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Canada’s “Rock to Road” Magazine
September/October
2004 Issue
For a copy of the issue
that contains these articles with colour photos, click
here.
Rolling
Mix leads mixer revolution
By Robert L. Consedine, Editor
An Alberta ready-mix
concrete producer recently became the first in Canada to purchase new
mixer trucks equipped with a revolutionary lightweight non-steel drum.
In
our business, weight is money”, states Rod Taverner, managing
partner of Rolling Mix Concrete (Edmonton) Ltd., a member of the Rolling
Mix Group which operates a total of 54 mixer trucks and two central
wet mix plants in Edmonton and Calgary.” Every kilogram that can
be trimmed off the dry weight of a mixer truck means more payload capacity
and increased revenues for us.” A visit to the World of Concrete
(WOC) three years ago alerted Taverner to a radically new 8 m3 capacity
drum under development by Minnesota-based McNeilus Companies, Inc. that
promised a substantial weight reduction over conventional mixers without
sacrificing the toughness of steel. Through the use of advanced composite
materials to construct the shell structure, McNeilus was able to shave
nearly a tonne off the weight its comparably-sized standard 4.76 mm
thick abrasion resistant (AR) steel model. The manufacturer also claimed
a longer service life for the composite drum since corrosion was virtually
eliminated. Taverner immediately recognized the extra payload benefits
of the new drum and would have ordered several units on the spot had
it not been still in the pre-production stage.
The composite drum – named Revolution
– was officially launched with much fanfare on March 19, 2002
at the CONEXPO-Con/Agg Show in Las Vegas. Described by McNeilus as one
of the biggest advances in concrete mixer technology since drums were
first mounted on trucks back in the 1930s, the Revolution is the result
of a US$10 million, four-year research and design program undertaken
by McNeilus in conjunction with a team led by its Australian partner,
Anthony Khouri. A further US$20 million was invested by McNeilus in
new fabrication facilities before the Revolution went into full production
earlier this year.
According to the manufacturer, the proprietary
technology utilizes polyurethane, filament, resin and a gel coating
process to create an aerodynamic, seamless shell. The drum’s smooth
polyurethane interior incorporates an innovative dual-fin spiral design
with auto reverse fin action that minimizes concrete buildup, increases
discharge speed and reduces routine cleaning and maintenance requirements.
Sharing the overall dimensions of the other
8.4 m3 capacity steel models manufactured by McNeilus, the Revolution
drum features a 1066 mm wide drum opening and charge hopper, a 1544
cm2 steel inspection hatch, 98.4 mm diameter induction-hardened rollers,
a pre-formed machined roller track and an 18-bolt drive socket. A nylon
drum debouncer is standard.
Field testing of the prototypes with ready-mix
producers in three regions of the United States revealed the composite
drums equalled or exceeded conventional drum performance under a wide
range of ambient temperatures and job site conditions that transit mixers
routinely encounter.
To carry the new composite drum mixers, the
Rolling Mix Group purchased seven new wide track tri-drive trucks –
four Western Star 4900SAs and three Mack CV713 Granite-series models
– with wide track tri-drive rear axles.
Each Western Star and Mack truck was custom-built
to Rolling Mix’s specifications. The Western Star rigs feature
a 410 peak hp Caterpillar C13 engine, a 31 298 kg capacity Meritor rear
axle, a 9072 kg capacity Meritor front axle, an 18-speed Eaton-Fuller
transmission and Western Star’s AirLiner suspension system.
The Mack Granite-series trucks are equipped
with 405 peak hp Mack AMI-370 IEGR diesel engines, Mack 10-speed T310
MLR transmissions, Meritor 31 298 kg rear axles, 9072 kg Mack FXL20
front axles and Neway air-ride suspensions. Both truck models share
a host of driver-friendly options like air conditioning, power windows,
air seats, radios and right-side power mirrors. The Western Star trucks
were ordered through Sterling Western Star AB Ltd., of Calgary while
the Mack trucks were purchased from Edmonton-based Nortrux Inc. The
new trucks were shipped to the McNeilus plant in Dodge Center, Minn.
where they were fitted with the 8 m3 Revolution drums. Deliveries took
place in mid-September with five of the new composite drum mixers assigned
to the Calgary market with the remaining two units located in Edmonton.
