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Underground drilling and loading.

John Chadwick examines better blastholes, less overbreak, automation and larger machines

In development drilling, faster drilling of rounds, and deeper and more accurate holes have become possible through boom positioning systems and parallel drilling facilities. Hole depths and patterns are controlled by onboard computer systems. However, automation is largely still only found in production drilling.

According to Tanguy De Brosses of Montabert, which works together with Mining Technologies International (mti) and Andersen Mekaniske Verksted (AMV) producing development drilling machines: "The improvement of energy transmission in third generation hydraulic drifters [first seen from Montabert in 1982] and incorporation of highly sensitive yet rugged controls is providing benefits for mine operators by reducing running costs." He says that putting together the advantages of progressive shock wave transmission with proper drill management mines can now:

* Increase penetration by up to 50% compared with second generation drifters (without unduly increasing working pressures);

* Increase the life (in metres) of tooling by 200-400% on shank adapters and 3050% on couplings;

* Minimise deviation, and drill deeper holes - to 400 m; and

* Reduce drilling costs by two-and-a-half to four times if tooling costs are included.

The full text of the paper 'The new wave in jumbo drill technology' by Tanguy De Brosses can be found on the mti website at www.mti.ca

Overbreak remains a problem in development. Atlas Copco has put forward the main factors in reducing overbreak. Firstly, "close monitoring of the face is a must in order to register undue overbreak and to take counter measures - and a small bonus to the people involved can lead to great results. Geological conditions can have a great effect on hole direction. The drill string has a tendency to deviate perpendicular to the foliation in anisotropic rock like phyllite, schist and gneiss. Blasting is extremely important, and employing the smooth blasting technique with electronic detonators in the periphery holes can contribute greatly to a smooth contour. Tunnel size affects drilling accuracy. When booms and feeds are extended to the full, they are not so rigid and deflections can occur. Exact computerised compensation is not easy to achieve - and the further out the booms are, the greater the collaring and orientation errors can be."

Furthermore, "alignment of the feed is critical at the start of drilling and a face which is not orientated perpendicular to the drill rod may cause bending and an inaccurate starting point. Low feed force and reduced impact at the start saves drill tool wear and, after that, feed force should be just enough to maintain tight joints without bending the rod and risking deviation. Fast and accurate drilling requires dedication, experience and reliable, state-of-the-art drill rigs."

Reduced overbreak

Boliden's Garpenberg Norra mine has been pleased with its Atlas Copco Rocket Boomer 352 S jumbo, equipped with contour control drilling system, used to drive the new 1:7 underground ramp system (cross section 30 [m.sup.2]) that is now down to a depth of some 1,000 m. Lars Norling, project manager, said: "The Rocket Boomer has been working like clockwork. It is used for ramp and development work at different faces for 11 eight-hour shifts every week and its availability is very high, close to 100% when faces have been available for drilling. This is the result of regular preventive maintenance - daily checks by the operators and two major overhauls per year."

The contour control, while expensive, paid for itself in less than a year. "With a conventional rig we get minimum overbreak of 20%. Double that is quite common. Using our Rocket Boomer, the result is 9% in overbreak- which, in principle, is equal to the theoretical minimum required for managing the collaring of holes for the next round. To benefit from the precision in drilling it is also essential to have a well controlled blasting and efficient rock reinforcement process."

He notes savings have been achieved in mucking, hauling, scaling, rock reinforcement and particularly in shotcreting. "A reduction of the overbreak by 10% corresponds to a saving for us of some SEK2,000 per round. The cycle times are shorter and more even. The operator can start drilling immediately, without marking out the holes on the face, which saves some 20 minutes every round. Without contour control, the operators are always using more lookout than required and this, on top of the overbreak and longer times for mucking and transport, can extend the period for scaling from two to as many as eight hours, thus threatening a lost cycle."

