An order for a specially designed overhead crane and gantry to overcome the delivery and functionality constraints of a mine in Angola, has been placed by Consulmet Pty Ltd with crane and hoist manufacturer Condra. Manufacturing began in April.
A bespoke proposal for a product designed and manufactured in South Africa was successful against bids submitted by several competing companies based abroad.
There were two challenges. First, the mine needed to be able to position the crane over three crushing and screening areas that will be built in phases and served by several conveyors on each side. Secondly, the nature of the access roads to the site required that the 28 meter reach crane be dismantled into 12 meter containers.
The unsuccessful tenders offered a variety of designs based on gantry crane configurations limited to the first crusher only. These would have been unable to service future units due to the conveyors interrupting the portal’s railway line.
In contrast, Condra’s solution offered a double-girder overhead crane running alongside an extendable crane gantry initially erected only on the first milling area. The gantry legs will be placed between the conveyors to allow uninterrupted movement of the crane above them. The gantry will then be extended to allow the crane to serve additional milling areas as they are built.
Road transport limitations were overcome by designing the 26 meter long overhead crane beams to be spliced in two places and reducing the height of the gantry legs to match the 12 meter length of flat transports . The additional height of the completed gantry will be achieved by concrete plinths cast as part of the crushing area foundation and by steel plinths incorporating the crane beams secured below the crane beams.
The effective lifting height after commissioning will be 16 meters.
The 50 tonne crane and 29 meter long gantry crane from Consulmet Pty Ltd will initially assist in the construction of the crushing area before its role shifts to plant maintenance.
Condra will draw on decades of spliced beam experience when manufacturing this crane, which is a scaled-down replica of an 80-tonne machine installed at a mine in Rustenburg.
Each 26 meter box girder will be delivered in three fabricated sections with an integrated camber, then spliced on site in two places prior to installation. At the splices, steel plates welded to the four inner faces of the male section will provide a friction grip to enhance the strength and integrity of the beam beyond that provided by splice bolts alone. The bolt holes will be reamed and the bolts themselves machined for an exact fit that will retain camber after assembly.
“This proves once again that a tailored and customer-oriented approach will usually win out,” commented Condra’s Managing Director, Marc Kleiner.
“It would have saved the customer money by fabricating the beams entirely, but the roads leading to some African mines continue to present obstacles for the steerable carts needed for delivery,” he explained.
“In this case, no crane component will exceed the stipulated twelve meter load length of the five semi-trailer trucks that will transport everything to the site.”
To operate in the open, the 50 ton box girders are large enough to require Condra’s patented storm brakes against wind load. The anemometers will activate these safety devices in two stages, first sounding a siren at a wind speed of 50 km/h, then automatically engaging the storm brakes at a wind speed of 70 km/h, thus canceling the operation of the crane and securing the machinery against further movement. .
Weather protection covers will protect all motors and the crane will feature variable frequency drives throughout. The two 26 meter box girders of the crane will be fitted with full length catwalks. Crane control will be by radio remote control with emergency pendant.
Delivery of the 50 tonne overhead crane from Consulmet Pty Ltd is scheduled for the end of June.
Visit the Condra website: www.condra.co.za
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