Patent Publication Number: US-7708090-B2

Title: Excluder ring for earth-boring bit

Description:
BACKGROUND OF THE INVENTION 
   One type of earth-boring bit has a body with at least one rotatable cone mounted to a depending bearing pin. Typically there are three cones, each having rows of cutting elements. The cutting elements may be machined from the metal of the cone, or they may comprise tungsten carbide inserts pressed into holes in the exterior of the cone. 
   The cone has a cavity that inserts over the bearing pin, forming a journal bearing. The clearances between the bearing surfaces are filled with a grease or lubricant. A seal assembly seals between the bearing pin and the cone near the mouth of the cone. 
   The seal assembly serves to prevent loss of lubricant to the exterior. Also, the seal assembly serves to exclude debris and cuttings of the borehole from entering the journal bearing. Typically the outer diameter of the seal assembly rotates with the cone and the inner diameter seals against the bearing pin in dynamic contact. 
   Many different seal assemblies have been proposed and used in the prior art. A variety of shapes of elastomeric seals have been employed. Elastomeric seals that have different materials on the inner and outer diameters are known. Elastomeric seals with carbon fiber fabric on the dynamic portions of the seal are also known. In addition, metal face seal assemblies including an elastomer that urges the metal faces together are also known. 
   SUMMARY OF THE INVENTION 
   The seal assembly of this invention comprises a seal ring of an elastomeric material. The seal ring has an inner portion that seals against a sealing surface on the bearing pin and an outer portion that seals against a sealing surface in the cone. At least one excluder ring is mounted in one of the portions of the seal ring and has a face urged by the seal ring into contact with one of the sealing surfaces. 
   Preferably the seal ring has more than one excluder ring. One excluder ring may be more abrasion resistant than the seal ring to protect the seal ring from damage due to cuttings in the drilling fluid. Another of the excluder rings may be formed of a self-lubricating material for providing lubrication to the seal ring. An excluder ring may be located on the outer diameter of the seal rings, also, for frictionally engaging the cone to resist rotation of the seal ring relative to the cone. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational view of an earth-boring bit constructed in accordance with this invention. 
       FIG. 2  is an enlarged sectional view of one of the cones and bearing pins of the earth-boring bit of  FIG. 1 , illustrating a seal ring having imbedded excluder rings in accordance with the invention. 
       FIG. 3  is a further enlarged sectional view of a portion of the seal ring and excluder rings of  FIG. 2 . 
       FIG. 4  is a schematic sectional view of an inner diameter portion of one of the excluder rings imbedded within the seal ring of  FIG. 2 , illustrating a grooved pattern. 
       FIG. 5  is a partial sectional view of another embodiment of a seal ring and excluder ring. 
       FIG. 6  is a partial sectional view of another embodiment of a seal ring and excluder ring. 
       FIG. 7  is a partial sectional view of another embodiment of a seal ring and excluder ring 
       FIG. 8  is a partial sectional view of another embodiment of a seal ring and excluder ring. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , bit  11  has a body  13  with a threaded upper end for connection to a drill string for rotation about an axis of body  13 . Body  13  has at least one and preferably three bit legs  15 . A bearing pin  17  ( FIG. 2 ) depends downward and inward from each bit leg  15 . 
   A cone  19  mounts rotatably to each bearing pin  17 . Each cone  19  has a plurality of rows of cutting elements  21 . In the example shown, cutting elements  21  comprise tungsten carbide inserts pressed into mating holes drilled in the metal of each cone  19 . Alternatively, cutting elements  21  could comprise teeth machined into the metal of each cone  19 . 
   A lubricant compensator  23  supplies lubricant to bearing spaces between the interior of each cone  19  and bearing pin  17 . Lubricant compensator  23  also equalizes the pressure of the lubricant with the exterior pressure in the borehole. 
   Referring to  FIG. 2 , bearing pin  17  has a cylindrical journal surface  25  that serves as a bearing for the weight imposed on drill bit  11  ( FIG. 1 ). A last machined surface  27  encircles bearing pin  17  on the inside of each bit leg  15 . Cone  19  has a cavity  29  with interior surfaces that mate with the exterior surfaces of bearing pin  17 . Cone  19  and bearing pin  17  have means for locking cone  19  on bearing pin  17 . In this embodiment, the locking means comprises a plurality of balls  31  located within mating grooves formed on bearing pin  17  and in cone cavity  29 . 
   A seal groove  33  is formed in cavity  29  near its mouth. In this embodiment, groove  33  is rectangular when viewed in cross-section. Groove  33  has a flat base or outer diameter  33   a , when viewed in transverse cross-section, and two flat sidewalls  33   b.    
