| 摘要 |
<p>Knife edged cutting members on the conical face and cylindrical side of a rotating drilling head shear slivers of rock by exceeding the tensile strength of the formation being penetrated. Fluid such as air, water, or drilling mud, injected through ports in debris channels between cutting members direct such slivers and other debris upwardly for scouring the bottom of the hole to minimize debris interference with knife edge action. Cutting members are made from a very hard composition such as titanium diboride, boron carbide, boron, and/or mixtures of such hard materials. Guiding members having greater toughness than the cutting members may account for less than one fourth of the wearing surface abraded by the bottom of the hole. Near the bottommost tip, there are fewer cutting and guiding members than at the upper zone of the conical portion.</p> |
