Abstract:
An earth-boring bit has at least one steel tooth with a scoop-shaped profile. The scoop-shaped profile is formed by milling and hardfacing a tooth to have at least one flank with a concave profile. Additionally, the tooth may contain one flank with a concave profile and another with a convex profile. The centerline axis of the tooth may be moved to alter the angle between the flanks and the centerline to vary the manner in which the tooth engages the formation.

Description:
FIELD OF THE INVENTION  
       [0001]    This invention relates to improvements to earth-boring tools, especially to steel-tooth bits that use hardfacing to enhance wear resistance. 
       BACKGROUND  
       [0002]    The earliest rolling cutter earth-boring bits had teeth machined integrally from steel, conically shaped, earth disintegrating cutters. These bits, commonly known as “steel-tooth” or “mill-tooth” bits, are typically used for penetrating relatively soft geological formations of the earth. The strength and fracture-toughness of steel teeth permits the effective use of relatively long teeth, which enables the aggressive gouging and scraping action that is advantageous for rapid penetration of soft formations with low compressive strengths. 
         [0003]    However, it is rare that geological formations consist entirely of soft material with low compressive strength. Often, there are 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. 
         [0004]    Consequently, it has been common in the art since at least the early 1930s to provide a layer of wear resistant metallurgical material called “hardfacing” over those portions of the teeth exposed to the severest wear. The hardfacing typically consists of extremely hard particles, such as sintered, cast or macrocrystalline tungsten carbide dispersed in a steel, cobalt or nickel alloy binder or matrix. Such hardfacing materials are applied by heating with a torch a tube of the particles that welds to the surface to be hardfaced a homogeneous dispersion of hard particles in the matrix. After hardfacing, the cone is preferably heat treated, which typically includes carburizing and quenching from a high temperature to harden the cone. The particles are much harder than the matrix but more brittle. After hardening, the matrix has a hardness preferably in the range from 53 to 68 Rockwell C (RC). The mixture of hard particles with a softer but tougher steel matrix is a synergistic combination that produces a good hardfacing. There have been a variety of different hardfacing materials and patterns, including special tooth configurations, to improve wear resistance or provide self sharpening. 
         [0005]      FIG. 1  shows a prior art mill-tooth bit  11 . Earth-boring bit  11  includes a bit body  13  having threads  15  at its upper extent for connecting bit  11  into a drill string (not shown). Each leg of bit  11  may be provided with a lubricant compensator  17 . At least one nozzle  19  may be provided in bit body  13  for directing pressurized drilling fluid from within the drill string and bit  11  against the bottom of the bore hole. 
         [0006]    Cones  21 ,  23 , generally three (one of which is obscured from view in  FIG. 1 ), are rotatably secured to respective legs of bit body  13 . A plurality of inner row teeth  25  and outer row teeth  27  are arranged in generally circumferential rows on cones  21 ,  23 , being integrally formed on the cones, usually by machining. Outer or heel row teeth  27  are located at the outer edges of each cone  21 ,  23  adjacent gage surfaces  29 . Each bit leg has a shirttail portion  31  on its outer side adjacent gage surface  29  of cones  21 ,  23 . Typically, hardfacing will be applied to inner row teeth  25 , heel row teeth  27 , gage surface  29  and also to shirttail  31 . 
         [0007]      FIGS. 2 and 3  illustrate a tooth  28  that typically would be in a heel row in place of heel row  27  in cone  21  of  FIG. 1 . Tooth  28  is formed with a milling cutter which forms a root  43 , inclined flanks  33 .,  35  and an elongated crest  37 . An outer or gage end  39  is located at the outer side adjacent gage surface  29  ( FIG. 1 ), and an inner end  41  is located opposite outer end  39 . Hardfacing  45  is applied to the flanks  33 ,  35 , and crest  37 . Tooth  28  has a centerline  49  ( FIG. 3 ) which is substantially symmetrical and bisects tooth  28 . Centerline  49  extends through the axis of rotation of cone  21 . 
       SUMMARY OF INVENTION  
       [0008]    The earth-boring bit of this invention has at least one hardfaced steel tooth with a scoop-shaped profile. The scoop-shaped profile is formed by milling or hardfacing a tooth to have at least one flank with a concave profile. Additionally, the tooth may contain one flank with a concave profile and another with a convex profile. The centerline of the tooth may be moved to alter the angle between the flanks and the centerline to vary the manner in which the tooth engages the formation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a side elevation of a prior art earth-boring bit. 
           [0010]      FIG. 2  is a perspective view of one tooth of one of the cutters of the prior art bit of  FIG. 1 . 
           [0011]      FIG. 3  is a sectional view of the tooth of  FIG. 2 . 