The new tri-drive trucks and composite drums
are part of Rolling Mix’s mission to increase the legal payload
capacity of its mixers. Under Alberta highway load limits, tri-axle
configurations allow an extra 6000 kg of GVW over a tandem axle transit
mixer. They also give the trucks better traction and more precise handling
and manoeuvring capability on muddy work sites. According to Nortrux
sales representative John Stearns, tri-drives are common in Alberta’s
oil patch and are now finding their way into construction applications.
After using the new composite drums seven days
a week for the past month on a wide range of building projects in both
Calgary and Edmonton, Taverner told Aggregates & Roadbuilding that
the Revolution drums are more than proving themselves in increased productivity
and lower maintenance. He is confident that the 18-20 per cent price
premium for the Revolution drums will be recouped in a matter of months
not years.
”Instead of carrying a legal 5.5 m3 on
our weight-restricted roads, each new composite drum tri-drive truck
allows us to deliver an extra 2 m3 of concrete per trip. That adds up
to 9 m3 more concrete per shift based on a daily average of 4.5 trips
or potentially up to 180 m3 more concrete per month with no extra labour
costs,” said Taverner. “Furthermore, the weight savings
of the composite drums means less fuel is burned on the return trip
to the plant.”
A composite drum mounted on a tandem axle truck
would allow an extra .5 m3 of concrete per load. Taverner feels the
real cost advantage of the composite drum is achieved when making five
to six deliveries a day with each of the composite drum trucks.
Among the other benefits he cites for the composite
drums are improved mixing efficiency, significantly reduced mixer noise
due to the deadening effect of the composite materials and more insulating
ability to maintain controllable mix temperatures on both hot and cold
days. An example of the composite drum’s insulating ability was
demonstrated during a recent Edmonton basement pour in sub-zero temperatures.
Taverner said that the floor slab had to be poured at 27°C which
meant heating the concrete at the plant. The concrete left the plant
at 27°C and thirty minutes later arrived at the building site still
at 27°C even though the temperature was minus 8°C.
Driver reaction to the composite drums and tri-drive
trucks has been very positive, stated Taverner. Interior washout times
are much quicker as are loading and discharge speeds.
During Aggregates & Roadbuilding’s
late September site visit to Rolling Mix’s offices and concrete
plant in northwest Edmonton, four of the company’s new composite
drum mixers were being used to deliver concrete to the 111th St. interchange
project on the city’s new Anthony Henday Dr. arterial expressway.
The new units were part of a 20-truck fleet mobilized by Rolling Mix
from its Edmonton and Calgary operations to complete a two-stage weekend
bridge deck pour of some 700 m3 of 35 MPa low slump silica fume concrete.
According to Taverner, the Alberta Transportation mix design specified
a maximum of 70 minutes for the 30 km trip in urban traffic from the
batch plant to the concrete pump or the load would be automatically
rejected. High Concrete temperatures were a potential problem on this
occasion and were controlled by the addition of a precise quantity of
ice at the plant. Both stages of the pour were successfully carried
out several hours ahead of schedule. He credits the extra payload capacity
and fast turn-around capability of the composite drums with achieving
this feat. “The Revolution drums and tri-axle trucks enabled us
to complete the pour with 12 fewer round trips.”
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Automatic
highway trucks promise reduced repairs, improved performance
By Andy Bateman,
Engineering Editor
An Ontario
aggregate and ready-mix concrete producer is turning to automatic transmissions
to deliver results.
Earlier
this year, Barrie-based Sarjeant Co. Ltd. purchased a highway aggregate
truck equipped with automatic transmission, bringing to four the number
of automatic units in the company’s 42 truck fleet. Two automatic
ready-mix trucks have been in service since last year, while the fourth
automatic is in service in the company’s oil delivery fleet. Assistant
operations manager Doug Kelly reports that the company first became
interested in automatic trucks at a U.S. demonstration, where tractor-trailer
units were seen tackling fully loaded starts on grades up to 14 per
cent (1 in 7). Just as impressive, brake linings on the demonstration
units still had some 90 per cent life remaining after 140,000 km, thanks
to significant power train braking provided by their transmission and
retarder set up. Like other fleet operators, Sarjeant has its share
of repairs to its trucks fleet, including driveline repairs to broken
drive shafts, axles and rear ends. Ready-mix trucks in particular are
susceptible to driveline stresses while manoeuvring fully or partially
loaded in variable ground conditions. Kelly is optimistic that reduced
driveline repairs and extended brake life will deliver a direct payback
on the $20,000 incremental cost of each automatic transmission, aside
from any other benefits such as improved truck performance and reduced
driver fatigue.