Garpenberg Norra's Rocket Boomer had completed 1,200 rounds and 4,200 m of drifts in a little over a year. A round's 76-78 holes are 45 or 48 mm in diameter, with two 104 mm cut holes for each round. Spacing in the contour is 700 mm, the lookout is 300 mm in 4 m and 400 mm for the bottom holes. Each round is drilled in two to two-and-a-half hours at a penetration rate of 1.2-2 m/min, depending on rock hardness. The holes are charged in two hours, mucking and haulage takes two to three hours and scaling two to eight hours.

Narrow manoeuvrability

Sandvik Tamrock is looking to cause a sensation in narrow vein mines and other narrow drift applications with its new Axera DO6. This punchy little rig gives twin-boom jumbo performance in a single-boom environment. Applying its new, patented Auto-Balanced concept, Tamrock has produced a two-boom jumbo that is only 1.74 m wide and weighs 15.5 t. It can corner in drifts just 3.1 m by 3.1 m, and can tram at speeds up to 12 km/h. Nevertheless, it offers large boom coverage an auto-parallel coverage of up to 6.8 m wide by 5.3 m high.

The Auto-Balanced chassis is a new concept in carrier design and is crucial to the Axera. In conventional designs, a counterweight is required to avoid an 'unsafe' situation when narrow vein machines are cornering. However, a counterweight is an expensive extra cost that limits the flexibility of the machine by adding extra, largely useless, weight. The answer was to make better use of the weight of the carrier's components such that they provide the necessary counterbalance - hence the Auto-Balanced chassis. Its advantages include greater stability, better tramming conditions (due to the improved weight distribution and excellent power/weight ratio - tramming at 4.5 kW/t), and smarter hosing and wiring systems. The oil tank, the main hosing and wiring groups and the controls are on the front chassis, with only a few hoses having to pass through the articulation unit. The water pump and coolers are on the front chassis for the same reason design features that maintenance personnel will appreciate.

Operator comfort was a priority in the design of the Axera DO6, with optimised drilling controls, and a steering wheel and pedals for tramming. The roomy operator's station allows tramming and drilling from a comfortable seated position. Similarly, this jumbo has been designed for easy access to components for routine maintenance. The innovative layout includes a neat and well protected distribution of its hydraulic hoses.

Production drilling

Besides increased automation, production drilling has seen greater accuracy through the use of drilling tubes and guide rods. "This, combined with the use of more powerful drills, has resulted in the ability to increase development intervals while maintaining drill coverage and adequate blast fragmentation.[1]"

Australia's Cooperative Research Centre for Mining Technology and Equipment (CMTE) is working on high pressure water jets to improve drilling performance. It is using a rotary rig capable of drilling blastholes up to 150 mm in diameter. CMTE points out: "drilling of these blastholes can constitute around 20% of the total mining cost. Clearly any improvements obtained in blasthole drilling underground will impact directly on the cost of mining operations." The CMTE Drilling Group has estimated that the introduction of high pressure water jets to the blasthole drilling process can reduce the mining cost by about 8.5%.

The main aim is to increase penetration rates, improve hole accuracy and reduce wear on drill bits. CMTE expects "the development of new drill bits that maximise the effect that the high pressure water jets have on drilling performance."

Automated production...

Several years of research and development and co-operation between Sandvik Tamrock and LKAB, the mine operator, have led to a high level of production drilling automation at the Kiruna iron ore mine in Arctic Sweden. Typically, sometime before midnight, one can find an operator studying the digital display on a Tamrock Solo longhole production rig. You could see him align the feed with the reference direction for the crucial first hole of an overhead fan pattern, extend the front and rear stingers to brace and stabilise the feed and then press the 'go' button. Once the powerful HL1500 drifter has gone into action, driving the Sandvik ST68 drill string into the rock, the operator will switch the rig over to telecontrol and walk to an adjacent drift and repeat the procedure on a second Solo. He then returns to the central remote control cabin about 150 m away. In here, two computer screens give visual representations of the rigs and the operator can zoom-in the cameras to check the contact points between the stingers and the drift walls.

