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Bucket Wheel Excavator

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Construction Equipment
Mining Equipment
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DEMAG HD800 Crawler Bucket Wheel Excavator
The bucket wheel excavator (BWE) is a machine that digs and excavates dirt continuously with the help of buckets, chutes, and a conveyor apparatus. BWEs are used for cross-pit mining and large construction projects.

First developed in England, BWEs took off in a big way in Germany and the rest of the world followed shortly thereafter. Advancements including mounting them on crawler and wheeler bases to allow them to move forward for continuous excavation developed through time. The power and complexity of BWEs mean that they can take as much as five years to build but in return they are capable of mining more than 313,908 cubic yards (240,000 m3) of earth per day.

BWEs are typically some of the largest machines on earth, weighing as much as 11,000 tons and standing hundreds of feet tall. The largest one to date is the MAN Takraf RB293 at 310 feet (94 m) tall.

They have been used for projects such as the Athabasca Oil Sands project in Alberta, as well as countless other mining and construction projects.[1]


[edit] History

[edit] Early Attempts

Bucket wheel excavators first took form as water dredgers in Europe in the mid-19th century. Dredgers were used to excavate a large volume of material in a continuous manner. The first bucket chain excavator was developed as early as 1908 by a British Engineer by the name of A.R. Grossmith. Grossmith’s bucket chain excavator was used in an ironstone field in Corby, England.

Grossmith’s attempt was not a complete success and he reduced the excavator to a shovel. Other companies set out to produce an apparatus that could effectively and continuously extract materials from the earth. It was not until fifty years after Grossmith’s first bucket chain excavator, was this fully realized.[2]

[edit] Humboldt's Development

The first successful bucket wheel excavator to be produced was by a German named Humboldt in 1919. Humboldt’s bucket wheel excavator was used at the Luise Mine in Braunkohlemwerke, Germany in 1925. The machine was such a success that other companies clamored to imitate it.  ATG Leipzig  purchased the rights to manufacture and distribute Humboldt’s machine and took it upon itself to make improvements. ATG’s involvement with bucket wheel excavators was proven a success, as it had sold as many as fifty machines by 1938.

[edit] The Evolution of BWEs

The first BWEs were powered by steam and mounted on railway tracks. Traditionally, the buckets would empty dirt into carts that could be driven on the railroads. Eventually they became electric and were driven with hydraulics and oil engines.

A German company, Backau-Wolf AG, developed the first BWE mounted on a crawler in 1928.

Another prominent manufacturer was Orenstein & Koppel. With the assistance of German company, Lubecker Maschinenbau-Gesellschaft (LMG), O&K built its first bucket wheel prototype in 1934.

O&K BWEs were consistently being revised throughout the years. In 1935, the company's bucket wheel excavator was capable of extracting 3,500 cubic yards (2,676 m3) per hour. Within two years, O&K revealed the first crawler mounted BWE, which transformed the machines. Whereas before it could take days to dismantle a large BWE, it could now travel by itself for relatively short distances.

One of the biggest BWEs to appear during this time was from Rheinische Braunkohlenwerke AG (now called RWE Rheinbraum), a company from Cologne, Germany. Their machine was the largest at the time, weighing at 6,120 tons with the ability to remove more than 5,000 cubic yards of dirt per hour.

German manufacturing companies weren’t the only ones to get on board. In the U.S., the United Electric Coal Co. (now known as Freeman Energy Co.) developed a BWE called the W3A for its Illinois-based mines in 1944. President of United Electric Coal Company, Frank Kolbe, produced six cross-pit BWEs that were built on the bases of stripping shovels and consisted of four two-crawler tracks. This revision resulted in a machine that was five times more effective than the shovels they were mounted on. The W3As were rebuilt in 1981 and are still in operation at present day.

Bucyrus-Erie began producing BWEs after the Second World War. Its models, such as the 684-WX, weighing 810 tons, were based on Kolbe’s designs. The 684-WX was used for excavating 40 million cubic yards (31 million m3) of earth for the San Luis Dam in California.

German manufacturers were still going strong in the BWE world during the 1960s. So much so, in fact, that the two major manufacturers, Krupp and O&K devised an agreement called the Bucket Wheel Export Union. The agreement meant that the two major companies would work together to establish complex and efficient BWEs for distribution throughout the world. A system of developing the names of BWEs was established as SchR—a German term which translated to “slewable crawler mounted bucket wheel excavator”.

One particularly inventive company was Mechanical Excavators, based in Los Angeles. MX built compact BWEs and mounted them on wheels or crawler tracks. Digging was achieved by an angular digging wheel which transferred material directly to a conveyor belt apparatus, removing the chute step. MX later sold its compact BWE line to Hoist & Derrick in 1982.