Ready-mix
concrete
Sarjeant’s two automatic ready-mix trucks
have now been in service for about 12 months in a variety of operating
conditions, including winter work. The tandem/tandem Western Star units
are equipped with 6-speed Allison HD-4560P automatic transmissions teamed
with Caterpillar 410 hp engines and compression (engine) brakes. Company
driver Rick Kelly was initially sceptical but now prefers the automatic,
particularly in curb laying operations. “Sarjeant often supplies
concrete for curb construction on residential subdivisions. In this
situation, the automatic can crawl to match the pace of the curb laying
machine, unlike a standard transmission where repetitive stop and go,
sometimes uphill, is hard on clutches. The automatic is also useful
in soft or sandy conditions where the gradual application of power improves
traction. On the road, the transmission shifts to match engine speed
with road speed, providing some driveline braking on the overrun as
well as good pick up under power.”
Literature produced by Allison Transmission
describes how an electronic control unit (ECU) within its automatic
transmission receives information on engine input speed and transmission
output speed, as well as engine load and road conditions. The ECU then
processes this information and times gear shifts to optimize engine
and vehicle performance. Shifts are said to be precise whether the truck
is loaded or empty. Another characteristic of the automatic transmission
is the cushioning effect provided by its torque converter. During operation,
the converter reduces shock and strain on the entire driveline and helps
extend the life of driveline components such as engine, universal joints
and rear axle.
Allison adds that its transmission output retarder
(when fitted) provides auxiliary braking power that is not dependent
on engine speed and/or gear ratio and is said to be compatible with
antilock braking systems (ABS). Thanks to the retarder, service brakes
are said to be generally only necessary to bring the vehicle to a complete
stop, resulting in reduced wear on service brake linings, fewer brake
replacements and lower maintenance repair costs.
Aggregate
truck
Sarjeant’s automatic highway truck went
into service at the end of May, just three weeks after a new truck with
the same specifications apart from its standard transmission. This parallel
purchase is no coincidence and gives Sarjeant the opportunity to directly
compare the performance of automatic and standard trucks in a real life
application. Both trucks are Western Star pup units with a legal payload
capacity of 42 tonnes. In addition, both units are generally on the
same duty, hauling aggregates from Sarjeant’s 7th line pit to
the Barrie ready-mix concrete plant, a 40 km round trip on paved roads
that includes rural and highway driving as well as a short stretch in
town. The automatic unit is equipped with a 6- speed Allison HD-4560P
automatic transmission, while the standard unit has a Fuller Road Ranger
18-speed standard transmission. Both trucks are powered by Detroit Diesel
engines rated at 435-500 hp and both are also equipped with Jacobs compression
(engine) brakes.
Sarah Heino, Sarjeant’s customer representative,
has been tracking the performance of each truck and has found no significant
differences in fuel consumption to date. Based on data for a full month
of operation, Heino reports that each truck consumed an average of 300
litres of diesel fuel in an 11.5-hour shift. Productivity is similar,
with both trucks hauling a daily average of 400 tonnes in 10 loads,
for unit fuel consumption of 0.75 litres/tonne. In an informal test
with both trucks loaded, the automatic provided better acceleration
from a standing start up to highway speeds. Plans are in hand to obtain
additional feedback by switching drivers and also assess the impact,
if any, of different driving styles on fuel consumption.
Allison Transmission is part of the General
Motors Group.
Western Star and Freightliner are both part
of the DaimlerChrysler group.
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Out
with the old,in with the new at CBM
By Andy Bateman,
Engineering Editor
CBM Aggregates’
new portable processing plant will replace aging capacity, provide portability
and free up pit reserves.
This fall sees the commissioning of a new aggregate processing plant
in CBM’s Aberfoyle, Ont. pit. Demand for products from this pit
continues to grow, driven by the combination of strong market growth,
a well established customer base and a prime location near Highway 401.
CBM’s John Pennings explains that
new portable spread has been set up in a depleted area of the pit that
provides extensive real estate for the processing and stockpiling of
products. Equally important, the new plant location will allow access
to reserves currently underneath the existing fixed plant. These reserves
will provide most of the raw material for the new spread, supplemented
by material from the McNally pit just south of Highway 401 as well as
the company’s new Tikal pit on nearby Victoria Rd. Material will
be hauled in conventional end dump highway trucks so as to provide the
best possible fit between feed material gradation and the required finished
product mix.
