Abstract:
The present disclosure provides a back reamer roller cone that is configured so that the bearings assemblies therein can be relatively easily removed and replaced. Methods of replacing the bearing assemblies in a back reamer are also provided.

Description:
This application is a National Stage Application of PCT/US2012/055507, filed Sep. 14, 2012, which claims benefit of U.S. Provisional Patent Application Ser. No. 61/535,623, filed Sep. 16, 2011, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above-disclosed applications. 
    
    
     TECHNICAL FIELD 
     The present disclosure provides a roller cone for a back reamer and related methods. 
     BACKGROUND 
     The process known as horizontal directional drilling is utilized to install a variety of underground utilities in a manner that does not disrupt the surface. In use, a drill machine is used to drill a pilot bore that extends beneath the ground surface from an entry hole at the ground surface (i.e., a starting point) to an exit hole at the ground surface (i.e., an ending point). The pilot bore is drilled by rotating and pushing a ground engaging tool (e.g., a drill bit) that is attached to the end of a drill rod. The length of the pilot bore is extended by stringing multiple rods together to form a drill string. The direction of drilling can be controlled (i.e., the drill string can be “steered”) by various techniques to control the depth of the pilot bore as well as the location of the exit hole. The location of the drill string, after the pilot bore is completed, represents the desired location of the utility to be installed. 
     After the pilot bore is drilled, the drill bit is typically removed and a second ground engaging tool installed onto the end of the drill string. This tool is typically known as a back reamer or a hole opener. Its function is to ream/open the drilled bore to a diameter sufficient to allow installation of the utility. To provide a reaming function, the back reamer is typically pulled back through the pilot bore by the drill string as the drill string is withdrawn from the pilot bore. Oftentimes the utility being installed is attached with a swivel located at the end of the back reamer such that the utility is pulled into the reamed bore immediately behind the back reamer. (See  FIG. 1 .) In this way, the act of withdrawing the drill string will simultaneously result in the installation of the utility. 
     The type of utilities installed typically includes telecommunications, power, water, natural gas, liquid gas pipelines, potable water pipes and sewers. Due to this large variety of utilities, there is a large variety in the size requirements for the final reamed borehole, and thus a wide range of back reamer sizes is required. 
     Back reaming can be of the type that includes a plurality of roller cones attached to a tool body. For an example of such a back reaming tool, see U.S. Pat. No. 7,243,737, which is incorporated by reference herein it its entirety. There is a need for improved back reamers that are configured to withstand extreme use conditions and are easily rebuildable. 
     SUMMARY 
     The present disclosure provides a back reamer roller cone that is configured so that the bearing assemblies therein can be relatively easily removed and replaced. Methods of replacing the bearing assemblies in a back reamer are also provided. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic representation of a horizontal directional drilling system in accordance with the principles of the present disclosure; 
         FIG. 2  is an enlarged view of a portion of  FIG. 1  showing the back reamer according to the principles of the present disclosure attached to a utility; 
         FIG. 3  is a front perspective view of the back reamer of  FIG. 2 ; 
         FIG. 4  is an exploded assembly view of a portion of the back reamer of  FIG. 2 ; 
         FIG. 5  is an exploded assembly view of the roller cone of the back reamer of  FIG. 2 ; 
         FIG. 6  is a partial side view of the shaft of the roller cone of  FIG. 2 ; 
         FIG. 7  is a partial end view of the shaft of the roller cone of  FIG. 2 ; 
         FIG. 8  is an end view of a roller cone of the back reamer of  FIG. 2 ; 
         FIG. 9  is a cross-sectional view along lines  9 - 9  of  FIG. 8 ; 
         FIG. 10  is a cross-sectional view of the roller cone with the disengagement tool inserted into the disengagement aperture in the roller cone shaft; 
         FIG. 11  is a cross-sectional view of the roller cone with the disengagement tool inserted into the disengagement aperture in the roller cone shaft and the shaft partially extending out of the roller cone body; 
         FIG. 12  is a partially assembled view of  FIG. 5 ; 
         FIG. 13  is a cross-sectional view of a step in the assembly of the roller cone of  FIG. 5 ; 
         FIG. 14  is a cross-sectional view of an alternative step in the assembly of the roller cone of  FIG. 5 . 
         FIG. 15  is a cross-sectional view of an alternative embodiment of the roller cone of  FIG. 10  in an assembled configuration; and 
         FIG. 16  is a cross-sectional view of the roller cone of  FIG. 15  with the roller cone shaft disassembled. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will be made in detail to example embodiments that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or alike parts. 
