Grabbing cranes are usually large machines with wide spans and high lifting heights. Not so with the Condra grabbing crane installed in February at the railhead serving Sishen Iron Ore mine near Kuruman.
Completed in December last year and delivered in January, the crane is the
final link in Sishen’s ore spillage recovery chain, using its 0,5 cubic metre clamshell grab to transfer dumps of ore spilled by the conveyor system and subsequently recovered into railway cars.
This finely engineered double-girder electric overhead travelling grabbing crane is a relatively small machine with a capacity of 1,5 tons, a span of just 7,2m and a lifting height of a fairly standard 5,7m.
Condra has previously manufactured much bigger grabbing cranes
for various applications, such as the 25 ton 30m span machine for a cement factory in Mozambique, but the Sishen specification called for a very high
degree of operational precision, resulting in the need for low-tolerance engineering of the crane clamshell grab so that it can move smoothly in
and out of the railway cars.
Working speeds are quick for the short distances involved. Cross-travel speed is 16m/min for the 7,2m end-to-end travel distance. Long travel speed
is 32m/min for a gantry length of just 20 metres. Hoist speed is 6,2m/minute.
A Condra spokesman explains that the design challenge lay in configuring a crab 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 spokesman says.
Sishen’s grabbing crane is feature rich, with variable frequency drives incorporated throughout, a remote control with optional pendant control, down lights, four red-and-green proxy lights to indicate movement clearance on the gantry and grab and a digital scale monitor on the remote control to show the exact grab load on a continual basis.
“There is a second, bigger digital scale read-out on the crane itself to transmit grab load status at a glance when not reading the remote control,”
concludes the spokeman.
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