Much of mine maintenance these days is based on the idea you can predict when a machine will fail. The reasoning goes like this: If you know when a component is going to fail and it costs less to replace it before it fails than it costs to replace it after it fails, then it’s worth your while to replace the component before it fails. So most mines spend a lot of money measuring the health of their mechanical components in order to nail down when they are likely to fail. In open-pit mines, maintenance accounts for anywhere from 24% to 50% of the mine’s total operating costs. As a consequence, miners schedule comprehensive inspections of major pieces of equipment, usually twice a year or after a set number of operating hours (15,000 hours for wheel motors on haulage trucks, for example). In addition machine operators are continuoually inspecting their equipment, and electricians and mechanics are available around the clock for emergency and routine repairs.
To reduce the costs of maintaining equipment and to prevent equipment from being tied up in the repair shop, mines have reorganized their maintenance departments, introduced computerized information systems, and made personnel more responsible by reducing maintenance staff to a bare minimum. Your mine has probably done one or all of these things.
You probably haven’t heard of “reliability-centred” maintenance (CRM), though. It is a more sophisticated system used in aerospace and other complex, capital-intensive industries. But as mining systems become more complex, you might do well to take heed. Engineers at the Aitik copper mine, near Gallivare, Sweden (Europe’s largest copper mine) are doing just that. Having decided to purchase larger, 240-tonne trucks to replace 19 Lectra-Haul (M-36) 154-tonne trucks, they are considering RCM techniques to manage the high cost of maintenance associated with the larger machines.
According to Jan Rutquist and Per- Eric Jadmolm of Aitik (authors of the paper The changes in the concepts of maintenance for a large mechanized surface mine and its cost effectiveness: A case study) the trick to RCM is to identify the items which require significant maintenance tasks, evaluate the consequences of their failure using decision theory and select an effective interval for each item to be repaired or replaced.
The first step requires an understanding of how each item in a system can fail and the related economic and safety consequences of that failure. From this, maintenance personnel can identify those items that require intensive studies to avoid major economic and safety consequences.
“Once the significant items are identified, their effective maintenance interval can be identified based either on the operating time or on the basis of information extracted from the periodic or continuous condition monitoring system,” the authors say.
The cost of implementing such a system is, of course, much higher than relatively simple preventative or predictive maintenance programs used to date. So once again, miners will be asking themselves: Is it worth it? MAXIMUM UTILITY Underground miners have a habit of using whatever piece of equipment is available to perform odd jobs such as transporting materials, installing pipe, working on ventilation systems, etc. All too often the piece of equipment they choose for the job is a production vehicle.
To explain why this is not such a good idea, Matti Koskinen, of NORMET, an equipment manufacturer located in Peltosalmi, Finland, compared the total owning and operating costs of a typical load-haul-dump (LHD) machine with a utility vehicle.
“It is simply not economical to use a 3-times more expensive LHD, which has more than double the operating costs, for transporting and installing services when a unit designed for the purpose does the job cheaper,” Koskinen says.
Not many mine operators would know this because they do not monitor the costs of owning and operating utility vehicles as closely as they monitor their production equipment. But maintenance of utility vehicles should be taken seriously.
While underground production equipment is becoming bigger and more sophisticated, he says, utility vehicles have remained virtually untouched by this way of thinking about machine design. One notable exception is the concept of using one carrier for a number of modules or cassettes — a man-riding cassette for transporting men, a work platform for installing pipe, an explosives carrier for charging blastholes and a shotcrete manipulator for applying shotcrete.
How efficient can one of these vehicles be? Since multipurpose vehicles are less capital-intensive than owning a separate vehicle for each function, quite a bit. How much, depends on your optimum fleet size. Koskinen’s findings are explained in his paper, The cost-effective use of underground utility vehicles. NEW COAL MINE POSSIBLE For the past five years, coal has been regarded as less than a growth mineral. A glut on world markets and low prices have been so persistent that it looks as though no new mines are able to make a buck. But that hasn’t stopped Esso Resources Canada of Calgary from looking at potential new coal mines in Alberta.
The company needs the most economic fuel available for its heavy oil project at Cold Lake. Natural gas is being used now, but Esso would like to be able to change, and the provincial government would like to see them switch to coal should prices for natural gas climb. Esso has been investigating three coal deposits of its own in Alberta and two other coal-mining companies, Luscar Ltd. and Fording Coal, have undeveloped properties in the province which could supply the necessary coal for the project. One of the more promising, according to Howard Lutley of Esso, is the Judy Creek property, near Whitecourt. Known locally as the Virginia Hills, it is divided into a south block and a north block. Extensive studies by Golder Associates in 1978 and Monenco Consultants in 1983 considered the possibilities of mining four coal seams in the north block (which is owned 50-50 by TransAlta and Esso), using dragline methods.
The coal lies within a rock unit 4 to 8 m thick which contains interbeds of mudstones, bentonitic claystones and sandstones. Overburden varies from 5 m to more than 40 m in thickness.
Now, Mark Hawley and Frederic Claridge of Piteau Associates, a geotechnical consulting firm based in Vancouver, B.C., have concluded (in their paper Preliminary geotechnical & mine planning investigations for the Judy Creek South block coal project, Alberta), that a mine plan using trucks and shovels to strip the overburden and continuous surface mining machines to remove the coal from the south block appears technically feasible. Based on sketchy geotechnical information from a number of boreholes, they calculate that such an operation should consist of four benches, 15 m high, with berms 30 m wide, giving an overall slope in overburden of 22 . “It is likely that local conditions may be worse than those assumed,” Hawley and Claridge warn in their paper Preliminary geotechnical & mine planning investigations for the Judy Creek South block coal project, Alberta.
