Drop Ball / Magnet Scraphandler
Drop ball use is one of the most destructive crane applications; every cycle is a shock load. Lift cranes are
generally used and are undersized for the work. In reality they are two-rope, friction machines built for lift
crane service. They are not designed for duty cycle service and have historically incurred extreme maintenance
expenditures. PLM Cranes has introduced a crane specifically designed as a drop ball and scraphandling
machine. The PLM crane is able to work continuously in this service without damaging the structure, slew
bearing, mechanical components, and without overheating.
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.
No multiple reeving is necessary and ropes are all on one layer on the drum, which is Ideal for magnet work.
PLM cranes use only one layer on the drum for holding the wire ropes, including the boom hoist. The drums are
driven hydraulically using Mannesman Rexroth pumps and motors. Final drives are Lohman.
PLM cranes have the power necessary to attain high load speeds and include the following features:
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High power using Cat or Cummins diesel engine. Electric power also available.
5000 psi hydraulic system running at 2500 psi.
High capacity hydraulic cooler, 50% of the engine horsepower.
No frictions, no brakes, no linkage
Oil filtering on pressure and low pressure side.
Closed loop hydraulics, one pump for each function of the crane.
Oversized slew bearing with large rolling elements.
Automatic lubrication systems.
Self-contained to retain any spilled fluids inside the machinery house.
Cast steel sheaves with aluminum bronze bushings.
All wire ropes contained on one layer on the drums.
Enhanced cab with heating, A/C and CD player.
260 fpm hoisting speed under full load.
350 fpm lowering speed.
Several undercarriage options
Of primary importance is the ease of operation. PLM Cranes have no frictions, no brakes, and no foot pedals.
All functions are performed with two joystick controls, including but not limited to barge positioning.
Controls and Magnet Features
The PLM is equipped with a hydraulic drive generator set. This is used to power the magnet, no separate engine
is required. A lifting block is provided that attaches to the two holding lines coming down to the magnet. The
closing line will now be reeved through a revolving fairlead to the magnet as a drag cable.
Generator Set
The boom is 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.
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
to allow for solid footing.
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 pressurized to keep the cab cool and clean.
The cab is equipped with three panes of bulletproof glass.
The electric cable for the magnet is controlled using a sliding counterweighted take-up system on the boom.
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Parts and Service
PLM cranes use standard parts supplied by Mannesman Rexroth, Cat, Cummins, and others. There are no parts
specific to PLM machines. The part numbers included in the PLM manuals are the original equipment maker's
numbers, not PLM numbers so you can buy your parts off the shelf almost everywhere in the world. PLM stocks
parts for a complete crane of every size at their factory in the Netherlands. PLM Cranes USA has sales, parts,
and service in Granville, Illinois.