Process cranes are crucial to many industries that need bulk handling of raw ...

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Georg Fischer Automotive in Herzogenburg, Austria manufactures around 35,000 tonnes of castings every year. The castings, for crankshafts, exhaust manifolds and other vehicle parts, are made from nodular cast iron, which itself is produced on-site. The cast iron for the different parts is made from raw materials in exactly defined proportions.

To this end, the foundry sends ‘recipes’ to the raw material mixing plant, which is a large hall, shrouded in dark grey dust. Inside it, 25 separate bunker areas are each piled with heaps of metal and scrap that tower metres high. There the process crane fills containers with the right quantities of different materials and transports them via a rail system to the smelting furnace. The fast high-tech crane from Stahl CraneSystems’s Austrian cranebuilding partner works both manually and fully automatically.

Just as a chef mixes their ingredients, so the crane operator mixes the different types of metal according to the foundry’s recipe. The composition needed is sent to him by the control system and shown on the display in his crane cab. For this, the crane controller communicates with the foundry’s charging system by Profibus link. In manual operation the crane operator drives to one of the numbered bunkers and picks up the bulk material by magnet, to a maximum of five tonnes per lifting movement. The operator’s display shows information on the amount of material that has been picked up and the amount still required from that particular bunker. He can release excess material from the magnet in fine steps, touch-button controlled, to give the exact proportions for his ingredients.

The casting ingredients are unloaded into a material container. The two containers for this are located in a frame carried underneath the crane bridge, so they are always close to the magnetic grab, making for short distances travelled during loading. The large size of the hall, which is 60m long, the number of bunkers, and the required charging rate of 15t/h necessitate high crane and crab speeds and therefore a robust construction. The crane bridge can be accelerated smoothly up to 63m/min by four drives. The cross travel speed is 40m/ min and the lifting speed 20m/min. An SH wire rope hoist from Stahl CraneSystems with a high FEM classification of 3m (ISO M6) serves for these exacting demands.

Apart from manual operation during the day the crane is also equipped for automatic operation at night. In this mode the crane automatically drives to the raw material bunkers required by the foundry’s recipe, picks up the required quantities and fills the material containers as specified. Depending on the composition, it takes a maximum of 20 minutes to fill a container in continuous automatic mode.

The heart of the crane is a doublegirder trolley with special headroom equipped with Stahl CraneSystems’ SH 6025 wire rope hoist with true vertical lift. A calibratable weighing system on the trolley frame is used for exact determination of the weight that has been picked up. Stahl CraneSystems helped to develop and build this demanding crane technology.

The exact position of the crane and travel carriage must be known for automatic operation. The position is determined redundantly by multiple safe absolute angle encoders to monitor the long travel, cross travel and rope drum, and by an additional laser-based distance measuring system between the crane bridge and hall wall.

For safety reasons the hall must be completely empty of people when the crane is working in automatic mode. This must be confirmed at ground level with a switch before automatic mode can be activated. The doors are locked electrically. Automatic mode is started at the height of the crane operator’s entrance, about eight metres above the hall floor.

The bunkers can only be refilled in manual mode, but it is possible to fill the cycle boxes by lift truck to a limited extent in automatic mode as well.

GRABBING GRAVEL

A gravel production company installed a double girder ‘ZP’ electric overhead travelling crane of 3x16t capacity, manufactured by Kuli. With a maximum capacity of 40t—32t payload and 8t tare weight—and a relatively short 5m span, it has a lifting height of 19m and lifting speed variable from zero to 8m/min, using frequency inversion control. It has three lifting motors, each of 30kW, and a profile girder; the design is to DIN 15018, H2B3, while the hoist cable is to FEM 3m. Platforms and guard railings are installed throughout, with a safety door for access. In operation, trucks arrive carrying loads of gravel. They discharge their loads into a hopper which at that stage is at ground level. Under operator control the crane lifts the hopper first upwards, then laterally to a position above one of seven silos, each silo being for a different grain size.

Process cranes are crucial to many industries that need bulk handling of raw materials