In , after almost years of trial and error, a commercially successful revolving-wheel cutter for undercutting the coal seam was introduced in England. This first powered cutting tool was soon improved by introduction of compressed air as a power source in place of steam. Later, electricity was used. The longwall cutter was introduced in Originally driven by compressed air and later electrified, it could begin at one end of a long face the vertical, exposed cross section of a seam of coal and cut continuously to the other.
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The conventional mining techniques described above, made up of the cyclic operations of cutting, drilling, blasting , and loading, developed in association with room-and-pillar mining. The oldest of the basic underground methods, room-and-pillar mining grew naturally out of the need to recover more coal as mining operations became deeper and more expensive.
During the late s, conventional techniques began to be replaced by single machines, known as continuous miners, that broke off the coal from the seam and transferred it back to the haulage system. The Joy Ripper was the first continuous miner applicable to the room-and-pillar method. The other principal method of modern mining, longwall mining, had been introduced as early as the 17th century and had found general use by the 19th century, but it had long been less productive than room-and-pillar mining. Pulled across the face of the coal and guided by a pipe on the face side of a segmented conveyor , the plow carved a gash off the bottom of the seam.
The conveyor snaked against the face behind the advancing plow to catch the coal that chipped off from above the gash. Substantially reducing the labour required at the coal face except that needed to install roof support , the Loebbe system quickly became popular in Germany, France, and the Low Countries. The plow itself had limited application in British mines, but the power-advanced segmented conveyor became a fundamental part of equipment there, and in a simple continuous machine called the shearer was introduced. Pulled along the face astride the conveyor, the shearer bore a series of disks fitted with picks on their perimeters and mounted on a shaft perpendicular to the face.
The revolving disks cut a slice from the coal face as the machine was pulled along, and a plow behind the machine cleaned up any coal that dropped between the face and the conveyor. The technique of supporting the roof by rock bolting became common in the late s and did much to provide an unobstructed working area for room-and-pillar mining, but it was a laborious and slow operation that prevented longwall mining from realizing its potential.
In the late s, however, powered, self-advancing roof supports were introduced by the British. Individually or in groups, these supports, attached to the conveyor, could be hydraulically lowered, advanced, and reset against the roof, thus providing a prop-free area for equipment between the coal face and the first row of jacks and a canopied pathway for miners between the first and second rows of jacks.
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In the first shaft mines, coal was loaded into baskets that were carried on the backs of men or women or loaded on wooden sledges or trams that were then pushed or hauled through the main haulage roadway to the shaft bottom to be hung on hoisting ropes or chains. In drift and slope mines, the coal was brought directly to the surface by these and similar methods. Sledges were pulled first by men and later by animals, including mules, horses, oxen, and even dogs and goats. Steam locomotives designed by Richard Trevithick were used in the fields of South Wales and Tyne and later in Pennsylvania and West Virginia , but they created too much smoke.
Compressed-air locomotives, which appeared in the s, proved expensive to operate. Electric locomotives, introduced in , rapidly became popular, but mules and horses were still working in some mines as late as the s. The loading by hand of broken coal into railcars was made obsolete early in the 20th century by mobile loaders. The Stanley Header, the first coal-loading machine used in the United States, was developed in England and tested in Colorado in Others were developed, but few progressed beyond the prototype stage until the Joy machine was introduced in Employing the gathering-arm principle, the Joy machine provided the pattern for future successful mobile loaders.
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After the introduction in of electric-powered, rubber-tired shuttle cars designed to carry coal from the loading machine to the elevator, mobile loading and haulage rapidly supplanted track haulage at the face of room-and-pillar mines. In a conveyor belt was successfully used in an anthracite mine in central Pennsylvania to carry coal from a group of room conveyors to a string of cars at the mine entry. By the s belts had almost completely replaced railcars for intermediate haulage.
The history of coal preparation begins in the 19th century, with the adaptation of mineral-processing methods used for enriching metallic ores from their associated impurities. In the early years, larger pieces of coal were simply handpicked from pieces composed predominantly of mineral matter.
Washing with mechanical devices to separate the coal from associated rocks on the basis of their density differences began during the s. At first, coal preparation was necessitated by the demand for higher heating values; another demand was for such special purposes as metallurgical coke for steelmaking.
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In recent years, as concern has grown over the emission of sulfur dioxide in the flue gases of power plants, coal preparation has taken on greater importance as a measure to remove atmospheric pollutants. You are using an outdated browser. Please upgrade your browser to improve your experience and security. Coal mining. Article Media. Info Print Print. Table Of Contents. Submit Feedback. Thank you for your feedback. Albert Evans.
Most of the coal was shipped south to California by boat. In January , the sternwheel, steamer Chehalis was pulling a barge containing 18 wooden coal cars across Lake Washington.meskatisifca.gq
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As the Chehalis was rounding the northwest point of Mercer Island, a gale blowing from the south struck the steamer and barge. The wind tipped the barge and sent the 18 coal cars plunging to the bottom of the lake.
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The wooden coal cars remain where they sank, well preserved in the cold 45 degree water, most of them upright and still carrying their cargo of coal. The coal cars were located by Underwater Atmospheric Systems, Inc. Robert Mester using side scan sonar, and reported to the Washington Office of Historic Preservation as a submerged cultural resource.
The coal cars are presently located south of the Evergreen Point Bridge in the middle of Lake Washington. Bottom depth is feet. There is a main group of approximately 10 coal cars, with the remaining cars scattered around the main group. Most of the cars sit upright on the bottom and most of them are still loaded with coal.
The bottom of the lake around the cars is littered with pieces of coal. Most of the cars are substantially intact, although many have their wheels buried in the soft silty bottom. The Sinking In January , the sternwheel, steamer Chehalis was pulling a barge containing 18 wooden coal cars across Lake Washington.