While grabbing cranes are usually large machines with wide spans and high lifting heights, the Condra grabbing crane installed in February at the railhead serving Sishen Iron Ore Mine, near Kuruman, was designed to manoeuvre through relatively tight spaces, Condra Cranes announced in a statement last week.
Completed in December and delivered by road in January, the crane is the final link in Sishen’s ore spillage recovery chain, using its 0.5 m3 clamshell grab to transfer dumps of ore spilled by the conveyor system onto railway cars.
The double-girder electric overhead travelling grabbing crane is a relatively small machine with a capacity of 1.5 t, a span of just 7.2 m and a lifting height of a fairly standard 5.7 m.
Condra has previously manufactured much bigger grabbing cranes for various applications, including the 25 t, 30-m-span machine for a cement factory in Mozambique, but the Sishen specification called for a high degree of operational precision, resulting in the need for low-tolerance engineering of the crane clamshell grab to enable smooth movement in and around the railway cars.
Its cross-travel speed is 16 m/min for the 7.2 m end-to-end travel distance. Long travel speed is 32 m/min for a gantry length of just 20 m, while hoist speed is 6.2 m/min.
The Condra spokesperson explained in the statement that the design challenge lay in configuring a grab to operate within the relatively tight travel and lift dimensions.
“For a grabbing crane, this is a very confined area in which to work. Spans and lifting heights are usually much larger,” the spokesperson said.
He added that there was also a design requirement to enable dismantlement beyond the normal requirement for transporting abnormal loads by road. This was because shipping was scheduled to take place in the second half of December, during the road network embargo on abnormal loads, meant to facilitate free flow of peak seasonal holiday traffic.
Although the dismantling requirement was met and the crane completed on schedule, transport was still delayed to January.
The spokesperson said manufacture of the crane was relatively straightforward and standard, though the lead time of 12 weeks was tight.
He noted that one of the challenges was working with the galvanised grating required for full-length walkways on either side of the hoist. “The material tends to distort when cut, because of the internal stress caused by galvanising. Checker plate could not be used because of its propensity to collect dust.”
Sishen’s grabbing crane has multiple features, including variable-frequency drives incorporated throughout, radio remote control, with optional pendant control, downlights, four red and green proxy lights to indicate movement clearance on the gantry and grab, and a digital scale monitor on the remote device to show the exact grab load on a continuous basis.
There is also a second, bigger digital scale read-out on the crane itself to transmit grab load status at a glance.
“As far as crane technology goes, this was a very interesting crane to build, with several design and fabrication challenges,” the spokesperson commented, adding that Condra was happy to have it in its portfolio of successfully engineered bulk handling products.