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Drop
Ball / Grapple / Magnet
Can one machine
do all ?
Drop Ball is one of the simplest yet
most destructive operations you can
put a crane into. Every cycle is a
shock load. Making matters worse,
people generally use liftcranes which
are undersized for the work and in
reality are two rope, friction machines
built for lift crane service.
Drop Ball is not
a continuous operation but may occupy
10 days per month. It would be great
to have a duty cycle machine that
could withstand drop ball and convert
within a few minutes to grapple.
PLM cranes of the
Netherlands has introduced such a
machine in three size ranges ranging
from the PLM 65, similar in size to
a Bucyrus Erie 88b, the PLM 80, similar
in size to a Manitowoc 3950, and the
PLM 2020 which is similar in size
to a Manitowoc 4600.
The
PLMs are built as a true duty cycle
crane for clamshell, dredging, scrap
handling and many other applications.
PLM are the only true duty cycle hydraulic
crane built in the world to-day.
Crane
Details
PLMs use three drums with two wire
ropes from each drum. One drum is
holding, one is closing and the third
is for the boom.
One
rope is right lay, the other is left
lay with two wires for holding and
two wires for closing. Using this
system, the clam is able to be lowered
to more than 100ft below the base
of the crane without spinning and
without any tagline. With this arrangement,
all four wires haul up simultaneously
to give enormous line pull.
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The line
pull on 4 ropes on a plm 80 is 64,000
lbs and on the 2020 for example is
80,000 lbs ! No multiple reeving is
necessary and your ropes are all on
one layer on the drum. This is a dream
come true for magnet work.
PLM cranes use only one layer on the
drum for holding the wire ropes, including
the boom hoist. This ensures that
wire ropes will last for more than
1000 hours of use. The drums are driven
hydraulically using Mannesman Rexroth
pumps and motors. Final drives are
Lohman.
In
order to get work done, you need horse
power. PLMs have the power needed
to attain high load speeds. The plm
80 for example uses a Cat 3508 engine
at 700 hp, more than double the power
of traditional machines.
PLM cranes have the following features:
1. high power
using cat or cummins diesel engine.
2. 5000 psi hydraulic system running
at 2500 psi.
3. high capacity hydraulic cooler,
50% of the engine horsepower.
4. no frictions, no brakes&ldots;crane
drives like an excavator.
5. oil filtering on pressure and
low pressure side.
6. closed loop hydraulics, one
pump for each function of the crane.
7. well oversized slew bearing
with large rolling elements.
8. automatic lubrication systems.
9. self-contained to retain any
spilled fluids inside the machinery
house.
10.
cast sheaves with aluminium bronze
bushings.
11.
all wire ropes contained on one layer
on the drums.
12. enhanced cab with heating,
a/c and cd player.
13. 260 fpm hauling up speed under
full load.
14.
350 fpm lowering speed.
15. cat undercarriage.
Of primary importance
is the ease of operation. With only
two joysticks and no brakes or pedals
to worry about, a totally inexperienced
person can become very proficient
in a short period of time. If you
can operate an excavator, you can
operate this crane.
Controls
and Magnet Features
The PLM is equipped with a 40kw electric
generating plant running off the diesel
engine. This is used to power the
magnet, no separate engine is required.
A selector switch is provided in the
operator's cab to select grapple mode
or magnet mode.
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In magnet
mode, a lifting block is provided
that attaches to the two closing lines
and the two
holding lines to provide 4 wire ropes
coming down to the magnet.
The holding and closing drum are locked
so that when the operator hauls up,
both drums come together and similarly
go down together. The crane is able
to operate in this mode continuously
without losing synchronizing of the
drums.
The
PLM crane is able to work continuously
in this service without damaging the
structure, slew bearing and mechanical
components and without
overheating, even if the temperature
outside is above 110 degrees.
The boom is very
heavily constructed with heavy chords
and lattice members and large section.
This is very important in drop ball
as the member stresses are low. This
greatly reduces the effect of shock
loading.
The
slew bearing on the 80 is a large
diameter ball bearing with oversized
rolling elements. The 2020 is a triple
roller element design which is also
used on the PLM 3520. This bearing
is grossly oversized for the smaller
machines and they are able to withstand
several million cycles.
