Abstract:
An earth boring drill bit that includes a cutting cone with a cutting disk. Compacts are inserted within the disk having a chisel shaped end set flush with the cutting disk periphery. The compact crests and cutting disk periphery form a generally seamless cutting surface. The cutting cone can further include cutting teeth thereon also having flush mounted compacts. The compacts can be made from a material such as cemented carbide, hardfacing, tungsten, tungsten alloys, tungsten carbide and the cutter made from steel.

Description:
BACKGROUND 
     1. Field of Invention 
     The disclosure herein relates in general to rolling cone earth boring bits and in particular to improving the performance of a roller cone bit. 
     2. Description of Prior Art 
     Drilling systems having earth boring drill bits are used in the oil and gas industry for creating wells drilled into hydrocarbon bearing substrata. Drilling systems typically comprise a drilling rig (not shown) used in conjunction with a rotating drill string wherein the drill bit is disposed on the terminal end of the drill string and used for boring through the subterranean formation. 
     Drill bits typically are chosen from one of two types, either drag bits or roller cone bits. Rotating the bit body with the cutting elements on the outer surface of the roller cone body crushes the rock and the cuttings may be washed away with drilling fluid. One example of a prior art roller cone bit  11  is provided in a side partial perspective view in  FIG. 1 , the bit  11  having a body  13  with a threaded attachment  15  on the bit  11  upper end for connection to a drill string (not shown). The bit  11  further includes legs  18  extending downward from the bit body  13 . Each bit leg  18  is shown having a lubrication compensator  17 . 
     The bit body  13  is further illustrating having a nozzle  19  for directing pressurized drilling fluid from within the drill string to cool and clean bit  11  during drilling operation. A plurality of cutter cones  21  are rotatably secured to respective bit legs  18 . Typically, each bit  11  has three cutter cones  21 , and one of the three cutter cones is obscured from view in  FIG. 1 . 
     Each cutter cone  21  has a shell surface including a gage surface  25  and a heel region indicated generally at  27 . Teeth  29  are formed in heel region  27  and form a heel row  28  of teeth. The heel teeth  29  depicted are of generally conventional design, each having leading and trailing flanks  31 ,  32  that converge to a crest  33 . Each tooth  29  has an inner end (not shown) and an outer end  35  that joins to crest  33 . 
     Typically steel tooth bits are for penetration into relatively soft geological formations of the earth. The strength and fracture toughness of the steel teeth permits the use of relatively long teeth, which enables the aggressive gouging and scraping actions that are advantageous for rapid penetration of soft formations with low compressive strengths. However, geological formations often comprise streaks of hard, abrasive materials that a steel-tooth bit should penetrate economically without damage to the bit. Although steel teeth possess good strength, abrasion resistance is inadequate to permit continued rapid penetration of hard or abrasive streaks. 
     A layer of wear-resistant “hardfacing” material (not shown) may be applied on portions of roller cone bits  11 , including the body  13 , legs  18 , cutter cones  21 , and teeth  29 . Hardfacing typically consists of extremely hard particles, such as sintered, cast, or macrocrystalline tungsten carbide, dispersed in a steel matrix. Typical hardfacing deposits are welded over a steel tooth that has been machined similar to the desired final shape. Generally, the hardfacing materials do not have a tendency to heat crack during service which helps counteract the occurrence of frictional heat cracks associated with carbide inserts. The hardfacing resists wear better than the steel cone material, therefore the hardfacing on the surface of steel teeth makes the teeth more resistant to wear. 
     A front view of a prior art cutter cone  21  is illustrated in  FIG. 2 . Shown formed on the cutter cone  21  is an inner row  36  having inner row teeth  37  extending radially inward from the heel  27  (see  FIG. 1 ). The inner row teeth  37  have flanks and crests similar to the flanks  31 ,  32  and crests  33  of the heel teeth  29 . An apex  38  is shown proximate to the cutter cone  21  center, the apex  38  having grooves radially extending from the apex  38  midpoint to its outer periphery. A layer of hardfacing  39  is shown having been applied to surfaces of the heel teeth  29  and the inner row teeth  37 . The span between oppositely facing leading  32  and trailing flanks  31  can be filled with hardfacing to form a disk shaped cutting row on the cutter cone  21 . 
