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"Back in the 1970s, we
used to sell 6,000 scrapers a year, but last year we sold 340 of
them," states industry analyst Frank Manfredi, referring to the
North American market for self-propelled scrapers. By contrast,
he reports that sales of articulated dump trucks (ADTs) reached
3,000 units per year in the late 1990s. Manfredi tracks equipment
sales through Uniform Commercial Code filings with state government
offices.
For a number of reasons,
both articulated trucks and tow-type scrapers have emerged to take
the place of self-propelled scrapers. Fred Casten, director of articulated
truck and scraper product lines for Terex Construction Americas,
describes "artic" trucks as very versatile tools. Artics have proven
useful for reclaiming wet areas, capping landfills, golf course
construction, quarry work, highway and interchange construction,
and general excavation.
In addition, ADTs can
work under conditions not suited for scrapers. "The combination
of artics and excavators can get into confined areas you could never
get into with a scraper - places where you need a lot of maneuverability,"
explains Casten.
And ADTs can forge through
sloppy, even swampy conditions. Artics can climb steeper grades
- up to 35% - whereas tandem-powered scrapers are limited to 25%
grades or less, according to Caterpillar literature.
An example of artics'
maneuverability comes from the Grandview Triangle project, a major
interstate interchange in Jackson County, MO. Clarkson Construction
Company of Kansas City, MO, won Phase I and II contracts to rebuild
the interchange, says Tom Kellerman, the contractor's chief engineer.
For the $65 million Phase
II project, Clarkson had to move a total of 400,000 yd.3
of earth and rock, both suitable and unsuitable, from an overexcavation
on-site, a borrow area, and some onsite required excavation. Suitable
material was used as required for building highway fill.
Clarkson's tools of choice:
a Hitachi EX-700 excavator and a fleet of some 10 ADTs, most of
them Volvo A-40 units. "We had to stage our operations and work
in such confined areas where scrapers wouldn't have worked," relates
Kellerman. Clarkson owns some scrapers and, adds Kellerman, in the
right conditions scrapers are better than artics. But at the Grandview
Triangle, the cut areas were small and the footing ranged from wet
and mucky to solid. "The artics have maneuverability that scrapers
don't have," he notes.
New on the Market
Case Construction Equipment
marks its recent entry into the market with the 300 Series of articulated
trucks - the Case 325 and 330 models, which have rated payloads
of 25.4 and 30 tons, respectively. The trucks have Cummins engines
rated at 248 and 286 hp. "The 300 Series boasts a design that hauls
more material per load and is more fuel-efficient in the process,"
claims Wes Lee, director of marketing for Case.
Limited slip axles are
standard all around, and a longitudinal differential lock can be
engaged with the flip of a switch to counter adverse ground conditions.
The suspension uses rocking beams attached to the axles by steel
castings, allowing the axles to float independently of each other.
Case uses ZF axles and transmissions in the artic trucks.
Case's sister company,
New Holland Construction, also offers two artic trucks: the AD250,
with a 25-ton payload, and the AD300, which has a 30-ton capacity.
The smaller machine hauls 17.4 yd.3 heaped, while the
larger one can take on 20.9 yd.3 heaped.
Caterpillar offers five
artic trucks. At the smaller end is the 725 with a 26-ton payload,
and the largest machine is the 740 Ejector with a 42-ton payload.
In March 2002, Caterpillar introduced the 740 Ejector truck at the
CONEXPO-CON/AGG trade show. In June 2002, the company brought out
the 735 artic truck.
The 740 Ejector features
an ejector blade that uses technology similar to that proven by
Cat's wheel tractor-scrapers. Powered by a double-acting hydraulic
cylinder, the blade simply pushes loaded material rearward, out
of the body to the fill area. According to Cat, the truck "ejects
on the move, with no stopping or starting in the fill, spreading
the load while almost totally eliminating carry-back. The ejector
is best utilized in restricted overhead areas, in soft underfoot
conditions, and on sideslopes - where raising the body would destabilize
the machine. The ejector reduces the need for spreading equipment
and demonstrates faster cycle times, thereby increasing productivity."
