Surface mining equipment

[Mary Mallozziberg]

An Auger machine is a large, horizontal drill, generally 3 feet or more in diameter and up to about 100 feet long. It can remove coal at a rate of more than 25 tons per minute. A bucket-wheel excavator is a continuous digging machine equipped with a broom on which is mounted a rotating wheel with buckets along its edge. The buckets scoop up material, then empty onto a conveyor leading to a spoil bank. It is best suited for removing overburden that does not require blasting. This excavator is not widely used in the United States. A bulldozer is a tractor with a movable steel blade mounted on the front. It can be used to remove overburden that needs little or no blasting. A carryall scraper (or pan scraper) is a self-loading machine, usually self-propelled, with a scraper-like retractable bottom. It is used to excavate and haul overburden. A continuous surface miner, used in some lignite mines, is equipped with crawlers, a rotating cutting head, and a conveyor. It travels over the bed, excavating a swath up to 13 feet wide and 2 feet deep. A dragline excavator removes overburden to expose the coal by means of a scoop bucket that is suspended from a long boom. The dragline digs by pulling the bucket toward the machine by means of a wire rope. A walking dragline is equipped with large outrigger platforms, or walking beams, instead of crawler tracks. It walks by the alternate movement of the walking beams. A drilling rig is used to determine the amount and type of overburden overlying a coal deposit and the extent of the deposit, to delineate major geologic features, and to drill holes for explosives to fragment the overburden for easier removal. A front-end loader is a tractor with a digging bucket mounted and operated on the front. It is often used to remove overburden in contour mining and to load coal. An hydraulic shovel excavates and loads by means of a bucket attached to a rigid arm that is hinged to a broom. A power shovel removes overburden and loads coal by means of a digging bucket mounted at the end of an arm suspended from a broom. The shovel digs by pushing the bucket forward and upward. It does not dig below the level at which it stands. A thin-seam miner resembles an auger machine but has a drum-type cutting head that cuts a rectangular cross section.