Once satisfied that everything is in order, the operator can leave the mine and go home to bed. When the day shift arrives next morning it will find both rigs shut down having completed 115 mm diameter blastholes 12-50 m deep, for a total of some 600 drill metres.

Production leader at the mine, Algot Inga, says "Effective automation is the key to profitability and even to the very viability of many mines today, particularly those in affluent labour markets. Due to intense competition from opencast [iron ore] mines abroad, we have to extract and process the ore at the lowest possible cost and, at the same time, assure the quality of our product. To achieve this goal, we are very dependent on advanced technology and work closely with manufacturers who can meet our needs."

He further pointed out his satisfaction with the Solos. "I am impressed with the robustness and stability of the rigs, and also with their remarkable manoeuvrability, which enables us to drill in places difficult to access with other rigs of similar size. Together with Sandvik's tube drilling equipment, they give us not only high performance and reliability, but also the kind of hole straightness that is critical to good fragmentation and minimal dilution in large-scale sublevel caving operations."

To reap the full benefit of automation, Kiruna needed each Solo to drill at least one complete round- some 300 drill metres - with no manual intervention. However, until then, bit life had only been about 80 m. Sandvik Tamrock's Kiruna-based rockdrill doctor, drillmaster and customer liaison officer quickly isolated the rapid temperature change from hot to cold as a particular accelerator of bit wear in the heat-generative Kiruna magnetite.

One answer was grade 82, a new blend of cemented carbide that is highly resistant to the usually adverse effects of heat. To customise grade 82 buttons for Kiruna magnetite, which varies from about 50 to 150 MPa in compressive strength, they were given a semi-ballistic shape for good performance in both the softer and harder zones of the orebody. Also, a central recess was milled into the face of the bit and the flushing holes were directed to open into the recess, thus creating a continuous cushion of water over the face of the bit. This both keeps the bit cool and improves cuttings removal.

The new bit was the complete answer for automation to work effectively. Algot Inga explains that "The facility to drill a full 300 m round automatically without changing the drill bit gave a phenomenal boost to production. The time saving per round can quite literally be measured in hours." Production targets in this area of the mine were raised by 30-35% and were achieved with less personnel.

The next thing at Kiruna will be cable-free remote supervision of machines like these Solos. LKAB is developing a new communications network for the mine. Kimmo Ulvelin, product manager of Tamrock's Solo rigs explained that: "The automated rigs currently working in Kiruna receive digital signals from the control [area] via a cable, which is a component LKAB plans to eliminate. To accommodate their needs, our designers are working on a special interface that will enable radio signals to be transmitted to the rigs via the mine communications frequencies. In addition to raising their flexibility, most particularly the practical control range, radio transmission will eliminate the possibility of damage to signal cables."

Looking to the future, Algot Inga suggests that: "If we can have one man monitoring two drill rigs remotely from an underground station today, the next step must be for him to supervise four rigs from the comfort of a climate-controlled office on the surface," or even from home.

... and automated loading

Kiruna has been using the largest LHDs in the world for some years, Tamrock's Toro 2500E (MM, August 1996, pp.66-68). More recently, one of these electrically-powered machines has been automated with the installation of communications, traffic control and navigation systems. It is automatically controlled and guided by the system during tramming and dumping, and is loaded tele-remotely from a control room[2]. Testing of that unit was being undertaken until June, after which any necessary modifications were to be made before full implementation of automation. The mine hopes to have four 25 t capacity automated 2500Es in full operation by early 2000, and expects that anything up to 15 such machines could be operated from up to six operator stations in the mine's central control room.

Operating under this system, LHDs are provided with data from the mine planning department, generating tasks for the machines. Each bucket load dumped into an ore pass is reported to Kiruna's production monitoring system.