     SUMMARY OF INVENTION 
     Disclosed herein is an earth boring drill bit having a body, a leg depending from the body, a bearing shaft extending radially inward from the leg, a cutting cone mounted on the bearing shaft, a cutting disk on the cutting cone, and compacts set flush within the cutting disk. The earth boring bit may include a cutting surface defined by a path on the cutting disk surface where the crests of the compacts are arranged. The cutting disk, in an example, has an upper surface, a lower surface, and an outer edge that extends between the upper and lower surfaces, and wherein the compacts are arranged so that their crests are aligned with the outer edge to thereby define a cutting surface along the outer edge and the crests of the compacts. The upper and lower surfaces may be angled towards one another proximate to the outer edge and wherein the compacts include profiled surfaces depending downward from the crests, so that when the compacts are disposed in the cutting disk, the profiled surfaces are coplanar with the upper and lower surfaces. The cutting disk can be coaxially disposed on the cutting cone. The compacts can be formed from cemented carbide. 
     Optionally, the earth boring bit can further include serrations provided on the cutting disk outer edge. In another alternative, the serrations are provided between adjacent compacts. Teeth may be included on the cutting cone having compacts flush within the teeth. Each compact may include a chisel shaped tip on an axis and a cylindrically shaped body about an axis that is angled with respect to the axis of the chisel wherein adjacent compacts are rotated so their respective bodies are spaced apart in the cutting disk. The ratio of compact material hardness to cutter material hardness can, in one example be about 1.2:1, about 1.8:1, about 2:1, about 3:1, or about 3.3:1. 
     Also disclosed herein is a method of forming an earth boring bit. In one example the method includes providing a bit that has a body, a leg depending from the body, a bearing shaft extending radially inward from the leg, a cutting cone mounted on the bearing shaft, a cutting surface on the cutting cone, and bores extending from the cutting surface into the cutting cone. The method of this example can further include providing compacts with an elongated body portion, a chisel shaped tip on an end of the body portion, and coupling each compact within one of the bores and arranging the compacts so that each tip is substantially flush with the cutting surface. Each compact of the method can be formed from cemented carbide. Coupling be applying a press fit between the compact and the bore or brazing the compacts in the bore. The tip and body of each compact may be canted with respect to one another and wherein adjacent bores in the cutting cone project along non-parallel paths so that the respective bodies of adjacent compacts are disposed in non-interfering positions. 
     The cutting cone of the method can further include teeth arranged on the cutting cone having bores formed into the teeth, and the method can further involve coupling compacts flush into the bores in the teeth. Counterbores can be provided in the cutting disk prior to creating bores therein where the counterbores are covered during a step of heat treating the bit. The compacts can have an optional diamond covering. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side perspective view of a prior art roller cone bit. 
         FIG. 2  depicts a bottom view of a prior art milled steel tooth cutting cone. 
         FIG. 3  depicts in a perspective view an example of a compact for use in an earth boring bit. 
         FIG. 3A  illustrates a side sectional view of an alternative compact for use in an earth boring bit. 
         FIG. 4  portrays an example of a cone of a roller cone having compacts flush within a disk row. 
         FIG. 5  illustrates in an enlarged side perspective view, a portion of the cone of  FIG. 4 . 
         FIG. 6  depicts in side perspective view an example of a roller cone with flush compacts and serrations on a disk row. 
         FIG. 7  provides in a perspective view an example of a roller cone with compacts flush within cutting teeth. 
         FIG. 8  illustrates in perspective view an example of a step of forming a roller cone. 
     
    
    
     While the subject device and method will be described in connection with the preferred embodiments but not limited thereto. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the present disclosure as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
     Shown in a side perspective view in  FIG. 3  is an example of a compact  50 ; also alternatively referred to herein as an insert. In an example, the compact  50  is formed from cemented carbide. The compacts  50  may have a Rockwell “A” hardness ranging from about 83 up to about 95. The compact  50  of  FIG. 3  is shown having a chisel-shaped tip  52  and a substantially cylindrical barrel  54  depending downward from the tip  52 . As shown, the tip  52  includes a recumbent crest  58  on its upper terminal edge with downwardly depending planar surfaces or flanks  56 ,  57  formed along opposite lateral sides of the crest  58  terminating at the upper end of the barrel  54 . Flanks  56 ,  57  incline at different angles relative to the axis of barrel  54 . Flanks  56 ,  57  are on inner and outer sides of compact  50 , not leading and trailing sides. Crest  58  and flanks  56 ,  67  may be substantially flat surfaces or they may be curved slightly. 