           [0012]      FIG. 4  is a sectional view of a hardfaced tooth constructed in accordance of this invention. 
           [0013]      FIG. 5  is a sectional view similar to  FIG. 4 , but showing an alternate embodiment of the hardfaced tooth. 
           [0014]      FIG. 6  is another sectional view similar to  FIG. 4 , but showing a second alternate embodiment of a tooth hardfaced in accordance with this invention. 
           [0015]      FIG. 7  is another sectional view similar to  FIG. 4 , but showing a third alternate embodiment of a tooth hardfaced in accordance with this invention. 
           [0016]      FIG. 8  is another sectional view similar to  FIG. 4 , but showing a fourth alternate embodiment of a tooth hardfaced in accordance with this invention. 
           [0017]      FIG. 9  is another sectional view similar to  FIG. 4 , but showing a fifth alternate embodiment of a tooth hardfaced in accordance with this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 4  illustrates a tooth  53  constructed in accordance of this invention. Tooth  53  is formed with a milling cutter (not shown) which forms a root  51 , inclined flanks  55 ,  57  and a crest  59 . Flank  55  is milled with a concave profile, and flank  57  is milled with a convex profile. The terms “concave” and “convex” are used broadly to mean inward and outward curved surfaces. Flanks  55 ,  57  are not portions of a sphere. Flanks  55 ,  57  incline and converge toward each other, joining at a crest  59 . The result is a scoop-shaped tooth  53 . Hardfacing  61  is preferably applied in an even thickness to flanks  55 ,  57 , and crest  59 . 
         [0019]    In one embodiment, tooth  53  has a centerline  63  that bisects tooth  53 , with flank  55  on one side and flank  57  on the other. Centerline  63  extends through the axis of rotation of the cone: centerline  63  would equally bisect flanks  55 ,  57  if they were flat. Of flanks  55 ,  57 , one is a leading flank and the other a trailing flank, considering the direction of rotation of cone  21 ,  23 . The leading flank faces into the direction of rotation. The leading flank may be concave and the trailing flank convex. Alternatively, the leading flank may be convex and the trailing flank concave. Because of the different configurations of flanks  55 ,  57 , tooth  53  is not symmetrical about axis  63  when viewed in the sectional plane of  FIG. 4 . If viewed in a sectional plane perpendicular to that of  FIG. 4 , tooth  53  could appear symmetrical. 
         [0020]      FIG. 5  illustrates an alternate embodiment tooth  66  constructed in accordance of this invention. Tooth  66  is formed with a milling cutter which forms a root  67 , inclined flanks  69 ,  71  and a crest  73 . Flanks  69 ,  71  incline and converge toward each other, joining at a crest  73 . Flanks  69 ,  71  are flat and identical prior to the application of hardfacing. Hardfacing  75  is applied in varying thickness to flanks  69 ,  71 , and crest  73 . In the embodiment shown, the hardfacing  75  thickness varies on the concave flank  69  and convex flank  71  between the crest  73  and the root  67 . More specifically, the hardfacing  75  thickness on the flank upper section  69   c  proximate the crest  73  and the flank lower section  69   a  proximate the root  67  is greater than the hardfacing  75  thickness proximate the flank middle section  69   b . The hardfacing  75  thickness change between these three sections defines a semi-circular surface on the hardfacing  75  curving outward from the flank  69  at the upper and lower sections  69   a ,  69   c  to thereby form a concave surface. Hardfacing  75  is applied to flank  71  with a thickness at section  71   b  of flank  71  that is greater than that at sections  71   a ,  71   c . The result of applying hardfacing  75  in this manner is a convex profile formed on flank  71 . Combining a concave flank  69  and a convex flank  71  forms a scoop-shaped tooth  66 . 
         [0021]    Tooth  66  has a centerline  77  bisects tooth  66  and extends through the axis of rotation of the cone. Prior to hardfacing, flanks  69 ,  71  are symmetrical about centerline  77  in the plane shown in  FIG. 5 . Of flanks  69 ,  71 , one is a leading flank and the other a trailing flank, considering the direction of rotation of cone  21 ,  23 . The leading flank faces into the direction of cone  21 ,  23  rotation. The leading flank may be concave and the trailing flank convex. Alternatively, the leading flank may be convex and the trailing flank concave. 
         [0022]      FIG. 6  illustrates a second alternate embodiment tooth  81  constructed in accordance of this invention. Tooth  81  is formed with a milling cutter which forms a root  79 , inclined flanks  83 ,  85  and a crest  89 . Flanks  83 ,  85  incline and converge toward each other, joining at a crest  89 . A recess  87  is milled into flank  85  at a location between root  79  and crest  89 . In the embodiment illustrated, hardfacing  91  is applied in an even thickness to flanks  83 ,  85 , recess  87 , and crest  89 . Recess  87  forms a concave like profile on flank  85 . The result is a scoop-shaped tooth  81 . 
