Trends in surface mining equipment.
This article is not so much about new equipment as about trends in new equipment, and what those trends mean to the mining industry.
Perhaps the two most obvious trends in the past few years have occurred in haul trucks. The 240-st-capacity haul trucks are here to stay. And so are the mechanical-drive, 170-st haul trucks from Caterpillar.
Because the 240-st truck is larger, we shall look at it first. The idea for a 240-st haul truck has been around for quite some time. But now, it appears the reliable 240-st trucks have arrived for good. GE (General Electric) Transportation Systems reports a dramatic spurt in sales of the large wheel drives for the 240-st truck. More than 90 of the GE 787 truck systems for 240-st haul trucks have been shipped by GE, with another 60-90 on order.
The merits of the 240-st electric-wheel drives are abundant. Electric-wheel drives have been the system of choice in the mining industry for over two decades. Properly trained maintenance crews are not in short supply. Parts distribution networks are well established. And perhaps best of all, all the bugs have been worked out of it long ago. The electric-wheel drive motor is a dependable unit. The enlarged version of the unit to handle the larger 240-st trucks requires a bit of extra training, but the basic supply and support infrastructure is in place. To date, there have been no reports of reliability problems with the larger electric-wheel units.
Caterpillar has made history by introducing the first large, mechanical-drive haul trucks, the 785 and the 789. Using some newly developed electrical and mechanical technology, the company has managed to mechanically link a 1,800-hp engine to a set of drive wheels. This was no small task, and is described in the accompanying article.
Do the mechanical-drive trucks work? So far, of the more than 500 mechanical-drive trucks placed in operation around the globe, there have been no reports of any major problems, or operating bugs. In 1970, 100% of all haul trucks shipped were electric-wheel drive. In 1985, only 2-3% were mechanical drive, with that number rising to 39% in 1989. Selling more than 500 trucks in less than four years, with many more on order, is perhaps the largest endorsement possible, especially with no major complaints.
One major trend common to both mechanical-drive and electric-drive systems trucks is the rapidly improving electronic control systems. At first, more electronics would appear to be a major complication, especially for a system that has proved itself in the past 10 years, the large, off-highway haul truck. However, electronics can actually simplify trouble-shooting, if designed correctly. Internal, self-diagnostic programs can be built into the electronic components. Not only do these units point to what is wrong with them if they should malfunction, they are designed to announce what is wrong with the haul truck if it should need repairs.
Electronics promise to do to equipment what electronics have done for the pocket camera: simply operation to the point where the operator can concentrate on the job at hand, and the give the maintenance crews time to concentrate on preventive maintenance rather than being continually tied up with major failures.
Often, the most time-consuming part of any repair is just trying to find out what is wrong, not just what has broken, but what caused a component to break. All too often, a truck that will run poorly in the field will run perfectly when brought into the shop for tests. When it is returned to the haul roads, it will resort to performing poorly, a most frustrating experience for the driver, mine superintendent, and maintenance personnel. There are electronics being developed that will overcome this problem. A memory logger can be placed on board to record the readings of a wide assortment of gages. When problems occur, they can be played back in the shop, revealing under what conditions the problem appeared, much like a flight recorder.
And if a failure occurs, the onboard electronics can not only determine which component has failed, but how serious the failure is, whether it requires immediate attention or whether service can wait till end of shift, or later in the week.
There was a time when routine mine practice dictated that about 80% of components should fail before they were replaced. Now the target in most mines is to replace 75% to 80% of the components before they fail. It is slowly being discovered that it is less expensive to change many components before they fail, when the machine is conveniently in the shop, rather than risking a massive, catastrophic failure in the field. Some failures cost the same either at failure or with preventative changing. However, some failed parts take many other healthy parts with them, or contaminate an entire fluid system, those are the parts that truly require preemptive maintenance.
General Electric manufactures most of the electric-wheel motors for large haul trucks in use today. These systems are manufactured in Erie, Penn., in the same plant where the railroad locomotives are produced. (GE produces about one diesel-electric train locomotive per day.) The technology for the electric-wheel motor, in many ways similar to locomotives, is well-developed.
