Earthmoving moves on.
In terms of growth in the capacity of earthmoving machines, one focus of recent months has been the development of larger haul trucks. Both Komatsu Mining Systems (KMS) and Unit Rig now have units of over 300 st capacity in the field -- the Haulpak 930E (nearly 100 around the world) and Lectra Haul MT4400 (MM, August 1995, pp. 70-73) -- while Caterpillar and Liebherr have similar sized machines under development.
Belaz in Belarus also has a new large truck (307-325 t) under development. The latest model is based on the Belaz 7550 that offers a payload of 280 t, and both models feature an innovative articulated frame design.
But, as we have seen in previous stages of truck development, each incremental rise in capacity brings operational problems that have to be ironed out. And, as trucks get larger so fewer units are required for a given production rate -- providing the trucks are reliable.
Most truck purchases today involve comprehensive service and support agreements. Some are so extensive that, save for actually running the trucks at the mine, they go as far as taking all truck operations away from the mine operator, with manufacturers or dealers taking on all maintenance roles and offering productivity guarantees. Allied with this, mines must employ `best practice' maintenance and well designed and maintained haul roads become even more critical as truck sizes increase.
However, it may be that a period is approaching when increasing truck size becomes of little importance in the capacity race as manufacturers develop autonomous trucks (both Caterpillar and KMS having advanced projects) and make further use of GPS systems. For example, taking deadweight out of the truck (operator cabs, etc.) will allow greater payloads to be carried without increasing truck size, and with commensurate savings in energy use.
Communications are becoming ever more important as the trucks `talk' to maintenance personnel and even their manufacturers. And today even the humble tyre is talking to its maker.
Tyres have always been a major contributor to open pit operating costs but the large tyres required by today's massive haulers are in relatively low volume demand (compared with the many other tyres manufacturers supply), making them expensive. They must be reliable and achieve high operating hours, requiring great durability -- they can each be carrying almost 100 t of the gross vehicle weight on today's largest trucks.
Truck capacity increase has, of course, been preceded by advances in large tyres, from manufacturers like Michelin and Bridgestone, and has lead to announcements from the wheel loader manufacturers regarding larger units. At the same time, there have been major improvements in machine sizes with which the industry has become very familiar, such as Caterpillar s 992G wheel loader.
O&K Mining sees the major trends in surface mining to be low grade mining, increasing stripping ratios and the two leading to high volume mining. Research by O&K discussed during the launch of the world's largest hydraulic mining shovel, the 800 t class RH 400, last July (MM, October 1997, pp.MNA10-12), showed cumulative worldwide sales for 240 st (218 t) trucks achieving around 1,200 units in 1997, with some 80 320 st (290 t) units sold.
Thus, its RH 400 with an 80 st capacity bucket was designed to three-pass load the former and four-pass load the latter, and its attachment geometry was designed for these two truck sizes. Projections for RH 400 sales lead O&K to hope demand will be such that it can build five to ten RH 400s each year. The great interest in hydraulic shovels of this size worldwide is such that the company should see substantial sales of the RH 400.
Caterpillar is developing the 797 haul truck, a two-axle, mechanical drive unit. It will incorporate design refinements to further enhance the performance characteristics of the mechanical drive system, and the truck's efficiency and Cat claims it "will offer haulage cost per ton leadership to the industry." The preliminary specifications show the 797 rated at a 327 t (360 st) payload capacity with a gross machine weight of 558,000 kg (1.23 Mlb).
Liebherr Mining Equipment Corp. (the new name for Liebherr Mining Truck) has introduced new nomenclature for its trucks -- the T and TI series. These mining trucks are noted for their Load Management System, ensuring optimum distribution of forces to the main frame. This prolongs service live and reduces maintenance intervals.
The T series comprises three rear dump trucks with twin rear wheels. Output of the diesel-electric drive is between 1,342 and 2,387 kW. The T 252 has a maximum capacity of 189-219 t or 108 [m.sup.3] and a turning circle radius of only 13.6 m. Offering a maximum load capacity of 240-260 t or 119 [m.sup.3] the T 262 is the current flagship of Liebherr's mining truck programme. The T 282, with a maximum load capacity of 340 t or 165 [m.sup.3] will be available from mid-1998 onwards.