         [0023]    Tooth  81  has a centerline  93  which bisects tooth  81  equally prior to forming recess  87 . Centerline  93  intersects the axis of rotation of the cone. After hardfacing, flanks  83 ,  85  are asymmetrical about centerline  93  in the plane shown in  FIG. 6 . Of flanks  83 ,  85 , one is a leading flank and the other a trailing flank, considering the direction of rotation of cutters  21 ,  23 . The leading flank faces into the direction of cone  21 ,  23  rotation. The leading flank may be milled with a recess to form a concave profile. Alternatively, the trailing flank may be milled with a recess to form a concave profile. 
         [0024]      FIG. 7  illustrates a third alternate embodiment tooth  97  constructed in accordance of this invention. Tooth  97  is formed with a milling cutter which forms a root  95 , inclined flanks  99 ,  101  and a crest  103 . Flanks  99 ,  101  incline and converge toward each other, joining at a crest  103 . Flanks  99 ,  101  are flat and identical prior to the application of hardfacing  105 . Hardfacing  105  is applied in varying thickness to flank  99 . More specifically, the hardfacing  105  thickness on the flank upper section  99   c  proximate the crest  103  and the flank lower section  99   a  proximate the root  95  is greater than the hardfacing  105  thickness proximate the flank middle section  99   b . The hardfacing  105  thickness change between these three sections defines a recess  100  on the hardfacing  105  curving inward toward the flank  69  at the middle section  99   b  to thereby form a concave like surface. Hardfacing  75  is applied evenly to crest  103  and flank  101 . The result is a scoop-shaped tooth  95 . 
         [0025]    Tooth  95  has a centerline  107  which bisects tooth  95  prior to applying hardfacing. After hardfacing, flanks  99 ,  101  are asymmetrical about centerline  107  in the plane shown in  FIG. 7 . Of flanks  99 ,  101 , one is a leading flank and the other a trailing flank, considering the direction of rotation of cutters  21 ,  23 . The leading flank faces into the direction of cutter  21 ,  23  rotation. The leading flank may be hardfaced with a recess to form a concave profile. Alternatively, the trailing flank may be hardfaced with a recess to form a concave profile. 
         [0026]      FIGS. 8 and 9  illustrate another alternate embodiment tooth  111  constructed in accordance of this invention. A milling cutter forms a root (not shown), inclined flanks  113 ,  115  and a crest  117 . Flanks  113 ,  115  incline and converge toward each other, joining at a crest  117 . Hardfacing  119  is applied in an even thickness to flanks  113 ,  115 , and crest  117 . 
         [0027]    Referring to  FIG. 8 , radial line  123  extends from crest  117  through the axis of rotation  121  of the cone  124 . Cone  124  direction of rotation is indicated by the arrow. Centerline  125  is substantially equidistant between flanks  113 ,  115 , assuming flanks  113 ,  115  were straight, flat surfaces. Centerline  125  is not normal to the cylindrical surface of the cone  124  and does not intersect axis  121 . Tooth  111  tilts to the left. Centerline  125  lags radial line  123 . Centerline  125  and radial line  123  intersect each other at crest  117  at an acute angle  127 . 
         [0028]    Referring to  FIG. 9 , radial line  131  extends from crest  117  through the axis of rotation  129  of cone  135 . Cone  135  direction of rotation is indicated by the arrow. Centerline  133  is substantially equidistant between flanks  113 ,  115 , assuming flanks  113 ,  115  were straight, flat surfaces. Centerline  133  is not normal to the cylindrical surface of the cone  135  and does not intersect axis  129 . Tooth  111  tilts to the right. Centerline  133  leads radial line  131 . Centerline  133  and radial line  131  intersect each other at crest  117  an acute angle  137 . 
         [0029]    The various orientations of a bit tooth may be varied by changing the lead or lag of the centerline relative to the radial line, and the angle at which to two lines intersect. Various orientations may have some structural advantages per bending moments, etc. The orientation of the tooth may be varied with all the embodiments of the present invention, and is not limited to tooth  111 . 
         [0030]    The invention has significant advantages. By forming a steel tooth with a scoop-shape with convex and concave flanks, the localized interaction between the tooth structure and the formation are altered, leading to higher rate of penetration or longer production life. By varying the centerline axis of a steel tooth, the local force on the formation may be increased. 
         [0031]    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. For example, although shown only on a heel row tooth, the milling and hardfacing in accordance with this invention could also be applied to inner row teeth and various tooth geometries.