Reduction in frictional ignition due to conical coal-cutting bits. Report of Investigations/1987

The Bureau of Mines conducted laboratory tests to investigate the ease of frictional ignition with frozen (nonrotating) conical bits cutting into sandstone. The number of strikes with a new bit to obtain ignition of a combustible methane-air environment was measured. Tests were made with bits tipped with both tungsten carbide and steel at several bit attack angles (angle between bit axis and sandstone surface) and initial tip angles (included angle at the tip of the new bit). Carbide-tipped bits required more strikes for ignition than steel-tipped bits by a factor of 7 to 10.