| 摘要 |
<p>An earth boring bit having a cone rotatably secured to a cantilevered bearing shaft and a nozzle that discharges a jet stream of fluid having a high velocity core and a lower velocity skirt. The high velocity core is fully contained in a space bounded by the backside of the cone, bit leg, borehole wall and a radial plane tangent to the tips of the heel teeth and intermittently strikes the exposed ends of the erosion and wear resistant teeth when the cone rotates the teeth on the trailing side in and out of the jet stream. Less than half of the fluid in the lower velocity skirt strikes the surface of the cone, while the remainder continues on a path toward the wall and the borehole bottom. The centerline of the high velocity core is aimed no lower than the corner of the borehole. The jet stream is confined on more than about 75 percent of its periphery by either the cone, bit leg or the wall of the borehole, reducing undesirable recirculation and turbulence and opening a large return flow area unobstructed by a high velocity jet stream.</p> |
