Patent Publication Number: US-7900718-B2

Title: Earth-boring tools having threads for affixing a body and shank together and methods of manufacture and use of same

Description:
TECHNICAL FIELD 
     Embodiments of the invention relate generally to earth-boring tools and methods of forming and using earth-boring tools. More particularly, embodiments of the present invention relate to earth-boring tools having features for effecting the attachment of a body to a shank and to methods of forming such tools. 
     BACKGROUND 
     Rotary drill bits are commonly used for drilling bore holes or wells in earth formations. One type of rotary drill bit is the fixed-cutter bit (often referred to as a “drag” bit), which typically includes a plurality of cutting elements secured to a face region of a bit body. The drill bit is attached to a drill string including tubular pipe and component segments coupled end-to-end between the drill bit and other drilling equipment at the surface. Equipment such as a rotary table or top drive may be used for rotating the drill string and the drill bit within the bore hole. Alternatively, the drill bit may be coupled to the drive shaft of a down-hole motor, which then may be used to rotate the drill bit, alone or in combination with rotation of the drill string from the surface. 
     In order to attach the drill bit to the drill string, the bit body of a conventional rotary drill bit typically is secured to a hardened steel shank having an American Petroleum Institute (API) thread connection for attaching the shank to the drill string. The bit body is typically secured to the shank by coupling the bit body and shank together and then securing the bit body to the shank. Many conventional drill bits comprise a bit body or bit crown having threads on a proximal connector portion. The threads are configured for aligning the longitudinal axis of the bit crown to the longitudinal axis of the shank. The shank and bit crown are then mechanically secured together. In some conventional drill bits, such as U.S. Publication No. 2007/0102198 to Oxford et al., the shank and bit body are mechanically secured together by welding the two pieces at a point of intersection to prevent detachment or unthreading during use. 
     For at least some materials used for conventional bit bodies, the use of a weld for affixing the bit body and the shank together may be detrimental to the material&#39;s performance. For example, a bit body may be formed from a material including a carbide material. Welding a carbide material to a steel shank commonly leads to a significantly weakened carbide base material, and may, in some cases, also weaken the material substantially so that cracks may form in the bit body through the heat affected zone of the carbide material. 
     BRIEF SUMMARY 
     Various embodiments of the present invention comprise earth-boring tools comprising a shank and a bit body configured to be secured together with at least one threaded connection. In one or more embodiments, the earth-boring tool may comprise a shank comprising a proximal connector at one longitudinal end and a distal connector at an opposing longitudinal end. The distal connector may comprise at least one set of threads thereon. A bit body may be coupled to the shank and may comprise a face at one longitudinal end thereof and a shank connector at an opposing longitudinal end. The shank connector may comprise threads configured to mate with the set of threads on the distal connector. The set of threads on the distal connector and the threads on the shank connector may be at least substantially bound together. 
     Other embodiments comprise methods for forming an earth-boring tool. One or more embodiments of such methods may comprise forming a shank comprising a distal connector including a set of threads thereon. A bit body may also be formed comprising a shank connector with threads thereon. At least a portion of the threads on the shank connector may be configured to at least partially bind with the set of threads on the distal connector. The distal connector of the shank and the shank connector of the bit body may be screwed together to secure the shank to the bit body. 
     Further embodiments of the invention comprise a method of securing an earth-boring tool to a shank. One or more embodiments of such methods may consist of providing a bit body comprising a shank connector at a trailing end thereof. The shank connector is formed to include threads formed thereon. A shank is provided and configured to attach to a drill string. The shank may comprise a distal connector at a leading end thereof, the distal connector comprising a set of threads thereon. The shank connector of the bit body and the distal connector of the shank may then be screwed together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an elevation view of a drill bit according to at least some embodiments of the present invention. 
         FIG. 2  illustrates an elevation view of a drill bit comprising a bit body comprising alignment structure according to some embodiments of the invention. 
         FIG. 3  is a partial cross sectional view of a drill bit comprising a bit body comprising a body alignment portion and a body locking portion, and a shank comprising a shank alignment portion and a shank locking portion. 