Development of the new TI mining truck models is under way. Innovations in specific areas have cut the curb weight of this new design by about 15% and thus enhance its efficiency when transporting ore or overburden. In addition, the new rear-axle design helps to optimise load distribution and thus prolong tyre life. Practical tests carried out on a preproduction model have been completed successfully. The 300 t TI 272 mining truck is planned to be launched as the first series model early in 1999. The TI 272 features a new diesel-electric drive system developed jointly with external partners.
Liebherr has worked with BHP in Australia on this innovative, six-wheeled truck design, originally known as the ILMT (MJ, March 21, 1997, p.232). According to BHP Coal's manager for the large truck project, this could potentially achieve improvements in the economics of large mining truck haulage of up to 15%. The innovations of the ILMT are in the reduction of the ratio of empty vehicle weight to payload (thereby reducing the dead weight the unit has to haul) and improved load sharing between the tyres. Together, these allow increased payloads without raising operating costs.
The original design was conceived by BHP Research and a prototype with a capacity of 218 t was built by Liebherr for BHP Coal in 1995. BHP reports that after 3,200 hours of trials at its Saraji mine, the design potential was looking promising with improved haulage economics achievable. Additional improvements were noted in truck stability, operator comfort and traction. Liebherr has now signed a technology licence agreement with BHP to promote further development and manufacture of this large (TI) truck concept.
Liebherr remains committed to mining product development with a new large wheel loader and dozer planned.
AC drive systems
Euclid's R260 (238 t capacity) is now available, featuring AC drive, and a 272 t unit is not far off (MM November 1996, p.295). Dr. Stephen Grant, Euclid-Hitachi's vice president engineering, stresses the importance oflistening to customers when designing new haulers.
Among the aspects of design on the new big machines that underwent careful review were the frame, front and rear axle and suspension systems, hydraulics, propulsion, maintenance requirements and the operators' environment.
"For instance," Dr. Grant notes, "through advanced finite element modelling, full frame testing and strain gauge analysis, we have developed highly successful criteria for [truck] frame design. Proof of this is that we have never had to replace a frame on any our units, and many the Euclid R170s have achieved over 100,000 hours of operations."
Similarly front and rear axle systems have been designed using finite element analysis and fatigue testing. Service and maintenance requirements have been eased by positioning the stations for wheel power packs so that suspension can be set up without having to use an overhead crane.
Euclid's new C models, meanwhile, offer increased gross machine weight, the R60 being raised from 96 to 101.6 t, the R65 from 102 to 108.4 t and the R90 from 149.7 to 100 t The R90's payload is increased from 94 a to 100 t. These haulers feature the latest Allison transmission systems, the proven Allison transmission commercial electronic control (CEC) system, lock-up in all ranges for improved fuel economy, two-speed reverse to offer improved manoeuvring in loading and dumping areas, and self diagnostics. The Contronic system, fitted as standard on all four models, monitors all onboard systems, alerting the operator to malfunctions and indicating when the hauler needs servicing.
The KMS 930E was the first haul truck to have an AC electric drive system. This offers several advantages over DC systems used on most other electric drive trucks. These include higher reliability, easier service, lower maintenance costs, more dynamic retarding and higher truck speeds. For example, the DC-powered 830E has a top speed of 56.8 km/in, compared with the 64.4 km/in top speed of the 930E with the AC motor system.
KMS continues to improve the design of the 930E and is now offering it with the new Detroit Diesel 4000 series engine that has shown impressive test results in terms of fuel economy (25-20% more fuel efficient than the original 930E engine) and reduced noise and emissions.
A new Bridgestone tyre, 51 mm wider than the Bridgestone tyre originally developed for this truck is also now available. A wider, lighter weight body maintains the truck's capacity at 184 [m.sup.3] but raises its payload capacity to 290 t (320 st).