Much work has been done on the automation of both LHDs and underground haulage trucks this decade. Besides the work at Kiruna, Inco and its suppliers have accomplished a great deal at various of Inco's Sudbury (Canada) operations. For example, at the Centennial meeting of the Canadian Institute of Mining, Metallurgy and Petroleum, Automated Mining Systems (AMS) demonstrated its advanced remote control technology, showing how a miner in Montreal was able to operate three drills 800 km away and over 600 m underground at Inco's Stobie mine in Sudbury. AMS is working in partnership with Tamrock, Dyno Nobel, Canmet, Bell Canada, Precarn Associates and Inco.

Earlier this year, Caterpillar Elphinstone delivered its 500th LHD. At that time the company previewed some of the technological advances and innovations that will be incorporated into its loaders in the coming years. Elphinstone expects its auto-guidance and auto-dig facilities to be among the most interesting as they will allow automated operations.

The motivations for automation are primarily safety and productivity. The former is more obvious, removing operators from the underground workplace as much as possible, and the productivity advantage has certainly been proven at Inco's Stobie mine (MM, November 1996, pp.258-264). Reducing the number of operators required, and raising their output per manshift can greatly improve the economics of underground mining.

If employees operate one or more machines from a surface console, their productive period increases significantly. Even just operating one machine, work can begin immediately the shift starts, with no time lost in travelling to and from the work place. A surface operator can still be running a machine while his or her conventional counterpart from underground is showering before the shift finally ends. Furthermore, operating a machine from surface, such as an LHD, means that there is no waiting time for noxious fumes to be exhausted after blasting, also providing many more operating hours each day. It should also be noted that an operator can therefore be productive without the need for any associated underground support personnel, such as cage tenders.

Once multiple machines are brought under the control of one operator, productivity really starts to increase. Inco's trials have achieved outputs of over 2,000 t/manshift with three units controlled by one operator and possible improvements could see one operator handling some 3,400 t / shift controlling five LHDs.

Further improvements can be achieved in utilisation and increased LHD speed. With the PLC navigating the machine, speed increases of 10-25% are achievable compared with an onboard driver. Furthermore, reduced maintenance derives from operating the LHD consistently within its engineering operating parameters.

The safety benefits are enormous. Driving an LHD is strenuous; injuries range from physical problems such as back injuries and injuries related to the hazards of working around muckpiles, to heat exhaustion and respiratory problems.

Inco now has full-scale testing going on in its research mine[3], with teleremote control of development jumbos, Tamrock DataSolo longhole teleproduction drills, Dyno Nobel's latest emulsion explosive loader using microprocessor based caps, and teleremote LHDs and trucks.

Dr. Greg Baiden[3] explains that the development jumbo's computer system is "linked to the underground network to provide on-line engineering information for the drilling of the pattern. The underground positioning system provides machine location co-ordinates for rapid setup and accurate drilling. These types of control systems are a must [for tele-remote operations].

Automation/remote control of LHDs is also a goal of the new Northparkes copper-gold block cave mine in New South Wales, Australia. The mine was brought into production with a fleet of six electrically powered Toro 450Es on manual control, with a commitment to move forward with teleremote operation once the machines had proved themselves. These machines are critical to productivity, loading ore from the block cave drawpoints and hauling it to orepasses, producing over 4 Mt/y on a single dedicated extraction level. They operate on 260 m of cable, fed from Tamrock's flat cable reel. Monitoring of these LHDs is critically important, so each one is equipped with Tamrock's CECAM onboard monitoring system.

Malcolm Broomhead (North Ltd.) and Ross Bodkin (Northparkes Mines)[1] note that the reduced number of accidents associated with remote control equipment has lead to much greater interest in tele-remote systems. They also comment that: "Electric LHD and truck haulage is used in a number of mines worldwide but despite the improved working environment and increased energy efficiency leading to reduced operating costs they remain a small minority. This is primarily due to the reduced flexibility and higher infrastructure costs associated with electric haulage." At Northparkes, "the energy costs are estimated to be about one sixth of diesel costs. However, the trailing cable costs reduce this margin. Reduced ventilation requirements and improved operator environment are additional advantages."