         FIGS. 4-6  are partial cross sectional views illustrating various embodiments of drill bits comprising one or more gaskets according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The illustrations presented herein are, in some instances, not actual views of any particular drill bit or threads, but are merely idealized representations which are employed to describe the present invention. Additionally, elements common between figures may retain the same numerical designation. 
     Various embodiments of the present invention are directed toward embodiments of earth-boring tools or drill bits comprising a bit body including threads configured to fixedly attach the bit body to a shank.  FIG. 1  illustrates a drill bit  100  in the form of a fixed cutter or so-called “drag” bit, according to at least some embodiments of the present invention. As shown in  FIG. 1 , drill bit  100  includes a bit body  110  having a face  120  at a leading longitudinal end thereof and generally radially extending blades  130 , forming fluid courses  140  therebetween. Bit body  110  may comprise a particle-matrix composite material, as well as a metal or metal alloy, such as steel, as are well known in the art. 
     Blades  130  may also include pockets  150 , which may be configured to receive cutting elements  160 , for instance, superabrasive cutting elements in the form of polycrystalline diamond compact (PDC) cutting elements. Generally, such a PDC cutting element may comprise a superabrasive region that is bonded to a substrate. Rotary drag bits employing PDC cutting elements have been employed for several decades. PDC cutting elements are typically comprised of a disc-shaped diamond “table” formed on and bonded under a high-pressure and high-temperature (HPHT) process to a supporting substrate such as cemented tungsten carbide (WC), although other configurations are known. Drill bits carrying PDC cutting elements, which, for example, may be brazed into pockets in the bit face, pockets in blades extending from the face, or mounted to studs inserted into the bit body, are known in the art. It is also contemplated that cutting elements  160  may comprise, by way of example and not limitation, suitably mounted and exposed natural diamonds, thermally stable polycrystalline diamond compacts, cubic boron nitride compacts, or diamond grit-impregnated segments or integral portions of the bit body, as known in the art and as may be selected in consideration of the subterranean formation or formations to be drilled. 
     Each of blades  130  may also include a gage region  170  which is configured to define the outermost radius of the drill bit  100  and, thus the radius of the wall surface of a bore hole drilled thereby. Gage regions  170  comprise longitudinally upward (as the drill bit  100  is oriented during use) extensions of blades  130 , extending from the face  120  and may have wear-resistant inserts or coatings, such as cutting elements in the form of gage trimmers of natural or synthetic diamond, hardfacing material, or sintered tungsten carbide on radially outer surfaces thereof as known in the art to inhibit excessive wear thereto. 
     The bit body  110  of drill bit  100  further includes a shank connector  180  at a trailing end thereof, longitudinally opposite from the face  120 . The shank connector  180  comprises threads configured to be mated and at least substantially bound to a distal connector  210  of a shank  190 . The shank  190  may comprise a proximal connector  200  at one longitudinal end thereof having an American Petroleum Institute (API) thread connection for attaching the shank  190  to a drill string (not shown). At an opposing longitudinal end of the shank  190  is a distal connector  210  comprising a set of threads configured to mate with the threads on the shank connector  180  of the bit body  110 . Although the shank connector  180  is illustrated in  FIG. 1  as being configured as a male connector and distal connector  210  as a female connector, such a configuration is not intended to be limiting. Instead, shank connector  180  may be configured as either a male or female connector with distal connector  210  of the shank  190  being properly configured to mate with the shank connector  180 . 
     The threads for both the shank connector  180  and the distal connector  210  may comprise coarse and robust thread configurations. By way of example and not limitation, a suitable thread configuration may comprise a 3.500-12UN-2A thread. The thread combination between the shank connector  180  and the distal connector  210  may be configured to at least substantially bind with each other by galling or other mechanical interference, by introducing a particulate material on and between the threads, or both. 
     In some embodiments, the set of threads on the distal connector  210  and the threads on the shank connector  180  may be bound together by galling. By way of example and not limitation, such galling may be produced with threads on the shank connector  180  comprising a pitch that is at least slightly different from the pitch of the set of threads on the distal connector  210 . In other embodiments, galling may be effected by providing at least one set of threads including a pitch which varies as the threads travel from the initial point of contact inward. In other words, the pitch of at least one set of threads (on shank connector  180  and/or distal connector  210 ) may at least slightly increase or decrease as the threads extend along the particular connector. By way of example and not limitation, the pitch of the shank connector  180  may be configured to at least slightly increase so that there is little or no binding when the shank connector  180  and distal connector  210  are initially coupled. However, as the shank connector  180  and distal connector  210  progress in being screwed together, the increase in the pitch of the shank connector  180  may result in galling between the two parts. 
