Proceedings of the 4th Conference on Ground Control for Midwestern U. S. Coal Mines, November 2-4, 1992, Mt. Vernon, Illinois. Chugh YP, Beasley G, eds. Carbondale, IL: Southern Illinois University, 1992 Nov; :291-314
Recently developed polycrystalline diamond compact (PDC) roof-bolt drill bits were tested by the U.S. Bureau of Mines in nine coal mines in the Utah, Pennsylvania, and West Virginia Coal fields. Roof rock in these mines consisted of shale, silty shale, silty sandstone, mudstone, and sandstone. Compressive strengths of the rock varied from 6,000 to 32, 4000 psi, and the quartz content varied from 10 to 85 pct. Results from the study show that PDC bits have 200 to 600 times greater life than tungsten carbide-cobalt alloy (WC-Co) bits, thereby reducing drill bit cost by more than 60 pct. In test mines containing shale, limestone, and dolomite as roof rock, PDC bit life ranged from 4,500 to 6,000 ft versus an average of 10 ft for a WC-Co bit. In mines where the roof rock contained 1 or 2 ft of shale, overlaid by hard sandstone, PDC bit life averaged more than 1,000 ft. For optimal PDC bit life, it was determined that drill operators must maintain water pressure at 200 to 300 psi, rotational speed at 450-500 rpm, and thrust below 3,000 lb. PDC bits have the .potential to reduce the coal industry's bit cost by several million dollars per year. In addition, by reducing the number of operations a worker must perform, PDC bits may significantly reduce the number of non-fatal accidents that result in lost-time injuries associated with roof-drilling operations.
Proceedings of the 4th Conference on Ground Control for Midwestern U. S. Coal Mines, November 2-4, 1992, Mt. Vernon, Illinois