At the smaller, but ever important, end of the market, Terex has just upgraded its 55 t capacity 3360. The main improvements in the 3360B are in operator enhancements. The FOPS-certified cab has a greatly increased glass area with a positively raked windshield for improved visibility. The glass is bonded in place, a technique used successfully in Terex's ADTs since the introduction of the C' range. The instrument panel has been completely redesigned to provide a more ergonomic control system and it has also been lowered to improve forward vision over the hood.
The truck has a new taper rail frame for enhanced fatigue life, and a longer wheelbase to improve weight distribution, ride and handling. The dump body has been lengthened to give a larger loading target and the load over height has been reduced. Also, the tailchute has been shortened to improve clearance with the body raised and the body hoist cylinders are of larger diameter to provide greater lifting capacity.
Articulated dump trucks (ADTs) are attracting interest for surface mining in certain regions, particularly in southeast Asia, as noted of the Volvos in the Vietmindo article in this issue. Here they are popular for overburden-haulage in poor underfoot conditions that are exacerbated by high rainfall.
Southern Africa is another region where ADTs are performing well, with Bell noting considerable sales success. For example, the long and steep gradients of the haul roads out of Samancor's Tweefontein chrome open pit in South Africa have proved a good test for six B18s, hauling both overburden and ore. The haul out of the pits is a long 300 m with gradients up to 14 [degrees] on rugged roads. The units are hauling about seven 22 t loads each hour.
Contractor Rock Movers' Louis Swart comments: "This is an arduous haulage application and the Bell ADTs, whose excellent traction and gradeability make them ideally suited to cope with the steep gradients, have provided an average mechanical availability in excess of 90%, while their fuel consumption has averaged in the region of 13.5 litres/h."
A third generation of ADTs, the C Series, has been launched by Bell. The B17, B20, B25, B30 and B40 models have all been modified and upgraded. Today 12 variants of the Bell ADT exist, ranging from the specialised B16 two-wheel drive truck to the top of the range B40. The primary design criteria for the C Series were enhanced machine performance, increased reliability and improved ergonomics. This has been achieved by upgrading the drivetrain and hydraulic and electrical systems, together with suspension modifications and a new cab design.
The Allison planetary transmission provides more engine power to the wheels, increasing performance by 10-12% the B Series. This transmission is used in conjunction with a `simple' single speed drop box. Features include simplicity of design with large helical cut gears for quiet and reliable performance. An interaxle differential with lockup gives improved traction in bad underfoot conditions.
There is also increased engine power/torque on the B17C and B25C, providing approximately 8% more power.
The previous axle differentials have been replaced with the ZF limited slip unit for enhanced traction and reduced wheel spin. Along with the change on the axles, a heavier duty final drive has been fitted for longer life and durability.
Low profile Michelins
Michelin has developed two large earthmover tyres, a 55/80 R 63 and 44/80 R 57, with load, speed and size characteristics that give machine designers greater freedom. The largest of these two tyres will support a load of 93 t per tyre. They are designed to operate at low pressure, the first time this has been possible on large hauler tyres. Until now, increased load capacity has been provided by larger diameter tyres or by increasing tyre pressure for a given dimension. The latter is detrimental to tread life and lowers resistance to accidental damage.
The new low pressure tyres, Michelin reports based on its testing should have a life up to 20% longer than conventional tyres, significantly reducing costs. Also important is that being low profile tyres, their external diameters do not produce transportation problems.
Also new is the Michelin Earthmover Manager System (MEMS), to monitor tyre performance. Developed initially for large trucks, MEMS continually measures inflation pressure and tyre temperature, and compares them with reference values. Performance of the tyre can be monitored, in real time, taking corrective action if necessary. Thus, the frequency of maintenance intervals, requiring the truck to be stopped, can be reduced. Accidental damage leading to pressure loss and heat generation within the tyre can be identified quickly, thus preventing further damage. Correct inflation pressure optimises tread life, helps reduce fuel consumption and is important for safety.
One stop shopping
We have seen considerable consolidation in earthmover suppliers since Caterpillar embarked on its programme of developing large mining machines, which now include large trucks, hydraulic shovels, the 994 wheel loader and the largest grader currently available, the 24H.
