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The single most important
feature of an articulated dump truck (ADT), when compared to other
dirt-hauling trucks, is the lack of a rigid frame. Conventional
10-wheeled dump trucks consist of a single rigid frame that joins
the cab and dump body together. When operating over rough terrain,
the weight of the payload can cause the frame to twist, over time
reducing the life expectancy of the truck by fatiguing the frame.
Tractor-trailer combinations reduce this problem somewhat by allowing
the body and tractor units to flex separately, but the increased
weight of up to five-axles reduces payload and can increase maintenance
costs from broken springs and twisted drive shafts.
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These problems are eliminated
by the use of ADTs. Since the truck is designed primarily for off-road
operations as opposed to those combining on- and off-highway operations,
greater durability is achieved. The body and cab move independently
of each other, allowing the entire truck to flex as it moves over
irregular terrain. And because the tractor unit is self-contained
in a single unit, greater tractive effort can be applied to help
move the unit through wet soils.
"I think an articulated
dump truck was developed to be something that is quite versatile,"
states Ian Marshall, product consultant for ADTs at John Deere.
"You've got rigid dump trucks, which are traditionally
a four-by-two configuration. The articulated dump truck was made
to be more versatile. It's able to go into areas that most
other off-road hauling equipment could not go into. You can load
a bigger variety of material into a dump truck and can haul it longer
distances."
According to Marshall,
ADTs have six characteristics. First is the articulation that provides
a way to steer the machine. Second is the oscillation tube that
allows the machine to oscillate almost 360º and ensures that
the six wheels maintain equal contact with the ground. Third, they
have a robust steel frame that provides long-term durability. Fourth,
ADTs have strong suspension systems that can handle the higher payloads.
Fifth, they use automated transmissions to provide better handling
characteristics. And finally, they use very high flotation tires
to allow the trucks to operate in various soil conditions.
The Productivity Equation
Manufacturers understand
that operator safety and comfort are critical to ensuring productivity.
"Anytime an operator is in control of a piece of equipment,
they remain a critical component of the production overall,"
remarks Dan Harms, marketing manager for Caterpillar. "Before,
we had the operator located on the left of the cab; now they're
in the center, and that's the best place to have an operator. The
cab has been redesigned so that it's a lot bigger. We've got tremendous
visibility by moving the radiator to the back of the tractor and
then sloping the hood down significantly. We also spent a lot of
time laying out the controls, making sure they're really easy to
use and logical. Frankly there are not a lot of choices that the
operator has to make, which is good because we don't need that distraction
in the cab, just a focus on production and getting the job done."
Selecting the right dump
truck requires understanding the total dirtmoving operation. The
advantage of having a machine that can move a large quantity of
dirt quickly might be lost if the excavation equipment can't
keep up with the machine. "Make sure that you know what you're
going to do from a loading-tool standpoint," stresses Harms.
"A lot of times on the job, I'll see an excavator that's
making 10 passes per truck. That's a real issue because, for
excavators, the best pass is four to six passes with a truck and
then you're on your way. That's really the key to figuring
out which loader you're going to be using and then what kind
of truck you're going to match with it."
According to Marshall,
there are computer programs available that can help match the tools
to the production needs. "The owner will look and see what
type of loading tools he has, then use a computer program that will
actually predict how many trucks you'd need for a certain job
and what size of truck is the best for optimal use. Also, you've
got to remember that if you've ever transported your machinery
around, the larger equipment is more expensive because you have
to put it on transports, and special permits cost a lot more."
The type of road and
the distance that the ADT must move the material also can play a
factor in the size of the machine. "The articulated trucks
are wonderful because they are truly an all-terrain vehicle,"
notes Harms. "But I would also emphasize that your haul roads
have to be in good shape because if they're not, that's
going to slow your cycle times down. That might influence either
the size of the truck or the loader you're going to use to
get more production because your cycle times are going to be slower.
If you have a motor grader on-site and it can keep the haul road
clean between the cut and the fill area, this will speed up your
cycle times."
