On-site
crushing means you haul away a value-added base material, not waste.
Here’s what to look for in a portable plant.
 As roads built in the 1950s and 1960s are reaching
the end of their design lives, more and more highway contractors are bidding
on jobs that require the demolition and removal of the old pavement.
Contractors can often optimize costs on these jobs by putting a
road-portable concrete/asphalt crushing plant on the job site to process the
rubble into commercially sized aggregate for use as base material or another
value-added application.
To meet the needs of this market, crushing plant
manufacturers have developed a selection of mobile plants that are easy to
transport, set up on site quickly, and can efficiently convert rubble to
base aggregate.
Many of these units can also be used to crush
aggregates, and most can be customized to fit the specific needs of the
user.
Carl Emigh, a marketing communications professional
who represents several crushing and screening companies, shared his
guidelines for contractors looking for a mobile concrete/asphalt crushing
plant with Better Roads editors.
Emigh says the crusher should be a primary impactor,
rather than a jaw or cone crusher, because of its speed and versatility.
Because of its large reduction ratios (as much as 30 to 1 in closed
circuit), an impactor normally needs no secondary crusher whether recycling
pavement or crushing limestone, unless minus 1-inch product is required. In
the latter case, a secondary impactor is generally used to relieve loading
on the primary impactor and maintain maximum volume of uninterrupted
material flow.
Secondary impactors are sometimes adapted for
primary use by opening the crusher inlet to accept larger materials, but
Emigh recommends against this because the secondary units don’t hold up well
in that application.
The hydraulic apron control system can improve
production capacity by 15 to 20%, says Emigh, with significant improvement
in control of product size.
Emigh also recommends a discharge design that moves
crushed material directly out the side of the crusher onto a conveyor in a
short, straight line for the best flow and least amount of clogging. Designs
that discharge material directly onto a belt or discharge feeder, then
through a 90-degree turn to a side discharge conveyor, are susceptible to
clogging in the chute as bulky pieces of rebar get caught in the sharp turn.
For pavement processing, a powerful electromagnetic
separator should be mounted atop the discharge conveyor to pull ferrous
tramp metals from the crushed material. It should be mounted in line with
the discharge conveyor for efficient material flow, and to prevent clogging
that can be caused by perpendicular mounting. It should also be mounted high
enough that the separated metals can be deposited directly into a truck or
dumpster below to eliminate extra handling.
Mobility is crucial, and Emigh says the selection
process has to take into account your state’s load requirements for
highways. In many states, he says, the crusher and feed hopper will have to
be transported on separate chassis to meet weight requirements; where this
is true, designs that allow the hopper to be moved from the trailer to the
crusher by means of a wheel loader and block and tackle — rather than a
crane — will save time and money.
Some designs use hydraulic jacks to support the
crushing plant until braces or blocks can be put in place. Others use
hydraulic legs that do not require any other support. The latter enable
faster setup and provide infinite, accurate height adjustment.
Power for crushing plants comes from either a diesel
engine or an electric motor. With diesel power, says Emigh, you can regulate
crusher speed according to material types and product sizes. An electric
motor runs at one constant speed, and any change requires that you shut down
and change V-belt pulley sheaves. Diesel power puts constant noise at the
operator station, and dust from crushing can damage the engine. The electric
motor is quiet and basically unaffected by dust. In recent years, says Emigh,
the trend has been toward electric-powered crushing plants run from a
generator or a power line.
 Finally, if your crushing jobs will be relatively
small — under 150 tons per hour — and you will be moving your plant fairly
often, Emigh says you should consider a compact, highly mobile
“mini-crusher.” These diesel-powered plants are designed with the impact
crusher, discharge conveyor, and magnetic separator all on one chassis. They
can be driven to the job site and set up, ready to run, in as little as 15
minutes.
