The latest addition to Edilmac’s fleet of nine raiseborers is a ‘new’ Atlas Copco Robbins rig. It is a major upgrade of the contractor’s existing Robbins 73R rig with hydraulic drive. Only the main structural parts: mainframe, cross head, columns and hydraulic thrust cylinders of the 31-year-old rig remain.
The raiseborer is already on it second job in the half-million-tonne-per-year Sedrina limestone mine, not far from its base in Gorle, Bergamo, Italy, between the city and the foothills of the Italian Alps. Its first task was at Val Fabbrica, for the Chiascio dam hydro project, in the Perugia area. The need was for a ventilation shaft linked to a complex of irrigation aqueducts for agricultural use.
Adriano Facchinetti, technical manager for raiseboring at Edilmac says that despite the strata content on the first task, it was not difficult to bore and carried marly lenses in cemented, quartzitic sandstone. The result was a vertical shaft, 280m deep and 2.44m in diameter. A pilot hole was first drilled using a directional drilling tool (rotary vertical drilling system – RVDS) made by Micon, to ensure high accuracy in mixed and karstic ground with a long bore. The karst structure prevented the use of normal directional drilling with high-pressure water, so the new drill, of which this was the world premiere on site, employed air drive.
Following this initial drilling, the Robbins 73RVF C then came into play.
“Thanks to the newest technologies available, and to the technical choices made during the upgrade of the machine, this is now powerful almost as much as an Atlas Copco Robbins 83,” reports Edilmac, “keeping the dimension and weights of a Robbins 73.”
Sedrina mine
Edilmac has been working at Unicalce’s Sedrina mine as development contractor ever since underground exploitation of the limestone resource started in 1978. This was related to a decrease in open quarry work, which was becoming impractical in the limited space available in the valley, until production from the quarry fully ceased in 2000. Now the mine reaches from the lowest tunnel to the top quarry bench; a height of 430m.
“Our first shaft was excavated in the same year (’78) as we started in the quarry, and we drove the first tunnel in 1986,” relates Facchinetti. “We’ve bored all sizes from a pilot bore diameter up to 5.76m, and all with one-pass reaming. The 5.76m bore is still working as a main mucking shaft.”
At Sedrina Unicalce produces mainly fine lime and slaked lime (Calcium Hydroxide) for a wide range of industrial uses at an average rate of 2,000t per day. Poorer quality limestone that is excavated is crushed to aggregate sizes for road construction etc. The total rock excavated is around 4,000t per day.
Nearly all extracting now takes place from a series of large ‘rooms’ or open stopes, with tunnel and shaft connections that are the responsibility of Edilmac under a series of contracts.
Full product processing takes place on site in the former quarry in a valley where space is at a premium.
Edilmac completed its first pilot hole in 35 hours, followed by reaming back to 3.05m in one pass. The reaming progress rate was 0.65m/h in the 160MPa UCS massive limestone from a depth of 116m.
At Sedrina mine the main mining method is to create large rooms with intervening support pillars. Each of the main rooms is planned as 120m high, 40m wide and 180m long, with a 40m wide supporting pillar between. First the zone is prepared by development tunnels at three levels (top, middle and underneath) from which blastholes can be drilled later. At the end of each room a rock pass and slot is created by raiseboring.
When T&TI visited the mine the raiseborer was being set up at the end of room C8, with the power packs, cooling unit, operator’s cabin, and an Atlas Copco XAHAS 536 mobile compressor for pilot hole cuttings removal, all in close proximity. The Edilmac crew was changing the drive head for one with a bigger thread to suit larger 11.25in (286mm) diameter rods rather than the 10in (267mm) diameter rods used before.
The raiseborer to used to form the first opening at one end, approximately 116m deep, using a pilot hole 12.25in (311 mm) reamed out to a full 3.06m diameter. The rooms are also in rows on two levels, with main rock removal level drives beneath each, thus exploiting the resource to the maximum extent without caving or additional support in most cases.
“The limestone rock here at Sedrina is much harder (around 160 MPa UCS) and massive,’ says Facchinetti, “so it will be a real test for the new rig (compared to Chiacio). But it now has a high power at 450 kVA instead of 350 kVA. We are a lot happy with the ‘new’ rig. Really a lot happy. It really is an improvement in performance on the old 73R. The rod handling system is also a little better, but the real improvement is in performance.”
After this bore at Sedrina mine the 73RVF C is destined to carry out further rock pass provision in slots at the end of the parallel rooms. This allows the blasted limestone to be transported most efficiently by gravity to crushers and conveyors at a lower level.
The rock removal tunnels with belt conveyors all reach the surface at the old quarry face to drop the crushed material onto the main old quarry level. From there the rock feeds through one of three, 10m diameter shafts, that were also excavated by Edilmac, to reach the main preparation plant.
