Design of anti-incendive conical cutting bits

Cheng, L.
Organization: Society for Mining, Metallurgy & Exploration
Pages: 6
Publication Date: Jan 1, 1990
Almost all modern cutting bits use a cemented tungsten carbide tip to provide adequate hit life against wear. Laboratory tests by the US Bureau of Mines have indicated that the number of strikes for ignition increased by a factor of three with a new non-rotating bit impacting a sandstone block when the clearance angle was increased by 10Ā°, and that carbide-tipped bits allowed more strikes before ignition than steel-tipped bits by a factor of 7 to 10. Recent field tests in an operating coal mine indicate a dramatic reduction in the frequency of frictional ignitions and improvement in hit life by using a mushroom-shaped hit cap and a larger initial clearance angle. The latter was achieved by increasing the hit attack angle. Improved hit performance through selection of the grade of tungsten-carbide is a comĀ¬promise between fracture resistance and wear resistance. A large clearance angle should he maintained by various techniques, such as a variable attack angle holder, or a reusable hit that can he reground.
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