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Stripping Shovel

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Mining Equipment
Stripping Shovel Parked Next To Bulldozer
Stripping Shovels
are machines used to strip away the overburden that appears on the surface of minerals and hard materials that are being extracted for mining purposes. They are commonly used in surface mines and quarries to uncover minerals such as coal, ironstone, and limestone.

Stripping shovels are among some of the heaviest mobile machines in the world. The largest was the Captain Shovel, weighing 15,000 tons, until it was beaten out by another Bucyrus-made shovel weighing 18,000 tons. Very few shovels are present in today’s mines due to different mining methods that no longer require them.

Contents

[edit] History

[edit] The First Stripping Shovel

Mining, along with agriculture, is one of the oldest applications for man. It can be traced as early as 450,000 years ago when miners extracted non-metallics from stone. Tools for mining have been very primitive, even up until the last two hundred years, relying on the brute force of man.[1]

The first stripping shovels took the form of a railroad shovel, built by a company named Vulcan in 1899. The steam-operated shovel was fitted with a long boom. Success was limited because of the restricted motion of the swinging boom.

[edit] Shovel Advancements

Shovels that could perform a full 360 degree revolution appeared in 1910. Again, these were mounted on rails, relied on steam, and were heavy enough to require two sets of railroad tracks to hold their weight.

By this time, shovel companies were forming all over the U.S. The Marion Power Shovel Co., the Bucyrus-Erie Co. (now Bucryus International) were well-known competitors in the shovel industry. Outside of the U.S., Whitaker, Grossmith, and Taylor & Hubbard were formed. Marion produced the first 250 steam stripping shovel in 1911. Bucyrus, a company that would engage in an intense rivalry with Marion, produced its first stripping shovel less than a year later.[2]

[edit] Bucyrus vs. Marion

By the 1920s, stripping shovels had abandoned their railroad tracks and adopted crawler tracks. This was a slow transition because crawlers were somewhat more expensive, but once they made an appearance and their efficiency was demonstrated, many manufacturers never went back to the old railroad mounted shovels. Typically, stripping shovel were mounted on eight crawler tracks, but this could vary. The first company to try this was Bucyrus in 1925 when it placed its 320-B on a set of crawler tracks to make it more mobile.

Being the rival company, Marion did the same and placed its Model 350 with an eight-cubic yard (6.1-m3) dipper on a set of crawler tracks to produce the larger version of stripping shovels on crawlers.

Bucyrus noticed drawbacks to this method. The mounting of such a large piece of equipment was almost too much for the crawler tracks to support, so Bucyrus used a power-driven screw system that consisted of two legs to take the stress off the two crawlers while the other two were supporting the equalizing beam. It made for an impressive invention that served well when traveling on terrain that was not consistent.

Marion, once again recognizing the competition, invented its own hydraulic system that attached two crawlers to a vertical hydraulic cylinder. The effect leveled the machine with the help of a pendulum system. This system was so effective that by the 1930s, all manufacturers had adopted it for their stripping shovels. It also solidified the configuration of eight crawler tracks as the industry standard.

[edit] More Powerful Shovels

Another change that occurred involved the power from the motor. Previously, it was transferred via a pintle into spur gears. By the end of the First World War, stripping shovels were operated by propel motors that were fitted onto each individual crawler set. Shovels could contain as many as eight motors for the eight crawler sets it possessed.

Once run by steam, manufacturers embraced the electric motors that appeared in during this time. Some shovels were too large to for the traditional electric motor and implementing it ran the risk of burning out the motor and stalling the machine’s progress. Marion and Bucyrus sought the same solution, which was the Ward-Leonard Control System. Ward-Leonard utilized an AC motor generator set to transfer the power to a DC motor. It first appeared on Bucyrus' model 225-B and Marion’s model 300-E. Upon introduction from these two companies, the Ward-Leonard system became standard within the industry.

The end of World War II led to the standard equipment that is seen today. Modern buckets with a 40-cubic yard (31-m3) capacity made the machines able to tackle more in a short amount of time.[3]

[edit] Rivalries

The “era of super strippers” took place in 1965 when rivals Marion and Bucyrus were in constant competition with one another for the biggest shovels. Marion produced the Model 5760 with a 60-cubic yard (46-m3) dipper, capable of stripping a face of more than 100 feet (30.5 m) high.

Bucryus produced the 3850-B with buckets as large as 140-cubic yard (107-m3) capacity. The models, which were produced from 1965-67, broke records but did not compare to the Gem and the Silver Spade.

The Gem was 170 feet (52 m) with a dipper handle of 102 feet (31 m). It was replaced with the Silver Spade, which stood at 220 feet (67 m) tall and had a boom of 200 feet (61 m). The spade had four crawler assemblies, each measuring at 34 feet (10 m) long and eight feet (2.4 m) high.[4]

Marion responded with the Marion 6360—the Captain shovel—which was used at the Captain Mine in Illinois. It weighed 15,000 tons with a bucket capacity of 180 cubic yards (138 m3) and a crowd handle of 102 feet (31 m). The horsepower for this machine reached a total of 33,000. It beat out the Bucyrus model; however, Marion was soon acquired by Bucyrus before it produced its final stripping shovel, the 5900 model.[5]

[edit] The Largest Stripping Shovel

The largest stripping shovel was produced by Bucyrus for Peabody Coal Co.'s Sinclair Mine located in western Kentucky. It weighed 18,000,000 pounds (8,164,663 kg), towered at 460 feet (140 m) and was capable of removing 100,000 cubic yards (76,455 m3) of material and uncovering 14,000 tons of minerals per day. It was the largest self-powered, mobile land machine. It was shipped to the Kentucky mine site using 300 railroad cars. It is three times larger than the next largest shovel and is as tall as a 20-story building

The King shovel has 52 electric motors, which have horsepower ranging from ¼ to 3000. The shovel’s dipper is “bigger than a two-car garage” and can “uncover enough coal to heat 7,500 average homes one month or 1,500 homes for an entire heating season”. Additionally, the width of the shovel is comparable to an eight-lane highway. It took two years to design and construct a shovel of this magnitude.[6]

[edit] Decline

A decline in the production of stripping shovels occurred during the 1980s due to the rise in coal output in the western part of the U.S. Coal had very little overburden and it was no longer necessary for it to be stripped using expensive stripping shovels.

[edit] Features/How it Works

Stripping shovels are similar to shovels except they don’t require a separate apparatus to collect the materials. To remove the surface material, stripping shovels are positioned above the mineral and move forward slowly as they strip away the surface. They dig relatively long strips of overburden at a time for removal.

Because of the complexity and the expenses involved in producing stripping shovels, very few manufacturers have endeavored to make them.

[edit] Common Manufacturers

[edit] References

  1. Kennedy, Bruce. et al. Surface Mining. SME: 1990.
  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. History of a Strip Mining Giant. Fast Pitch Press. 2008-09-25.
  5. Sheryn, Hinton J. An Illustrated History of Excavators. Ian Allan Publishing: Shepperton, 2000.
  6. How to Tear Down a Skyscraper. Science and Mechanics. 2008-09-25.