What is in this article?:
- Crane combines power, size, safety
- Design considerations
Hydraulics delivers the power, precision, and reliability that make the world's largest mobile crane an awesome display of engineering.
Perhaps the most challenging design requirement of the PTC III design was that all crane parts had to be transportable within 88 standard 20- or 40-ft shipping containers with a maximum weight per container of 30.4 t. Standard containers and weights mean permits and escort vehicles are not required for truck transport.
For marine transport, each container can be handled in terminals at standard rates, and rail transport is also routine. These all add up to substantial savings in transport charges, time, and effort. In fact, transport costs of the PTC III are about half that of cranes with a comparable lifting capacity.
Much of this savings can be attributed to hydraulics because it transmits high power from relatively small, lightweight components. In addition, most parts have a double function, one during operation of the crane and one during transportation of the crane. For example, ballast blocks at the end of mast sections can be assembled to form containers.
Another requirement was to minimize assembly time. Normally, cable must be unreeled in preparation for shipping a crane, but with the PTC III, unreeling is unnecessary. This not only saves time prior to transport, but when the crane is reassembled at a new job site as well.
The upper structure of the crane's slew ring consists of two longitudinal beams, connected by quick connection pins to one transverse beam at the front. Multiple components — such as the power pack, lower ballast beam, upper ballast beam, several winches, backmast erection frame, boom stops, and operator cabin — are mounted on a longitudinal beam. All components feature modular design with quick-connection pins to enable rapid assembly and disassembly. As many components as possible are made identical so they are interchangeable.
For example, front and rear bogies are identical. Each axle is hydraulically driven to enable smooth slewing motion and free rolling. Most winches — hoist winches, topping winch, back-mast erection winch, and an auxiliary hoist winch — share a similar design to simplify assembly and disassembly procedures. Each winch has a 52-mm wire and a maximum line pull of 60 t.
Track drives for propulsion
However, one more requirement still hasn't been mentioned — the PTC III is also self propelled. Cranes often need to be moved to different locations within a job site. You might expect a crane of this size to require at least partial disassembly before being moved. But the PTC III's rigid ring construction also serves as a stable transport chassis. When the crane needs to be moved, four track drives can be deployed via massive cylinders, to lift the base off the ground. Hydraulic motors then actuate each track drive to move and steer the PTC III to a new location at the job site. Considering its size, it is easy to maneuver and can be operated in relatively tight areas.
A multitude of materials
The PTC III is a marvel of engineering encompassing more than its hydraulic system. For example, its construction required: 1000 t of steel for the structure 2100 m of electrical cable 5300 m of 50.4-mm steel cable and 2650-m of 30-mm steel cable 1500 t of steel for counterweight 1280 m of hydraulic hose 6000 l of hydraulic oil 6000 l of paint.
Henk Veulings, branch manager — mobile hydraulics, Bosch Rexroth BV, Boxtel, Netherlands, provided technical details on this application.