   A seal ring  35  is carried within groove  33  for sealing lubricant against leakage to the exterior. Seal ring  35  is formed of an elastomeric material of a type that is conventional for elastomeric seals for earth-boring bits. Preferably this material comprises a nitrile rubber such as hydrogenated nitrile butadiene rubber, but it could be other types of material as well. Seal ring  35  has an outer portion or diameter  37  that seals against groove  33 . Seal ring  35  has an inner diameter or portion  41  that may have a cylindrical portion, thus appears flat when viewed in the transverse cross-section of  FIG. 2 . Inner diameter  41  seals and normally rotatably slides against bearing pin journal surface  25 . Seal ring  35  has an exterior side  42   a  and an interior side  42   b , which are shown in parallel planes, but could be other shapes. Side  42   a  is on the exterior side of seal ring  35  and is exposed to drilling fluid during operation through the clearance between last machined surface  27  and the backface of cone  19 . Side  42   b  is on the interior side of seal ring  35  and is in contact with lubricant contained in the bearing spaces. Sidewalls  42   a ,  42   b  are spaced slightly from groove sidewalls  33   b  so as to accommodate deformation. 
   At least one thermoplastic excluder band or ring  43  is located within seal ring  35 . Three excluder rings  43  are shown in this embodiment, but the number could be less or more. Referring to  FIG. 3 , in this embodiment, each excluder ring  43  is located within an annular recess  45  formed in seal ring inner diameter  41 . Excluder rings  43  may be bonded within annular recesses  45  or held by friction. Each excluder ring  43  has a contacting face  47  on its inner diameter that is substantially flush with seal ring inner diameter  41  and which is urged by seal ring  35  into dynamic contact with bearing pin journal surface  25 . 
   In this example, excluder rings  43  are spaced apart from each other along the axis of bearing pin  17 . The spacing results in annular sections  49  of seal ring  35  located on each lateral side of each excluder ring  43 , each section  49  sealing against bearing pin journal surface  25 . One of the sections  49  is located between exterior side  42   a  and its closest excluder ring  43  and another between interior side  42   b  and its closest excluder ring  43 . Also, a section  49  exists between each of the excluder rings  43 . The width of seal ring  35  from interior side  42   b  to exterior side  42   a  is greater than the total combined width of the contacting face  47  of each excluder ring  43 . 
   In  FIG. 2 , excluder rings  43  are shown with a rectangular configuration when viewed in transverse cross-section, each having a cylindrical contact face  47  and a cylindrical outer diameter. However, other cross-sectional configurations are feasible. In  FIG. 3 , excluder rings  43  are shown with a circular configuration. 
   Excluder rings  43  also slidingly and sealingly engage journal surface  25 , but typically do not seal as well as seal ring  35  because they serve other purposes. For example, one or more of excluder rings  43  may be formed of a harder and more wear resistant material to trap or exclude debris. One or more of excluder rings  43  may be formed of a known self-lubricating material for providing lubrication. In the preferred embodiment, excluder rings  43  are formed of one of the following materials: polyether ether ketone, polytetrafluoroethylene, polyphenylenesulfide and fiber reinforced composite thereof. However, other materials are also feasible. The material should be resistant to relative high temperatures and resistant to abrasion due to cuttings and other erosive particles in the drilling fluid. One preferred material for providing more resistance is polyether ether ketone with reinforcing fibers, either glass or carbon. If used to trap and exclude debris, the wear rate of each excluder ring  43  is preferably less than seal ring  35 . The hardness of each excluder ring  43  used to trap and exclude debris is greater. If one of the excluder rings  43  is used primarily for lubrication, its hardness may be less than that of seal ring  35 . A referred material for providing self-lubrication of an excluder ring  43  is polytetrafluoroethylene. An excluder ring  43  for providing lubrication would contain polytetrafluoroethylene and have less wear resistance than seal ring  35 . 
   Micro texturing may be formed in the inner diameters  47  of each excluder ring  43  to enhance sealing. Micro texturing comprises very shallow recesses formed in the surface by known techniques, such as by laser. A wide variety of texturing is feasible. As an example, 
     FIG. 4  shows generally sinusoidal grooves  51  extending in three rows around the inner diameter  47 . Grooves  51  enhance sealing even if the lubricant flow due to rotation of excluder rings  43  is bi-directional. 
   In operation, as bit  11  rotates, each cone  19  will rotate about its bearing pin  17  ( FIG. 2 ). Each seal ring  35  will tend to rotate with its cone  19  and sealingly engage journal surface  25  of bearing pin  17  in dynamic sliding contact. Excluder rings  43  also engage journal surface  25  in dynamic contact. As seal ring  35  wears due to abrasive drilling fluid, excluder rings  43  will eventually be contacted by the drilling fluid. Those that are harder and more resistant to abrasion than seal ring  35  will retard the wear rate of seal ring  35 . Generally, the wear would be from the exterior side  42   a  toward the interior side  42   b . As one seal ring section  49  wears away, the next inward excluder ring  43  will be contacted by the abrasive drilling fluid, delaying the contact of the abrasive drilling fluid with the sealing sections  49 . 
