Abstract:
A roller cone body defines a circumferential channel or race into which a plurality of cutter or wear segments are mounted. The wear segments may be of any appropriate contour or shape, such as for example chisel, spherical, or even flat face and are preferably made or carbide. The wear elements may be all the same within a channel or race, or they may be varied within a race as needed for a particular application.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of rock bits for boring into earth formations, and, more particularly, to a roller cone bit with tooth segments which mount to the cone. 
     BACKGROUND OF THE INVENTION 
     Roller cone bits are well known in the art for boring into earth formations. Such bits may have one or a plurality of cones, typically three, each of which rotates about its own axis as the bit body is rotated about its axis. Each cone has cutting elements on the exterior that gouge and scrape the borehole bottom. In known roller cone bits, cutting elements may generally classified as milled tooth, in which the cutting elements are formed from a solid workpiece, or insert type, which individual cutter inserts are press fit into mating holes formed in the cone of the bit body. In mining and tunnel boring operations, rolling cone cutters often have disk type cutting elements. 
     For harder formations, tungsten carbide inserts define teeth extending from the exterior surface of the cone. These inserts are press fit into mating holes in the cones. Each insert has a cylindrical base that fits with an interference fit into the cone body. A cutting tip, which may have various shapes, protrudes from the base of the insert. 
     As the drill bit is used to bore into an earth formation, the inserts are worn away until the bit must be extracted from the hole and a new bit inserted. Such bits typically last approximately 40 to 100 hours of drill time in a typical formation. The useful lifetime of the inserts, and therefore the bit, depends on a number of well known factors, including the hardness of the material from which the inserts are made, the hardness of the earth formation, the weight on bit, and other factors. In very abrasive formations the useful lifetime of the bit is often limited by the total amount of carbide material available for resisting wear, especially the amount of carbide in the gage cutting area, a factor which is not well appreciated in the art. Increasing the number of inserts has been tried as a solution to this limiting factor, but the inserts must be spaced apart by a minimum distance so that sufficient body material is left between inserts in order to provide adequate mechanical support for the inserts. Use of diamond enhanced inserts (DEI) has been another solution that is often used, but this is a very expensive solution. 
     Thus, there remains a need for a structure and a method of installing wear elements in a roller cone bit that increases the total amount of material available for resisting abrasion. The present invention is directed to this need in the art. 
     SUMMARY OF THE INVENTION 
     The present invention primarily comprises a roller cone body including a circumferential channel or race into which are mounted a plurality of wear elements, referred to herein as segments. The wear elements may be of any appropriate contour or shape, such as for example chisel, spherical, or even flat face. The wear elements may be all the same within a channel or race, or they may be varied within a race as needed for a particular application. 
     The cone body may have more than one such channel or race formed therein, and the cone may also or alternatively include mill tooth forms or inserts on other portions of the cone body. 
     A keyway is provided into which the segments are inserted into the channel for mounting upon the cone body. Once an appropriate number of segments have been inserted into the channel, a key is then inserted and secured in place, such as for example by pinning. If desired, the segments may then be soldered in place, or the segments may allowed to remain unsoldered. Each of the segments includes an enlarged section to fit within the channel, and to retain the segment on the cone body. The enlarged section may be subject to stress in some applications, and thus a stress relieve annulus is provided to eliminate the possibility of failure due to excess stress on the segments. 
     These and other features and advantages of this invention will be readily apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to embodiments thereof which are illustrated in the appended drawings. 
         FIG. 1  is a perspective view of a tri-cone drill bit using the present invention. 
         FIG. 2  is a perspective, partially exploded view of a bit constructed in accordance with the teachings of this invention. 
         FIG. 3A  is a section view of a cone body, depicting a preferred embodiment of locking segments into the race or channel. 
         FIG. 3B  is a section view of a cone body, depicting another preferred embodiment of locking segments into the race or channel. 
         FIG. 4A  is a perspective view of a cone body, illustrating details of locking segments into the race or channel. 
         FIG. 4B  is a perspective view of a cone body, illustrating details of inserting segments into the race or channel. 
         FIG. 5  is a perspective of a cone and supporting structure constructed in accordance with this invention. 
         FIG. 6  is a perspective view of a roller cone of the invention with integral milled teeth on the cone body. 
