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Reduction in frictional ignition due to conical coal-cutting bits
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1987
[PDF-5.60 MB]
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Description:"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. With a carbide-tipped bit, the number of strikes for ignition increased by a factor of about 3 if the bit attack angle increased by 10 degrees or if the initial tip angle decreased by 10 degrees. During use, abrasive wear of the frozen bit caused a flat surface to form at the tip of the bit, thereby decreasing the tip angle. As the attack angle increased, however, the new bit involved a smaller wear-flat area whereby abrasive wear was decreased." - NIOSHTIC-2
NIOSH no. 10005872
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