   In  FIG. 5 , a cone  53  is mounted on a roller bearing pin  55  with rollers, generally as in the first embodiment. Seal ring  57  has an inner portion that seals in rotating dynamic contact with bearing pin journal surface  59  and an outer portion that seals against cone cavity  61 . In this embodiment, a single excluder ring  63  is mounted in a groove on the inner portion of seal ring  57 . Excluder ring  63  has a generally flat face that contacts journal surface  59 . The remaining cross-sectional shape of excluder ring  63  is curved and convex. Portions of the inner portion of seal ring  57  on the interior and exterior sides of excluder ring  63  sealingly engage journal surface  59 . Excluder ring  63  is formed of a material as described above that is harder than seal ring  57  for excluding debris and retarding wear on seal ring  57 . 
   In  FIG. 6 , a cone  65  is mounted on a bearing pin  67  generally as in the first embodiment. Seal ring  69  has an inner portion that seals in rotating dynamic contact with bearing pin journal surface  71  and an outer portion that seals against cone cavity  73 . In this example, there are two excluder rings  75 ,  77 , and each has a contacting face with a different configuration. Excluder ring  75  is located on the exterior side of excluder ring  77  and is shown to have a triangular face with an apex that dynamically contacts journal bearing surface  71 . Excluder ring  77  has a convex or rounded cross-sectional shape, including its contacting face. Excluder ring  75  is preferably formed of a harder and more wear resistant material than seal ring  69 . Excluder ring  77  may be formed of a material that provides lubrication and may be softer and less wear resistant than excluder ring  75  and seal ring  69 . 
   In  FIG. 7 , a cone  79  is mounted on a bearing pin  81  generally as in the first embodiment. Seal ring  83  has an inner portion that seals in rotating dynamic contact with bearing pin journal surface  85  and an outer portion that seals against a groove  87  in cone  79 . Groove  87  is triangular shaped in this example. Seal ring  83  has a flat exterior side  89   a  and a flat interior side  89   b  that wedge against the sides of groove  87 . A single excluder ring  91  in shown on the inner portion of seal ring  83  in engagement with journal bearing surface  85 , but more than one is feasible. Excluder ring  91  may be of various shapes and is shown to have a shape generally like that of excluder ring  63  in  FIG. 5 . Excluder ring  91  is preferably formed of the same material as excluder ring  63  and serves the same purpose. 
   In  FIG. 8 , a cone  93  is mounted on a bearing pin  95  generally as in the first embodiment. Seal ring  97  has an inner portion that seals in rotating dynamic contact with bearing pin journal surface  99  and an outer portion that seals against a groove  101  in cone  93 . Two excluder rings  103  are shown on the inner diameter of seal ring  97 . Excluder rings  103  are shown with shapes similar to that of excluder ring  63  in  FIG. 5 . At least one of excluder rings  103  is of a material harder than seal ring  97  for excluding debris. The other excluder ring  103 , if desired, may be of a lubricating material. 
   An outer excluder ring  105  is shown embedded within a groove on the outer diameter of seal ring  97  and in frictional engagement with the base of cone groove  101 . Outer excluder ring  105  serves to frictionally grip cone  93  to resist slippage and rotation of seal ring  97  relative to cone  93 . Outer excluder ring  105  may be formed of a material that has good gripping properties, the hardness of which may be less than seal ring  97 . Outer excluder ring  105  may have a variety of shapes, but is shown as having a shape similar to excluder ring  63  of  FIG. 5 . Although not expected, it is possible that one prefers to cause seal ring  97  to remain stationary on bearing pin  95  while cone  93  rotates. If so, excluder ring  105 , having good gripping properties, would be located on the inner diameter of seal ring  97  and one or more excluder rings  103  for retarding wear and/or enhancing lubrication would be located on the outer diameter of seal ring  97 . 
   The term “excluder” has been used in connection with the rings, whether designed to exclude and trap debris, or to lubricate, or to resist rotation. This term is used only for convenience and not in a limiting manner. 
   The invention has significant advantages. The inclusion of more wear resistant excluder rings into a seal ring reduces the rate of wear on the seal ring. The reduction in wear rate increases the life of the drill bit by retaining lubricant in the journal bearing. Excluder rings with lubricating properties may be used to add lubrication, which reduces heat and prolongs the life of the seal ring. Excluder rings with gripping properties may be used to resist rotation of the seal ring. 
   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.