         FIG. 7  is a perspective view of a roller cone with gage row wear segments in accordance with the invention, with inserts on the conical section of the bit. 
         FIG. 8  is a perspective view of a roller cone with sharp wear segments on the gage row and interior rows. 
         FIG. 9  is a perspective view of a disk cutter formed by inserting segments into channels in accordance with this invention. 
         FIG. 10  is a side view of a tunnel boring disk cutter formed by inserting disk segments into channels in accordance with this invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a tri-cone rotary drill bit  10  using the structure of the present invention. The bit  10  is used for illustrative purposes, although it is to be understood that the present invention may be employed on any rotary cone cutter, such as for example a one cone bit, a bi-center bit on which a rotary cone is used, and the like. 
     The drill bit  10  has a threaded section  12  on its upper end for threading to a drill string or mud motor (not shown) for rotation. The threaded section  12  extends into an elongate body  14  which, at its lower end, provides support for three rotary cone cutters  16 , constructed in accordance with the present invention. The body  14  has fluid nozzles  18  for directing drilling fluid downward and toward the leading edge of the cone bit  16 . The bit  10  includes other portions constructed as shown and described in my U.S. Pat. No. 6,167,975, incorporated herein by reference. The bit  10  further includes a gage row of cutter or wear segments  24 , inserted into a race or channel, as further described below. 
     The structure of the cone bit  16  will now be described with reference to  FIGS. 2 ,  3 A,  3 B,  4 A, and  4 B. Other preferred embodiments of the cone bit will be described with reference to other drawing figures. The cone  16  comprises a cone body  20  of high alloy steel into which is machined or otherwise formed one or more circumferential channels or races  22 , shown most clearly in  FIG. 4B . The channels or races receive a plurality of cutter segments  24  which may vary in shape and contour according the particular earth formation into which the bit is to bore. The cutter or wear segments  24  are preferably tungsten carbide, although diamond enhanced cutters may be used, or other appropriate long lasting wear material. Each of the plurality of cutter segments  24  is placed into a keyway or slot  26  and slid into the channel  22 . Two such keyways are shown in  FIG. 2 . The keyways of  FIG. 2  may be referred to as “radial” keyways, because segments inserted into the keyways are inserted in a radial direction. It is to be understood that other configurations of keyways are possible within the scope and spirit of this invention. Each segment is then slid along the channel in turn, until the channel is substantially full of segments. Steel shims  28  may be used to insure a complete filling of the channel. Shims  28  of a given thickness may be placed between each segment to reduce the number of carbide segments being used. Thin steel shims may be used between each segment to prevent carbide against carbide breakage during the severe operating conditions experienced by rock bits. A final segment  30 , in the nature of a key or locking wedge, then slid into the keyway and locked into place with a pin  32 , for example, into a pin hole  34 . Alternatively, the key  30  may be welded or otherwise secured in place. Also, the spaces in the channel and between the segments may be filled with silver solder or other suitable material, if desired. Silver solder may be used to bond the segments, key, and cone together as an additional safety factor to minimize the chances of leaving junk down hole in the case of cutting structure failure. 
     While the keyways of  FIG. 2  were described as radial,  FIGS. 3A ,  4 A, and  4 B depict an “axial” keyway, in that the segments  24  are inserted into a slot  36  in an axial direction, and the slot  36  is cut axially into the cone body. After the last segment is inserted in place, a plug  38  is inserted behind the last segment, and preferably welded in place, thereby locking the segments in place. This embodiment of the invention provides the advantage in that the entire race or channel  22  is filled with segments, with no space allotted for the locking wedge  30 , as in  FIG. 2 . 
       FIG. 3B  depicts a section view of a portion of a cone body  20  with a section view of a wear segment  24  installed within the channel  22 . Another segment  24  is shown within another channel  22 ′, to illustrate another structure for supporting a segment, and also to illustrate a channel on the conical portion of the cone body. The channel  22  comprises a bottom surface  44  and side walls  46  and  48 . Each of the side walls defines an “S” or ogee shape to provide a widened portion to receive a lobe  40  ( FIG. 4B ) of each segment  24 . The segment  24  is subjected to a sideways force, resulting in torsion stress to the segment. This torsion stress may result in premature failure of the segment, so stress relieving annular grooves  50  and  52  are provided in the bottom  44  of the channel. In other words, the force on the wear segment  24  is transmitted to the cone through the bottom surface  44 . Force on the lobes  40  could cause them to break, so relief grooves  50  and  52  are provided to eliminate that probability. An alternative to using surface  44  to transmit the load is to use the tapered side walls  46  and  48 , as shown with regard to the segment  24 ′ in the channel  22 , including a gap  54  therebetween. This will also protect the retaining lobes  40  from being broken. 
