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A contract won by Witbank company GTB Industrial Services will see Condra manufacturing a technically complex crane to service an Mpumalanga colliery’s dragline excavator.

GTB is Condra’s authorised agent for the Witbank region.

The order, won against strong competition, calls for a maintenance crane capable of working within the very constricted area of the dragline house, which contains motors and gearboxes controlling the excavating boom and dragline, and large hydraulic cylinders to control the pontoons. Space is at a premium.

Condra proved better able than its rivals to meet the complex criteria of the specification, chief of which was the requirement that the hoist be capable of separating completely from the maintenance crane, and moving away along individual roof beams as an independently operated underslung hoist to recover machine components to the central working space.

The hoist has also to be able to independently deliver loads to transport waiting outside the dragline house, should component repair within the house not be possible.

The requirement was met by designing the crane’s 12,5-ton hoist as a beam changing machine, and fitting the crane with an interlock to prevent the hoist from leaving it unless the crane is securely connected to the selected beam.

Power to the hoist is supplied via a cable drum instead of by the crane’s cable loop system.

Managing director Marc Kleiner said that Condra was able to draw upon previous experience of dragline maintenance cranes, overcoming engineering complexities to deliver a machine that allows a single hoist to carry out work that would more usually be undertaken by multiple units.

“Our design office tabled an innovative proposal that was also able to deliver more working room than our competitors,” he said.

“We can quite often pull a rabbit out of the hat when nobody else can, but we think that this time it was also our ability to manufacture within a short lead time that helped win the order.”

Lead time for the contract is just fourteen weeks.

A key component of Condra’s overall design for the crane is its manual beam interlock, which incorporates an anti-derailment limit switch to prevent hoist movement until beams are locked together.

Besides rendering impossible any movement of the hoist close to the end of the beam, this design also delivers the large tolerances needed to cope with beam movement when the dragline moves position. Dragline movement takes place by “walking” on pontoons which are repositioned for each step, tilting the machine house forward and placing stress on the structure as well as on the crane itself.

A hoist from Condra’s K-Series was chosen for the design because of its adaptability and particularly robust construction, well suited to these stresses.

Open-drum and closed-drum Condra K-Series hoists (painted green).

K-Series hoists are produced in three main configurations: foot-mounted, underslung monorail and double-rail crab. Fully covered hoists in the series provide lifting capacities to 32 tons, while open-drum units have capacities in excess of 250 tons. Features on all models include electromagnetic DC disc brakes, standard frame-size motors with parallel rotors, double-acting limit switches, solid bronze rope guides and totally enclosed splash-lubricated gearboxes. Lifting and reeving arrangements include centre-lift.

Condra will deliver the dragline maintenance crane during the month following the easing of Covid-19 quarantine restrictions.
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