are designed for direct, fast and accurate positioning between holes, with improved linkage bearings in the main joints and new axial bearings in all boom joints.

The articulated 4WD carrier, which weighs 14.1 tonnes on the boom end and 5.5 tonnes on the engine axle, is powered by a turbo-charged four-cylinder water-cooled low-emission diesel engine, with the machine’s set-up stabilised by four jacks.

Including a two-degree lookout angle, the M2D drills a loaf-shaped coverage area 9.125 metres wide and 6.76 metres high, with the COP 1838 rock drills featuring a double-reflex dampening system for optimum drill speed and steel economy. A new system separates the driver and gear-gives lubrication, while pressurised sidebolts and mating surfaces optimise reliability, reduce maintenance costs, and extend the intervals between overhauls.

The BMH 6800 heavy-duty aluminium hydraulic feeds are double-bottomed for high torsional resistance, and feature snap-on stainless steel sleeves and polymer contact pads for long life and low maintenance. The basic rig includes a FOPS-approved protective roof, a fixed seat for tramming, a cable reel, water booster pump, screw compressor and work lights.

The Rocket Boomer M2D is offered with an exhaustive catalogue of optional equipment ranging from adjustable roof height, to water mist flushing, exhaust catalyser and Ansul dry or wet fire suppression system.