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Canada's “Rock to Road” Magazine
January-February
2007 Issue
For a copy of the issue
that contains these articles with colour photos, click
here.
Ready
mix producers take the front discharge route
By Andy Bateman, Engineering
Editor
New
trucks are delivering customer satisfaction for two ready mix concrete
producers.
Sarnia Concrete Products and Forest City Redi-Mix have several things
in common. Both are established Ontario ready mix producers who serve
urban markets with similar sized fleets. Both have also recently added
new front discharge trucks to their respective fleets. The similarity
ends there, however, as these companies are at very different points
on the front discharge learning curve. Sarnia Concrete Product’s
new unit joined one of Canada’s largest and longest established
front discharge fleets, while the new arrival at Forest City Redi-Mix
was added to an otherwise rear discharge fleet.
President Roy Botma explains that Sarnia Concrete
Products (SCP) has probably one of the largest front discharge fleets
in the country, with twelve front units in a fleet of fourteen. SCP
first saw a demonstrator front discharge truck in action in 1991, but
did not acquire any at the time. Renewed interest in1993 led to visits
to producers in Michigan operating front discharge fleets and the subsequent
investment in three front units in 1994.
Further additions to the fleet since that time
have enabled SCP and, perhaps equally important, its customers, to build
up a wealth of operating experience with the units. The two most recent
additions are Oshkosh S Series trucks, one of which is fitted with a
weight-saving Revolution composite drum. (See Aggregates & Roadbuilding,
Oct-Nov 2004 issue for a report on Canada’s first Revolution drum
mixers.) Botma reports that the front units are popular with contractors,
who find that faster and more accurate manoeuvring into the best discharge
position reduces set up time, while good visibility also enables the
mixer operator to set up without a spotter. During the pour, chute position
and concrete discharge are both controlled by the mixer operator, thus
freeing up one of the contractor’s crew who would otherwise be
tied to the chute.
The front discharge units are also said to perform
well in moving operations such as curb or median wall construction,
where the combination of visibility and automatic transmission enables
the mixer operator to stay coupled to the moving plant. Reversing cameras
on the three most recent units provide further assistance to operators
during set up and loading.
Some 115 km east of Sarnia, London-based Forest City
Redi-Mix is a newcomer to the world of front discharge but reports similar
operating experience. Here, the latest addition to the company fleet
is an Oshkosh S-Series front discharge mixer fitted with a steel drum.
Understandably, the fit of a new type of truck into a rear discharge
fleet raised a number of issues including operator training, cycle times,
reliability, and customer acceptance. General manager Al Gardiner adds
that the unit was purchased only after lengthy research and discussions
with existing operators, including SCP. With the benefit of a season’s
operating experience, Gardiner is now able to report that the new truck
has met expectations and integrated well into the existing fleet. In
most site situations, the front discharge unit has been more efficient
than a rear discharge unit and particularly where job involves multiple
discharge points with little manoeuvring room.
One job, for instance, necessitated repositioning
three times and was completed in much less time. Even in straightforward
applications such as feeding a concrete pump, front discharge reportedly
improves site access and egress. Mixer operator Wes Thompson adds that
hydraulic chutes improve control over discharge position and allow the
operator to stay in the cab until wash down on many jobs. This suits
Gardiner, as Thompson is more accessible for radio contact to obtain
updates on job status or truck location. Six-wheel drive has already
kept the unit moving on one muddy site, while road travel is relatively
quiet for the operator, thanks to the rear mounted engine.
So what are some of the potential downsides
of front discharge compared to a rear discharge truck of similar capacity?
Botma comments that initial cost may be a deterrent to some potential
owners who, absent operating experience, may find it harder to justify
the higher capital investment. Ironically, the popularity of these trucks
with customers can itself be problematic for dispatchers working with
a mixed fleet. Clearly, dispatchers cannot always provide the requested
vehicle type and customers can be somewhat less than sympathetic if
one is not available. In the same vein, Gardiner notes that customer
acceptance of Forest City’s single front unit is growing, although
acceptance would be faster if there was more than one unit in the fleet.
For owners of existing large rear discharge
fleets, there are additional capital considerations. Such owners have
already made a significant capital investment in the existing fleet,
so a switch to different equipment, however desirable from a customer
perspective, will likely take several years. During that extensive transition
period, the owner will have to deal with any disadvantages, real or
perceived, of a mixed fleet. Botma also points out that the front discharge
units are typically 150 mm to 300 mm taller than a rear discharge
truck of similar capacity in order to accommodate their long mixer drums.
In most cases that extra height is not an issue, but may be enough to
necessitate some changes at plants with tight headroom under the loading
sock. At Forest City’s ready mix plant, Gardiner explains that
trucks drive down a short laneway between two buildings to reach the
loading bay.
For the front discharge, this means driving
nose first empty and reversing full in a fairly tight space. This loading
process has been uneventful to date, but does require some care to ensure
the truck chutes are kept clear while loading. One of SCP’s new
units is equipped with a weight saving composite drum, manufactured
from polyurethane and a filament wound structure. Botma says it is too
early to comment on the durability of their particular drum, but the
lighter drum is certainly delivering increased payload and quiet operation
compared to an equivalent steel drum.
Manufacturer’s data states that
the Oshkosh S-Series front discharge mixer combines an Oshkosh S type
chassis with a McNeilus mixer drum. Standard chassis specifications
for these six wheel drive units include a Cummins ISM 350V engine developing
350 bhp at 1600 rpm, an Allison HD-4060, 5-speed automatic transmission
and an Oshkosh two-speed transfer case. Numerous axle configurations
are available to comply with provincial weight limits.
