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To be competitive in today's volatile energy market, mineral developers continuously seek out innovative technologies that reduce production costs and increase profitability. Highwall mining, a system that extracts coal reserves lying beyond the reach of conventional surface mining operations, is a profitable method of coal extraction. A remotely controlled continuous miner extracts the coal and conveys it through augers or chain conveyors to the outside for stockpiling and transporting. The result is substantially less capital cost and reduced lead time.

Located in Beckley, WV, in the heart of the Appalachian coal fields, for the past 10 years Terex SHM (formerly Superior Highwall Miners) has manufactured machinery for many of the world's most successful and productive highwall mining operators. SHM works with mine operators to evaluate the coal seam, estimate production costs and, later, train personnel to operate and maintain its highwall miner.

SHM had determined that the string pot encoders, pressure switches and infrared switches used in its machines were less efficient and more costly than customers wanted. After exploring available solutions, SHM replaced these parts with magnetostrictive sensing technology.

The mining machine

The Superior highwall mining system is a self-contained, productive, cost-efficient coal mining machine. The system is operated and maintained on the surface. At no time does any crew member go underground. Like an auger, the highwall miner (HWM) works in front of a highwall. The HWM mines parallel entries, rectangular and up to 1,000 ft. deep. SHM is the first practical highwall mining system that can mine parallel entries to predetermined depths.

The machine is generally operated from a rock "bench" that is created by the removal of overburden and coal by way of contour surface mining. A minimum bench width of 42 ft. is required, with 55 ft. or more being ideal.

A typical cycle includes sumping (pushing forward) and shearing (raising or lowering the cutterhead boom to cut the entire height of the coal seam). As the cutting cycle continues, the cutterhead is progressively pushed into the coal seam for 20 ft. Then, the pushbeam transfer mechanism (PTM) inserts a 20-ft. long rectangular pushbeam into the center section of the machine between the powerhead and the cutterhead.

The configuration of the HWM is such that it is capable of mining coal seams ranging from 30 in. to 16 ft. in thickness and to depths of up to 1,000 ft. Mining this height range is accomplished through the HWM's interchangeable cutterhead modules.

When preparing to mine, the HWM, which travels on four hydraulically powered tracks, is aligned perpendicular to the exposed coal face.

The coal is cut by an electric cutterhead module attached to the powerhead assembly in the center of the machine. Here, two hydraulically powered sump cylinders, each with a 20 ft. stroke, push the powerhead forward as they provide up to 380,000 lbs. of force. Cutterhead modules are available with 24- to 44-in. dia. drums. The bits rotate, breaking the coal out of the seam. As the coal falls, it is gathered in a pan that uses two mechanical loading arms to assist in gathering the coal and propel it to the rear of the pan where it is picked up by a chain conveyor.

Near the mid-point of the cutterhead, the chain conveyor loads the coal into a pair of 18 in. dia. horizontal augers that transport the coal through the remainder of the cutterhead. Horizontal augers are located inside of the powerhead, and each is powered by 400 hp. water-cooled electric motors.