Mechanising small mines

Mine mechanisation in narrow veins requires small yet strong machines, and Paus has developed the PFL series of small LHDs:
Type     Payload      Bucket         Power    Width   Length

           (t)      ([m.sup.3])      (kW)      (m)      (m)

PFL 12     2.0          1.2           50       1.40     6.1
PFL 18     3.8          1.7           78       1.45     6.8
PFL 30     5.5          2.5          112       1.70     6.9


However, working in certain areas of a mine can be dangerous unless there is adequate support, and the cost of support may be too much for an economic narrow vein operation. For these reasons, remote control of LHDs is becoming more and more popular in these smaller operations. Remote control means that anywhere in the mine can be accessed, without risk to personnel. So Paus and Canadian company Nautilus have together improved the controls and cab layout and developed a new line of LHDs suitable for teleremote control, based on the PFL series. These tough, rugged machines are the Tiger series.

Tiger LHDs have no foot pedals, gear lever, parking brake lever or steering wheel, and almost all gauges have been removed. All of the LHD's control functions are achieved by using two joysticks in the cab, plus a slim control an display panel mounted direct in front of the operator. The basic Tiger is just equipped with joystick control, however, it can easily be upgraded to a full remote or teleremote control system, enabling the LHD to be operated from a distance. Two cameras are mounted on the front of the machine and one on the rear, for remote control operation.

The first Tiger LHD, the Tiger-300D (based on the PFL 30) will be shipped to Canada and tested in Falconbridge's Kidd Creek Mine in Ontario.

The Tiger was designed with automation in mind from the very beginning, so, besides the teleremote control system, there are three other systems that Nautilus has designed for LHD automation: an automated guidance system, a personnel proximity detection system and an automatic bucket loading system. These can easily be incorporated in the Tiger machines. An automatic brake system will stop the unit if it detects someone in the path of the LHD.

Is bigger better?

Larger capacity LHDs, such as Toro's 25 t 2500E or Elphinstone's 20 t R2900 Supa, are also finding favour in operations where the ability to tram heavier loads can increase productivity.

It is claimed by mti that the 38,200 kg tractive effort of its new LT-1650 LHD, combined with its 32,925 kg breakout force, gives this loader muck pile penetration that is superior to all other units in its class. The machine can carry 18 t and is offered with 7-12 [m.sup.3] capacity buckets. High pressure hydraulics facilitate the use of smaller cylinders - dramatically increasing boom bucket speed, mti reports.

Atlas Copco Wagner's product marketing business unit manager, Chuck Chelin, says larger LHDs will be developed. However, there is always the trade off between larger, higher capacity machines and the extra capital required to drive drifts large enough to accommodate ever larger machines; very large machines may not be economic compared to a greater number of smaller machines in smaller drifts.

Low profile machines

The thin tabular lenses worked in the copper mines of KGHM Polska Miedz in Silesia, Poland, led Boart Longyear's Polish company, Boart Lena, to develop some interesting products. At one of the four interlinked mines, Polkowice-Sieroszowice, large areas of the richest ore reserves are found in lenses with heights lower than 2 m. In 1996, it was decided that drilling and bolting machines capable of working in heights of no more than 1.5 m should be developed and by the end of that year four machines of each type, designed and manufactured by Boart Lena, were in operation.

The tramming height of the machines was kept below 1.25 m, requiring operators to drive the rigs in a reclining position. This severely restricted their view of the rear of the machine. To overcome this problem, two small video cameras are mounted on the rear of each machine, feeding pictures to a monitor in the operators' station.

Boart Lena's first machines for KGHM, to operate in areas of roof height down to 2 m, were the Face Master 2.0 drill jumbo and the Roof Master 2.0 bolter, manufactured in cooperation with J.H. Fletcher. KGHM bought 18 Face Masters and nine Roof Masters by the end of 1996. Meanwhile, development of ultra-low machines for 1.5 m heights was completed and KGHM purchased these machines.