Properly loading a haul truck means putting the exact weight, not necessarily volume, of material into the truck. Often a truck will be hauling both ore and waste during the same shift, each with different densities. The question arises, how can the shovel runner know when the truck is properly loaded. Overloading can shorten tire life and increase wear on the drive train and the entire truck structure. Underloading is also a waste of resources because full productivity is not achieved. Controlling payloads by dipper count or by visual means leads to inconsistent and usually unsatisfactory results. Mine engineering production and planning is based on a rated payload figure, as was the decision to buy that particular truck. Planning and carrying out of the mine plan are greatly helped when trucks carry their rated capacities on a consistent basis.
Haulpak (Komatsu-Dresser) is one of several manufacturers offering its own onboard weighing system. In the Haulpak system, sensors are mounted in strategic places in the truck's frame, and connected to a microprocessor in the payload meter located mounted in the driver's cab. While the driver watches the weight, the shovel operator watches the light-assembly mounted outside on the deck. The lights flash green, amber, and red, depending on whether the truck is underloaded, loaded between 90% and 105% of rated capacity, or overloaded. Because the system has a microprocessor, it is capable of recording the final weight just before the truck begins its haul. The payload meter has the capacity to store data for 200 haul cycles. A printout is available which typically lists the driver, total number of loads, the weight of each load, the time each haul cycle began, the date, and the total weight moved for that shift.
Haulpak was also offers the DDEC 11 advanced electronic diesel-control system. DDEC 11 is a unit fuel-injector system operating under microprocessor control. Introduced in 1985, unit injectors are a simple fuel system that allows high-injection pressure for maximum fuel efficiency and lower emission levels. Because each unit injector provides the pressure, there is no need for external high pressure lines. Maintenance is eased because each injector can be serviced individually. Also, there are fewer mechanical parts with the electronic system than standard fuel injection units, reducing the need for frequent tune-ups. The system monitors 54 critical functions in addition to the lube and cooling systems.
High quality is another trend. All manufacturers are gaining a solid reputation for reliable machines. Problems inherent with the larger haul trucks have largely been overcome. Haulpak, for example, has a multi-million test center where entire truck frames, pulled off the assembly line at random, are tested with bending and twisting loads, simulating years of normal stress in just a few days time. Any potential problems show up in the laboratory where they are corrected before they have a chance to cause downtime. The result is that their frames have become very reliable indeed.
One trend slowly becoming apparent within the mining industry is an increased sensitivity to the community. When Hibbing Taconite received its first 240-st Haulpak truck, it was pleased to have the first 830E on the Iron Range of northern Minnesota. Rather than put the truck into immediate use, it held an open house, allowing everyone in the community to view the machine close up, sit in the driver's seat, and take a good look. "We were surprised by the response," reported Steve Zeitler, of Hibbing Taconite. "There was a steady flow of people through the machine all day. Of course, the children always seemed to like the horn the best."
Unit Rig, a division of Terex Corp., has produced the MT-3700, the newest in its line of off-highway mining trucks. With a maximum gross vehicle weight of 685,000 lb, the Lectra Haul MT-3700 is rated to provide an optimum shovel-loader match over a payload range of 190 to 205 st. A new suspension system features nitrogen-oil struts with externally adjustable damping in the front. Dual rate, two-stage damping in the rear is designed to give the MT-3700 the smoothest ride possible for a mining truck. Other standard equipment on the MT-3700 includes an 1,800-hp Detroit Diesel or Cummins diesel engine, General Electric 788 drive system, and 37- by 57-in. tires. The MT-3700 is the ninth truck in Unit Rig's line of Lectra Haul products ranging from the Mark 24 with a capacity of 100 st to the BD-270 with a capacity of 270 st, which is a bottom-dump coal hauler. Unit Rig's MT-4000 Lectra Haul 240-st rear dump trucks, introduced in 1988, are working successfully worldwide.