Key process elements of the plant include
primary screening, primary and secondary crushing stages, twin wet rinsing
screens and a separate sand plant. All products from the 300 tonnes/h
capacity new plant are washed and include coarse and fine concrete aggregates,
38 mm, 13 mm and 6.3 mm round sizes as well as winter (by-product) sand
and washed screenings. Skid mounting makes most of the plant portable,
although it is expected that it will stay in its present location for
at least five years.
When running, raw material is drawn from
nearby stockpiles and fed to the plant by a Caterpillar 980G on load
and carry duty. The next step in the production process is the separation
of the feed into 38 mm plus and 38 mm minus sizes by a 6 x 20 ElRus
triple-deck primary dry screen fitted with 13 mm thick punch plate to
deal with the occasional 450 mm boulders found in the Aberfoyle deposit.
Screened feed that is naturally smaller than 38 mm bypasses the plant’s
crushing stage and is conveyed directly to the north wet rinsing screen.
At the same time, material larger than 38 mm passes through primary
and secondary crushing stages before being conveyed to the south wet
rinsing screen. An Elrus 24x42 primary jaw crusher reduces the oversize
to 102 mm minus before further reduction by a Sandvik H4800 CC cone
crusher in the secondary position.
The screen cloths fitted to the two rinsing
screens, both ElRus 6x20 triple-deck units, reflect the plant’s
required product range. The north screen (receiving naturally sized
material) is fitted with 23.8 mm and 14.3 mm screen cloths on its top
and middle decks respectively. Material retained on its top deck is
stockpiled as 38 mm round roofing stone, while the minus 23.8 mm plus
14.3 mm material retained on the middle deck joins crushed coarse material
from the south screen to produce coarse concrete aggregate.
The bottom deck of the north screen is
fitted with 9 mm opening cloths on the first four panels and a 7 mm
opening cloth on the last (discharge end) panel. Material retained on
this bottom deck (minus 14.3 mm plus 7 mm) is stockpiled as 12.7 mm
rounds. Meanwhile, the material passing the bottom deck is split; sand
slurry from the first four panels discharges into the slurry tank beneath
the screen while 6.3 mm minus rounds are stockpiled separately.
The south screen (receiving crushed material)
is normally fitted with 23.8 mm, 7.9 mm and 5 mm screen cloths on its
top, middle and bottom screens respectively. Material larger than 23.8
mm is returned to the cone crusher for further reduction, while minus
23.8 mm plus 7.9 mm material retained on the middle deck is stockpiled
as 19 mm concrete stone. Material retained on the bottom deck, minus
7.9 mm plus 5 mm, is stockpiled as 6.3 mm chip. Coarse fractions from
both screens are collected and routed as required by three reversible
transverse conveyors at the end of each screen’s discharge chutes.
Sand (fine) fractions from both screens
are pumped to a separate sand plant where they are sized and dewatered
by a classifying tank and two dewatering screws. Normally, all the natural
sand slurry from the north screen is pumped to the classifying tank
while manufactured (crushed) sand slurry from the south screen is pumped
directly to one of the dewatering screws before being stockpiled as
winter sand. If required however, the crushed sand fraction from the
south screen can added to the natural sand fraction from the north screen
to adjust the plant’s concrete sand gradation. In this case, the
bottom screen cloth in the south screen is changed to 3.2 mm and the
resulting slurry is pumped into the north slurry tank. Here, it joins
the 5 mm natural sand slurry and the mixture is pumped up to the classifying
tank by a Metso 10x8 slurry pump. Sand slurry arriving at the 3.3 m
x12.2 m McLanahan Sand Manager classifying tank is separated into concrete
sand and winter sand grades. Concrete sand discharges into twin McLanahan
1.1 m x 10.1 m long dewatering screws, while the winter sand is dewatered
by a single McLanahan 1.1 m x 10.1 m screw.
Products are carried away from the new
spread on an extensive network of field conveyors before being stockpiled.
Concrete coarse and fine aggregates are stockpiled by 914 mm x 45.8
m long Assinck conveyors, while 38 mm round and 6.3 mm round products
are stockpiled by 914 mm x 36.6 m long Assinck conveyors. Power for
the plant is provided by a Caterpillar genset with a 3412 engine driving
a 1200-hp generator. The plant’s control system utilises Rockwell
Automation’s RSView32 software with custom graphics designed by
Aggressor Automation.
CBM Aggregates is part of the Votorantim
Cementos Group of Brazil.
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Paver
tackles large and small projects
By Andy Bateman,
Engineering Editor
An
Ontario roadbuilder’s new paver is seeing action in applications
ranging from large scale commercial work to narrow residential streets.