The S series mixer is available with a steel
drum or the new Revolution composite drum, with both having a rated
capacity of 8.41 m3. The composite drum is 907 kg lighter than
the comparable steel drum and that weight saving reportedly translates
into an additional 0.38 m3 of concrete delivered with every load. The
composite drum’s seamless, aerodynamic shape and unique, auto-reversing
fin technology are said to work together to improve mixing quality,
reduce discharge time and make cleanup faster. Additional claimed benefits
for the composite drums are the virtual elimination of corrosion as
well as reduced noise during batch operations and pours. In-house testing
results show that the drum is more durable and abrasion resistant than
a typical steel drum, while customer field tests indicate that reduced
truck weight translates into significant fuel savings.
The claimed annual payload gain is an extra
150 to 375 m3, saving between $3474 and $8684 for low and high volume
operations respectively. The 67 per cent increase in drum life versus
a comparable steel drum (without fin replacement) saves from $695 to
$868 annually, while fuel savings are in the range of $463 to $811 per
truck per year. Total annual savings are estimated at $4632 to $10,363
for low and high volume operations respectively. The corresponding payback
period is estimated at 36 months and 16 months respectively. Footnotes
add that these estimated annual savings are based on four loads a day
for 250 days a year and $22.70 transportation costs per cubic metre
for a high volume operation. Unmeasured benefits not reflected in these
estimated annual savings include quieter operation, smoother discharges,
more consistent concrete temperature, as well as reduced wear and tear
on chassis, tires and brakes.
Sarnia Concrete Products offers concrete
pumping through its SCP Concrete Pumping subsidiary as well as stone
slinger delivery.
Forest City Redi-Mix is part of an independent business that also includes
Meter Mix Concrete Limited and Forest City Concrete Finishing Ltd.
Back to
top
How
to spec a transit mixer
What you need to consider before purchasing
a ready0mix truck
A
mixer is a highly specialized piece of equipment which is expected to
put in a number of years of service. To ensure efficiency over the life
of the vehicle, it’s important to spec wisely.
A key consideration is the local length and weight regulations. The
first step is to find out what the length and weight regulations are
in your province or territory since these will dictate axle spacing
needed to maximize payload. Try to take maximum advantage of the weight
laws to maximize payload. Some provinces require compliance with certain
aspects of the bridge formula used in the United States; others don’t.
This will have a big influence on how the axles are set up and spaced.
“A bridge formula truck will tend to be longer
to spread the weight and this will define where the steer axle goes
and have an impact on frame dimensions,” said Brian Lindgren,
vocational sales director at Kenworth Truck Company in Kirkland, Wash.
“In most cases, you would spec a booster axle at the rear to increase
the weight allowed. You need at least 1.08 m from the centerline of
the front steer axle to the centerline of the booster axle to be sure
to qualify for a 10.98 m bridge.
“At the same time you need to stay within the
12.2 m overall length limit, so the steer axle needs to be as far forward
as possible. A 10.8 m bridge length in a 1.21 m overall length leaves
only 341.9 cm for front and rear overhang. The rear mudflap is usually
63.5 cm from the center of the booster axle, so the steer axle needs
to be within 71.1 cm of the front bumper,” Lindgren said. “Also,
be careful not to spec a permanently-mounted tow hook which extends
out front since it could make you over length.”
In provinces and territories where you don’t
need to comply with similar regulations, you can spec trucks shorter,
making them more maneuverable on jobsites.
But you may need to spec lift axles to carry the extra
weight. Depending on the weight carried by the steer axle and the laws
in your area, you may also need to spec wide-based front tires. “In
the provinces where tire footprint is regulated, it’s typically
272 kg per 25 mm of tire width,” said Kenworth’s Lindgren.
“That will require a wide tire such as a 425/65R22.5 size to get
to 9072 kg on the two front tires.”
Location
issues
Where you expect to be delivering concrete will
also have an influence on specs. The heavier the load and the rougher
the terrain, the more you will need to beef up the chassis and suspension.
“Most mixer chassis often need to get into some pretty rough jobsites,”
said Lindgren, “so be sure to spec a suspension with a lot of
articulation.” The frame rail specs are impacted by the type of
mixer barrel used.
“If the barrel has a subframe welded to
the chassis rails that is approved by the OEM, a single 295 mm frame
is fine,” said Lindgren. “You’ll want a transition
plate bolted to the frame at back of the cab which goes as far as forward
as possible. This eases the stress on the rails.
“But if the mixer pedestals are mounted
directly to the frame rails, you’ll need an inserted frame of
at least 273 mm,” he said. “Remember, it’s not just
strength you’re looking for, but stiffness, too. And, if you have
more than one pusher axle, you should have an inserted rail to withstand
the higher side loads.”
Another thing to remember about the frame: Mixer
suppliers often request crossmembers in specific locations. It’s
a good idea to check with them before the truck is built.
The type of construction sites you are typically
visiting will affect the amount of traction you require. “I always
recommend side-to-side differential locks in both rear axles for traction
off the pavement. In areas with sandy or muddy soil all-wheel drive
– also known as 6x6 – has been more commonly spec’d
so that mixers don’t get stuck on jobsites,” Lindgren said.
“More recently, we’ve seen operators spec’ing a 6x4
configuration with active tire-pressure control systems which allow
the driver to reduce tire pressure when they’re off-road to get
the needed traction in the sand.”