There has been the tie-up between Euclid (part of Volvo Construction Equipment) and Hitachi. Last year, Komatsu Mining Systems (KMS) was established with responsibility for the global marketing of Komatsu, Haulpak, Demag-Komatsu and Modular Mining equipment and services for the industry. KMS is a $65 million company, 100% owned by Komatsu America Corp. Its 1997 sales target was $800 million.
Also last year, Bucyrus International took over Marion Power Shovel, developing a major loading (rope shovels and draglines) and blasthole drill operation. Earlier, Liebherr had purchased Wiseda and is rapidly developing the Liebherr Mining Truck line. P&H MinePro continues to add to the services and products it supplies, in particular adding some interesting dealerships to its portfolio in recent months, such as distribution of LeTourneau loaders in Spain and Africa, and Unit Rig trucks in Latin America -- though the latter will have to go now that Terex Mining, of which Unit Rig is a part, has purchased O&K Mining.
Prior to the acquisition, Terex Equipment Ltd. (TEL) in Scotland was already working with O&K Mining, supplying trucks with capacities up to about 100 t. Globally, the Terex Trucks segment of Terex Corp. combines the products of TEL and higher capacity units manufactured by Unit Rig in the US. In China, there is also the North Hauler joint venture that, in 1995, achieved around 85% of all rigid truck sales in China. Terex Mining will be headquartered in the O&K Mining facilities in Dortmund, Germany.
Terex is in extremely acquisitive mode currently. Closely following the O&K news came the completion of the acquisition of Illinois-based truck manufacturer, Payhauler Corp. Payhauler manufactures the 350C all wheel drive 50 t rigid truck, which compliments the existing Terex truck line. Payhauler has a good market in North America, some in mines, and is particularly strong in re-engineering machines.
O&K Mining is, of course, a leading supplier of hydraulic excavators to the mining industry. The best selling excavator in its class is the RH 120 with an operating weight of 230 t. The 200th machine was delivered during the second half of last year. Also leading in its class there is the 47a t RH 200, introduced in 1989. About 60 of these units have now been sold.
O&K has seen much success with large hydraulic excavators, now claiming to be the world leader in sales of machines over 200 t (operating weight). The RH 400 was developed in partnership with Syncrude which is replacing its current draglines/bucketwheel excavators/conveyors mining system with a shovel and truck operation. It believes that advances in shovel and truck technology now make that this most economic mining system.
Syncrude took delivery of its first two Komatsu Haulpak 930Es late last year and is in discussion with Liebherr and Caterpillar about future large capacity trucks. It is likely that this first RH 400 will be followed by two more machines for Syncrude and the company could be operating ten 800 t class excavators by 2000. In the long term, the mine will possibly be operating up to 50 320 st trucks and 10 240 st trucks.
At the RH 400 launch, Leroy Van Wieren, Syncrude production advisor, noted that his company liked the flexibility, mobility; availability, reliability and breakout force of hydraulic excavators, which it has used since 1980. Syncrude has had considerable success with the operation of its RH 200 shovels at the Mildred Lake mine, and the RH 400 project drew heavily on RH 200 design and operating experience. O&K also learnt a lot from its RH 300, a 500+ t unit launched in 1979.
Based on O&K's proven dual-engine concept, the first Syncrude machine is powered by two water-cooled Cummins K 2000 E diesel engines with a total output of 2,500 kW. As soon as it becomes available, probably towards the end of 1998, Cummins' new QS60 engine will replace the engines on the first unit and will power future units.
Mr Van Wieren said that Syncrude chose O&K to develop this new large machine because of its good experience with the RH 200. He also expressed his confidence that the RH 400 would be a success, basing that on the RH 200 experience and the co-operation in its development between Syncrude and O&K Mining -- resulting in a new machine ready for delivery in less than two years after the two came together, and a development period of just less than a year from the initial planning discussions to the finished product.
This was made possible by applying previously tried and tested design principles on a larger scale. Project teams from both companies met regularly and added specifications, practical operating experience and new technical solutions to the development process. The RH 400, with a cycle time of less than 30 seconds, was expected to achieve peak production of over 8,000 t/h.
Weighing more than 800 t and equipped with a 42 [m.sup.3] bucket, the first RH 400 started work.
