This invention relates in general to earth boring bits and in particular to an improved bearing for an earth boring bit used in gaseous fluid drilling.
In certain types of mining, shallow holes approximately 50 foot deep are drilled for receiving explosives. Typically a rotary rock bit is used of the type having three rotatable conical cutters, each having earth disintegrating teeth, such as shown in U.S. Pat. No. 3,921,735. Each cutter has a cavity for mounting on a depending bearing pin. A thrust bearing is located at the bottom of the cavity for transmitting axial thrust along the bearing pin. A radial load bearing is located in the lower or nose portion of the cavity and another at the outer or entrance of the cavity for transmitting radial forces to the bearing pin. The outer radial load bearing comprises cylindrical roller bearings.
Air is pumped through the drill pipe and through passages in the drill bit to the bearings for cooling and for keeping the bearings clean. While air cools the outer roller bearings adequately, air cooling does not work as well in the nose area of the bit. The thrust bearing is a frictional bearing instead of a rolling contact bearing. Also there is less space in the nose area through which air can pass. Consequently, the bearing surfaces in the nose area may eventually overheat, resulting in excessive wear and early failure.
In deep well drilling, the bearings are sealed and lubricated by grease. The drilling fluid that discharges into the borehole is a liquid. A pressure compensator in the drill bit reduces the pressure differential between the sealed bearing areas and the borehole. This type of bit is not suitable for drilling with air as the drilling fluid.