Equipment automation: mining's new frontier?
CONTROL OF INDIVIDUAL MACHINES IS A REALITY, BUT MINE-WIDE AUTOMATION IS STILL A DISTANT DREAM
In a tight market, primary-metal producers can't increase their market share by offering a "better" product than the competition. Market clout is gained by achieving lower unit costs, and when the market turns sour, mine operators have relied on reorganization and cost-cutting measures to survive and stay competitive.
These are effective but short-lived solutions; once this strategy is exhausted, what other means are available to reduce unit costs?
Development and integration of automated machinery into the production process offers a longer-lasting remedy, according to J. Pathak and J.E. Udd of the Canadian Centre for Mineral and Energy Technology. But it's a goal that can't be reached overnight.
Automation technology developed for the manufacturing sector generally can't be directly transferred to mining applications. Equipment has to be designed specifically for mining environments to be successful, explained the two researchers, who spoke at the 4th Canadian Symposium on Mining Automation, held in Saskatoon, Saskatchewan, in September. Developing and producing specialized equipment for a relatively small market such as mining is a difficult, expensive process that results in longer payback periods for manufacturer and producer alike.
However, increased automation is one of the few remaining options available to miners to cut costs and improve productivity. The industry--traditionally slow to accept leading-edge technology--is showing a higher degree of interest in automated equipment, but to fully develop and realize the benefits of automation, fundamental changes may be required in the way in which mines are both managed and operated.
Technical management of mines has primarily been the responsibility of generalists, said Pathak and Udd; this has caused the mining engineering profession to lag behind others, such as medicine, in which the trend is toward specialization. Dealing with the increasing complexity of minerelated technical problems and their solutions will require a team approach that draws upon the strengths of individuals trained in specific disciplines. In order to accomplish this transformation, universities must adjust their curricula to reflect the multi-disciplinary nature of mining, and a way must be found to retrain mining engineers without necessitating their removal from the field.
BETTER COMMUNICATIONS NEEDED
Even with a move toward greater specialization in technical management, the mine of the future can't become fully automated without improved communications systems. Present telephone and radio links in use underground don't have sufficient data-transmission speed or capacity to enable mine-wide computer control of all systems and equipment; they typically can only cope with automation of individual systems or machine units, according to Pathak and Udd. Because of the constantly changing nature of mine geometry and the large number of potential radio-interference sources underground, development of suitable mine-wide data transmission systems will be a challenge for years to come.
At Molycorp's Questa, N.M., underground molybdenum mine, the challenge is being met. Automation of underground operations began with the mine's conveyor and electrical systems and now includes an automated rail-haulage system. According to Larry G. Stolarczyk of Stolar Inc., mechanical controllers on 35-st trolley-powered locomotives were replaced with C(4)M (computerized communications, command, control and monitoring) controllers. Integration of these controllers, radio remote controls, and a main computer allows manual or automated dispatching of 17-car trains from a holding area to a loading point along an 18,000-ft track loop beneath the orebody. Loading is managed by a worker at the draw-point using a handheld controller unit
Under control of the supervisory computer located at the surface, the loaded train can then proceed to a dump site where the cars unload into a conveyor surge pocket. The locomotive operates semi-automatically under computer control as it moves along the loop, with fail-safe shutdown capabilities that bring the train to a safe stop in case of communications or propulsion systems failure. The main computer communicates with the train-mounted controller by medium-frequency band radio, using existing electrical conductors such as air or water piping, ac power cabling, rail/dc bus, and telephone wiring for signal transmission.
Stolarczyk said that mining equipment creates "incredible" levels of radio-frequency interference (RFI), but at Molycorp a robust communications protocol was developed to provide low-bit-error-rate data transmission capabilities despite the RFI caused by machines, arcing, and power-system switching transients. The protocol, when combined with the semi-autonomous C(4)M design strategy, enables the trains to operate safely in the high-noise environment of the rail haulage system.
AUTOMATING MACHINE UNITS
Across the mining equipment spectrum, significant progress toward automatic control is also taking place at the machine unit level. Computerized production-drilling rigs and control systems, mechanical excavation equipment, and automated haulage systems have improved significantly because of ongoing research and development. Several speakers at the symposium described the direction and scope of advances in these specific areas.
