More than 90% of today’s goods are shipped by sea. The logistical task is nowhere near finished when the ship has reached port safely: the big job of unloading the cargo has to commence immediately. Unloading of containerized cargo routinely uses automated equipment where procedures have been honed to a science. But what happens when the ship’s hold is full of grain? Sayga Flour Mills, Sudan’s largest mill operator, masters this challenge every day.
It would take ten men nearly 4,000 days to unload the 70,000 metric tons of freight that a modern freighter can haul. Thanks to the proven technology of Buhler AG, Uzwil, Switzerland, this massive volume of grain can be offloaded in no more than five days by just a single worker — at the controls of a powerful machine.
Right into the corners
For more than ten years, Buhler, a recognized specialist in food production technology, has been enhancing the entire production chain for Sayga Flour Mills. The most recent addition is the Portalink ship unloader, with an offloading capacity of 600 metric tons of grain per hour. Four hydraulic cylinders stabilize the Portalink’s 335 tons of operating weight while it digs deep into its work.
The Portalink’s main hydraulic power unit is located above the ship unloader’s slew ring. A diesel engine delivers 317 kW to drive the three axial-piston pumps, ensuring that the grain is extracted gently from the ship’s hold. From the intake nozzle, the grain passes into the vertical conveyor shaft, forming a dense column of grain that moves steadily upward. When it reaches the level of the boom, the grain is transported via a horizontal chain conveyor to a down tube, which discharges it to waiting trucks.
Speeds of the chain conveyors are infinitely variable so that they can be matched perfectly to the product. But the Portalink needs to make an extra effort if it is to unload every last bit of cargo. Therefore, a kick cylinder aligns the vertical conveyor in the kick-in or kick-out position, letting it reach into the corners of the holds and efficiently offload all the grain. All movements are controlled by proportional valves for smooth, even motions.
Amazingly maneuverable
Space is scarce and time is money in international ports, so the Portalink must be just as flexible when its work is done. Sixteen wheels, each about 2-m in diameter, are mounted on eight axles, making this powerful mechanical stevedore — 28-m tall and 54-m long — not merely mobile, but surprisingly maneuverable as well. Bosch Rexroth Switzerland equipped this behemoth with a hydrostatic drive capable of speeds to 10 m/min.
When the Portalink is stationary, its hydraulic system controls cylinders and motors for unloading operations. When it needs to be moved, the Portalink’s HPU drives four Bosch Rexroth fixed displacement axial-piston motors, which drive the wheels.
The Portalink can be remotely controlled using a joystick — allowing it vacate its quayside slot in no time. And so the Portalink is on its way to the next massive challenge while the first ship is still weighing anchor.
This information was provided by Urs Storchenegger, of Bosch Rexroth, Switzerland. For more information on Bosch Rexroth hydraulics, visit www.boschrexroth-us.com.
