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Dragline excavation systems are heavy equipment used in civil engineering and surface mining. In civil engineering the smaller types were used for road and port construction. The larger types are used in strip-mining operations to move overburden above coal, and for tar-sand mining. Mining Draglines are amongst the largest mobile equipment (not water-borne), and can weigh in the vicinity of 2000 metric tonnes, though specimens weighing up to 13,000 metric tonnes have also been constructed.
A dragline bucket system consists of a large bucket which is suspended from a boom (a large truss-like structure) with wire ropes. The bucket is manoeuvred 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 the skillful manoeuvring of the hoist and the dragropes the bucket is controlled for various operations. A schematic of a large dragline bucket system is shown below.
In a typical cycle of excavation, the bucket is positioned above the material to be excavated. The bucket is then lowered and the dragrope is then drawn so that the bucket is dragged along the surface of the material. The bucket is then lifted by using the hoist rope. A swing operation is then performed to move the bucket to the place where the material is to be dumped. The dragrope is then released causing the bucket to tilt and empty. This is called a dump operation.
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, only a few extra metres may be reached.
Draglines in miningEdit
A large dragline system used in the open pit mining industry costs approximately $50–100 million. A typical bucket has a volume ranging from 30 to 60 cubic metres, though extremely large buckets have ranged up to 168 cubic metres. The length of the boom ranges from 45 to 100 metres. In a single cycle it can move up to 450 metric tonnes of material.
Most mining draglines are not diesel fuel powered like most other mining equipment. Their power consumption is so great that they have a direct connection to the high-voltage grid at voltages of between 6.6 to 22 kV. A typical dragline, with a 55 cubic metre bucket, can use up to 6 megawatts during normal digging operations.
The smaller machines of 10 to 50 ton class were common in smaller sand and gravel pits in the uk. These have tended to be replaced by long reach hydraulic excavators, which can now dig down to 24 m depth plus with buckets of up to 2 cu m + capacity
Most large mining draglines, movement is accomplished by "walking" using feet or pontoons, rather than Caterpillar tracks as the distances moved during operation is small, tracks are over complicated and the walking feet mechanism is far simpler as the machine sits on a base called a "Tub" during operation with the feet off the ground so as not to suffer wear and tear. Maximum speed is only at most a few hundred metres per hour since the feet must be repositioned for each step. If travelling medium distances, (about 30–100 km), a special dragline carrier can be brought in to transport the dragline. Above this distance, disassembly is generally required.
Due to cost and the time involved to build them few new machines are build, as modern hydraulic excavators have got larger they have become more common due to the relative ease of moving them about. These machines have now grown to include several makes with models of near the 1000 ton size.
Early machines were rail mounted, steam machines. Others just sat on the ground and were moved on rollers.
The primary limitations of draglines are their boom height and boom length, which limits where the dragline can dump the waste material. Another primary limitation is their dig depth, which is limited by the length of rope the dragline can utilize. Inherent with their construction, a dragline is most efficient excavating material below the level of their base. While a dragline can dig above itself, it does so inefficiently and is not suitable to load piled up material (like a rope shovel can).
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 large (1400-1800 ton) excavators, the largest in Europe at the time. Power was from internal combustion engines driving generators. One, named SUNDEW, was used in a Iron stone quarry from 1957 to 1974. After its working life at the first site in Rutland was finished it walked 13 miles to a new life at Corby; the walk took 9 weeks. The machine has been scraped but the control cabin was saved and is awaiting restoration at a museum.
Smaller draglines were also commonly used before hydraulic excavators become widespread. Firms such as Priestman, Ruston and Bucyrus who merged to became Ruston-Bucyrus in the UK, 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 Fens of Cambridgeshire, Lincolnshire and parts of Norfolk.
The coal mining dragline known as Big Muskie, owned by the Central Ohio Coal Company (a division of American Electric Power), was the world's largest mobile earth-moving machine, weighing nearly 13,000 metric tons and standing nearly 22 stories tall. It operated in Guernsey County, Ohio, in the U.S. state of Ohio from 1969 to 1991, and was powered by 13,800 volts of electricity. It was dismantled in 1999.
The dragline was invented in 1904 by John W. Page of Page Schnable Contracting for use digging the Chicago Canal. In 1912 it became the Page Engineering Company, and a walking mechanism was developed a few years later, providing draglines with mobility. 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.
In 1910 Bucyrus entered the dragline market 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.
In 1914 Harnischfeger Corporation, (established as PH Mining in 1884 by Alonzo Pawling and Henry Harnischfeger), introduced the world’s first gasoline engine-powered dragline. An Italian company, Fiorentini, produced dragline excavators from 1919 licensed by Bucyrus.
In 1939 the Marion Steam Shovel Dredge Company (established in 1880) built its first walking dragline. The company changed its name to the Marion Power Shovel Company in 1946 and was acquired by Bucyrus in 1997. In 1988 Page was acquired by the Harnischfeger Co., makers of the PH line of power shovels, draglines, and cranes. The new company became known as P&H.
Since draglines are typically large, complicated and very expensive, training new operators can be a tricky process. In the same way that flight simulators have developed to train pilots, mining simulator software has been developed to assist new operators in learning how to control the machines.
- K. Pathak, K. Dasgupta, A. Chattopadhyay, "Determination of the working zone of a dragline bucket - A graphical approach", Doncaster, The Institution of mining engineers, 1992.
- Peter Ridley, Peter Corke, "Calculation of Dragline bucket pose under gravity loading", Mechanism and machine theory, Vol. 35, 2000.
- Bucyrus International – Manufacturer of draglines
- Marion Power Shovel
- NCK Rapier
- Ransomes & Rapier
- Thomas Smith & Sons (Rodley) Ltd
Hydraulic Excavator CompetitorsEdit
- Big Muskie- now scraped
- Ace of Spades= sold off & exported
- xxxx @ St. Aidans Leeds
- SUNDEW - scrapped (Cabin Retained)
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