The
drivetrain
Big horsepower is not a requirement for mixer
applications. “You should get just enough horsepower to do the
job,” said Kenworth’s Lindgren. “Generally, 320 to
350 hp is plenty for most applications. Extra horsepower just uses more
fuel, puts more strain on the rest of the drivetrain, and adds cost
up front.”
The transmission you put behind the engine needs
a lot of ratio range. You need a low enough gear to inch along at a
jobsite and a high enough top gear to attain decent highway speeds.
Lindgren said that, “The Eaton Fuller –9ALL is a common
transmission spec for mixers. It has a really low ratio for crawling
while pouring curbs or other continuous pours. But there’s also
a high enough top end for traveling at highway speeds,” he said.
“We’re seeing more automatic transmissions
being spec’d,” he noted. “With the electronic controls
on the newer automatics, the shifting is very smooth and responsive.
They’re easier on drivers and reduce stress on the drivetrain,
and the truck can keep up in traffic much easier. The only downsides
are higher up-front cost, and a slight decrease in fuel mileage.”
The power take-off (PTO) must come directly from the engine in order
to provide enough power for the mixer system. Whether you use front
engine or rear engine PTO depends on the chassis configuration.
Lindgren recommends rear engine PTOs any
time you can make it fit. “Front engine PTOs can reduce the size
of the radiator,” Lindgren said. “With 2007 engines emitting
more heat, you need a larger radiator to cool the same horsepower, not
to mention the added heat load of transmission coolers, power steering
coolers, air conditioner, and so on. And with a front engine PTO, the
pump is out front in a vulnerable spot. The hydraulic lines have to
snake past the engine, and often close to the exhaust, to get back to
the mixer drive motor. Rear engine PTOs make a cleaner installation.”
But in those areas where the front pedestal must be mounted immediately
back of cab, front engine PTO is the only alternative. “A front-mounted
PTO makes sense in areas where the weight laws give you an incentive
to get more load on the steer axle,” he said.
If you spec an automatic transmission, you definitely
want a rear-engine PTO because it will provide 30 per cent higher output
speed due to the gearing at the flywheel. This allows much less slip
in the torque converter when you are crawling along and want to keep
the drum speed up to pour the concrete. Too much slip in the torque
converter can lead to overheating the transmission or the engine’s
cooling system.
According to Lindgren, the rear axle ratios
should be evenly matched with the transmission so that engine speed
is around 1,600 rpm at highway speeds. “You should also be able
to go as slow as 2.4 km/h at 1,400 or more rpm,” he said. “A
4:30:1 ratio with 11R22.5 tires and the -9ALL transmission works well.
With a 6-speed automatic transmission, use a 4.88:1 or slower ratio.”
Another thing to remember is air filtration. Lindgren recommends a pre-cleaner
on underhood air cleaners to filter out large particles and plenty of
element area on the main filter. Dual external air cleaners are better,
and many like the look. “A little money spent up front on a better
air cleaner is cheap compared to a dusted engine,” he said. And
better filtration will usually mean longer life for the filter elements.
Weight
watching
Weight is an issue with mixers,
but you have to save a lot to be able to haul an extra half yard of
concrete. The cost of lightweight components has to be considered. You
can slim down by spec’ing components – such as wheels, air
tanks, and clutch housings – in aluminum rather steel. “Use
the smallest fuel tank you can get away with,” Lindgren added.
“Most mixer applications burn about 15 to 17 litres per hour.
So a 208- to 227-litre tank is usually plenty of fuel for one shift.”
Lindgren suggests engines such as the Cummins ISL or Caterpillar C9
to save up to 800 pounds compared with a 12-litre block.
“With 350 horsepower and 1,250 lb-ft
of torque, these 9-litre engines have all the power most operators need.”
Lindgren also advises selecting an aluminum cab for its light weight
and corrosion resistance. You can save valuable pounds by choosing the
right suspension. “The difference can be as high as 180 kg,”
Lindgren said of the different suspension options. “You can also
leave shock absorbers off the rear because the weight of the mixer means
you will never be running light.”
Using wide-base “super single”
tires instead of duals on the rear can save hundreds of pounds in wheel
and tire weight. “The trade-off is that you get a narrower track
if you stick with standard track axles,” said Lindgren. “You
can go with a wider track, but then you may not have the option to go
back to duals later.”
Drive
performance
Finally, let’s look at a few driver
performance-related items. To get the best turn performance and road
feel from steering, Lindgren recommends dual small gears rather than
a large single steering gear with an assist ram. The dual system usually
requires less maintenance than a single system with assist.
Try to spec as many windows as possible.
“It’s a good idea to mount the exhaust behind the cab rather
than at the side to keep out of the way of the corner windows,”
Lindgren states. While we’re talking windows, Lindgren suggests
picking low-replacement cost windshields when they are available. “Most
mixer fleets replace at least one windshield side per truck per year.
Two-piece flat-glass windshields with roped-in seals can be replaced
in half an hour for a total cost of under a hundred dollars. This can
save thousands of dollars over the life of the truck.”
With lift axles, it’s smart to get
a six-channel ABS system. “Lift axles, especially steerable ones,
are normally over-braked for the load,” Lindgren says. “By
including them in the ABS system, it’s much easier for the driver
to avoid locking them up and flat spotting the tires.”
Back
to top
New
Mack cabover model
Mack
Trucks, Inc. took the opportunity of this year’s World of Concrete
show in Las Vegas to introduce the TerraPro™ Cabover model –
the latest, most advanced offering from the company.