     In other embodiments, the minor diameter, major diameter, or both of the male and female threads may be configured so that at least the minor diameter of one thread set is slightly too large for the correlating major diameter of the other thread set. In such a configuration, the minor diameter of the one thread set will at least slightly gall or interfere with the correlating major diameter of the other thread set, resulting in at least partial binding between the two thread sets. 
     In still other embodiments, the center of the male threads may be offset from the center of the female threads. In such embodiments, the male and female threads are non-concentric or not axially aligned. By way of example and not limitation, in some embodiments, the centers of the male and female threads may be offset a distance between about 0.005 inch (0.127 mm) and 0.100 inch (2.54 mm). In some non-limiting embodiments, the centers of the male and female threads may be offset a distance between about 0.010 inch (0.254 mm) and 0.020 inch (0.508 mm). Generally, a smaller offset may be more applicable for harder materials while a larger offset may be employed for softer, more malleable materials. 
     Those skilled in the art will recognize that there may be additional thread combinations between the shank connector  180  and the distal connector  210  forming an interference fit exhibiting the galling necessary to at least substantially retain or affix the shank connector  180  and distal connector  210  together. 
     In some embodiments, the set of threads on the distal connector  210  and the threads on the shank connector  180  may be bound together by disposing a particulate material comprising a plurality of hard particles between the threads of the shank connector  180  and the distal connector  210 . The particulate material may be employed alone or in combination with threads configured to gall. By way of example and not limitation, the particulate material may comprise hard particles such as diamond grit, silicon carbide (SiC), alumina, and combinations thereof. Such hard particles may be sized and configured less than or equal to approximately 250 microns. In some embodiments, the plurality of hard particles may comprise hard ceramic particles sized between 5 and 50 microns. 
     In some embodiments of the present invention, the male and female threads may comprise a portion configured to align the shank and the bit body and a portion to secure the shank and bit body.  FIG. 2  illustrates an elevation view of a drill bit  100 A comprising a bit body  110  comprising alignment structure according to some embodiments of the invention. The shank  190  comprises a distal connector  210  including a shank alignment portion and a shank locking portion, which may also be referred to, respectively, as shank alignment threads  220  and shank locking threads  230 . The distal connector  210  may also include a shank alignment feature  240 . The shank alignment threads  220  comprise any conventional threads used in conventional drill bits for aligning a shank and bit body prior to being secured together. The shank alignment feature  240  may comprise a stepped portion of the distal connector  210  and may comprise an outer diameter exhibiting a substantially tight tolerance. 
     The bit body  110  comprises a shank connector  180  including related alignment structure to correlate to the alignment structure of the distal connector  210 . The shank connector  180  comprises a body alignment portion and a body locking portion, which may also be referred to herein as body alignment threads  250  and body locking threads  260 , respectively. The shank connector  180  may also include a body alignment feature  270 . The body alignment threads  250  are configured to correlate to the shank alignment threads  220  for aligning the shank  190  and the bit body  110 . The body locking threads  260  are configured to correlate to and at least substantially bind together with the shank locking threads  230 . In addition, the body alignment feature  270  is configured to receive the shank alignment feature  240 , both features comprising a substantially tight tolerance so that the longitudinal axis  280  of the shank  190  and the bit body  110  are at least substantially aligned. 
     In at least some embodiments, the body locking threads  260  and the shank locking threads  230  may be configured to not bind initially. In such embodiments, the portions of the body locking threads  260  and the shank locking threads  230  which initially engage may be configured to not bind, similar to the body alignment threads  250  and the shank alignment threads  220 . As the bit body  110  and shank  190  are screwed together, the body locking threads  260  and shank locking threads  230  may be configured to bind. The position in which the body locking threads  260  and shank locking threads  230  begin to bind may be configured so that the bit body  110  and shank  190  may mate at interface  300 , or at least substantially mate in some embodiments employing one or more gaskets  290  ( FIGS. 4-6 ), as described below. Thus, the binding of the body locking threads  260  and shank locking threads  230  may occur near the last or final rotations of the bit body  110  and the shank  190  as the two are screwed together. 