In late December, it passed Syncrude's final acceptance test, achieving an average of 4,200 [m.sup.3]/h (bank), equivalent to 9,700 t, with a cycle time of 29 seconds. The second machine will be operational in the second quarter of 1998.
O&K has developed and patented a novel track cleaning and track guide shoe, now available on all its excavators. Instead of lateral guiding plates, the shoe, centred in the crawler chassis, prevents material from accumulating on & sprocket and idler, and causing damage to the undercarriage. It also keeps the track in its exact position and prevents it from coming off.
Liebherr's proven R 984 B (112 t), R 992 (140 t), R 994 (214 t) Litronic hydraulic excavators and its flagship, the R 996 (571 t), will be joined from mid-1998 by the new R 995 Litronic with a service weight of 390 t. The R 995 Litronic is powered by a 1,600 kW V16 diesel engine a 23 [m.sup.3] backhoe or a shovel bucket is the standard working attachment. With the backhoe attachment the R 995 Litronic achieves high digging and breakout forces of 1,159 and 1,400 kN respectively; with the shovel the equivalent values are 1,600 and 1,400 kN.
An undercarriage roller has been developed by Intertractor for the R 995 with dimensions above the ordinary (diameter 680 mm and weight 1.6 t). On large mining shovels, the roller is subjected to high loads during operation, especially if track and track roller are obliquely angled to each other, and the tread edges are highly stressed. There is also a completely new track design. Forging track links, bushing and track shoes in one part with appropriate ribbing results in a heavy-duty unit with a weight of more than 540 kg (the raw forged part).
To date, Liebherr has sold 16 of its largest unit, the R 996, and 10 more are scheduled for this year. The biggest user is Kaltim Prima Coal in Indonesia. Liebherr has provided information on production tests in Australia, where the 996 Litronic is popular. At Burton Downs a backhoe is loading blasted, sandstone overburden with a density of 1.8 t/[m.sup.3] from face heights of 10-12 m. Loading 200 t capacity Cat 789B trucks with a 30 [m.sup.3] bucket, the fill factor was 93% and productivity 2,070 bank [m.sup.3]/h (5,378 t). In three-pass loading the trucks, the cycle time was 29.7 s (truck loading time 89.1 s). At Mt Owen the 33 [m.sup.3] backhoe loads 1.6 t/[m.sup.3] blasted overburden from the same face height. Productivity was 2,440 bank [m.sup.3]/h four-pass loading 235 t capacity Cat 793s in a cycle time of 24.9 s (truck loading 99.6 s).
KMS has just released the Komatsu Demag H255S hydraulic shovel, for mid-size haulers. Features include the increased weight (240 t) over the H185S it supercedes, front shovel or backhoe configuration and standard 14 [m.sup.3] bucket. The Cummins K1500E engine increases power output over previous models by 12% to 900 kW. The parallel shovel linkage design increases crowd force by 17% for higher bucket fills and greater productivity.
The new single parallel guidance system offers increased parallel bucket action via the stick cylinders, resulting in easier, more automatic bucket capability. The fully hydraulic controls of the H255S are short throw low effort and armrest integrated. The ETM diagnostics system that monitors vital excavator functions is standard equipment.
The travel gear is now mounted inside the sprocket hub assembly for added protection, longer life and ease of service. Finally, hydraulic flow rates have been increased by 12.5%, the total to 2,700 litres/min and swing system flow to 900 litres/min, for faster cycling and increased production.
Caterpillar's 5130B, meanwhile, builds on the proven performance of its first generation mining shovel, the 5130, introduced in 1992. It has been sized to load 777D or any 91 t truck in five passes or, for example, the 69 t payload 775D in three passes. It also has a new model in the 45-50 t range. The 345B is a replacement for the earlier 235D and offers a bucket range of 1.8 to 3.5 [m.sup.3].
Caterpillar significantly upgraded a workhorse of the industry last year, the 91.8 t 992G, that is attracting great interest among MM's readers. Particularly interesting is the cast box section boom, the first major change in wheel loader design in about 20 years. This increases dump clearance, improves bucket visibility and requires no maintenance. According to Caterpillar it offers three times the torsional strength of a traditional design.
