| 摘要 |
<p>A rotary drill bit comprises a bit body having a leading surface (10) formed at least in part from solid infiltrated matrix material, a major part (11) of the leading surface being impregnated with abrasive particles (9) of diamond or other superhard material. There are also mounted at the leading surface a plurality of larger cutting elements (16) having cutting edges formed of superhard material which project above the surface, the larger cutting elements being so spaced as to define a substantially continuous cutting profile, so that the cutting elements in combination sweep over the whole of a bottom of a hole being drilled by the bit, during each revolution. The abrasive particles (9) normally carry out the majority of the drilling action in hard formations, but the larger cutting elements (16) serve to cut more rapidly through temporary obstructions which may be encountered in the borehole, such as a shoetrack. <IMAGE></p> |