       FIG. 5  depicts a cutting structure designed with this invention for a very specific type of formation. The Bromide Sand in South Eastern Oklahoma is an example of this type formation. This very abrasive formation is drilled with a crushing and grinding action rather than with crushing, scraping, chipping and spalling actions like most other formations. Bits continue to drill Bromide Sand even after all the carbide is worn away. The bare steel of the cone continues to drill by crushing and grinding the formation. Therefore, sharp protruding points and ridges are not necessary on the segments  24  of the bit depicted in  FIG. 5 . Prior art bits used in Bromide Sand are plagued with short life due to early cutting structure wear, especially in the gage area. This invention was conceived to improve bit performance in the Bromide Sand drilling. 
     The bit of  FIG. 5  includes a plurality of segments  24  installed in the gage row, and a plurality of interior row segments  24 ′ and  24 ″ along the conical portion of the bit. In this way, the greatest amount of wear resistant material, such as tungsten carbide, is presented to the abrasive wear area. 
     Returning briefly to  FIG. 2 , a gage row wear segment  24  is shown. The gage row wear segment  24  may preferably include an outside diameter beveled edge  60  and a bottom beveled edge  62 . The beveled edges  60  and  62  are useful because the gage row segments are used as scrapers against the outside portion of the bore hole, while the interior row segments  24 ′ and  24 ″ are used to crush against the bottom of the bore hole, and thus the interior row segments  24 ′ and  24 ″ present a substantially flat aspect to the bore hole. The cone body  20  may also include a spherical insert  64  at the apex of the cone ( FIG. 5 ). 
       FIG. 6  depicts a presently preferred embodiment of the invention which the wear cutters or segments of this invention are installed on a milled tooth cutter  70 . The milled tooth cutter  70 , including a plurality of milled teeth  78 , is formed in the conventional manner, and then a channel as previously shown and described is formed in the cone body. In this embodiment, a cutter or wear segment  72  includes a transverse groove  74  on the outer, exposed surface thereof. The gage row is completed with a wedge segment  76 . The groove  74  allows crushed or sheared formation material to flow away from the points of contact where formation failure is actually taking place. This makes the crushing action more efficient. As the segments rotate away from contact with the formation, the detritus is washed from these grooves by fluid from the nozzles  18 . The drilling mud or fluid picks up cuttings or crushed material removed from the borehole, and carries that material to be washed away by fluid from the nozzles. 
       FIG. 7  depicts another preferred embodiment of the invention, comprising a roller cone bit  80  with gage row segments  82  and  84 , with inserts  86  on the conical portion of the bit  80 . The segments  82  are sharper than those previously described, and form chisel segments for more aggressive cutting of the formation. The inserts  84  present a substantially flat aspect between the chisel segments  82 . The insert  86  are made in the conventional manner, and are inserted into holes drilled or otherwise formed in the bit. 
     Similarly,  FIG. 8  shows a bit  90  with chisel segments  82  and substantially flat segments  84 , as previously described. The bit  90  further includes chisel segments  82 ′ and  82 ″ on interior rows, with substantially flat segments  84 ′ and  84 ″ therebetween. 
       FIG. 9  illustrates a disk cutter  100  constructed in accordance with the invention. The disk cutter  100  comprises a plurality of disk segments  102  is a gage row, and disk segments  102 ′ and  102 ″ in interior rows. The disk segments present a sharp substantially circular edge to the formation for aggressive cutting of the formation. Similarly,  FIG. 10  shows a tunnel boring disk cutter  110  with segments  112  inserted into a channel formed in a disk cutter body  114 . This structure provides the advantage of allowing virtually a solid ring of tungsten carbide, which allows the disk to have a sharper cutting radius and longer lifetime than previously known. These cutters cut faster and last longer than known disk cutters, permitting the tunneling machine to run with less down time. 
     The principles, preferred embodiment, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.