When evaluating mini crushers, says Emigh, pay
careful attention to the crusher inlet size (he recommends at least
36-inches wide), discharge clearance, and closed circuit design as they
compare to a separate crusher and screen. Durability, of course, is a vital
factor: the mini-crusher should be a smaller version of the manufacturer’s
full-size primary impactors, says Emigh, not a cheaper version.
Mobile and stationary plants
 Grasan mobile and stationary wet or dry screen
plants are available in sizes up to 8 feet by 24 feet and in horizontal and
inclined configurations. Standard and custom designs are available for
applications in concrete and asphalt recycling, crushed stone, gravel,
concrete and asphalt rubble, ores, coal, coke, and slag.
Mobile units are designed for high mobility with
fast setup. The horizontal screen plant is driven into place under the feed
conveyor and the legs are blocked. No other setup procedure is required.
Plants are mounted on single-, tandem-, or triple-axle trailers. Standard
equipment includes fold-up support legs, fifth wheel kingpin hitch, dual
11:00 by 22.5 tires, air brakes, signal lights, and mud flaps.
Each mobile model has a low-profile travel height
with ample room under the discharge chutes for radial stackers or transfer
conveyors.
Body frames are fabricated with high-strength wide
flange beams. They have walkways with access ladders, and fixed or folding
support legs. Feed boxes and discharge chutes have wear liners, and the
entire chute assembly removes easily in one piece for maintenance.
Standard features include an oversize electric motor
for fast startup in cold weather. The fines-gathering conveyor and
reversible side discharge conveyor come complete with discharge chutes.
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Two cubical products per pass
 Eagle Crusher’s
portable UltraMax 1200-25CC combines closed-circuit crushing and screening
capabilities. The self-contained unit has a vibrating grizzly feeder and
double-deck screen designed to produce two aggregate or recycled products in
a single pass.
Its 32,500-pound horizontal shaft impactor has a 48-
by 34-inch feed opening. Its crushing chamber design is said to easily
handle all sizes of reinforced concrete and asphalt.
Designed for production capabilities of more than
250 tons, the unit has a hydraulic lift-leveling system that includes six
hydraulic legs for quick setup and teardown.
Power comes from a 305-horsepower diesel; a
250-horsepower electric motor with two-stage starter is also available.
Eagle Crusher says its sculptured three-bar,
solid-steel rotor is backed by the industry’s first five-year rotor
guarantee.
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Mobile unit produces two products at once
 Metso Minerals has added the Nordberg LT1213S to its
line of mobile crushing plants for contractors. The new track-mounted unit
features a single-deck screen and an extended discharge conveyor. This
combination allows the unit to produce two aggregate grades in a
single-stage crushing operation, or to operate as a normal primary crusher
with the screen removed.
The new model uses an entirely new impact crusher,
the NP1213M, developed specifically for the LT1213S and its stable mate, the
LT1213. Engineered for mobile applications, the crusher is designed to
handle blasted rock and any mineral-based demolition debris.
The LT1213S removes fines from the feed material by
means of a 3-foot, 7-inch by 13-foot, 8-inch grizzly feeder. The unit also
has an 8-cubic-yard feed hopper with hydraulic folding walls.
The unit’s TK screen allows the plant to produce two
products at once. Screen mesh sizes of 0.75 to 3 inches can be used. The
screen can be opened easily for servicing and screen-mesh changes by using
the hydraulic lowering system.
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High-capacity unit sets up in 20 minutes
 Powerscreen says its Warrior 1400 Reclaimer sets up
on site in about 20 minutes and screens up to 550 tons per hour. Its
8.87-cubic-yard hopper has a 4-foot-wide exit opening and no material
restrictions to the screen box.
The incline/horizontal belt feed hopper discharges
onto the screen box from above so the weight of the material causes it to
spread on impact and flow more equally over the screen, says Powerscreen.
The rear hopper door folds down hydraulically to allow level material feed
from the crusher discharge conveyor.
