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Dragline excavator

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Dragline excavator

A dragline excavator is a heavy-duty excavator used in civil engineering and surface mining. It was invented in 1904, and presented an immediate challenge to the steam shovel and its diesel and electric powered descendant, the power shovel. Much more efficient than even the largest of the latter, it enjoyed a heyday in extreme size for most of the 20th century, first becoming challenged by more efficient rotary excavators in the 1950s, then superseded by them on the upper end from the 1970s on.

The largest ever walking dragline was Big Muskie, a Bucyrus-Erie 4250-W put online in 1969 that swung a 220 cu yd (170 m3), 325 ton capacity bucket, had a 310 feet (94 m) boom, and weighed 13,500 tons.

The largest walking dragline produced as of 2014 was Joy Global’s digital AC drive control P&H 9020XPC, which has a bucket capacity of 110–160 cu yd (84–122 m3) and boom lengths ranging from 325–425 ft (99–130 m); working weights vary between 7,539 and 8,002 tons.

Draglines fall into two broad categories: those that are based on standard, lifting cranes, and the heavy units which have to be built on-site. Most crawler cranes, with an added winch drum on the front, can act as a dragline. These units (like other cranes) are designed to be temporarily dismantled and transported over the road on flatbed trailers. Draglines used in most civil engineering are of this smaller, crane type. These are used for road construction, port construction, pond and canal dredging, and as pile driving rigs. These types are built by crane manufacturers such as Link-Belt and Hyster.

The much larger type which is erected on site is commonly used in strip-mining operations to remove overburden above coal and more recently for oil sands mining. The largest heavy draglines are among the largest mobile land machines ever built, weighing up to 13,500 tons, while the smallest and most common of the site-erected type weigh around 8,000 tons.

A dragline bucket system consists of a large bucket which is suspended from a large truss-like boom (or mast) with wire ropes. The bucket is maneuvered by means of a number of ropes and chains. The hoist rope, powered by large diesel or electric motors, supports the bucket and hoist-coupler assembly from the boom. The dragrope is used to draw the bucket assembly horizontally. By skillful maneuver of the hoist and the dragropes the bucket is controlled for various operations. A schematic of a large dragline bucket system is shown below.

The dragline was invented in 1904 by John W. Page (as a partner of the firm Page & Schnable Contracting) for use in digging the Chicago Canal. By 1912, Page realized that building draglines was more lucrative than contracting, so he created the Page Engineering Company to build draglines. Page built its first crude walking dragline in 1923. These used legs operated by rack and pinion on a separate frame that lifted the crane. The body was then pulled forward by chain on a roller track and then lowered again. Page developed the first diesel engines exclusively for dragline application in 1924. Page also invented the arched dragline bucket, a design still commonly used today by draglines from many other manufacturers, and in the 1960s pioneered an archless bucket design. With its walking mechanism badly behind that of competitor Monighan (see below), Page updated their mechanism to an eccentric drive in 1935. This much improved mechanism gave a proper elliptical motion and was used until 1988. Page modernized its draglines further with the 700 series in 1954. Page's largest dragline was the Model 757 delivered to the Obed Mine near Hinton, Alberta in 1983. It featured a 75-yard bucket on a 298-foot boom and an operating weight of 4,500 tons. In 1988, Harnischfeger Corporation (P&H Mining Equipment) purchased Page Engineering Company.

Harnischfeger Corporation was established as P&H Mining in 1884 by Alonzo Pawling and Henry Harnischfeger. In 1914, P&H introduced the world's first gasoline engine powered dragline. In 1988, Page was acquired by Harnischfeger which makes the P&H line of shovels, draglines, and cranes. P&H's largest dragline is the 9030C with a 160-yard bucket and up to a 425-foot boom.

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