The trend toward increased automation in underground production drilling has been expedited by the development of drilling rigs that provide easier programming of drilling plans, advanced control systems, improved maintenance features with self-diagnosis capabilities, and onboard and remote monitoring of drilling performance. Pasi Latva-Pukkila and Matti Pulkkinen of Tamrock, explained that automation and instrumentation of drilling equipment should be regarded as a tool to achieve production objectives at minimum cost, and for best results, automated drilling cannot be separated from development of other mine information-gathering techniques.
Computerized production-drilling rigs have been in use since 1986. Current models don't provide full automation; they can only drill a hole and then uncouple the drill string. Even with these limited capabilities, experience gained with computerized percussion-drilling rigs in use in Canada (at Hemlo's Golden Giant mine), in Australia (at the Hellyer mine, with others scheduled for installation in 1990), Sweden (Viscaria mine), and Finland (Outokumpu's Enonkoski nickel mine) has shown that use of new-generation equipment can provide:
Higher productivity--Computer-controlled rigs can drill unattended during employee work breaks and in the presence of blast-generated dust and fumes. Today's long-hole rigs will drill a hole to a preprogrammed depth after manual alignment and collaring. After the desired depth is reached, the rig will flush the hole and uncouple the drill string. According to the Tamrock representatives, the increase in drilling productivity during a normal 8-hr shift can be as much as 15 to 30%, measured in drilling footage.
In tunnelling applications, drilling cycle time can be reduced by up to 20% because computerized jumbos don't need a marked-up face to locate hole collars; the machine is positioned using a reference laser beam and the boom can be moved from one hole to the next straight away.
Lower production costs--The consistency and accuracy of hole alignment and depth control provided by computerized equipment leads to better blast fragmentation, more efficient loading, and less secondary blasting, according to Pulkkinen. Operators using computerized rigs can drill more feet of hole length in the same amount of time, thus reducing labor costs. Savings can be achieved in drill-steel costs, as well; computerized drill rigs using rods can reduce steel costs by 5 to 25%, compared with manual rigs.
An important element in industry acceptance of next-generation computerized drill rigs will be improved user-friendliness of drill control systems. Drilling crews must learn new operational and maintenance routines to effectively use automated rigs; on the other hand, the control systems of the future will have increased program capacity, a more refined user interface, and higher sensitivity toward management of drilling variables and parameters that will match the performance of the best drill operators.
THE END OF DRILL-AND-BLAST?
In the near future, mining will likely have to deal with increasing economic burdens stemming from intensifying environmental concerns, the necessity of mining lower grade ore, and competition from synthetic materials. These factors may compel the industry to embrace innovative rock excavation methods in place of slow, but tried-and-tested drill-and-blast techniques. Dr. Levant Ozdemir, Colorado School of Mines, outlined several areas of development in hard-rock mechanical mining technology that could lead to lower-cost rock removal.
Recent design of mechanical excavation machinery has benefitted from increased knowledge of the factors involved in rock fragmentation by mechanical means. Manufacturers, recognizing a potential market for mechanical excavators in underground applications, have incorporated this increased knowledge into machine designs that are more mobile, powerful, and in general, more attuned to the specific needs of miners.
These new machines potentially offer the mining industry certain advantages over drill-and-blast operations that civil construction operators have enjoyed for years. In particular, mechanical excavators can provide the following benefits:
* Increased personal safety from elimination of blasting and the cyclic nature of drill-and-blast operations. As well as the fact that mechanical excavators generate practically no ground vibrations. * Machine excavation generally doesn't disturb the surrounding rock, thus reducing ground-support requirements. The smooth walls created by mechanical excavators require less rockbolting and improve ventilation performance, which means that mine development costs can be reduced because ventilation drifts with smaller cross-sections can provide capacity equal to larger openings created by blasting.
