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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a heyday in extreme size for most of the 20th century, first becoming challenged by more efficient in the 1950s, then superseded by them on the upper end from the 1970s on.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 , 325 ton capacity bucket, had a 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 and boom lengths ranging from ; working weights vary between 7,539 and 8,002 tons. Digging big – the world’s biggest draglines Mining Technology, July 6, 2014
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 Big Muskie 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 . The bucket is maneuvered by means of a number of ropes and chains. The hoist rope, powered by large Diesel engine or , 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.
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 power shovel, draglines, and cranes. P&H's largest dragline is the 9030C with a 160-yard bucket and up to a 425-foot boom.
In 1907, Monighan's Machine Works of Chicago became interested in manufacturing draglines when local contractor John W. Page placed an order for hoisting machinery to install one. In 1908, Monighan changed its name to the Monighan Machine Company. In 1913, a Monighan engineer named Oscar Martinson invented the first walking mechanism for a dragline. The device, known as the Martinson Tractor, was installed on a Monighan dragline, creating the first walking dragline. This gave Monighan a significant advantage over other draglines and the company prospered. The cam mechanism was further improved in 1925 by eliminating the drag chains for the shoes and changing to a cam wheel running in an oval track. This gave the shoe a proper elliptical motion. The first dragline using the new mechanism was the 3-W available in 1926. So popular were these machines that the name Monighan became a generic term for dragline. In the early 1930s, Bucyrus-Erie began purchasing shares of Monighan stock with Monighan's approval. Bucyrus purchased a controlling interest and the joint company became known as Bucyrus-Monighan until the formal merger in 1946. The first walking dragline excavator in the United Kingdom was used at the Wellingborough iron quarry in 1940.
Ransomes & Rapier was founded in 1869 by four engineers to build railway equipment and other heavy works. In 1914 they started building two small steam shovels as a result of a customer request. The rope-operated crowd system they built for this was patented and later sold to Bucyrus. After WWI, demand for excavators increased and in 1924 they reached an agreement to build Marion draglines from 1 to 8 cubic yards capacity. In 1927, they built Type-7 1-yard and Type-460 1.5-yard models. The deal to build Marion machines ended in 1936. R&R began building their own designs with the Type-4120 followed by the 4140 of 3.5 cubic yards. In 1958 the Ramsomes & Rapier division was sold to Newton, Chambers & Co. of Sheffield, which was combined with their NCK Crane & Excavator division. This became NCK-Rapier. The walking dragline division of NCK-Rapier was acquired by Bucyrus in 1988.
The Marion Power Shovel Company (established in 1880) built its first walking dragline with a simple single-crank mechanism in 1939. Its largest dragline was the 8950 sold to Amax Coal Company in 1973. It featured a 150-cubic yard bucket on a 310-foot boom and weighed 7,300 tons. Marion was acquired by Bucyrus in 1997.
Bucyrus-Erie entered the dragline market in 1910 with the purchase of manufacturing rights for the Heyworth-Newman dragline excavator. Their "Class 14" dragline was introduced in 1911 as the first crawler mounted dragline. In 1912 Bucyrus helped pioneer the use of electricity as a power source for large stripping shovels and draglines used in mining. An Italian company, Fiorentini, produced dragline excavators from 1919 licensed by Bucyrus. After the merger with Monighan in 1946, Bucyrus began producing much larger machines using the Monighan walking mechanism such as the 800 ton 650-B which used a 15-yard bucket. Bucyrus' largest dragline was Big Muskie built for the Ohio Coal Company in 1969. This machine featured a 220-yard bucket on a 450-foot boom and weighed 14,500 tons. Bucyrus was itself acquired by heavy equipment and diesel engine maker, Caterpillar, in 2011. Caterpillar's largest dragline is the 8750 with a 169-yard bucket, 435-foot boom, and 8,350 ton weight.
The market for draglines began shrinking rapidly after the boom of the 1960s and 1970s which led to more mergers. P&H's acquisition of Page in 1988 along with Bucyrus' acquisition of Ransomes & Rapier in 1988 and Marion in 1997 cut the number of worldwide suppliers of heavy draglines by more than half. Today, P&H and Caterpillar are the only remaining manufacturers of large draglines.
On crane-type draglines, the bucket can also be 'thrown' by winding up to the jib and then releasing a clutch on the drag cable. This would then swing the bucket like a pendulum. Once the bucket had passed the vertical, the hoist cable would be released thus throwing the bucket. On smaller draglines, a skilled operator could make the bucket land about one-half the length of the jib further away than if it had just been dropped. On larger draglines, this is not a common practice.
Most mining draglines are not diesel-powered like most other mining equipment. Their power consumption on order of several megawatts is so great that they have a direct connection to the High voltage grid at voltages of between 6.6 and 22 kV. A typical dragline weighing 4000 to 6000 tons, with a 55-cubic-metre bucket, can use up to 6 megawatts during normal digging operations. Because of this, many (possibly apocryphal) stories have been told about the blackout-causing effects of mining draglines. For instance, there is a long-lived story that, back in the 1970s, if all seven draglines at Peak Downs Mine (a very large BHP coal mine in central Queensland, Australia) turned on simultaneously, they would Power outage all of North Queensland. However even in the 2000s if they have been shut down, they are always restarted one at a time due to the immense power requirements of startup.
In all but the smallest of draglines, movement is accomplished by "walking" using feet or pontoons, as caterpillar tracks place too much pressure on the ground, and have great difficulty under the immense weight of the dragline. Maximum speed is only at most a few metres per minute, "Maid Marian's journey becomes a 'drag'" The Daily Gleaner (10 October 2008) accessed 1 November 2008] since the feet must be repositioned for each step. "Paradise for Sidewalk Superintendents" Popular Mechanics, October 1947, p. 153-157, detailed drawings and photos of dragline operation If travelling medium distances (about 30–100 km), a special dragline carrier can be brought in to transport the dragline. Above that distance, disassembly is generally required. But mining draglines due to their reach can work a large area from one position and do not need to constantly move along the face like smaller machines.
Despite their limitations, and their extremely high capital cost, draglines remain popular with many mines, due to their reliability, and extremely low waste removal cost.
The British firm of Ransomes & Rapier produced a few diesel-electric excavators rather over 1/10th its size, the largest in Europe in the 1960s at 1400-1800 tons. One, named SUNDEW, was used in a quarry from 1957 to 1974. After its working life at the first site in Rutland wrapped it walked in 9 weeks to Corby, where it continued on till being scrapped from January to June 1987.
Smaller draglines were also commonly used before hydraulic excavators came into common use, the smaller draglines are now rarely used other than on river and gravel pit works. The small machines were of a mechanical drive with clutches. Firms such as Ruston and Bucyrus-Erie made models such as the RB10 which were popular for small building works and drainage work. Several of these can still be seen in the English The Fens of Cambridgeshire, Lincolnshire and parts of Norfolk. Ruston's are a company also associated with drainage pumping engines. Electric drive systems were only used on the larger mining machines, most modern machines use a diesel-hydraulic drive, as machines are seldom in one location long enough to justify the cost of installing a substation and supply cables.
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