Unusually Large Overhead Cranes

Condra has introduced additional shifts to complete a glut of unusually large overhead cranes under manufacture at the Johannesburg factory, among them three with box-girders more than 30 metres long. The cranes are for mines in Zambia, Namibia and South Africa.

On the floor at the moment are two 50-ton cranes with spans of 34 metres, and a third, high-lift, 5-ton crane with a 35-metre span. Condra is simultaneously completing manufacture of a further four 50-ton cranes with spans of around 20 metres. All six 50-tonners are for a mine in Zambia. The 5-tonner is for a Namibian mine.

Manufacturing challenges

Spans of 34 and 35 metres present unusual manufacturing challenges because of girder dimensions. Apart from length, box girders for these spans stand two metres high and just under one metre wide. “These are very big, very long, very heavy fabrications to manage,” a Condra spokesman says 

“Manufacture involves intricate welding and very careful jigging to incorporate the correct camber to counter girders’ natural tendency to sag under load.

“Girders this long are also quite delicate to manoeuvre on the shop floor. They require resource and workflow planning, and tie up use of our factory cranes.” 

End-carriage design

“End-carriage design has been important to ensure crane longevity, because the wheels must accommodate continuously changing stresses imposed by the girders as they flex under different loads. 

“Our design team paid attention to both camber and end-carriage design to ensure durability,” he adds. “Condra cranes are known for their low overall lifetime cost.” 

Single-girder

Also under manufacture for Namibian mines are three single-girder overhead cranes, two portal cranes and a jib crane. The company behind these orders is an engineering and project management consultancy with representation worldwide. This company has additionally ordered 18 electric hoists of between 2 and 25-ton capacity, and four chain blocks.

Condra and the consultancy have an association going back many years. 

Northern Cape

In South Africa’s Northern Cape province, Condra is currently commissioning two cranes at Gamsberg Phase Two, where the same consultancy contributed to metallurgy and process plant design. These, too, are big machines, one a 40/5 ton crane with 22-metre span, the other an 80/20 ton machine with 18-metre span. 

Gamsberg Phase Two is an expansion of the open-cast zinc mine near the town of Aggeneys, to double annual ore output from 4 million to 8 million tonnes.  

Further orders expected

Besides the cranes undergoing commissioning, Condra has completed delivery of two other cranes to Gamsberg Phase Two, for installation as the structural steelwork progresses. 

Condra anticipates further orders from southern and east Africa, notably Tanzania and Mozambique, where a marketing drive is currently under way.