PLMs
are provided with automatic greasing
for every point on the crane including
the sheaves and slew bearing.
In drop ball application,
the PLM will run with normal maintenance
for 40,000 hours. At 40,000 hours,
the pumps and drives will need to
be overhauled. The crane is then good
for another 40,000 hours. The overhauling
cost is about $200,000.00.
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After 10
years in this service, the PLM will
have a re-sale value of 80% or better
of the original purchase value.
Grapple
Mode
To switch to grapple, the mode selector
switch is switched from magnet to
grapple. This disengages the electric
generator and frees the drums for
independent operation.
The
lifting block is unhooked and the
grapple is connected, two ropes from
the holding winch and two ropes from
the closing winch.
To open the grapple, the driver shifts
the right joystick to the right. The
closing winch pays out enough line
to open the grapple and then stops.
The grapple is then lowered by moving
the joystick to the top right corner.
The grapple then hoists down open
until it comes to rest on the material
to be grabbed.
To
close the grapple, the operator brings
the joystick back to the left back
corner. The holding winch hauls in
until the the grapple is closed.
The holding and
closing winches then haul together,
40% on the holding and 60% on the
closing. Two-blocking is prevented
by drum rotation counters.
Undercarriage
In duty cycle work, the longevity
of the undercarriage is of paramount
concern.
PLM
builds a massive carbody to which
heavy side frames are bolted or pinned.
The crawlers are not retractable unless
this is an option and the configuration
is extremely tough.
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Side track components are Cat. For the 80,
the undercarriage is cat B7 design
and for the 2020, B8. This means that
you are getting the heaviest components
for the class of machine.
Track drives are lohman and the motors
are Mannesman Rexroth. These are the
best components money can buy.
Crawler chain and
track rollers are Cat exclusively
on every PLM.
Mill
Environment
Due to the
extreme dusty nature of the operation,
PLM builds in filtering for air entering
the machinery house. This ensures
that coolers, radiator and components
do not get plugged and covered in
dust. Radiator and cooler are
located for easy cleaning
The electric panel is completely enclosed
and has an ac unit to circulate and
cool the air in the panel. A heat
sink is used to take the heat out
of the a/c unit.
The
operator's cabin is equipped with
an overpressure system to keep the
cab cool and clean.
The
control system can either be electric
joysticks with plc control over the
drums or it can be hydraulic pilot
line control.
Dragline / Tag Line
For dropball
applications, PLM can provide a fourth
drum and dragline fairlead to allow
the operator to better stabilize the
magnet to aim the ball and allows
the operator to " sweep " with the
magnet.
PLM
can also provides a hydraulic tagline
just in case you need it.
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The electric
cable for the magnet is controlled
using a sliding counterweighted takeup
system on the boom.
Summary
The PLM combination
drop ball, scrap handler is a perfect
solution for steel mills. The machine
can be kept busy continuously in either
service and can take the place of
three or four machines.
The
PLM can also be used as a liftcrane
for handling coils and steel products.
It can also be fit with a clamshell
bucket for handling slag products.
With a life expectancy
of 40,000 hours before rebuild, the
PLM outlasts alternative machines
many times over. After 40,000 hours,
the PLM is re-fit with new pumps,
motors and drives and is then ready
as new.
Because
there is no multiple reeving and all
wire rope is on a single layer on
the drum, wire ropes will last a long
time. Generally the hoisting wires
last six to eight months in continuous
service and the boom hoist wire lasts
a year.
The
money that can be saved by replacing
several machines with one along with
saving the maintenance cost usually
incurred with traditional drop ball
machines will pay for a plm 80 in
short order. After 10 years of service,
your PLM will have a value very close
to what you paid for it when it was
new.
You cannot
find a tougher, more versatile and
easy to operate machine than a PLM.
Service Depots
are located in North America in Manheim,
Pennsylvania and Butler, Wisconsin.
All parts for a complete machine are
stocked in the Netherlands and most
parts are available off the shelf
in North America.
PLM
is fully dedicated to building the
toughest, highest powered, lowest
cost, lowest maintenance, easiest
to operate machines in the world with
the best components money can buy.
You cannot buy better.
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