Abstract:
A roller cone drill bit having detachable rotatable arms. The arms are connected at a mounting pad to the bit body. Each arm has its own grease delivery system to provide lubrication to the interface between the arms and rolling elements at an end of each arm. The forward-facing contact surface between the bit body and the arms is at an angle, relative to the central axis of the bit, that is ninety degrees or more.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 61/845,621 filed on Jul. 12, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention relates generally to roller cone drill bits. 
       SUMMARY 
       [0003]    The present invention is directed to a bit. The bit comprises a body, a plurality of bit arms, a cone and a pin. The body comprises a center axis and a mounting pad and is connectible to a drill string. The bit arms are mounted on the body at the mounting pad. The cone is rotatable attached to each bit arm and comprises a plurality of teeth. The pin is located within each bit arm and the body through the mounting pad. 
         [0004]    In another embodiment the invention is directed to a method for lubricating internal components of a bit having a bit body, a plurality of removable arms attached to the bit body, rolling elements attached to each of the removable arms, and at least one ball bearing located between the rolling elements and each of the removable arms. The method comprises connecting a removable arm with the bit body using a pin comprising a hollow passage, providing grease to a pressurized reservoir in the bit body, conveying grease into the removable arm through the hollow passage of the pin, providing a continuous passage through the removable arm proximate the ball bearings, and rotating the rolling elements to distribute grease from the continuous passage to the ball bearings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a side perspective view of a tricone rolling element bit. 
           [0006]      FIG. 2  is a side perspective view of a ⅓rd segment of a tricone bit. 
           [0007]      FIG. 3  is a perspective view showing three preassembled segments of a tricone bit. 
           [0008]      FIG. 4  is a perspective view of an alternative tricone bit. 
           [0009]      FIG. 5  is a sectional side view of the tricone bit of  FIG. 4 . 
           [0010]      FIG. 6  is another sectional side view of the tricone bit of  FIG. 4 . 
           [0011]      FIG. 7  is a detail view of the joint shown in  FIG. 6  labeled “A”. 
           [0012]      FIG. 8  is a side view of a horizontal directional drilling apparatus. 
       
    
    
     DESCRIPTION 
       [0013]    With reference to  FIG. 1 , shown there in is a tricone drill bit  10 . A tricone hit  10  is characterized by three rolling cone cutting elements  24 . A tricone bit, used in the oilfield, may have a useful life of a single bore. Tricone bits are also used in installation of buried utilities. This application, known as Horizontal Directional Drilling or “HDD”, typically has shorter length runs and less economic consequence in the case of bit failure. HDD typically involves bores between 300 and 1,200 feet, allowing for inspection, evaluation and service of the bit between bores. To improve the per-foot cost of operation of tooling, parts are typically rebuilt and reused to the limit of endurance and wear. A brief discussion of HDD is given with reference to  FIG. 8 . 
         [0014]    With reference to the figures in general and  FIG. 1  specifically, a tricone bit  10  is shown therein. The bit  10  comprises a body  12  and a plurality of arms  14 . The body  12  comprises a base  16  and a mounting pin  18 . The mounting pin  18  is threaded as shown herein for connection to a drill string ( FIG. 8 ). Alternatively, the mounting pin  18  may be splined or geometrically aligned for connection to a drill string. The base  16  supports a fluid delivery system  20  and the plurality of arms  14 . As shown, the fluid delivery system  20  comprises a plurality of nozzles  22 . The plurality of nozzles  22  supply a fluid, such as drilling mud, for lubrication of the bit  10 . As shown, each of the plurality of nozzles  22  is directed to a corresponding one of the plurality of arms  14 . 
         [0015]    Each of the plurality of arms  14  comprises a rolling element  24  comprising carbide teeth  26 , a ball port  28 , and a grease port  30 . The carbide teeth  26  engage material to be moved by the tricone bit  10 . The teeth  26  may be equalized and dispersed about the rolling elements  24 . The precise pattern of the teeth  26  may vary by size of the bit  10  and material being removed. The teeth  26  may take on various profiles as a function of the insert orientation. For some bits  10 , this may result in three different unique rolling elements  24   a,    24   b,    24   c  making up bit assembly  10 . 
         [0016]    Bearing balls ( FIG. 5 ) may be used to reduce friction and facilitation rotation of rolling elements  24 . These may be assembled through the ball port  28 . Preferably, the ball port  28  is closed with a plug ( FIG. 5 ) after assembly. Drilling mud is used by the fluid delivery system  20  to facilitate removal of the cuttings and clean the rolling elements  24   a,    24   b,    24   c . Drilling mud is discharged through the nozzles  22 , which are supplied with mud through the drill pipe bolted to mounting pin  18 . Grease port  30  allows access to an internal reservoir for lubrication. Grease may be added through grease port  30 , and the reservoir is pressure balanced to maintain lubricant pressure similar to that of the bore hole. Bore hole pressure is accessed through a pressure port  32 . 
         [0017]    In operation, the bit  10  of  FIG. 1  bores through a subsurface by rotation of the rolling elements  24  and grinding of the subsurface by the carbide teeth  26 . Drilling fluid provided by the nozzles  22  softens the area being drilled and prolongs the life of the carbide teeth. As material is removed from the subsurface, forming a borepath, the bit  10  is advanced along the bore path by sections of drill string (not shown). 