     As shown in  FIG. 2 , the body and shank alignment threads  250 ,  220 , respectively, have a smaller diameter than the body and shank locking threads  260 ,  230 , respectively. However, in other embodiments, as illustrated in  FIG. 3 , the respective body and shank alignment threads  250 ,  220  may comprise at least substantially the same diameter as the respective body and shank locking threads  260 ,  230 . By way of example and not limitation, in some embodiments, the body alignment threads  250  and the body locking threads  260  may comprise the same thread configuration and may have substantially the same nominal diameter (inner diameter for a female configuration, outer diameter for a male configuration). The shank alignment threads  220  may be configured to mate with the body alignment threads  250  and the body locking threads  260  with minimal binding, much like conventional alignment threads. The shank locking threads  230 , however, are configured to at least substantially bind with the body locking threads  260  as described above with reference to  FIG. 1 . 
     Thus, in the embodiment shown in  FIG. 3 , when the bit body  110  and the shank  190  are screwed together, the shank alignment threads  220  initially engage and mate with the body locking threads  260  with minimal to no binding. The shank alignment threads  220  continue through the body locking threads  260  and subsequently engage the body alignment threads  250  with minimal to no binding. The bit body  110  and the shank  190  may, therefore be properly aligned. About the same point or soon after the shank alignment threads  220  engage the body alignment threads  250 , the shank locking threads  230  engage the body locking threads  260 . As the shank locking threads  230  and the body locking threads  260  are screwed together, the shank locking threads  230  and the body locking threads  260  at least substantially bind together. 
     The location at which the shank locking threads  230  engage the body locking threads  260  may be configured to allow the bit body  110  and the shank  190  to be screwed together so as to contact at an interface  300 , wherein such contact may include physically contacting each other or contacting one or more gaskets  290  ( FIGS. 4-6 ) positioned at the interface  300 . The force on the bit body  110  and shank  190  at the interface  300  may aid in loading the threads to prevent or at least reduce the chance of backing off of the connection. 
     Although the shank connector  180  is illustrated in  FIGS. 2 and 3  as being configured as a female connector and distal connector  210  as a male connector, such a configuration is not intended to be limiting. Instead, shank connector  180  may be configured as either a male or female connector with distal connector  210  of the shank  190  being properly configured to receive the shank connector  180 . 
     Additional embodiments of the present invention may include one or more gaskets  290  positioned and configured to seal at least a portion of the interface  300 , also referred to herein as a “mating surface,” between the bit body  110  and the shank  190  from drilling fluid and other materials.  FIGS. 4-6  illustrate various embodiments of gasket configurations according to some embodiments of the present invention. In some embodiments, a gasket  290  may be positioned at the interface  300  located adjacent an exterior wall of the drill bit  100 , at the interface  300  located adjacent an interior wall of the drill bit  100 , or both. In some embodiments, the gasket  290  may be positioned in a grooved region, such as annular groove  310 , positioned in an interface surface of the bit body  110  (see  FIG. 5 ), an interface surface of the shank  190 , or both (see  FIG. 6 ). 
     In some embodiments, the gasket  290  may comprise a compliant material capable of deforming, such as rubber or nylon. In such embodiments, the gasket  290  may comprise a conventional O-ring positioned at the interface  300 , including within the annular groove  310 , when present. In other embodiments, the gasket  290  may comprise a metal material having a low melting point. By way of example and not limitation, the metal material may comprise a solder or other metal having a melting point below about 640° F. (about 338° C.). 
     Further embodiments of the present invention are directed to methods of forming earth-boring tools configured to fixedly attach the bit body  110  to the shank  190 . Forming a drill bit  100 , according to some embodiments, may comprise forming a shank  190  comprising a distal connector  210  having a set of threads thereon. A bit body  110  is formed comprising a face  120  and a shank connector  180 . Threads may be formed on the shank connector  180  with at least a portion of the threads being configured to at least partially bind with at least a portion of the set of threads on the distal connector  210 . The shank  190  may be affixed to the bit body  110  by screwing together the distal connector  210  of the shank  190  and the shank connector  180  of the bit body  110 . 