Wiseda Ltd. has been a manufacturer of the KL-2450, 240-st truck since 1980. The 2,400-hp engine, alternator, and radiator are mounted on a separate roll-out frame to allow fast change-out of the complete power-module assembly. GE 787 wheel motors drive the unit. Built-in test equipment and onboard diagnostics reduce troubleshooting time. The GE Statex control system has strategically placed arrays of light-emitting diodes (LEDs) located on the control and logic panels. These LEDs indicate power supply and logic functions that speed fault detection. A built-in oscillator test system on the control panel permits maintenance personnel to check all logic functions, and make adjustments while the truck is parked. Diagnostic test points are also provided for faster measurement of reference voltages, power supplies, and horsepower.
Marathon LeTourneau's Titan T-200 diesel-electric, rear-dump hauler has a rated capacity of 200 st. The Titan is powered by a 2,000-hp Cummins, Detroit Diesel, or MTU turbocharged engine. The electric-drive system features twin, axle-mounted Marathon LeTourneau traction motors. The electrodynamic traction system changes from propel to retard in less than one second and delivers up to 3,200 continuous retarding horsepower to the wheels. The retard system assists the service brakes resulting in reduced brake maintenance. The unit achieves speeds of more than 30 mi/hr. Four pinion and bull-gear ratios are available to allow hauler power traction to be matched to shallow or deep-pit haul-road conditions. Onboard diagnostics speed trouble-shooting. The Marathon-LeTourneau L-1100 wheel loader is designed specifically to efficiently load the Titan.
Dresser has recently celebrated its 50th anniversary of making front-end loaders. The first Pay loader was made by Frank G. Hough in 1939. Prior to that time, bulk materials were handled by farm tractors equipped with hydraulic-shovel attachments. The only alternative was steam shovels or hand shovels. To illustrate how far his idea has come, the original Pay loader can be placed inside the 22-yd(3) bucket of a Dresser 580 Pay loader. John Verworn of Dresser says that improvements will continue, but at a slower pace than the past 50 years. "I think we'll see more design improvements on the component level, aimed at increasing reliability and serviceability. Certainly we'll see more use of microprocessors and other electronics on wheel loaders, to optimize machine and alert the operator to any malfunctions."
Many remarkable trends are found in front-end loaders (FELs). Not only are they growing larger and more powerful, but they are also benefiting from the electronics revolution. Loaders are also beginning to compete with shovels in some applications. Not only are loaders more mobile than shovels, but they can clean up after themselves.
Many mines have introduced in-pit crushing with mobile crushers, and many more are considering it. Conveyors can move material inexpensively, but need an in-pit crusher to insure the proper size material. For mobile crushers with mobile connecting belts, FELs are required to move the material from the short distance from the face to the crusher head.
Big loaders in easily diggable material offer shovels more competition. The FEL is more maneuverable than a shovel, and requires a lower initial investment. It can be easily moved to get out of the way of blasts. The FEL can also do limited load-and-carry work.
This trend toward using FELs as short-haul units is causing a change in their design. FELs are required to haul material further as distances increase between the face and the crusher hopper. Suspensions of FELs are notorious for having very little shock absorption, causing them to bounce wildly at increased speeds. Now, Caterpillar has introduced a Ride Control System to allow FELs to move material longer distances at higher speeds.
Caterpillar has come up with a clever way for a FEL to weigh the material in the bucket, not just while the machine is at rest, but while it is on the move. Knowing how much is in each bucket can greatly aid loading a truck to its proper capacity, not underloading or overloading. Taking the loader's system dynamics, geometry, and knowing where the various loads will be, the FEL can precisely report the load in the bucket. The scales have an accuracy of 8% when the loader is moving, and 1% when stationary. The hardware is the same as for Caterpillar's haul-truck payload monitors, but the software is different, taking into account the fact that the FEL will be moving while the load is being measured. It is under field tests now, and is expected to be commercially available in early 1991.