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| The
DumpWagon is available as a water truck: Operators can unhook
the dump box and hook onto a pull-type water truck. |
The biggest truck is
not always the best truck for the job. For example, trucks that
can handle between 25 and 40 tons might be production marvels, but
in certain situations a smaller truck that can handle less volume
might be a better tool. "The smaller trucks have superior flotation
so you can go in very difficult soil conditions," points out
Rich Ginder of Low Country Machinery, the JCB dealer in Pooler,
GA. "It is specifically good for golf courses because it has
super flotation: You can use it for shaping and forming a golf course
and not destroy or rut the soil with big tires. If you have very
poor soil conditions, the bigger articulated trucks rut the haul
road and go axle-deep in mud."
ADTs are used more predominantly
on the East Coast, where higher rainfalls can make clay soils into
goopy sludge. But that trend is changing. "That trend on the
East Coast seemed to fit the need of the ADTs more so than out here
where we have more wide-open spaces," reports Tom Walton, sales
and marketing manager for RDO Equipment in Phoenix, AZ. "The
contractors out here are finding that it's more cost-efficient
to put an excavator or a four-wheel-drive loader and load up an
articulated dump truck than to run a fleet of scrapers."
Walton points out that
the suspension systems on the ADTs can play an indirect but crucial
role in their productivity. "When you have a smoother ride
for the operator, generally his travel speed can be increased. When
you've got 30 or 40 tons of material in the back and you've
got independent suspension, it eliminates a lot of the bind. It
allows the truck to have a longer structural life and gives more
operator comfort in operating the vehicle."
According to Jeff Akel,
product manager for articulated trucks and wheel loaders with LBX
Company in Lexington, KY, "The advantages and versatility of
articulated haulers versus rigid-frame trucks are very apparent.
When operating in poor underfoot conditions, the articulated hauler
can negotiate the roughest terrains and steepest slopes. The rigid-frame
trucks usually require a road that is built on firm ground.
"When operating
on a grade, the articulated truck shows its flexibility. The artic
hinge allows the front and rear frames to rotate independently,
keeping all wheels on the ground. This resulting lower center of
gravity gives the articulated truck more stability, enhanced safety,
and better machine utilization. The rigid-frame truck traversing
the same slopes will create high torsional stresses on its frame
and will be more likely to roll over, creating a safety hazard for
the operator and potential machine damage, as well as downtime to
upright the truck."
Cash Flow Vs. Dirt
Flow
With a price tag that
can approach $400,000, depending on options or features, only the
biggest contractors with high-volume machines can rush out and write
a check for an ADT. But there are a variety of financing options
that can bring one to your next job site. "There are several
different leases that are available to offer the customer,"
observes Walton. "There's a job lease where the contractor
will lease the truck for the length of a job, and then if he doesn't
have another job to take it to, he says, ‘I'm done with it,'
and we come get it. There's an operating lease where he will commit
to a certain amount of time, whether it's 24, 36, 48, or 60 months,
and basically pay for just the use of the vehicle and no ownership.
Then there's the purchase-type lease where he owns it at the end
of the term."
Contractors might need
to look at their total financial picture to see which of the financing
options works best for them in acquiring ADTs. "Leases are
an avenue for a contractor to get into because of his tax situation,"
remarks Walton. "It may be a cash-flow issue–the fact
that the down payment requirements on a lease are nonexistent."
There are certain tax advantages to leasing versus ownership of
equipment, and while each company's situation needs to be evaluated
by a professional tax advisor, the general rule is to lease a depreciating
asset and to purchase an appreciating asset.
A lower-cost alternative
to a self-propelled ADT is a new product line offered by Miskin
Scraper Works of Ucon, ID. The company began making pull scrapers
for the agriculture industry in 1917. In the 1990s, the company
recognized the need for versatile construction equipment. In the
past year, Miskin introduced the first pull-type ADT that combines
the capacity of the typical ADT with the flexibility of build-your-own
systems that allow the contractor to buy a power unit separate from
the body, giving versatility to the entire approach.
"The biggest advantages
are in the initial costs," explains Mark Miskin, company president.
"The customer can buy about the equivalent of a 25-ton dump
truck. Most of those self-propelled units have 200 to 225 horsepower.
They can buy a 250-horsepower farm tractor, put on one of our 25-ton
pull-type dump beds, and his total cost will be under $200,000.
That's compared to $250,000 for the self-propelled version."
Flexibility becomes the
key in this system. "[The user] can pull a scraper with the
same tractor," comments Miskin. "Our DumpWagon also is
available as a water truck so [the operator] can unhook the dump
box and hook onto a pull-type water truck. The cost savings become
even more significant when you take that same tractor and put two
wagons behind it. Then you've got a 50-ton carrying capacity
and you're still only about $275,000, so you're about
half the cost of a 40-ton dump truck."
