Bearing assembly with flow restrictor for a dual rod directional drilling apparatus and method of use
A rock housing for horizontal directional drilling machine includes a cylindrical housing body with walls defining a longitudinal cavity. A bearing assembly is provided as a part of the housing and is located above a bit box region of the housing. The bearing assembly is lubricated by drilling mud which flows through the drill string of the drilling machine. A portion of the drilling mud is diverted and passes through a gap formed between the bearing races of the bearing assembly, the gap being sized so as to create the necessary back pressure to divert the needed flow of drilling mud to the assembly. In some cases, an additional flow restrictor can be provided in the gap between the bearing races when needed, as when the driller is using a very low viscosity drilling fluid.
1 . A horizontal directional drilling apparatus, the horizontal directional drilling apparatus comprising:
a horizontal boring machine having a frame, a rotary machine supported on the frame, a drill string and a directional boring head, the rotary machine producing a rotation of the drill string, where the drill string has a first end, which is operatively connected to the rotary machine to drive the rotation of the drill string, and a second end, which is attachable to the directional boring head, the drill string itself being comprised of a plurality of lengths of dual-rod pipe which include drill string passageways for conducting drilling mud to the directional boring head to cool the directional boring head and remove cuttings produced during drilling operations;
wherein the rock housing is located in the drill string at a lower extent thereof, the rock housing having an upper connecting end for connection in the drill string and an opposite, lower end, the lower end including a lower housing and a bearing mandrel bit box for connection to the directional boring head, the lower housing containing a bearing assembly and also containing an internal flow path which communicates with the drill string passageways for the passage of drilling mud;
wherein the bearing assembly is lubricated by special bearing passageways formed within the bearing assembly which divert a portion of the flow of drilling mud passing through the drill string passageways and through the rock housing to the directional boring head, a remaining flow of drilling mud from the drill string passageways passing toward the directional boring head, the special bearing passageways serving as a metering device for the flow of drilling mud through the bearing assembly;
wherein the bearing assembly includes a plurality of inner bearing races and a plurality of companion outer bearing races, the inner and outer bearing races having a plurality of bearing elements located therebetween, and wherein all of the inner and outer bearing races are intentionally machined so that a gap of a predetermined width exists between all of the bearing races when the bearing races are assembled with the bearing elements located therebetween;
wherein the bearing assembly is made up of five or more of the inner bearing races and companion outer bearing races, including a first inner bearing race and a companion first outer bearing race, separated by the plurality of bearing elements, and wherein the gap which exists between the first inner bearing race and its companion first outer bearing race is smaller in size than the gap which exists between each remaining inner and outer pairs of bearing races in the bearing assembly in the downhole direction toward the directional boring head;
wherein the size of the gap between the inner and outer bearing races can be adjusted to provide a desired amount of back pressure in the special bearing passageways which control the amount of drilling mud that is allowed to pass through the bearing assembly, the remaining flow being encouraged to flow toward the directional boring head; and
wherein an additional flow restrictor is provided, integral to the bearing assembly, within the special bearing passageways defined by the gap between the inner and outer bearing races.
2 . The horizontal directional drilling apparatus of claim 1 , wherein the additional flow restrictor is a circumferential band which is located within a groove cut in a selected face of one of the inner and outer bearing races.
3 . The horizontal directional drilling apparatus of claim 2 , wherein the circumferential band is a flat, circumferential member having a square or rectangular cross section, the circumferential band having a section removed therefrom to thereby form an opening which allows drilling fluid to pass through.
4 . The horizontal directional drilling apparatus of claim 2 , wherein the circumferential band is round in cross section.
5 . The horizontal directional drilling apparatus of claim 2 , wherein the circumferential band is formed of a metal, synthetic or composite material.
6 . The horizontal directional drilling apparatus of claim 2 , wherein the circumferential band is formed of an Ultra-High-Molecular Weight thermoplastic material.
7 . The horizontal directional drilling apparatus of claim 2 , wherein the circumferential band is formed of Ultra-High-Molecular-Weight polyethylene.
8 . The horizontal directional drilling apparatus of claim 2 , wherein the circumferential band is formed of stainless steel.
9 . The horizontal directional drilling apparatus of claim 1 , wherein the bearing elements are a plurality of ball bearings.
10 . The horizontal directional drilling apparatus of claim 1 , wherein the bearing assembly is characterized by the absence of any type of sealed cavity containing oil or grease lubricant, but instead relies solely on the flow of drilling mud through the bearing assembly.
11 . A method of lubricating a bearing assembly for a rock housing used in a horizontal directional drilling apparatus, the method comprising the steps of:
providing a bearing assembly for a horizontal boring machine having a frame, a rotary machine supported on the frame, a drill string and a directional boring head, the rotary machine producing a rotation of the drill string, where the drill string has a first end, which is operatively connected to the rotary machine to drive the rotation of the drill string, and a second end, which is attachable to the directional boring head, the drill string itself being comprised of a plurality of lengths of dual-rod pipe which include drill string passageways for conducting drilling mud to the directional boring head to cool the directional boring head and remove cuttings produced during drilling operations;
wherein a rock housing is located in the drill string at a lower extent thereof, the rock housing having an upper connecting end for connection in the drill string and an opposite, lower end, the lower end including a lower housing and a bearing mandrel bit box for connection to the directional boring head, the lower housing containing the bearing assembly and also being provided with an internal flow path which communicates with the drill string passageways for the flow of drilling mud;
wherein the bearing assembly is provided with a plurality of inner bearing races and a plurality of companion outer bearing races, the inner and outer bearing races having a plurality of bearing elements located therebetween, and wherein all of the inner and outer bearing races are intentionally machined so that a predetermined gap exists between all of the inner and outer bearing races when the inner and outer bearing races are assembled with the bearing elements located therebetween, and wherein the inner and outer bearing races include a first inner bearing race and a companion first outer bearing race, the gap between the first inner and outer bearing races in the bearing assembly being less than the gap which exists between any of the remaining inner and outer pairs of bearing races in the bearing assembly, the gap forming special bearing passageways within the bearing assembly which divert a portion of the flow of drilling mud passing through the drill string passageways and through the rock housing to the directional boring head, a remaining flow of drilling mud from the drill string passageways passing toward the directional boring head, the special bearing passageways serving as a metering device for the flow of drilling mud through the bearing assembly; and
wherein an additional flow restrictor is provided, integral to the bearing assembly, within the special bearing passageways defined by the gap between the inner and outer bearing races.
12 . The method of claim 11 , wherein the additional flow restrictor is a circumferential band which is located within a groove cut in a selected face of one of the inner and outer bearing races.
13 . The method of claim 12 , wherein the circumferential band is a flat, circumferential member having a square or rectangular cross section, the circumferential band having a section removed therefrom to thereby form an opening which allows drilling mud to pass through.