Abstract:
An earth boring bit has three cones, each cone being mounted for rotation about a cone axis while the bit rotates about a bit axis. An outer row and an adjacent row of cutting elements are integrally formed on each of the cones. Each of the cutting elements of the adjacent row on each of the cones has a crest extending perpendicular to a direction of rotation of the cone. Annular spaces are located between the outer row and the adjacent row on each of the cones. The annular space on one cone has a width that is less than the annular spaces on the other cones. The width of the narrowest annular space is greater than the width of the crests of the adjacent row.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to provisional patent application 60/598,952 filed Aug. 5, 2004. 

   FIELD OF THE INVENTION 
   This invention relates in general to earth boring bits, and in particular to the spacing between the rows of cutting elements of a roller cone bit. 
   BACKGROUND OF THE INVENTION 
   A typical roller cone earth boring bit, such as used to drill wells, has three cones that roll around a common axis. The cones are mounted to bearing pins that depend from head sections. The head sections are welded together to form a body that is threaded at the upper end for connection to a drill string. 
     FIGS. 1-3  illustrate a typical prior art rolling cone bit  11 . Bit  11  has three cones  13 ,  15  and  17 . Cone  13  has a spear point cutting element  19  on its inner end and a heel or outer row  21  of cutting elements on its outer end. The outer side of each tooth of outer row  21  joins a gage surface  22 . The cutting elements in this instance comprise teeth that are integrally formed with cone  13  and milled into desired shapes. Milled teeth are generally chisel-shaped, each having a crest  28  that is perpendicular to the direction of rotation of the bit. Alternately, the cutting elements could be cast with the body of the cone or comprise tungsten carbide inserts pressed into mating holes. 
   Cone  13  also has an inner row  23  spaced a short distance from outer row  21 . A groove  25  locates between outer row  21  and inner row  23 . A layer of hardfacing  27 , shown by phantom lines, covers each cutting element in outer row  21  and inner row  23 . Groove  25  is generally triangular in cross-section and has a width  26  that may be measured between tips of teeth  21 ,  23  at the crests  28 . In the prior art, width  26  is normally less than the width of crest  28  of a cutting element of inner row  23  or of outer row  21 . 
   Referring to  FIG. 1 , cone  15  has an outer row  29  and an inner row  31  spaced apart by a groove  33 . Groove  33  has a much wider width  34  than width  26  of cone  13 . In the prior art, width  34  is typically equal or greater than the width of crest  28  of one of the teeth of inner row  31 . Cone  17  has an outer row  35  and an inner row  37  spaced apart by a groove  39 . Groove  39  has a width  40  that is wider than width  34  and width  26 . Width  40  is greater than the width of crest  28  of one of the outer row teeth  35  or inner row teeth  37 . 
   The various rows  21 ,  23 ,  29 ,  31 ,  35  and  37  are arranged for a desired bottom hole coverage, as indicated in  FIG. 2 . In  FIG. 2 , all of the rows of teeth are rotated into a single sectional plane. Some of the teeth intermesh with each other as shown in  FIG. 1 . The number of rows per cone in the prior art can be more or less than those shown in  FIG. 1 . In the prior art example shown, there are a total of seven rows, and the narrowest groove width  26  is located on cone number one, which has the spear point. In an eight row bit, the narrowest groove width  26  would be normally on cone  17 , which is cone number two. In a nine row bit, the narrowest groove width  26  would be on cone  15 , which is cone number three. A narrow groove on one of the cones has been necessary in the prior art in order to achieve intermesh and the desired bottom coverage. While workable, in certain formations such as shales, the cuttings tend to ball up in rows separated by narrow grooves, reducing the rate of penetration. 
   SUMMARY OF THE INVENTION 
   The bit of this invention has first, second, and third cones, each cone being mounted for rotation about a cone axis while the bit rotates about a bit axis. An outer row and an adjacent row of cutting elements are located on each of the cones. Each of the cutting elements of the adjacent row on each of the cones has a crest extending perpendicular to a direction of rotation of the cone. An annular space or groove is located between the outer row and the adjacent row on each of the cones. 
   To reduce balling, the narrowest groove between the outer and adjacent rows is made larger than in comparable sized bits of the prior art. The increased width is accomplished by reducing the widths of the crests and re-positioning the rows for bottom coverage. The inner side of the outer row of one of the cones is moved inward a considerable distance for bottom coverage between the widest groove. 
