Minning a rich seam

20 March 2008

New double girder bridge cranes with SWF Nova electric wire rope hoists. The crane in the foreground

New double girder bridge cranes with SWF Nova electric wire rope hoists. The crane in the foreground has two 80 tonne capacity trolleys, one of which has a 10 tonne capacity auxiliary hoist. The secon

VR Steel has a product portfolio that includes shovels for scraper excavators used in the surface mining industry in South Africa, Australia and the United States. To lift and move the buckets, which can be the size of a truck, during production and refurbishment, VR Steel needed a specific crane system.

To this end Johannesburg-based independent crane builder Pro Crane Services was contracted to plan and construct the necessary cranes. In partnership with hoisting specialist SWF Krantechnik GmbH in Germany, Pro Crane Services designed seven cranes. Each was custom designed and uses the SWF Nova electric wire rope hoists.

The components, including travel motors, end carriages, electrical control system and power supply, were delivered from SWF Krantechnik, in Mannheim, Germany. Pro Crane Services took on the planning, steelwork and installation of the cranes. The most recent crane built was designed for the handling of VR Steel's large excavator shovels.

The double girder crane system has a maximum load capacity of 80 tonnes and the bridge spans 19.7 m. Two Nova double girder trolleys are fitted, each with 80 tonnes maximum load capacity and a maximum hoisting height of 10.4 m. The two hoists are also used together to move and position parts, for example, when working on the lower side of the excavator shovels.

In addition, one of the two 80 tonne trolleys has an extra 10 tonne Nova hoist to help move lighter parts into position. It has a two step hoisting speed of 5or 83 m/min.

As standard there is frequency inverter control on the trolley and hoist for smooth load movement. VR Steel specified the NovaMaster electric hoist monitoring system, that offers continual hoist monitoring and protects from overload. The crane operator can read all the hoist's relevant data, for example, current load on the hook or the remaining safe working period, directly on the control switch on a LCD display, which helps contribute to the safe operation of the crane.

According to SWF, the NovaMaster also means the two hoists can be connected via CAN Bus and the data processed for tandem lifts. It also helps protect the mechanical parts, for example, the hoist motor and brakes, because it has soft start and stop ramps. Braking and hoisting always automatically start at the lower hoisting speed, which reduces wear on the hoist motor and brake, which means less wear and lower maintenance costs.

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