Cost sensitivity charts (Table 1) would seem to indicate that an increase in production would produce the most favorable change in cost per tons. One might think that a logical way to improve FEL productivity would be to simply increase the bucket size. Of course, this depends on the needs of the dump point. An improperly sized bucket could cause a mismatch with crusher capacity, truck size, or how much the plant can handle. If the dump point is an in-pit crusher, looking at larger buckets might make sense, unless the FEL delivers material faster than the crusher can process it. For loading trucks, a bucket too large might be too wide for the receiving truck box (the ideally loaded truck has two-thirds of the load on the rear wheels and one-third of the load on the front. Will the loader with a larger bucket be able to distribute the load to meet these optimum loading conditions?)
Looking again at the cost sensitivity chart, the next most important variable (after production is matched to the total system), is availability. The past decade has seen a strong trend towards conscientious maintenance. Perhaps it is because more and more mines are keeping better production records, finding out with some alarm exactly how expensive even 10 minutes of down-time really is. The old question was simply, how many tons can I move per hour. The new question is how much does it cost.
According to Caterpillar researchers, the next generation of electronic systems will monitor performance over the life of the machine, allowing performance trends to be easily spotted. This should happen soon because electronic memory is steadily becoming less expensive. Variabilities in performance can be traced to shifts, operators, or other variables. Also, a telemetry system would send operational data to a central point with more detailed software capable of spotting trends common to all trucks. Ultimately, these systems will provide a warning before a major failure, not just on an individual-truck basis, but on a fleet-wide basis.
Another important factor in Table 1 is fuel consumption, especially important with recent developments in the world's oil supply. One obvious trend is that fuel costs will become more critical on the cost-sensitivity graph. Electronics have proved useful for improving fuel consumption by allowing the engine to run more efficiently. An important side-effect of a properly tuned engine is improved emissions.
When a mining company spends more than $1 million on a large piece of equipment, it is generally very thorough in checking out all the obvious details. One item almost universally overlooked is the operator's point of view. Sometimes a company will spend many man-hours to match the equipment to the job at hand, and almost zero time considering the most important factor of all: the operator. Not just whether the operator is properly trained, but whether the environment inside the operator's cab is conducive toward efficient operation. If the operator is unhappy in the cab, that piece of equipment will not operate at peak efficiency, no matter how well designed.
The working environment is as important to the person in the cab as it is important to a person in an office. Factors to be considered are many. People over the world come in different sizes, can people of all heights operate the equipment? This involves not just whether the seat is comfortable, but whether people of all sizes can reach all of the controls comfortably.
If the air conditioner breaks, for example, it makes no difference how well trained the operator is: After a few hours at 110 [degrees] F, any operator can not help but lose concentration and make mistakes. The importance of a proper heater and air conditioner are fairly well accepted, but one item often overlooked is an efficient air filter for the cab. Nothing is more damaging to morale than a dusty environment. There also is a growing trend to pay attention to noise levels in the cab, especially in European countries.
One way to measure how well a manufacturer pays attention to details is to check whether there is anywhere for the operator to put a coffee cup in the cab. This may seem like a trivial detail, until a haul-truck driver spills boiling-hot coffee while driving a giant haul truck at 35 mi/hr.
Microprocessors have provided opportunities for more control then mechanical systems have allowed in the past. Laws requiring lower emissions have forced the development of microprocessor systems and sensors. At first there was some market hesitation for the new gadgets, but now they have reached an acceptable level of reliability.
At first, the technology was applied to on-highway vehicles. As systems evolved, the systems were applied to offhighway trucks as well. The U.S. industry practice is to standardize microprocessors and make them as self-diagnostic as possible. Sometimes this involves establishing new standards for electrical reliability. The level of control these devices can have on an engine is growing in sophistication. Although it was first designed as a way to reduce emissions, the devices have proved that, once properly designed and developed, they can improve fuel consumption as well. They can also coordinate the entire gear-shifting process. This trend to increase efficiencies and reduce emissions by the use of microprocessors should continue.