   Each of the grooves has a width, measured between tips of the outer and adjacent rows, that is greater than a width of the crests of the adjacent row on the same cone. In the embodiments shown, each of the grooves has a width that is greater than one-half of a width of at least one, and preferably all of the other grooves on the same cone. The outer row of one of the cones has an inner side that is tangent to an inner side plane perpendicular to the cone axis. The inner side plane is closer to the bit axis than to a plane containing a backface of said one of the cones. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a layout of a prior art three-cone bit. 
       FIG. 2  is a layout of the prior art bit of  FIG. 1 , with the teeth of the cones rotated into a single section plane. 
       FIG. 3  is a side view of the number one cone of the prior art bit of  FIG. 1  before the application of hardfacing. 
       FIG. 4  is a side view of a comparably sized number one cone before the application of hardfacing and constructed in accordance with this invention. 
       FIG. 5  is a layout of a three-cone bit constructed in accordance with this invention, the bit including the number one cone shown in  FIG. 4 . 
       FIG. 6  is a layout of the bit of  FIG. 5 , with the teeth of the cones shown rotated into a single section plane to show bottom coverage. 
       FIG. 7  is a layout of an alternate embodiment of a bit constructed in accordance with this invention. 
       FIG. 8  is a layout of the bit of  FIG. 7 , with the teeth of the cones shown rotated into a single section plane to show bottom coverage. 
       FIG. 9  is a top view of the third cone of the bit of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 5 , bit  41  has three cones  43 ,  45  and  47 . Cone  43  has a cutting element  49  referred to as a spear point on its inner end and a heel or outer row  51  on its outer end. Cutting element  49  extends closer to the bit axis of rotation  50  than any cutting structure on cones  45  and  47 . Cone  43  has an outermost adjacent row  53 , referred to herein as adjacent row  53 , spaced from outer row  51  by an annular space or groove  55 . The teeth or cutting elements of cones  43 ,  45  and  47  are covered with hardfacing  54 , shown by the fragmentary lines. The teeth of cones  43 ,  45  and  47  are milled teeth that are machined from the metal of the body of the cones. Alternately, the teeth could be cast with the body of the cone, or comprise tungsten carbide compacts press-fitted into holes in the bodies of cones  43 ,  45  and  47 . 
   Groove  55  is triangular in cross-section and has a width  57  measured between the tips (after hardfacing  54  is applied) of the teeth in outer and inner rows  51 ,  53 . Width  57  is considerably greater than width  26  of groove  25  ( FIG. 1 ) of a comparably sized bit of the prior art. Preferably, width  57  is greater than the width of a crest  59  of one of the teeth of adjacent row  53  or outer row  51 , including hardfacing  54  contained on each tooth. Crest  59  on each tooth is perpendicular to the direction of rotation of cone  43 . In this embodiment, the width of crest  59  of each tooth of adjacent row  53  or outer row  51  is less than the width of crest  28  ( FIG. 1 ) of each tooth of inner row  23  or outer row  21  of a comparably sized prior art bit. The reduction in widths of crests  59  over the prior art bit partly accounts for the increase in width  57  of groove  55 . 
   Cone  45  has an outer row  61  and an adjacent row  63  separated by a groove  65 . Groove  65  has a width  66  measured at the tips of the teeth between rows  61 ,  63  that is greater than width  57  of groove  55 . However, the amount of difference is not so much as in the prior art bit of  FIGS. 1-3 . In this example, width  57  is more than half the amount of width  66 . In the prior art bit of  FIG. 1 , width  26  is only about one-third of width  34 . In this example, width  66  is greater than width  34  of the comparably sized prior art bit  11  of  FIG. 1 . The inner side of adjacent row  63  is preferably spaced closer to the inner end of cone  45  than in the comparably sized prior art bit of  FIG. 1 . 
   Cone  47  has an outer row  67  that has an outer side spaced inward from gage surface  68  in this example. In this embodiment, the outer side of outer row  67  is spaced inward from gage surface  68  by an annular space  69  having a width  70 . Annular space width  70  is slightly less than the width of crest  59  of each of the teeth of outer row  67  in this example. The width of each tooth of outer row  67  is less than a comparably sized tooth of outer row  35  ( FIG. 1 ). 
   The inner side of outer row  67  is closer to bit axis  50  than the inner side of outer rows  51  and  61  of cones  43  and  45 . Furthermore, the inner side of each tooth of outer row  67  is located more inward than the comparable teeth of prior art outer row  35  ( FIG. 1 ). Referring to  FIG. 6 , plane  71  is perpendicular to cone axis of rotation  73  and is tangent to the inner side of outer row  67  of cone  47 . Plane  71  is spaced a distance d 1  from the cone backface  75  and a distance d 2  from bit axis  50 . Distance d 2  is smaller than distance d 1 , placing the inner side of outer row  67  of cone  47  closer to bit axis  50  than to cone backface  75 . A similar plane (not shown) in the prior art example of  FIG. 2  would intersect the cone axis closer to the backface than the bit axis. 