In one of the more successful applications of tunnelboring machines (TBMs) to underground mining, the Stillwater Mining Co. is using a modified Robbins 4-m-dia TBM to cut 48,000 ft of footwall laterals in its platinum-palladium mine near Nye, Mont. The TBM reportedly has cut the cost of driving laterals by 30% and it has also reduced rockbolting requirements by more than 80% compared with drill and blast methods. * Machine excavation provides the ability to conduct selective mining of ore, minimizing dilution and cutting material haulage and processing costs. In addition, mechanical excavators are able to produce rock cuttings of uniform size and gradation, reducing or eliminating primary crushing requirements and allowing for continuous material transport systems. * Mechanical excavators are relatively easy to adapt to remote-control and automation technology. These machines are designed for continuous operation, which makes them highly suitable for partial or full automation.
There are also drawbacks, according to Ozdemir. TBMs generally have been designed for civil construction use and are not well-suited to mining conditions that demand more power, agility, and durability than most TBMs could provide. Cutter design has been inadequate for the types of materials encountered in hard-rock mines. And, many operators didn't feel comfortable with the round cross-sectional shape of entries produced by TBMs.
Newer TBMs and other mechanical excavators, some still in prototype stage, promise an end to these deficiencies. TBMs are now equipped with high-capacity disk cutters that combine good rock-cutting ability with superior wear performance. Robbins Co., Seattle, and Snyder Engineering, Denver, have designed 4.5- and 4.8-m-dia TBMs, respectively, that can turn within a 40-ft-radius. Both machines allow cuttings to be loaded into existing mine haulage units such as LHDs or trucks, and offer horizontally/vertically rotatable gripper mechanisms that allow excavation through existing underground intersections.
The concept of remote-controlled, unmanned raise boring operations has gone from theory to reality as a result of recent technological innovations in electronics and drive systems. Robbins Co. has developed packages offering semi- to full automation of raise drills. Increasingly, mining companies are requesting new machines with automation features built in, but the new automation packages are also suitable for retrofitting on drills currently in use.
Robbins' automation package begins with a system that offers automatic shutdown control. At the end of a stroke or when blocky ground is encountered, the shutdown control kicks in automatically, preventing machine damage. The machine is then restarted by the operator and reaming resumes. The next option includes automatic rpm and thrust control for optimal boring in any given ground condition. Mt. Isa Mines recently purchased this package for its 63RM-H, a hydraulic-drive machine that has achieved 99% availability at the Hilton mine.
Other packages include all of these features plus automated thread make-up and breakout for rapid pipe handling and faster advance rates; automatic wrenching; and complete automation of the boring operation, including remote-monitored operation and unattended pipe loading. Data logging during raise boring operations can be accomplished either locally or remotely with all of the packages offered.
Boretec, primarily known as a rebuilder of conventional TBMs, designed a specialized underground excavator called the CUB (compact underground borer). Developed under a joint venture involving Boretec, Falconbridge, Placer Dome, J.S. Redpath and the Canadian government, the prototype offered high thrust capacity, a short (25-m) turning radius, and modular construction which allowed the machine's subassemblies to fit through existing mine openings. The CUB's first underground trial took place at Falconbridge's Frazer Ni-Cu mine near Sudbury, Ontario, Canada, where it encountered ground-failure problems and was taken out of service to permit a redesign of the machine's shielding equipment. The modified CUB will also tow a drilling sled to provide for immediate rockbolt installation after excavation, and is scheduled to re-enter service early in 1991.
Ozdemir explained that the circular-shaped opening created by TBMs is usually not suitable for mine operations, but this problem can be solved by backfilling behind the machine to create a flat floor, secondary drilling and blasting after excavation to create a more suitable cross-section, or by mounting a set of boom cutters on the sides of the TBM to create a horshoe-shaped entry.
Perhaps the most formidable obstacle to mechanical-excavator use in mining is the fact that these machines are designed for cutting long, relatively straight drives; whereas much mining development consists of short entries, inclines, and declines. Ozdemir suggested that future mine-design techniques, particularly that of new operations, could be tailored around the capabilities and limitations of these machines to extract the greatest benefit from their use.