Aggregates & Roadbuilding
first saw the new paver in the Rosedale area of Hamilton where TCG Asphalt
& Construction Inc. was completing resurfacing work on behalf of
Dufferin Construction Co. Less than two weeks later, the same crew was
busy paving the vast trailer parking yard of Procter & Gamble’s
new Canadian Distribution Centre in Brantford.
Work at Rosedale included the paving of
some 600 tonnes of the city’s HM3 surface mix on Erin Ave., Nelligan
Place, Dundonald Ave., Parklands Dr. and Court as well as Connor Court.
For the paving crew, this contract’s short streets, turn loops
and utilities meant numerous short runs and extensive hand work. By
contrast, the work at Proctor & Gamble involved relatively long
runs in an open area, although even here there was detail work around
utilities and along the edges of the periodic concrete strips that will
carry trailer dollies. This job called for some 22 000 tonnes of hot
mix asphalt to be supplied from TCG’s nearby Hardy Road plant
and, when operational, will provide parking for 450 truck trailers.
TCG’s paver on both jobs was a Cedarapids
362 unit that the company bought new in May of this year. The operational
method was also similar on both jobs with the paver fed directly from
end dump trucks in the conventional manner. Both jobs also utilised
similar compaction equipment with a Bomag BW164AD-2 dual steel drum
breakdown compactor followed by a pneumatic roller in the secondary
position and a Bomag BW120AD finishing roller. The pneumatic roller
on the Hamilton contract was a Bomag BW12R, while a MPLS Bros SP-6000
was utilised at Brantford.
TCG’s Ted Van Ryn reports that this
year’s acquisition of the 362 and its larger stable mate the 462
brings to at least ten the total number of Cedarapids pavers owned and
operated by TCG. Drawing on 33 years experience with the operation and
maintenance of paving equipment, Van Ryn feels these pavers generally
produce the best mat, adding that, in terms of performance, the two
new machines are almost as fast as the equivalent rubber-tired pavers.
TCG’s 362 unit is fitted with a Stretch 16 screed, equipped with
electric heating in order to eliminate the excessive fumes associated
with the 15-20 minutes heat up period of diesel-heated screeds.
First reported in the January/February
2003 edition of Aggregates & Roadbuilding, the 362 is one
of Cedarapids 300 series of Tier 2 Pavers and replaces the CR361R. Designed
as an all purpose paver for commercial work, the 362 is equipped with
direct hydrostatic drive and the manufacturer’s frame raise system
for manoeuvrability. It has a maximum rated paving width of 5.5 m, a
maximum rated paving depth of 305 mm and weighs 15.7 tonnes. The rated
paving speed range is zero to 63 m/min, with a maximum travel speed
of 9 km/h.
A Cummins engine provides 121 kW of motive
power while a generator mounted directly above the screed provides electrical
power for the screed heating system. The 20 kW system on the Stretch
16 has 4-Zone Thermostatic Control and Volts, Amps and Hz (frequency)
read out. The electric screed is said to offer smoke free operation
and, according to the manufacturers, provides uniform heat distribution
from the front to the back of screed. The screed’s heating elements
are insulated from the upper section for added operating efficiency
and reportedly provide fast heat-up time. Reusable or replaceable heating
elements provide lower ownership costs and simple maintenance with plug
in design for fast screed bottom replacement. Heated bolt-on screed
extensions are available.
The Cummins QSB Series engines in the
new range of Tier 2 pavers are designed to meet all US Environmental
Protection Agency (EPA) Tier 2, CARB Tier 2 and Stage 2 European emission
standards. Increased maintenance intervals of up to 500 hours on these
engines are said to improve machine uptime while larger fuel tanks are
said to provide a full day’s paving without refuelling. The new
Tier 2 muffler system handles engine exhaust together with asphalt vapours
from the screed fume recovery system. Its design reportedly allows higher
temperatures to be maintained inside the exhaust stack, thereby reducing
screed smoke discharge from the exhaust stack. The muffler design is
also said to significantly reduce noise levels around the operating
environment.
TCG Asphalt & Construction Inc. and
Dufferin Construction are both business units of St. Lawrence Cement.
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Less
is more at Lafarge plant
Changes at a Lafarge
aggregate operation demonstrate how some process improvements can be
achieved by reducing rather than increasing the amount of equipment
involved.