   Adjacent row  77  of cone  47  is spaced from outer row  67  by a groove  79 . Groove  79  has a width  81  that is approximately the same as width  40  of a comparably sized prior art bit  11  ( FIG. 1 ). The width of the crest  59  of each tooth of adjacent row  77  is less than the width of crest  28  of prior art bit  11  ( FIG. 1 ). 
   Referring still to  FIG. 6 , the reduction in widths of crests  59  of some of the rows and the placement of the various rows provides approximately the same bottom coverage as in the prior art bit of  FIG. 2 . In the first embodiment of this invention, the center line of outer row  67  of cone  47  locates equidistant between outer row  51  and adjacent row  53  of cone  43 . Outer row  67  of cone  47  and adjacent row  53  of cone  43  locate between rows  61  and  63  of cone  45 . Both cone  43  adjacent row  53  and cone  45  adjacent row  63  locate between cone  47  outer row  67  and cone  47  adjacent row  77 . 
   When the bit has more or less than seven rows of teeth, the location of narrowest width  57  might be on cone  45  or cone  47 . When the bit has more or less than seven rows of teeth, the location of outer row  67 , which has reduced width crests  59  and is off-gage, might be on cone  43  or cone  45 . Increasing the narrowest width  57  does not necessarily require providing an outer row  67  that has reduced width crests  59  and is off-gage. Outer row  67  could have crests  59  of conventional width and have its outer sides flush with the gage. Alternately, outer row  67  could be staggered, with alternating teeth of varying width crests. 
   A second embodiment is shown in  FIGS. 7-9 . Cone  83  has an outer row  85  and an adjacent row  87  separated by a groove  89 .  FIG. 8  shows width  91  between the tips of outer row  85  and adjacent row  87  after the application of hardfacing  93 . Cone  95  has an outer row  97  in which all of the teeth have outer sides flush with gage surface  99 , unlike outer row  67  of  FIG. 5 . An adjacent row  101  is separated from outer row  97  by annular groove  103 . Groove  103  has a width  105  that is less than width  91 , as shown in  FIG. 8 . This differs from the first embodiment where width  57  is less than width  81  ( FIG. 5 ). 
   Cone  107  has a staggered outer row with outward cutting elements  109   a  and inward cutting elements  109   b . As shown in  FIG. 9 , cutting elements  109   a  and  109   b  alternate with each other, with each cutting element  109   b  located equidistant between two cutting elements  109   a . The number of cutting elements  109   a  is the same as the number of cutting elements  109   b  in this example. The outer sides of outward cutting elements  109   a  are flush with gage surface  99  ( FIG. 7 ). The outer sides of inward cutting elements  109   b  are spaced inward from gage surface  99 . In the embodiment shown, the outer sides of inward cutting elements  109   b  are inward from the inner sides of outward cutting elements  109   a . Adjacent row  111  is not staggered and is located inward from inward cutting elements  109   b.    
   An annular groove  112  is located between outer row cutting elements  109   a ,  109   b  and adjacent row  111 . Groove  112  has a width  113   a  from outward cutting elements  109   a  to adjacent row  111  and a width  113   b  from inward cutting elements  109   b  to adjacent row  111 , as shown in  FIG. 8 . Width  113   a  is larger than widths  91  and  105 . Width  91  is larger than width  105  in this embodiment, thus the narrowest annular groove between adjacent and outer rows in this embodiment is groove  103  of cone  95 . Although smaller, width  105  of groove  103  is greater than one-half the widths  91 ,  113   a  or  113   b . Also, width  105  of groove  103  is greater than the width of the crests of adjacent row  101 . 
   The inner side of the outer row of cone  107  is considered to be the inner sides of inward cutting elements  109   b , which is spaced farther inward than outer rows  85  and  97 . Plane  115  is tangent to the tips of outer row cutting elements  109   b  on the inner side and perpendicular to cone axis  117 . Plane  115  intersects cone axis  117  closer to bit axis  119  than backface  121 . 
   The invention has significant advantages. The arrangement of the teeth reduces balling of shale in the rows adjacent to the narrower grooves and improves removal of drill cuttings because of the greater widths than in the prior art for comparable sized bits. The reduction in balling and better cuttings removal has resulted in greater performance of the bit. 
   While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.