Structure

A bucket wheel excavator (BWE) consists of a superstructure to which several more components are fixed.
The bucket wheel from which the machines get their name is a large, round wheel with a configuration of scoops which is fixed to a boom and is capable of rotating. Material picked up by the cutting wheel is transferred back along the boom. In early cell-type bucket wheels, the material was transferred through a chute leading from each bucket, while newer cell-less and semi-cell designs use a stationary chute through which all of the buckets discharge.
A discharge boom receives material through the superstructure from the cutting boom and carries it away from the machine, frequently to an external conveyor system.
A counterweight boom balances the cutting boom and is cantilevered either on the lower part of the superstructure (in the case of compact BWEs) or the upper part (in the case of mid-size C-frame BWEs). In the larger BWEs, all three booms are supported by cables running across towers at the top of the superstructure.
Beneath the superstructure lay the movement systems. On older models these would be rails for the machine to travel along, but newer BWEs are frequently equipped with crawlers, which grant them increased flexibility of motion.
To allow it to complete its duties, the superstructure of a BWE is capable of rotating about a vertical axis (slewing). The cutting boom can be tilted up and down (hoisting). The speeds of these operations are on the orders of 30 m/min and 5 m/min, respectively. Slewing is driven by large gears, while hoisting generally makes use of a cable system

Size

The scale of BWEs varies significantly and is dependent on the intended application. Compact BWEs designed by ThyssenKrupp may have boom lengths as small as 6m, weigh 50 tons, and move 100 m³/h of earth. Their larger models reach boom lengths of 80m, weigh 13,000 tons, and move 12,500 m³/h. The largest BWE ever constructed is TAKRAF's Bagger 293, which weighs 14,200 tonnes and is capable of moving 240,000 cubic metres of overburden every day. Excavations of 380,000 cubic metres per day have been recorded. The BWEs used in the United States tend to be smaller than those constructed in Germany.

Operation

BWEs are used for continuous overburden removal in surface mining applications. They use their cutting wheels to strip away a section of earth (the working block) dictated by the size of the excavator. Through hoisting, the working block can include area both above and below the level of the machine (the bench level). By slewing, the excavator can reach through a horizontal range.
The overburden is then delivered to the discharge boom, which transfers the cut earth to another machine for transfer to a spreader. This may be a fixed belt conveyor system or a mobile conveyor with crawlers similar to those found on the BWE. Mobile conveyors permanently attached to the excavator take the burden of directing the material off of the operator. The overburden can also be transferred directly to cross-pit Spreader, which reaches across the pit and scatters overburden at the dumping ground.

Applications

Bucket wheel excavators and bucket chain excavators take jobs that were previously accomplished by rope shovels and draglines. They have been replaced in most applications by hydraulic excavators, but still remain in use for very large-scale operations, where they can be used for the transfer of loose materials or the excavation of soft to semi-hard overburden