Static ejecting still is a simple alternative if practicality dictates.
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Cat recently boosted
the body sizes on its 725 and 730 machines; the 725 went from 25
to 26 tons of capacity, and the 730 went from 30 to 31.5 tons of
capacity. The increases provide end users with higher productivity
and a lower cost per ton of material moved, the company reports.
Early in 2000, John Deere
launched four models of artics: the 250D, 300D, 350D, and 400D.
"Our focus when developing these ADTs was lowering the overall operating
cost," states Bob Herman, John Deere business analysis manager.
"These machines offer simplified maintenance, greater fuel economy,
faster cycle times, and the best possible operator comfort."
Deere's ADTs feature:
- fully automatic planetary-drive
transmission for ease of operation;
- torque converter with
automatic lockup for faster haul speed and improved fuel economy;
- Adaptive Shift Logic
programming, which permits instant adjustments to the gear-shift
instructions to suit load and terrain - and smoother shifting;
- variable hydraulic
transmission retarder for more constant travel downhill at higher
speeds;
- oil-immersed hydraulic
wet disc service brakes for 20% more braking force on the 400D;
- service brake mud
covers to prevent dirt from entering the rear of the wheel trims;
- an engine valve brake
to reduce wear and provide more control over braking.
Smaller Trucks
Last year, JCB Inc. introduced
two smaller ADTs: the 714, with a 14-ton payload capacity, and the
718, with an 18-ton payload capacity. "These trucks are more versatile
because they're better suited to the average job-site development
[than larger trucks]," maintains David Morice, JCB's product manager
for wheel loaders and ADTs. He says smaller ADTs are matched more
efficiently to the average-size excavators that many contractors
own. "The most popular excavator size is the 21- to 24-ton size,
and those excavators have 1.25- to 1.5-cubic-yard buckets," states
Morice. "With a bucket that size, it only takes seven to eight passes
to load a 714 or a 718. So you get shorter loading cycles than with
bigger trucks. A 30-ton truck would take twice as long to load with
the same excavator."
JCB's smaller ADTs fill
a niche, Morice believes. "If you have smaller excavators, the per-ton
initial cost - and the operating cost - will be lower for the smaller
trucks."
Earlier this year, at
the Intermat trade show in France, JCB introduced its Model 722
ADT. The company planned to make the new three-axle, 22-ton-capacity
machine available in North American toward the end of 2003.
All of JCB's artic trucks
have ZF Smoothshift transmissions. The ZF transmissions are fully
automatic and have modulated gear shifting. The 714 and 718 have
two limited slip differential axles, and the 722 has three limited
slip differential axles. Engines all meet Tier II standards. Cummins
engines with ratings of 152, 179, and 225 hp power the 714, 718,
and 722, respectively.
LBX Company, which markets
the Link-Belt brand of equipment, offers three models of ADTs: the
D16, D25, and D300, which can handle payloads of 16, 25, and 30
tons, respectively. A 300-hp Cummins engine drives the D300. According
to Link-Belt, it uses a ZF automatic power-shift transmission to
get steady rim pull even under load. In addition, the D300 uses
self-proportioning limited slip differentials to pull through tough
ground conditions. No input is required from the operator.
The high rotational axis
and forward-mounted artic hinge on the D300 provide excellent stability,
especially when cornering, the company maintains. The machine has
an extra-wide frame and a low center of gravity. All-hydraulic brakes
on all wheels offer good braking capability, even in cold weather.
The operator-selectable Jake (air) brake can be used to prolong
the life of the service brakes.
The D16 and D25 feature
Cummins engines rated at 137 and 255 hp, respectively. Both of those
artics have Deere Funk transmissions. The D16 has a selectable power-shift
option. A lockable interaxle differential splits the drive power
to the front and rear axles.
Moxy offers four models
of ADTs: the MT26, with a payload capacity of 26 tons; MT31; MT36
Series II; and MT40B Series II. (In each case the number indicates
the tons of payload.) The MT 40B Series II and MT36 Series II are
more recent introductions.