     In  FIG. 3A , an alternative embodiment of a compact  50 A is shown in a side view. In this embodiment, the tip  52 A is canted with respect to the barrel  54 A. The compact  50 A is canted by setting the barrel  54 A around an axis A S  and setting the tip  52 A around a corresponding axis A T ; wherein the axes A S  and A T  are at an angle with respect to each other. As will be described in more detail below, providing canted compacts  50 A can avoid interference between adjacently disposed compacts  50 A. 
     An example of a cutting cone  62  in accordance with the present disclosure is provided in perspective view in  FIG. 4 . In this example, the cutting cone  62  includes an apex or nose  64  on its uppermost surface having cutting elements on its upper surface that coaxially circumscribe the axis A x  of the cutting cone  62 . Also coaxial with the cone axis A x  is an inner row or disk  66  shown on the cutting cone  62  that is generally smooth along its periphery. Included within the inner row  66  are compacts  50 ; their respective barrels  54  are directed radially inward towards the cone axis A x  from the peripheral edge of the cutting cone  62 . The cutting cone  62  also includes an outer row  70  coaxial with the cone axis A x  and disposed on a side of the inner row  66  opposite the apex  64 . The outer row  70  includes a series of teeth  72  arranged around the cutting cone  62  forming a cutting surface. An example of cutting cone  62  material includes steel having a Rockwell C hardness from about 40 to about 54. 
       FIG. 5  is an enlarged side perspective view of a portion of the disk or inner row  66  of  FIG. 4 . The inner row  66  includes an inner surface  68  facing the apex  64  ( FIG. 4 ) and intersected by the cone axis A x . Inner surface  68  is a continuous conical surface, but it could be a substantially flat surface perpendicular to axis A x . The inner row  66  further includes an outer surface  69  forming an opposite side of the inner row  66 . Outer surface  69  is shown as a continuous conical surface at a greater angle relative to cone axis A x  than inner surface  68 . In one embodiment, the outer surface  69  could be a substantially flat surface perpendicular to axis A x . The row circular ridge or peripheral edge  67  defines the row  66  periphery and connects between the inner and outer surfaces  68 ,  69  on their respective terminal ends. In this view, the compacts  50  are shown flush-mounted within the inner row  66  so that the flanks  56 ,  57  on each compact  50  coincide with the inner and outer surfaces  68 ,  69  of the inner row  66 . This orients the flank  56  of the compact  50  substantially flush with the inner surface  68  of the inner row  66  and the flank  57  of each compact  50  coplanar and aligned with the outer surface  69  of the inner row  66 . Additionally, the crest  58  of each compact  50  is set so that it is substantially seamless with the inner row peripheral edge  67 . The peripheral edge  67  and compact crests  58  combine to form a disk-shaped cutting surface with a continuous circular periphery. If flanks  56 ,  57  and crest  58  are substantially flat, they will not be quite flush with inner and outer surfaces  68 ,  69  and peripheral edge  67  because these surfaces are curved in conical and circular shapes. Flanks  56 ,  57  and crest  58  could be curved to be precisely flush, if desired. Optional hardfacing  78  is shown on the outer edge  67  and upper and lower surfaces  68 ,  69  of the inner row  66 . The hardfacing  78  can be applied on all other surfaces of the cone  62  and may be flush with or project above the compacts  50 . 
     One of the advantages of the embodiment shown herein is the hardened composition of the compacts  50  resist wear longer than the typical ferrous materials used as a base material of the inner row  66 . Accordingly, the compacts  50  will experience less erosion during use than the inner row  66  and provide a cutting function for a longer period of time. Moreover, it is expected that the portion of the inner row  66  adjacent the trailing edge of each compact crest  58  will experience less erosion than the portion of the peripheral edge  67  proximate the compact leading edge. The presence of this portion of the peripheral edge at the trailing edge portion of each compact  50  supports the compacts  50  within the respective bores  65  formed within the inner row  66 . The compacts  50  may be coupled with the inner row  66  by a press or interference fit technique. Optionally, the compacts  50  may be brazed within the bores  65 . Hardfacing may be applied over the inner row  66 , outer edge  67 , upper surface  68 , and/or lower surface  69 . 
