Immense blades and horsepower ratings between 300 and 900 allow large dozers to take on tough, high-production jobs
The largest crawler dozer Construction Equipment has encountered—in a West Virginia coal mine—was the Komatsu D575-2 Super Dozer, with a standard 90-cubic-yard blade, 1,150 horsepower, and an operating weight in excess of 330,000 pounds. The D575 is no longer sold in North America, but this market is not without its “super dozers,” as evidenced by such tractors as the 850-horsepower Cat D11T and the 890-horsepower Komatsu D475A, both with operating weights approaching a quarter million pounds.
The specifications chart (available for download below) for crawler dozers with more than 300 horsepower shows standard blade capacities approaching 60 cubic yards for the largest of these models, but keep in mind that most manufacturers offer specialty blades—for coal or woodchips, for example—that can exceed 100 cubic yards. Markets for these large-blade, 300-horsepower-plus machines are diverse, but the largest models, understandably, are less utilitarian than their smaller (relatively) counterparts.
Large Dozer Ownership Costs
Size (hp) List Price Hourly Rate* 260 - 358 $560,984 $192.39 360 - 519 $742,344 $250.65 520 and higher $1,618,274 $485.97
*Hourly rate is monthly ownership costs divided by 176, plus operating cost. Adjusted unit prices in the calaculation: Diesel fuel, $4.13/gallon; Mechanic’s wage/hour $50.76; and Cost of money, 2.00%. Source: EquipmentWatch.com.
For tractors in the highest horsepower and weight classes, says Mel Busch, Caterpillar’s senior account manager for large tractors, customary markets include surface mining, quarry and aggregates. Big dozers in size classes somewhat smaller than the very largest machines, he says, work in varied applications, including heavy construction and landfill.
According to Komatsu’s Bruce Boebel, product manager-crawler tractors, the overall market for large dozers dropped significantly in 2009 amidst economic uncertainty. Today, the market is recovering, he says, but has not yet returned to historic levels.
“Many users held up purchasing larger dozers in recent years,” says Boebel, “and now they might be into a second rebuild and recognizing that a third isn’t cost effective. Some of these people are now starting to replace machines, so we’re starting to see the market come back. Mining is strong, and gas and oil exploration is steady.”
Komatsu’s Jackie Haney, product manager-mining dozers and excavators, adds that during the recent economic downturn, dealers may have auctioned off larger machines in their rental fleets to maintain viability.
“Much of that inventory is no longer here,” says Haney, “because many of these machines, especially those with lower-tier engines, were attractive to overseas buyers. Dealers are now starting to build up rental fleets, replacing what went to auction or replacing units that are aging.”
According to Bob Schenk, manager of marketing, Dressta North America, a significant number of large dozers have historically resided in dealer-owned rental fleets. In the North American market segments in which Dressta’s 515-horsepower TD40E competes, he says, the rental segment accounts for some 14 percent of the big-dozer population; for the company’s smaller (330 horsepower) TD25M Extra, the rental segment of the market, says Schenk, approaches 30 percent.
According to Komatsu’s Boebel, building up dealer-owned rental fleets is a way to support customers who need machines, but are not yet ready to make a purchase.
“Rental fleets probably are not going to include the largest mining machines,” says Boebel, “but machines such as Komatsu’s D155 [with 354 horsepower and blades to 15.6 cubic yards] are good rentals. They’re relatively easy to transport and might be rented—even though smaller—as temporary replacements for larger machines.”
Jon Gilbeck, crawler dozer global product marketing manager, John Deere Construction & Forestry, sums up the present state of the market:
“The market for production-class dozers is very positive. As the overall construction equipment industry has been going through the recovery process, production-class dozer sales have grown as well. Sales in 2011 were significantly higher than in 2010, and based on 2012 year-to-date sales, the annual volume is expected to exceed that for 2011.”
Overall, the largest of the dozers placed in service will remain on the job for quite some time.
“For the [Cat] D10 and D11 size class,” says Caterpillar’s Busch, “a 45,000- to 60,000-hour life is average, but with correct maintenance and repair practices, it’s not unusual to see these machines with more than 100,000 hours still being used in front-line service—depending on application and customer asset-management practices.”
