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Draglines and Front Shovel Excavator

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Priestman Face Shovel

Restored Priestman face Shovel at Ruston show 2008

Face shovel at work in chalk

A Ruston No.4 Face shovel at work at GDSF 2008 digging into the local chalk

Dragline excavators are heavy equipment used in civil engineering and surface mining projects. A Variation of the same basic machine is the Front Shovel excavator also used in Civil engineering and Mining projects.

History Edit

The earliest machines were steam powered and were the first mechanical excavators used by man, in the 1800s. The steam shovel was invented by William S Otis in 1835, and ran on rails with a boom that rotated on a king post like a crane.They made possible projects like the Panama Canal, and large dams. [1] 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 shovels, draglines, and cranes.

In civil engineering the smaller types are 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. Draglines are amongst the largest mobile equipment (not water-borne), and weigh in the vicinity of 2000 metric tonnes, though specimens weighing up to 13,000 metric tonnes have also been constructed. The largest machines do not have tracks but sit on a large base called a Tub, and have large Feet on Excentric cranks to "WALK" on, hence the term walking dragline.

At one time it was thought that Hydraulic Mining Excavators would make them redundant, due to high costs. But the world demand for minerals and coal as well as oil from Tar Sands has lead to a renewed interest in them. In the UK previously redundant machines were scraped, But recently 2 machines that have finished working for UK Coal (formerly British Coal Open Cast Division) have been sold and will be striped down and shipped abroad.

Front Shovel ExcavatorsEdit

RB 110 Bucket

The Bucket on the RB 110 at the Vintage Excavator Trusts Site at Threlkeld in Cumbria. This is the largest working "Face Shovel" in preservation in the UK

RB110 Excavtor side VET 2007

110 RB at the VET site at Threlkeld, Cumbria

Also called a "Face Shovel" These have a shorter boom fitted with a large bucket facing away from the machine on a Arm mounted in a pivot in the boom. The bucket arm is pulled back to drive the bucket into the loose rock or Coal face then lifted up by the boom and the machine then swings and dumps the load usually into a large Dump truck sat at the side by opening the back of the bucket which is a hinged flap on the back, then swinging back and digging in again. usually the trucks are sized such that 3 or for buckets fill them.

UK Preserved MachinesEdit

Lots of small machines which had been abandoned have now been restored by enthusiasts.

The largest Machine is near LEEDS, at the side of a former open cast site, The ST Aidans machine is not working, but is open to view several times a year. This is a Bucyrus-Erie 1150-B fitted with a 22-Yd bucket, the machine weighs in at 1220 tons. It was originally owned by British Coal but passed to UK Coal, when British Coal's opencast operations were sold off. This machine for all it size only has a bucket that is 1/10th the size of what was the worlds biggest machine, Big Muskie, in the USA.

The Vintage Excavator Trust has a collection of machines at it site in Threlkeld, nr Keswick in Cumbria. The Largest being a Ruston-Bucyrus RB110 Face shovel, and An NCK 605 Front shovel. They also have the Dipper and 5.3 mcu (7yd) bucket from a RB 150 that was operating in South Wale's

The RB 110 is a 154 ton Electric face shovel, running off a large 3.3 Kv supply from a generator set. It as moved to The VET site at Threlkeld, Cumbria in May 2006 from Castle Cements Ribblesdale quarry, by Heanor Haulage Ltd, a firm that specialises in moving oversize loads such as excavators.

Operation Edit

Priestman offset dragline

A Priestman offset dragline from Adrian Pattersons collection on display at the Mining Museum in Cumbria. Design for digging and maintaining drainage ditches

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 hoistrope, 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 skillfull manoeuvre of the hoist and the dragropes the bucket is controlled for various operations.

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

Walking Dragline at St Aidans Leeds

Odd Ball a preserved Walking Dragline at a former open cast mine, at St. Aidans near Leeds

A large dragline system used in the open pit(cast) mining industry costs approximately US$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.[1] 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 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. Because of this, many (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 of the Peak Downs (a very large coal mine in central Queensland, Australia) draglines turned simultaneously, they would black out all of North Queensland.

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 difficultly under the immense weight of the dragline. 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.

Researchers at CSIRO in Australia have a long-term research project into automating draglines and have moved over 250,000 tonnes of overburden under computer control.[1]

LimitationsEdit

Cab at St Aidans Leeds

View from the cab of Odd Ball the dragline at St Aidans open cast site nr Leeds

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 overburden (waste) removal cost.

Draglines have different cutting sequences. The first is the side cast method using offset benches; this involves throwing the overburden sideways onto blasted material to make a bench. The second is a key pass. This pass cuts a key at the toe of the new highwall and also shifts the bench further towards the low-wall. This may also require a chop pass if the wall is blocky. A chop pass involves the bucket being dropped down onto an angled highwall to scale the surface. The next sequence is the slowest operation, the blocks pass. However, this pass moves most of the material. It involves using the key to access to bottom of the material to lift it up to spoil or to an elevated bench level. The final cut if required is a pull back, pulling material back further to the low-wall side.

ExamplesEdit

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 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.

Smaller draglines were also commonly used before hydraulic machines become widespread. Firms such as Ruston and Bucyrus 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, usually associated with drainage pumping engines.

UK Built / Operated Machines Edit

UK Largest Machine (and most Famous)Edit

This was a Bucyrus-Erie 1550-W fitted with a 65yd bucket on a 265 ft boom, and capable of digging to a depth of 150 ft. Was called "Big Geordie" and worked at the Radar North opencast site near Newcastle, England from 1969 to 1976 for Derek Crouch Mining, Then at the Butterwell site of Taylor Woodrow Ltd from 1977 till 1991, when coaling was completed. The machine was scrapped as world demand for machines was such that stripping it down was not viable and the UK market had moved to the new Large Hydraulic machines, as most sites were smaller and manoeuvrability was an issue.

Worlds Largest DraglineEdit

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.[2] It operated in Guernsey County, in the U.S. state of Ohio from 1969 to 1991, and was powered by 13,800 volts of electricity. It was dismantled (scrapped) in 1999.[3]

Scale ModelsEdit

Dragline working model DSC01209

A Working scale model of a walking dragline

There are several accurate Engineering Models of large excavators often demonstrated at shows in the Model engineering display tent. Some of the operating companies have commissioned versions for the site or head office.

See alsoEdit

ReferencesEdit

  1. http://www.ict.csiro.au/page.php?did=150

External linksEdit

Smallwikipedialogo This page uses some content from Wikipedia. The original article was at Dragline excavators. The list of authors can be seen in the page history. As with Tractor & Construction Plant Wiki, the text of Wikipedia is available under the Creative Commons by Attribution License and/or GNU Free Documentation License. Please check page history for when the original article was copied to Wikia

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