Compared with previous models, Caterpillar reports a 15-20% increase in productivity from the 597 kW 992G, payload raised by 7% and cycle times cut by 10%.
Caterpillar is expanding its G-series wheel loader line with seven new models in the important 93 to 224 kW class. The new additions comprise five general purpose wheel loaders -- the 938G, 950G, 962G, 966G and the 972G -- designed for production loading applications; and two integrated tool carriers -- the IT38G and IT62G -- for customers that need a machine to perform a variety of jobs with different buckets and attachments.
Powered by Cat diesel engines and built around a rugged main frame, the G-series machines generate up to 7% more rated horsepower than on the F-series. The high torque rise engine and electronic, automatic powershift transmission provide improved productivity and fuel efficiency.
A four plate loader tower provides a solid base for the machine's solid plate loader arms, whilst the Z-bar linkage makes them ideal for production loading applications. The seven machines are offered with a choice of buckets with rated capacities from 2.0 [m.sup.3] on the 938G up to 5.5 [m.sup.3] of the 972G.
Further attention has been paid to operator comfort. The ergonomic G-series cab benefits from 50% more space than on its predecessor and a larger glazed area, coupled with a characteristic sloping engine enclosure, improves all round visibility. On the larger models, optional Command Control Steering/electro-hydraulic controls are available which require significantly less movement and effort than a conventional steering/loader layout.
Five of six recent world orders for big draglines went to the P&H 9020. The first went into production early in 1996 for Bulga in Australia's Hunter Valley where, P&H reports, it is setting production records.
P&H recently sold a 9020 walking dragline to Luscar for the expansion of its Estevan coal mine in Saskatchewan' Canada. The first large machine of its kind sold in North America since 1990, this 5,710 t unit is due to be commissioned in late 1999. Estevan's 9020 will carry a 76 [m.sup.3] Optima Plus bucket on a 107 m boom. It will work on a 22 m diameter high-strength patented gradial tub, which efficiently handles multiple load paths in any direction. Exceptional maintenance access is provided by the 2,030 mm clearance between the tub and revolving frame.
Newly designed from the tub up in a major development programme, the 9020 possesses ultra-high power to increase production rates. Six planetary swing motors, six drag motors, six hoist motors and two walk motors provide a total power of 26,250 kW. The Estevan machine will feature the latest P&H high technology advances in PLC control and operator interface to maximise diagnostic capabilities, availability and productivity.
Complementing the 9020 is the large concept machine, the 7,710 t 9060 walking dragline. This should be able to move as much as 122 [m.sup.3] per cycle, compared with the maximum of 92 [m.sup.3] per cycle for the 9020.
Caterpillar has redesigned the D11R. It now features a more powerful 3508B Electronic Unit Injection (EUI) engine, rated at 634 kW (60 kW more than its predecessor), offering a 25% net torque rise for excellent lugging performance. Its operating weight is 102.3 t. Blade capacity is 34.4 [m.sup.3] (universal) and 27.2 [m.sup.3] (semi-U). Track on the ground is 4,444 mm and the ground contact area is 6.3 [m.sup.2].
Komatsu's monster is of course the D575A-2. Its Super Dozing blade offers a capacity of 69 [m.sup.3] for rock or soil overburden. Powered by a Komatsu SA12V170 engine, this 142.5 t machine develops 858 kW for powerful dozing performance. Princess Coal operates the largest Super Dozer fleet (five units) for mountain top coal removal in West Virginia.
"My philosophy for the last 23 years," explains owner Pete Moran, "has been to use bulldozers to move the overburden. You can shove it for half the cost that you can load it.
One tractor can produce the same as a loader and two trucks. The bigger the tractor, the easier it is to move the material." Today they are moving more than 18.3 million [m.sup.3] annually. Pete
Moran further comments on the D575A-2:" It's been a major help in our productivity since the tractors have been here. We figure each tractor will increase the mine's production by an average of 200,000 t/y. And that's basically how we raised our production [from 100,000 t/y in 1990 to 2 Mt/y]."