AUTOMATED POTASH BORER
The Potash Corporation of Saskatchewan (PCS), Rocanville Division, has taken a first step along the road to development of a mine-wide control system by automating one of its 250-mt Marietta 780-AW4 continuous boring machines. Stephen J. Fortney and James L. Lewis of PCS described the company's ongoing efforts since 1983 to achieve automatic control of a boring machine--a goal that was accomplished in October 1989 when testing conducted at Rocanville successfully demonstrated all aspects of automatic machine control.
The PCS program had four objectives: to maximize ore recovery by computerized machine control and continuous ore-grade analysis; to free operators from routine control duties such as steering and maintaining proper cutting pressures; to reduce electrical and mechanical stress on the machine caused by abrupt control adjustments; and to establish a consistent level of machine operation that could enhance predictive and preventive maintenenace efforts.
The four-rotor, 800-mt/hr Marietta machines are used to develop entries and mining rooms up to 6,000 ft long. Mining rooms are excavated in three passes to produce a 66-ft-wide opening. During the second and third passes, the operator follows the profile of the first-pass excavation, allowing the machine to overlap 6 ft into the first-pass excavation. When cutting second and third passes, a cross conveyor transfers ore from the mining machine to an extensible conveyor belt anchored in the first-pass entry.
To ensure a smooth back, the machine must be kept in consistent face contact while following the roof elevation of the first pass. Maintaining the proper horizontal and vertical machine orientation and a constant cutting rate at the face is a demanding job for the machine operator.
In order to provide the required degree of machine control, the borer was equipped with seven primary subsystems that provide data to the microprocessor: ore-grade analysis, laser guidance, first-pass position and cross-conveyor alignment systems monitor external mining conditions, while motor current sensors, inclinometers, and other miscellaneous sensors monitor machine condition. A display screen at the borer's control console continuously provides machine condition and ore grade information.
The automated boring machine offers four control modes: manual, semi-automatic, first automatic, and second automatic. The manual mode removes all automatic control authority from an onboard-mounted Allen-Bradley microprocessor. In semi-automatic mode, the microprocessor maintains operator-selected cutting amperage at each of the machine's four 400-hp ac motors driving the cutting heads.
The first automatic mode provides complete automatic control during first-pass cutting, including ore-grade analysis to position the machine correctly in relation to the maximum height of recoverable ore, laser guidance to keep the machine on a correct heading, and cutting amperage control. The
second automatic mode also provides complete control during the second- and third-pass cutting involving first-pass location, cutting amperage maintenance, and cross conveyor positioning.
Fortney and Lewis reported that the machine had, under complete automatic control, cut 5,000 ft of first-pass and 15,000 ft of second-pass ore between its commission date and March 1990. During this period, only 4 hr of operating downtime was attributed to microprocessing failures. Meanwhile, several operational improvements became evident:
The frequency of cutting-bit changes was reduced by about half, and machine shutdowns caused by motor over-amperage and high-temperature faults were reduced.
Laser guidance of the machine, combined with microprocessor-controlled steering, resulted in straighter cutting and a smoother wall during the first-pass development. The more consistent first-pass wall conditions lead to better second-pass performance.
The ore-grade analysis capability of the machine's control system resulted in a 3% improvement in recovery of available ore grade during both manual and automatic control. All five mining machines in use at Rocanville had since been equipped with ore-grade analyzers.
Equally as important as the technological advances offered by the automated machine is the high degree of acceptance by operators. While the microprocessor relieves the operator of tedious and continual control adjustments, it also provides a ready means for testing new control philosophies. According to Fortney and Lewis, the ability to alter the control logic and to select various degrees of automation provides an environment that gives the operator a key role in developing new technological advances.
PHOTO : Tamrock's DataSolo H 1006 RA drill is typical of the new generation of its automated drills.
PHOTO : The Compact Underground Borer (CUB), shown here in the assembly shop, produces an 8-ft-dia opening using twenty 18-in. high-capacity cutters. CUB operates under PLC control and provides performance data to the operator via a display terminal in the cab.
Russell A. Carter, Western Editor
|Printer friendly Cite/link Email Feedback|
|Author:||Carter, Russell A.|
|Publication:||E&MJ - Engineering & Mining Journal|
|Date:||Feb 1, 1991|
|Previous Article:||Production drilling technologies.|
|Next Article:||The largest cat on Earth is a loader.|