       FIG. 1  illustrates an example horizontal drilling system in which reamers in accordance with the principles of the present disclosure may be used. The horizontal drilling system includes a drilling machine  100  depicted as a track-type vehicle. The drilling machine  100  includes anchors (e.g., augers) for securing the machine to a ground surface  102 . The drilling machine  100  also preferably includes a thrust mechanism for pushing a drill string  108  into the ground to form a pilot bore, and for withdrawing the drill string from the ground. The horizontal drilling machine  100  further preferably includes a rotational drive mechanism for rotating the drill string  108  as the drill string is thrust into the ground or removed from the ground. It will be appreciated that the thrust mechanism of the horizontal drilling machine  100  can be oriented at an angle relative to the ground surface  102  to facilitate driving the drill string into the ground at a desired angle. 
     In use, the horizontal drilling machine  100  is used to drive the drill string  108  into the ground  102  as shown in  FIG. 1 . The far end of the drill string  108  is typically equipped with a cutting tool for cutting the pilot bore. To lengthen the pilot bore, pipes are sequentially added to the drill string until the drill string  108  extends from an entry point  104  adjacent to the drilling machine  100  to an exit point  106 . Thus, the drill string  108  is formed by a plurality of drill rods connected together. By rotating the drill string  108  while concurrently applying thrust to the drill string, the cutting tool at the end of the drill string cuts the pilot bore. 
     After the drill string  108  has been pushed from the entry point  104  to the exit point  106 , the cutting tool is removed from the far end of the drill string and replaced with a back reamer  119 . A utility  110  (i.e., a utility pipe) can be attached to the back reamer  119  with a swivel  112  such that the drill string  108  can rotate independent of the utility  110 . Once the back reamer  119  and the utility  110  have been attached to the drill string  108 , the horizontal drilling machine  100  is used to withdraw the drill string  108 . As the drill string  108  is withdrawn, the drill string  108  is rotated causing the back reamer  119  to enlarge the pilot bore. As the drill string is withdrawn, the utility  110  is concurrently pulled into the back reamed bore. As shown in  FIG. 1 , the back reamer  119  has been pulled about halfway back through the pilot bore, and the utility  110  has been installed along about half of the bore path. 
     Referring generally to  FIGS. 2-14  the back reamer  119  is described in greater detail. In the depicted embodiment the back reamer  119  includes a tool body  120  including a first end  122  configured to be connected to a drill string  108  and a second end  124  configured to be connected to a utility  110 . The back reamer includes a plurality of roller cones  126 ,  128 ,  130  (e.g., three roller cones) connected to a tool body  120  via roller cone shafts  132 . In the depicted embodiment, the roller cones  126 ,  128 ,  130  are interchangeable and share the same features. Therefore, only one of the roller cones will be described in further detail below. 
     The depicted roller cone  128  includes an outer surface  134  including a plurality of cutter teeth  136  (e.g., carbide buttons) thereon. During use the roller cone  128  freely rotates about the shaft  132 . In the depicted embodiment, the roller cone  128  includes a major diameter end  162  and a minor diameter end  164  and a central cavity  172  therebetween. In the depicted embodiment the roller cone shaft  132  includes a first end  152  configured to be arranged adjacent the major diameter end  162  of the roller cone  128  and a second end  154  configured to be arranged adjacent the minor diameter end  164  of the roller cone  128 . 
     The first end  152  of the shaft  132  includes an annular shoulder  150  that is configured to cap and seal an aperture in the roller cone that receives the roller cone shaft. In the depicted embodiment the shoulder  150  includes a front surface  144  that engages a bearing assembly  160  and an annular groove  148  that retains a sealing ring  146 . 
     The second end  154  of the shaft includes a lock assembly  138  configured to retain the roller cone shaft  132  in the roller cone. In the depicted embodiment the lock assembly  138  is configured to be unlocked by inserting a lock release tool  140  into an aperture  142  located on an end of the roller cone shaft  132 , which extends outside of the minor diameter end  164  of the roller cone  128 . In the depicted embodiment the aperture  142  is axially aligned and centered in the roller cone shaft  132  and serves as a grease conduit to central cavity  172  of the roller cone  128 . In the depicted embodiment, the lock assembly  138  includes a snap ring  166  that engages an annular groove  168  on the roller cone shaft  132 . In the depicted embodiment the lock assembly  138  includes a plurality of pins  170  (e.g., six pins) that extend from the annular groove  168  radially into the roller cone shaft and are configured to expand the snap ring  166  when the lock release tool  140  is inserted in the aperture  142 . It should be appreciated that many other lock assembly configurations are possible, including, for example, embodiments that do not include pins or include different configurations of pins (e.g., three pins instead of six pins). 