By Andy Bateman,
Engineering Editor
The
Lafarge Stouffville pit, located 40 km northeast of downtown Toronto
is among the country’s largest sand and gravel operations, with
some 1.2 million tonnes of production last year. Recent changes to Stouffville’s
primary loading and secondary crushing processes have increased plant
efficiency and reduced costs, even though less equipment is used in
both cases. At the pit face, the primary loader fleet has been trimmed
from two machines to one, with the loader’s working location determined
by required feed gradation. This change has reduced primary loading
costs, matched the capacity of the primary loading and hauling fleets
and also helped match pit run gradation with finished product gradation.
Over at the pit’s secondary plant, a single new crusher has replaced
two old crushers, a change that has increased plant availability, reduced
maintenance costs and eliminated several bottlenecks.
Primary loading
Primary loading was, until recently, completed
here by two Caterpillar 988G wheeled loaders. Each loader was teamed
with two Caterpillar 773 haul trucks and assigned to a specific face
location to obtain a suitable mix of coarse and fine plant feed material.
Like virtually all sand and gravel operations, there are local variations
in the ratio of coarse to fine material in this deposit. Also like other
operations, there is rarely an exact match between the natural gradation
of the deposit and the gradation required to make all finished products
with minimal waste. Although the system worked reasonably well, maintaining
the required coarse/fine material balance could be a challenge and also
meant duplicate load and haul teams. That all changed with the recent
switch from two Caterpillar 988G loaders to one Caterpillar 990 Series
II machine. Now, the 990 Series II loads all four trucks and the gradation
balance is maintained by utilising the 6000 tonnes of live capacity
in the plant’s secondary surge pile. Explains plant manager Mark
Campbell, “There are five feeders in the reclaim tunnel under
the surge pile with coarse material stockpiled over feeders 1,2 and
3 and fine material stockpiled over feeders 4 and 5. During production,
the live inventory over each feeder is monitored by the QC department
and dig location adjusted accordingly.
“The new system works well and delivers
a more accurate fit between feed and production requirements. Given
the high throughput of this plant, good communication between QC and
the production crew is essential. The inventories of coarse and fine
feed can change quickly, and that can sometimes mean changing dig location
a number of times in the same day.”
At the pit face itself, the switch to one loader
has improved the capacity fit between primary loading and hauling. Previously,
the combined capacity of the two 988G loaders was about 1400 tonnes/h,
some 25 per cent greater than the 1000–1200 tonnes/h combined
capacity of the four trucks and thereby resulting in some waiting time
for the loaders. With its loading capacity of up to 1250 tonnes/h, the
new 990 Series II loader is now closely matched to the four trucks.
Loading times have also been reduced, with the 990 Series II requiring
four passes to load each 60-tonne capacity truck compared to the five
passes of a 988G. In all other aspects, the new loader is a good fit
for the trucks, having similar reach and a slightly wider bucket than
a 988G.
So how have these changes impacted operating
costs? Campbell estimates that the improvements have been attained in
parallel an impressive reduction in monthly loading costs, lower capital
cost, reduced depreciation as well as lower fuel and maintenance costs.
Secondary plant crusher
replacement
At the pit’s secondary plant, two old
4 1/4 cone crushers (circa 1954 and 1956) have been replaced by a single
Metso Nordberg HP 300 cone crusher. The new crusher is performing the
same duty as both of the old units, reducing 102 mm minus feed material
at an average rate of 300 tonnes/h. This change has increased both availability
and productivity, thanks to the elimination of several causes of downtime.
In addition to unscheduled repairs on the old equipment, downtime was
also caused by a plugged feed bin, plugged crushers and the manual adjustment
of crusher settings.
“The crusher change provided the opportunity
for us to rectify a long standing problem with the crusher feed system,”
says Campbell. “Before, the two crushers were fed from a surge
bin, but an awkward side feed arrangement from the bin to the crushers
caused uneven material flow and plugged material inside the bin. The
bin is still in use under the new set up, but crusher feed is now drawn
from the centre of the bin to maintain even material flow. The change
has also reduced maintenance and repair costs by the elimination of
duplicate feeder belt, crusher and take away belts. In addition, the
heavy manual work associated with cleaning out plugged crushers and
resetting them has also been eliminated, thanks to the push button hydraulic
release and reset of the new crusher.
As an added bonus, the crusher change has resulted
in an improvement in product shape, with the ratio of flat and elongated
particles being reduced by 2 per cent. Overall, downtime in the secondary
crushing system has reduced significantly and we are now monitoring
plant performance to determine the actual reduction compared to previous
years.”
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September/October
2004 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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