This subject invention relates to bearings and more particularly to thrust bearings as employed, for example, in the downhole drilling art.
Downhole drilling motors have been in use for quite some time in the drilling of boreholes in the earth, especially for oil and/or gas. In a typical downhole drilling motor, the motor is suspended at the lower end of a string of drill pipe which is a series of pipe sections connected together at joints and supported from the surface. A drill bit is supported at the lower end of the downhole motor. Drilling fluid, which is commonly called drilling mud, is circulated down through the pipe string through the motor to cause it to rotate the drill bit. Then the drilling fluid is returned to the surface through the annular space between the drilled borehole and the drill string. The circulating drilling fluid causes the downhole fluid motor to rotate, thus rotating the bit to drill the borehole, and then carry the cuttings of the drilling operations back to the surface.
Virtually all downhole drilling motors have vertical thrust bearings. These downhole motors have stators and rotors. There is a rotor disc which rotates with the shaft of the downhole fluid motor and a stator disc which does not rotate and is supported next to the motor housing. In a typical setting, the stator disc and the rotor disc are each provided with a plurality of hard bearing surfaces such as diamond studs. The stator disc and rotor disc are placed in adjacent positions so that the diamond studs of each contact the other to form the bearing contacts. U.S. Pat. No. 4,410,054, entitled: "Well Drilling Tool with Diamond Radial/Thrust Bearings" describes one of the prior art diamond thrust bearings for downhole drilling fluid motors. U.S. Pat. No. 4,468,138, entitled "Manufacture of Diamond Bearings", describes a prior art method of securing a diamond bearing to a supporting plate or ring in a plurality of recesses. This requires that the assembly be heated to a specified temperature so that the metal pad softener melts and allows the metal pads to extrude around and braze the diamond bearing inserts in place. When the assembly is cooled, the bearing's inserts have their diamond bearing faces locked in a co-planar relation by the extruded metal from the metal pads. When these bearings or diamond inserts wear out, the whole retainer rings must be replaced. There is no way of replacing the diamond inserts in the field.