A highwall mining system has recently been developed by Mining Technologies, Inc. and is generally described in, for example, U.S. Pat. Nos. 5,112,111 and 5,261,729 to Addington et al. Highwall mining is particularly useful where the coal seam is located at a significant depth below the surface and the amount of overburden that must be removed to reach the coal makes further strip mining economically unfeasible.
The highwall mining system includes a self-propelled miner or mining machine for cutting material from the seam and a conveyor for conveying the won aggregate material from the mining machine for recovery. The conveyor is formed by a series of individual conveyor units that are coupled or interconnected in series so as to form a train. The last unit of the conveyor train is supported on a launch vehicle anchored to the bench outside the mineral seam. The launch vehicle includes an underlying belly conveyor that receives aggregate material from the last unit of the conveyor train and delivers this material to a discharge conveyor for loading a coal transportation vehicle.
In the past, the mining machine adapted for utilization in such a highwall mining system has generally comprised a continuous miner of conventional design. Such a miner is typically of the milling or drum-type that breaks coal through the picking action of bits arranged in a pattern over the surface of a cylindrical drum rotated parallel to the coal face. The drum is mounted on a boom structure or support that raises or lowers so that the rotating drum may be fed or sumped into the coal at the roof line of the cut and then moved down through the solid coal toward the mine bottom or floor of the cut. There a gathering pan, with loading arms, pulls the coal into a self-contained conveyor system for subsequent transfer of the coal from the rear of the miner.
Such a continuous mining machine is particularly useful and efficient in the mining of coal in accordance with room-and-pillar and shortwall mining methods. A conventional continuous miner does, however, have some drawbacks or disadvantages when operating within the scheme of a highwall mining system.
More specifically, as disclosed and discussed in detail in co-pending U.S. patent application Ser. No. 08/328,642, filed Oct. 25, 1994, and entitled "Continuous Miner" (the full disclosure of which is incorporated herein by reference), one important drawback relates to the provision of the gathering mechanism including independent gathering arms that operate on the gathering pan to feed cut coal into the self-contained conveyor system. This is a bulky, space consuming system that is expensive to maintain.
Another drawback relates to utilization of a cylindrical drum that cuts a rectangular opening in the seam. Such an opening leaves a straight, horizontal roof line. As coal is won from the mineral seam, the previous equilibrium of the geologic strata is upset and stresses develop. A straight horizontal roof line is generally not capable of handling or distributing these stresses efficiently and, accordingly, the roof fall risk is significantly increased. While no individuals are underground in the drive cut in the seam by the highwall mining system, such a roof fall would cause production delays and could even limit the depth of mining penetration of any particular drive. Further, a severe roof fall could actually trap the continuous miner and other equipment underground. Accordingly, all possible efforts should be made to minimize the risk of roof fall in any highwall mining operation.
A need is therefore identified for an improved, self-propelled mining apparatus capable of cutting an opening or drive in a seam having a roof line of greater structural integrity and stability.