     In the depicted embodiment, the bearing assembly  160  includes a bearing unit  174  that includes a plurality of bearings between internal bearing race ring  176  and external bearing race ring  178 . In the depicted embodiment the internal bearing race ring  176  is press fit onto the external surface of the shaft  132 . The snap ring  166  is configured to retain the shaft  132  relative to the bearing unit  174 . In the depicted embodiment, a second snap ring  182  engages a groove  180  on the central cavity  172  at the major diameter end  162  the roller cone  128 . The second snap ring  182  is configured to retain the bearing unit  174  in the roller cone  128 . 
     Referring to  FIGS. 9-12 , the method of disassembling the roller cone  128  to replace the internal bearing unit  174  and seals is described in further detail. In the depicted embodiment the method includes the step of releasing the lock assembly  138  and biasing (pushing or pulling) the shaft  132  out of the roller cone  128 . The step of releasing the locking assembly includes the step of removing a grease cap  184  located at the end of the roller cone shaft  132  and plunging a tapered distal end of the lock release tool  140  in an axial direction into the aperture  142  thereby forcing the pins  170  to move radially outward and expand the snap ring  166  such that it disengages from the groove  168 . With the lock release tool in place, the shaft  132  can be pulled or pushed out of the roller cone  128 . The force necessary to bias the shaft  132  out of the roller cone  128  once the snap ring  166  is disengaged is the lesser of the force needed to overcome frictional engagement between the inner race ring  176  of the bearing unit  174  or the retention force of the second snap ring  182 . In other words, either the shaft  132  will slide out of the bearing unit  174  or the snap ring  182  will fail and the bearing unit  174  will exit the roller cone  128  with the shaft  132 . In either case the bearing unit  174  can be accessed and repaired or replaced with a new or a rebuilt bearing unit. 
     Referring to  FIGS. 13 and 14 , two alternative ways to assemble the roller cone  128  are shown.  FIG. 13  illustrates a method wherein the bearing unit  174  is first inserted into the roller cone  128 . A tapered snap ring expander tool  186  is inserted into the roller cone  128  before the shaft  132 . The tapered lead-in tool  186  expands the snap ring  166  as the shaft  132  is pressed into position in the roller cone  128 . Once the assembly is complete (i.e., the snap ring  166  engages the groove  168  on the shaft  132 ), the tapered lead-in tool  186  is forced out of the minor diameter end  164  of the roller cone.  FIG. 14  illustrates an alternative assembly method wherein the bearing unit  174  is first connected to the shaft  132 . In the depicted embodiment the bearing unit  174  is press fit onto the shaft  132  and the snap ring  166  is provided in the groove  168  to secure the bearing unit  174  in the shaft. A funnel tool  188  is used to depress the second snap ring  182  located adjacent the shoulder  150  of the shaft  132  so that it can move into engagement with an annular groove  180  in the central cavity  172  of roller cone  128 . 
     Referring to  FIGS. 14 and 15 , an alternative embodiment of the roller cone is shown. Roller cone  200  has similar structural components as roller cone  128 . The primary difference between roller cone embodiments relate to the shaft configurations. The shaft  202  of roller cone  200  includes a first part  206  that is separable from a second part  206 . In the depicted embodiment the second part  204  includes a threaded boss that is configured to be threaded into a threaded aperture in the first part  206 . Apart from the threaded aperture, the first part  206  has similar features to the first end  152  of the shaft  132 . 
     In the depicted embodiment, the second part  204  includes a shoulder  210  that retains and engages bearing assembly  160  and an enlarged diameter portion  208  adjacent the shoulder  210  that caps and seals the minor diameter end of the roller cone  200 . In the depicted embodiment, the distal end of the second part has generally the same diameter as the diameter of the second end  154  of the shaft  132  so that the roller cones  200  and  128  are interchangeable. 
     The roller cone  200  does not include the same lock assembly  138  including a snap ring  166  that is described above. The locking assembly of the roller cone  200  is the threaded arrangement between the two parts of the shaft  202 . The roller cone can be disassembed by unthreading the shaft  202  and pulling the shafts out of the roller cone body exposing snap ring  182 . Removing snap ring  182  allows the bearing assembly to be removed from the roller cone body. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.