Evolving from the company’s popular MR model, the TerraPro Cabover
is built for construction applications, including concrete pumping.
First and foremost, the new truck design incorporates a major upgrade
of the driver’s work environment.
“We’ve learned a lot from
our long history of success with heavy-duty cabover trucks,” said
Steve Ginter, Mack vocational products manager. “And one of these
lessons is that while the vehicle has to be extremely durable, it also
needs to be comfortable. Comfortable drivers are more productive drivers.
That became one of our driving principles in developing the TerraPro
Cabover model.”
Features of the interior upgrade include:steering
column positioned for ample belly room; ergonomic seats; integrated
armrest; easy-to-read gauges and easy-to-reach switches; accelerator
and brake pedals suspended above the cab floor and mounted in-line to
reduce driver effort (the suspended pedals also make the floor area
easier to clean); and an efficient HVAC climate control system.
According to the manufacturer, the TerraPro
Cabover model offers a smooth quiet ride thanks to the design of its
engine mounts, cab bushings and rubber isolators, and electronically
controlled fan – all of which minimize noise and vibration on
the job.
The vehicle’s low-profile electronic
dash enhances the driver’s visibility while at the same time incorporating
comprehensive information displays. The instrument cluster features
25 indicator lights and an automatic transmission temperature gauge.
Electronic gauges improve accuracy and reliability while eliminating
oil lines and most air lines from the gauge cluster. An engine hour
meter that features a wake-up display when the ignition is off is included
as well. A battery backup protects vital information stored in the engine
control systems.
The TerraPro Cabover model features the
next generation of Mack’s Vehicle Management and Control System
– V-MAC® IV – allowing customers to better control costs
and closely monitor truck and engine performance. V-MAC IV offers more
than 100 programmable features, and adds a host of new items, including
road speed tamper detection, integrated starter protection and programmable
daytime running light override. The system’s electronics also
include DataMax™, advanced software that captures information
such as vehicle trip histories, duty cycle information and scheduled
maintenance intervals.
Offered with the proven Mack camelback
suspension, the TerraPro Cabover can also be spec’d with the Mack
M-Ride™ 6-rod suspension, allowing up to 431 mm articulation for
extra maneuverability on jobsites.
The new model comes standard with the
EPA’07-certified 11-litre Mack MP7 engine, offered in a horsepower
range from 325 to 405 hp with torque ratings from 1,200 – 1,560
lb.-ft. Also available is the EPA’07-certified 13-litre MP8 engine
with a horsepower range from 415 to 485 hp and torque levels from 1,540
– 1,700 lb.-ft. Offering superior low-end torque and power, both
the Mack MP7 and MP8 feature single overhead cams, electronically controlled
ultra-high-pressure fuel injection, one-piece steel pistons, and robust
bearings and cylinder heads.
Back to
top
Stability protection
for Mack transit mixers
Now
available from Mack Trucks is a unique stability system for concrete
mixer vehicle. The Mack Road Stability Advantage by Bendix (Mack RSA)
is designed to reduce incident potential and enhance profitability.
The fully electronic stability system is offered for mixer applications
on the Mack Granite model of heavy-duty Class 8 trucks.
“We’re very proud to be the
first heavy-duty truck manufacturer to offer this technology to vocational
customers,” said Steve Ginter, Mack vocational products marketing
manager. “Concrete customer demand for stability protection is
strong because mixers, in general, are recognized to have a high centre
of gravity and carry dynamic loads.”
Mack RSA uses the existing ABS wheel speed
sensors, along with steering, yaw and lateral acceleration inputs, to
deactivate the throttle and selectively apply the brakes in sharp curves,
sudden lane changes, or obstacle avoidance maneuvers, reducing the potential
of a rollover.
In conjunction with Bendix Commercial
Vehicle Systems, Mack first began offering full electronic stability
on its highway vehicles in late 2005.
“Engineering this technology for
tractors is more straight-forward,” said Tom Kelly, Mack vice
president of marketing. “But as a leader in the heady-duty vocational
truck market, we’re committed to getting this technology in the
hands of mixer and dump customers as soon as possible. We targeted mixers
initially per customer demand.
www.macktrucks.com
Back to
top
Oshkosh
introduces side roll protection system
Oshkosh Truck Corp. and its subsidiaries McNeilus
Truck and Manufacturing and London Machinery, have unveiled series of
advancements under the companies’ Safety @ 360žSM initiative designed
to enhance safety for the ready mix industry. “Improving operator
safety and developing new safety features are part of our company heritage,
and this new generation of advancements sets an industry standard that
we hope others will follow,” said Mike Wuest, president of McNeilus
Companies. “Through these initiatives we aim to reduce accidents
that occur when traveling to or within the job site, and protect those
inside the cab and outside.”
Side Roll Protection
System
The Side Roll Protection System, developed together
with LifeGuard Technologies, a leader in commercial truck occupant protection,
uses a roll sensor to detect a rollover by monitoring the vehicle’s
roll angle and rate, and then triggers safety devices in a pre-programmed
sequence. In the event of a vehicle side-roll, the Side Roll Protection
System automatically initiates the following actions:
• Tightens the seat belt to reduce driver
motion
• Lowers the seat to its lowest position
to increase survivable space
• Locks the seat down to eliminate movement
• Pre-tensions the seat belt to position
the driver for contact with the side airbag, and
• Deploys an inflatable tubular
side-curtain airbag that protects and cushions the head and neck and
prevents excessive head motion.