Low-profile LHDs have been a speciality of GHH for some years. Its line of Super Low Profile LHDs covers five units carrying payloads from 3.5 to 17 t. Their various heights are: LF-4.2 (3.5 t capacity) 1.3 m, LF-7.4 (8 t) 1.7 m, LF-9.2 (9 t) 1.6 m, LF-12.2 (12 t) 1.8 m and the LF 17.2 (17 t) 2.1 m. Much of GHH's low profile LHD development has been by GHH Mining Vehicles in South Africa.

Recent years have seen a wide variety of new underground trackless machines from German manufacturers. For example, after more than a year of research and development, BTZ Dietlas has released its new top of the range blasthole drill wagon. It features fully automated operation and carries 28 1.9 m drill rods in its magazine, allowing holes up to 100 m in depth to be drilled. Drill rods are added to the string automatically. Adding drill rods in this way typically takes less than 20 seconds. Drilling speed should average 15 m/min.

BTZ Dietlas also offers rigs for cut holes (either three 280 mm holes drilled simultaneously or a single 450 mm diameter hole), charging vehicles, low profile (1.7 m high) LHDs suitable for use in narrow vein mines (bucket capacities from 5-14 t), roofbolting rigs and a backfill transport vehicle.

Similarly Herbst Forder- und Hebetechnik (HFH) specialises in tailor-made trackless units for specific solutions. HFH has been providing custom-made utility vehicles since 1981. More than 30 different types of vehicle have been developed and sold. The latest units are LHDs with payload capacities of 6-18 t and a new heavy-duty scaler (MM, June 1999, p.G14). The low emission LHDs can be customised to mines' requirements. The product line also includes underground dump trucks with capacities from 5 to 50 t. To build and maintain roads underground, to improve the efficiency of LHD operation, there is the F 166 A UT motor grader. This unit features a quick change system to convert between blade and vibrating compactor use.

The future

Groups like Atlas Copco, mti and Sandvik Tamrock can offer complete loading and hauling packages. Atlas Copco Wagner's view on this, expressed by Chuck Chelin: "is that a complete face-equipment package, that is drills, LHDs and trucks, is important for two primary reasons. The first is the direct benefit of convenience to mines in partnering with one supplier. The secondary benefit is in reliability and cost improvements. A supplier with many machines on a site will benefit from the economy of scale in product support, and is much more likely to be able to provide thorough and timely parts and service."

On the automation subject he comments that: "Machines can be developed totally for automated/remote use, but likely LHDs and mine trucks will have a minimal on-board operator station for convenience in moving the machine off duty."

He agreed that there is increasing acceptance of the use of LHDs to load underground trucks, making use of rubber-tyred haulage. Its advantages he suggests are: "primarily due to its versatility and its low mine infrastructure cost. Rail haulage is efficient, but is expensive to install and move, and must be on relatively flat grades. Conveyer systems handle grades better than rail, but are even more expensive to acquire and time-consuming to move.

"The 50 t size [underground truck] is a customer focus at present," he continues, "but certainly higher-capacity trucks can be considered. Again, a practical limit is the size of haulage drifts mines are willing to construct, and whether the drifts' turns, grades, and manoeuvring areas will allow speeds necessary for increased cycle time."

References

1. Broomhead, Malcolm and Bodkin, Ross, State of technology in underground mining, Mining for Tomorrow's World, June 8-10, 1999, Dusseldorf.

2. Samskog, Prof. Dr. Per-Olof, Wigden, Dr. Irving and Tyni, Hakan, Process automation in ore mining, Mining for Tomorrow's World, June 8-10, 1999, Dusseldorf.

3. Baiden, Dr. Greg, Telemining systems applied to hard rock metal mining at Inco Limited, Mining for Tomorrow's World, June 8-10, 1999, Dusseldorf.
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Title Annotation:mining machinery
Author:Chadwick, John
Publication:Mining Magazine
Date:Aug 1, 1999
Words:4568
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