     The shank  190  may be formed from a metal or metal alloy, such as steel. Some embodiments may further comprise forming a set of threads on the proximal connector  200  as well as the distal connector  210 . The threads on the proximal connector  200  may be formed to comprise an API thread connection for attaching the shank  190  to a drill string. The threads on both the proximal connector  200  and the distal connector  210  may be formed according to conventional methods, including, but not limited to, machining, rolling, casting and grinding. 
     The bit body  110  may be formed of a material such as a metal or metal alloy, such as steel, or a particle-matrix composite material. The threads on the shank connector  180  of the bit body  110  may be formed by machining, rolling, casting, grinding, or any other conventional means. In embodiments where the bit body  110  is formed of a particle-matrix composite material, the bit body  110  may be formed by conventional infiltration methods (in which hard particles (e.g., tungsten carbide) are infiltrated by a molten liquid metal matrix material (e.g., a copper based alloy) within a refractory mold), as well as by newer methods generally involving pressing a powder mixture to form a green powder compact, and sintering the green powder compact to form a bit body  110 . The green powder compact may be machined as necessary or desired, prior to sintering using conventional machining techniques like those used to form steel bodies or steel plate structures. Indeed, in some embodiments, the threads on the shank connector  180  may be formed with the bit body  110  in a green powder compact state, or in a partially sintered brown body state. Furthermore, additional machining processes may be performed after sintering the green powder compact to the partially sintered brown state, or after sintering the green powder compact to a desired final density. 
     In some embodiments, at least a portion of the threads on the shank connector  180  may be configured to at least partially bind by forming at least a portion of the threads to gall with at least a portion of the set of threads on the distal connector  210  of the shank  190 . When the bit body  110  comprises a particle-matrix composite material, the threads on the shank connector  180  may be formed when the bit body  110  is in the green powder compact or the brown state. Subsequently, when the bit body  110  is sintered to the desired final density, the thread configuration may deflect or deform slightly to produce the desired interference to enable the set of threads on the shank connector  180  to gall with the set of threads on the distal connector  210 . 
     In some embodiments, forming the bit body  110  with threads configured to at least partially bind with the set of threads on the distal connector  210  may comprise disposing a particulate material between the threads on the shank connector  180  and the set of threads on the distal connector  210 . The particulate material may be disposed on the set of threads on the shank connector  180 , the distal connector  210 , or both prior to screwing them together. The particulate material may be disposed on threads configured to gall with each other as well as threads configured to be free from any substantial galling. 
     Some embodiments include disposing a gasket  290  at the interface  300  between the bit body  110  and the shank  190 . In embodiments which comprise an annular groove  310 , the gasket  290  may be disposed at least partially within the annular groove  310 . In embodiments in which the gasket  290  comprises a compliant material, the gasket  290  may be depressed at least partially within the annular groove  310  and at least substantially locked into place. 
     In embodiments in which the gasket  290  comprises a metal having a low melting point, the material comprising the gasket  290  may be disposed in a molten or solid form on an interfacing surface and/or in a groove of the bit body  110 , the shank  190 , or both. The bit body  110  and shank  190  may be screwed together as described above and the assembly may be heated to a temperature greater than or equal to the melting point of the metal gasket material to reflow the metal gasket material. In other embodiments, the metal gasket material may be brazed at the interface  300 . 
     Additional embodiments of the present invention relate to methods of securing a bit body of an earth-boring tool to a shank. In at least some embodiments, the method may include providing the bit body  110  comprising a shank connector  180 . The shank connector  180  comprises threads formed at a trailing end thereof. A shank  190  comprising a distal connector  210  is provided with a set of threads on the distal connector. The shank connector  180  of the bit body  110  may be coupled to the distal connector  210  of the shank  190  by screwing the shank connector  180  and the distal connector  210  together. 
     While certain embodiments have been described and shown in the accompanying drawings, such embodiments are merely illustrative and not restrictive of the scope of the invention, and this invention is not limited to the specific constructions and arrangements shown and described, since various other additions and modifications to, and deletions from, the described embodiments will be apparent to one of ordinary skill in the art. Thus, the scope of the invention is only limited by the literal language, and legal equivalents, of the claims which follow.