Dropball / Grapple / Magnet

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.


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.

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.


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.

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.

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.

The electric cable for the magnet is controlled using a sliding counterweighted takeup system on the boom.

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.