Meeting Extreme Challenges
At a quarry being developed
south of Lafayette, IN, the Case 330 articulated truck did well
in extreme conditions, according to Bryan Gick of MacDonald Machinery
Company, a Case dealer in Lafayette. The contractor was stripping
away 8-10 ft. of material to expose gravel underneath for the new
quarry. Pan scrapers did not fare well at the site, so ADTs and
excavators were brought in.
"Conditions were
pretty nasty ... muddy," Gick recalls. "The tracks were
so deep they ran between your knees and your waist. They were loading
up the Case 330 pretty heavy, but it had plenty of power and went
through the mud well."
The two operators who
ran the 330 liked the visibility into the dump bed, as well as the
way the seat is positioned in the center of the machine, Gick reports.
"They thought it had a really good ride, and both were impressed
with its good visibility."
Because the truck has
sloping sides in the dump bed, operators were able to heap more
material in it per load than the other models they were running
without losing load due to spillage, Gick notes.
Fast-Moving Dirt
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| Operators
of today's ADTs like the better seat positioning and overall
ride and the improved visibility into the dump bed. |
The faster that dirt
is moved and the fewer number of times it has to be handled means
an improvement on the profitability of a project. One of the latest
innovations relating to ADTs is the introduction of the ejector
system that permits the load to be emptied while the truck is in
motion instead of having to stop, raise the bed, and dump the load
in a single pile that must be handled. This system, introduced by
Caterpillar, is designed to eject the dirt while the truck is in
motion, allowing the operator to spread the dirt in a layer.
John P. Moyna is the
president of C.J. Moyna & Sons, a major earthmoving company
in Iowa that has worked extensively with the ejector system from
its original inception. "Our first project that we took our
first ejector to was a sand project," he recalls. "We
loaded the E-ject truck with sand and went out to the fill and dumped,
laying out 4 inches of sand. When the E-ject returned with a second
load, the dozer operator stopped the operator and said, ‘You're
going to have to stop and dump that in a pile, otherwise I won't
have anything to do here.' What it did on that sand project was
eliminate the need for a fill dozer, reducing our cost per yard."
Moyna sees the manufacturers
moving to design and develop products to meet the changing needs
of the dirt-hauling industry. "The future of articulated trucks
is going to change fast, it's really going to be exciting,"
he predicts. "The competition to sell will be fierce. People
will just keep coming up with new innovations to make it a better
product. The articulated truck has fierce competition from the aspect
of newer, better trucks in an extremely crowded field."
Innovation is going to
be necessary since earthwork is so competitive. "It's
important to manage our cost per yard," Moyna continues. An
example of this management involves loading of ADTs. "You want
to make sure you don't underload or overload your trucks. When
the excavator operator drops the last bucket and the material falls
off the truck, your operation's not good. You don't have
your loading tool and your hauling tools matched up. During loading
operations, you want to get that truck moving when you start dumping
your last bucket, saving valuable cycle time."
According to Moyna, eliminating
the need for a bulldozer to push the dirt and tightening up on load
cycle times can move overhead costs right down to the bottom line.
"When you're running articulated trucks, if the backhoe
stops swinging, then your income stops. It's not how many loads
of dirt you haul in a day, it's how many buckets of dirt you
swing."
For Cindy and David Wittwer
of the Wittwer Group in Wichita, KS, the ADTs provide flexibility
for job sites. "We looked at the application we had for them
and the amount of usage we saw we could get out of them," reports
David Wittwer. "They literally go anywhere. We've had
some projects where they were plowing through 3 feet of mud. We
did one canal project in Wichita where we had to work underneath
two overpasses that were about a quarter of a mile long. We figured
out that we could take the headache rack off these trucks, lower
the exhaust pipe, and run the trucks underneath the bridges. Originally
we bid the job to utilize the end dumps and haul the material out
on the streets, but with our ATs, we loaded them and just hauled
them right down underneath the bridges and through the canal. It
just worked beautifully and made a tremendous amount of difference
on this project."
"You can do anything
with these trucks and they hold up," adds Cindy Wittwer. "I
would call them the Arnold Schwartzenegger of trucks."
Guest author Lynn
Merrill is director of public services for the City of San Bernardino,
CA.
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