Bucket-wheel excavator

Bucket-wheel excavators are heavy equipment used in surface mining and civil engineering. They are among the largest vehicles ever constructed, and the biggest bucket-wheel excavator ever built, the MAN Takraf RB293, is the largest terrestrial vehicle in human history.



Operation

The excavation component itself is a large rotating wheel mounted on an arm or boom. On the outer edge of the wheel is a series of scoops or buckets. As the wheel turns, the buckets remove soil or rock from the target area and carry it around to the backside of the wheel, where it falls onto a conveyor, which carries it up the arm toward the main body of the excavator. Additional conveyors then may carry it further; in some cases, several long conveyors are placed end-to-end, each supported by a large vehicular base, usually with caterpillar tracks.



Size

The largest bucket-wheel excavators in the world are used in German strip-mining operations. These tremendous earth-movers can cost over $100 million, take 5 years to assemble, require 5 people to operate, weigh more than 13,000 short tons (12,000 t), and have a daily capacity of 240,000 short tons (220,000 t) of brown coal or m³ overburden. One of them, Bagger 288, is working in stripmine Garzweiler (Tagebau Garzweiler), and five others in stripmine Hambach (among them Bagger 293). Bagger 288 (the oldest, assembly completed in 1978) is 240 metres (790 ft) long and 96 metres (310 ft) high. Until 2001 it worked in Hambach, and then drove as a giant caterpillar vehicle to Garzweiler, a distance of 22 kilometres (14 mi) through the fields, crossing a few roads, a railroad, and a river. Bagger 293 (formerly RB293, manufactured by Tenova Takraf), the heaviest among these 240,000ers, was recognised by the Guinness Book of Records (2001–2009) as the largest and heaviest land vehicle.

RB293 was the name given by former brown coal company Rheinbraun to their biggest excavator; Rheinbraun's successor RWE calls it simply Bagger 293; and manufacturer Tenova Takraf generally refers to it as an excavator of the type SRs 8000.

From http://en.wikipedia.org/