Caterpillar admits that just 10 years ago it did not have a large electrical-engineering department, but that now it has over 200 electrical engineers in research and development. It will readily admit that it is easy to design an electronic control system, but difficult to actually build the thing so that it can withstand the rigors of a mining environment. Shock, vibration, moisture, temperature swings, and dust are only a few of the problems. Plus, "it must be as reliable as a bolt and as easy to fix" to minimize downtime.
Microprocessors can help answer three questions: Am I going to have a problem soon? Do I have a problem now? If so, where is it? There is also another question that the microprocessor and sensors need to answer, and that is, Am I the problem? A design philosophy has developed that says, "what creates sophistication also solves it," meaning that with increasing complexity there is also more capacity for self-diagnosis. Even self-diagnosing sensors, or smart sensors are being developed.
With more sensors in place on the machine, another microprocessor will take advantage of this extra data, telling the health of the machine at any one time, and recommending a course of action. It will convert the data from the sensors into useful information. Perhaps someday, there will only be one readout on the truck dashboard, saying either "All systems go," or "Get fuel soon." Someday, the system will not just be able to say, "The engine is a little hot," but why as well.
Another trend at Caterpillar is that as new components are added, engineers seek to standardize them with existing equipment. A good example is the corporate wire harness, designed to simplify testing and troubleshooting.
There is a trend toward modular components. For example, in order to decrease downtime, many large units, especially haul trucks, have engines that can be changed out easily, while their waiting replacements can be slipped back into place, and the machine is immediately operational, with the shop free to repair or overhaul the engine without the intense pressure of getting the truck back out on line again immediately.
The world's largest wheel dozer, the Tiger 690B, has been introduced to Europe following successful sales in the United States and its home country, Australia. The Tiger 690B marries the rear power unit of a Cat 992C wheel-loader to a dozer front-end manufactured by Tiger Engineering Pty. Ltd. A Cat 773 truck torque-convertor, which will lock-up, substitutes the standard 992C torque-convertor. Big-footprint radial tires supply the necessary traction.
With a maximum 22 km/hr, the Tiger 690B offers speed and mobility to a variety of dozing operations such as pit-floor shovel and truck cleanup, stockpile, reclamation, and push-loading of scrapers. Duty cycles for the wheel dozers are much less onerous than for wheel loaders. In addition to new units, Tiger engineering is marketing conversion kits for Cat 992C loaders that have already completed their first service cycle.
Jim Duke is one of four people that signed the patent for the elevated-sprocket drive on the Caterpillar D10 crawler tractor (commonly referred to as a dozer). The elevated sprocket provides several advantages: the drive sprocket, as well as the power train, is taken out of the undercarriage; overall machine balance is improved; machine design and maintenance are simplified; and the design lends itself to easy rebuilding or upgrading. "Four things make a crawler tractor work," says Duke, "weight, horsepower, balance, and tractive effort. The better the balance and tractive effort, the more efficient use is made of the horsepower and machine weight."
Duke has been active in setting trends in the crawler-tractor field for years. He sees the several trends in crawler tractors; stronger power-trains, more horsepower, and a strengthened undercarriage.
Duke does not see any technological revolutions on the horizons, just evolutions. For example, one recent area of study is the move toward higher pressure injection-systems coupled with electronic controls for diesel engines. Higher pressures should provide cleaner burning of fuel that reduces emissions, plus a better engine response for the operator. There has been some modest resistance to cleaner diesel exhaust, with many operators remarking, "If the diesel isn't smoking, it isn't working hard enough." Duke says what smoke really means is that the air filter is probably plugged. The net result of high-pressure electronically controlled injection will be more horsepower per in. [.sub.3].
The area that will change the most the soonest, in his opinion, will be an increase in the number of cab improvements. Specifically, the cabs will be quieter, have less dust, and be more comfortable overall. Some changes will come about to meet new laws (not only in the United States, but elsewhere as well), and some changes will be motivated by competition.
