| 摘要 |
<p>A rotary drill bit comprises a bit body (10), a shank (11) for connection to a drill string, a plurality of cutters (14) mounted on the bit body, and a gauge structure (20) which extends around the bit body and, in use, engages the surrounding formation forming the sides of the borehole being drilled. At least a section of the gauge structure (20) is rotatably mounted on the bit body so that, in use, the gauge section may remain substantially non-rotating in engagement with the formation while the bit body rotates relative to it. The external surface of the non-rotating gauge section (20) may be formed with longitudinal grooves (25) to permit the flow of drilling fluid past the gauge section to the annulus. Alternatively the outer surface of the gauge section may be generally cylindrical, in which case internal passages (9) are provided through the gauge section, and/or the bit body, for the flow of drilling fluid past the gauge section to the annulus. <IMAGE></p> |
