Open Cut » Overburden Removal
The goal of this project was to investigate the way the bucket connection points could be varied to reduce the rope load variations, increase the dumpability of the bucket, and identify an approach for retrofitting an existing bucket and/or developing a new bucket for use with an 8050 UDD machine.
Project Goal - Bucket Design for Parallel/Udd Rigs
Bucket design is particularly relevant to the Parallel/UDD rigs for several reasons.
- The relative rope loads for the rigs are almost completely determined by the position of the pivot points (drag, front and rear hoist) on the bucket, the mass distribution of the bucket and payload, and the preferred carry angle. The relative rope loads have implications for rope life. Also, when combined with the drive capabilities, the relative rope loads control the hoist times for the dragline.
- The goal of reducing the bucket/rigging mass is comprehensively interlinked with the design of the bucket. For example, attaching the rear rope to the centre rear of the bucket may allow most of the hoist chains, spreader bar, and two host trunnions to be removed, but the new connection point will require additional structure, a new trunnion link, some hoist chain and so on - the calculation of the nett mass removed from rigging is not simple.
- The size of the dumping envelope can be increased or reduced by pivot point movements.
It can be seen from these points that in many respects the bucket design either dictates the sizing and capacity of the Parallel/UDD design, or can be used to optimise the performance of a given dragline setup.
- A conventional bucket with standard connection points gives acceptable rope loads and hoist times. Rigging mass reduction would be ~4 tonnes. Arch will need strengthening with a small mass increase.
- Simply moving the rear rope connection to the back wall (reduce rigging by further 5 tonnes) causes higher rope loads and unacceptably slow hoist times. Arch can be modified to compensate (leant forward) but mass implications are unknown.
- High front rope loads during hoisting are reduced by carrying the bucket at a lower carry angle. The carry angle during hoisting should be reduced as far as possible without decreasing the payload.
- The rear rope has high loads during dumping, typically higher than the front rope load during hoisting.
- Hoist times for Parallel/UDD rigs are faster than for conventional rig (2-4 sec in 24sec)
- Scoop as built for conventional rig would be unacceptable, but with modified hoist trunnions could be ideal.
- Dump zone needs to be determined and cues given to operator. Height of rear trunnion is the main control of dumpability.
- If steel mass reductions of 10 tonnes are achieved, filling efficiency issues will be critical. Practically, an 8200/1570 sized bucket will be needed which can be filled by an 8050/1370 as fast as the 8200/1570 would fill it.