| 摘要 |
A drill bit is disclosed for drilling large diameter shafts. The drill bit comprises a main bit body having a plurality of rolling cutters rotatively mounted thereon. The cutters function to contact and disintegrate the earth formations at the bottom of the shaft thereby creating rock chips or cuttings. Water or drilling mud is pumped down the shaft and across the face of the main bit body for cooling the drill bit and for flushing the chips away from the shaft bottom. An auxiliary flow enhancer is attached beneath the main bit body for increasing the radial flow velocity of the drilling mud across the face of the bit body in order to remove the chips more efficaciously. The flow enhancer comprises a shaft mounted impeller such as a screw conveyor, a spiral brush, or a paddle-blade configuration. The shaft of each device is attached radially on the main bit body with each shaft having a drive wheel mounted thereon adjacent the bit body periphery. A radial flexible skirt extending to the hole bottom is attached beneath the main bit body on the trailing side of the flow enhancer in order to create a channel for the fluid flow. The drive wheel is adapted to contact and ride on the shaft bottom in order to drivingly rotate the conveyor, brush or paddle-blade, which in turn imparts a driving force on the drilling fluid along the flow channel.
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