The side-curtain airbag activates in a
fraction of a second, and remains inflated for several seconds –
enough time to protect the driver for the duration of the accident.
Obstacle detection
system
The Eagle Eye™ obstacle detection
system alerts drivers to objects hidden in vehicle blind spots up to
20-feet away. For the operator, this means that turning, backing up,
and lane changing are less risky and potential collisions (and accident
related expenses) are easier to avoid. The Eagle Eye Obstacle detection
system is available exclusively in the ready mix industry on Oshkosh,
McNeilus, and London mixer trucks.
Non-pressurized composite
water tank
The new McNeilus lightweight composite
water tank is claimed to offer a number of benefits including a substantial
109 kg. weight advantage over a comparable steel water tank. This unique,
non-pressurized unit is claimed safer to operate, yet powerful enough
for faster clean-up. The unit also contains fewer parts and fittings
for added ease and simplicity of service.
Trimble® DriveSafe™
System
The Trimble DriveSafe technology is now
available exclusively on Oshkosh, McNeilus and London mixer trucks.
The DriveSafe system helps train ready mix drivers as it measures the
accelerations exerted on the truck during various driving maneuvers
such as turns, starts and stops. The system also takes into account
the loaded or unloaded status when measuring turns. The DriveSafe system
also:
• Measures average vehicle speed
via high resolution GPS positioning
• Calculates a score for each maneuver
• Reports scores for individual
drivers as well as a composite score
• Compares individual scores to
the average scores for the fleet
The system functions as a valuable driver-training
tool. In many cases, drivers just need to be reminded about certain
elements of their driving behaviour. In other cases, drivers need to
be trained to significantly alter their driving style when the truck
is loaded to avoid potential rollover situations.
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top
Tracked
crusher delivers for Ontario cement producer
In
an unusual application, a track-mounted crusher is providing one of
the raw materials for cement production.
By Andy Bateman, Engineering
Editor
The
vibrant southwestern Ontario town of St Marys earned its nickname of
“Stonetown” through the use of locally quarried limestone
to build a number of fine late 19th century and early 20th century buildings.
More than 100 years later, local limestone still plays an important
role in the town’s economy as the principal raw material in cement
production.
Gerald Lodge is quarry and raw materials supervisor
at the original St Marys Cement plant located on the town’s outskirts.
Lodge explains that, in addition to limestone, the cement production
process here utilises silica, alumina, clay, fly ash and iron ore. Limestone
and clay are extracted from separate site operations, while the remaining
raw materials are imported. Before entering the cement production process,
material excavated from the clay pit is crushed to reduce any oversize
in the deposit.
For many years, clay crushing was completed
by a stationary clay mill. More recently, the process was changed to
in-pit clay crushing and done by contractors using portable equipment.
In the fall of 2005, the company made the move to in-house, in-pit clay
crushing with the acquisition of a track mounted impact crusher. Lodge
adds that a tracked machine was selected for its ability to travel in
relatively soft pit floor conditions and keep close to active faces.
When visited by Aggregates & Roadbuilding,
a mixture of excavated bank clay and recycled clinker was being crushed
in a stand-alone operation. As a result of unusually wet fall weather,
the Cedarapids CobraTrack 1300 track-mounted impact crusher was set
up outside the main clay pit and was working a 10 m high clay face containing
a small percentage of cobble and larger sized stone pieces. Alternate
buckets of excavated clay and clinker were fed to the crusher by a Caterpillar
330CL excavator. Oversize material retained on the 1300’s double
deck vibrating grizzly was crushed, whereas material falling through
the grizzly bypassed the crusher and was conveyed directly to a 1067
mm wide product conveyor. The resulting crushed and blended product
was loaded directly into Caterpillar 769C and Terex 40-tonne capacity
haul trucks and hauled some 150m to a pair of beehive storage sheds.
Each shed provided dry storage capacity of 18 000 – 20 000 tonnes.
The clay crushing operation worked with a crew
of three including the excavator operator and two haul truck operators.
The crusher’s grizzly and stop functions were controlled remotely
by the excavator operator, who could also control track speed when required.
In this application, the crusher was typically being moved 12-15 m every
14 days to keep it within the operating radius of the face excavator.
Overall, this set up delivered a reported production rate of 250-300
tonnes/h. Operating hours were determined by a number of factors such
as crushed clay inventory levels, projected demand for cement production
and the weather. Typically, the cement process requires some 12 tonnes/h
of the clay/clinker mixture, representing about 6-8 per cent of total
raw materials feed.
Lodge explains that a number of modifications
have been made to the unit to suit the clay crushing application. At
the feed end, the side discharge bypass conveyor has been removed, while
the bars on the vibrating grizzly feeder have been set relatively wide
to allow a relatively high percentage of the feed to bypass the crusher.
At the product end, the standard product conveyor has been extended
by 2.75 m to facilitate direct loading into haul trucks, thereby avoiding
potential contamination from ground stockpiling as well as the cost
of reloading.
Manufacturer’s specifications indicate
that the CobraTrack 1300 is equipped with a Cedarapids 5048 horizontal
impact crusher, a Cedarapids 1067 mm x 4267 mm vibrating grizzly feeder
and “B5” tracks with individual hydrostatic drive motors.
The product conveyor has hydraulic drive, as
does the 1041 mm long cross belt equipped with an Eriez magnet. Standard
equipment also includes a 610 mm wide side discharge bypass conveyor
and two-way bypass chute.
