Methods of working with a bucket wheel excavator

A bucket wheel excavator is employed to operate on 1) full block method, or   2) the lateral block method.

\Full Block Method

This is commonly adopted and is shown in fig. 5.26. The position of the excavator is shown by the numerals 1,2,3. Fig. 5.26A shows the full block method as practised with a bucket wheel excavator having a boom that can be pushed out and pulled back, i.e., capable of thrust forward. Fig. 5.26B shows the full block method as practised with an excavator having a bucket wheel boom that can be lifted and lowered but has no thrust movement.

Where selective winning of minerals is not necessary, full block method is employed so that the bucket wheel cuts in full blocks and in parallel operation with "cuts which are made as wide as possible. The blocks removed by giant bucket wheel excavators have a width of 45 m to 100 m. This large width of cut which can be maintained along the whole face, not only reduces the travel way for the crawlers, and consequently, the time required for this displacement, but also the shifting work required for the transport system used to dispose of the mineral. The method is therefore simple and economical.

Fig. 5.26

 

Full block method.                                                     

  Method of cutting lateral blocks

During cutting, the excavator cuts its own ramp of 1:20 into the new block and finally excavates the ramp also.

Lateral Block Method

In order to remove continuously waste partings or mineral seams of minor thickness selectively, the excavator adopts the method of cutting lateral blocks. Both bucket wheel excavators with thrust or without thrust — can dig the necessary lateral slopes. The width of the block depends, however, always on the length of bucket wheel boom (Fig, 5.26). Bucket wheel excavators with a short bucket-wheel boom are not suitable for cutting lateral blocks. Should the level of the selected seam lie high above the travel-way of the machine, and taking into account the necessary slope angle, a "super" bucket wheel would be required, i.e., with a diameter larger than that which would actually be needed for the output required.

In any case, the amount of crawler travel increases with decreasing width of blocks. The travel-way is reduced if an excavator with thrust is employed.

The excavated rock is transported by a system of belt conveyors mounted on the machine to hopper cars and thence to belt conveyors or rail wagons. The loading belt of the machine is also mounted on a boom.