RELATED ARTICLE: Cat 797 preliminary specifications
Gross power 2,5353 kW Drive train 7-speed mechanical Top speed 64 km/in Tyres 55/80R63 Length 14.5 m Width 9.1 m Overall height 7.3 m Loading height 6.9 m
RELATED ARTICLE: Caterpillar offers guidance for choosing loading tools:
* Dig ability - Above all, the machine must be able to dig effectively in the various face conditions of a particular mine. Wheel loaders are the best for well-fragmented and free-flowing faces. Mass excavators (hydraulic backhoes) and face shovels can cope with tough digging situations--consolidated and tightly shot faces. Both are ideal for selective digging.
* Mobility can be a key factor, especially in operations that require blending from multiple faces. The Wheel loader is, of course, the most mobile. It can be moved quickly away from faces to be blasted and can be used as a utility unit for cable shovels. It will also rehandle stockpiled material as required. Shovels and mass excavators are productive where mobility is not crucial but can lose 5-10% of production time in travel. Caterpillar warns: "Don't overlook the time needed to move away from shots."
* Bench height is determined by the mine plan and in turn heavily influences choice of loading tool. Wheel loaders can work any bench height as long as the material flows down to the loader. Mass excavators excel in conditions where face height is no greater than stick length and material has high angle of repose. They are very effective when loading trucks positioned below. With a more vertical face, a front shovel can effectively dig at varying height;
* Bench width determines the manoeuvring room available and this space is another important criterion in loader choice. Wheel loaders require manoeuvring room to quickly cycle between the face and dump target Shovels or excavators work well in tight quarters because they swing within the dimensions of the machine envelope--but must sit close to the face to be productive.
* Floor conditions affect cycle times, machine life and overall cost. Wheel loaders are most cost-effective on floors that are dry, smooth, level and firm, They can work drop cuts on grades of 8-10%. While preferred for work on wet, soft, spongy, jagged or uneven conditions, or excavators can also work well in pitching conditions.
Circle RSC No. Belaz, Belarus. Tel: (+375 172) 587839. Fax: 589996. 252 Bell, Equipment, PO Box 25391 East Rand 1462, South Africa. Tel: (+27 11) 928 9700. Fax: 928 9702. 253 Bucyrus International, 1100 Milwaukee Ave, PO box 500, South Milwaukee, W153172-0500, US. Tel: (+1 414) 768 4213. Fax: 768 4474. 254 Caterpillar, PO Box 10097, Peoria, IL 61612-0097, US. 255 Demag Komatsu, Postf. 180361, 40599 Dusseldorf 13, Germany. Tel: (+49 211) 71090. Fax: 715822. 256 Komatsu, Komatsu Bldg. 2-3-6, Akasaka, Minato-Ku, Tokyo 107, Japan. Tel: (+81 3) 5561 2790. Fax: 5561 4766 257 Komatsu Mining Systems, PO Box 8112, Vernon Hills, IL 60061-8112, US. Tel: (+1 847) 837 3067. Fax: 970 5693. 258 LeTourneau, PO Box 2307, Longview, TX 75602, US. Tel: (+1 903) 236 6500. Fax: 236 6585. 259 Michelin, (Earthmover & Industrial), Campbell Rd, Stoke-on-Trent, ST4 4EY, UK. Tel: (+44 1782) 402000. Fax: 402011. 260 O&K Mining, Postfach 17 01 06, D-44060 Dortmund, Germany. Tel: (+49 231) 1760 424. Fax: 1760 429. 261 P&H, Box 310 Milwaukee, WI53201, US. Tel: (+1 414) 671 4400. Fax: 671 7236. 262 Terex, Newhouse Ind Est, Motherwell, ML1 5RY, Scotland. Tel: (+44 1698) 503051. Fax: 503214. 263 Unit Rig, PO Box 3107, Tulsa OK 74101-3107, US. Tel: (+1 918) 446 5581. Fax: 446 0721. 264
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||includes related article|
|Date:||Mar 1, 1998|
|Previous Article:||Every bit helps(Editorial)|
|Next Article:||Mine pumps.|