Gantry alternative

06 May 2008

Iron ore, mined near Sishen in the Northern Cape, South Africa, has been shipped from the Port of Saldanha since 1973 and periodic maintenance of the bulk handling machinery is essential to ensure the reliable handling of 30 million tonnes a year.

Machine Moving and Engineering's job was to position a new iron ore railroad wagon tippler in a conveyance system at the port in Saldanha Bay, about 160 km (100 miles) from Cape Town, up the west coast. Metso Minerals (South Africa), the world's largest manufacturer of crushing and screening equipment, awarded MME the contract for the three-month project.

The tippler is a mechanical device that grasps and rotates two railroad gondola cars at a time to quickly and cleanly dump their ore loads into the mouth of a hopper for conveyor transport to the nearby steel mill. Trains are 110 wagons long and the tippler operation continues until the whole train has been unloaded. The tippler is big and it is heavy.

The 110 tonne tippler cage, which is the biggest single component, was built in Gauteng and transported the 1800 km by MME to the Orex railroad terminus at Saldanha. The 22 m long, 7 m wide and 5.5 m high load made the 16 day road journey on a specialized multi-wheeled carrier accompanied by police and municipal and MME escorts. The vehicle and load's gross weight was 143 tonnes.

With the tippler cage on site alongside the hopper, MME aligned and fitted two 40 tonne end rings to the cage, thereby completing the basic structure. Further accessories attached to the main frame increased the weight to about 260 tonnes.

The challenge then was to lift the tippler assembly from this fabrication point to its point-of-use above the hopper. For the lifting operation MME used its new 500 US ton (450 US ton) capacity J&R Engineering 1000 series Lift-N-Lock gantry from the US to raise the load by 8 m.

An hydraulic jack and slide system then pushed the load over the upper vault of the civil works along specially fabricated 14 m long steel girders spanning the 11 m hopper opening over a 10 m sheer drop. Support beams were removed and the gantry lowered the structure 9 m onto its support rollers and drive mechanism. While this was happening a freak storm with 70 km/h winds hit the site but the equipment, at the time under full load, was unaffected, said MME chairman EH Seeley.

Subsequent fitting of various power, control, and minor structural components completed the tippler's fabrication.

Seeley says the method used was much cheaper than crane hire, which enabled MME to beat competitors. On the back of the success of this operation Seeley says MME has been asked to tender for larger contracts.

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