Solving problem one:

Double bogeys fitted to the end-carriages of this overhead crane represent the key to a puzzle recently solved by Condra: how to meet customer specifications while still being able to install the completed crane in a factory with no roof access and limited headroom.

Usually, installation of a crane of this type involves lifting the disconnected end-carriages onto the gantry first, then attaching the girders to form the frame of the crane, and finally lowering the crab and hoist into position from above.

Different installation sequence

The problem in this case is there is not enough factory headroom to do that, even though Condra has designed the crane with a lowered profile to achieve maximum lifting height.

The company’s solution was to fit both 12-metre-span steel girders with bogeys at each end, four bogeys in all, and develop a different installation sequence. Fitting the girders with bogeys frees up an additional 20 millimetres of headroom through reduced wheel loading and smaller-diameter wheels on the end-carriages.

Two double-bogey end-carriages

Integral bogeys also allow placement of the girders on the factory gantry as the first step. Moving the girders apart then delivers space to allow lifting of the hoist into position between them, instead of lowering it into position from above. Closing up the girders, then linking and fixing their bogeys results a completed crane with two double-bogey end-carriages.

Condra specialists carried out this installation at the customer’s Johannesburg factory in April this year.

Solving problem two:

The unusually large rope drum on this hoist, seen here nearing completion at Condra’s Germiston factory, has been designed to hold and manage nearly 700 metres of rope, winding and unwinding it at high speed during very high lifts of 150 metres within a narrower-than-normal mineshaft.

Careful calculation of rope drum dimensions and winding sequence was the focus of the drum’s design. Drum PCD (pitch-circle-diameter) is 1600mm. A 4:2 centre-lift reeving arrangement will avoid snagging the mineshaft sides. The drum will carry 676 metres of 18mm rope, lifting and lowering loads at 30 metres per minute, almost ten times faster than lifts in standard overhead crane workshop applications.

Four ropes

Condra’s design team had to coordinate the drum width with a PCD and reeving arrangement that will precisely control and restrict lateral movement of the four ropes moving vertically as they lift or lower the load. The rope will wind onto or unwind from the drum in opposite directions as the drum rotates.

The hoist features improved drives, gearboxes and safety devices, and enhanced operation by remote control. Motor design is such that the load placed on the electric motor will remain manageable despite the non-stop nature of the work at the mineshaft.

Crab span is 6972mm with a wheelbase of 3400mm. Crab and hoist disassemble to fit into a standard 12-metre shipping container.

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