The three levels of room development tunnels are also the responsibility of Edilmac using their two Atlas Copco L2C jumbo drilling rigs. These tunnels are then used by Unicalce production teams to carry out drilling with fans of blast holes. Formerly only one tunnel per level per room was driven, through the centre of the block, but now two tunnels are driven at each level on the edge of the demarcation. This gives better blasting results.
Retrofitting
The upgrade of the raiseborer was made possible by cooperation between Atlas Copco, Edilmac and the electrical motor manufacturer in Austria.
“Raiseborer rigs can easily last for 20-30 years,” explains Atlas Copco Line Product Manager for raiseborers, Johnny Lyly, “but even with good maintenance their performance will be much less than what is currently possible. The mechanical side, mainly gearboxes, can be easily updated, but the installation of modern hydraulics and electric control is more difficult, which is why we have introduced upgrade kits. These can include new power-packs and drive systems for electric or hydraulic motor upgrades as the customer prefers.”
With hydraulic systems the twin powerpack supplies both rotation and thrust, but with electric drives there is one powerpack with electrical controls for the electric drive motor and a hydraulic power pack for the thrust unit. The electrical controls include the variable frequency drive for excellent speed and torque control, and a resistor unit for controlled stop in the event of power loss.
“After trials, Edilmac has a preference for AC electric motors, due to their higher efficiency compared to hydraulic motors or DC electrics, which means variable frequency (VF) drive control,” explains Lyly. “An AC motor with VF control can be adjusted for speed and torque similarly to a DC motor, but with the higher efficiency. It was decided to go for a complete upgrade with modern equipment, not only for the drive but for control and cooling systems.”
The retrofit package for Edilmac’s existing Atlas Copco Robbins 73RH consists principally of the water-cooled AC electric rotary drive motor, a new gearbox, a hydraulic power pack for thrust, Atlas Copco’s universal computerised rig control system (RCS) with compact electronic console, and a self-contained cooling unit for the hydraulic system and drive train that requires no external water supply.
Development
The new package has been backed by a lot of internal development at Atlas Copco. “We hadn’t built a raiseborer with a variable-frequency electric drive at Atlas Copco since 2002, and there has been a lot of component development in the meantime,” explains Lyly. “So we had to test the whole drive-train first. Using a new, water-cooled compact motor, we carried out the tests over two days with the powerpack at the premises of the motor manufacturer Elin in Austria, with our system connected to a load motor for simulations. These included stalling, backspin and fluctuating load to simulate all the conditions that might occur with a raiseborer. And the results were very good, meaning we could go ahead with the retrofit work.
“In the meantime Edilmac had fitted the new gearbox themselves, and so we put the two together at their Gorle premises, carrying out further successful tests for another two days,” reports Lyly. “One result was a big increase in torque to 250 kNm. The rig could then be designated as an Atlas Copco Robbins 73RVF C.”
A small but important part of the retrofit, for operator acceptance, is the desktop control console, with a flat-screen display portraying a simple operator layout normally showing rotary speed, net thrust force and torque as analogue dials. The system also gives a lot of information feedback on performance and faults, which can help in maintenance.
Atlas Copco engineers are also developing a reporting system that can be integrated with the existing Tunnel Manager software. As only instrumentation cables should go into the cabin, there is at lot less mechanical noise for the operator to tolerate during excavation.
More Atlas Copco Robbins 73R raiseborers have been sold worldwide than any other raisebore system says Atlas Copco, and now, with the upgrade to the 73RVF C, it has also become the most energy-efficient raiseboring system in the Atlas Copco range.
Improvement acceptance
Explaining some of the finer points of raiseboring Facchinetti says, “Raiseboring is not really a matter of speed, but getting through without problems, so the rig’s available torque and thrust are very important to keep on boring without jamming. This rig’s new 280kW VF motor gives a maximum torque of 250kNm instead of the previous 180kNm.”
On the compact control system with easily understood instrumentation on a flat screen desktop console, Facchinetti says, “The new console really is an improvement too. The operators like it a lot.
If all goes well we are looking to upgrade our other 73R raiseborer next year, also with a VF AC electric drive.”
Edilmac’s new Atlas Copco Robbins 73RVF C at its first job site on the Chiascio Dam water project in Umbria Entrance to Unicalce’s compact preparation plant in Sedrina with mine Left to right, the new hydraulic power pack, cooling unit, electrical powerpack and switchgear, and the raiseborer itself with control cabin behind Some of the Edilmac team in Sedrina including (left) Roberto Ferrari, vice-foreman and shotfirer, (right) Dr Ing Adriano Facchinetti, RB technical manager (2nd right) Ing Manual Carli, and (3rd right) Sergio Moioli, RB foreman The compact operator’s panel with simple instrumentation, as rig preparation and drill-pipe drive changing is being carried out