     In an optional method of forming the cutting cone  62  of  FIG. 4 ; the bores  65  are not formed along a line normal with the circular peripheral edge  67 . Instead adjacent bores  65  may alternatingly be angled inward towards the apex  64  or outward toward the outer row  70 . Thus when the compacts  50  are set in the adjacent bores  65  the risk of interference within the body of the cutting cone  62  is eliminated. In one example of use, when the canted compacts  50 A of  FIG. 3A  are set in adjacent bores they may be rotated 180° with respect to one another. The respective angled barrels  54 A of adjacent compacts  50 A are offset in opposite directions along the axis A x  and not in an interfering arrangement. The canted configuration allows the tip  52 A of each compact  50 A to be positioned flush with the outer periphery of the cutting disk  66  of the cutting cone  62 . 
     An alternate embodiment of the present device is illustrated in a side perspective view in  FIG. 6 . In this embodiment, a cutting cone  62 A is shown having an inner row  66 A with bores formed therein that project radially towards the cone axis and having compacts  50  provided in the bores  65 . In this embodiment, serrations  74  are formed along the inner row  66 A peripheral edge  67 A and between adjacent compacts  50 . Removing material between adjacent compacts  50  can enhance boring operations by maximizing contact between the harder compacts  50  and the formation. The circumferential extent of each serration  74  is preferably less than the circumferential distance between adjacent compacts. Each crest of each compact  50  is thus flush with a portion of peripheral edge  67 A. Serrations  74  are illustrated as being curved, partially circular recesses, 
     Referring now to  FIG. 7 , an alternative embodiment of a cutting cone  62 B is shown in a perspective view. The cutting cone  62 B of  FIG. 7  includes an inner row  66 A with compacts  50  in bores  65 , and serrations  74  between the compacts  50 . The cutting cone  62 B farther includes an outer row  70 B of teeth  72 B, the teeth  72 B having bores  65 B formed therein. The bores  65 B, shown in dashed outline, extend towards the cone axis (not shown) from the crest of each tooth  72 B. Set within the bores  65 B, the crests of compacts  50 B are shown flush with the upper terminal portion or crest of each tooth  72 B. The inner and outer flanks of compacts  50 B are illustrated flush with the inner and outer sides of each tooth  72 B. The presence of the hard material compacts  50 B provides added wear resistance to an inner core of each tooth  72 B, thereby increasing their useful life. 
       FIG. 8  illustrates an example of an alternate method of forming the cutting cone  62  described herein. A counter bore  75  is shown formed in the periphery of an inner row of a cutting cone  62 . Counter bore  75  was formed during an intermediate stage of forming the cutting cone  62  and prior to heat treatment. Counter bore  75  has the same diameter as compact bore  65  (shown in dashed outline) but a smaller depth. The depth of counter bore  75  is approximately equal to the length of tip  52  ( FIG. 3 ) of compact  50 . During heat treatment and carburizing, at least the base of each counter bore  75  is covered by a plug or flat disk so that carburization does not precipitate proximate to where the bores  65  will be formed. After heat treatment, the plug is removed and the bore  65  is formed by drilling into the base of counter bore  75  for the length of barrel  54  ( FIG. 3 ). The total distance from the bottom of bore  65  to the peripheral edge  67  will equal the total height of compact  50 . The diameter of bore  65  will be the same as the diameter of counter bore  75 . 
     The scope of the present disclosure is not limited to roller cone bits with flush mounted compacts; but also includes earth boring bits having inserts flush with the bit cutting surface, where the hardness of the inserts exceeds the hardness of the cutting surface material. In an example, the ratio of insert hardness to cutting surface material hardness can range from about 1.2:1 to about 3.3:1. Specific hardness ratios include about 1.2:1, about 1.8:1, about 2:1, about 3:1, and about 3.3:1. These example ratios of hardness are also applicable to the respective material of the compacts  50  and cutting cones  62 . 
     The improvements described herein, therefore, are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While presently preferred embodiments have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, embodiments exist wherein a row or rows on cutting cones  62 ,  62 A,  62 B can include the compacts  50  of  FIG. 3  and the compacts  50 A of  FIG. 3A . Optionally, compacts  50  can be within one row on a cutting cone and compacts  50 A on another row of the same cutting cone. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present disclosure and the scope of the appended claims.