| 摘要 |
A mine tool roof bit insert having a leading face inclined at a constant angle of 0 DEG -3 DEG with respect to the axis of rotation, and a frontal face with a variable relief angle decreasing with increasing radial distance from the axis from 25 DEG -55 DEG at the axis to 15 DEG -25 DEG at its radially distal edge, the rate of decrease being at least 10 DEG /in. A method of drilling a hole in a mine roof involves positioning a mine tool including the variable rake bit, insert, or the like, and rotating the bit, insert or the like at about 250-600 rpm and about 1000-8000 lb thrust for a time sufficient to drill the hole in the mine roof.
|