However, the economics of such a mine plan hinges on the price of natural gas. LEARNING FROM BIG BROTHER Big mines can be a fountain of information for mine planners at even the smallest mines. Mega-mines are those which handle tens of thousands of tonnes per day. At that rate, planning and scheduling is so complex that they are typically delegated to many individuals. The information they gather and generate must then be communicated to other planners and shared with operations people in order for things to run smoothly. How that process is orchestrated can be emulated by the small operator who has to wear many hats at once.
Ten years of mining the Athabaska Tar Sands at Fort McMurray, Alta. puts the Suncor and Syncrude mines into a mega class all their own. Mining at a rate of about 500,000 tonnes per day at the Syncrude operation has created a pit 7 km long and 5 km wide — an immense hole that is getting bigger at a rate of 160 m per year.
Over these past 10 years a number of planning engineers and mine operations personnel have developed a complex set of planning criteria and procedures. Now Syncrude is increasing the use of computers in this process by providing an integrated technical system which includes common planning tools and data bases for all departments. “A computer workstation environment with graphics/ computer-aided-design (cad) tools is planned. It will produce dragline cut plans, daily dragline and bucketwheel reclaimer plans, one-year mine plans and an economic analysis of the orebody for mine limit determination,” says Senior Mining Engineer Ken Jonah.
Syncrude has two Marion 8750 draglines and two Bucyrus-Erie 2570W walking draglines which mine the oilsand and deposit it in windrows where four bucketwheel reclaimers manufactured by O&K and KRUPP of West Germany, scoop it up and dump it on a conveyor system which delivers the oilsand to the extraction plant. CAD AND THE MINE PLANNER Computer-aided-design (CAD) would seem to be a marvelous tool for the mine-planner. After all, it allows him to generate a variety of mine plans, animates the mining sequence and allows for a quick evaluation of a number of “what if” scenarios. In reality, though, very few comprehensive underground mine planning CAD systems are available. Most professionals still suffer the ammonia of the blueprint machine rather than spend time building up a comprehensive computer package of their own.
To perform several different jobs, a computer system must have a number of modules with the capability to run interactively with the user and produce graphics and output reports as well.
Dr Khosrow Badiozamani and Donald Bott, both of Morrison-Kudsen Engineers in Bois, Idaho, say they have developed such a system for underground coal mines. A mine design layout can be quickly created, cloned or modified using the system, which has been dubbed ULTRA. Room-and-pillar and longwall panel designs, generated from a given set of dimensions supplied by the user, can be stored in a panel library, ready to be snapped out and placed on the layout. And pillars, for example, can be modified for local mining conditions and replicated throughout a mining block. For existing mines, the relevant portions of the current mine panel are digitized and pillars are generated automatically.
The sequencing portion of ULTRA combines the who (which mining systems and crews will be working), the what (what areas of the mine plan are to be mined and in what order), the when (at what times will those crews be working) and the how fast (at what rates will the mining systems be advancing). Information such as shift length, scheduled holidays, time off, partial shifts, advance rates, mining thickness and so on is typed in by an engineer and the ULTRA generates the sequence according to this information. An expert system is used to ensure that no area of the mine can be started until all required development to reach that area has been completed. Once the mining sequence has been completely generated, the engineer can review the results and determine if the sequence meets his requirements.
An animation feature allows the engineer to identify delays before they happen, so he can modify the sequence in advance to meet his needs.
“We cannot emphasize too strongly the value of a user-friendly graphics interface,” Badiozamani and Bott say. “The speed with which the layout and sequence can be generated and modified is of prime importance to busy professionals who are required to produce correct answers under short deadlines.” BREAKING NEW GROUND Imagine operating a shovel in an open pit, knowing the precise digging conditions of each part of the muck pile before you even take the first bucketful. That’s the situation researchers at McGill University in Montreal and mine engineers at British Columbia’s Fording River mine, near Elkford, are confident will become a reality. The key of the research sponsored by Natural Sciences and Engineering Research Council, is to step back and take a close look at the geotechnical information that can be gathered from blasthole drills. That information, it turns out, can tell you a lot about how to break the ground.
Last year, three researchers from McGill and Fording outfitted one of Fording’s four B&E 45-R blasthole drills with a device which monitors six different drill parameters while the machine is drilling. The microprocessor-based device recorded the displacement of the bit, instantaneous penetration rate, downpressure, rotary torque, rotary speed and air-flushing pressure in a total of 74 blastholes. Information was gathered at every 10-cm interval of the 1,349 m drilled. Nine of these holes were then logged with a geophysical borehole probe which uses gamma radiation to give an accurate picture of the changes in lithology.
From the data collected from the blasthole drill, the researchers calculated how much energy the drill bit imparted to the rock to fracture it and advance the bit. From this, they assumed that a change in energy was related to a change in rock strength and could therefore draw a precise picture of where the weak coal seams are located within the stratigraphy, dominated by relatively stronger sandstones, mudstones and siltstones.
“Correlation between the relative response in specific energy and the locations of rock units identified from geophysical logs proved to be excellent,” researchers Malcom Scoble and John Peck of McGill University and D. Kennedy of Fording say in their paper Blasthole drilling research at the Fording River Mine.
The next step is to integrate this information into the mine’s existing drilling and blasting computerized information system. That way, engineers should be able to cut explosives costs by designing explosive loads based on accurate geotechnical information. This, in turn, should lead to reduced dilution of the coal ore and should give engineers an accurate picture of ore and waste volumes in each muck pile. From this information, the loader which can do the job with minimum effort and in the shortest period of time (i.e. the most efficient loader) can then be selected to muck a given muck pile — taking a lot of the guesswork out of equipment selection.
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