Power for the unit is provided by a Cummins
QSM 11 diesel engine developing 400 hp at 800 rpm, while accessories
include a dust suppression spray system with atomizer nozzles, chassis,
walkways, platforms and guard. Dimensions include a plant overall length
of 15.7 m, overall track width of 2.84 m and plant operating height
of 3.66 m. The plant’s transportation height is 3.66 m plus the
trailer deck height, while total plant weight is 42.2 tonnes.
St Marys Cement Inc. is a wholly-owned
subsidiary of Votorantim Cimentos, an international cement manufacturer
based in Sao Paulo, Brazil. Products of St Marys Cement Inc. include
cementitious materials from St Marys Cement, ready-mixed concrete and
aggregate from St Marys CBM and logistic services from Hutton Transport
Ltd.
Back
to top
Wet
deposits demanding for producers, operators and machines
Wet sand and gravel deposits
play an important role in the overall aggregate supply mix, but aggregate
extraction from below the water table can be challenging for pit owners,
equipment operators and the machines involved.
By Andy Bateman, Engineering
Editor
High
quality sand and gravel deposits are an important source of mineral
aggregates for virtually all urban markets and the only economic source
for some. At most pits, the deposit is above the water table and loose
enough for extraction simply by a wheeled loader or excavator. It is
a different story where the deposit is beneath a body of water which,
for a variety of reasons, cannot be dewatered. In such cases, the pit
must be worked wet and the wet extraction process places a special set
of demands on pit owners, operators and the extraction equipment. A
number of sand and gravel pits near Aberfoyle, Ont. are worked wet to
help protect the Mill Creek watershed and illustrate some of the challenges
of wet pit operation. For
pit owners such as Dufferin Aggregates, operating here involves extensive
water monitoring procedures and site specific safety procedures, all
in addition to the customary demands of a large aggregate business.
For dragline subcontractor Higgs & Higgs,
safe and efficient material extraction depends on close cooperation
with pit owners, skilled dragline operators and draglines able to withstand
the arduous duty cycle work. Higgs & Higgs has been in the dragline
and crane business since 1954. Founded by Norman Higgs to excavate large
irrigation ponds for farmers in the southern Ontario “tobacco
belt”, five generations of Higgs including Verne Senior, Wayne,
Verne and Travis have all been part of the growth of this specialist
contracting business.
Ron Van Ooteghem, site manager for Dufferin
Aggregates, explains that the company’s Aberfoyle 2 pit was originally
licenced for dry extraction. The licence was amended in 1997 to allow
for underwater extraction, subject to additional operating conditions.
Similarly, the Mill Creek Pit was licensed for
underwater extraction, also with very stringent environmental monitoring
conditions. These conditions include a water monitoring and reporting
program to help maintain suitable conditions for Mill Creek’s
fish population and specifically its trout population. Trout are particularly
sensitive to their habitat and so provide an excellent natural barometer
of overall creek conditions. Under the program, quantities such as tonnage
of material extracted below the surface water table, volume of water
pumped and pond levels are reported monthly to the province’s
Ministry of Natural Resources (MNR). Van Ooteghem adds that that this
monitoring reflects the origins of the deposit and its relationship
with the local water regime. The sand and gravel being extracted was
originally deposited by a melting glacier and overlies a layer of glacial
till or glacial clay. The clay layer in turn overlies the same limestone
deposits that outcrop nearby as the Niagara Escarpment. Within this
geological structure, there are two interconnected water zones; the
surface or shallow groundwater aquifer in the gravel and the deep groundwater
aquifer in the bedrock. Groundwater gradients must be maintained at
or above a minimum stipulated level to maintain an up welling of water
into the creek.
In the winter, this up welling maintains creek flow
to prevent freezing and so maintain the necessary flow conditions for
fish hatching in the spring. During the spring and summer months, the
up welling facilitates a good hatch of healthy eggs and helps keeps
the creek water sufficiently cool for adult trout. Van Ooteghem adds
that the provincial Ministry of Natural Resources (MNR) is looking at
coordinating the monitoring by the companies in the area to balance
responsibilities to provide necessary monitoring while avoiding unnecessary
or duplicated effort.
At both Dufferin Aggregates’ Mill Creek and
Aberfoyle 2 pits, aggregate is extracted by an excavator and dragline
combination to typically extract 9 m of sand and gravel material from
the bottom of the respective pit ponds. A long stick excavator removes
the first 6 m of material and is followed by a dragline to recover the
bottom 3 m of material. Van Ooteghem adds that this two-machine approach
has been found to provide the lowest overall excavation cost per tonne.
Excavated material from both machines is cast into a stockpile to drain,
with the stockpile set back a minimum distance from the water’s
edge for safe recovery later.
As a further safety measure, wheel loaders build
a safety berm along the water’s edge as material is recovered
from the stockpiles. Other potential safety issues associated with dragline
operations have been recognised in safe work procedures, the result
of a multi-party effort by Dufferin, Higgs & Higgs and others. These
procedures detail work steps and control measures to address, for instance,
the potential hazards of slope instability, tipping and cave in. The
procedures also draw on a special geotechnical report, commissioned
by Dufferin to determine the appropriate minimum set back distance to
be maintained for each make and model of machine working the underwater
material.
Van Ooteghem adds that the typical freeboard above
the water level is less than one metre, reflecting safety, flooding
and efficiency considerations. Going lower means safer operation and
better reach by the dragline, but at the risk of local flooding during
a seasonal rise in water level. Increased freeboard, on the other hand,
means reduced safety from undercutting and increased set back requirements
but does avoid the flooding risk. Still on safety, Wayne Higgs points
out some of the unique safety measures required for safe dragline operation.
