"This report describes the initial results of long-range research on bit life conducted by the Bureau of Mines. 3 Commercial bit designs- -a round-nose radial, 60 deg conical, and 90 deg conical with tungsten carbide (wc) inserts--and 5 experimental bits were tested. 4 Of the experimental bits were radial designs using polycrystalline diamond compact (pdc) inserts. The fifth was a 90 deg conical with an oversize wc insert. Bits were worn on a high-silica sandstone typical of coal mine roofs. The bits were mounted on a 34-in-diam drum section that provided a bit speed of 565 ft/min. Cutting forces were measured on a modified vertical slotter using a 3-axis force dynamometer and recorded on an fm magnetic tape recorder. Changes in cutting forces, bit weight, and airborne dust due to gradual abrasive wear and catastrophic insert failure are presented. The results show that bit life ranged from approx. 16,000 Ft for the wc round-nose radial bit to over 125,000 ft for a pdc round-nose radial. Performance, in terms of bit life, cutting forces, wear rate, frictional sparking, machine vibration, and noise, was in general best with the pdc bits, followed by the rotating wc bits, with the nonrotating wc bits (round-nose radial and locked 60 deg conical) being the worst. The results show variations in the included tip angles of new conical bits have an insignificant influence on bit performance when the effects are averaged over the life of the bit. In addition, new bits were generally found to entrain more primary respirable dust for a given cutting distance than wornout bits." - NIOSHTIC-2

NIOSHTIC no. 10006198

National Institute for Occupational Safety and Health