One of Moxy's main design
features is the location of the front turning ring in relation to
the swing point. The turning ring is positioned in front of the
swing point, which always ensures equal weight distribution to the
front wheels in all situations, including during a maximum turn.
Equal weight distribution to the front wheels makes it possible
to use the differential with only 45% locking value. That provides
drive to both wheels in all situations without completely locking
up the wheels - while having the possibility to steer with good
maneuverability.
Moxy designs its ADTs
with a similar concept to rigid-frame dump trucks. That is, the
body is sloped downward from the hinge point to the front. That
lowers the center of gravity of the loaded truck. By contrast, Moxy
says competitors design ADTs with a level dump body, which will
produce a higher center of gravity.
All Moxy trucks have
permanent six-wheel drive. The trucks have two transverse differentials
and one longitudinal differential. The interaxle longitudinal differential
proportions torque with one-third to the front axle and two-thirds
to the rear axles, providing equal drive to all rear wheels.
The MT36 Series II has
a 400-hp Scania engine and a six-speed Komatsu transmission. The
larger MT40B Series II has a 450-hp Scania engine and a six-speed
ZF transmission that is an electronically controlled automatic with
torque converter.
Terex offers five ADTs
- the TA25 (25-ton capacity), TA27, TA30, TA35, and TA40. Recently
Terex introduced its beefed-up Generation 7 models of the TA25,
TA27, and TA30. The new machines have more power, torque, and capacity,
Casten points out. The TA25/TA27 units have been powered up from
260 to 280/330 hp. And the TA30 received an increase of 50 hp to
350. Each has a Cummins engine that is Tier II - certified for exhaust
emissions.
Casten says the TA27
and TA30 have a rotational pressure-compensated (RPC) design for
new transmissions. Each forward gear has a clutch pack, and the
RPC system provides better, faster filling of the clutch packs with
oil. By prefilling the clutch packs to fill more quickly, the truck
shifts gears more smoothly.
What are Terex's edges
over the competition? "I think we have a better horsepower-to-weight
ratio with our increased power," comments Casten. "And on the TA40
we have liquid-cooled brakes. We have the RPC, which gives us a
smoother shift, and we have increased body capacity and a smooth,
sleek design."
Volvo, which has helped
lead the trend to artic trucks, offers four 6x6 models: the A25D,
A30D, A35D, and A40D. Those trucks have capacities of 26.5, 31,
36, and 41 tons, respectively.
Regarding an ejector
system, Volvo believes the ejector is useful in applications with
height restrictions only. The company does not offer an ejector
but says aftermarket suppliers do.
"We at Volvo find it
hard to justify spending the additional cost of the ejector system
[about $70,000] in addition to the increased maintenance time and
cost and extra care required during loading to prevent damage to
the guides and rollers," states Buddy Goodman, a Volvo product marketing
specialist. "Additionally, the ejection cylinder is a multistage
unit mounted in a horizontal fashion. During unloading while transporting,
this puts a severe stress on the cylinder assembly. One must also
consider the types of materials they will transport as the ejector
system will have its limits."
Other features with Volvo
ADTs include the following:
- The D-series units
are all Tier II - certified (the engines all meet current exhaust
emission standards).
- The D-series has one
common cab with virtually the same cab layout. This simplifies
operator training and familiarization.
- Payload volumes,
horsepower, and torque all were increased in the D-series.
- A push-button Load-and-Dump
brake (a Volvo patent) was introduced. The operator simply stops
the unit and, while still in gear, pushes the Load-and-Dump button,
which electronically puts the hauler into neutral and applies
the trailer brakes. That simplifies the loading and dumping process
by eliminating the need to apply the parking brake.
In sum, the product ranges
have broadened across the manufacturers, so you have more models
to choose from than ever. As always, a well-informed choice is the
best.
Dan Brown is the owner
of TechniComm, a communications business based in Des Plaines, IL.
GEC
- July/August 2003
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