         [0018]    With reference now to  FIG. 2 , shown therein is one third of the tricone bit  10  of  FIG. 1 . This section is referred to as a “shirttail sub-assembly”  40 . The shirttail sub-assembly  40  comprises one third of the cylindrical bit body  12  with one arm  14  and one nozzle  22 . Each shirttail sub-assembly  40  is joined into the tricone bit  10  ( FIG. 1 ) via welding along split plane  42 . After welding, the mounting pin  18  may be threaded or geometrically formed. Alternatively, the threads or geometric characteristics of the mounting pin  18  may exist on the shirttail subassembly  40  prior to welding. Three shirttail sub-assemblies  40  are formed into the tricone bit  10  of  FIG. 1  through welding at the split plane  42 , as shown in  FIG. 3 . With reference now to  FIG. 4 , an alternative tricone bit  10   a  comprising a mounting pad  50  is shown. The mounting pad  50  is generally the interface between the arms  14  and bit body  12 . The arms  14  are attached to the bit body  12  at the mounting pad  50  by bolts  54 . As shown, there are three bolts  54  in each arm  14 . The arms  14  are disposed about a center axis  58 . The grease port  30  provides access to internal lubrication systems ( FIG. 5 ) from the outside of the bit body  12 . The ball port  28  provides access to internal ball bearings ( FIG. 5 ) located proximate each rolling element  24 . 
         [0019]    With reference to  FIG. 5 , the tricone bit  10   a  comprises a fluid delivery system  60  in each of the arms  14  and the bit body  12 . The fluid delivery system  60  comprises a pressurized pocket  62 , a spring  64 , a lubrication piston  66 , a shear pin  68  comprising a hollow central passage  69 , a middle grease passage  70 , an upper grease passage  72 , and a bushing  74 . The lubrication piston  66  produces grease pressure within the fluid delivery system  60  by the applied load of the spring  64 . As shown, the piston  66  and spring  64  are at the full range of travel within the pressurized pocket  62 . Thus, grease pressure may only be increased further by addition of additional grease pressure through grease port  30 . 
         [0020]    Grease flows through the central passage  69  of shear pin  68 . This cylindrical pin  68  is a close fit seal through mounting pad  50 , a shear pin to resist shear forces due to bit torque and as a conveyance tube. Grease from pocket  62  is able to flow to the bushing  74  through middle grease passage  70  and upper grease passage  72 . A plug  76  is shown within ball port  28 . Preferably, the plug  76  has a reduced diameter proximate the central passage  70  and upper grease passage  72  to enable flow of grease through the fluid delivery system  60 . Fluid for lubrication reaches the bushing  74  and greases ball bearings  80  to allow free rotation of the rolling elements  24  relative to the bit arms  14 . In this way, fluid for lubrication, or grease, travels through a continuous passage from the shear pin  68  to the bushing  74 . 
         [0021]    The bit arms  14  further comprise a cone seal  82 . The cone seal  82  seals the bushing  74  and limits lubricant leakage as the rolling element  24  rotates in operation. Preferably, the grease port  30  is formed inside a pocket  84  formed in the bit body  12  to protect the grease port from damage when bit  10   a  rotates in use. 
         [0022]    The bit  10   a  defines a central fluid cavity  90  and nozzle feed passages  92 . Drilling fluid enters the central fluid cavity  90  from the drill string (not shown), is discharged into the nozzle feed passages  92 , and exit the bit  10   a  through nozzles  22 . As shown in the figures, three independent nozzles  22  exist, one feeding each bit arm  14  and rolling element  24 . Alternative designs are contemplated, including the use of a greater number of nozzles  22  to direct drilling fluid at the rolling elements  24 . 
         [0023]    With reference now to  FIG. 6 , the bit  10   a  is shown in cross-section. The bit arms  14  comprise a counterbore  100 . Connectors, such as bolts  54  are shown within the counterbores  100 . The counterbore  100  protects the bolt  54  from wear as the bit  10   a  operates. The bolt  54  extends through bit arm  14  through the mounting pad  50  into the bit body  12 . The bit body  12  comprises a threaded hole  102  corresponding to the counterbore  100  of each bit arm  14 . Insertion of the bolt  54  into the threaded hole produces a clamping load between the arm  14  and bit body  12 , engaging the features of the mounting pad  50 . 
         [0024]    The mounting pad  50  comprises lands  110  located on each bit arm  14  and grooves  112  located on the bit body  12 . The lands  110  and grooves  112  correspond and may be straight, circular, curved, geometrically shaped, or any other corresponding configuration. With reference now to  FIG. 7 , detail section “A” of the mounting pad  50  is shown in greater detail. The lands  110  of arm  14  engages groove  112  of bit body  12  upon tightening of bolt  54 . The grooves  112  comprise a front-facing wall of the bit body  12  for engagement of the lands  110  at a corresponding surface. Note that a reference line  114 , parallel to a center axis  58  ( FIG. 4 ) of the bit body  12 , creates an angle  116  with a line  118  collinear to one of the grooves  112 . The angle  116  as shown is 105 degrees. Preferably, this angle is not less than 90 degrees. With an angle  116  greater than 90 degrees, thrust loads applied primarily to the front of the bit  10   a  and generally directed along its central axis encounter greater stability. 
         [0025]    With reference now to  FIG. 8 , a horizontal directional drilling system  200  for use with the bit  10  disclosed herein is shown. The system comprises a drilling machine  202 , a drill string  204 , and the bit  10 . The bit  10  is advanced through a subsurface  205  by thrust and rotation of the drill string  204  provided at the drilling machine  202 . As a result of this operation, a borehole  206  is created in the subsurface  205 . The bit  10  exits the borehole  206  at an exit side  208 . A utility line (not shown) may be pulled in behind the drill string  204 , or alternatively, a separate backreaming assembly (not shown) is attached at the exit side  208  and pulled back through the borehole  206  to the drilling machine  202 . 
         [0026]    Various modifications can be made in the design and operation of the present invention without departing from its spirit. Thus, while the principal preferred construction and modes of operation of the invention have been explained in what is now considered to represent its best embodiments, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.