In frozen or icy conditions, the working surface must be scarified by
an excavator to make sure that there is sufficient friction to keep
the dragline in place when dragging or swinging a loaded bucket. Undercutting
of frozen material by wave action can also can occur and precipitate
the sudden failure of an apparently safe working surface.
Unusual conditions aside, Higgs notes that even
the normal dragline process is demanding for both operators and machines.
For one thing, the material being extracted is not visible, so accurate
working depends on the operator’s skill to maximise material recovery
without penetrating the clay layer or, in some locations, a stipulated
mining depth. Some liken the skill requirements of a dragline operator
to those of a fly fisherman, as efficient machine operation is dependent
on the ability to accurately cast and drop the bucket, then drag, hoist,
swing, dump and cast again in a smooth continuous cycle. Good concentration
over long periods is required, as well as the use of both hands and
feet to perform multiple functions.
For the dragline itself, Higgs has found
that only machines built for duty cycle can withstand wet aggregate
extraction for any length of time. The repetitive action of dragging
a loaded bucket through wet, compacted material imposes high stresses
on drives, winches and cables, while simultaneously causing rapid wear
of buckets, bucket teeth and cable in contact with wet abrasive material.
Draglines assigned to this work by Higgs are from the Liebherr stable,
either a HS 855 HD or the larger HS 885 HD. For this duty, the HS 855
HD is equipped with a 2.7 m3 bucket and, according to Higgs, has an
average production rate of 300 tonnes/h. The HS 885 HD has a 3.8 m3
bucket and an average production rate of 350 tonnes/h.
Liebherr specification data indicates that the
HS 855 HD equipped for dragline duty has a 26.3-tonne counterweight
and a boom length of up to 29 m. With a 29 m boom at 45 degrees, the
rated dumping radius and capacity of the HS 855 HD are 22.5 m and 7.5 tonnes
respectively. For the same duty, the HS 885 HD is equipped with a 32.5-tonne
counterweight and a boom length of up to 33 m. A 33 m boom at 45 degrees
gives the HS 885 HD a rated dumping radius and capacity of 25.3 m and
8.5 tonnes respectively.
Both machines are equipped with proportional
control for all movements and all movements can be carried out simultaneously.
For dragline operation, a special interlock control is an option designed
for power lifting of the dragline bucket without using the drag winch
brake. An additional option is the redundant control system which allows
restricted operation of the machine in the event of a failure on the
electronic base control or its sensors. Custom designed control systems
are offered for free fall winches. In operation, the left joy stick
is used for boom winch and swing while two directional levers are operated
by the right hand for the drag and hoist winches. Crawler control is
actuated with two central foot pedals.
Back to
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What's
new in asphalt pavers
Bomag
Paver offers faster paving speed
The redesigned, gravity-fed 3313 asphalt paver from
BOMAG Canada features a new engine and a single-speed drive motor that
results in improved maximum paving speed.
The 3313 paver is powered by a fuel-efficient
50-hp Cummins water-cooled diesel engine. Exclusive hydrostatic drive
with load sensing design saves on fuel consumption by delivering power
only when needed. A new single-speed drive motor provides travel and
working speeds up to 76.2 m/min.
With paving widths ranging from 2.44 m
to 3.96 m, the 3313 is designed for driveways, parking lots and asphalt
repair and resurfacing applications. The paver’s gravity-fed hopper
holds up to 5.44 tonnes of asphalt for long intervals between refills.
Dual 75 mm diameter cylinders elevate
the hopper bed during operation to dump asphalt through the gates to
the screed. The cylinders raise the deck without bending or deflection,
thus extending the life of the paver. Additionally, the 3313 offers
9.52 mm thick hydraulically actuated hopper wings for maximum material
control.
A full-width floating screed provides
variable paving widths and features heat and high-speed vibration to
help maintain material flow and consistency. Screed wear plates made
from 400 Brinell hardness steel are designed to withstand harsh job-site
conditions and are bolted on for easy replacement.
Two 762 mm adjustable hydraulic screed
extensions feature replaceable 6.35 mm abrasion-resistant wear plates.
The extensions are single-ratcheted, allowing operators to easily adjust
both height and attack angle with one turn of the crank. Lower walk
boards are also extendable.
The 3313 model features manual hydraulic
controls and ergonomic dual operator positions, providing control from
either side of the paver.
Other standard features include
an enclosed engine area for quiet operation, hydraulic shut-off gates,
wash-down spray system and an automatic shutdown system when encountering
high engine water temperature or low engine oil pressure.
Optional equipment includes operator
seats, a spray-down hose reel, power depth controls, urethane track
pads and screed automation.
www.bomag-americas.com
Terex
Cedarapids
Highway class features in commerical paver line
Based
on customer feedback, the new Terex® Cedarapids CR300L Series asphalt
pavers from Terex Roadbuilding have been designed to incorporate offer
more highway-class features in a 2.4 m commercial paver. The 228.9 mm
longer CR300L Series offers contractors an 11 per cent increase in hopper
capacity to 9 tonnes, delivering more paving time between truck exchanges.
While the new pavers are longer and include more heavy-duty components,
all CR300L Series machines – the rubber tire CR352L, rubber track
CR362L and steel track CR362LS – keep the same weight as their
previous model counterparts, allowing transport from site to site without
permits.