The conveyor belt is 3-feet wide and has a hydraulic
height adjustment. A one-piece side conveyor for midsize material is
designed to eliminate spillage. The oversize tail conveyor has impact bars
over its full length and raises hydraulically for easy access to change
bottom deck meshes.
Total unit’s weight is 56,438 pounds. Transportation
dimensions are 9-feet wide, 43-feet, 3-inches long, and 10-feet, 6-inches
high.
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Crushes, screens, and re-circulates
 Terex Pegson’s 1000SR Automax tracked crusher is a
combination crushing and screening plant with a feed hopper, feed controls
system, screen re-circulating system, and stockpiling conveyors all on one
chassis. With its ability to re-circulate oversize material, it can produce
up to three products using an optional third stockpiler.
The 1000SR has a travel and working width of 10
feet, 2 inches, a travel length of 56 feet, 8 inches, and a travel height of
11 feet, 4 inches.
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New reclaimer sets up fast
 Finlay Hydrascreen’s designed the 883 Reclaimer for
fast setup, high mobility, and long service life in high-volume recycling,
sand/gravel, crushed stone, topsoil, coal, and compost applications.
Design features include a heavy-duty screen with a
16- by 5-foot top deck and a 12- by 5-foot bottom deck, hydraulic drive,
heavy-duty bearings, and a 6.54-cubic-foot hopper. Screen meshes are side
tensioned on the top deck and end tensioned on the bottom deck.
The horizontal, wide-mouth apron feeder has a Hardox
steel pan with hydraulic variable-speed chain drive through a high-torque
gearbox.
Twin-motor hydraulic drive powers the oversize
conveyor, which features a 48-inch-wide, three-ply belt with impact bars at
feed-in point.
A 100-horsepower diesel engine powers the unit.
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Unique drive-system is fully hydraulic
 Komatsu’s newest mobile jaw crusher is the
69,450-pound BR380JG-1. Designed for highway construction, demolition,
quarry, and excavation work, the unit incorporates many parts from the
Komatsu excavator series, including the patented HydrauMind hydraulic
technology. The company claims to be the only OEM to offer a fully hydraulic
drive-system crusher.
Powered by a 180-horsepower diesel and
large-capacity KCJ4222 jaw crusher, the new unit has a production output of
55 to 265 tons per hour. Komatsu says a new load-presetting semi-automatic
feeder and increased crusher rotation speed have improved the unit’s
performance for crushing concrete debris, fine-crushing natural stone, and
producing large volumes of high-quality product.
Other features include what Komatsu calls the first
hydraulic protection mechanism in the world that allows the jaw crusher to
protect itself when it is clogged or jammed with metal or uncrushable
debris; the mechanism uses the locking cylinders release system to allow for
the discharge port to open fully, making it easy to remove clogged
materials.
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Full line of primary and secondary impactors
 Stedman manufactures a 10-model line of Grand Slam
horizontal shaft impactors with capacities ranging from 5 to 700 tons per
hour, and a five-model line of Mega-Slam primary/secondary horizontal shaft
impactors with capacities ranging up to 700 tons per hour.
Grand Slam models use high-chrome metallurgy to
increase the wear life of components. The impactor design incorporates both
primary and secondary aprons for maximum product control, eliminating the
need for high-maintenance grate bars and discharge screens. The impactors’
two-stage crushing action is said to produce more product on the first pass
with reduction ratios up to 30:1.
Mega-Slam primary/secondary impactors produce a
cubical product and handle feed sizes beyond the range of secondary
impactors. In some operations, the Mega-Slam can eliminate the need for
primary reduction equipment, according to Stedman. The series features solid
rotors which are contoured and computer designed for maximum efficiency. The
largest model, the Stedman Mega-Slam 6460, can deliver 550 to 700 tons per
hour with a 61- by 46-inch feed opening; it handles limestone, sand and
gravel, and asphalt applications.
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Reprinted from Better Roads Magazine
April 2004 |
