Rotary drill bit with improved cutter and seal protection

Abstract

A rotary cone drill bit for forming a borehole having a body with an underside and an upper end portion adapted for connection to a drill string. The drill bit rotates around a central axis of the body. A number of angularly-spaced arms are integrally formed with the body and depend therefrom. Each arm has an inside surface with a spindle connected thereto and an outer shirttail surface. Each spindle projects generally downwardly and inwardly with respect to the central axis, has a generally cylindrical upper end portion connected to the inside surface, and has an inner sealing surface within the upper end portion. A number of rotary cone cutters equal to the number of arms are each mounted on one of the spindles. Each of the cutters includes an internal generally cylindrical wall defining a cavity for receiving the spindle, a gap with a generally cylindrical first portion defined between the spindle and cavity wall, an outer sealing surface in the cavity wall concentric with the inner sealing surface, and a seal element spanning the gap and sealing between the inner and outer sealing surfaces. The gap has an opening contiguous with and directed outwardly from the shirttail surface. The rotary cone cutters are preferably composites formed from different types of material.