With the mining industry still quite lucrative in the 1980s, Bucyrus produced the 5872-WX for the Captain Mine in Illinois in 1986. It reached heights of 442 feet (135 m) with a cutting radius of 259 feet (79 m) and weighing 3,500 tons. The 5872-WX model was developed on the base of an older Marion shovel.[3]

[edit] Special Equipment

Cross-pit BWEs were first developed by Bucyrus-Erie Co. in 1954 after obtaining a license from United Electric Coal Co. Its BWE consisted of nine buckets, each capable of containing one cubic yard (0.76 m3).

Bucyrus also produced a BWE capable of removing glacial till and other hard materials. The 1050-WX which was mounted on an old stripping shovel, weighed 1,600 tons and had a cutting face capability of 1000 feet (305 m) high with its 1000 horsepower.

A crawler based BWE, the 1060WX, was developed by Bucyrus in 1967. This model was built using entirely new parts and was mounted on eight crawlers with hydraulic leveling cylinders. It was capable of crowding 57 feet (17 m) and weighed 1,735 tons in 1967.

One of the largest BWEs to be built was Demag Lauchhammer’s Schr 1900/5 28. It consisted of 12 buckets holding 2.4 cubic yards. It had tracks that were nine feet wide, with 5,230 horsepower and 12 crawler tracks that reduced ground pressure to 10.7 pounds per square inch (73.77 kPa).

The largest cross-pit BWE was built by United Electric Coal Co. It was used for the Cuba Mine in Illinois in 1959. With a digging wheel of 27 feet (8.2 m) and measuring 150 feet (46 m), it was capable of removing two million cubic yards (1.5 million m3) of earth per month.

One of the smallest BWEs was the Krupp 50. Built in 1958, it weighed a mere 52 tons and could dig 275 cubic yards (210 m3) per hour.

One of the largest BWEs used in North America was the 5872 by Bucyrus. It was used for the Captain Mine of Arch Coal Inc. in Illinois in 1986. It consisted of a 40-foot (12 m) diameter wheel, 12 buckets with 2.14 cubic yards (1.63 m3) capacity, and weighed 5,380 tons. It towered at 25 stories, or 250 feet (76.2 m) high.[4]

[edit] The “Largest Terrestrial Vehicle in Human History”

The largest BWE to date, according to the Guinness Book of World Records, is the MAN Takraf RB293. It has been listed as the “largest terrestrial vehicle in human history.” Used primarily for large surface mining projects, it stands at 310 feet (94 m) and is 722 feet (220 m) long. It can extract 8.475 million cubic feet (0.2 million m3) of dirt per day, the equivalent of an entire football field. The RB2903 weighs 31.3 million pounds (14.2 million kg) and moves at a slow pace of under 0.62 miles (1 km) per hour. It took the massive machine three weeks to travel the 14-mile (22-km) trip to the Garzweiler Mine.

The RB293 excavates dirt using a large rotator wheel that is located at the end of the arm. A series of buckets penetrate the earth and dig. The wheel is consistently turning, allowing the bucket to collect earth and dump it onto a conveyor apparatus.[5]

[edit] Features/How it Works

The first BWEs were powered by steam and mounted on railway tracks. Traditionally, the buckets would empty dirt into carts that could be driven on the railroads. Eventually they became electric and were driven with hydraulics and oil engines.

In their early days, BWEs consisted of booms that were raised and lowered by cables pulled by men. Eventually, manpower was replaced by winches that raised the cables of the excavator.

To excavate materials continuously, the BWE uses a rotating wheel that is positioned at the rear of the boom. The wheel consists of backets, also known as buckets. It can have any number of buckets, depending on the project and model. The rotating wheel penetrates the face while the boom swings from both sides and the bucket collects the dirt. As the material falls onto the conveyor belts, it is transported to further conveyors until it reaches a discharge point. The conveyors used are usually connected so they can be dismantled when the BWE needs to be transported.[6]

[edit] Common Manufacturers

[edit] References

  1. Excavators. Worsley School. 2008-09-24.
  2. Sheryn, Hinton J. An Illustrated History of Excavators. Ian Allan Publishing: Shepperton, 2000.
  3. Haddock, Keith. The Earthmover Encyclopedia. Motorbooks: St. Paul, 2003.
  4. Haddock, Keith. The Earthmover Encyclopedia. Motorbooks: St. Paul, 2003.
  5. Largest Land Vehicle. Softpedia. 2008-09-24.
  6. Sheryn, Hinton J. An Illustrated History of Excavators. Ian Allan Publishing: Shepperton, 2000.