"I believe we will see more of an office-like atmosphere in the cabs, with better air-filtering, more ease of operation, better instrumentation," says Duke.
Computer design has been put to work on designing blades. The result has been that the new blades allow more material to be moved with less horsepower and less fuel.
When can we expect the D12 dozer? "The size of the crawler tractor is not limited by technology but by economics. It would require a pretty heavy capital investment for a low-volume business the economies of scale have a finite point," says Duke. "The cost of moving material is lower with a D11 than with a D8," but the market for the D12 has not yet arrived.
JUST IN TIME PARTS
Much has been reported about maintenance improvements. There is another trend that could spread, bringing important savings to mines. Warehousing spare parts for equipment is costly. Now, it is possible for the distributor to set up shop in the mine, not just down the road from the mine. Caterpillar reports that after several trials at various mines, it can warehouse spare parts more economically than the mine. This way, the mine does not have to buy a huge inventory of spare parts, but will buy them only as needed.
Some mines have found cost advantages to allowing the dealer to do all maintenance at a guaranteed cost per hour. In the past, isolated mines had to build up heavy infrastructure to repair any problem on the premises, because they were so remote. Self-sufficiency was emphasized, but now there is more cooperation between mine and supplier, and many mines want dealers to do more repairs for them.
Major failures are noticed immediately, especially now that general-mine management is paying more attention to maintenance costs. However, minor problems are often not given major attention. A simple part, such as a broken headlight, can stop a 240-st haul truck just as dead as a major failure. No lights, no night driving. One mine found that smashed tail lights were causing more downtime than engine and power-train failures combined. There is a growing trend to focus on random, minor repairs, not just the big problems, but whatever is causing downtime.
240 ST AT 45 MI/HR
Electric-wheel drives can be geared up to achieve higher speeds than the standard 30-35 mi/hr. Haulpak reports a top speed of 45 mi/hr. Although this exceeds the rated st/mi/hr (TMPH) of the tire manufacturers, this problem can be overcome by altering haul routes to allow the tires to cool off. Tire temperatures can be computed with a special subroutine on some truck-dispatching software systems, which routes the warmer trucks to cooler circuits, or even sends them to a "penalty box" where they are serviced for fuel and lube systems as well. The fast speeds are achieved when the trucks are running empty or are on flat hauls.
There are no trends toward higher speeds other than those just mentioned. Trucks have a high center of gravity that is often above the center of the tires. Also, the coefficient of friction, even with the best tires, limits top speeds to the most excellent and straight road conditions. Trucks will continue to grow larger as the technology comes of age. Big trends now are in lowered operating costs through improved maintenance. One trend that most every one is predicting is more training for drivers and maintenance staff.
There is a limit to economies of scale. There has been some consideration of a system to allow a truck to be shovel loaded in three passes. This does not appear practical at this point because it means 33% of the load would be dumped onto the truck all at once. From a production point of view, it would be a fine idea, but it would place enormous stress on the haul truck. Ideally, the first bucket should be limited to fines only, but it is unproven whether this could be done consistently. Normally, trucks will continued to be loaded in four to five passes. It should be noted that there are a few mines using the three-pass loading system, although it is questionable whether they will start a widespread trend toward three-pass systems.
PHOTO : A new day dawns on this mechanical-drive truck. Electronics, tougher metals and materials and improved maintenance systems will continue to be major trends in mining equipment.
PHOTO : Equipment must be easy to service if it is to last in a mine today. Electronics not only speed troubleshooting on this haul truck, but are also designed to be self-diagnostic.
PHOTO : Quality has been Improved again and again. This giant machine (blue) will rigorously prove the integrity of an entire truck frame (yellow), compressing years of use into a few days.
PHOTO : Sensitivity to the community is one unmistakable trend in mining. An open house held for this Haulpak 830E drew "much larger crowds than anticipated."
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|Author:||Zaburunov, Steven A.|
|Publication:||E&MJ - Engineering & Mining Journal|
|Date:||Oct 1, 1990|
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