Although every big dozer will not see 100,000 hours, these machines all reflect robust designs, which customers buying machines of this size take for granted.
“Customers expect high durability from components in production-class machines,” says Deere’s Gilbeck, “which is a determining factor in the re-life or sale of the crawler. Customers for these machines are focused on maximum uptime and lowering their cost of operation.”
To those ends, manufacturers of large crawlers dozers have, indeed, kept the technical refinement of their products on the move.
“Advancements have come in many forms to meet customer needs,” says Deere’s Gilbeck. “Today’s buyers can expect greater longevity in their machines, for instance, due to advancements in major components—such as engines, final drives, and hydraulic pumps and motors.”
Says Caterpillar’s Busch, overall technical refinement of these machines in the past few years has included electro-hydraulic controls, GPS-based systems for grading and bulk earthmoving, operator safety improvements, and vehicle-health monitoring.
Available features for the new Cat D11T, for example, include an automatic ripper-control system (that monitors tractor speed via GPS technology and adjusts engine speed and ripper depth to minimize track slip)and an auto-carry system (that monitors speed and automatically adjusts the blade load to keep operating efficiency at an optimal level). Also new is a dynamic inclination monitor, which provides readouts for tractor pitch angle and side-to-side slope angle, plus an enhanced auto shift system that selects the optimal gear and engine speed for a given load and desired ground speed.
Komatsu’s design criteria for large dozers, says Boebel, include the use of lock-up torque converters for greater drive-train efficiency and reduced fuel consumption, plus the company’s K-Bogie undercarriage, designed to allow track-roller assemblies to oscillate around two fulcrums for optimum ground contact in rough terrain and for a smoother ride. Features that reduce operator fatigue, says Komatsu, include an auto-pitch control that switches between the blade’s digging and dump positions at the push of a button, an automatic-shift mode that selects the gear range most suitable for the load, and an optional automatic system to control track slip when ripping.
Most of the large dozers available today also feature such refinements as electronic control of the transmission and low-effort, single-lever control of both travel and blade functions. Steering system designs, generally, are aimed at responsiveness and precise maneuvering, whether the tractor is pushing a loaded blade around a turn or maintaining straight-line travel when benching.
According to Dressta, for example, its two-speed, geared steering module provides gradual turns while maintaining full power to both tracks, plus conventional clutch/brake performance for tight or pivot turns. The two speeds of the steering system, coupled with a three-speed, powershift transmission, provide six speeds forward and reverse.
Liebherr’s PR 754 and PR 764 feature hydrostatic drive, as does the John Deere 1050J. These tractors use a dual-path system that powers each track independently with its own hydraulic pump-and-motor combination. According to Liebherr, the drive system provides automatic speed and torque adjustment to keep the engine working at optimal power as the load changes. Other benefits of hydrostatic drive, says Deere, include infinitely variable control of track speed side-to-side and smooth counter-rotation.
The Cat D8T and D9T use Caterpillar’s proprietary differential steering system, which uses three planetary gear sets, a dedicated variable-displacement steering pump, and a bi-directional, fixed-displacement steering motor to provide a speed differential between the tracks during a turn. The D10T and D11T are fitted with multi-disc, oil-cooled steering clutches, which are hydraulically applied, and electronically controlled brakes that are applied by springs and hydraulically released.
The Komatsu D155AX-7 and the D275AX-5 use the company’s hydrostatic steering system to provide uninterrupted power to both tracks during turns. Counter-rotation allows a minimum turning radius. The D375A-6 and D475A-5 are equipped with an electronic control system that automatically modulates the stroke ratio of steering clutches and brakes to match the load, allowing a smooth push though turns.
If we could add just one more word about the refinement of these big machines, it would be reserved for the operator stations, which are, across the board, spacious, nicely appointed and isolated from operating shocks, having finger-touch controls, powerful climate-control systems, electronic monitors with full diagnostic capability, acres of glass and the best seats available.
And they’re quiet, says Komatsu’s Haney about the company’s largest dozers: “The in-cab sound level for the larger machines is only 70 to 72 dB(A). The interior of the new Ford 150 pickup is 69.5 dB(A).”