The additional 228.6 mm hopper length
offers more tailgate clearance for end-dump trucks, enabling more efficient
truck unloading. Material is discharged in the middle of the paver hopper
for more effective use of total hopper capacity.
With these new pavers, asphalt mix is
now channelled from the hopper to the spread augers by the same heavy-duty
chain, sprocket and slat bar delivery system found on the manufacturer’s
CR400 and CR500 Series mainline pavers. Increasing component service
life, a beefy 78 mm pitch roller slat chain with hardened eight-tooth
slat drive sprockets replace the 66 mm pitch roller chain with four-tooth
sprockets found on previous CR300 Series pavers.
The new CR300L 2.4 m pavers now have the
same propel pumps found on larger Terex® Cedarapids pavers. The
Sauer-Danfoss 90 Series pumps run at higher pressures, giving the pavers
18 per cent more tractive effort than previous CR300 Series pavers.
According to the manufacturer, the higher traction enables them to push
heavy tandem axle trucks up steep grades. Coinciding with the pump change,
these new pavers offer higher paving speeds: the rubber tire CR352L
is 10 per cent faster at 122 m/min; the rubber track CR362L is 22 per
cent faster at 76 m/min; and the steel track is 21 per cent fast at
61 m/min.
The new CR362L paver now features the
Terex® Cedarapids patented Smartrac™ system previously found
only on the CR400 and CR500 Series rubber track pavers. This exclusive
feature automatically maintains proper track tensioning at all times,
eliminating the need for manual track adjustments, extending track component
life and significantly reducing the chance for track disengaging. Front
bogie positioning on the CR352L rubber tire pavers has been extended
by 228.6 mm, lengthening the wheel base for stable operation.
The CR300L models are powered by the 165-hp
Cummins 6BTAA5.9 turbocharged diesel engine. The series offers paving
widths from 2.4 m to 5.5 m. Contractors can choose from three different
screed – the electric or fuel-oil heated Stretch 16®, electric
VersaScreed 8, or fuel-oil Fastach® 8.
www.terexrb.com
Roadtec
Slide-out operator stations now available
Roadtec’s
latest enhancements to its RP-190 and RP-195 paver models are slide
out seats for optimum operator visibility. Two stations are provided,
one on the right and one on the left side of the paver. Roadtec operator
seats with their spring suspension are described as having the same
comfort level as high-quality truck seats, and include swivel and reclining
functions. Roadtec operator stations have the most common functions
grouped within easy reach next to the armrest, with propel functions
on one side and material feed functions on the other. The new slide
out seat design rounds out this package for optimal operator comfort
and performance. Other recent Roadtec paver changes include the use
of Caterpillar Tier 3 engines, which provide better fuel economy and
lower engine noise levels.
www.roadtec.com
Bergkamp
Paver reduces construction joints
Bergkamp
Inc. offers the M1, a self-propelled continuous slurry seal/microsurfacing
paver that is designed to reduce the number of construction joints by
receiving an endless supply of material while the machine is working.
It is claimed to be the only full size continuous slurry seal/microsurfacing
paver available.
According to the manufacturer, slurry seal and
microsurfacing are among the most efficient methods of preventive maintenance
for highways, roads and parking lots. The mixture of aggregate, emulsion,
water and additives is applied by the M1 in a smooth layer over existing
pavement and can extend the life of the surface up to seven or more
years. The main difference between slurry seal and microsurfacing is
that slurry seal uses a standard emulsion which requires evaporation
to occur and sets in several hours. Microsurfacing uses a polymer modified
emulsion that produces a chemical reaction to force the moisture out
and can set in less than an hour so traffic can return quickly.
The M1 is powered by a 335-hp Cummins diesel
engine and is equipped with a hydrostatic drive system that can be controlled
by either the front or rear operator station, and wet disc brakes. The
operator stations can be accessed from both sides of the machine and
have hand rails to protect the operator. The front operator station
also has dual-driver stations, a detailed instrument panel and provides
excellent visibility of the aggregate hopper.
www.bergkampinc.com
Ingersoll
Rand
Paver has innovative technology
Available
from Ingersoll-Rand is the Titan 7820, a versatile paver designed for
placing any kind of wearing, binder, and base course material in large
paving widths and thicknesses.
The Titan 7820 paver can install hot-mix asphalt,
roller-compacted concrete (RCC), cement-treated base, non-treated base,
stone and soil cement. The paver is designed for a number of applications
including highways, secondary roads and airports.
The Ingersoll Rand Electronic Paver Management
II (EPM II) control unit is a standard feature. The EPM II provides
information on functions of the paver, vital operating-condition information,
and diagnostic checks to the operator through an intuitive interface.
The paver has a hopper capacity of 13.2 tonnes.
A 231-hp Duetz diesel engine gives the Titan 7820 variable speed control
up to 20 m/min when paving and 3.6 km/h in transport.
The Titan 7820 will accommodate a variety of
screeds, including fixed and hydraulically extendable units, to place
material up to 10 m wide and 30 cm thick.
Standard features include two seats that
can extend laterally for improved operator visibility; an adjustable
and revolving operator console; lifetime lubricated crawler track rollers;
forged and hardened crawler track links; an automatic track tension
system; four independent drives for conveyors and augers; ultrasonic
sensors for proportional material feed control and an all-weather canopy.
www.ingersollrand.com
Back to
top
January-February
2007 issue
Aggregates
and Roadbuilding Magazine
4999 St Catherine Street West.
Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 487-9868 Fax: (514) 487-9276
EMail: rocktoroad@sympatico.ca
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